+-------+---------------------------------------------------+---------+
| # Las | # Surge Protection Anthology                      | #       |
| t upd |                                                   | Surges  |
| ated  | **Part 6 -- Tutorials, Textbooks, and Reviews**   | Happen! |
| April |                                                   |         |
|  2004 | ######### Text of "Site Surveys" files            |         |
+-------+---------------------------------------------------+---------+

 

FOREWORD

This file contains the text part of the nine papers listed below:

-   Power quality site surveys: Facts, fiction and fallacies (1988)

-   Power quality measurements: Bringing order out of chaos (1988)

-   Monitoring power quality (1988)

-   Systems and instruments in site surveys (1990)

-   No joules for surges: Relevant and realistic assessment of surge
    stress threats (1986)

-   Surge recordings that make sense: Shifting focus from voltage to
    current measurements (1996)

-   Surge recordings that make sense: Joule deposition: Yes. "Joule
    content": Never ! (1997)

-   The fallacy of monitoring surge voltages: SPDs and PCs galore!
    (1999)

-   Some enlightening case histories on lightning damage (2000)

This file is formatted as MS Word, allowing you to do a search for
keywords, but it does not support graphics as it was derived from an OCR
scan of hard-copy archives. However, should you wish to examine the
complete original format, each page in this file has an identifying
header and footer that contain a hyperlink to the pdf file for the
document being displayed on that page, regardless of the font size that
you select for optimum viewing. These headers and footers and hyperlinks
become accessible when you select the "Print Layout" in the "View" mode.

Best wishes and good browsing !

![](media/image1.png){width="0.875in" height="0.42777777777777776in"}

**Power Quality Site Surveys: Facts, Fiction, and Fallacies**

Francois D. Martzloff, Fellow, IEEE, and Thomas M. Gruzs, Member, IEEE

**Abstract** *-- The quality of the power supplied to sensitive
electronic equipment is an important issue. Monitoring disturbances of
the power supply has been the objective of various site surveys, but
results often appear to be instrument-dependent or site-dependent,
making comparisons difficult. After a review of the origins and types of
disturbances, the types of monitoring instruments are described. A
summary of nine published surveys reported in the last 20 years is
presented, and a close examination of underlying assumptions allows
meaningful comparisons which can reconcile some of the differences.
Finally, the paper makes an appeal for improved definitions and
applications in the use of monitoring instruments.*

#### 

#### INTRODUCTION

Site surveys are generally initiated to evaluate the quality of the
power available at a specific location with the aim of avoiding
equipment disturbances in a planned installation or of explaining (and
correcting) disturbances in an existing installation. In either case,
survey results constitute one of the inputs in the decision-making
process of providing supplementary line conditioning equipment, either
before or after disturbances have become a problem. Depending on the
reliability requirements of the load equipment, its susceptibility, and
the severity of the disturbances, various line conditioning methods have
been proposed: surge suppressor (with or without filter), isolating
transformer, voltage regulator, magnetic synthesizer, motor-generator
set, or uninterruptible power supply (UPS).

Because this additional line conditioning equipment may require
significant capital investment, the choice of corrective measures is
generally made by economic trade-off which is the prerogative and
responsibility of the end user. However, if technical inputs to this
trade-off are incorrect because errone­ous conclusions were drawn as a
result of a faulty site survey, the whole process is worthless, or worse
yet, misleading.

For this reason, a good understanding of the merits and limitations of
site surveys is essential for reconciling expecta­tion with reality
before expensive line conditioning equipment is called for; one should
deal, not with fiction or fallacies, but with facts.

Power disturbances that affect sensitive electronic loads have a variety
of sources. Lightning, utility switching, and utility outages are
often-cited sources of power disturbances. However, power disturbances
are often caused by users themselves, through switching of loads, ground
faults, or normal operation of equipment. Computer systems, as one
example of these so-called sensitive loads, are not only sensitive loads
but also can generate some disturbances themselves. Their nonlinear load
characteristics can cause interactions with the power system such as
unusual voltage drops, overloaded neutral conductors, or distortion of
the line voltage.

Utility systems are designed to provide reliable bulk power. However, it
is not feasible for them to provide continuous power of the quality
required for a completely undisturbed computer operation. Because normal
use of electricity gener­ates disturbances and because unexpected power
system failures will occur, every site will experience some power
disturbances. The nature of these power disturbances, their severity,
and their incidence rates will vary from site to site.

To place the problem in perspective, however, one should keep in mind
that poor-quality power is only one of the many causes of computer
downtime. Hardware problems, software problems, and operator errors also
contribute to computer downtime.

Sometimes there is too great a tendency to attribute operational
difficulties to power supply problems. For example, studying
power-related computer problems at U.S. Navy installations, Key \[1\]
found that only 5 to 10 percent of the observed computer downtime was
attributable to power problems. Reviewing case histories, Martzloff
\[2\] described a safety problem created by panic actions of the
computer system operators who pulled out power cords of the remote
terminals (including the safety grounding conductor) because they
suspected power line surges when, in fact, the problem was incorrect
grounding practices for the shields of the data lines.

Historically, transient overvoltage effects on novel semiconductor
systems were the first concern; by now, the importance of undervoltages
or loss of power has also been recognized. In the nine surveys reviewed
in this paper, four address all types of disturbances and five are
concerned exclusively with the transient overvoltages. While this review
is mostly concerned with the reports of transient overvoltages, this
limited discussion does not mean that other disturbances are less
significant.

Power quality surveys have been performed, reported, and discussed by
many authors, but their results or conclusions are not consistent
\[3\]-\[14\]. Quotations from these surveys, out of context, have
perhaps also contributed to the confusion. In an attempt to clarify the
issues, this paper presents a brief review of the origins and
definitions of disturbances, and then it describes the development of
monitoring instruments. Comparisons are made among nine published
surveys with attempts at reconciling results. Finally, an appeal is made
for improved measurement methods to provide more consistent reporting of
recorded power disturbances.

#### 

#### DEFINITION DEFICIENCIES

As will become painfully apparent in the review of site surveys, the
terms used by the workers reporting their measurements do not have
common definitions. An effort is being made within the IEEE to resolve
this problem, as described later in this paper, but consensus has yet to
be reached. In this paper, terms describing disturbances are consistent
with the IEEE Standard Dictionary of Electrical and Electronics Terms
\[15\] and with established usage within the community of surge
protective devices engineers. Two examples of this lack of consensus are
described here to make the point; resolving them is beyond the scope of
this paper.

The generally accepted meaning of surge voltage, in the context of power
systems, is a short-duration overvoltage, typically less than 1 ms or
less than one half-cycle of the power frequency. This meaning is not
that which has been established by manufacturers and users of monitoring
instruments and line conditioners. This unfortunate second meaning is a
momentary overvoltage at the fundamental frequency with a duration of
typically a few cycles. In this paper, this second meaning of the word
\"surge\" (a momentary overvoltage) will be signaled by the use of
quotation marks. What the surge protective devices engineers call surge
is called \"impulse\" or \"spike\" by the monitoring instrument
community. Fig. 1 shows by graphic descriptions the confusion created by
the dual meaning of the word surge. Acknowledging the desire of users
for terse labels, we propose for consideration the word \"swell\"
instead of \"surge\" for a momentary overvoltage.

## Figure 1 -- Graphic definitions of disturbances

The term \"outage\" is another example of confusion created by unsettled
definitions. Most users agreed that it meant a complete loss of line
voltage, but the duration of this outage was quite different when it was
defined by computer users (as short as one half-cycle) or power
engineers (seconds, perhaps minutes). Now, the users and manufacturers
of line conditioners do not make a clear distinction between complete
loss of line voltage (zero voltage condition), severe undervoltages
(\"deep sags\"), or the single-phasing of polyphase power systems. For
example, a momentary flicker of fluorescent lighting caused by a brief
loss of voltage might be considered an outage; however, a brief sag to
less than 80 percent of nominal voltage will produce the same visible
effect. Some UPS manufacturers consider input voltage sags that cause
transfer to the battery backup operation as outages. Part of the problem
may be that the definition of \"outage\" has regulatory implications for
evaluating the performance of public utility companies. No such
distinction has been made in this paper, because taking sides on that
issue is not within its scope.

The term \"sag\" has not yet been defined in the IEEE Dictionary, but it
is now generally accepted as meaning a momentary voltage reduction at
the ac power frequency. However, details (threshold, duration, etc.) of
what character­izes a sag are not well defined.

#### 

#### MOTIVATION FOR SITE SURVEYS

Protection from power disturbances now essential because increasing
dependency on computer-based systems for industry, commerce, and
consumers makes disruptions less and less acceptable. The most visible
indication of power disturbances is the occurrence of operational
problems such as hardware damage, system crashes, and processing errors.

Some users of computer systems may accept, albeit reluc­tantly,
operational problems because they see them as unavoidable. Other users
may be unaware that otherwise invisible power disturbances could be the
cause of operational problems. A single power disturbance can cost more
in downtime and hardware damage than the investment in power protection
that would have prevented the disturbance; almost all sites could
benefit from a reduction of operational problems by improving the
quality of the power supplied to the computer systems \[13\].

Power line monitoring with sophisticated power disturbance recorders has
often been advocated as a way to determine if any line conditioning is
required. While monitoring appears to be a logical first step, it has
limitations. For example, severe disturbances occur infrequently or on a
seasonal basis. Therefore, monitoring periods of less than a year might
not produce an accurate power disturbance profile; most users are
unwilling to wait at least 1 year. Also, power line monitoring produces
only past performance information, for changes within the site, at
neighboring sites, or by the utility can drastically alter the power
disturbance profile.

While exact prediction of the disturbances to be expected at a specific
location is almost impossible and attempting it would be a fallacy,
general guidelines can be formulated. An attempt has been made by
standards-writing groups to provide guidance \[16\] or specifications
reflecting expected disturbances \[17\]-\[19\]. Users, however,
generally seek specific data for their particular case; hence site
surveys will still be necessary.

Another fallacy would be to attempt correction of power line
disturbances revealed by monitoring and then to expect operational
problems of equipment to disappear with­out having first determined the
exact susceptibility of the equipment.

#### 

#### CAUSES OF POWER LINE DISTURBANCES

Transient overvoltages, historically among the first disturbances to be
recorded by users, have two major causes: lightning and load switching.
Depending on local conditions one can be more important than the other,
but both need to be recognized.

Lightning surges are the result of direct hits to the power system
conductors as well as the result of indirect effects, where the
lightning bolt strikes an object close to the conductors but not the
conductors themselves. A lightning strike to the power system may cause
the operation of gap-type surge arresters, producing a severe reduction
or a complete loss of the power system voltage for one half-cycle. A
flashover of line insulators can cause a breaker to trip, with reclosing
delayed by several cycles, causing a power outage. Thus lightning can be
the obvious cause of overvoltages near its point of impact but also a
less obvious cause of voltage loss or sag at a considerable distance
from its point of impact. This latter effect has been clearly observed
in the Goldstein-Speranza \[8\] study.

Power system load switching is also a major cause of disturbances.
Switching large loads on or off can produce long-duration voltage
changes beyond the immediate transient response of the circuit. Whether
the switching is done by the utility or by the user is immaterial from
the technical point of view, although the responsibility may be the
subject of a contractual dispute. When power factor correction
capacitors are switched, high-frequency (500 Hz-5 kHz) oscillations
occur which can reach 120-percent overvoltages (2.2 pu) for milliseconds
\[20\]. Fault clearing by current-limiting fuses can also create
substantial overvoltages \[21\].

In a study of 100 computer system failures attributable to power supply
disturbances, Key \[1\] considered power line monitoring, computer
operation logs, data from the National Weather Service, and local
utility data to determine the cause of the power disturbance (Fig. 2).
Weather was cited as the major cause of disruptive sags and outages;
sags were found to disrupt computer operations four times as often as
outages, a finding that agrees with the results of the comparison
between the Allen-Segall and Goldstein-Speranza studies discussed later.

## Figure 2 -- Causes of computer failures as reported in the Key study

The type of power distribution system also has a strong influence on the
incidence of disturbances. In his study, Key compared the rates of
incidence of sags and outages (Fig. 3). A similar analysis was performed
by Allen and Segall in another study \[22\], reaching essentially the
same conclusions. Both studies found that the rate of occurrence of
disturbances is significantly lower for underground and network systems
than for overhead and radial systems, respectively.

## Figure 3 -- Effect of power distribution system configuration

**on incidence of disturbances as reported in the Key study**

#### 

#### TYPES OF DISTURBANCES

Power line disturbances can be classified into two categories: common
mode disturbances and normal mode disturbances. The two terms were first
defined in the context of communication circuits; a recent IEEE Guide
\[23\] has established an expanded definition which is used in this
paper, as outlined in the following paragraphs. The IEEE Dictionary
\[15\] and the IEC Dictionary \[24\] define symmetrical and asymmetrical
voltages akin to but not interchangeable with the definitions of normal
mode and common mode, respectively.

#### Common Mode Disturbances

Common mode disturbances are defined as unwanted potential differences
between any or all current-carrying conductors and the grounding
conductor or earth. In three-phase grounded-wye power supplies typical
of large computer systems, common mode disturbances could also be
defined as the potential difference between neutral and ground.

Two different types of common mode disturbances can affect a sensitive
load. The first type is a disturbance on the input power conductors
relative to the input power grounding conductor. Fig. 4 shows in 1 and 2
examples of origins for these disturbances. This type of disturbance can
be limited somewhat by a line conditioner, but it is also influenced by
the location of the line conditioner and the wiring practices.

**Figure 4 -- Three examples of the origin of common mode disturbance on
power input**

**Figure 5 -- Three examples of the origin of normal mode disturbance on
power input**

The second type is a ground potential difference between elements of the
computer or remote peripherals connected to the computer. Fig. 4 shows
in 3 an example of this type. This type of disturbance is more difficult
to limit because it is influenced by factors such as the system
configuration and the impedance of the grounding system. These two
factors are generally beyond the direct control of the user except in
the construction of a new facility.

Because of the broad frequency band involved, wiring resonances can make
equalizing ground potentials difficult. Proper computer system
grounding, including a signal reference grid, has been found to be
effective against most common mode disturbances \[25\]. However, when
remote elements are connected to the computer systems by data cables,
large ground potential differences are possible. Proper surge protec­tion
of the power supply and proper grounding of data cables will help
eliminate hardware damage but might not prevent data corruption. When
dealing with the situation of example 3 in Fig. 4, fiber optic links are
very effective because they provide complete metallic separation of the
various elements in the system, a separation that might not be
sufficiently achieved by the discrete opto-isolation devices sometimes
proposed for that function \[2\].

#### Normal Mode Disturbances

Normal mode disturbances are defined as unwanted poten­tial differences
between any two current-carrying circuit conductors. Fig. 5 shows three
examples of the origins of such disturbances. Usually a sine wave of
nominal voltage is desired for a computer power supply. Any deviation
from this sine wave is a normal mode disturbance. Computer users and
monitoring instruments designers characterize these distur­bances by a
variety of terms not always clearly defined such as sags, surges
(\"swells\"), outages, impulses, ringing transients, waveform
distortion, and high-frequency noise. Unfortunately, there is no
consensus at the present time on the exact meaning of these terms and
their underlying quantitative definitions such as amplitude, duration,
and thresholds, Later in this paper, a new effort to remedy this
situation is described.

#### 

#### HISTORY OF THE DEVELOPMENT OF DISTURBANCE MONITORS

Historically, the first (unintended) disturbance monitors were the
actual load equipment; only later, when confronted with unexplained
failures or malfunctions, did the users start monitoring the quality of
their power systems. Monitoring power quality at the fundamental
frequency had long been performed by utilities, but the precise
characterization of microsecond-duration surges in the early 1960\'s
required special oscilloscopes. For the next 15 years, combinations of
oscilloscopes or simple peak-detecting circuits were the basic
instruments for monitoring transient overvoltages. In the 1970\'s
commercially-produced digitizers became available, and the technology
has made continuing progress as experi­ence has been accumulated and
faster digitizing circuits have been developed.

Early site surveys were generally limited to voltage measurements in the
normal mode. This limited scope reflected concerns for damage to
sensitive electronic components connected across the line. The fact that
the source impedance of the surge was not recognized as being important
in these surveys led to the generation of some performance standards
that do not specify the current-handling requirements for the surge
protective devices \[19\]. With the introduction and widespread
application of clamping protective devices (silicon avalanche diodes or
metal oxide varistors), the surge current diverted through these devices
became a very important factor for proper device selection.

Therefore, the need emerged for characterizing current as well as
voltage surges, but few surveys to date have addressed this need. This
need offers a challenge to designers of monitoring instruments and to
would-be surveyors.

This challenge has produced attempts to define an \"energy\" measurement
with an instrument which is only a voltmeter. By assigning a parametric
value to the source impedance of the surges and integrating the product
(volts)^2^-seconds of the surges, some knowledge on the energy involved
would be obtained as suggested in \[14\]. However, the real question
concerns the sharing of energy between the impedance of the source and
the impedance of the load, in this case the nonlinear impedance of the
protective device. A lengthy discussion of the energy contained in the
surge versus the energy delivered to the protective device is beyond the
scope of this paper, but the difference needs to be recognized to
prevent further confusion as future monitoring instruments include an
\"energy\" parameter in their readouts.

With the present development of sophisticated multichannel digitizing
instruments, it should be feasible in future surveys to monitor both
voltage and current in the normal mode as well as in the common mode.
Note, however, that the current of interest is that which the surge
source (of otherwise unknown impedance) would force through a proposed
surge protective device. This device would he shunt-connected at the
point being monitored so that the current to be monitored is not the
surge current in the direction of undefined downstream loads. The
amplitude as well as the waveform of the surges needs to be
characterized for correct application of surge protective devices.
Peak-reading monitors provide useful information on surge activity at a
given site, but assessment of the surge severity level for the proper
sizing of protective devices requires waveform and source impedance
information \[20\], \[26\].

Recent monitoring instruments offer the capability of recording
potential differences between the neutral and the grounding conductor
which constitutes one form of common mode disturbances. To our
knowledge, no instrument has been offered for explicit monitoring of
potential differences within the grounding system itself such as 1 and 2
in Fig. 4. Some types of monitors include current probes and could
record current in grounding conductors, but this parameter has not yet
been reported in published surveys.

One difficulty encountered by users of monitoring instruments in this
fast-paced technology is that manufacturers introduce improved features
in response to specific wishes of the users or as a result of their own
research; data collected by different instruments become
equipment-dependent. While this continuing progress is a welcome
development, it makes comparison of survey results difficult without the
details on the instrument characteristics and methods of measurement.

Occasionally, an instrument might have limitations or might introduce
artifacts which are not immediately apparent so that the survey results
suffer some loss of credibility when these possible limitations are
discovered \[11\], \[12\]. Users may also have difficulty in
interpreting complex instrument outputs, and excessive simplification of
a complex data base can lead to some misunderstanding or misapplication
of published docu­ments; a tutorial effort is then necessary to avoid
these pitfalls \[27\], \[28\].

#### TYPES OF MONITORS

The instruments used in the various surveys reflect technol­ogy progress
as well as logistics constraints resulting in a diversity of approaches.
Nevertheless, all monitoring instruments used in past surveys were
voltmeters (with one exception, combining voltage and current
measurements) from which disturbance parameters were derived. Some of
the monitors recorded a single parameter such as the actual voltage peak
or the fact that the voltage exceeded a preset threshold. Other monitors
combined time with voltage measurements describing voltage waveforms.
The recording functions of instruments used in the surveys may be
classified in broad categories.

Threshold counters-The surge is applied to a calibrated voltage divider,
triggering a counter each time a preset threshold is exceeded. The early
types were analog; more recent types are digital.

Digital peak recorders-The surge is converted to a digital value which
is recorded in a buffer memory for later playback or printed out
immediately after it occurs. In the early types of recorders, only the
peak was recorded; in later types, the duration of the surge was also
recorded, opening the way to the more complex digital waveform recorders
now available.

Oscilloscope with camera-The surge triggers a single sweep on the CRT of
the oscilloscope which is recorded as it occurs by a shutterless camera
with automatic film advance. The oscilloscopes available at that time
(the early 1960\'s) did not allow differential measurements.

Screen storage oscilloscope-The surge is displayed and stored on the
cathode ray tube. The writing-speed capability of these oscilloscopes
was a limitation in the late 1960\'s.

Digital storage oscilloscope-The surge is digitized and stored in a
shift register for subsequent playback and display whenever a preset
threshold is exceeded. An important feature is the capability of
displaying events prior to the beginning of the surge.

Digital waveform recorder-The surge is digitized and stored in a manner
similar to the digital storage oscilloscope, but additional data
processing functions are incorporated in the instrument, allowing
reports of many different parameters of the disturbance relating voltage
to time.

Although some surveys might aim at great accuracy, the real world
experiences such an infinite variety of disturbances that any attempt to
describe them in fine detail only restricts general usefulness of the
data. Seeking such fine and definitive detail is another fallacy. Some
simple instruments can be considered useful (and inexpensive) indicators
of frequent disturbances; other, more sophisticated (and more expensive)
instruments can provide quite comprehensive data on distur­bances (but
only on past events from which future disturbances can be extrapolated
only by assuming that the causes will remain unchanged). Thus there is a
practical limit to the amount of detail that a survey can yield, and
unrealistic expectations of very precise information should be avoided.

Before attempting yet another broad survey of power quality, would-be
surveyors need to consider not only improvements in instrumentation but
also changes that have occurred in modern power systems, in particular
the proliferation of surge protective devices. These two differences
between earlier surveys and the more recent surveys should be kept in
mind when comparing results and when planning future surveys.

Prior to the proliferation of surge protective devices in low-voltage\'
systems, a limitation had already been recognized \[17\] for peak
voltages: the flashover of clearances, typically between 2 and 8 kV for
low-voltage wiring devices. For that reason the expected maximum value
cited in the IEEE Guide on Surge Voltages \[16\] reflects this possible
truncation of the distribution around 6 kV. Unfortunately, some readers
of this Guide interpreted the upper practical limit of 6 kV as the basis
for a withstand requirement, and they have included a 6-kV test
requirement in their performance specifications. A new version of this
Guide, currently under preparation as a Recommended Practice, will
attempt to avoid this misinter­pretation.

The number of surge protective devices such as varistors used in the
United States on low-voltage ac power circuits since their introduction
in 1972 may be estimated at 500 million. Therefore, a new limitation
exists in the voltage surges that will be recorded. A surge-recording
instrument installed at a random location might be close to a varistor
connected near the point being monitored. Such a proximity of surge
protective devices and recording instruments may impact present and
future measurements in several ways, as contrasted to previous
measurement campaigns. Four are outlined below.

1\) Locations where voltage surges were previously identified-assuming
no change in the source of the surges-are now likely to experience lower
voltage surges, while current surges will occur in the newly installed
protective devices.

2\) Not only will the peaks of the observed voltages be changed, but
also their waveforms will be affected by the presence of nearby
varistors as illustrated in Figs. 6, 7, and 8.

A\) If a varistor is located between the source of the surge and the
recording instrument (Fig. 6), the instrument will record the clamping
voltage of the varistor. This voltage will have lower peaks but longer
time to half-peak than the original surge.

## Figure 6 -- Varistor upstream of monitor

## Figure 7 -- Varistor downstream of recorder

## Figure 8 -- Voltages measured at beginning and end of 75-m branch circuit

**for surge applied in normal mode at service entrance**

B\) If the instrument is located between the source of the surge and a
varistor, or if a parallel branch circuit contains a varistor (Fig. 7),
the instrument will now record the clamping voltage of the varistor,
preceded by a spike corresponding to the inductive drop in the line
feeding the surge current to the varistor.

**TABLE 1**

**DETAILS OF THE LOCALES AND INSTRUMENTATION**

C\) If a varistor is connected between the line and neutral conductors,
and the surge is impinging between line and neutral at the service
entrance (normal mode), a new situation is created, as shown in Fig. 8.
The line-to-neutral voltage is clamped as intended; however, the
inductive drop in the neutral conductor returning the surge current to
the service entrance produces a surge voltage between the neutral and
the grounding conductors at the point of connection of the varistor and
any downstream point supplied by the same neutral. Because this surge
has a short duration, it will be enhanced by the open-end transmission
line effect between the neutral and grounding conductors \[29\].

3\) The surge voltage limitation function previously performed by
flashover of clearances is now more likely to be assumed by the new
surge protective devices that are constantly being added to the systems.

4)  These three situations will produce a significant reduction in the
    mean of voltage surge recordings from the total population of
    different locations as more and more varistors are installed.
    However, the upper limit will remain the same for locations where no
    varistors have been installed. Focusing on the mean of voltage
    surges recorded in power systems can create a false sense of
    security and an incorrect description of the environment.
    Furthermore, the need for adequate surge current handling capability
    of a proposed suppressor with lower clamping voltage might be
    underes­timated because some diversion is already being performed.

#### REVIEW OF PUBLISHED SURVEYS

This summary includes nine papers published in the United States and in
Europe, with a brief description of instrumentation design, definition
of parameters, and results. Papers are listed in chronological order.

Table I shows details of the locale, system voltage, instrument type,
and connection mode as described in the papers. Other surveys may have
been published, particularly in Europe, which did not come to the
attention of the authors. Suggestions for including additional published
data in the revision process for the Guide on Surge Voltages \[16\] are
invited.

Bull and Nethercot, in a 1964 article \[3\], report monitoring performed
in the mid 1960\'s on 240-V systems in Great Britain with instruments of
their design. Their initial instrument used vacuum tubes, leading to the
development of a solid-state circuit which may be considered the
forerunner of modern monitors. The instrument had several channels, each
with a different threshold. Eventually, the solid-state instrument was
made available commercially, and several units were used in some of the
monitoring performed in the United States and reported in the data base
of \[16\].

The monitoring locations were selected to include a variety of
conditions, with data being collected for several weeks at each location
over a total period of 2 years. The results do not mention transients
above 600 V; it seems that no channels were provided above that level
because the authors were only concerned with the range of 50-600 V.

Martzloff and Hahn, in a 1970 paper \[5\], report the highlights of
measurements made in the 1963 to 1967 period on residential, commercial,
and industrial circuits, mostly single-phase 120 V. Further details,
originally held proprietary, were eventually released \[30\] for sharing
information with other interested parties. Waveform data were obtained
with commercial, custom-modified oscilloscopes fitted with motor-driven
cameras. These oscilloscopes were installed at various locations where
transient activity was suspected. In addition, a peak counter circuit
was developed, and 90 units with a 1200- or a 2000-V threshold were
deployed at 300 locations where there was no prior suspicion of unusual
transient activity.

The oscilloscope data gave one of the first indications that the
traditional unidirectional impulse, long used for dielectric testing,
might not be representative of surges occurring in low-voltage circuits.
The threshold data indicated locations where surges above 1200 V occur
frequently (about 3 percent of the sample), while other locations appear
far less exposed to surges. The 100:1 reduction of an alarming failure
rate of clock motors, achieved by increasing the surge withstand
capability of the motors from 2000 to 6000 V, is documented in that
paper.

Cannova, in a 1972 paper \[6\], reports the monitoring of surges on U.S.
Navy shipboard 120- and 450-V power systems in the late 1960\'s.
Instrumentation used for the initial phase of the monitoring program
consisted of oscilloscopes similar to those used by Martzloff. Provision
was also included for the option of measuring the transients alone
(through filters) or superimposed on the ac line voltage; this option
reflects the old dichotomy, still unsettled to this day, as to whether
the transients should be measured as an absolute value or as a deviation
from the instantaneous value of the ac sine wave (see the surge and
impulse descriptions in Fig. 1, and the last column of Table 1).

The results are not reported separately for 120- and 450-V systems, it
is not possible to express them in terms of per-unit or percentage of
nominal system voltage. The statistical treatment aims at fitting the
recorded transients to a normal distribution and concludes that a log
normal distribution is a better fit. A brief statement is made on the
durations of the recorded transients (without a statement on how those
durations are defined), citing a majority of durations between 4 μs and
6 μs, with a few at 19 μs.

From the data base, acknowledged to be a small total number of events, a
voltage protection level of 2500 V was defined. The specification of a
2500-V 1.2/50-μs voltage withstand by DOD STD 1399 was derived from this
survey.

Two aspects of the conclusions are especially worth noting: 1) there was
no information on the source impedance of the surges, and yet the data
eventually served to specify requirements for surge protective devices;
and 2) a large difference in frequency of occurrence was noted among
ships of the same type and class, similar to the observations on land
surveys.

Allen and Segall, in a 1974 paper \[7\], report the monitoring of
several types of power disturbances at computer sites, performed with
oscilloscopes, oscillographs, and digital instruments, in the 1969-1972
period. Details of the instrumentation were described in a separate
paper \[31\]. Disturbances are described as overvoltages and
undervoltages, oscillatory decaying disturbances, voltage spike
disturbances, and outages. The terms sag and \"surge\" (\"swell\") had
not yet made their appearance in the jargon.

The survey was conducted in two phases. In a first phase, preliminary
information was obtained on ranges of disturbances, leading to the
development of a second generation of monitors deployed in the next
phase. The recorded disturbances are described by plots and histograms.
The highest surge recorded in the first phase is shown as 350 V. In the
second phase, the monitors grouped all surges into three categories, the
highest having a range of 100 percent (of line voltage) to infinity, so
that no detailed information is provided to describe high peak values.
The survey does report in detail the occurrence of undervoltages and
overvoltages, providing a basis for the comparisons with the
Goldstein-Speranza study made later in the present paper.

Goldstein and Speranza, in a 1982 paper \[8\], report the monitoring of
several types of disturbances at a variety of locations in the Bell
System, with digital multiparameter instruments, in the 1977 and 1979
period. The conditions of the survey are documented, including
instrument locations and definitions of the parameters as well as the
methods of data processing.

The findings are briefly reported with emphasis on predic­tions for
disturbances expected at specific sites. The prediction is obtained by
using a statistical model derived for all sites and making adjustments
reflecting specific site conditions determined by a limited survey at
that site. The authors are emphatic on the point that the lack of
correlation between sites prevents blanket application of the overall
findings to any specific site, but that useful predictions are possible
by combining the overall data with limited knowledge on specific site
data. This concept is echoed in the Guide on Surge Voltages \[I 6\],
where the frequency of occurrence is presented in graphic form with
well-defined slopes but with a wide band of possible exposures,
depending on the particulars of the site.

A Polya distribution is identified by Goldstein and Speranza as the best
fit for this type of rare events data, in contrast to other surveys
where their authors attempted to fit a normal distribution or a power or
exponential law profile.

Wernstrom, Broms, and Boberg, in a 1984 report published in Sweden and
circulated in the United States as an English draft translation \[10\],
report monitoring of industrial 220/380-V systems by digital
multi-threshold instruments, corroborated by waveform recording with
digital storage oscilloscopes. The parameters to be recorded and
reported are defined in an introductory section; however, their
description of \"common mode\" and \"differential mode\" in the English
translation does not correspond exactly to symmetrical and asymmetrical
voltages defined by the IEC.

In the section discussing transient sources and propagation, they make a
significant comment that \"common mode voltages are the most interesting
and at the same time are the voltages most difficult to defend
against.\"

The range of surges recorded extends from 200 to 2000 V. In a summary
tabulation, rise times are shown as ranging from 20 to 200 ns and
duration from 0.2 to 2.5 μs. An interesting additional measurement was
made by simultaneous recordings at two distant points of the power
system, showing some aspects of the propagation and attenuation of a
surge. The survey also shows a wide difference of surge activity among
sites but a relatively constant slope of the rate of occurrence versus
level.

Aspnes, Evans, and Merritt, in a 1985 paper \[11\], report a survey of
the power quality of rural Alaska at isolated power generation
facilities. The monitoring instruments are identified as one of the
contemporary commercial digitizing monitors. A very comprehensive
summary of the recordings is presented including frequency deviations (a
unique situation in these isolated systems), sags and \"surges\"
(\"swells\"), impulses (i.e., surges), and outages.

Because the sites were in isolated systems (their installed capacity or
system impedance is not stated), one would expect differences from the
typical survey of interconnected power systems. In fact suspected
differences were the motivation for conducting the survey. Thus finding
differences in the results would not be particularly meaningful from the
point of view of this paper aiming at comparisons. However, bringing up
this survey serves the purpose of noting that some ambiguity surfaced in
connection with the possibility that built-in surge protection in the
monitors might have attenuated the surges being recorded. Knowing the
source impedance of the surges (not the impedance at power frequency)
would have settled the issue. This case history point out again the
desirability of including surge current monitoring in future surveys as
a method of characterizing the source impedance of the surges.

Odenberg and Braskich, in a 1985 paper \[12\], report the monitoring of
computer and industrial environments with a digital instrument capable
of the simultaneous recording of voltage surges and current surges. This
new capability for relating voltage and current shows a growing
awareness of the need to monitor current surges-an improvement over
previous surveys limited to the measurement of voltages. However, the
reported surge currents are those of a current toward undefined loads
downstream from the instrument; they do not include any measurement of
the current through a shunt-connected surge diverter, a measurement that
would have provided new information on the source impedance of the
surges.

The digital processing applied by the instrument yields two points of
the surge: the peak value with the time to reach peak and the time
elapsed until decay to 50 percent of the peak value. From these two
points, a \"waveform\" description is proposed without any other
information on the actual waveform. From a large number of recorded
surges (over 250 000 events) a startling finding is cited: 90 percent of
the recorded surges have their 50-percent point in a narrow window of
900-1100 μs. Attempts to reconcile this singular finding with the
observations reported by other surveys have not been successful.

Goedbloed, in a 1987 paper \[14\], describes in detail a custom-built
automated measurement system monitoring 220/ 380-V networks in Europe.
The automated measurement system reflects the progress made in
digitizing techniques since the Bull-Nethercot days of vacuum tubes. By
combining two commercial recorders with a custom interface, the
developers obtained detailed recordings with a 10-ns sampling interval
and 20-uus window on the first recorder and a \]-\[is sampling interval
and 2-ms window for the second recorder.

The system included a provision for automated data reduction, yielding
raw data as well as statistical information on amplitude, rate of rise,
energy measure, spectral density, and conversions from time domain to
frequency domain. With a relatively low threshold of 100 V above the
line voltage, the distribution of occurrences is weighted toward low
ampli­tudes; nevertheless, occurrences are reported above 3000 V.

The paper also addresses indirectly the question of normal mode versus
common mode surges by discussing symmetrical voltage and asymmetrical
voltage as defined in the IEC Dictionary \[24\]. An indirect definition
is proposed for a third type identified as the \"so-called
non-symmetrical voltage\" which was the mode of monitoring used in this
survey: line to grounding conductor (called \"protective earth\" or
\"protective conductor\" in Europe). This third type is currently
incorporated in the more general definition of common mode proposed by
the IEEE Guide on Surge Testing, which might leave some ambiguity on the
definitions (see Fig. 5), or lead to considering \"pure common mode\" as
opposed to some combined mode in which both normal and common (pure)
modes are combined. Looking for guidance in IEC definitions does not
help much; the IEC definition addresses delta networks, but the
Goedbloed paper states that nearly all networks monitored were of the TN
type-that is, phase, neutral (implying a wye), and protective-earth
conductors. The paper clearly states the mode of connection so there is
no ambiguity, but this instance serves again to illustrate the need to
harmonize definitions. *\[Footnote: A related issue, now being addressed
but not yet resolved, is the effect produced on the amplitudes of common
mode surges by different practices for grounding the neutral (at the
service entrance or at the remote substation). Comments are invited on
this aspect of characterizing the environment.\]*

#### COMPARISONS AMONG SURVEYS

**Relative Occurrence of Different Types of Disturbances**

Two of the surveys reviewed in this paper have been widely cited, one
performed in the early 1970\'s by Allen and Segall (A-S for short)
\[7\], and the other performed in the late 1970\'s by Goldstein and
Speranza (G-S) \[8\]. However, the findings do not a first appear to be
in agreement; a detailed comparison of these two surveys provides a good
illustration of the pitfalls of superficial interpretation of survey
results.

A cursory comparison of the results (Table 11) might lead one to
conclude that a significant change in power disturbances at computer
sites occurred between 1972 (end of the A-S study) and 1979 (end of the
G-S study).

A-S reported 88.3 percent of observed disturbances as spikes, impulses,
and transients, 11.2 percent as sags, and 0.47 percent as outages . G-S,
on the other hand, reported 87 percent of the observed disturbances as
sags, 7.4 percent as impulses, 0.7 percent as \"surges\" (\"swells\"),
and 4.7 percent as outages (which they call power failures).

**TABLE II**

**UNRECONCILED COMPARISONS BETWEEN THE GOLDSTEIN-SPERANZA**

**AND ALLEN-SEGALL RESULTS**

**TABLE III\
MONITOR THRESHOLDS**

Taking a more careful look at the monitoring thresholds used in each
study (Table 111) helps to explain why the number of impulses appear to
have decreased and the number of sags appear to have increased. Since
G-S use a threshold of -4 percent for sags while A-S use -10 percent,
one can expect the G-S study to indicate a higher percentage of sags,
because the sags between -4 and -10 percent are not included in the A‑S
study. Oscillatory decaying disturbances are not specifically identified
in the G-S study but are included under the category of impulses. The
threshold for impulses used by G-S (200 V for 120-V lines, or 118
percent) is higher than that used by A-S (± 10 percent). Because the
rate of occurrence increases steeply for lower amplitude disturbances,
one can expect a drastic reduction in the percentage of impulses
reported by the G-S study as compared to the A-S study.

The increase in percentage of power outages reported by G-S may be
explained by the shift in the number of disturbances observed due to
other threshold changes. Per­centages can be a very misleading basis for
comparison unless all conditions are equal. For example, the incidence
of power outages observed in both studies is very similar, even though
the percentages are one order of magnitude apart; A-S report 0.6
occurrence per month while G-S report 0.4 occurrence per month.

Both studies present summaries and statistical analyses of their
disturbance data in difference ways. A-S use only the observed
disturbances as a data base and present results as incidence rate
graphs. Incidence rates of sags and impulses at different thresholds are
given by A-S, allowing a more direct comparison with the disturbance
thresholds of the monitoring instruments used in the G-S study.

The G-S study presents a statistical model of the disturbance rates to
predict the incidence rates at predefined disturbance levels, selected
to correspond to those levels generally expected to cause computer
systems problems: impulses greater than 200 V (118 percent of nominal
peak voltage), sags greater than - 20 percent of the nominal voltage,
and \"surges\" (\"swells\") greater than 10 percent of nominal. The G-S
model states the disturbance rates in terms of probability, such as 50
percent of the sites will have less that \"x\" disturbances per year or
90 percent of the sites will have less than \"y\" disturbances per year,
but with a cautionary note that there is no firm correlation between
sites, making specific predictions from overall results somewhat
uncertain.

When the disturbance rates at the same thresholds are compared for the
A-S data and the G-S model (for 75 percent probability), the results are
surprisingly similar (Table IV). The conclusions of these two studies
are that deep sags contribute about 62 percent of the power system
problems which are related to normal mode disturbances, severe impulses
are responsible for 21 percent outages for 14 percent and \"surges\"
(\"swells\") for 2 percent.

# Differences in Surge Amplitudes

The amplitudes of the surges reported in the surveys vary over a wide
range, and comparisons are difficult because the data are not presented
in a uniform format. An attempt was made to get a quantitative
comparison of the amplitudes reported in the surveys; however, the
exercise was quickly found to be futile because of the following two
main reasons.

1\) Looking at \"maximum values,\" one finds that in some surveys the
quoted maximum is actually a value in excess of the range of the
instrumentation, while for others it is the measured value. There are
too few points and insufficient information to attempt a statistical
treatment of this truncated data base (censored data in statistical
terms). Furthermore, the quoted value in some surveys is the total
voltage (instantaneous value of ac sine wave plus surge), while in
others the sine voltage has been filtered out. When surges are in the
range of several thousand volts (the concern being damages), the
difference between the two definitions is not significant; however, when
surges are in the range of a few hundred volts (the concern being
malfunctions), the difference is significant.

2\) Because the lower threshold of the recorder varies among surveys,
and the frequency of occurrences increases dramatically with lower
threshold, the labels of average, median, most frequent, typical, etc.,
are not meaningful for comparing amplitudes. The preceding discussion of
A-S and G-S results has illustrated the profound effect of threshold
selection on reported results when they are expressed in percentages.

For these two reasons, any comparison at the present stage of
inconsistency in report formats can only be qualitative. Conjecture or
speculation, rather than hard facts, might explain differences, as
illustrated in the following two examples.

**TABLE IV**

#### RECONCILED COMPARISONS

The relatively small number of high-amplitude surges reported by
Allen-Segall compared to other surveys \[16\] might be explained by a
limitation of their instrument. This explanation was submitted as a
written discussion of the paper, but because of the \"conference paper\"
status of the paper it was not published by the IEEE. \[***Editor's 2003
Note***: *That Conference paper, together with its discussion, is now
accessible, with permission of the IEEE, in this Anthology Part 5.*

Briefly stated, the storage oscilloscopes used by A-S had the limited
writing speed of contemporary technology; further­more, the small
amplitude set for full scale was such that a high-amplitude transient
would have its peak off screen and the steep rise would not be seen on
the phosphor. Fig. 9 shows a set of oscillograms recorded in the
laboratory by Martzloff in 1974, with the same model of oscilloscope as
used by A-S: an actual 2200-V transient overvoltage appears as a benign
400-V transient if the oscilloscope sensitivity is set in anticipation
of relatively low-amplitude transients and relatively slow speed, as was
the case in the A-S study \[31\].

**Figure 9 -- Appearance of recordings made with storage oscilloscope
and high-speed oscilloscope**

Another difference in observed amplitudes is found in the results of the
Alaska power survey \[11\]. One possible explanation for the relatively
low surge level observed was suggested in the discussion of that paper:
the built-in surge protection of the power supply for the internal
electronics of the monitor might have reduced the levels of the surges
observed by the monitors which had their power cord and monitoring probe
connected to the same duplex receptacle.

A general explanation of differences in amplitudes found in the various
surveys might be the observation by some of their authors of the lack of
correlation between sites. Furthermore, some surveys include sites where
equipment failures were experienced or expected, while other surveys
were made at sites not singled out for particular problems. Thus the
differences in overall results of various surveys might simply be the
result of the different surge exposure at the points of monitoring. This
explanation implies that surveys will still be needed where specific
information is desired.

#### Differences in Waveform

From those surveys made with waveform recording capability, the
\"typical\" forms suggested by each author have been collected in Fig.
10. The finding of ringing waves, as opposed to the traditional
unidirectional impulses, seems general in these low-voltage circuits.
*\[Footnote: The data base of the Guide on Surge Voltages \[16\] shows
oscillograms of ring waves recorded in the Bell System during a survey
before the Goldstein­/Speranza study, but not otherwise published.\]*

Martzloff and Hahn were among the first to report ring waves. Their
reported measurements were incorporated into the data that resulted in
the eventual selection of a 100-kHz ring wave with a 250- or 500 ns rise
time for the UL Standard Ground Fault Circuit Interrupters \[32\] and
the 0.5-μs 100­kHz ring wave of the IEEE Guide on Surge Voltages \[16\].

While Cannova does not report detailed descriptions of the waveforms,
the statements \"4 to 6 μs\" and \"up to 19 μs\" could be interpreted
either as a time to half-value or as the time between the initial rise
and the first zero crossing of a ringing wave. Interestingly, that data
base led to the specification of a unidirectional longer impulse, the
classic 1.2/50-μs voltage impulse, for conservative rating of candidate
surge protection devices to be installed in the shipboard environment
\[19\].

Wernstrom, Broms, and Boberg show three examples of recordings. The
first is indeed a ring wave with a frequency of about 500 kHz and a rise
time of 200 ns. The second example is a burst of nanosecond-duration
transients, similar in shape to the proposed IEC/TC65 Electrical Fast
Transients \[33\]. The third example is (of all things) a unidirectional
(almost) impulse.

The data reported by Odenberg and Braskich are different from the others
in that only two points of the waveform are reported: peak and 50
percent of peak amplitude. As such, this description is not a complete
waveform; furthermore, their report that 90 percent of their 250 000
recordings show the 50­percent point occurring between 900 and 1100 μs is
unique among all the surveys.

The Goedbloed data presentation reflects concerns address­ing
interference rather than damage; hence, the emphasis was given to
amplitude, rate of rise, and energy rather than waveform. An oscillogram
characterized as \"typical\" is presented in Fig. 10: it is a ring wave
with a frequency of about 800 kHz. In the data processing by conversion
of the recorded events to a standardized trapezoidal pulse, the median
of the time to half-value is found to be about 2 μs, which is an
indirect measure of the relatively short duration of the observed
surges.

## Figure 10 -- "Typical" waveforms reported in surveys

**Agreement and Disagreement on Rate of Occurrence versus Levels**

Several of the survey authors have attempted to fit a classic
distribution or a simple relationship between the rate of occurrence and
the amplitude of the surges.

In making such attempts, the frequency of occurrence is presented in
different forms such as histograms, cumulative frequency, or number of
occurrences in excess of a stated surge level. Fig. 11 shows on a single
chart the relative distributions of the findings, normalized for voltage
level and frequency of occurrence for each survey result: the slope of
the lines is what can be compared, not the absolute rate of occurrence.
It is remarkable that slopes are similar among the surveys if one keeps
in mind that the absolute frequency of occurrence is site-dependent.

## Figure 11 -- Comparison of slopes of frequency of occurrence versus level of surges among surveys

#### 

#### WORKING TOWARD MORE CONSISTENT SURVEYS

The ambiguities plaguing the field of site surveys have become apparent
to many interested workers, resulting in the formation of a new Working
Group Monitoring Electrical Quality sponsored by the Power Systems
Instrumentation and Measurements Committee. The scope of the document
being developed by this Working Group is as follows.

This Recommended Practice covers monitoring the electri­cal quality of
single-phase and polyphase ac power systems.

-   To obtain consistent descriptions of disturbances in the electrical
    quality of power systems, this document presents definitions of
    nominal conditions and of deviations from these nominal conditions
    that may originate within the source of supply or from interactions
    between the source and the load.

-   To identify which deviations may be of interest, a brief generic
    description is presented of the susceptibility of load equipment to
    deviations from nominal conditions.

-   To obtain comparable results from monitoring surveys performed with
    different instruments by different operators, this document presents
    recommendations for measurement and application techniques, and
    interpretations of results.

-   While there is no implied limitation on the voltage rating of the
    power system being monitored, signal inputs to the instruments are
    limited to 1000 V or less. Fundamental frequencies of the ac power
    systems being monitored are in the range of 45 to 450 Hz.

-   Although it is recognized that the instruments may also be used for
    monitoring de supply systems or data transmission systems, details
    of application to these cases are under consideration and are not
    included in the present scope. It is also recognized that the
    instruments may perform monitor­ing functions for environmental
    conditions (temperature, humidity, high-frequency electromagnetic
    radiation). How­ever, the scope of this document is limited to the
    conducted electrical parameters derived from voltage or from current
    measurements, or both.

Contributions to the development of this document are invited and
welcome, and further information may be obtained from the authors.

#### 

#### CONCLUSIONS

A review of power quality site surveys conducted over the last twenty
years reveals interest facts, and close examination of the results can
dispel some fictions and fallacies.

1\) Considerable progress has been made in recording capability of
monitoring instruments, mostly as the result of progress in the hardware
and software used in digitizing systems. Improvements include
multichannel synchronized recording of different parameters, fast data
acquisition, automated data reduction, and improved resolution.

2\) With the steady progress and expanded capability of instruments, it
becomes increasingly important to achieve greater consistency in
definitions of the disturbance parameters and the methods of application
of the monitoring instruments.

3\) Site-to-site variations in exposures preclude making precise
predictions for a specific site from an overall data base, but useful
predictions can be made by adjusting the overall data base only slightly
by limited data collection at the site of interest.

4\) The steady increase in the number of surge protective devices being
installed in low-voltage power circuits in the last several years can be
expected to continue. The result might be a lowering of the mean values
of observed surges but not necessarily the extreme values of the
distribution.

5)  Differences among results indicated by a cursory comparison can in
    many cases be resolved by a closer examination of the conditions
    under which the surveys were conducted. However, some differences
    appear less likely to be explained if raw data have been processed
    and the initial parameter measurements are no longer available for
    consideration. Providing greater detail in the published reports and
    sharing of experiences at technical meetings might help overcome
    this difficulty.

6\) A new IEEE Working Group on Monitoring Electrical Quality has been
formed with a broad scope that encom­passes this process of improving
consistency in the definitions and interpretation of power disturbances.
In addition, the IEEE Working Group on Surge Characterization is also
attempting to obtain a broader data base for the revision of the Guide
on Surge Voltages. These two groups are ready to provide counsel and
forum to any would-be surveyor in planning and reporting the collection
of new data on disturbances, thus avoiding later difficulties in
incorporating the results in a shared data pool. This paper is presented
in support of this effort and to promote greater participation among
interested workers and users.

#### 

#### ACKNOWLEDGMENTS

The contributions to this review by Arnold Perrey, Catherine Fisher, and
Robert Palm, Jr., respectively, in the literature search, organization,
and graphic presentation, are gratefully acknowledged.

#### 

#### REFERENCES

\[1\] T. S. Key, \"Diagnosing power quality-related computer problems,\"
IEEE Trans. Ind. Appl., vol. IA-15, no. 4, July/Aug. 1979.

\[2\] F. D. Martzloff, "The protection of computer and electronic
systems against power supply and data line disturbances,\" General
Electric Company, Schenectady, NY, Report 85CRD084, 1985.

\[3\] J. H. Bull and M. A. Nethercot, \"The frequency of occurrence and
magnitude of short duration transients in low-voltage supply mains,\"
Radio Electronic Engineer, Sept. 1964.

\[4\] Committee Report, \"Bibliography on surge voltages in ac power
circuits rated 600 V and less,\" IEEE Trans. Power App. Syst., vol.
PAS-89, no. 6, July/Aug. 1970.

\[5\] F. D. Martzloff and G. J. Hahn, \"Surge voltages in residential
and industrial power circuits,\" IEEE Trans. Power App. Syst., vol.
PAS­89, no. 6, July/Aug. 1970.

\[6\] S. F. Cannova, \"Short-time voltage transients in shipboard
electrical systems,\" in IEEE IAS 1972 Annual Meeting Conference Record.

\[7\] G. W. Allen and D. Segall, \"Monitoring of computer installation
for power line disturbances,\" presented at the IEEE PES Winter Meeting
Conference, New York, Jan. 1974, Paper C74199-6.

\[8\] M. Goldstein, and P. D. Speranza, \"The quality of U.S. commercial
ac power,\" in Proc. INTELEC Conf., 1982.

\[9\] O. B. Laug, and D. L. Hillhouse, Analysis of Requirements for
Shipboard Voltage Spike Suppressors, NBSIR 84-2844, National Bureau of
Standards, 1984.

\[10\] H. Wernstrom, M. Broms, and S. Boberg, \"Transient overvoltages
on ac power supply systems in Swedish industry,\" Foorsvarets
Forskningsanstalt, Huvudavdelning 3, Sweden, Report FOA E 30002­E2, 1984.

\[11\] J. D. Aspnes, B. W. Evans, and R. P. Merritt, \"Rural Alaska
electric power quality,\" IEEE Trans. Power App. Syst., vol. PAS- 104,
no. 3, Mar. 1985.

\[12\] R. Odenberg and B. Braskich, \"Measurements of voltage and
current surges on the ac power line in computer and industrial
environments,\" IEEE Trans. Power App. Syst., vol. PAS- 104, no. I0,
Oct. 1985.

\[13\] T. M. Gruzs, \"Power disturbances and computer systems: A
compari­son of the Allen-Segall and the Goldstein-Speranza power line
monitoring studies,\" in Proc. 1986 Electrical Overstress Exposition,
Nelson Publishing Company, Nokomis, FL, Jan. 1986.

\[14\] J. J. Goedbloed, \"Transients in low-voltage supply networks,\"
IEEE Trans. Electromagn. Compat., vol. EMC-29, no. 2, May 1987.

\[15\] IEEE Standard Dictionary of Electrical and Electronics Terms,
ANSI/IEEE Std 100-1984.

\[16\] Guide on Surge Voltages in Low-Voltage AC Power Circuits,
ANSI/IEEE C62.41-1980.

\[17\] Insulation Coordination within Low-Voltage Systems, Including
Clearances and Creepage Distances for Equipment, IEC 664-1980.

\[18\] Electromagnetic Emission and Susceptibility Requirements for the
Control of Electromagnetic Interference, DOD-STD-46 I B.

\[19\] Interface Standard for Shipboard Systems, DOD-STD- 1 399, Sec.
300, 1978.

\[20\] F. D. Martzloff, \"Varistor versus environment: Winning the
re­match,\" IEEE Trans. Power Del., vol. PWRD- 1, no. 2, Apr. 1986.

\[21\] W, Meissen, \"Uberspannungen in Niederspannungsnetzen,\"
(Over­voltages in Low-Voltage Networks), Elektrotechnische Zeitschrift,
vol. 104, 1983.

\[22\] G. W. Allen and D. Segall, \"Impact of utility distribution
systems on power line disturbances,\" presented at the IEEE PES Summer
Meeting Conf., July 1976, Paper A763884.

\[23\] IEEE Guide on Surge Testing for Equipment Connected to
Low-­Voltage AC Power Circuits, ANSI/IEEE C62.45-1987.

\[24\] IEC Multilingual Dictionary of Electricity, published by IEEE and
distributed in cooperation with Wiley-Interscience.

\[25\] Guideline on Electrical Power for ADP Installations, FIPS Pub 94,
National Bureau of Standards, 1983.

\[26\] F. D. Martzloff, \"Matching surge protective devices to their
Environ­ment,\" IEEE Trans. Ind. Appl., vol. IA-21, no. 1, Jan./Feb.
1985.

\[27\] T. S. Key and F. D. Martzloff, \"A consensus on powering and
grounding sensitive electronic equipment,\" in Conf. Rec. IEEE IAS
Annual Meeting, vol. 2, Sept. 1986, pp. 1054-1060.

\[28\] Recommended Practice on Powering and Grounding Sensitive
Electronic Equipment in Commercial and Industrial Power Sys­tems, IEEE
P1100.

\[29\] F. D. Martzloff and H. A. Gauper, \"Surge and high-frequency
propagation in industrial power lines,\" IEEE Trans. Ind. Appl, vol.
IA-22, no. 4, July/Aug. 1986.

\[30\] F. D. Martzloff, \"Transient overvoltages in secondary systems,\"
General Electric Company, Schenectady, NY, Report 81CRD121, 1981.

\[31\] G. W. Allen, \"Design of power-line monitoring equipment,\" IEEE
Trans. Power App. Syst., vol. PAS-90, no. 6, Nov./Dec. 1971.

\[32\] UL Standard for Safety 943, Ground Fault Circuit Interrupters,
Underwriters Laboratories, 1976.

\[33\] Electrical Fast Transients-Burst Requirements, IEC Standard 80 1
­4.

POWER QUALITY MEASUREMENTS:

BRINGING ORDER OUT OF CHAOS

François D. Martzloff

National Bureau of Standards

ABSTRACT - The quality of the power supplied to sensitive electronic
equipment is an important issue. Quantifying this quality, however, is
difficult under the present state of nonexistent or uncoordinated
standards concerning two related questions: (1) what levels of power
quality are required for what types of loads, and (2) what measurement
techniques are required to determine reliably the level of disturbances
that reduce quality. Development of standards by the consensus process
and voluntary compliance, although a slow process, is a mechanism for
reaching technically sound and cost-effective solutions. Several
standards projects are in progress, but need an industry-wide support to
become the generally accepted basis for valid and useful measurements of
power quality.

# INTRODUCTION

The issue of Power Quality has gained increased recognition as the
result of two unrelated but parallel developments: (1) an increase in
the sophistication of electronic systems, sometimes resulting in an
unintentional increase in their sensitivity to power supply
disturbances. and (2) an increase in the number and power rating or
power conversion equipment, generally resulting in the distortion of the
power system voltage. Improvements in the situation described as .poor
power quality\' can be achieved by reducing the sensitivity of equipment
to power line disturbances, or by limiting the injection of disturbances
\-- or better yet, by reducing both in a coordinated approach. While
these remedies might seem obvious in principle, their implementation
(enforcement) appears more difficult. Voluntary standards provide a
guide for such an implementation. To that end three types of standards
are necessary. The first concerns measurements, to obtain correct and
universally acceptable data. The second concerns equipment performance,
to define both its tolerance to disturbances and its limits on emission
of disturbances. The third concerns acceptable disturbance levels on the
utility supply, to promote compatibility of equipment with the utility
supply. These standards are developed by reconciling purely technical
objectives with economic reality. For a standard to be effective and
acceptable, both aspects must have an accurate basis. This paper gives
emphasis to the technical aspects of the measurements, specifically
field measurements of power quality.

**THE GOAL: MATCHING EQUIPMENT CAPABILITY WITH POWER QUALITY**

To achieve a satisfactory operational environment regarding power
quality, a coordinated approach is needed to match the characteristics
of equipment with those of the power supply. The concept of matching is
important: it implies actions on both sides of the issues, not
unilateral demands for corrective action based on a posture that the
other party is the offender. Three approaches will read to this
matching, separately or in combination:

> 1\. Increasing equipment tolerance for disturbances,
>
> 2\. Controlling the emission of disturbances by equipment, utility
> equipment
>
> as well as end-user equipment)
>
> 3\. Providing interface devices when necessary.

Each of these three approaches requires accurate information on power
supply disturbances for any action to be effective. Action can be
preventive, when a potential problem is identified before new equipment
is installed. Action can be curative, when a problem arises after new
equipment is installed. The problem can appear in two forms: (1) the new
equipment is sensitive to disturbances already present in the system
(the equipment is the victim); (2) the new equipment creates a
disturbance that affects equipment already in service (the new equipment
is the offender).

These two terms used to label the situation reveal the adversarial
postures that can exist. In an ideal world, one would consider total
system goals to optimize economical and technical solutions, rather than
point fingers. In the real world, cooperation can lead to a mutually
satisfactory solution between the source and the receiver of
disturbances (note the neutral words) in contrast with the other labels.

The first step towards recognizing the need for improving the power
quality situation is to determine the level of disturbances occurring in
the system. The parameters characterizing a power supply are: frequency,
voltage amplitude, waveform, and symmetry. Therefore, the nature of
disturbances may be classified by their effect y of disturbances is
associated d the probability of occurring at a given site over a time
period.

The level of disturbances is determined by measurements conducted at the
site of an existing installation or at a future installation of
potentially sensitive equipment. These measurements are described as
\'site surveys.\' If the tolerance of the equipment for disturbances is
defined (a need that is not always recognized) and the level of
disturbances determined by the site survey is excessive, then the three
matching actions mentioned above come into play. Any one of the three,
or a combination, can be the most effective solution. Knowledge of the
situation will point toward a solution, rather than reliance on a common
misconception that providing a simple interface (line conditioning) will
solve all problems. This misconception is nurtured by frequent
observations that many problems have in fact been solved by simply
inserting a line conditioner. However, one should not yield to
temptation of making a general rule from these isolated success stories,
and ignore other, more effective or more economical approaches achieving
inherent compatibility.

Because this additional line conditioning equipment may require
significant capital investment. the choice of corrective measures is
made by economic trade-off. However, if technical inputs to this
trade-off are incorrect because erroneous conclusions result from a
faulty site survey, the whole process is worthless or misleading. For
this reason, a good understanding of the merits and limitations of site
surveys is essential for reconciling expectations with reality before
specifying expensive line conditioning equipment. In their review of
power quality site surveys, Martzloff and Gruzs \[1\] discussed how one
should deal, not with fiction or fallacies, but with facts.

In an attempt to clarify the issues. this paper first presents a review
of the origins and definition, of disturbances. Next, the development of
monitoring instruments during the last 25 years is described. Finally,
an appeal is made for improving measurement methods to provide more
consistent reporting power disturbances recorded in future surveys.

## CLASSIFICATION AND ORIGIN OF POWER LINE DISTURBANCES

The four power system parameters identified above -- frequency,
amplitude, waveform, and symmetry -- can serve as frame of reference to
classify the disturbances according to their impact on these four
parameters.

Frequency disturbances are associated with power system faults.
Interconnection of the utility grid ensures frequency stability, except
when a fault occurs that isolates the local system from the grid.
leaving local generation more sensitive to load variations. Transient
frequency disturbances, just before an outage. occur in a system
containing large rotating machines: should the system trip out, the
machines will maintain some voltage, with decaying amplitude and
frequency, while they coast to a final stop

Amplitude variations can occur in several forms; their description is
inextricably associated with their duration. They range from extremely
brief durations to steady-state conditions, making the description and
definition difficult, even controversial at times. Their causes and
effects need close examination to understand the mechanisms and to
define an appropriate solution.

Waveform variations occur when nonlinear loads draw a current which is
not sinusoidal. One could also describe an amplitude variation as
momentary waveform variation, but the intended meaning of the term is a
steady variation of the waveform, or lasting at least over several
cycles. This type of disturbance is also described as harmonic
distortion because it is easy to analyze as the superposition of
harmonics to the fundamental frequency of the power system.

Dissymmetry, also called unbalance, occurs when unequal single-phase
loads are connected to a three-phase system and cause a loss of
symmetry. This type of disturbance primarily concerns rotating machines,
and as such is not receiving broad attention. It is important however,
for machine designers and users. The percentage by which one phase
voltage differs from the average of all three is the usual description
of this type of disturbance.

The origin of disturbances can be described as external to the
particular power system, or as. internal. In a typical situation, the
boundary of a power system is defined as the watthour meter, and
reference is made to the utility side of the meter (external source), or
to the user side of the meter (internal source). A different approach is
to describe the origin in technical terms, such as lightning, load
switching. power system fault, and nonlinear loads. Depending on local
conditions, one can be more important than the others, but all need to
be recognized. The mechanism involved in generating the disturbance also
determines whether the occurrence will be random or permanent.
unpredictable or easy to define.

Lightning surges are the result of direct strikes to the power system
conductors as well as the result of indirect effects. Indirect effects
include induction of overvoltages in loops formed by conductors and
ground potential rises resulting from lightning current in the soil. A
lightning strike to the power system can activate a surge arrester,
producing a severe reduction or a complete loss of the power system
voltage or one half-cycle. A flashover of line insulators can cause a
breaker to trip, with reclosing delayed by several cycles, causing a
momentary power outage. Thus, lightning can be the obvious cause of
overvoltages near its point of impact, but also a less obvious cause of
voltage loss at a considerable distance from its point of impact.
Clearly, the occurrence of this type of disturbance is unpredictable at
the microscopic level. At the macroscopic level, it is related to
geography. seasons, and local system configuration.

Load switching is a major cause of disturbances. Switching large loads
on or off can produce long-duration voltage changes beyond the immediate
transient response of the circuit. Whether the switching is done by the
utility or by the user is immaterial from the technical point of view,
although the responsibility may be the subject of a contractual dispute.
The occurrence of these disturbances is somewhat predictable, but not
necessarily under controlled conditions. The introduction of power
conversion equipment and voltage regulators operating by switching on
and off at high frequency has created a new type of load switching
disturbance. These disturbances occur steadily, although their amplitude
and harmonic content will vary for a given regulator as the load
conditions vary.

Power system faults occur on both sides of the meter, resulting from
equipment failure or external causes (vehicle collisions, storms, human
errors). These disturbances can range from a momentary voltage reduction
to a complete loss of power lasting for minutes, hours, or days. Their
accidental origin makes them unpredictable, although the configuration
of a power system and its environment can make it more or less prone to
this type of disturbance.

Nonlinear loads draw non-sinusoidal currents from the power system, even
if the power system voltage is a perfect. These currents produce
non-sinusoidal voltage drops in the system source impedance, which
distort the sine wave produced by the power plant generator. A typical
nonlinear load capacitor-input filter, such as used in most computers,
drawing current only at the peaks of the voltage sine wave.

Characterizing these four types of disturbances and disturbance
mechanisms involves detection (measurement) of their occurrence and
description of the results of these measurements. What might appear a
simple process is in fact made difficult by deficiencies in de fining
disturbances observed when making site survey measurements.

### DEFICIENCIES IN DEFINITIONS

One difficulty in coordinating efforts for improving power quality is
that terms used to describe power disturbances are poorly defined. An
effort is being made by standards-writing organizations to resolve this
problem, as described later in this paper, but consensus has yet to be
reached. The following two examples of this lack of consensus illustrate
the point; resolving them is beyond the scope of this paper.

***What is a surge?*** The accepted meaning of surge. in the context of
power systems, is a short-duration overvoltage, typically less than a
few milliseconds. These surges are caused by lightning, power system
switching, or faults. Protection against them is obtained by protective
devices called surge arresters (formerly called lightning arresters) for
utility systems, and surge suppressors, or spike suppressors for
end-user systems. This first meaning of the word 'surge' is not that
established by manufacturers and users of disturbance monitors and line
conditioners. The unfortunate second meaning, a consequence of
nonexistent standards on the subject, is a momentary overvoltage at the
fundamental frequency, with a duration of typically a few cycles. What
the designers and users of surge arresters or suppressors call 'surge'
is called 'impulse' or 'spike' by the monitoring instrument community.
Figure 1 shows graphic descriptions of the confusion created by the dual
meaning of the word 'surge.'

***What is an outage?*** Most users agree that it means a loss of line
voltage. The duration of this event, however, is quite different when
'outage' is cited by computer users (as short as one half-cycle), or by
power engineers (seconds, perhaps minutes). Furthermore, some users and
manufacturers of line conditioners do not make a clear distinction
between complete loss of line voltage (zero voltage condition), severe
undervoltages ('deep sags'), or the single-phasing of polyphase power
systems. Part of the problem may be that the definition of 'outage' has
regulatory implications for evaluating the performance of public utility
companies.

As another example of definitions deficiencies, standards dictionaries
do not define the term "sag". It is accepted as meaning a momentary
voltage reduction at the ac power frequency. However, there is no
consensus on the details (threshold, duration, etc.) of what
characterizes a sag.

With the present definition deficiencies, manufacturers and users of
disturbance monitors are left without guidance and consequently define
terms independently from each other, hence the confusion. In fact, the
development and widespread use of disturbance monitors should motivate a
more coordinated and rational approach toward resolving these
deficiencies. Progress in technology of monitoring instruments during
the last two decades is remarkable and worthy of a brief review.

## DISTURBANCE MONITORS DEVELOPMENT HISTORY

Historically, the first (unintended) disturbance monitors were the
actual load equipment. Only later, when confronted with unexplained
failures or upsets, did the users start monitoring the quality of their
power systems. Electric utilities have been monitoring the parameters of
their systems, but the precise characterization of microsecond-duration
surges in the early 1960s required special oscilloscopes. For the next
15 years, oscilloscopes or simple peak detectors were the basic
instruments for monitoring transient overvoltages. Starting in the
1970s, commercially-produced digitizers became available. Since then,
technology has made continuing progress as experience has accumulated.

Early site surveys were limited to voltage measurements. This limited
interest reflected concerns for damage to sensitive electronic
components connected across the line. Ignoring the importance of the
source impedance led to some performance standards \[2\] that do not
specify the current-handling requirements for surge protective devices.
With the introduction and widespread application of new clamping
protective devices (silicon avalanche diodes or metal oxide varistors),
the surge current diverted through these devices became a very important
factor for proper device selection.. Therefore, the need emerged for
characterizing current surges as well as voltage surges, but few surveys
to date have addressed this need. This need offers a challenge and an
opportunity to designers of monitoring instruments.

This challenge has also produced attempts to measure "energy" with an
instrument which is actually only a voltmeter. By assigning parametric
values to the source impedance of the surge and integrating the product
(volts seconds) of the surge, some knowledge of the energy involved
would be obtained. Computing true energy, of course, requires the
measurement of both voltage and current. However, the real question
concerns the sharing of energy between the impedance of the source and
the impedance of the load. A discussion of the energy in the surge
versus energy delivered to the protective device is beyond the scope of
this paper. The difference between the two must be recognized, however,
to prevent further confusion as future monitoring instruments include an
"energy" parameter in their readouts.

With. the present development of sophisticated multi-channel digitizing
instruments, future surveys should monitor both voltage and current.
Note, however, that the current of interest is that which the surge
source would force through a surge protective device. The amplitude as
well as the waveform of the surges needs to be characterized for the
correct application of surge protective devices. Peak-reading monitors
provide useful information on surge activity at a given site, but
assessment of the surge severity level for the proper sizing of
protective devices also requires waveform and source impedance
information.

One difficulty facing users of monitoring instruments in this fast-paced
technology is that manufacturers are steadily improving their
instruments. These improved features respond to specific wishes of the
users or result from their own product research and development, a
desirable situation. On the negative side, however. data collected by
different instruments become equipment-dependent. Comparison of survey
results by third parties is then difficult in the absence of details on
the instrument characteristics and methods of measurement.

## TYPES OF MONITORS

The instruments used in past surveys reflect technology progress as well
as logistics constraints, resulting in a diversity of approaches. Until
recently, all monitoring instruments were just special voltmeters. Some
of the monitors recorded a single parameter, such as the value of
voltage peaks, or the occurrence of voltage peaks above a preset
threshold. Other monitors combined time with voltage measurements, to
characterize the voltage waveforms. The following list shows the
evolution of simple surge monitors into complex disturbance monitors.

***Threshold counters*** -- The surge is applied to a calibrated voltage
divider, triggering a counter each time it exceeds a preset threshold.
The early types had analog circuitry; more recent types have digital
conversion of signals.

***Digital peak recorders*** -- The surge is converted to a digital
value and recorded in a buffer memory for later playback. In the early
types of recorders, only the peak was recorded. In later types, the
duration of the surge was also recorded opening the way to the more
complex digital waveform recorders now available.

***Oscilloscope with camera*** -- The surge triggers a single sweep on
the cathode !ay tube of the oscilloscope, and is recorded as it occurs
by an automatic shutterless camera.

***Screen storage oscilloscope*** -- The surge is displayed and stored
on the cathode ray tube. and a camera is used for permanent recording
after the surge has occurred. The writing speed capability of these
oscilloscopes was a limitation in the late 1960s.

***Digital storage oscilloscope*** -- The surge is digitized and stored
in a shift register for subsequent playback and display whenever it
exceeds a preset threshold. An important feature is the capability of
displaying events occurring before the beginning of the surge.

***Digital waveform recorder*** -- With the advent of compact, portable
instruments, a revolution has taken place in the field of disturbance
and recorders. The earlier surge waveform recorders were large and
difficult to transport to field sites \[3\]. \[4\]. New
microprocessor-based instruments have introduced a. portable storage and
computing power which has made waveform analysis and graphic display
;possible. In these instruments, voltage and current signals are
digitized and stored, allowing reports of many different parameters of
the disturbance. The range of parameters which can be monitored is
expanded. Long trends can be detected, harmonic analysis can be
performed, and the types of possible measurements are limited only by
the creativity of the instrument designers and the curiosity of the
users.

Although some site surveys might aim at high accuracy, the real world
experiences an infinite variety of disturbances, making it difficult to
fit them into simple, orderly categories. Any attempt to describe these
disturbances in fine detail restricts general usefulness of the data and
can lead to illusions on applicable accuracy. Some simple (and
inexpensive) instruments are useful indicators of frequent disturbances.
Other instruments, more complex (and more expensive), provide
comprehensive data on disturbances. A general observation from many
surveys conducted by different researchers is that results vary widely
from site to site. Thus, there is a practical limit to the detail that a
survey can yield, and unrealistic expectations of precise information
should be avoided. What is really needed is a more uniform and
compatible recording and reporting of the data.

## COMPARISONS AMONG SITE SURVEY REPORTS

***Relative occurrence of different types of disturbances.*** Two site
surveys have been widely cited. One was performed in the early 1970s the
other in the late 1970s by Allen and Segall \[5\], the other in the late
1970s by Goldstein and Speranza \[6\]. Each of these surveys presented
results by describing various kinds of disturbances (overvoltages, sags,
etc.) and cited the percentages of each type of disturbance in the total
of all the observed disturbances. The findings did not at first appear
to agree, raising questions on the likelihood of a change in power
systems between the first and second survey. However, a detailed
comparison of these two surveys \[1\], revealed that the disagreement
was rooted in a difference of the thresholds built into the monitors,
rather than a change in the behavior of power systems.

***Differences in surge amplitudes.*** Amplitudes of surges reported in
several surveys vary over a wide range. Comparisons are difficult
because the reports do not present the data in a uniform format.
Attempting to get a quantitative comparison of the amplitudes reported
seems a futile exercise, because of the following reasons:

1\. Looking at the "maximum values" cited in the reports, one finds that
in some surveys this maximum is actually a value known only as being
above the range of the instrument, while for others it is the measured
value.

2\. Because the threshold of the recorder varies among surveys. and the
frequency of occurrences increases dramatically with \' a\' lower
threshold, the labels of average, median, most \' frequent, typical,
etc., are not meaningful for comparing amplitudes.

***Differences in surge waveforms***. What a 'typical' surge might be
has been the subject of many discussions. Several surveys confirm the
finding of ringing waves, as opposed to the traditional unidirectional
impulses. However, wide differences still exist among the reports. The
following examples illustrate this point.

Martzloff-Hahn \[7\] were among the first to report ring waves, recorded
by 1960 vintage oscilloscopes. Their findings were incorporated into the
data that resulted in the selection of a 100 kHz ring wave for the UL
Standard Ground Fault Circuit Interrupters \[8\] and the IEEE Guide on
Surge Voltages \[9\].

Odenberg and Braskich \[10\] used different instruments recording only
two points of the waveform: (1) the peak amplitude and time to peak, and
(2) the time to 50% of the peak amplitude. As such, this description is
not a complete waveform. Furthermore, they reported that 90% of their
250,000 recordings show the 50% point occurred between 900 and 1100
microseconds. This finding is unique among all the surveys.

Wernstrom et al. \[11\] report ring waves of 500 kHz, bursts of fast
transients lasting a few microseconds, and even some unidirectional
isolated impulses.

Goedbloed \[12\] is more concerned with interference than damage; his
report gives emphasis to amplitude, rate of rise, and 'energy' rather
than to waveform.

With the advent of portable monitors capable of presenting the digitized
data with graphic details as well as summaries, an explosion in the
volume of data can expected. Just the detail and weight of the
information being collected might swamp the researchers, unless data
reduction procedures are implemented. However, whenever data reductions
are performed by different persons, there is a high probability that
criteria for reduction will be different, making comparisons difficult,
even impossible. Thus, this increased sophistication of available
instrumentation makes coordination even more imperative. The added
availability of harmonic analysis by portable monitors will also lead to
an expansion of data supporting standards on harmonic control \[13\].

Agreement and disagreement on rate of occurrence versus levels. Several
survey authors have attempted to fit a classic statistical distribution
or a simple relationship between the rate of occurrence of surges and
their amplitudes. The motivation for such a simplified presentation
might be rooted in a belief that nature obeys simple mathematical laws.
The reality, however, is that so many different mechanisms contribute to
the generation of surges that a simple relationship is unlikely.
Notwithstanding this rationale. a remarkable finding emerges from
plotting the results of all the surveys on the same graph. Figure 2
shows the relative distributions of the findings, normalized for voltage
level and frequency of occurrence for each survey report. The slope of
the lines is what can be compared, not the absolute rate of occurrence.
It is remarkable that slopes are similar among the surveys. although the
absolute frequency of occurrence is site-dependent.

## WORKING TOWARD MORE CONSISTENT SURVEYS

The ambiguities plaguing the field of site surveys have become apparent
to many interested researchers, resulting in the formation by IEEE of a
new Working Group on Monitoring Electrical Quality. The scope of a
Recommended Practice being prepared by this group reads:

> This Recommended Practice concerns the application of instruments used
> for monitoring electrical disturbances on power systems. The scope
> includes the definition of disturbance terms, the calibration and
> connection of the instruments, and the interpretation and reporting of
> the results. It does not include specific design aspects of the
> instruments.
>
> The disturbances of interest are those conducted on ac power lines for
> single or polyphase systems with direct operating voltage connections
> to the instruments not exceeding 1000 V RMS. Depending on the design
> of the instruments, the duration of the recorded disturbances may
> range from nanoseconds to many seconds, or more.

*While the prime interest is focused on monitoring low-voltage ac power
systems (50, 60 or 400 Hz), suitable interfaces may allow monitoring
systems of higher voltage; dc systems may also be monitored with these
instruments. It is also recognized that available instruments may be
capable of monitoring other parameters such as radiated EMI or
environmental conditions; however. the scope of this document is limited
to conducted electrical parameters (voltage, current, and derived
parameters).*

**EXPECTATIONS VERSUS REALITY ON POWER QUALITY**

Improved credibility of power quality data offers an opportunity to
revisit existing standards or develop new standards dealing with power
quality. The areas would benefit from this review:

***More realistic definitions of the limits of system voltages.*** The
limits currently defined are relatively small percentages (5 to 15%) of
nominal values. Many anecdotal stories have been told on momentary
overvoltages exceeding the limits of the only standard addressing these
limits, ANSI C84.1 \[16\]. Until well documented, these stories can only
remain anecdotal. However, ignoring them can lead to misapplication of
surge protective devices by attempting to suppress surges at a level too
close to the momentary overvoltages that do occur.

***Improved consensus on the characteristics of surges.*** The IEEE
Guide on Surge Voltages \[9\], dating back to 1980, attempted to
simplify the situation by describing the surge environment with only two
waveforms and an upper practical limit. Unfortunately. this Guide was
misconstrued by some users as a mandatory standard. A revision is
underway, proposing two additional waveforms and presenting the
information in a manner that should discourage the misguided use of the
document as a performance standard.

***Improved Consensus on harmonic control.*** Harmonic causes and
effects have been the subject of many studies and technical papers. but
no performance standard exists to settle potential disputes between
sources and receivers of harmonic distortion. The prevailing document is
a Guide. \[13\]; significant improvements are expected from a revision
currently being conducted.

## CONCLUSIONS

Power quality measurements, typically performed by site surveys have
evolved from the simple monitoring of surge voltages to the
sophisticated analysis of many criteria of power quality. There is still
room for improvement in the procedures -- an improvement that can be
guided by voluntary standards. Detailed observation of the issues lead
to the following conclusions:

1\. Considerable progress has been made in the recording capability of
monitoring instruments as the result of progress in the hardware and
software used in digitizing systems. Improvements include multi-channel
synchronized recording of different parameters, fast data acquisition,
automated data reduction, and improved resolution.

2\. Improvements in consistency must be made, commensurate with the
steady progress and expanded capability of instruments. This greater
consistency is needed in the definitions of the disturbance parameters
and the methods of application of the monitoring instruments.

3\. Site-to-site variations in the occurrence of disturbances prevent
making precise predictions for a specific site from an overall data
base.

4\. Differences among results indicated by a cursory comparison can be
resolved by a closer examination of the conditions under which the
surveys were conducted. However, some differences are less likely to be
explained if raw data have been processed and the initial parameter
measurements are no longer available for review.

5\. A new IEEE Working Group on Monitoring Electrical Quality has been
formed with a broad scope that encompasses this process of improving
consistency in definitions and interpretation of power disturbances. In
addition, the IEEE Working Group on Surge Characterization is also
attempting to obtain a broader data base for the revision of the Guide
on Surge Voltages.

6\. Improved cooperation promoted by the process of voluntary standards
development and the exchange of ideas made possible by forums such as
the Energy Technology Conference, will avoid some of the difficulties on
sharing the data pool recited in this paper. This paper is presented in
support of this effort and to promote greater participation among
interested workers and users.

#### REFERENCES

\[1\] Martzloff, F.D., and Gruzs, T.M., "Power Quality Site Surveys:
Facts, Fiction, and Fallacies," Conference Record, IEEE Industrial
&Commercial Power Systems Conference, May 4-7, 1987.

\[2\] Interface Standard for Shipboard Systems, DOD-SM13\", Sec. 300,
1978.

\[3\] Allen, G.W. "Design of Power-Line Monitoring Equipment," IEEE
Transactions on Power Apparatus and Systems, Vol. PAS-90 No.6, Nov/Dec
1971.

\[4\] Key, T.S, "Diagnosing Power Quality-Related Computer Problems,"
IEEE Transactions on Industry Applications, Vol. IA- 15, No. 4,
July/August 1979.

\[5\] Allen, G.W. and Segall, D., "Monitoring of Computer Installation
for Power Line Disturbances," IEEE PES Winter Meeting, Conference Paper
C74199-6, January 1974.

\[6\] Goldstein, M., and Speranza, P.D., "The Quality of U.S. Commercial
AC Power," Proceedings. INTELEC Conference, 82Ct(1818-4.1982.

\[7\] Martzloff. F.D., and Hahn, G.J., "Surge Voltages in Residential
and Industrial Power Circuits," IEEE Transactions on Power Apparatus &
Systems, Vol. PAS-89, No. 6, July/August 1970.

\[8\] UL Standard for Safety 943, Ground Fault Circuit Interrupters,
Underwriters Laboratories, 1976.

\[9\] Guide on Surge Voltages in Low-Voltage AC Power Circuits, ANSI/
IEEE C62.41-1980.

\[10\] Odenberg, R. and Braskich, B., "Measurements of Voltage and
Current Surges on the AC Power Line in Computer and Industrial
Environments," IEEE Transactions on Power Apparatus and Systems, Vol.
PAS-104, No. 10, October 1985.

\[11\] Wernstrom, H.. Broms, M., and Boberg, S., Transient Overvoltages
on AC Power Supply Systems in Swedish Industry, Report FOA E 30002-E2,
Foorsvarets Forskningsanstalt, Huvudavdelning 3. Sweden. 1984.

\[12\] Goedbloed, J.J., "Transients in Low-Voltage Supply Networks,"
IEEE Transactions on EMC, May 1987.

\[13\] IEEE Guide for Harmonic Control and Reactive Compensation of
Static Power Converters ANSI/IEEE Std 519-1981.

\[14\] Bull, J. H. and Nethercot, M.A., "The Frequency of Occurrence and
Magnitude of Short Duration Transients in Low-Voltage Supply Mains,"
Radio Electronic Engineer, September 1964.

\[15\] Cannova, S.F., "Short-time Voltage Transients in Shipboard
Electrical Systems," Conference Record, IEEE-IAS 1972 Annual Meeting,
CH0685-8-IA.

\[16\] American National Standard for Electric Power Systems and
Equipment - Voltage Ratings (60 Hz), ANSI C84.1-1982

**Monitoring Power Quality**

François D. Martzloff

National Institute of Standards and Technology

Gaithersburg, Maryland

Thomas M. Gruzs

Liebert Corporation

Columbus, Ohio

Site surveys are generally initiated to evaluate the quality of the
power available at a specific loca­tion with the aim of avoiding
equipment distur­bances in a planned installation or of explaining (and
correcting) disturbances in an existing installation. In either case,
survey results constitute one of the inputs in the decision-making
process of providing supplementary line conditioning equipment, either
before or after power disturbances have become a problem. Depending on
the reliability requirements of the load equipment, its susceptibility,
and the severity of the dis­turbances, various line conditioning methods
have been proposed: surge suppressor (with or without filter), isola­tion
transformer, voltage regulator, magnetic synthesizer, motor-generator
set, or uninterruptible power supply (UPS).

Because this additional line conditioning equipment may require
significant capital investment, the choice of corrective measures is
generally made by economic trade­off which is the prerogative and
responsibility of the end user. However, if technical inputs to this
trade-off are incorrect because erroneous conclusions were drawn as a
result of a faulty site survey, the whole process is worthless -- or
worse yet, misleading.

For this reason, a good understanding of the merits and limitations of
site surveys is essential for reconciling expectation with reality
before expensive line condition­ing equipment is called for; one should
deal, not with fiction or fallacies, but with facts.

Power disturbances that affect sensitive electronic loads have a variety
of sources. Lightning, utility switching, and utility outages are
often-cited sources of power distur­bances. However, power disturbances
are frequently caused by users themselves, through switching of loads,
ground faults, or normal operation of equipment. As one example,
computer systems are not only sensitive loads, but can also generate
disturbances themselves. Their non­linear load characteristics can cause
interactions with the power system such as unusual voltage drops,
overloaded neutral conductors, or distortion of the line voltage.

Utility systems are designed to provide reliable bulk power. However, it
is not feasible for them to provide continuous power of the quality
required for a completely undisturbed computer operation. Because normal
use of electricity generates disturbances, and because unexpected power
system failures will occur, every site will experience some power
disturbances, but their nature, severity, and incidence rates will vary
from site to site.

**Confusion in Term Definitions**

As will become painfully apparent in next month's review of site
surveys, the terms used by the workers reporting their measurements do
not have common defini­tions. An effort is being made within the IEEE to
resolve this problem, as described later in this paper, but con­sensus
has yet to be reached. In this paper, terms describ­ing disturbances are
consistent with the IEEE Standard Dictionary of Electrical and
Electronics Terms \[1\] and with established usage within the community
of surge protec­tive devices engineers.

The generally accepted meaning of surge voltage, in the context of power
systems, is a short-duration overvoltage, typically less than 1 ms or
less than one half-cycle of the power frequency. This meaning is not
that which has been established by manufacturers and users of monitoring
instruments and line conditioners. This unfortunate sec­ond meaning is a
momentary overvoltage at the funda­mental frequency with a duration of
typically a few cycles.

**Figure 1 -- Graphic depictions of disturbances with multiple
meanings**

In this article, this second meaning of the word "surge" (a momentary
overvoltage) will be signaled by the use of quotation marks. What power
engineers call surge is referred to as "impulse" or "spike" by the
monitoring instrument community. Figure 1 shows by graphic descriptions
the confusion created by the dual meaning of the word surge.
Acknowl­edging the desire of users for terse labels, we propose for
consideration the word "swell" instead of "surge" for a momentary
over­voltage.

The term "outage" is another example of confusion created by unsettled
definitions. Most users agree that it means a complete loss of line
voltage, but the duration of an outage can be quite different when
defined by computer users (as short as one half-cycle) or power
engineers (seconds, perhaps min­utes). Part of the problem may be that
the definition of "outage" has regulatory implica­tions for evaluating
the performance of public utility companies. Users and manufacturers of
line conditioners do not make a clear distinction between complete loss
of tine voltage (zero voltage condition), severe undervoltages ("deep
sags"), or the single-phasing of polyphase power systems. For example, a
momentary flicker of fluores­cent lighting caused by a brief loss of
voltage might be considered an outage; however, a brief sag to less than
80 percent of nominal voltage will produce the same visible effect. Some
UPS manufacturers consider input voltage sags that cause transfer to the
battery backup operation as outages.

The term "sag" has not yet been defined in the IEEE Dictionary, but it
is now gener­ally accepted as meaning a momentary voltage reduction at
the ac power frequency. However, details (threshold, duration, etc.) of
what characterizes a sag are not well defined.

**Motivation For Site Surveys**

With the increasing dependency on computer-based systems for industry,
commerce, and con­sumers, disruptions from power disturbances are less
and less acceptable. Operational problems such as hardware damage,
system crashes, and pro­cessing errors are the most visible indications
of power disturbances. Some computer system users may accept (albeit
reluctantly) such problems because they see them as unavoidable. Others
may be unaware that otherwise invisible power dis­turbances could be the
cause of these problems. A single power disturbance can cost more in
down­time and hardware damage than the investment in power protection
that would have prevented the effect of the disturbance. Nearly all
sites can bene­fit from a reduction of operational problems by improving
the quality of power supplied to the computer systems \[2\].

Power line monitoring with sophisticated power disturbance recorders has
often been advocated as a way of determining if any line conditioning is
required. While monitoring appears to be a logical first step, it has
limitations. For example, severe disturbances occur infrequently or on a
seasonal basis. Therefore, monitoring periods of less than a year might
not produce an accurate profile of power disturbance, and most users are
unwilling to wait at least a year to characterize the problem. Also,
power line monitoring only produces data on past performance. Changes
within the site (or at neighboring sites) or by the utility can
drastically alter the power disturbance profile in ways that line
monitoring cannot predict.

**Figure 2 -- Origins of common mode disturbances**

While exact prediction of the disturbances to be expected at a specific
location is almost impossible -- and attempting it would be a fallacy --
general guidelines can be formulated. An attempt has been made by
standards-writing groups to provide guidance \[3\] or specifications
reflecting expected disturbances \[4-6\]. However, users will still seek
specific data for their particular case, and site surveys will still be
necessary. Another fallacy would be to attempt correction of power line
disturbances revealed by monitoring and then to expect operational
problems of equipment to disappear without having first determined the
exact susceptibility of the equipment. Operational problems are the
results of more than just power distur­bances.

**Types of Disturbances**

Power line disturbances can be classified into two cate­gories: common
mode and normal mode disturbances. The two terms were first defined in
the context of com­munication circuits; a recent IEEE Guide \[7\] has
estab­lished an expanded definition which is used in this article, as
outlined in the following paragraphs. The IEEE Dic­tionary \[1\] and the
IEC Dictionary \[8\] define symmetrical and asymmetrical voltages akin
to, but not interchangea­ble with, the definitions of normal mode and
common mode, respectively.

Common mode disturbances are defined as unwanted potential differences
between any or all current-carrying conductors and the grounding
conductor or earth. In three-phase grounded-wye power supplies typical
of large computer systems, common mode disturbances can also be defined
as the potential difference between neutral and ground.

Two different types of common mode distur­bances can affect a sensitive
load. The first type is a disturbance on the input power conductors
relative to the input power grounding conductor. Points 1 and 2 of
Figure 2 show examples of the origins for these disturbances. This type
of disturbance can be limited somewhat by a line conditioner, but it is
also influenced by the location of the line condi­tioner and the wiring
practices.

The second type is a ground potential difference between elements of the
computer or remote peripherals connected to the computer. Point 3 of
Figure 2 is an example of this type of disturbance, which is more
difficult to limit because it is influ­enced by factors such as system
configuration and the impedance of the grounding system. These two
factors are generally beyond the direct control of the user except in
the construction of a new facility.

Because of the broad frequency band involved, wiring resonances can make
equalizing ground potentials difficult. Proper computer system
ground­ing, including a signal reference grid, has been found to be
effective against most common mode disturbances \[9\]. However, when
remote elements are connected to the computer systems by data cables,
large ground potential differences are possi­ble. Proper surge protection
of the power supply and proper grounding of data cables will help
elimi­nate hardware damage but might not prevent data corruption. When
dealing with the situation of example 3 in Figure 2, fiber optic links
are very effective because they provide complete metallic separation of
the various elements in the system -- a separation that might not be
sufficiently achieved by the discrete opto-isolation devices sometimes
proposed for that function \[10\].

Normal mode disturbances are defined as unwanted potential differences
between any two current-carrying cir­cuit conductors. Figure 3 shows
three examples of the origins of such disturbances. Usually a sine wave
of nomi­nal voltage is desired for a computer power supply; any deviation
from this sine wave is a normal mode distur­bance. Computer users and
monitoring instruments designers characterize these disturbances by a
variety of terms not always clearly defined such as sags, surges
("swells"), outages, impulses, ringing transients, waveform distortion,
and high-frequency noise. Unfortunately, there is no consensus at the
present time on the exact meaning of these terms and their underlying
quantitative definitions such as amplitude, duration, and thresholds.

**Figure 3 -- Origins of normal mode disturbances**

**Types of Monitors**

The instruments used in the various surveys reflect technological
progress as well as logistics constraints resulting in a diversity of
approaches. Nevertheless, all monitoring instruments used in past
surveys were voltme­ters (with one exception, combining voltage and
current measurements) from which disturbance parameters were derived.
Some of the monitors recorded a single param­eter such as the actual
voltage peak or the fact that the voltage exceeded a preset threshold.
Other monitors com­bined time with voltage measurements describing
voltage waveforms. The recording functions of instruments used in the
surveys may be classified in broad categories:

Threshold counters --- The surge is applied to a calibrated voltage
divider, triggering a counter each time a preset threshold is exceeded.
The early types were analog; more recent types are digital.

Digital peak recorders --- The surge is converted to a digital value
which is recorded in a buffer memory for later playback or printed out
immediately after it occurs. In the early types of recorders, only the
peak was recorded; in later types, the duration of the surge was also
recorded, open­ing the way to the more complex dig­ital waveform recorders
now available.

**Figure 4 -- Effect upon voltage peak and waveforms with varistor
placed upstream of monitor**

Oscilloscope with camera --- The surge triggers a single sweep on the
oscillo­scope's CRT, which is recorded as it occurs by a shutterless
camera with automatic film advance. The oscillo­scopes available at that
time (the early 1960s) did not allow differential measurements.

Screen storage oscilloscope --- The surge is displayed and stored on the
cathode ray tube. The writing-speed capability of these oscilloscopes
was a limitation in the late 1960s.

Digital storage oscilloscope --- The surge is digitized and stored in a
shift register for subsequent playback and display whenever a preset
threshold is exceeded. An important feature is the capability of
displaying events prior to the beginning of the surge.

Digital waveform recorder --- The surge is digitized and stored in a
man­ner similar to the digital storage oscilloscope, but additional data
pro­cessing functions are incorporated in the instrument, allowing
reports of many different parameters of the dis­turbance relating voltage
to time.

Although some surveys might aim at great accuracy, the real world
experiences such a variety of distur­bances that any attempt to describe
them in fine detail only restricts gen­eral usefulness of the data.
Seeking such fine and definitive detail is another fallacy. Some simple
instru­ments are useful (and inexpensive) indicators of frequent
disturbances; other, more sophisticated (and more expensive) instruments
can provide quite comprehensive data on disturbances (but only on past
events from which future disturbances can be extrapolated only by
assum­ing that the causes will remain unchanged). Thus there is a
practical limit to the amount of detail that a survey can yield, and
unre­alistic expectations of very precise information should be avoided.

# Previous And Future Surge Recordings

Before attempting yet another broad survey of power quality, would-be
surveyors need to consider not only improvements in instrumenta­tion but
also changes that have occurred in modem power systems -- in particular
the proliferation of surge protective devices. These two dif­ferences
between earlier surveys and the more recent surveys should be kept in
mind when comparing results and when planning future surveys.

Prior to the proliferation of surge protective devices in low-voltage
sys­tems (those defined by IEEE and IEC as 1000 V or less), a limitation
had already been recognized \[4\] for peak voltages: the flashover of
clearances, typically between 2 and 8 kV for low-voltage wiring devices.
For that reason the expected maximum value cited in the IEEE Guide on
Surge Voltages \[3\] reflects this possible trun­cation of the
distribution around 6 kV. Unfortunately, some readers of this Guide
interpreted the upper practi­cal limit of 6 kV as the basis for a
withstand requirement, and they have included a 6-kV test requirement in
their performance specifica­tions. A new version of this Guide, currently
under p repa­ration as a Recommended Prac­tice, will attempt to avoid this
misinterpretation.

The number of surge-pro­tective devices such as varis­tors used in the
United States since their introduction in 1972 on low-voltage ac power
circuits may be estimated at 500 million. Therefore, a new lim­itation
exists in the voltage surges that will be recorded. A surge-rec­ording
instrument installed at a ran­dom location might be close to a varistor
connected near the point being monitored. Such a proximity of surge
protective devices and rec­ording instruments may impact pres­ent and
future measurement campaigns. Four are outlined below.

> 1\) Locations where voltage surges were previously identified --
> assuming no change in the source of the surges -- are now likely to
> experience lower voltage surges, while current surges will occur in
> the newly installed protective devices.
>
> 2\) Not only will the peaks of the observed voltages be changed, but
> also their waveforms will be affected by the presence of nearby
> vanistors as illustrated in Figures 4, 5, and 6.
>
> A\) If a varistor is located between the source of the surge and the
> recording instrument (Figure 4), the instrument will record the
> clamping voltage of the varistor. This voltage will have lower peaks
> but longer time to half-peak than the original surge.
>
> B\) If the instrument is located between the source of the surge and a
> varistor, or if a parallel branch circuit contains a vans­tor (Figure
> 5), the instrument will now record the clamping voltage of the
> varistor, preceded by a spike corresponding to the inductive drop in
> the line feeding the surge current to the varistor.
>
> C\) If a varistor is connected between the line and neu­tral
> conductors, and the surge is impinging between line and neutral at the
> service entrance (normal mode), a new situation is created, as shown
> in Fig­ure 6. The line-to-neutral voltage is clamped as intended, but
> the inductive drop in the neutral con­ductor returning the surge
> current to the service entrance produces a surge voltage between the
> neu­tral and the grounding conductors at the point of connection of the
> varistor and any downstream point supplied by the same neutral.
> Because this surge has a short duration, it will be enhanced by the
> open-end transmission line effect between the neutral and grounding
> conductors \[11\].

3)  The surge voltage limitation function previously per­formed by
    flashover of clearances is now more likely to be assumed by the new
    surge protective devices that are constantly being added to the
    systems.

> 4\) These three situations will produce a significant reduc­tion in the
> mean of voltage-surge recordings from the total population of
> different locations as more and more varistors are installed. However,
> the upper limit will remain the same for locations where no varistors
> have been installed. Focusing on the mean of voltage surges recorded
> in power systems can create a false sense of security and an incorrect
> description of the environ­ment. Furthermore, the need for adequate
> surge cur­rent handling capability of a proposed suppresser with lower
> clamping voltage might be underestimated because some diversion is
> already being performed.

**Figure 6 -- Protective device installed between line and neutral
conductors,**

**for surge applied in normal mode**

## References

> \[1\] *IEEE Standard Dictionary of Electrical and Electronics Terms*,
> ANSI/IEEE Std. 100, 1988.
>
> \[2\] T.M. Gruzs, "Power Disturbances and Computer Sys­tems: A
> Comparison of the Allen-Segall and the Goldstein-Speranza Power Line
> Monitoring Stud­ies," *Proceedings, 1986 Electrical Overstress
> Exposition,* Nelson Publishing Co., Nokomis, FL, Jan. 1986.
>
> \[3\] *Guide on Surge Voltages in Low-voltage AC Power Cir­cuits*,
> ANSI/IEEE C62.41, 1980.
>
> \[4\] *Insulation Coordination within Low-Voltage Systems, Including
> Clearances and Creepage Distances for Equip­ment*, IEC Std 664, 1980.
>
> \[5\] *Electromagnetic Emission and Susceptibility Requirements for
> the Control of Electromag­netic* Interference, DOD-STD-461B.
>
> \[6\] Interface Standard for Shipboard Systems, DOD-STD-1399, Sec.
> 300, 1978.
>
> \[7\] *IEEE Guide on Surge Testing for Equipment Connected to
> Low-Voltage AC Power Cir­cuits,* ANSI/IEEE C62.45, 1987.
>
> \[8\] *IEC Multilingual Dictionary of Electricity*, pub­lished by IEEE
> and distributed in coopera­tion with Wiley-Interscience.
>
> \[9\] *Guideline on Electrical Power for ADP Installa­tions*, FIPS Pub
> 94, National Bureau of Standards, 1983.
>
> \[10\] F.D. Martzloff, "The Protection of Com­puter and Electronic
> Systems Against Power Supply and Data Line Distur­bances," *General
> Electric Report 85CRD084*, Schenec­tady, NY, , 1985.
>
> \[11\] F.D. Martzloff and H.A. Gauper, "Surge and High-Frequency
> Propagation in Industrial Power Lines," *IEEE Transactions IA-22*, no.
> 4., July/Aug. 1986.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Part II of this article, a detailed review of several site sur­veys, will
appear in the March issue of Powertechnics. This article was based on
"Power Quality Site Surveys: Facts, Fiction, and Fallacies," by F.D.
Martzloff and T.M. Gruzs, which first appeared in IEEE Transactions on
Industry Applications, Vol. IA-24, No. 6, pp. 1005-1018, Nov./Dec. 1988.
© 1988 IEEE

**Systems and instruments** **in site surveys**

François D. Martzloff

> National Institute of Standards and Technology

Thomas M. Gruzs

Liebert Corporation

Every on-site survey of power quality utilizes a variety of methods and
instruments, requiring careful interpretation of survey results. A close
examination of underlying assumptions in nine published surveys shows
that some differences can be reconciled, but indicates the need for new
or improved standards.

Power quality surveys have been conducted for two rea­sons: 1) to
identify potential problems or causes of equip­ment disturbances at a
specific site, and 2) to develop a broad data base with the hope that
the general findings will be applicable in specific cases. This article
gives a review of nine papers reporting broad data base surveys, but the
conclusions are also applicable for site-specific surveys. The review
shows problems that readers encounter when different authors use
different instruments, different definitions, and as a result sometimes
reach contradictory conclusions. The nine surveys were conducted in the
United States and Europe over the last 25 years. Power systems have not
changed much, but the load equipment characteristics, as well as the
capabilities of disturbance monitoring instruments, have changed
considerably. Table 1 shows details of the locale, system voltage,
instrument type, and connection mode as described in the papers.

Bull and Nethercot, in a 1964 article \[11, report monitoring performed
in the mid 1960s on 240-V systems in Great Britain with instruments of
their design. Their initial instrument used vacuum tubes, leading to the
development of a solid-state circuit which may be considered the
forerunner of modem monitors. The instrument had several channels, each
with a different threshold.

The monitoring locations were selected to include a variety of
conditions, with data being collected for several weeks at each location
over a total period of 2 years. The results do not mention transients
above 600 V; it seems that no channels were provided above that level
because the authors were only concerned with the range of 50-600 V.

Martzloff and Hahn, in a 1970 paper \[21, report the highlights of
measurements made in the 1963 to 1967 period on residential, commercial,
and industrial circuits, mostly single-phase 120 V. Waveform data were
obtained with commercial, custom-modified oscilloscopes fitted with
motor-driven cameras. These oscilloscopes were installed at various
locations where transient activity was suspected, not at randomly
determined locations. In addition, a peak counter circuit was developed,
and 90 units with a 1200- or a 2000-V threshold were deployed at 300
locations where there was no prior suspicion of unusual transient
activity.

The oscilloscope data gave one of the first indications that the
traditional unidirectional impulse, long used for dielectric testing,
might not be representative of surges occurring in low-voltage circuits.
The threshold data indicated locations where surges above 1200 V occur
frequently (about 3 percent of the sample), while other locations appear
far less exposed to surges. The 100:1 reduction of an alarming failure
rate of clock motors, achieved by increasing the surge withstand
capability of the motors from 2000 to 6000 V, is documented in that
paper.

**Cannova**, in a 1972 paper \[3\], reports the monitoring of surges on
U.S. Navy shipboard 120- and 450-V power systems in the late 1960s.
Instrumentation used for the initial phase of the monitoring program
consisted of oscilloscopes similar to those used by Martzloff. Provision
was also included for the option of measuring the transients alone
(through filters) or superimposed on the ac line voltage; this option
reflects the old dichotomy, still unsettled to this day, as to whether
the transients should be measured as an absolute value or as a deviation
from the instantaneous value of the ac sine wave (see the last column of
Table 1).

The results are not reported separately for 120. and 450-V systems;
therefore, it is not possible to express them in terms of per-unit or
percentage of nominal system voltage. Cannova\'s statistical treatment
aims at fitting the recorded transients to a normal distribution and
concludes that a log normal distribution is a better fit. A brief
statement is made on the durations of the recorded transients (without a
statement on how those durations are defined), citing a majority of
durations between 4 μs and 6 μs, with a few at 19 μs.

From the data base, acknowledged to be a small total number of events, a
protection level of 2500 V was defined. The specification of a 2500-V
1.2/50-μs voltage withstand by DOD STD 1399 was derived from this
survey.

Two aspects of the conclusions are especially worth noting: 1) there was
no information on the source impedance of the surges\' and yet the data
eventually served to specify requirements for surge protective devices;
and 2) a large difference in frequency of\' occurrence was noted among
ships of the same type and class, similar to the observations on land
surveys.

**Allen and Segall**, in a 1974 paper \[4\] report the monitoring of
several types of power disturbances at computer sites, performed with
oscilloscopes, oscillographs, and digital instruments, in the 1969-1972
period. Details of the instrumentation were described in a separate
paper \[5\]. Disturbances are described as overvoltages and
under-voltages, oscillatory decaying disturbances, voltage spike
disturbances, and outages. The terms sag and \"surge\" (\"swell\") had
not yet made their appearance in the jargon.

The survey was conducted in two phases. In a first phase, preliminary
information was obtained on ranges of disturbances, leading to the
development of a second generation of monitors deployed in the next
phase. The recorded disturbances are described by plots and histograms.
The highest surge recorded in the first phase is shown as 350 V. In the
second phase, the monitors grouped all surges into three categories, the
highest having a range of 100 percent (of line voltage) to infinity, so
that no detailed information is provided to describe high peak values.
The survey does report in detail the occurrence of under-voltages and
overvoltages, providing a basis for the comparisons with the
Goldstein-Speranza results.

**Goldstein and Speranza**, in a 1982 paper \[61, report the monitoring
of several types of disturbances at a variety of locations in the Bell
system, with digital multiparameter instruments, in the 1977 and 1979
period. The conditions of the survey are documented, including
instrument locations and definitions of the parameters as well as the
methods of data processing.

The findings are briefly reported with emphasis on predictions for
disturbances expected at specific sites. The prediction is obtained by
using a statistical model derived for all sites and making adjustments
reflecting specific site conditions determined by a limited survey at
that site. The authors are emphatic on the point that the lack of
correlation between sites prevents blanket application of the overall
findings to any specific site, but that useful predictions are possible
by combining the overall data with limited knowledge on specific site
data.

**Werntrom, Broms, and Boberg**, in a 1984 report published in Sweden
and circulated in the United States as an English draft translation
\[71, report monitoring of industrial 220/380-V systems by digital
multithreshold instruments, corroborated by waveform recording with
digital storage oscilloscopes. The parameters to be recorded and
reported are defined in an introductory section; however, their
description of \"common mode\" and \"differential mode\" in the English
translation does not correspond exactly to symmetrical and asymmetrical
voltages defined by the IEC.

The range of surges recorded extends from 200 to 2000 V.

In a summary tabulation, rise times are shown as ranging from 20 to 200
ns and duration from 0.2 to

2.5 μs. The results show a wide difference of surge activity among sites
but a relatively constant slope of the rate of occurrence versus level.

**Aspnes, Evans, and Merritt**, in a 1985 paper \[81, report a survey of
the power quality in rural Alaska at isolated power generation
facilities. The monitoring instruments are identified as one of the
contemporary commercial digitizing monitors. A very comprehensive
summary of the recordings is presented including frequency deviations (a
unique situation in these isolated systems), sags and \"surges\"
(\"swells\"), impulses (i.e., surges ), and outages. Some ambiguity
arose because of the possibility that built-in surge protection in the
monitors might have attenuated the surges being recorded.

**Odenberg and Braskich,** in a 1985 paper \[9\], report the monitoring
of computer and industrial environments with a digital instrument
capable of the simultaneous recording of voltage surges and current
surges. This new capability for relating voltage and current shows a
growing awareness of the need to monitor current surges - an improvement
over previous surveys limited to the measurement of voltages. However,
the reported surge currents are those of a current toward undefined
loads downstream from the instrument; they do not include any
measurement of the current through a shunt-connected surge diverter, a
measurement that would have provided new information on the source
impedance of the surges.

The digital processing applied by the instrument yields two points of
the surge: the peak value with the time to reach peak and the time
elapsed until decay to 50 percent of the peak value. From these two
points, a \"waveform\" description is proposed without any other
information on the actual waveform. From a large number of recorded
surges (more 250,000 events) a startling finding is cited: 90 percent of
the recorded surges have their 50-percent point in a narrow window of
900-1100 μs. Attempts to reconcile this singular finding with the
observations reported by other surveys have not been successful.

**Goedbloed,** in a 1987 paper \[10\], describes in detail a
custom-built automated measurement system monitoring 220/380-V networks
in Europe. The automated measurement system reflects the progress made
in digitizing techniques since the days of vacuum tubes. By combining
two commercial recorders with a custom interface, the developers
obtained detailed recordings with a 10-ns sampling interval and 20-μs
window on the first recorder and a 1-μs sampling interval and 2-ms
window for the second recorder.

The system included a provision for automated data reduction, yielding
raw data as well as statistical information on amplitude, rate of rise,
energy measure, spectral density, and conversions from time domain to
frequency domain. With a relatively low threshold of 100 V above the
line voltage, the distribution of occurrences is weighted toward low
amplitudes; nevertheless, occurrences are reported above 3000 V.

# Relative Occurrence of Different Types of Disturbances

Two of the surveys reviewed in this paper have been widely cited, one
performed in the early 1970s by Allen and Segall (A-S for short) \[4\],
and the other performed in the late 1970s by Goldstein and Speranza
(G-S) \[6\]. However, the findings do not at first appear to be in
agreement; a detailed comparison of these two surveys provides a good
illustration of the pitfalls of superficial interpretation of survey
results.

A cursory comparison of the results might lead one to conclude that a
significant change in power disturbances at computer sites occurred
between 1972 (end of the A-S study) and 1979 (end of the G-S study). A-S
reported 88.3 percent of observed disturbances as spikes, impulses, and
transients, 11.2 percent as sags, and 0.47 percent as outages. G-S, on
the other hand, reported 87 percent of the observed disturbances as
sags, 7.4 percent as impulses, 0.7 percent as \" surges\" (\"swells\"),
and 4.7 percent as outages (which they call power failures).

Taking a more careful look at the monitoring thresholds used in each
study helps to explain why the number of impulses appear to have
decreased and the number of sags appear to have increased. Since G-S use
a threshold of -4 percent for sags while A-S use - 10 percent, one can
expect the G-S study to indicate a higher percentage of sags, because
the sags between - 4 and - 10 percent are not included in the A-S study.
Oscillatory decaying disturbances are not specifically identified in the
G-S study but are included under the category of impulses. The threshold
for impulses used by G-S (200 V for 120-V lines, or 118 percent) is
higher than that used by A-S (+-l0 percent). Because the rate of
occurrence increases steeply for lower amplitude disturbances, one can
expect a drastic reduction in the percentage of impulses reported by the
G-S study as compared to the A-S study,

The increase in percentage of power outages reported by G-S may be
explained by the shift in the number of disturbances observed due to
other threshold changes. Percentages can be a very misleading basis for
comparison unless all conditions are equal. For example, the incidence
of power outages observed in both studies is very similar, even though
the percentages are one order of magnitude apart; A-S report 0.6
occurrence per month while G-S report 0.4 occurrence per month.

When the disturbance rates at the same thresholds are compared for the
A-S data and the G-S model (for 75 percent probability), the results are
surprisingly similar. The conclusions of these two studies are that deep
sags contribute about 62 percent of the power system problems which are
related to normal mode disturbances, severe impulses are responsible for
21 percent, outages for 14 percent and \"surges\" (\"swells\") for 2
percent.

## Differences in Surge Amplitudes

The amplitudes of the surges reported in the surveys vary over a wide
range, and comparisons are difficult because the data are not presented
in a uniform format. An attempt was made to get a quantitative
comparison of the amplitudes reported in the surveys; however, the
exercise was quickly found to be futile because of the following two
main reasons.

1)  Looking at \"maximum values,\" one finds that in some surveys the
    quoted maximum is actually a value in excess of the range of the
    instrumentation, while for others it is the measured value. There
    are too few points and information is insufficient to attempt a
    statistical treatment of this truncated data base. Furthermore, the
    quoted value in some surveys is the total voltage (instantaneous
    value of ac sine wave plus surge), while in others the sine voltage
    has been filtered out. When surges are in the range of several
    thousand volts (the concern being damage), the difference between
    the two definitions is not significant; however,, when surges are in
    the range of a few hundred volts (the concern being malfunction),
    the difference is significant.

2)  Because the lower threshold of the recorders varies among surveys,
    and the frequency of occurrences increases dramatically with lower
    thresholds, the labels of average, median, most frequent, typical,
    etc., are not meaningful for comparing amplitudes. The preceding
    discussion of A-S and G- S results has illustrated the profound
    effect of threshold selection on reported results when they are
    expressed in percentages.

A general explanation of differences in amplitudes found in the various
surveys might be the observation by some of their authors of the lack of
correlation between sites. Furthermore, some surveys include sites where
equipment failures were experienced or expected, while other surveys
were made at sites not singled out for particular problems. Thus the
differences in overall results of various surveys might simply be the
result of the different surge exposure at the points of monitoring. This
explanation implies that surveys will still be needed where specific
information is desired.

## Differences in Waveform

From those surveys made with waveform recording capability, the
\"typical\" forms suggested by each author have been collected in Figure
1.The finding of ringing waves, as opposed to the traditional
unidirectional impulses, seems general in these low-voltage circuits. 4

**Martzloff and Hahn** were among the first to report ring waves. Their
reported measurements were incorporated into the data that resulted in
the eventual selection of a 100-kHz Ring Wave with a 250- or 500-ns rise
time for the UL Standard Ground Fault Circuit Interrupters \[11\] and
the 0.5-μs 100-kHz Ring Wave of the IEEE Guide on Surge Voltages \[12\].

While **Cannova** does not report detailed descriptions of the
waveforms, the statements \"4 to 6 μs\" and \"up to, 19 μs\" could be
interpreted either as a time to half-value or as the time between the
initial rise and the first zero crossing of a ringing wave.
Interestingly, that data base led to the specification of a
unidirectional longer impulse, the classic 1.2/50 μs voltage impulse,
for conservative rating of candi­date surge protection devices to be
installed in the shipboard environment \[13\].

**Wernstrom, Broms, and Boberg** show three examples of recordings. The
first is indeed a ring wave with a frequency of about 500 kHz and a rise
time of 200 ns. The second example is a burst of nanosecond-duration
transients, similar in shape to the proposed IEC/TC65 Electrical Fast
Transients \[14\]. The third example is (of all things) a unidirectional
(almost) impulse.

The data reported by **Odenberg and Braskich** are different from the
others in that only two points of the waveform are peak amplitude. As
such, waveform; furthermore, of their 250,000 recordings show between
900 and 1100 μs in Power Quality Surveys unique among all the surveys.

**The Goedbloed** data presentation reflects concerns addressing
interference rather than damage; hence, the emphasis was given to
amplitude, rate of rise, and energy rather than waveform. An oscillogram
characterized as \"typical\" is presented in Figure 1, a ring wave with
a frequency of about 800 kHz.

Thus, the ambiguities plaguing the field of site surveys have become
apparent to many interested workers, resulting in the formation of a new
Working Group Monitoring Electrical quality sponsored by a new IEEE
Standard Coordinating Committee on Power Quality. Stay tuned in this
area; contributions to the development of a new standard by this working
group are invited and welcome, and further information may be obtained
from the authors.

####### Conclusions

A review of power quality site surveys conducted over the last twenty
years reveals interesting facts, and close examination of the results
can dispel some fictions and fallacies.

1\) Considerable progress has been made in the recording capabilities of
monitoring instruments, mostly as the result of progress in the hardware
and software used in digitizing systems. Among the many improvements are
multichannel synchronized recording of different parameters, fast data
acquisition, automated data reduction, and improved resolution.

2\) With the steady progress and expanded capability of instruments, it
becomes increasingly important to achieve greater consistency in
definitions of the disturbance parameters and the methods of application
of the monitoring instruments.

3\) Site-to-site variations in exposures preclude making pre­cise
predictions for a specific site from an overall data base, but useful
predictions can be made by adjusting the overall data base only slightly
by limited data collection at the site of interest.

4\) The steady increase in the number of surge protective devices being
installed in low-voltage power circuits in the last several years can be
expected to continue. The result might be a lowering of the mean values
of observed surges but not necessarily the extreme values of the
distribution.

5\) Differences among results indicated by a cursory com­parison can in
many cases be resolved by a closer examina­tion of the conditions under
which the surveys were conducted. However, some differences appear less
likely to be explained if raw data have been processed and the initial
parameter measurements are no longer available for consideration.
Providing greater detail in the published reports and sharing of
experiences at technical meetings might help overcome this difficulty.

6\) A new IEEE Working Group on Monitoring Electrical Quality has been
formed with a broad scope that encompasses this process of improving
consistency in the definitions and interpretation of power disturbances.
In addition, the IEEE Working Group on Surge Characterization is also
attempting to obtain a broader data base for the revision of the Guide
on Surge Voltages. These two groups are ready to provide counsel and
forum to any would-be surveyor in planning and reporting the collection
of new data on disturbances, thus avoiding later difficulties in
incorporating the results in a shared data pool.

**References**

\[1\] J. H. Bull and M. A. Nethercot, \"The Frequency of Occurrence and
Magnitude of Short Duration Transients in Low-Voltage Supply Mains,\"
Radio Electronic Engineer, Sept. 1964.

\[2\] F. D. Martzloff and G. J. Hahn, \"Surge Voltages in Residential
and Industrial Power Circuits,\"

IEEE Trans. Power App. Syst., vol. PAS-89, no. 6, July/Aug. 1970.

\[3\] S. F. Cannova, \"Short-Time Voltage Transients in Shipboard
Electrical Systems,\" in IEEE IAS 1972 Annual Meeting Conf. Rec.

\[4\] G. W. Allen and D. Segall, \"Monitoring of Computer Installation
for Power Line Disturbances,\" presented at the IEEE PES Winter Meeting
conference, New York, Jan. 1974, Paper C74199-6.

\[5\] G. W. Allen, \"Design of Power-Line Monitoring Equipment,\" IEEE
Trans. Power App. Syst., vol. PAS-90, no. 6 Nov/Dec. 1971.

\[6\] M. Goldstein, and P.D. Speranza, \"The Quality of U.S. Commercial
AC Power,\" in Proc. INTELEC Conf., 1982.

\[7\] H. Wernstrom, M. Broms and S. Boberg, \"Transient Overvoltages on
AC Power Supply Systems in Swedish Industry,\" Foorsvarets
Forskningsanstalt, Huvudavdelning 3, Sweden, Report FOA E 30002-F2,
1984.

\[8\] J. D. Aspnes, B. W. Evans and R. P. Merritt, \"Rural Alaska
Electric Power Quality,\" IEEE Trans. Power App Syst., vol. PAS-104, no.
3, Mar. 1985.

\[9\] R. Odenberg and B. Braskich, \"Measurements of Voltage and Current
Surges on the AC Power Line in Computer and Industrial Environments,\"
IEEE Trans. Power App. Syst., vol. PAS-104, no. 10, Oct. 1985.

\[10\] J. J. Goedbloed, \"Transients in Low-Voltage Supply Networks,\"
IEEE Trans. Electromagn. Compat., vol. EMC-29, no. 2, May 1987.

\[11\] UL Standard for Safety 943, Ground Fault Circuit Interrupters,
Underwriters Laboratories, 1976.

\[12\] Guide on Surge Voltages in Low-Voltage AC Power Circuits,
ANSI/IEEE C62.41-1980.

\[13\] Interface Standard for Shipboard Systems, DOD-STD-1399, Sec. 300,
1978.

\[14\] Electrical Fast Transients - Burst Requirements, IEC Standard
801-4.

**No Joules for Surges:**

**Relevant and Realistic Assessment of Surge Stress Threats**

**Thomas Key** and **Arshad Mansoor** **François Martzloff**

Power Electronics Applications Center National Institute of Standards
and Technology

Knoxville, TN 37932 USA Gaithersburg, MD 20899 USA

***Abstract:*** The paper challenges attempts to characterize the surge
environment in low-voltage end-users power systems by a single number -
the \"energy in the surge\" - derived from a simple voltage measurement.
Our thesis is that such attempts are neither realistic nor relevant. The
paper shows that these erroneous attempts, based on the classical
formula for computing the energy dissipated in a linear load of known
resistance, cannot be applied to characterize the environment per se,
but only to a well-defined combination of source and load. In
particular, there is no meaningful relationship between the \"energy\"
in a surge event and the energy actually deposited in a varistor by this
surge event. A review of equipment failure or upset mechanisms related
to the occurrence of a surge voltage reveals that none of these
mechanisms are related to this so-called \"energy in the surge.\"
Several failure mechanisms other than energy-related are identified,
pointing out the need to describe the surge events with a more
comprehensive set of parameters in conducting future surveys.

# I. INTRODUCTION

In an attempt to characterize the potential threat of surges to
voltage-sensitive equipment, recordings of the surge voltages occurring
in low-voltage power circuits have been conducted in the last
quarter-century, driven by the increasing concern about the
vulnerability of new electronic appliances to transient overvoltages.
However, practically all the recording conducted by organizations such
as Bell Laboratories \[I\], Canadian Electrical Association \[2\],
General Electric \[3\], IBM \[4\], National Power Laboratory \[5\] and
other researchers, including Goedbloed \[6\], Hassler & Lagadec \[7\],
Meissen \[8\], and Standler \[9\] have been limited to the measurements
of transient voltages

Interest in these measurements has been re-kindled by several
investigations aimed at assessing power quality in end-user facilities.
These recordings, initially limited to measurement of peak voltages,
were perfected with the help of increasingly sophisticated voltmeters.

Early surveys were conducted with conventional oscilloscopes and later
on, portable digital instruments with on­board computing became
available. While these instruments made possible the recording of a
voltage transient as a function of time and graphical presentation of
data, the recording of such a surge voltage profile does not lend itself
to a simple description by a single number. To circumvent this
difficulty, many researchers called upon the basic concept of energy to
characterize the level of surge threat in terms of voltage.

Referring now to classical electrical engineering, the instantaneous
power dissipated in a resistor by a transient voltage is merely the
square of the applied voltage, divided by the resistance.

Taking the integral over the duration of the transient yields the
energy. By analogy, the \"energy\" of a surge could then be computed
from the voltage measured at some point of a power system. According to
this intuitive concept \-- but fallacious as we will show \-- the
greater the measured voltage, the greater the \"energy\" and thus the
greater the threat to potential victim equipment.

A review of the known failure or upset mechanisms of various types of
devices and equipment identifies several surge parameters other than
energy-related. These include source impedance, peak amplitude, maximum
rate of rise, tail duration, and repetition rate. Therefore, future
surveys of surge events conducted with present monitoring instruments or
with even better instruments will need to include more comprehensive \--
and hopefully standardized methods of presenting and interpreting the
results.

## II. THESIS

Our thesis is that neither the threat nor the \"energy level\" of a
surge can be characterized by simply measuring the voltage change during
a surge event. Any reference to the concept of \"energy of a surge\"
should definitely not be introduced. Such avoidance is based on two
facts:

1\. A voltage measurement of the surge event cannot alone predict the
energy levels affecting the devices exposed to that surge. This is
particularly true for nonlinear surge-protective devices where energy
deposited in the device is relevant, but has little to do with the
misleading concept of \" energy in the surge\" derived from an
open-circuit voltage measurement.

2\. There are other than energy-related upset or failure modes of
equipment. These effects require consideration of other parameters when
describing a surge event to yield relevant and realistic assessment of
surge stress threats.

Our thesis will be supported by an analysis of the impact of surges on
equipment, and illustrated by numerical examples of varistor
applications showing how the description of a surge by its \"energy\"
could then lead to vastly different conclusions.

## III. INTERACTIONS BETWEEN SURGES AND VICTIM EQUIPMENT

At this point we need to identify the devices and equipment that may
become the victims of a surge, and their failure mechanisms.
After-the-fact investigations and experimental data show a wide range of
surge-related upset and failure mechanisms.

These mechanisms include insulation breakdown, flashover, fracture,
thermal and instantaneous peak power overloads, dv/dt and di/dt limits
being exceeded. The following list gives some generic types of surge
victims and the typical failure or upset mechanisms.

1\. ***Electrical insulation***, where the failure mechanism (breakdown
or sparkover) is principally a function of the surge voltage, with the
complication of a volt-time characteristic such that failure under
impulse occurs at a level that increases when the rise time or duration
of the impulse decreases. \"Insulation\" is to be taken in the broadest
sense of solid or liquid material separating energized conductors in
equipment, clearances on a printed circuit board, edges of semiconductor
layers, etc. A distinction must be made between the initial breakdown of
insulation, related to voltage only, and the final appearance of the
damaged insulation, related to the total energy dissipated in the
breakdown path. In another situation, the insulation of the first turns
of a winding may be subjected to higher stress than the others as the
result of the uneven voltage distribution resulting from a steep front
rather than only the peak value of the surge.

***2. Surge-protective devices***, for which the voltage across the
device is essentially constant, and the energy deposited is a function
of the surge current level and duration. One failure mode of such a
device will occur when the energy deposited in the bulk material raises
the temperature above some critical level. Failure modes associated with
the current level, such as flashover on the sides of a varistor disc,
failure at the boundary layers of the varistor grains, or fracture of
large discs, have also been identified and are not related to energy.

3\. ***Semiconductor devices***, such as thyristors responding to the
rate of voltage change can be turned on by a surge \[10\], resulting in
failure of the device or hazardous energizing of the load they control.
In a similar way, a triac may be turned on by a voltage surge without
damage, but still fail by exceeding the peak power limit during a
surge-induced turn-on with slow transition time.

4\. ***Power conversion equipment***, with a front-end dc link where the
filter-capacitor voltage can be boosted by a surge, resulting in
premature or unnecessary tripping of the downstream inverter by on-board
overvoltage or overcurrent protection schemes.

5\. ***Data-processing equipment***, where malfunction (data errors) \--
not damage \-- may be caused by fast rate of voltage changes (capacitive
coupling) or fast rate of current changes (inductive coupling) that
reflect the initial characteristic of the surge event. This response is
insensitive to the \"tail\" of the surge, where all the \"energy\" would
be contained according to the misleading energy-related concept.

6\. ***Light bulbs,*** which of course have a limited life associated
with filament evaporation and embrittlement - a long-term process where
the short burst of additional heating caused by a few microseconds of
overcurrent is negligible \-- but also fail under surge conditions when
a flashover occurs within the bulb, triggering a power-frequency arc
that melts out the filament at its point of attachment \-- another
failure mechanism originating with insulation breakdown.

Among these types of victims, only the clamping-type varistor,
exemplified by the metal-oxide varistors that became so prevalent after
their introduction in the mid-seventies, is directly sensitive to an
energy level associated with a surge event \-- and at that, the energy
deposited in the device\', not the \"energy in the surge.\" (To be
absolutely correct, the ultimate failure mode of a triac or a light bulb
may be indirectly influenced by the energy dissipated in the device
during the surge, but the root cause, the trigger, of the failure is not
the energy.) Considering the explosive proliferation of varistors,
however, one might find some extenuating circumstances in emphasizing
the significance of energy in describing the effect of surges on its
principal target \-- the ubiquitous metal-oxide varistor \-- but this is
a pitfall, a mental trap.

## IV. BAITING THE TRAP

From the interactions described above, it is clear that using a single
voltage measurement to determine surge threat is not sufficient. The
trap was baited by the simplicity and ease of using a single parameter
obtained by analogy with the power dissipated in a fixed resistance,
v2/IR by an instantaneous voltage, v. Clearly in that limited case, the
total energy involved over the surge event would be the time integral of
v2/R, expressed by a number having the same dimensions as watt-seconds,
or joules in the SI system. And thus some power quality monitors placed
on the market in the early eighties were printing out surge event
characterizations expressed in joules. This \"joule\" number was
obtained by computation of the ƒv**^2^** / R dt, where the voltage v was
measured by the instrument, divided by a resistance (taken arbitrarily
as 50 Ω), and integrated over the duration of the event. Manufacturers
of power quality monitor soon recognized the potentially misleading
aspects of such reporting and discontinued the practice

Nevertheless, some researchers continued the practice and are to this
day attempting to characterize the surge environment by the single
parameter of \"energy in the surge.\" As a half-way measure, some are
now proposing a new parameter \"specific energy\" to be understood as
the integral of voltage-squared divided by a reference resistance of 50
Ω (why that particular value ?) and they would report results in
watt-seconds. Figure 1 shows an example of this type of reporting
\[11\].

**Figure 1 -- Example of survey results with number of occurrences**

**as a function of "energy" in milliwatts-seconds**

Acknowledging that indeed, the selection of an appropriate varistor
should reflect the level of threat to which it will be exposed, there is
a need to characterize the threat in terms of the energy that will be
deposited in the varistor by a specific surge event. ***However, there
is no way that a voltmeter measurement only, even if it includes time,
can provide that information.***

**V.** **THESIS DEMONSTRATION BY VARISTOR APPLICATIONS**

To demonstrate our thesis by the ad absurdum process, we will compute
the \"energy in the surge\" as defined by the trap-baiting definition of
\"specific energy\" for three surge events such that all have the same
\"specific energy\" but different voltage levels, waveforms, and
durations. Then, making a further assumption for the unknown impedance
of the surge source, we will compute the energy actually dissipated in
the varistor for these different voltage levels, waveforms, and
durations, and observe that the resulting deposited energy is not the
same!

**1. Elementary example -- basic calculation, fixed impedance**

As a first easy-to-follow step, we take three rectangular pulses, all
selected to have the same \"specific energy\" but different voltage
levels and corresponding durations, and compute the energy deposited in
a (nonlinear) varistor having a given maximum limiting voltage, assuming
that the source of the surge is a voltage source with some arbitrary,
fixed impedance.

It is noteworthy that some source impedance has to be presumed, because
the varistor clamping action rests on the voltage divider effect of the
source impedance and the dynamic varistor impedance prevailing for the
resulting cur-rent.

Start with an assumed surge measurement of 1000 V with duration of 50
μs. The specific energy of such a surge event, according to the proposed
definition, is:

> (1000 V)**^2^** x 50 μs / 50 Ω = 1 joule.

Now consider a surge with amplitude of 316 V (1000 / √10) and duration
of 500 μs (50 x 10). Its specific energy, is:

> (316 V)**^2^** x 500 μs / 50 Ω = 1 joule.

To complete the bracketing range, consider a surge of 3160 V (1000 x
√10), and a duration of 5 μs (50 / 10). Its specific energy is:

> (3160 V)**^2^** x 5 μs / 50 Ω = 1 joule.

We now apply each of the three voltage surges to a 130-V rated varistor
(200 V at 1 mA dc), assuming an arbitrary source impedance of Zs = 1 Ω.
One can compute the resulting current or, for this simple example, make
a fast-converging manual iteration without the help of a computer, as
follows:

> \(a\) assume a current I, and look up the resulting voltage Vv on the
> varistor I-V characteristic;
>
> \(b\) compute \[Zs x I\];
>
> \(c\) is \[Zs x I\]+ Vv = 1000V?

(d) If yes, I is correct, the energy deposited in the varistor is

> I x Vv x ∆t

If no, go back to (a) with a converging assumption for I.

Table I shows the results from this manual iteration for the three
surges defined above. It is quite apparent that the constant \"specific
energy\" for the three surges does not result in the same energy
deposition. The dynamic impedance (Vv/I) of the varistor is also shown,
to illustrate the well-known theorem that the power dissipated in a
resistive load reaches a maximum for matched source-load impedance. This
theorem is yet another reason why a surge to be applied to a varistor
cannot be characterized in the abstract: one needs to know the source
impedance (real and imaginary components) as well, to assess the energy
sharing between source and load.

**2. Calculation with changing the surge source impedance**

As the next step toward reality, we repeat the manual computations for
different values of the impedance of the voltage source, still for the
same \"measured specific energy\" and for the case of the 1000 V
rectangular pulse. Somewhat arbitrarily, but no more arbitrary than the
50-Ω value used in the definition of \"specific energy\", we select
three values of the source impedance.

Bear in mind that the reported measurements of surge voltages have never
provided any information on the system source impedance to be associated
with the reported surge. As a further oversimplification (an unjustified
step in the real world), we will accept the assumption implied in the
computation of the \"specific energy\" that this impedance has only real
components, or is a characteristic impedance. Three values are used in
the following examples.

**TABLE I**

**Energy deposited in a varistor by a surge, as a function of surge
parameters**

\- 50 Ω to go along with the proposed definition of \"specific energy\"
(high-frequency measurements are often made in a 50-Ω environment and
may be the reason for the value selected in the proposed definition).

\- 2 Ω, the so-called effective impedance of a Combination Wave
generator, which is \"deemed to represent the environment\" as stated in
the ANSI/IEEE Recommended Practice C62.41-1991 \[12\];

\- 400 Ω, a number sometimes cited as the characteristic impedance of an
overhead line.

Again here, a simple manual iteration yields the result by postulating a
varistor current, looking up the corresponding voltage on the I-V curve,
such that this voltage is equal to the driving surge voltage, reduced by
the voltage drop in the source for the postulated current. Table 2 shows
the results for the three **examples of assumed source impedance and a
130-V rated varistor.**

**3. Computer calculation with multiple combinations**

We now compute the energy deposited in three varistors of three
different maximum limiting voltages, for three combinations of voltage
levels and durations that produce the same \"specific energy,\" each
with classical waveform (Ring Wave, Combination Wave, Long Wave), sized
to produce 1 joule of energy dissipation in a 50-Ω resistor, according
to the classical formula cited earlier, and for three values of source
impedance. We can anticipate that the peaks will be quite different,
foreboding very different effects on equipment. In fact, the peaks
turned out to be 3 kV, 1.2 kV, and 220 V respectively for the three
waveforms. Applying these three waveforms to a family of varistors
typically used in 120-V or 240-V power systems, we computed the energy
deposited in these varistors for three arbitrary source impedances
(assumed to be ohmic), using the EMTP program \[13\] to input
closed-form equations for the open-circuit surge voltage. With the 220-V
level of the Long Wave, predictably the current in a 130-V rated
varistor is very low and the resulting energy deposition is negligible.
The results for the Ring Wave and Combination Wave are shown in Table 3.
These simple illustrations show that the concept of \"specific energy\"
cannot be used to select a candidate varistor energy-handling rating.

## VI. HOW TO PROCEED IN FUTURE SURVEYS

In an effort to acknowledge the legitimate quest for the single number
characterization, we should offer alternatives, not just stay with a
negative vote The solution might be to tailor the surge characterization
to the intended application, that is, take into consideration the
failure mode of the specific equipment, and present the data in a form
most suited for that equipment. Of course, this would mean not only
avoiding a single number, but actually providing combinations of
parameters, each combination best suited to a particular type of victim
equipment, according to their failure modes.

Another consideration that must be observed in conducting and reporting
the monitoring of surges is the proliferation of SPDs in end-user
installations. It is unlikely today to find an installation where some
SPD is not present, either as a deliberate addition to the system, or as
part of the connected equipment. Aware of this situation, some
researchers have attempted to disconnect all known SPDs from the system
being monitored so that results would represent the \"unprotected
location\" situation such as that initially described in IEEE 587-­1980
\[14\], the forerunner of ANSI/IEEE C62.41-1991 \[12\].

However, even this precaution of disconnecting all known SPDs does not
guarantee that some undetected SPD might not have been left connected
somewhere and thus invalidate the record. Thus, extreme caution must be
applied to reporting and interpreting voltage monitoring campaigns
conducted after 1980.

The recently-approved IEEE Recommended Practice Std 1159 on Monitoring
Power Quality \[15\] offers guidance on conducting surveys, including
not only surges, but other parameters. The Working Group that developed
this standard has now established task forces to develop further
recommendations on processing and interpreting the recorded data,
including more uniform formats.

Table 4 presents a matrix of surge parameters and types of equipment,
showing for each type of victim which surge parameter is significant or
insignificant. The authors have sought to identify all types of
potential victims (and invite additions to this list). Inspection of
Table 4 reveals that the \[v2 x dt\] integral, alone, is not directly
involved in the failure of any of the listed equipment.

**TABLE 2**

**Energy deposited in a varistor by a "1-joule surge" for three
different values of source impedance**

## 

## TABLE 3

Energy deposited in varistors by Ring Wave and Combination Wave
\"1-joule surges\" for different source amplitudes and varistor nominal
voltages

**TABLE 4**

**Significant surge parameters in the equipment failure modes**

**VII. CONCLUSIONS**

The attempt to characterize the surge environment by a single number \--
the \"energy in the surge\" or \"specific energy\" \-- is a misleading
approach that should most definitely not be used in Power Quality
research. There are at least three reasons for this prohibition:

1\. The concept that energy can be defined in the abstract from a single
measurement of voltage across the lines of an undefined power system is
a faulty oversimplification.

2\. The potential victims of a surge event have responses that reflect
their design and for many, their failure modes can be totally
independent of any energy consideration.

3\. The prime interest of energy consideration is related to the
energy-handling capability of metal-oxide varistors. The energy
deposited in such a device by a given surge event depends on amplitude,
waveform, source impedance, and varistor characteristics, and not on the
\"effective energy.\"

Future surveys should be conducted keeping in mind the relevant
parameters for characterization such as peak amplitude, maximum rate of
rise, tail duration \-- but not \"energy.\" Furthermore, a relevant and
realistic assessment of surge stress threats must consider not only all
the characteristics of a surge event, but also the source of the surge
and the failure mechanisms of potential victim equipment.

## VIII. ACKNOWLEDGMENTS

Support for the development of this thesis, motivated by the discussions
and contributions of IEEE and IEC colleagues, was provided by Delmarva
Power & Light and by Pacific Gas & Electric. Support for the modeling
was provided by the Electric Power Research Institute.

## IX. REFERENCES

\[1\] Goldstein, M. and Speranza, P., \"The Quality of U.S. Commer­cial
AC Power,\" IEEE - INTELEC Conference Proceedings, 1992.

\[2\] Hughes, B. and Chan, J.S., \'Canadian National Power Quality
Survey Results,\" Proceedings, PQA \'95 Conference, EPRI, 1995.

\[3\] Martzloff, F.D. and Hahn, G.J., \"Surge Voltages in Residential
and Industrial Power Circuits,\" IEEE Transactions PAS-89, No.6,
July/August 1970.

\[4\] Allen, G.W. and Segall, D., \"Monitoring of Computer Installations
for Power Line Disturbances,\" IEEE Winter Power Meeting Conference
Paper WINP WR C74, 1974.

\[5\] Dorr, D.S., \"Point of Utilization Power Quality Study Results,\"
IEEE Transactions L4-31, No.4, July/August 1995.

\[6\] Goedbloed, J.J., \"Transients in Low-Voltage Supply Networks,\"
IEEE Transactions EMC-29, No.2, May 1987.

\[7\] Hassler, R. and Lagadec, R., \"Digital Measurement of Fast
Transients on Power Supply Lines,\" Proceedings, Third Symposium on EMC,
Rotterdam, 1979.

\[8\] Meissen, W., \"Overvoltages in Low-Voltage Networks\" (In German),
Elektrotechnishe Zeitschrift, Vol. 104, 1983.

\[9\] Standler, R.B., \"Transients on the Mains in a Residential
Environment,\" IEEE Transactions EC-31, No.2, May 1989.

\[10\] Goulet, K, \"Susceptibility of Power Semiconductor-based
Equipment to Power Line Disturbances,\" Conference Proceedings, Power
Quality 1989.

\[11\] Scheuerer, F., \"Research on the Isolation Properties of Solid
Insulation Upon Occurrence of HF Overvoltages, (In German) Doctoral
Thesis, Darmstadt University, 1993.

\[12\] ANSI/IEEE C62.41-1991, IEEE Recommended Practice on Surge
Voltages in Low- Voltage AC Power Circuits, (Reaffirmed 1995).

\[13\] EPRI Report EL-6421-L, Electromagnetic Transient Program (EMTP),
Version 2.0, Volumes 1 and 2, July 1989.

\[14\] IEEE 587-1980, IEEE Guide on Surge Voltages in Low- Voltage AC
Power Circuits, 1980.

\[15\] IEEE 11 59-1995, IEEE Recommended Practice for Monitoring
Electrical Power Quality, 1995.

**SURGE RECORDINGS THAT MAKE SENSE:**

# Shifting focus from voltage to current measurements

François D. Martzloff

National Institute of Standards and Technology

Gaithersburg MD 20899 USA

Abstract - The paper proposes to establish a program for characterizing
surge events according to the capability of a surge event to deliver a
surge current through the power system in end-user facilities. This
characterization would replace the conventional and by now misleading
monitoring of surge voltages. The new approach will use a current
transducer including a silicon-avalanche diode with the lowest possible
voltage to \"attract\" surges away from other surge-protective devices
connected within the facility. The voltage signal from the current
transducer will then be recorded using any power quality monitoring
instrument available to the individual researchers, providing complete
current waveform parameters.

**1. INTRODUCTION**

**1.1 Background**

Characterizing the surge environment has been a subject of research for
the last forty years, driven by the increasing concern about the
vulnerability of new electronic appliances to transient overvoltages.
However, practically all the recording campaigns conducted by major
organizations such as ERA (Bull and Nethercott, 1964) \[1\], General
Electric (Martzloff & Hahn, 1970)\[2\], IBM (Allen & Segall, 1974)\[3\],
Bell (Goldstein and Speranza, 1982) \[4\], Canadian Electrical
Association (Hughes & Chan, 1995)\[5\], National Power Laboratory (Dorr,
1995)\[61 and other researchers, including Hassler & Lagadec (1979)\[71,
Meissen (1983)\[8\], Wernstrom et al. (1984)\[91, Goedbloed
(1987)\[10\], Standler (1989)\[11\], and Forti & Millanta (1990)\[12\]
have been limited to the measurement of transient voltages.

We now propose a change in the protocol for the monitoring of power
quality in ac power systems. This change has become necessary because
end-user power systems are no longer what they were at the time the
early surveys of transient overvoltages were conducted. Varistor-based
surge-protective devices (SPDs) have become so ubiquitous in low-voltage
ac power systems that hardly any location ea be found where there is not
some form of transient voltage limitation in effect. Attempting now to
characterize the environment so that appropriate SPDs could then be
prescribed for specific locations based on voltage measurements would be
quite misleading. What such measurement would yield today is no longer
the surge characteristics of the monitored system, as it was at the time
of the early surveys, but the residual voltages of whatever SPDs are
installed nearby.

**1.2 Making meaningful measurements**

The proposed change in monitoring practices is to insert a current
transducer between the low-voltage power system being monitored and the
existing monitoring instruments. This transducer would consist of an SPD
with the minimum tolerable voltage rating across the power line, to be
connected at some point of an installation, and serve as a \"magnet\"
for attracting the impinging surges. To use a metaphor, this SPD in
effect becomes the \"winning bidder\" by offering to the impinging surge
the path with lowest clamping voltage among all the parallel-connected
SPDs of the installation.

A current transformer with the \"magnet SPD\" in the primary and an
appropriate burden on the secondary would be used to feed the resulting
voltage signal into the existing power quality monitoring instruments
now used by many organizations and individual researchers. In this
manner, the surge current attracted by the \"magnet SPD\" can be
recorded to find the true character of surge events at that particular
location, despite the presence in the local system of any and many
unknown and uncontrolled SPDs.

**II. TRANSDUCER DESIGN**

**II.1 Breadboard design**

Preliminary results on the feasibility of such a recording system have
been obtained: a suitable silicon avalanche diode has been identified
and proven to act as a \"magnet,\" even in the presence of \"competing\"
metal-oxide varistors, and yet able to withstand the temporary
overvoltages that can occur in the system. At this point, the transducer
design principle is well defined, and concerns that the \"magnet\"
effect could be effective only within a small power system have been
addressed, as discussed later in the paper.

The current transducer would consist of a string of silicon avalanche
diodes (SADs) in series with the primary of a current transformer with a
burden connected across its secondary, an overcurrent protective fuse in
series with the diodes, and an indicating light to signal a blown fuse.
In the final design that would be used to deploy a number of these
transducers, all of these components will be included in a package
derived from the so-called \"plug-in SPD\" which are offered by many
manufacturers. Using the external package of such a device will provide
a low-cost envelope to build a few hundred transducers with no tooling
costs and yet provide a package suitable for connection to wall
receptacles in end-user systems.

The power system can include several branch circuits to supply the
loads, some of which featuring SPDs incor­porated into load equipment or
installed by the end-user. At some point of this system, selected for
convenience by the instrument operator, the transducer will be
installed. A key point of the proposal is that pinning down the actual
location of the monitor is no longer a concern because of the
,\'magnet\" effect of the low-clamping SAD string.

Figure 1 shows a schematic diagram of the transducer. Selection of an
appropriate string of SADs is an exercise in brinkmanship: the SAD
string must have a clamping voltage sufficiently low to make it the
winning bidder, and yet not so low that the temporary overvoltages
occurring in the power system would destroy it. In a preliminary
experiment, a SAD string with a nominal voltage of 185 V at 1 mA de was
found to survive exposure to 130% of nominal 120 V system voltage,
ensuring sufficient distance from the brink of failure.

###### Figure 1 -- Schematic of the transducer

It will be prudent to include a fuse in series with the SAD string for
the case where a large surge would exceed the current-handling capacity
of the SAD string and cause its failure. A visible indication of a blown
fuse can be added to the package, similar to the indication now
routinely provided by the commercial plug-in SPDs offered for
residential use.

A commercially available and low-cost current transformer\* has been
identified that can provide sufficient accuracy for the measurements
over a sufficient frequency range. Conventional current-viewing
transformers used in the laboratory are much more expensive and would
not be necessary for the purposes of the recordings. Considering the
wide range of surge events and the resulting statistical uncertainty in
citing \"representative values\" of the surge events, obtaining results
of current measurements within an order of magnitude is already a very
large improvement over the present lack of knowledge. In the example of
recording capability discussed later in the paper, there is a 50:1
difference in the cost of a laboratory-type current-viewing transformer
and the low-cost current transformer required for deployment of a large
number of monitors.

\* Please note that the author has no vested interest in promoting or
endorsing any hardware, and that the final selection of the current
transformer is still an open design tradeoff consideration. Commercial
availability is cited here only in support of the concept of using
readily available, low-cost component sfor the deployment of many
transducers.

Matching the burden values to the voltage requirements of the monitor
input circuits has not yet been done at the time of this writing, but
might be reportable by the time of presentation of the paper. Tradeoff
between the cost of the current transformer and its frequency response
is another area where improvements to the proposal can be made to obtain
meaningful recordings at a cost that will not be a deterrent to
acceptance of the proposal.

## II.2 Radius of attraction

By design, the string of diodes is intended to become the "magnet" that
will attract the impinging surges. We recognize that this winning bid
can be ensured only within a certain radius from the transducer.
Increasing distances between the transducer and competing SPDs
eventually produces a decoupling of the two devices and might allow a
competing SPd connected upstream from the transducer to divert the surge
first. This situation is the reverse of that sought when making studies
of the coordination of cascaded SPDs, where the concern is to ensure
that a heavy-duty SPD located upstream of a lower-duty SPD is
sufficiently decoupled so that an impinging surge will be diverted by
the upstream SPD. The parameters of cascade coordination have been
addressed at length in the literature \[13\]. \[14\], \[15\] and will
not be discussed here, but serve as a useful reminder to take a careful
look at possible limitiation in the radius of meaningful measurements.

To ascertain that the transducer will remain the winning bidder, a
simple test was performed by assembling a physical mock-up of an
installation with a service panel feeding three branch circuits, with
lengths of 4.5 m, 9 m, and 18 m respectively. The SAD string was
connected at the end of one branch circuit while metal-oxide varistors
(MOVs) with nominal 200 V at 1mA dc were connected at each end of the
other branch circuits.

##### Figure 2 -- Arrangement of competing SPDs

We can expect that the least favorable combination would be that of the
SAD connected at the end of the longest branch circuit, with an SPD of
relatively low clamping voltage installed at the end of the shortest
branch circuit. A Combination Wave \[16\] was applied to the service
panel, and the currents in the three branch circuits were monitored,
with the SAD string successively connected at the end of the 4.5 m, 9 m,
and 18 m branch circuits. In all three cases, the SAD attracted all the
surge current, with no current detected in the MOV-terminated branch
circuits.

More sophisticated analysis can be performed by applying the numerical
modeling techniques developed in the referenced modeling studies \[17\],
\[18\], extending the distances and combinations of competing SPDs from
the simple example shown in Figure 2 to determine how extensive an
installation can be and still have the transducer remain the winning
bidder. In this manner, the pitfall that threatens credibility of
contemporary voltage recordings (uncertainty about other unknown SPDs
connected in the system that can produce misleading results of low surge
activity) will be eliminated.

## III. BREADBOARD TEST

A simple breadboard was assembled with the 185 V SAD string connected to
the output of an 8/20 μs surge generator and a 100 Ω resistance inserted
in series to limit the current delivered by the low-impedance generator.
The resulting current (longer than 8/20 μs because of the inserted
resistance) was applied to the one-turn primaries of a laboratory-grade
current-viewing transformer and of the low-cost current transformer,
with a 2 kΩ burden across its secondary. Their secondary output voltage
was recorded by a laboratory-grade digital signal analyzer. Figure 3
shows the recorded voltage across the SAD string and the two current
signals.

###### Figure 3 -- Voltage across the SAD string and corresponding current signals

To make the comparison easier, the signal analyzer input sensitivity of
the two current-displaying channels was adjusted so that the two current
signals would coincide near their peaks. The point to be made here is
not the actual numerical values, but the quality of the frequency
response of the low-cost transducer, illustrated by a time-domain
representation of an impulse.

Inspection of the two current traces shows a loss of signal at the front
as well as in the tail, symptomatic of a limited frequency response.
While such a loss would be absolutely intolerable in a laboratory
environment, we must place it in its proper perspective. As outlined in
the introduction, we are now facing a new situation, brought about by
the proliferation of SPDs, where surge voltage measurements no longer
have the significance they once bad, so that we have no knowledge on the
real surge threat existing in the system. The current-delivery
capability of the surge event, as recorded by the imperfect current
transducer is an immense improvement over the present total lack of
knowledge.

Given the wide range of possible surge events, the relatively small loss
of information represented by the two areas separating the two current
signal traces is small compared to the common area that represents a
good estimate of the order of magnitude of the current-delivery
capability of the recorded surge event. In contrast to laboratory
measurement researchers, operators and users of field surveys are
already content to have the surge events characterized within one order
of magnitude when the alternative is no meaningful information at all.
As discussed earlier, tradeoff between transducer cost and quality of
the frequency response is still an open consideration, for which
comments from interested parties are earnestly invited before
implementation of the proposal is initiated.

## IV. PROGRAM IMPLEMENTATION

The next step in making the change from surge voltage recording to surge
current recording would be to recruit enough participants willing to
acquire the transducer and use their existing commercial monitor(s) to
record the occurrences of surge currents attracted by the transducer.
This transducer could be produced in cooperation with some manufacturer
of a plug-in SPD, so that a readily adaptable outside package could
contain the transducer components and provide a simple and safe way of
connecting it to a receptacle.

Within the IEEE, a new Task Force of the Standards Coordinating
Committee on Power Quality is developing protocols for reporting
monitoring results; hopefully, the concepts presented in this paper will
be taken into consideration by that Task Force and by other
organizations interested in making surveys for characterizing the
electromagnetic environment. The IEC is also considering the development
of guidance documents on measurement methods in the area of power
quality, where this shift of focus should be taken into consideration.

The author is volunteering to collect and compile the statistics of the
recordings that would be made with the new transducer. Individual
researchers and organizations are invited to contact the author with
comments, suggestions of alternate approaches, and ideas for
implementing this change in characterizing the surge environment that
will make sense in the new environment of proliferating surge-protective
devices.

### V. CONCLUSIONS

1 . Given the proliferation of SPDs, the need to replace the recording
of surge voltage events by the recording of the capability of surge
events to deliver a current into load equipment in particular SPDs has
been identified.

2\. Tests made on a breadboard design using readily available components
show that meaningful surge current recordings can be obtained, even with
a very low-cost design. Improvements in the frequency response could be
obtained by a tradeoff in component costs and refinements of the design.

3\. Implementation of a program may be possible if sufficient interest
is aroused by the proposed change in conducting field surveys of surge
events.

4\. Standards-writing bodies concerned with characterizing the
electromagnetic environment in low-voltage power systems could make an
important contribution by giving recognition to the new situation and
shifting focus from surge voltage measurements to surge current
measurements.

## VI. ACKNOWLEDGMENTS

Support for the development of this paper was provided by the Power
Quality research groups of Delmarva Power & Light, and Pacific Gas &
Electric. Support for the prototype testing was provided in part by the
Electric Power Research Institute.

**VII. REFERENCES**

\[1\] Bull & Nethercott \"The Frequency of Occurrence and the Magnitude
of Short Duration Transients in Low-­voltage Supply Mains,\" The Radio
and Electronic Engineer, Sept 1964, pp 185-190.

\[2\] Martzloff & Hahn, \"Surge Voltages in Residential and Industrial
Power Circuits, \" *IEEE Transactions PAS -89*, No.6, July/Aug 1970, pp
1049-1056.

\[3\] Allen & Segall, \"Monitoring of Computer Installations for Line
Disturbances,\" Pape*r C74199-6,* IEEE PES Winter Meeting, 1974.

\[4\] Goldstein & Speranza, \"The Quality of U.S. Commercial AC Power,\"
*Intelec Conference Proceedings*, 1982, pp 28-33.

\[5\] Hughes & Chan, \"Canadian National Power Quality Survey Results,\"
*Proceedings, PQA\'95 Conference,* EPRI, 1995.

\[6\] Dorr, \"Point of Utilization Power Quality Study Results,\" *IEEE
Transactions IA-31*, July/August 1995.

\[7\] Hassler & Lagadec, \"Digital Measurement of Fast Transients on
Power Supply Lines.\" *Proceedings, Third Symposium on EMC*, Rotterdam
May 1979, pp 445-448.

\[8\] Meissen, \"Ueberspannungen in Niederspannungs­netzen,\"
(\"Overvoltages in Low-Voltage Networks\"), *Elektrotechnishe
Zeitshrift*, Vol 104, 1983.

\[9\] Wernstroem, Broms, & Boberg, \"Transient Overvoltages on AC Power
Supply Systems in Swedish Industry,\" *Report FOA E 30002-E2*, Sweden,
1984.

\[10\] Goedbloed, \"Transients in Low-Voltage Supply Networks,\" *IEEE,
Transactions EMC-29*, May 1987.

\[11\] Standler, \"Transients on the Mains in a Residential
Environment,\" *IEEE Transactions EMC-31*, May 1989.

\[12\] Forti & Millanta, \"Power-Line Impedance and the Origin of
Low-Frequency Oscillatory Transients,\" *IEEE Transactions EMC-32*,
No.2, May 1990.

\[13\] Lai & Martzloff, \"Coordinating Cascaded Surge Protection
Devices: High-Low versus Low-High,\" *Conference Record, IEEE-IAS 1991
Annual Meeting*, pp 1812-1819. Also in *IEEE Transactions, IAS-29* No.4,
July/August 1993, pp 680-687.

\[14\] Hostfet, Hervland, Nansen, & Huse, \"Coordination of
surge-protective devices in power supply systems: Needs for secondary
protection,\" *Proceedings, 20th International Conference on Lightning
Protection,* 1992.

\[15\] Rousseau & Perche, \"Coordination of Surge Arresters in the
Low-Voltage Field,\" *Proceedings, 17^th^ International
Telecommunications Conference* (INTELEC 95), 95CH35824, pp 119-125.

\[16\] IEEE/ANSI C62.41-1991, *"Recommended Practice on Surge Voltages
in Low-Voltage AC Power Circuits.\"*

\[17\] Martzloff, Mansoor, Phipps, & Grady, \"Surging the Upside-Down
House: Measurements and Modeling Results,\" *Proceedings, PQA\'95
Conference*, EPRI, 1995.

\[18\] EPRI, \"Electromagnetic Transients Program (EMTP), Version 2;
Vol. I-, Main Program; Vol. 2: Auxiliary Routines\" *EPRI Report
EL-6421-L*, July 1989.

## 

## SURGE RECORDINGS THAT MAKE SENSE

# Joule Deposition: Yes! - \"Joule Content\": Never!

**Geoffrey Lindes** **Arshad Mansoor** **François Martzloff** **David
Vannoy**

Delmarva Power Power Electronics National Institute of Delmarva Power

& Light Company Applications Center Standards & Technology & Light
Company

**Abstract**

This paper offers a rationale for avoiding attempts to characterize the
surge environment in low-voltage end-user power systems by a single
number \-- the \"energy in the surge\" \-- derived from a simple voltage
measurement. Numerical examples illustrate the fallacy of this concept.
Furthermore, based on the proliferation of surge-protective devices in
low-voltage end-user installations, the paper draws attention to the
need for changing focus from surge voltage measurements to surge current
measurements.

### Introduction

Sensible application of surge-protective devices (SPDs) requires that
the capability of a candidate SPD be sufficient to absorb the energy
that an impinging surge could deposit in the device. This eminently
rational approach, however, was derailed when the erroneous concept was
proposed that one could measure the \"energy in the surge\" and thus
prescribe an easy match of the energy-handling capability of an SPD to
the \"energy\" of its environment.

In a more recent approach by standard developers, an attempt was made to
express this concept as a "specific energy" that would normalize it with
respect to a postulated resistance of a device exposed to the impinging
surge. Our thesis is that such attempts are neither realistic nor
relevant. We will show that these erroneous attempts, based on the
classical formula for computing the energy dissipated in a linear load
of known resistance, cannot be applied to characterize the environment.
There is no meaningful relationship between the "energy" in a surge
event as derived (erroneously) from the single voltage measurement and
the energy actually deposited in a varistor by this surge event.

Furthermore, the results obtained when recording ***surge voltages***
conducted since the mid-eighties have now become questionable as a
result of the proliferation of surge-protective devices. It is very
doubtful that a surge voltage monitor, installed in a typical end-user
facility, will record anything but the residual voltage of unknown SPDs
in the installation -- which is no measure of the threat of an incoming
surge. Only a ***surge current*** measurement in a candidate SPD can
assess the threat.

A review of equipment failure or upset mechanisms related to the
occurrence of a surge voltage reveals that none of these mechanisms are
related to this so-called \"energy in the surge.\" Several failure
mechanisms other than energy-related are identified, pointing out the
need to describe the surge events with a more comprehensive set of
parameters in conducting future surveys.

**The Fallacy of Joules Content**

In an attempt to characterize the potential threat of surges to
voltage-sensitive equipment, recordings of the surge voltages occurring
in low-voltage power circuits have been conducted in the last
quarter-century, driven by the increasing concern about the
vulnerability of new electronic appliances to transient overvoltages.
However, practically all the recording campaigns conducted by major
organizations such as ERA (Bull and Nethercott, 1964)**^1^**, General
Electric (Martzloff & Hahn, 1970)**^2^**, IBM (Allen & Segall,
1974)**^3^**, Bell (Goldstein and Speranza, 1982)**^4^**, Canadian
Electrical Association (Hughes & Chan, 1995)**^5^** , National Power
Laboratory (Dorr, 1995)**^6^** and other researchers, including Hassler
& Lagadec (1979)**^7^**, Meissen (1983)**^8^**, Wernstrom et al.
(1984)**^9^**, Goedbloed (1987)**^10^**, Standler (1989)**^11^**, and
Forti & Millanta (1990)**^12^** have been limited to the measurement of
transient ***voltages.***

Interest in these measurements has been re-kindled by several
investigations aimed at assessing power quality in end-user facilities.
These recordings, initially limited to measurement of peak voltages,
were perfected with the help of increasingly sophisticated
***voltmeters.*** Early surveys were conducted with conventional
oscilloscopes; later on, portable digital instruments with on-board
computing became available. While these instruments made possible the
recording of a voltage transient as a function of time and graphical
presentation of data, the recording of such a surge voltage profile does
not lend itself to a simple description by a single number. To
circumvent this difficulty, many researchers called upon the basic
concept of energy to characterize the level of surge threat in terms of
voltage. Referring to classical electrical engineering, the
instantaneous power dissipated in a resistor by a transient voltage is
merely the square of the applied voltage, divided by the resistance.
Taking the integral over the duration of the transient yields the
energy. By analogy, the "energy" of a surge could then be computed from
the voltage measured at some point of a power system. According to this
intuitive concept -- but fallacious as we will show -- the greater the
measured voltage, the greater the "energy" and thus the greater the
threat to potential victim equipment.

A review of the known failure or upset mechanisms of various types of
devices and equipment identifies several surge parameters other than
energy-related. These include source impedance, peak amplitude, maximum
rate of rise, tail duration, and repetition rate. Thus, future surveys
of surge events conducted with present or with even better monitoring
instruments will need to include more comprehensive and hopefully
standardized methods of presenting and interpreting the results.

**Thesis**

Our thesis is that neither the threat nor the "energy level" of a surge
can be characterized by simply measuring the voltage change during a
surge event. Any reference to the concept of "energy of a surge" should
definitely not be introduced. Such avoidance is based on two facts:

1\. A voltage measurement of the surge event cannot alone predict the
energy levels affecting the devices exposed to that surge. This is
particularly true for nonlinear surge-protective devices where energy
deposited in the device is relevant, but has little to do with the
misleading concept of "energy in the surge" derived from an open-circuit
voltage measurement.

2\. There are other than energy-related upset or failure modes of
equipment. These effects require consideration of other parameters when
describing a surge event to yield relevant and realistic assessment of
surge stress threats.

This thesis will be supported by an analysis of the impact of surges on
equipment, and illustrated by numerical examples of varistor
applications showing how the description of a surge by its \"energy\"
could then lead to vastly different conclusions.

**Interactions Between Surges and Victim Equipment**

At this point, we need to identify the devices and equipment that may
become the victims of a surge, and their failure mechanisms.
After-the-fact investigations and experimental data show a wide range of
surge-related upset and failure mechanisms. These include insulation
breakdown, flashover, fracture, thermal and instantaneous peak power
overloads, dv/dt and di/dt limits being exceeded. The following list
gives some generic types of surge victims and the typical failure or
upset mechanisms. It is highly significant that in all this list, the
term \[v^2^ x *dt\]* or its integral does not appear. Table 1 provides a
summary of this list of victims and relevant surge parameters associated
with the failure modes.

***1. Electrical insulation**,* where the failure mechanism (breakdown
or sparkover) is principally a function of the surge voltage, with the
complication of a volt-time characteristic such that failure under
impulse occurs at a level that increases when the rise time or duration
of the impulse decreases. "Insulation" is to be taken in the broadest
sense of solid or liquid material separating energized conductors in
equipment, clearances on a printed circuit board, edges of semiconductor
layers, etc. A distinction must be made between the initial breakdown of
insulation, related to voltage only, and the final appearance of the
damaged insulation, related to the total energy dissipated in the
breakdown path. In another situation, the insulation of the first turns
of a winding may be subjected to higher stress than the others as the
result of the uneven voltage distribution resulting from a steep front
rather than only the peak value of the surge.

***2. Surge-protective devices**,* for which the voltage across the
device is essentially constant, and the energy deposited is a function
of the surge current level and duration. One failure mode of such a
device will occur when the energy deposited in the bulk material raises
the temperature above some critical level. Failure modes associated with
the current level, such as flashover on the sides of a varistor disc,
failure at the boundary layers of the varistor grains, or fracture of
large discs, have also been identified and are not directly related to
energy.

***3. Semiconductor devices**,* such as thyristors responding to the
rate of voltage change can be turned on by a surge\", resulting in
failure of the device or hazardous energizing of the load they control.
In a similar way, a triac may be turned on by a voltage surge without
damage, but still fail by exceeding the peak power limit during a
surge-induced turn-on with slow transition time.

***4. Power conversion equipment**,* with a front-end de link where the
filter-capacitor voltage can be boosted by a surge, resulting in
premature or unnecessary tripping of the downstream inverter by its own
on-board overvoltage or overcurrent protection schemes.

***5. Data-processing equipment**,* where malfunction (data errors) --
not damage -- may be caused by fast rate of voltage changes (capacitive
coupling) or fast rate of current changes (inductive coupling) that
reflect the initial characteristic of the surge event. This response is
insensitive to the \"tail\" of the surge, where all the \"energy\" would
be contained according to the misleading energy-related concept.

***6. Light bulbs**,* which of course have a limited life associated
with filament evaporation and embrittlement -- a long-term process where
the short burst of additional heating caused by a few microseconds of
overcurrent is negligible -- but also fail under surge conditions when a
flashover occurs within the bulb, triggering a power-frequency arc that
melts out the filament at its point of attachment -- ­another failure
mechanism originating with insulation breakdown.

Among these types of victims, only the clamping-type varistor is
directly sensitive to an energy level associated with a surge event --
and at that, the energy deposited in the device, not the \"energy in the
surge.\" Considering the explosive proliferation of varistors, however,
one might find some extenuating circumstances in emphasizing the
significance of energy in describing the effect of surges on its
principal target -- the ubiquitous metal-oxide varistor -- but this is a
pitfall, a mental trap.

**Table 1**

**Significant parameters in equipment failure modes**

**Baiting The Trap**

From the interactions described above, it is clear that using a single
voltage measurement to determine surge threat is not sufficient. The
trap was baited by the simplicity and ease of using a single parameter
obtained by analogy with the power dissipated in a fixed resistance, by
an instantaneous voltage, v. Clearly in that limited case, the total
energy involved over the surge event would be the time integral of
v**^2^**/R, expressed by a number having the same dimensions as
watt-seconds, or joules in the SI system. And thus some power quality
monitors placed on the market in the early eighties were printing out
surge event characterizations expressed in joules. This \"joule\" number
was obtained by computation of the ∫v**^2^**/R.dt, where the voltage v
was measured by the instrument, divided by a resistance (taken
arbitrarily as 50 Ω), and integrated over the duration of the event.
Manufacturers of power quality monitors soon recognized the potentially
misleading aspects of such reporting and discontinued the practice.

Nevertheless, some researchers continued the practice and are to this
day attempting to characterize the surge environment by the single
parameter of \"energy in the surge.\" As a half-way measure, some are
now proposing a new parameter \"specific energy\" to be understood as
the integral of voltage-squared divided by a reference resistance of 50
Ω (why that particular value ?) and they would report results in
watt-seconds. Figure 1 shows an example of this type of reporting
**^14^**.

**Figure 1 -- Example of report of survey results ^10^ with number of
occurrences**

**as a function of "energy" in milliwatts-seconds**

# 

We completely agree that, indeed, the selection of an appropriate
varistor should reflect the level of threat to which it will be exposed,
so that there is a need to characterize the threat in terms of the
energy that will be deposited in the varistor by a specific surge event.
However**, *there is* no *way* that a *voltmeter measurement only, even
if it includes time, can provide that information****.* This observation
was presented at an earlier Power Quality Conference\", and discussions
in that forum, as well as in working groups developing standards on the
surge environment, indicated the need to give a wider distribution to
the message, hence this paper in this forum.

# 

**Thesis: Demonstration by Varistor Applications**

To demonstrate our thesis by the ***ad absurdum*** process, we will
compute the \"energy in the surge\" as defined by the trap-baiting
definition of \"specific energy\" for three surge events such that all
have the same \"specific energy\" but different voltage levels,
waveforms, and durations. Then, making a further assumption for the
unknown impedance of the surge source, we will compute the energy
actually dissipated in the varistor for these different voltage levels,
waveforms, and durations, and observe that the resulting deposited
energy is not the same!

***Elementary example: basic calculation with fixed impedance***

As a first easy-to-follow step, we take three rectangular pulses, all
selected to have the same \"specific energy\" but different voltage
levels and corresponding durations, and compute the energy deposited in
a nonlinear varistor having a given maximum limiting voltage, assuming
that the source of the surge is a voltage source with some arbitrary,
fixed impedance. It is noteworthy that some ***source impedance has to
be presumed**,* because the varistor clamping action rests on the
voltage divider effect of the source impedance and the dynamic
(variable) varistor impedance prevailing for the resulting current.

Start with an assumed surge measurement of 1000 V with duration of 50
μs. The \"specific energy\" of such a surge event, according to the
proposed definition, is:

> (1000 V)^2^ x 50 μs / 50 Ω = 1 joule.

Now consider a surge with a peak amplitude of 316 V (316 = 1000 x √10)
and a duration of 500 μs (500 = 50 x 10). Its \"specific energy\" is:

> (316 V)^2^ x 500 μs / 50 Ω = 1 joule.

To complete the bracketing range, consider a surge of 3160 V (3160 =
1000 x √10*),* and a duration of 5 μs (5 = 50/10). Its \"specific
energy\" is:

> (3160 V)^2^ x 5 μs / 50 Ω = 1 joule.

We now apply each of the three voltage surges to a 130-V rated varistor
(200 V at 1 mA dc), assuming an arbitrary source impedance of Zs = 1 Ω.
One can compute the resulting current or, for this simple example, make
a fast-converging manual iteration without the help of a computer, as
follows:

# 

> \(a\) assume a current I, and look up the resulting voltage Vv on the
> varistor I-V characteristic;
>
> \(b\) compute \[Z~s~ x I\];
>
> \(c\) is \[Z~s~ x I\] + V~v~ = 1000 V ?
>
> \(d\) If yes, I is correct, the energy deposited in the varistor is I
> x V~v~ x ∆t
>
> If no, go back to (a) with a converging assumption for *I.*

Table 2 shows the results from this manual iteration for the three
surges defined above. It is quite apparent that the constant \"specific
energy\" for the three surges does not result in the same energy
deposition. The dynamic impedance *(V~v~ /I)* of the varistor is also
shown, to illustrate the well-known theorem that the power dissipated in
a resistive load reaches a maximum for matched source-load impedance.
This theorem is yet another reason why a surge to be applied to a
varistor cannot be characterized in the abstract: one needs to know the
source impedance (real and imaginary components) as well, to assess the
energy sharing between source and load.

**Table 2**

**Energy deposition in a varistor by a surge, as a function of surge
parameters,**

**all surges having a 1-joule "specific energy" for a source impedance
of 1 ohm**

***Computer calculation with multiple combinations***

We now compute the energy deposited in three varistors of three
different maximum limiting voltages, for two combinations of voltage
levels and durations that produce the same \"specific energy,\" each
with classical waveform (Ring Wave or Combination Wave), sized to
produce I joule of energy dissipation in a 50-Ω resistor, according to
the classical formula cited earlier, and for three values of source
impedance. We can anticipate that the peaks will be quite different,
foreboding very different effects on equipment. In fact, the peaks
turned out to be 3 kV and 1.2 kV, respectively for the two waveforms.

Applying these two waveforms to a family of varistors typically used in
120-V or 240-V power systems, we computed the energy deposited in these
varistors for three arbitrary source impedances (assumed to

be ohmic), using the EMTP program **^16^** to input closed-form
equations for the open-circuit surge voltage. The results are shown in
Table 3. These simple illustrations show that even the concept of
\"specific energy" proposed as an improvement over the concept of
"energy in the surge" cannot be used to select a candidate varistor
energy-handling rating, and serves no useful purpose in characterizing
the surge environment.

**Table 3**

**Energy deposited in varistors by Ring Wave and Combination Wave
'1-joule surges"**

**for different source amplitudes and varistor nominal voltages**

**Conducting Future Surveys: Make Recordings That Make Sense!**

***Recording Relevant Parameters***

In an effort to acknowledge the legitimate quest for the single number
characterization, we should offer alternatives, not just stay with a
negative vote The solution might be to tailor the surge characterization
to the intended application, that is, take into consideration the
failure mode of the specific equipment, and present the data in a form
most suited for that equipment. Of course, this would mean not only
avoiding a single number, but actually providing combinations of
parameters, each combination best suited to a particular type of victim
equipment, according to their failure modes.

The recently-approved IEEE Recommended Practice Std 1159 on Monitoring
Power Quality **^17^** offers some guidance on conducting surveys,
including not only surges, but other parameters. The Working Group that
developed this standard has now established task forces to develop
further recommendations on processing and interpreting the recorded
data, including more uniform formats.

Table 1, discussed earlier, presented a matrix of surge parameters and
types of equipment, showing for each type of victim which surge
parameter is significant or insignificant. In compiling that table, the
authors sought to identify all types of potential victims. As it turned
out, the term ***\[v^2^ x dt\]*** or its integral, alone, is not
directly involved in the failure of any of the equipment listed in
Table 1. A more complete set of data, associated with specific equipment
sensitivity, will be needed to characterize the surge environment and
achieve compatibility between that environment and equipment to be
installed.

##### The fallacy of present-day voltage measurements

Another consideration that must be observed in conducting and reporting
the monitoring of surges is the proliferation of SPDs in end-user
installations. It is unlikely today to find an installation where some
SPD is not present, either as a deliberate addition to the system, or as
part of the connected equipment. Aware of this situation, some
researchers have attempted to disconnect all known SPDs from the system
being monitored so that results would represent the \"unprotected
location\" situation such as that initially described in IEEE 587-1980
**^18^**, the forerunner of ANSI/IEEE C62.41-1991 **^19^**.

However, even this precaution of disconnecting all known SPDs does not
guarantee that some undetected SPD might not have been left connected
somewhere and thus invalidate the record. Thus, extreme caution must be
applied to reporting and interpreting voltage monitoring campaigns
conducted after 1980 **^20^**.

We now propose a change in the protocol for the monitoring of power
quality in ac power systems.

This change has become necessary because end-user power systems are no
longer what they were at the time the early surveys of transient
overvoltages were conducted, a time at which measuring transient
voltages did indeed make sense. Varistor-based surge-protective devices
(SPDs) have become so ubiquitous in low-voltage ac power systems that
hardly any location can be found where there **is** not some form of
transient voltage limitation in effect. Attempting now to characterize
the environment so that appropriate SPDs could then be prescribed for
specific locations based on voltage measurements would be quite
misleading. What such a measurement would yield today is no longer the
surge characteristics of the monitored ***system,*** as it was at the
time of the early surveys, but the ***residual*** ***voltages*** of
whatever SPDs are installed nearby.

***Making meaningful measurements***

The proposed change in monitoring practices is to insert a current
transducer between the low-voltage power system being monitored and the
existing monitoring instruments. This transducer would consist of an SPD
with the minimum tolerable voltage rating across the power line, to be
connected at some point of an installation, and serve as a \"magnet\"
for attracting the impinging surges. To use a metaphor, this SPD in
effect becomes the \"winning bidder\" by offering to the impinging surge
the path with lowest clamping voltage among all the parallel-connected
SPDs of the installation.

A current transformer with the \"magnet SPD\" in the primary and an
appropriate burden on the secondary (Figure 2) would be used to feed the
resulting voltage signal into the existing power quality monitoring
instruments now used by many organizations and individual researchers.
Typically, the voltage channels have higher frequency response that
current channels. In this manner, the surge current attracted by the
\"magnet SPD\" can be recorded to find the true character of surge
events at that particular location, despite the presence in the local
system of any and many unknown and uncontrolled SPDs.

**Figure 2 -- Schematic of the transducer**

# 

The current transducer would consist of a string of silicon avalanche
diodes (SADs) in series with the primary of a current transformer with a
burden connected across its secondary, an overcurrent protective fuse in
series with the diodes, and an indicating light to signal a blown fuse.
Because the very principle requires that the SAD string have a clamping
voltage lower than any other SPD in the installation, it would be the
most vulnerable to a large swell. To remove the transducer from the
system in case of failure of the SAD string, the fuse is provided ahead
of the transducer circuits.

In the final design that would be used to deploy a number of these
transducers, all of these components would be included in a package
derived from the so-called \"plug-in SPD\" which are offered by many
manufacturers. Using the external package of such a device will provide
a low-cost envelope to build a few hundred transducers with no tooling
costs and yet provide a package suitable for connection to wall
receptacles in end-user systems.

It should be noted that only one channel of the monitor need to be
allocated for recording the surge current. While the determination of
power and energy deposited in the SAD requires knowledge of three
parameters: current, voltage, and time, for the calibrated SAD built in
the transducer, the voltage can readily be computed from the device I-V
characteristic when the current waveform is known.

Preliminary results on the feasibility of such a recording system have
been obtained: a suitable silicon avalanche diode has been identified
and proven to act as a \"magnet,\" even in the presence of \"competing\"
metal-oxide varistors, and yet able to withstand the temporary
overvoltages that can occur in the system. The current transformer can
be any of readily available low-cost transformers; for the purposes of
recording the surge events in the environment, the exacting accuracy of
a laboratory-grade pulse current transformer would not be necessary.

The power system can include several branch circuits to supply the
loads, some of which featuring SPDs incorporated into load equipment or
installed by the end-user. At some point of this system, selected for
convenience by the instrument operator, the transducer will be
installed. A key point of the proposal is that pinning down the actual
location of the monitor is no longer a concern because of the \"
magnet\" effect of the low-clamping SAD string.

By design, the string of diodes is intended to become the \"magnet\"
that will attract the impinging surges. We recognize that this winning
bid can be ensured only within a certain radius from the transducer.
Increasing distances between the transducer and competing SPDs
eventually produces a decoupling of the two devices and might allow a
competing SPD connected upstream from the transducer to divert the surge
first. This situation is the reverse of that sought when making studies
of the coordination of cascaded SPDs, where the concern is to ensure
that a heavy-duty SPD located upstream of a lower-duty SPD is
sufficiently decoupled so that an impinging surge will be diverted by
the upstream SPD. The parameters of cascade coordination have been
addressed at length in the literature **^21,\ 22,\ 23,\ 24^** and will
not be discussed here. For typical circuit lengths in a low-voltage
installation, our tests have demonstrated that the SAD string of Figure
2 offers a sufficiently low voltage path for impinging surges that it
will indeed be the magnet.

More sophisticated analysis can be performed by applying the numerical
modeling techniques developed in the referenced modeling studies
**^21-24^**, extending the distances and combinations of competing SPDs
to determine how extensive an installation can be and still have the
transducer remain the winning bidder. In this manner, the pitfall that
threatens credibility of contemporary voltage recordings (uncertainty
about other unknown SPDs connected in the system that can produce
misleading results of low surge activity) will be eliminated.

# 

##### Program Implementation

The next step in making the change from surge voltage recording to surge
current recording would be to recruit enough participants willing to
acquire the transducer and use their existing commercial monitor(s) to
record the occurrences of surge currents attracted by the transducer.
The transducer could be produced in cooperation with a manufacturer of a
plug-in SPD, so that a readily adaptable outside package could contain
the transducer components and provide a simple and safe way of
connecting it to a receptacle.

Within the IEEE, a new Task Force of the Standards Coordinating
Committee on Power Quality SCC22 is developing protocols for reporting
monitoring results; hopefully, the concepts presented in this paper will
be taken into consideration by that Task Force and by other
organizations interested in making surveys for characterizing the
electromagnetic environment. The IEC is also developing guidance
documents on measurement methods in the area of power quality, where
this shift of focus should be taken into consideration.

**Conclusions**

# 

The attempt to characterize the surge environment by a single number --
the \"energy in the surge\" or \" specific energy\" -- is a misleading
approach that should most definitely not be used in Power Quality
research. There are at least four reasons for this prohibition:

1\. The concept that energy can be defined in the abstract from a single
measurement of voltage across the lines of an undefined power system is
a faulty oversimplification.

2\. The potential victims of a surge event have responses that reflect
their design and for many, their failure modes can be totally
independent of any energy consideration.

3\. The prime interest of energy consideration is related to the
energy-handling capability of metal­oxide varistors. The energy deposited
in such a device by a given surge event depends on amplitude, waveform,
source impedance, and varistor characteristics, and not on the
\"effective energy.\"

4\. Last but not least, the proliferation of surge-protective devices
(SPDs) in low-voltage, end-user facilities makes the recording of surge
voltages a fallacy as the recorded voltages now represent the response
of the installed (and generally unknown) SPDs in the installation, not
the actual threat of impinging surges. That threat can now only be
assessed by installing an instrument that will attract impinging surges
to itself and measure the current that can be delivered by the surge.

Future surveys should be conducted keeping in mind the relevant
parameters for characterization such as peak amplitude, maximum rate of
rise, tail duration --but not \"energy.\" Relevant and realistic
assessment of surge stress threats must consider not only all the
characteristics of a surge event, but also the source of the surge and
the failure mechanisms of potential victim equipment. Standards-writing
bodies concerned with characterizing the electromagnetic environment in
low-voltage power systems could make an important contribution by giving
recognition to the new situation and shifting focus from surge voltage
measurements to surge current measurements.

**Acknowledgments**

# 

Support for the development of this paper was provided by the authors\'
parent organizations and by the Power Quality research group of Pacific
Gas & Electric. Gerald FitzPatrick and Thomas Key provided comments on
the initial two papers **^15,\ 20^** from which this new paper has been
developed.

# 

### References

1\. Bull and Nethercott \"The Frequency of Occurrence and the Magnitude
of Short Duration Transients in Low-Voltage Supply Mains,\" *The Radio
and Electronic Engineer,* Sept 1964.

2\. Martzloff and Hahn, \"Surge Voltages in Residential and Industrial
Power Circuits, \" *IEEE* *Transactions PAS-89,* No.6, July/Aug 1970.

3\. Allen and Segall, \"Monitoring of Computer Installations for Line
Disturbances,\" *Paper C74199-6,* IEEE PES Winter Meeting, 1974.

4\. Goldstein and Speranza, \"The Quality of U.S. Commercial AC Power,\"
*Intelec Conference* *Proceedings,* 1982.

5\. Hughes and Chan, \"Canadian National Power Quality Survey Results,\"
*Proceedings, PQA\'95* *Conference,* EPRI, 1995.

6\. Dorr, \"Point of Utilization Power Quality Study Results,\" *IEEE
Transactions IA-3* 1, No.4, July/August 1995.

7\. Hassler and Lagadec, \"Digital Measurement of Fast Transients on
Power Supply Lines.\" *Proceedings, Third Symposium on EMC,* Rotterdam
May 1979.

8\. Meissen, \"Oberspannungen in Niederspannungsnetzen,\"
(\"Overvoltages in Low-Voltage Networks\"), *Elektrotechnishe
Zeitshrift,* Vol 104, 1983.

9\. Wernstroem, Broms, and Boberg, \"Transient Overvoltages on AC Power
Supply Systems in Swedish Industry,\" *Report FOA E 30002-E2,* Sweden,
1984.

10\. Goedbloed, \"Transients in Low-Voltage Supply Networks,\" *IEEE
Transactions EMC-29,* No.2, May 1987.

11\. Standler, \"Transients on the Mains in a Residential Environment,\"
*IEEE Transactions EMC-31,* May 1989.

12\. Forti and Millanta, \"Power-Line Impedance and the Origin of
Low-Frequency Oscillatory Transients,\" *IEEE Transactions EMC-32,*
No.2, May 1990.

13\. Goulet, \"Susceptibility of Power Semiconductor-based Equipment to
Power Line Disturbances,\" *Conference Proceedings,* Power Quality 1989.

14\. Scheuerer, *\"Research on the Isolation Properties qf Solid
Insulation Upon Occurrence of HF* *Overvoltages,* (In German) Doctoral
Thesis, Darmstadt University, 1993.

15\. Key, Mansoor, and Martzloff, \"No Joules for Surges: Relevant and
Realistic Assessment of Surge Stress Threats,\" *Proceedings, IEEE
International Con rence on Harmonics and Power Quality,* Las Vegas,
October 1996.

16\. EPRI Report EL-6421 -L, *Electromagnetic Transient Program (EMTP),*
Version 2.0, Volumes I and 2, July 1989.

17\. IEEE 1159-1995, *IEEE Recommended Practice for Monitoring
Electrical Power Quality.*

18\. IEEE 587-1980, *IEEE Guide on Surge Voltages in Low- Voltage AC
Power Circuits.*

19\. ANSI/IEEE C62.41-199 *1, Recommended Practice on Surge Voltages in
Low- Voltage A C Power* *Circuits.*

20\. Martzloff, \"Surge Recordings that Make Sense: Shifting Focus from
Voltage to Current Measurements,\" *Proceedings, EMC\'96 ROMA
Symposium,* Rome, Italy, September 1996.

21\. Lai and Martzloff, \"Coordinating Cascaded Surge Protection
Devices: High-Low versus Low­High,\" In *Conference Record, IEEE-IAS 1991
Annual Meeting, pp 1812-1819.* Also in *IEEE* *Transactions, IAS-29*
No.4, July/August 1993, pp 680-687.

22\. Hostfet, Hervland, Nansen, and Huse, \"Coordination of
surge-protective devices \'in power supply systems: Needs for secondary
protection,\" In *Proceedings, 20th International Conference on*
*Lightning Protection, 1992.*

23\. Rousseau and Perche, \"Coordination of Surge Arresters in the
Low-Voltage Field,\" In *Proceedings,* *17th International
Telecommunications Conference* (INTELEC 95), 95CH35824.

24\. Martzloff, Mansoor, Phipps, and Grady, \"Surging the Upside-Down
House: Measurements and Modeling Results,\" In *Proceedings, PQA\'95
Conference,* EPRI, 1995.

**The Fallacy of Monitoring Surge Voltages:**

**SPDs and PCs Galore!**

Number range CHAPTER

+-------------------+------------------------------+------------------+
| ## Arshad Mansoor | ## François Martzloff        | ## Kermit Phipps |
|                   |                              |                  |
| EPRI PEAC Corp    | National Institute of        | EPRI PEAC Corp   |
|                   | Standards                    |                  |
| Knoxville TN      |                              | Knoxville TN     |
| 37932             | and Technology               | 37932            |
|                   |                              |                  |
|                   | Gaithersburg MD 20899        |                  |
+-------------------+------------------------------+------------------+

# Abstract

To support the recommendation of shifting transient monitoring from
voltage surges to current surges, the paper presents experimental
results as well as numerical modeling results demonstrating two
mechanisms causing an apparent decrease of surge activity in low-voltage
ac power circuits. The first mechanism is the proliferation of
surge-protective devices, a situation which is by now well recognized.
The second, which should also have been recognized, apparently escaped
scrutiny so far: the proliferation of electronic appliances containing a
switch-mode power supply that effectively places large surge-absorbing
capacitors across the ac power systems.

**1. Introduction**

This paper is unabashedly tutorial, and some of the themes presented
here might be quite familiar to some of our readers. However, we have
observed that these concepts, which could almost be characterized as
obvious when given the benefit of hindsight, are still not widely
recognized. Therefore, we will present them to this forum, and
illustrate their validity by experimental measurements and numerical
modeling.

The three major themes of this presentation are:

I. There is a logical explanation for the apparent decrease in the level
of voltage surges reported in recent power quality surveys: the
proliferation of surge-mitigating devices.

2\. The present practice of recording voltage surges can lead to
erroneous concepts on surge protection, which in turn can lead to
equipment failures.

3\. There is an unfulfilled need to develop and deploy power quality
monitors that can characterize the energy-delivery capability of a surge
event.

The first theme will be introduced by a historical perspective showing
how voltage surges became the focal point of monitoring surges, even
before the term "power quality" was coined. Experimental measurements
and numerical modeling will be described to illustrate the effect of the
proliferation of surge-protective devices (SPDs) and of new electronic
appliances that serve respectively as intended and unintended
surge-mitigating devices. The next two themes will be only briefly
discussed because, once the first is accepted, these two follow quite
logically.

> **2. Historical Perspective**

The proliferation of SPDs in low-voltage ac power circuits has been
recognized as one of the root causes of the apparent decrease of the
surge levels recorded in recent power quality surveys. The change in the
occurrence of surges began to be recognized \[Dorr, 1995\] and
explanations were offered attributing the phenomenon to the emerging
proliferation of SPDs in low-voltage ac power circuits \[Martzloff,
1996\]. It is noteworthy that for many people, the term "surge" is
equivalent to "transient overvoltage" to the point that the phenomenon
has generally been recorded by instruments acting as voltmeters, and the
term was without much scrutiny accepted in general as meaning a voltage
surge.

For instance, in the bi-lingual publications of the International
Electrotechnical Commission (IEC), the French text which parallels the
English text uses the term "[surtension]{.underline}" (meaning
[overvoltage)]{.underline}, because there is a mind set, reinforced by
the lack of a neutral term in French that could be applied to either or
both voltage surges and current surges. In the United States, the
Underwriters Laboratories perpetuates this narrow perspective by calling
SPDs "Transient Voltage Surge Suppressors" (italics ours) \[UL Std 1449,
1996\], although both recent IEC and IEEE definitions of SPDs introduce
and emphasize the concept of current surges as well as voltage surges.

Now less recognized but significant, a similar cause for the apparent
decrease of voltage surge levels is becoming important as more and more
electronic appliances depend on a switch-mode power supply with a
rectifier-capacitor DC link. Through the rectifier, the DC link
capacitor, which is typically in the order of 200 pF to 500 pF, offers a
low-impedance path to current surges impinging on the power port of
these appliances. With many such appliances connected in an end-user
installation, the effect is that of quite a large capacitor being
connected across the ac mains. Small wonder then that even large surge
currents (for instance, with the capability of delivering currents of 3
kA, 8/20 μs) \[ANSI/IEEE C62.4l-1995\] can no longer raise the voltage
across the mains to the high values sometimes reported in earlier
surveys of surge voltage occurrences.

Another historical mind-set has been to recognize the origin of surges
only as a voltage event while in fact it can be either a true
induced-voltage event, or the end-result of the injection of a surge
current somewhere in the power system. Typical induced-voltage surges
are associated with the electromagnetic coupling into the power circuits
of the field created by a nearby (but not direct) lightning flash. Such
voltage surges, which can develop substantial voltages in high-impedance
circuit loops \[Martzloff et al., 1995\] can easily be mitigated with
relatively small SPDs because their energy-delivery capability is
relatively small \[IEC document 64/1034/CD, 1998\]. In contrast, current
surges are produced either by the dispersion of the current associated
with a lightning flash when a direct strike injects current at some
point of the power system, in close vicinity or at a more remote point
of the power distribution system \[Mansoor et al., 1998\]. Another
source of current surges is switching surges involving the injection of
residual energy into parts of the power system. The energy-delivery
capability of these current surges can be substantial, and be a threat
to the survival of improperly sized SPDs. Note in passing the use of the
term "energy-delivery capability" and not "energy in the surge." Some of
our readers are by now familiar with that theme \[Lindes et al., 1997\]
--- perhaps even tired of seeing it repeated --- but the sad truth is
that usage of the term "surge energy" is still rampant.

The significance of making the distinction between recording current
surges versus recording voltage surges is very important for equipment
designers. A decision to provide only modest surge withstand capability
for an SPD incorporated at the power port of the equipment might be made
because the contemporary surveys reveal few and moderate (voltage)
surges. When combined with the misconception that "the lower the
clamping voltage, the better" \[Martzloff et al., 1989\], the result can
be disastrous. We have in our laboratory 'morgue' two examples of such
mass-produced devices incorporating an inappropriate SPD that led to
early mortality of the product. Without identifying the culprit ---
perhaps a harsh word for a designer who was lulled into this position by
referring to misleading reports on surge activity --- but to illustrate
the situation, we can name the two products: a compact fluorescent bulb,
and a remotely-controlled ceiling fan. To recite a recurrent theme in
our tutorial presentations ("Transients Are Here to Stay"), voltage
surges might appear to have faded away, but current surges are still
here, ready to destroy a small SPD incorporated in a design based on the
misperception of fading voltage surges, fostered by recording only
voltage surges.

**3. Experimental Measurements**

To illustrate the effect of nonlinear SPDs as well as linear capacitors
connected across the mains. the Power Electronics Applications Center
(PEAC) "Upside-Down House" \[Key et al., 1994\] was used to inject
surges into the service entrance of the Upside Down House with various
combinations of SPDs and/or personal computer (PC) power supplies
connected at the end of two branch circuits, one 9-rn long, the other
36-rn long. In Figure 1, currents in the branches and voltages at the
nodes are identified respectively as Is, I~9~, I~36~, and V~0~, V~9~,
V~36~ . The charging voltage setting of the Combination Wave surge
generator was kept constant to provide a 2 kV, 1.2/50 μs open-circuit
voltage (OCV). In a second series of experiments, the setting was
increased to 4 kV. This second series, not reported here in detail
because of limited space, confirmed the expected nonlinear response of
varistors and the linear response for capacitors only.

**Figure 1 - Upside-Down House branch circuits**

**3.1 Metal-oxide varistors only**

Given the known and predictable behavior of multiple SPDs --- often
reported in the literature to the point that bibliographic citations
would take several lines to list all of them --- this part of the
experiment was performed only to provide a baseline. Metal-oxide
varistors (MOVs) rated 150 V, 20 mm diameter, were used for this
experiment. To record all interesting currents and voltages, two shots
are necessary when using the 4-channel digital signal analyzer;
therefore each oscillogram in the figures contains the trace of V~0~ to
serve as a common reference (Figure 2).

**Figure 2-Typical recordings^1^ made during the first experiment---
SPDs only.**

In Figure 2, the current traces (left oscillogram) show the unequal
sharing between the two MOVs, reflecting the difference in the
inductance of the two branch circuits. Because the peaks of the two
branch-circuit currents are not simultaneous (the current in the longer
branch circuit takes longer to build up) their sum seems to exceed the
peak of the injected current, I~S~.

The voltage traces (right oscillograrn) show how the voltage at the
service entrance, V~0~, is mitigated from the 2 kV open-circuit voltage
supplied by the generator that would propagate without attenuation in
the absence of a surge-mitigating device \[Martzloff et al., 1986\].
This voltage V~0~ is the sum of the clamping performed by the varistor
at the node V~9~, and the inductive voltage drop in the 9-rn long
connection. Note that this inductive voltage is additive during the rise
of the current I~9~, and subtractive during the fall, hence the apparent
"overshoot" in the trace of V~0~, compared to the flat-top trace of the
varistor at V~9~. The voltages at V~9~ and V~36~ are the typical
clamping voltages of the MOVs corresponding to the current they carry.

In a subsequent experiment with a 4 kV open-circuit voltage setting of
the generator (twice the value of Figure 2, but not reported here in
detail because of limited space), the voltages across the varistors,
predictably, were not substantially increased. However, the
substantially increased current in the 9-rn long branch circuit (from
1000 A to 2800 A, resulting from the nonlinear response of the varistor)
produced an increased inductive effect to the point that the voltage at
the service entrance was raised to 1300 V from the 790 V recorded for
the case of Figure 2. Table 1, at the end of this section, presents a
summary of the peak values recorded in the various combinations of
components, branch circuits, and amplitudes of the injected surge.

**3.2 Capacitors only**

In a second set of experiments, less easily predictable would be the
behavior of the still all-linear circuit involving the capacitors of a
PC power supply (440 μF each in this experiment) when receiving a surge
originating from the complex RLC wave-shaping network of a Combination
Wave surge generator (Figure 3).

**Figure 3 - Typical recordings made during the second experiment ---
Capacitors only**

In Figure 3, the voltage at the service entrance, V~0~, is mitigated
from the 2 kV open-circuit voltage supplied by the generator. However,
because of the interaction between the RLC components in the
wave-shaping network of the Combination Wave generator on the one hand,
and the capacitances of the PC power supplies and inductances of the
branch circuits on the other hand, this voltage rings around an average
voltage level of 1300 V, reaching a peak of 1700 V. To reflect this
situation, the tabulation of the voltages in the figure shows two lines,
peak and average. Thus, the mitigation effect is degraded by the
ringing. Nevertheless, one can expect that as more PCs would be added,
the ringing frequency would become lower and the voltage peaks lower.

3.  **Capacitor and MOV**

In a third set of experiments, a capacitor was connected at the end of
the 9-m branch circuit and an MOV was connected at the end of the 36-m
branch circuit. Interest in this particular configuration was motivated
by the desire to show how an MOV would mitigate the ringing that was
observed in the preceding experiment at the end of the 36-m line (V~36~
in Figure 3).

**Figure 4 - Typical recordings made during the third experiment ---
capacitor and MOV.**

Experiments 2 and 3 (Figures 3 and 4) do show decreasing levels of
voltage surges at various points of the Upside Down House, compared to
the open-circuit conditions. However, the interactions between the
capacitors of the generator RLC wave-shaping network on the one hand,
and the PC capacitors on the other hand, make detailed interpretation of
the waveforms tedious and beyond the scope of our illustrative examples.
Numerical modeling with a current source, as reported in the following
section, avoids this interaction and provides further evidence on the
"PCs Galore" effect. For readers interested in the details, Table 1
documents the results concerning peak voltages noted from the
oscillograms kept on file but not reproduced here. Readers interested
primarily in the big picture may skip a close examination of this table.

**Table 1 - Summary of node voltages for component combinations**

**4. Numerical Modeling**

Our previous experience with modeling cascaded SPDs \[Lai et al., 1993\]
and the behavior of the Upside Down House with installed SPDs
\[Martzloff et al., 1995\] can be readily applied to the prediction of
the behavior of the three circuits subjected to the experimental
measurements, with an imposed current source, free from the unavoidable
interactions that occurred in the preceding experimental measurements.
This approach yields the best of the two methods: a computation that has
been well demonstrated as suitable for modeling nonlinear SPDs, and the
freedom to impose any fixed waveform --- what reality imposes on a
residence is not the surge from an impedance-limited surge generator ---
combined with the possibility to model many branch circuits and many
combinations of SPDs and/or capacitors.

**4.1 Modeling combinations of loads and branch circuit lengths**

In a series of modeling runs similar to the combinations of the
experimental measurements, the model used the circuit of Figure 5. A
current source feeds a fixed current surge via a common service drop to
the panel bus of the service entrance, where three branch circuits made
of 2-mm diameter conductors (#12 AWG) take off, with length of
respectively 5 m, 10 m, and 20 m. The choice of these lengths was based
on curiosity about the effect of the long distance connection (and thus
an effect that might be delayed or degraded) to the immediate occurrence
of an overvoltage at the end of shorter branch circuits. The currents in
the circuit are identified in Figure 5 respectively as I~S~, I~0~, I~5~,
I~10~, and I20 , with the node voltages at the service bus and branch
circuit ends respectively as V~0~, V~5~, V~10~, and V~20~.

**Figure 5 - Service drop and branch circuits for modeling
combinations**

As in our previous modeling applications, the EMTP program \[EPRJ,
1989\] was used. To avoid computational artifacts, a finite 10 kΩ
resistance was always postulated at the ends of all branch circuits,
whether these were left in "open" or "loaded" condition. The loads that
were modeled included combinations of SPDs, capacitors, and 100 Ω
resistors. The SPDs were all 20-mm diameter, 130-V rated MOVs. The
capacitors included a capacitance of 440 μF and a series resistance
("ESR") of 0.25 Ω to represent an electrolytic capacitor. Initial
conditions for the models stipulated an initial charge on the capacitor
to represent the normal condition of the DC link. The 100 Ω resistor was
selected as a typical value for a 150-W power-consuming appliance
connected at the end of the branch circuit.

Just to illustrate the point of a readily predictable behavior of a
purely linear circuit, Figure 6 shows the voltages and currents for the
case of 100 Ω) loads confronted with a current source. Compared with the
100 Ω) load at the end of the branch circuits, the series impedance has
a very small effect and the impinging surge current I~S~ divides almost
equally (3000 A /4 = 750 A) in the nearly identical four branches I~0~,
I~5~, I~10~, and I~20~ (I~0~ being the current in the service entrance
'branch', with a length of 0). Thus, the voltage developed by this 750 A
current across 100 Ω would simply be expected to be 75 000 V (seventy
five thousand volts). We say "would be expected" because, of course, the
insulation level of a real-world low-voltage insulation cannot withstand
such a voltage. The result of this theoretical case is another
illustration of the theme "More Begets Less," according to which a
high-amplitude, steep-front surge cannot propagate in branch circuits
because a flashover will occur at the origin \[Mansoor et al., 1998\].

**Figure 6 - Currents and voltages for the baseline case of 100 C) loads
without SPDs**

Figure 7 shows the example of two PCs, one at the end of the 5-m branch
circuit, the other at the end of the 10-m branch circuit: the surge
current is shared (unequally) between the two capacitors, with a
corresponding decrease of the voltage level at each DC link, and also a
reduction of the voltage at the open end (unprotected) of the 20-m
branch circuit. This example shows the beginning of the "PCs Galore !"
effect. Several intermediate and further steps were modeled by adding
combinations of surge-mitigating devices to build our case file and
confirm the expected effects, but we will spare the reader from a
tedious recitation.

The results shown in Figure 6 call for several comments:

• The unequal division of the currents I~5~ and I~10~ reflects the
effect of the larger impedance of the 10-m branch circuit, compared to
the 5-m branch circuit.

• Substantial mitigation is obtained at the nodes V~5~ and V~10~, as a
result of the filter-like action of the line inductance and the
capacitance of the PC power supply.

• The voltage surge developed at the node V~0~ propagates, unabated, to
the end of the open-circuited 20-m branch circuit, a reminder that the
notion of voltage surges being attenuated as they propagate in building
wiring \[IEC Report 664, 1980\] was incorrect.

**Figure 7 - Currents and voltages for the case of two PCs without
SPDs**

The voltage results are especially worth noting, in the context of what
a power quality monitor would report in such an installation, depending
upon its point of connection.

> • From the (impossible) high voltages of the 100 Ω baseline (no SPDs),
> the voltage that would be recorded by a monitor installed at the
> service entrance is now reduced to "only" 1960 V.
>
> • A voltage-only monitor installed at the point of use of the power
> (typical selection of point of installation in many surveys), namely
> the two receptacles at 5 m and 10 m feeding the PCs, would report
> respectively 510 V and 290 V, creating the illusion (fallacy) that
> there is no significant surge activity at these points.
>
> • In reality a current surge I~5~ of nearly 2000 A is carried by the
> PC rectifier into the capacitor, via a line fuse. Such a high current
> --- undetected by a voltage-only monitor --- could very well be fatal
> for the rectifier or the input fuse, or for the capacitor of the PC
> power port. Such failures were found in post-mortems of equipment
> recently performed at PEAC. That scenario is also what occurred in the
> experimental test of Section 3 for a 4 kV open-circuit voltage and
> capacitor-MOV combination (shown in next-to-last row of Table I).

**4.2 Modeling PCs Galore**

As a grand finale for illustrating our major theme, the case of an
increasing number of PCs was modeled, with each of the PCs connected at
the end of a dedicated branch circuit, with all branch circuits having
the same length of 20 m, still with the 10-m long service drop driving a
3 kA current surge into the installation.

Table 2 shows the resulting voltages at the service entrance and at the
point of connection of the PCs, as well as the imposed impinging current
and the resulting currents in the individual power ports of the PCs.
Indeed, the effect is linear with increasing numbers of PCs, and the
resulting decrease in the voltages expected to be reported by a power
quality monitor installed at the point of use is quite apparent.

**Table 2 - Effect of an increasing number of connected PCs**

Inspection of the table shows that the effect is practically
proportional to the number of PCs in use in the installation. While we
have used the short acronym of PC in the title and preceding
discussions, the proliferation that we observe is not limited to PCs,
but includes many electronic appliances, such as home entertainment,
heating and air conditioning with adjustable speed drive, that use a DC
link with large energy-storage capacitor.

**5. Action Items**

The customary closure of a paper is to list conclusions. However, in
this case we suggest action items for industry, rather than academic
conclusions:

> • The examples given here clearly show that the fallacy of little
> surge activity can be created by limiting power quality measurements
> to voltage surges. With undetected current surge activity, users of
> electronic appliances will be puzzled by unexplained failures in the
> face of reports of little voltage surge activity.
>
> • We offer the explanation that these unexplained failures are likely
> to be associated with the (heretofore not characterized) surge current
> delivery capability of the environment. Such failures could have been
> avoided, had designers been better informed.
>
> • With our leading theme now solidly established, questions arise
> about what to do about it. This matter requires the dedicated
> attention of both manufacturers and users of power quality monitoring
> instruments.
>
> • Unfortunately, more than three years after beginning the crusade to
> overcome the fallacy of limiting surge measurements to voltage surges
> \[Martzloff, 1995\], there is no commercially available power quality
> monitor capable of characterizing the energy-delivery capability of a
> surge event.
>
> • Worse yet, among the international delegates to an IEC working group
> chartered to develop a standard on measurement of power quality
> parameters (which is likely to dominate the design of future
> monitoring instruments), there are some claims being made that "a
> current surge is not a power quality parameter" and therefore it
> should not be included in the emerging standard prescribing
> measurements methods. This misconception needs to be corrected.
>
> • Therefore, the crusade must be pursued with perseverance, and it is
> the goal and hope of the authors that sufficient recognition of the
> fallacy will eventually create a market demand for appropriate
> instruments, which forward-looking manufacturers may have developed or
> may be in the process of developing in anticipation of such
> recognition.

**7. Bibliography**

ANSI/IEEE C62.41-1995, IEEE Recommended Practice on Surge Voltages in
Low-Voltage AC Power Circuits.

Dorr, D., "Point of Utilization Power Quality Results," IEEE
Transactions IA-31, No.4, July/August 1995.

EPRI, "Electromagnetic Transient Program (EMTP)," Version 2.0; Volume 1:
Main Program: Volume 2: Auxiliary Routines, EPRJ Report EL-6421-L, July
1989.

IEC Report 664-1980 (sic) Insulation coordination within low-voltage
systems including clearances and creepage distances for equipment, 1980.

IEC 64/1034/CD, General basic information regarding surge overvoltages
and surge protection in low-voltage a.c. power circuits, Committee
Draft, 1998.

Key, T.S. and Martzloff, F.D., "Surging the Upside-Down House: Looking
into Upsetting Reference Voltages," Proceedings, PQA '94 Conference,
1994.

Lai, J.S. and Martzloff, F.D., "Coordinating Cascaded Surge Protection
Devices: High-Low versus Low­High,"IEEE Transactions, IAS-29 No.4,
July/August 1993.

Lindes, G., Mansoor, A., Martzloff, F.D., and Vannoy, D., "Surge
Recordings that Make Sense --- Joule Deposition: Yes ! - 'Joule
Content': Never !" Proceedings, PQA '97 Conference, 1997.

Mansoor, A., Martzloff, F.D., and Nastasi, D, "Applying Reality Checks
to Standards on the Surge Environment," Proceedings, 23rd International
Conference on Liglitning Protection, Florence, 1996.

Mansoor, A. and Martzloff, F.D., "Driving High Surge Currents into Long
Cables: More Begets Less," IEEE Transactions PWRD-12, July 1997.

Mansoor, A. and Martzloff, F.D., "The Effect of Neutral Earthing
Practices on Lightning Current Dispersion," IEEE Transactions PWRD-13,
July 1998.

Martzloff, F.D. and Gauper, H.A., "Surge and High-Frequency Propagation
in Industrial Power Lines," IEEE Transactions IA-22, July/August 1986.

Martzloff, F.D. and Leedy. T.F., "Selecting Varistor Clamping Voltage:
Lower Is Not Better!" Proceedings, 1989 Zurich International EMC
Symposium, 1989.

Martzloff, F.D. and Lai, J.S., "Cascading Surge-Protective Devices:
Coordination versus the IEC 664 Staircase," Proceedings, PQA 91
Conference, 1991.

Martzloff, F.D., "Keeping up with the Reality of Today's Surge
Environment," Conference Proceedings, Power Quality Solutions, Intertech
Pub., Ventura CA, USA, September 1995.

Martzloff, F.D., Mansoor, A., Phipps, K., and Grady, W.M., "Surging the
Upside-Down House:

Measurements and Modeling Results," Proceedings, PQA '95 Conference,
EPRI, 1995.

Martzloff, F.D., "Surge Recordings that Make Sense: Shifting Focus from
Voltage to Current

Measurements," Proceedings EMC'96 ROMA Symposium, Rome, September 1996.

UL Std. 1449, Transient Voltage Surge Suppressors, Second Edition, 1996.

SOME ENLIGHTENING CASE HISTORIES ON LIGHTNING DAMAGE

Thomas Key Doni Nastasi Kermit Phipps François Martzloff

EPRI PEAC, Inc. National Institute of Standards and Technology

Abstract: Lightning-related damage stories abound, but it is not always
possible to document precisely the mechanisms and scenarios involved
when timely, first-hand knowledge is not obtainable. From a collection
of case histories accumulated by the authors, three cases are described.
Each of the three illustrates a different mechanism leading to
structural damage or equipment failure, in ways that might not have been
obvious from a casual investigation of the damage or sites, or from
second-hand reports.

Keywords: Lightning damage; system interactions; equipment immunity.

**1. INTRODUCTION**

In an area of Eastern Tennessee, U.S.A., where the three lightning
incidents reported here occurred in 1998, the ground flashes over an
area of 40 km radius average 22 000 per year. The year 1998 was
particularly active , a total of 27 993 ground flashes, or 5,5
flashes/km^2^ \[1\]. These incidents of damage came to the attention of
the authors, providing a unique opportunity to document the mechanisms
and failure modes of residential electronics.

The first incident involved a small house made primarily of wood where
the power service entrance and the cable TV entrance were at opposite
ends of the house - the classic error in installation practice -
compounded with a violation of ground bonding rules. The second incident
involved a residence with an elaborate audio-video system with a central
equipment rack distributing signals to speakers and monitors. A third
incident was the case of a direct lightning flash to the overhead
service of a house, resulting in severe fire damage to the structure.

**2. THE CASE OF THE COZY CABIN**

At this rural site, a wood-structure residence suffered two failures of
video equipment during lightning storms, a few months apart. The owners
allowed the authors to visit the site and acquire the second failed TV
receiver for a postmortem examination and tests.

The visit revealed a case of the incorrect but frequent practice of two
uncoordinated providers \-- the cable TV company and the power company
\-- installing their service entrance at opposite ends of the house
(Figure 1). The consequences of such practice are briefly described in
the following.

**2.1 The problem of shifting reference potentials**

The general problem of shifting reference potentials during surge events
has been described in previous work \[2\]; \[3\]. A brief description of
this problem is given here to place the \"Case of the Cozy Cabin\" in
perspective. In the scenario of Figure 1, a personal computer (PC) is
connected to both the power system and the telephone system. The surge
current \"Surge I\" flows from the telephone system toward the common
grounding point via the protective device \"NID\" at the point of entry,
and the equipotential conductor. This current produces a magnetic field
which couples into the loop formed by the power branch circuit, the
telephone premises wiring lines to the PC, and the equipotential
conductors. The voltage thus induced in the loop appears across the
telephone and power ports, with upsetting or damaging consequences.

In a laboratory replica of this configuration \[2\], a peak voltage of
4,3 kV was recorded across the two ports for a typical surge injected at
the telephone entrance. A similar situation exists for a surge impinging
on the video port of a TV receiver. The tests reported in 2.3 below show
that this level can cause damage.

**2.2 Cozy cabin site configuration**

I n the Cozy Cabin installation, the power service entrance was located
at one end of the house, while the cable TV service entrance was located
at the opposite end. Furthermore, a visit to the site revealed that the
cable TV shield was grounded only by a questionable ground rod next to
the house foundation (within the drip line, and thus in dry soil, see
Figure 2). This cable TV grounding electrode was not bonded to the
grounding electrode of the power service entrance, a clear violation of
the U.S National Electrical Code (\'NEC\", NFPA 70, 1999) \[4\].

Following the visit to the site by the authors, the local cable TV
company was informed of this situation and took what they believed an
appropriate action: the incoming cable was first routed under the house,
in the crawl space, to allow bonding the shield to the power service
grounding connection. From there, the cable was returned to its original
point of entry into the house, at the opposite end. This modification
did correct the NEC violation but left the arrangement in the topology
shown in Figure 1.

However, the interaction was not pursued further with the cable company.
A recommendation was made to the owner, to install a surge reference
equalizer \[5\] for each piece of video equipment. After that was done,
no damage occurred during the next lightning season. Of course, it is
still too early to declare victory over Zeus and Murphy, but encouraging
when compared to a previous history of two incidents within a few
months.

**2.3 Post mortem and surge tests**

One of the failed TV receivers from the Cozy Cabin was made available to
the authors for examination. No evidence of damage was found on the
power side of the chassis and the related components, but a clear
indication of surface flashover was observed along the insulation of the
gap intended to isolate the cable input \'ground\' termination
(connected to the incoming cable shield) from the shielding can of the
tuner (connected to one of the power cord conductors, see Figure 3).

After cleaning the carbonized path of the flashover, a 0,5 μs - 100 kHz
Ring Wave was applied in incremental steps between the two conductors of
the power cord, bonded together, and the shield connector of the cable
input: flashover occurred at 2 kV. By removing the material to a greater
depth and covering it with epoxy, the gap did withstand a greater level,
and failed at 2,5 kV. That flashover occurred at another part of the
original insulation, thus providing valid information on the original
withstand capability.

**2.4 Conclusions from the Cozy Cabin**

This case study illustrates the classic situation of separate service
entrances, compounded with incorrect bonding. The examination and test
demonstrate that at least 2,5 kV were developed across the power port
and the cable TV port of the receiver under a condition of distant or
nearby lightning strike.

Another significant finding from this case history is the anecdotal
confirmation of allegations that cable TV installation practices
prevailing in many residential situations might be in violation of the
U.S. National Electrical Code. This violation made even more hazardous
the now well-recognized occurrence of undesirable separation of the
service entrances.

**3. INPUT ISOLATION PRACTICES**

Interest aroused by the Case of the Cozy Cabin led to a brief survey of
what isolation schemes are applied by the manufacturers of video
equipment.

Televisions and VCRs are of a similar category of equipment in that they
both have the same input ports: ac power, and video (antenna or cable),
for which the \'ground\' reference can be raised to different potentials
during a surge event. The power port has no direct connection to the
equipment grounding conductor because a two-prong ac plug is used.
However, at the service entrance, the neutral - one of the two
conductors of the cord - is bonded to the ground bus of the service
panel. The video input is referenced to ground via a connection to a
grounding rod outside the residence and (per the NEC \[4\]), a bonding
conductor.

Manufacturers use various techniques to isolate these two ports from
each other inside the equipment. Surge tests were conducted on five
televisions and three VCRs to determine the voltage level at which
spark-over would occur between the power port and the video port. Using
a 0.5 μs - 100 kHz Ring Wave, incremental steps of 500 V were applied
between the power port and the shield of the video input port.

The units that had isolation built into the video port sparked-over at
the series capacitor of the video port. The breakdown voltage level was
approximately 2,5 kV in these units. Units in which the power supply
outputs were electrically isolated from the inputs via transformers
fared better. One sample survived and performed normally after all surge
tests. Physical size of the transformer seemed to have some impact on
the results. Larger transformers seemed to tolerate surges better than
smaller ones.

Based on this small number of VCR samples, a general observation is that
VCRs use power supply transformers as isolation, similar to the newer TV
sets, and do not have isolation between the cable or antenna input and
the tuner chassis. This type of isolation scheme withstood higher surge
voltages than the isolating ring that can be found in older television
sets and serving to isolate the chassis of the set from the
(\'grounded\') shield of the signal cable.

**4. THE CASE OF THE RAMBLING RESIDENCE**

An expansive residential estate, located in the same general area as the
Cozy Cabin, was the scene of a lightning incident where a tree adjacent
to the house was struck (and subsequently died). Extensive damage was
inflicted to the audio-video components that are connected to a central
rack, and are located throughout the residence and its surroundings
(large patio and swimming pool, with outdoor lighting and audio
speakers).

The home owners graciously allowed the authors to visit the residence
and observe the configuration of the system in an attempt to better
understand the mechanisms leading to the damage. They also made
available to the authors the complement of damaged or presumed damaged
equipment that had been replaced thanks to their insurance. Thus, this
case history, unlike most lightning incidents, offered an unusual

Three activities were undertaken to better understand the mechanism and
verify some hypotheses:

1\. Bench examination of returned equipment and surge testing of
undamaged equipment;

2\. Site visit of the residence;

3\. Laboratory coupling of electric field stress into a remote
speaker-to-amplifier connection.

**4.1 Bench Examination**

Bench tests for each electrical appliance began by plugging it into a
120-V a.c. outlet. Physical signs of normal operation were noted such as
illuminated displays, response of controls, audio/video output. The
equipment cover was removed for an internal inspection. In most of the
equipment, physical damage such as a burned-out transistor was very
apparent. Table 1 lists the home entertainment equipment that were
submitted, and their condition.

A significant finding was that all of the power supplies in the
equipment were functional, indicating that the lightning surge either
did not enter through the ac power port, or was not severe enough to
cause damage to the power supplies.

> **Table 1 Equipment submitted for bench tests**

The examination and, as appropriate, tests revealed the following
conditions:

· Except for its non-operational display, the stereo tuner/amplifier
appeared undamaged.

· The visible damage to the digital satellite receivers was nearly
identical in all three units. Apparently, the surge had entered through
the telephone port and had damaged the small surface-mount electronics
that make up the modem circuit. However, because the satellite receivers
could not be operated without their antenna and code-reading cards, the
extent of the functional damage could not be determined

The two 12-channel amplifiers had sustained damage to their output
transistors that drive the speakers. The power supplies and fuses were
not damaged. Furthermore, it was found that some speaker outputs were
still operational. This situation suggested a possible mechanism that
damaged only some of the output transistors, and therefore not
attributable to a \"power-line surge.\" In turn, that hypothesis was
later verified by a laboratory test, as described in 4.3 below.

· Speakers, tested by connecting them to an amplifier that was known to
be functioning properly, were found to have their woofers damaged, but
the tweeters still operational.

Other electrical appliances in the house including television- sets and
VCRs not connected- to the centralized system were not included in the
returned package and therefore presumed as not damaged. This finding
confirms the conclusion that the long leads interconnecting the
distributed- system components acted as energy collector&, feeding the
induced voltages or currents into the communications ports of the
equipment.

**4.2 Site Visit**

The purpose of the visit was to look for clues to explain the specific
damage that was observed in some of the equipment. The following
observations were made:

· Approximate distances between the lightning strike and affected
equipment

· Location and grounding at the service entrances of cable TV, power,
and telephone

· Other wiring and general installation practices

The overall physical layout of the house, damaged tree, and electronic
equipment are shown in Figure 4. The tree that was struck is much taller
than the house and is the tallest of the trees in the immediate area.
The bark was stripped from the tree trunk for most of its height. The
tree trunk is only approximately 15 m from the house and even closer to
the patio, where some of the audio speakers were installed. Outdoor
speakers are also located in the pool area and connecting walkways.

In the audio amplifiers, as noted above, the power supplies of the units
were not damaged, but their output transistors that drive the speakers
and the speakers them­selves were damaged. Thus, it was speculated that
the surge energy had been coupled into the speaker wires, which are
probably very long and very near to the lightning strike, rather than as
a \'power-line surge.\"

The visit to the installation verified this theory. The home
entertainment equipment, including amplifiers, is centrally installed in
the basement of the house. Speakers are located- throughout the house,
the patio, and- the swimming pool area. The wire length between the
outdoor speakers and the central amplifier is about 30 m, and some of
the wires run within 10 m of the tree trunk.

**4.3 Laboratory Coupling of Electric Field**

To validate the hypothesis of a failure mechanism involving the coupling
of electric field energy into the speaker wire ran, a qualitative
laboratory test war. staged, using the surviving channel of the
amplifier to drive a speaker. An audio signal from a tape deck was fed
into the amplifier input to monitor its operation during the test. A
conventional Marx impulse generator at the NIST High-Voltage Laboratory
was used to apply a 1,2/50 μs high-voltage field between two parallel
plates, each 2 m x 1 m.

A length of 5 m of speaker wire feeding the audio output from the system
audio amplifier was sandwiched between the two plastic foam sheets
separating the lower (grounded) plate, to which the amplifier chassis
was bonded, from the upper (impulsed) plate. The effective length of the
wire was increased by connecting to each wire a- piece of foil of about
0.02 m, simulating the increased capacitance effect of about 50 m of
wire. Both the amplifier and tape deck were isolated from the power
supply ground by an uninterruptible power supply.

The impulse was applied in increments. At 70 kV, a flashover occurred
between the two plate edges, but not involving the speaker wire.
Immediate failure of the amplifier output circuit was noted, From this
anecdote, we conclude that the rapid field change associated with the
flashover did have the capability to couple enough surge energy into the
capacitance divider of wire/ground plane and cause destructive failure
of the output transistor effectively connected across that capacitance.
Such a scenario can be considered a reasonable emulation of the
circumstances surrounding the \"Lightning Incident at the Rambling
Residence.\"

**4.4 Conclusions from the Rambling Residence**

The qualitative laboratory demonstration of coupling energy into the
speaker wires provides one more piece of evidence that electronic
appliances can be damaged- by surges impacting their communications
port, to the point that expecting protection by simple application of
SPDs on the power port is not enough, and comprehensive protection is a
necessity. In this case, there was no evidence of any damaging surge
introduced by the power supply connection of the residence.

**5. THE CASE OF THE STANDARD SUBURBAN**

**5.1 The aftermath**

In this case, which occurred in a suburban, semi-rural hilly area, the
post-strike investigation revealed that the overhead service drop to the
house (involving a span of about 20 m across the street) had been
severed by melting at the point of strike. From there, the current
traveled to the revenue meter (typically on the outside wall in U.S.
practice), where a ground conductor is normally installed with a short
run to the earthing electrode of the house. Instead, according, to the
practice when- constructed in the 1970s, a cold water pipe was allowed
to be the main earthing electrode. In this case, the conductor for the
earthing electrode entered the garage and was routed upward near the
ceiling with several bends before it was bonded to a copper water pipe.
Without any better path to earth, the lightning current had apparently
followed the same route, severing the bare conductor while seeking the
well-grounded water pipe (see Figure 5).

As shown in the photographs of Figure 5, the service entrances were
overhead and without any direct path to earth. This type of installation
would not be approved by current US practice, which requires a direct
connection to a driven ground rod in addition to any other supplemental
electrodes such as the cold water pipe. One of the main reasons that the
practice was modified is the growing use of PVC or plastic water pipe.

On a later visit, the engineers who made the first visit were allowed to
visit the repaired house. Indeed, the new service grounding point
includes not only the electric power but also the telephone and cable
company. The new water piping is PVC, and a driven ground rod has been
installed as the primary grounding electrode.

This new arrangement (Figure 6) reflects a recently issued recommended
practice \[6\] which, in addition to the NEC [minimum]{.underline}
requirements for safety, calls for inter­system bonding of all utilities
serving a residence, and this by having all the utility connections next
to each other.

**5.2 Conclusion from the Standard Suburban**

Architects and builders, guided by up-to-date codes, can provide
appropriate grounding practices in new construction. Surge-protective
devices at the service entrance can provide a path from ungrounded
conductors and equalize voltages between these conductors. The practice
is recommended as the first level of protection from surges in the
exterior electrical environment.

**6. GENERAL CONCLUSIONS**

· The Case of the Cozy Cabin and related tests confirm the need to pay
attention to the problems associated with the surge protection of
multi-port equipment. The solution of non-metallic communications media
is not yet ready for the consumer market, but an effective mitigation
approach is the surge reference

· The Case of the Rambling Residence and related tests illustrates that
the often-cited \"power line surge\" cause is not the only scenario
responsible for appliance failures. Other ports of equipment,
communication ports in particular, can be damaged by surges induced into
the cables used for incoming or outgoing signals, and therefore need
appropriate protection.

· The Case of the Standard Suburban shows that architects and builders
have not fully understood the necessity of appropriate wiring and
earthing practices. The same lack of understanding by some utility
providers was also evident in the Case of the Cozy Cabin.

· The recommended practice of intersystem bonding at the service
entrance described in this paper is compatible with the requirements of
the U.S. National Electrical Code. Codes applicable in other countries
might require a different arrangement, but the principles are the same.

**7. ACKNOWLEDGMENTS**

Resources for conducting these investigations were provided by the
members of the Electric Power Research Institute.

Lightning flash density data and comments on the manuscript were
contributed by Kenneth Cummins of Global Atmospherics, Inc.

The experiment on coupling energy into speaker wires, and a review of
the manuscript were contributed by Gerald Fitzpatrick.

8\. REFERENCES

\[1\] Personal communication, Global Atmospherics, Inc.

\[21 Key, T. S., and Martzloff, F.D., "Surging the Upside-Down House:
Looking into Upsetting Reference Voltages," *Proceedings, PQA94
Conference, Amsterdam*, October 1995.

\[3\] Martzloff, F.D., Mansoor, A., Phipps, K.O., and Grady, W.M.,
"Surging the Upside-Down House: Measurements and Modeling Results,\"
*Proceedings, PQA95 Conference*, May 1995.

\[4\] NFPA 70 - 1999, *National Electrical Code*, National Fire
Protection Association, 1999.

\[5\] IEEE Std 1100-1999 (Emerald Book) *IEEE Recommended Practice for
Powering and Grounding Electronic Equipment*, IEEE, 1999.

\[6\] EPRI PEAC, "Recommended Practice for Protecting Residential
Structures and Appliances Against Surges," *Report PEAC.0545.R*, EPRI
PEAC Corporation, Knoxville, TN, 1999.

+-----------------------------------------------------------------------+
| ## François Martzloff                                                 |
+-----------------------------------------------------------------------+
| ######## END OF FILE "Text Site Surveys"                              |
+-----------------------------------------------------------------------+
| ## April 2004                                                         |
+-----------------------------------------------------------------------+