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| # Las | # Surge Protection Anthology                         | #     |
| t upd |                                                      |  Surg |
| ated  | ######## Part 6 -- Tutorials, Textbooks, and Reviews | es Ha |
| April |                                                      | ppen! |
|  2004 | **Text of "Standards Reviews"**                      |       |
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FOREWORD

This file contains the text part from eight papers on the subject of
standards development:

-   A guideline on surge voltages in AC power circuits rated up to 1000
    V (1979)

-   The development of a guideline on surge voltages in LV AC power
    circuits (1979)

-   A consensus on powering and grounding sensitive electronic equipment
    (1986)

-   A standard for the 90s: IEEE C62.41 surges ahead (1991)

-   Standards: Transnational aspects (1991)

-   Power Quality work at the International Electrotechnical Commission
    (1997)

-   The Trilogy update of C62.41 (2000)

-   New IEEE standards foster next-generation system compatibility
    (2002)

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="1.0in" height="0.4909722222222222in"}

**A GUIDELINE ON SURGE VOLTAGES**

**IN AC POWER CIRCUITS RATED UP TO 600 V**

F.D. Martzloff

General Electric Company

Schenectady, New York 12345, U.S.A.

# Summary

Surge voltages occurring in ac power circuits can be the cause of
misoperation or product failure for residential as well as industrial
systems. The problem has received increased attention in recent years
because miniaturized solid state devices are more sensitive to voltage
surges (spikes and transients) than were their predecessors.

Although surge voltage amplitudes and their fre­quency of occurrence on
unprotected circuits are well known, their waveshapes and energy content
are less well known. On the basis of measurements, statistics, and
theoretical considerations, a practical guideline for out­lining the
environment for use in predicting extreme waveshapes and energy content
can nevertheless be estab­lished. The Surge Protective Device Committee
of the Institute of Electrical and Electronics Engineers has been
developing such a guideline, the essential elements of which are
presented in this paper.

Surge voltages \[1\] occurring in ac power circuits rated up to 600 V
can be represented by various waveshapes in an attempt to duplicate
actual surge voltages. Two major types of surges reflecting differences
in the environ­ment are described to represent the situation
realistically.

Systems located inside a building and separated from the overhead lines
by some line impedance experience surge voltages of waveshapes and
energy levels that differ from those of the outdoor environment. Outside
systems exposed to direct lightning strikes or lightning-induced
surges\--typically overhead lines\--experience levels implied by IEEE
standards for secondary arresters. This guideline addresses particularly
the hazards to these two types of systems \[2\].

**Scope**

The guideline presented here primarily addresses ac power circuits with
rated voltages up to 600 V, although some of the conclusions offered
could apply to higher voltages and also to some dc power systems. Other
standards have been established, such as IEEE 472, Guide for Surge
Withstand Capability (SWC) Tests, intended for the special case of
high-voltage substation environments, and IEEE 28, Standard for Surge
Arresters far ac Power Circuits, covering primarily the utilities
environment. The guideline presented here intends to complement, not
conflict with, existing standards, and to present a practical proposal
for the selection of voltage and current tests to be applied in
evaluating the surge withstand capability of equipment connected to
these power circuits, primarily in residential and light industrial
applications.

Some guidance is also presented on how to proceed from the environment
description to the selection of "standard" test waves.

The surge voltages \[1\] considered in this guideline are those
exceeding two per unit (or twice the peak operating voltage) and having
durations ranging from a fraction of a microsecond to a millisecond.
Overvoltages of less than two per unit are not covered here, nor are
transients of longer duration resulting from power equip­ment operation
and failure modes. Because these low-amplitude and long-duration surges
are generally not amenable to suppression by conventional surge
protective devices, they require different protection techniques.

**[1. The Origin of Surge Voltages]{.underline}**

Surge voltages occurring in low-voltage ac power circuits originate from
two major sources: load switching transients and direct or indirect
lightning effects on the power system. Load switching transients can be
further divided into transients associated with (1) major power system
switching disturbances, such as capacitor bank switching; (2) minor
switching near the point of interest, such as an appliance turnoff in a
household or the turnoff of other loads in an individual system; (3)
resonating circuits associated with switching devices, such as
thrusters; and (4) various system faults, such as short circuits and
arcing faults. Measurements and calculations of lightning effects have
been made to yield data on what levels can be produced, even if the
exact mechanism of any particular surge is unknown. The major mechanisms
by which lightning produces surge voltages are the following:

\(a\) A direct lightning strike to a primary circuit injects high
currents into the primary circuit, producing voltages by either flowing
through ground resistance or flowing through the surge impedance of the
primary conductors.

(b) A lightning strike that misses the line but hits a nearby object
    sets up electromagnetic fields which can induce voltages on the
    conductors of the primary circuit.

(c) The rapid collapse of voltage that occurs when a primary arrester
    operates to limit the primary voltage couples effectively through
    the capaci­tance of the transformer and produces surge voltages in
    addition to those coupled into the secondary circuit by normal
    transformer action.

\(d\) Lightning strikes the secondary circuits directly. Very high
currents can be involved, exceeding the capability of conventional
devices.

\(e\) Lightning ground current flow resulting from nearby
direct-to-ground discharges couples onto the common ground impedance
paths of the grounding network.

Fast-acting protection devices, such as current-limiting fuses and
circuit breakers capable of clearing or beginning to part contacts in
less than 2 ms, leave trapped inductive energy in the circuit upstream;
upon collapse of the field, very high voltages are generated.

Transient overvoltages \[1\] associated with the switching of power
factor correction capacitors have lower frequencies than the
high-frequency spikes with which this document is concerned. Their
levels, at least in the case of restrike-free switching operations, are
generally less than twice normal voltage and are therefore not of
substantial concern here, but should not be overlooked.

On the other hand, switching operations involving restrikes, such as
those produced by air contactors or mercury switches can produce,
through escalation, surge voltages of complex waveshapes and of
amplitudes several times greater than the normal system voltage. The
severest case is generally found on the load side of the switch and
involves only the device that is being switched. While this situation
should certainly not be ignored, in such a case the prime responsibility
for protection rests with the local user of the device in question.
However, switching transients can also appear on the line side across
devices connected to the line. The presence and source of transients may
be unknown to the users of those devices. This potentially harmful
situation occurs often enough to command attention.

**[2. Occurrence and Voltage Levels in Unprotected
Circuits]{.underline}**

1.  **[Rate of Occurrence Versus Voltage Level]{.underline}**

The rate of occurrence of surges varies over wide limits, depending on
the particular system. Prediction of the rate for a particular system is
always difficult and frequently impossible. Rate is related to the level
of the surges; low-level surges are more prevalent than high-level
surges (3\]. Data collected from many sources (Appendix I) have led to
the plot shown in Figure 1. This prediction shows with certainty only a
relative frequency of occur­rence, while the absolute number of
occurrences can be described only for an "average location." The "high
exposure" and "low exposure" limits of the band are shown as a guide,
not as absolute limits \[2\], to reflect both the location exposure
(lightning activity in the area and the nature of the system) and the
exposure to switching surges created by other loads. Such data are
useful in that they describe the maximum levels likely to be encountered
and give some estimate of the rate of occurrence of such surges. Of
equal importance is the observation that surges in the range of 1 to 2
kV are fairly common in residential circuits.

Figure 1. Rate of Surge Occurrence vs Voltage Level

From the relative values of Figure 1, two typical levels can be cited
for practical applications. First, the expectation of a 3 kV transient
occurrence on a 120 V circuit ranges from 0.01 to 1 per year at a given
location -a number sufficiently high to justify the recommendation of a
minimum 3 kV withstand capability. Second, the wiring flashover limits
indicate that a 6 kV withstand capability may be sufficient to ensure
device survival indoors, but a 10 kV withstand capability may be
required outdoors.

2.  [Timing of Occurrence]{.underline}

Surges occur at random times with respect to the power frequency, and
the failure mode of equipment may be affected by the power frequency
follow current. Furthermore, the timing of the surge with respect to the
power frequency may affect the level at which failure occurs \[4\].
Consequently, surge testing must be done with the line voltage applied
to the test piece.

**[3. Waveshape of Representative Surge Voltages]{.underline}**

1.  **Waveshapes in Actual Occurrences**

Indoor - Measurements in the field, measurements in the laboratory, and
theoretical calculations indicate that most surge voltages in indoor
low-voltage sys­tems have oscillatory waveshapes, unlike the well-known
and generally accepted unidirectional waves specified in high-voltage
insulation standards. A surge impinging on the system excites the
natural resonant frequencies of the conductor system. As a result, not
only are the surges typically oscillatory, but surges may have different
amplitudes and wave-shapes at different places in the system. These
oscillatory frequencies of surges range from 5 kHz to more than 500 kHz.
A 30 to 100 kHz frequency is a realistic measure of a "typical" surge
for most residential and light industrial ac line networks.

Outdoor - Surges encountered in outdoor locations have also been
recorded, some being oscillatory \[5\], others, being unidirectional.
Because the overriding concern here is the energy associated with these
surges, a conservative but realistic description of the surges can be
derived from the long-established specified duty of a secondary
arrester, as detailed in Paragraph 3.2. While this specification is
arbitrary, it has the strength of experience and successful usage.

2.  **Selection of Representative Waveshapes**

The definition of a waveshape to use as repre­sentative of the
environment is important for the design of candidate protective devices,
since unrealistic require­ments, such as excessive duration of the
voltage or very low source impedance, place a high energy requirement on
the suppressor, with a resulting cost penalty to the end user. The two
requirements defined below reflect this trade-off.

***Indoor*** - Based on measurements conducted by several independent
organizations in 120 and 240 V systems (Appendix I), the waveshape shown
in Figure 2 is reasonably representative of surge voltage in these power
circuits. Under the proposed description of a "0.5 μs x 100 kHz ring
wave," this waveshape rises in 0.5 μs, then decays while oscillating at
100 kHz, each peak being about 60% of the preceding peak.

Figure 2. The proposed 0.5 μs x 100 kHz Ring Wave (Open-circuit Voltage)

The fast rise can produce the effects associated with nonlinear voltage
distribution in windings and the dv/dt effects on semiconductors.
Shorter rise times are found in many transients, but, as those
transients propagate into the wiring or are reflected from
discontinuities in the wiring, the rise time becomes longer.

The oscillating and decaying tail produces the effects of voltage
polarity reversals in surge suppressors or other devices that may be
sensitive to polarity changes. Some semiconductors are particularly
sensi­tive to damage when being forced into or out of a conducting state,
or when the transient is applied during a particular portion of the 60
Hz supply cycle (Appendix II). The response of a surge suppressor can
also be affected by reversals in the polarity, as in the case of RC
attenuation before a rectifier circuit in a dc power supply.

The pulse withstand capability of many semiconduc­tors tends to improve
if the surge duration is much shorter than one microsecond. For this
reason, the first half-cycle of the test wave must have a sufficient
duration.

***Outdoor*** - In the outdoor and service entrance environment, as well
as in locations close to the service entrance, substantial energy, or
current, is still available. For these locations, the unidirectional
impulses long established for secondary arresters are more appropriate
than the oscillatory wave.

Accordingly, the recommended waveshape is 1.2 x 50 μs for open-circuit
voltage and 8 x 20 μs for short-circuit current or current in a
low-impedance device. The numbers used to describe the impulse, 1.2 x 50
and 8 x 20, are as defined in IEEE Standard 28. ANSI Standard C62.1;
Figure 3 presents the waveshape and a graphic description of the
numbers.

# Figure 3. Waveshapes for Outdoor Locations

**4. Energy and Source Impedance**

1.  **General**

The energy involved in the interaction of a power system with a surge
source and a surge suppressor will divide between the source and the
suppressor in accordance with the characteristics of the two impedances.
In a gap-type suppressor, the low impedance of the arc after sparkover
forces most of the energy to be dissipated elsewhere: for instance, in a
power-follow current-limiting resistor that has been added in series
with the gap. In an energy-absorber suppressor, by its very nature, a
substan­tial share of the surge energy - is dissipated in the suppressor,
but its clamping action does not involve the power-follow energy
resulting from the short-circuit action of a gap. It is therefore
essential to the effective use of suppression devices that a realistic
assumption be made about the source impedance of the surge whose effects
are to be duplicated.

The voltage wave shown in Figure 2 is intended to represent the
waveshape a surge source would produce across an open circuit. The
waveshape will be different when the source is connected to a load
having a lower impedance, and the degree to which it is lower is a
function of the impedance of the source \[6\].

The degree to which source impedance is important depends largely on the
type of surge suppressors that are used. The surge suppressors must be
able to withstand the current passed through them by the surge source. A
test generator of too high an impedance may not subject the device under
test to sufficient stresses, while a generator of too low an impedance
may subject protective devices to unrealistically severe stresses. A
test voltage wave specified without reference to source impedance could
imply zero source impedance - one capable of producing that voltage
across any impedance, even a short circuit. That would imply an infinite
surge current, clearly an unrealistic situation.

2.  **Proposed Approach**

Because of the wide range of possible source im­pedances and the
difficulty of selecting a specific value, three broad categories of
building locations are proposed to represent the vast majority of
locations \[7, 8\], from those near the service entrance to those remote
from it. The source impedance of the surge increases from the outside to
locations well within the building. Open-circuit voltages, on the other
hand, show little variation within a building because the wiring
provides little attenuation f\[9\]. Table I outlines the three
categories of building wiring.

Table 2 shows open-circuit voltages and short-circuit currents for each
of the three categories. The energy deposited in a 500 V suppressor has
been computed and is shown for each of the categories.

TABLE 1 - Location Categories

TABLE 2 - Ranges of Voltage and Currents

The values shown in the table represent the maximum range, Corresponding
to the "High Exposure" situation of Figure 1. For less exposed systems,
or when the prospect of a failure is not highly objectionable, one could
specify lower values of open-circuit voltages with corresponding
reductions in the currents.

The broad range of surge voltages occurring in low-voltage ac power
circuits can be simulated by a limited set of test waves, for the
purpose of evaluating their effects on equipment.

Field measurements, laboratory experiments, and calculations indicate
that two basic waves, at various open-circuit voltages and short-circuit
current values, can represent the majority of surges occurring in
residential, commercial, and light industrial power systems rated up to
600 V rms.

Exceptions will be found to the simplification of a broad guideline;
however, these should not detract from the benefits that can be expected
from a reasonably valid uniformity in defining the environment. Other
test waves of different shapes may be appropriate for other purposes,
and the present guideline should not be imposed where it is not
applicable.

**6. Acknowledgments**

The members of the IEEE Working Group contributed the data, shown in
Appendix I, that shaped this guideline. Helpful comments, discussions,
and reviews by all members of the Surge Protective Devices Committee are
also acknowledged. The author is particularly indebted to the
contributions of Catharine Fisher and Peter Richman for the presentation
and discussion of the concepts and recommendations made in this
guideline.

**Appendix I - Data Base**

*\[This format does not support the many graphics and tables of this
Appendix -- See the pdf file\]*

######### Appendix II - Effect of Transient Polarity Reversals on Semiconductors

Breakdown of semiconductors under various condi­tions of load and
transient overvoltage applications has been investigated. Evidence is
presented in the two investigations cited that a reverse voltage applied
during the conduction period of the power frequency produces lower
breakdown voltages than the application of the same transient with no
load or during blocking. Examples are given below, taken from these two
investigations, showing statistically significant differences in the
voltage levels.

*\[See the pdf file for tabulated data\]*

This effect is one of the reasons for selecting an oscillatory waveform
to represent the environment: it will be more likely to induce
semiconductor failures than a unidirectional wave. Also, it shows the
significance of the timing of the transient application with respect to
the power frequency cycle.

# Appendix III - Notes and References

**1. Surge Voltage**

Definitions of terms used in this guideline are consistent with IEEE
Standard l00-1977,Dictionwy of Elec­trical and Electronic Terms, 2nd ed.;
however, some dif­ferences exist. For instance, IEEE Std 100-1977 defines
a surge as a "transient wave of current, potential or power in the
electric circuit"\--a definition broader than that used here. Transient
overvoltage is defined as "the peak voltage during the transient
condition resulting from the operation of a switching device"\--a
definition more restricted than that of the present guideline.

**[2. Amplitudes of Strikes, Worst Case]{.underline}**

The surge voltages described in this guideline include lightning effects
on power systems, mostly strikes in the vicinity of a power line, or at
a remote point of the power system. The literature describes the
frequency of occur­rence vs amplitude of lightning strikes, from the low
levels of a few kiloamperes, through the median values of about 20 kA,
to the exceptional values in excess of 100 kA. Clearly, a secondary
arrester rated for 10 kA can protect adequately in case of a mild direct
strike, or of a more severe strike divided among several paths to
ground. However, a very high and direct strike will exceed the
capability of an ANSI-rated secondary arrester.

> References:
>
> Cianos, N. and E.T.Pierce, A Ground-Lightning Environ­ment for
> Engineering Usage, Stanford Research Institute, Menlo Park, CA 94205,
> August 1972.
>
> Bodle, D.W., A.J. Ghazi, M. Syed, and R.L. Woodside, Char­acterization
> of the Electrical Environment, Toronto and Buffalo, N.Y.: University
> of Toronto Press, 1976.
>
> Martzloff, F.D. and G.J. Hahn, "Surge Voltage in Residen­tial and
> Industrial Power Circuits," IEEE PAS-89, 6, July/August 1970,
> 1049-1056.

**3. Level vs Rate of Occurrence**

The relationship between the level and the rate of occurrence of surges
is partly caused by the attenuation of the surges as they propagate away
from the source of the surge and divide among paths beyond branching
points. Equipment at a given point will be subjected to a relatively
small number of high-level surges from nearby sources, but to a larger
number of surges from more remote sources.

**4. Timing of Surges with Respect to Power Frequency**

Lightning surges are completely random in their timing with respect to
the power frequency. Switching surges are likely to occur near or after
current zero, but variable load power factors will produce a
quasi-random distribution. Some semiconductors, as shown in Ap­pendix II,
exhibit failure levels that depend on the timing of the surge with
respect to the conduction of power frequency current. Gaps or other
devices involving a power-follow current may withstand this power follow
with success, depending upon the fraction of the halt-cycle remaining
after the surge before current zero. Therefore, it is important to
consider the timing of the surge with respect to the power frequency. In
performing tests, either complete randomization of the timing or
controlled timing should be specified, with a sufficient number of
timing conditions to reveal the most critical timing.

**[5. Oscillatory Surges During Lightning]{.underline}**

The "classical lightning surge" has been established as 1.2 x 50 μs for
a voltage wave and 8 x 20 μs for a current wave. Evidence has been
collected, however, to show that oscillations can also occur. Lenz
reports 50 lightning surges recorded in two locations, the highest at
5.6 kV, with frequencies ranging from 100 to 500 kHz. Martzloff reports
oscillatory lightning surges in a house during a multiple-stroke flash.

> References:
>
> Lenz, J.E., "Basic Impulse Insulation Levels of Mercury Lamp Ballast
> for Outdoor Applications," Illuminating Eng., February 1964.
>
> Martzloff, F.D. and G.J. Hahn, "Surge Voltage in Resi­dential and
> Industrial Power Circuit," IEEE PAS-89, 6, July/August 1970.

**[6. Surge Impedance and Source Impedance]{.underline}**

To prevent misunderstanding, a distinction between source impedance and
surge impedance needs to be made. Surge impedance, also called
characteristic impedance, is a concept relating the parameters of a long
line to the propagation of traveling waves. For the wiring practices of
the ac power circuits discussed here, this characteristic impedance
would be in the range of 150 to 300 Ω, but because the durations of the
waves being discussed (50 to 20 μs) are much longer than the travel
times in the wiring systems being considered, traveling wave analyses
are not useful here.

Source impedance, defined as "the impedance presented by a source of
energy to the input terminals of a device, or network" (IEEE Standard
100), is a more useful concept here.

**[7. Power System Source Impedance]{.underline}**

The measurements from which Figure 1 was derived were of voltage only.
Little was known about the impedance of the circuits upon which the
measurements were made. Since then, measurements have been reported on
the impedance of power systems. Bull reports that the impedance of a
power system, seen from the outlets, exhibits the characteristics of a
50 Ω resistor with 50 μH in parallel. Attempts were made to combine the
observed 6 kV open-circuit voltage with the assumption of a 50 Ω/50 μH
impedance. This combination resulted in low energy deposition
capability, which was contradicted by field experience of suppressor
performance. The problem led to the proposed definition of oscillatory
waves as well as high-energy unidirectional waves, in order to provide
both the effects of an oscillatory wave and the high-energy deposition
capability.

> Reference:
>
> Bull, J.H., "Impedance of the Supply Mains at Radio Frequencies,"
> Proceedings of 1st Symposium on EMC, 75CH1012-4 Mont., Montreux, May
> 1975.

**[8. Installation Categories]{.underline}**

Subcommittee 28A of the International Electrotech­nical Commission has
prepared a report, referenced below, in which installation categories
are defined. These installation categories divide the power systems
according to the location in the building, in a manner similar to the
location categories defined in this guideline. However, there are some
significant differences between the two concepts. First, the IEC
categories are defined for a "Controlled Voltage Situation," a phrase
that implies the presence of some surge suppression device or surge
attenuation mechanism to reduce the voltage levels from one category to
the next. Second, the IEC report is more concerned with insulation
coordination than with the application of surge protective devices;
therefore it does not address the question of the coordination of the
protectors, but rather the coordination of insulation levels - that is,
voltages. Source impedances, in contrast to this guideline, have not
been defined. Further discussion and work toward the application
guidelines of both documents should eventually produce a consistent set
of recommenda­tions.

> Reference:
>
> Insulation Coordination Within Low-Voltage Systems In­cluding
> Clearances and Creepage Distances for Equipment. International
> Electrotechnical Commission, Report 5C28A (Central Office) 5, to be
> published in 1979.

**9. Open-Circuit Voltages and Wiring Flashover**

Surges propagate with very little attenuation in a power system with no
substantial connected loads. Measurements made in an actual residential
system as well as in a laboratory simulation have shown that the most
significant limitation is produced by wiring flashover, not be
attenuation along the wires. Ironically, a carefully insulated
installation is likely to experience higher surge voltages than an
installation where wiring flashover occurs at low levels. Therefore, the
open-circuit voltage specified at the origin of a power system must be
assumed to propagate unattenuated far into the system, which is the
reason for maintaining the 6 kV surge specification when going from the
"B" location to the "C" location.

**REFERENCES:**

Martzloff, F.D. and K.E. Crouch "Coordination de la protection contre
les surtensions dans les réseaux basse tension résidentiels,"
Proceedings, 1978 IEEE Canadian Conference on Communications and Power,
78CH1373-O.

Martzloff, F.D. Surge Voltage Suppression in Residential Power Circuits,
Report 76CRD092, Corporate Research and Development, General Electric
Company, Schenectady, N.Y., 1976.

**THE DEVELOPMENT OF A GUIDELINE ON**

**SURGE VOLTAGES IN LOW-VOLTAGE AC POWER CIRCUITS**

F.D. Martzloff, Member, IEEE

General Electric Company

Schenectady, N.Y. 12345

**Abstract** - Surge voltages in ac power circuits become more
significant with the increased application of miniaturized electronics
in consumer and industrial products. A Working Group of IEEE is
preparing a Guideline describing the nature of these surges in ac power
circuits up to 600 V. The paper describes the data base and approach
used by the Working Group and the recommendations proposed to represent
typical surges, in order to obtain feedback before the final writing of
the Guideline. Two waveforms are proposed, one oscillatory, the other
unidirectional, depending on the location within the power system.
Recommendations for source impedance or short-circuit current are also
included.

**INTRODUCTION**

Surge voltages occurring in ac power circuits can be the cause of
misoperation or product failure for residential as well as industrial
systems. The problem has received increased attention in recent years
because miniaturized solid-state devices are more sensitive to voltage
surges (spikes and transients) than were their predecessors.

Although surge voltage amplitudes and their frequency of occurrence on
unprotected circuits are well known, their waveshapes and energy content
are less well known. On the basis of measure­ments, statistics, and
theoretical considerations, a practical guideline for outlining the
environment for use in predicting extreme wave-shapes and energy content
can nevertheless be established. A Working Group of the Surge Protective
Devices Committee is currently developing such a guideline; this paper
reports the status of the Guideline, presents the considerations which
led to the approach chosen, and provides a possible vehicle for
discussion before the final writing and publication of the Guideline.

**SCOPE**

The Guideline primarily addresses ac power circuits with rated voltages
up to 600 V, although some of the conclusions offered could apply to
higher voltages and also to some dc power systems. Other standards have
been established, such as IEEE 472, Guide for Surge Withstand Capability
(SWC) Tests, intended for the special case of high-voltage substation
environments, and IEEE 28, Standard for Surge Arresters for ac Power
Circuits, covering primarily the utilities en­vironment. The Guideline
intends to complement, not conflict with, existing standards.

The surge voltages considered in the Guideline are those exceeding two
per unit (or twice the peak operating voltage) and having durations
ranging from a fraction of a microsecond to a millisecond. Overvoltages
of less than two per unit are not covered, nor are transients of longer
duration resulting from power equipment operation and failure modes.
Because these low-amplitude and long-duration surges are generally not
amenable to suppression by conven­tional surge protective devices, they
require different protection techniques.

Definitions of terms used in the Guideline are consistent with IEEE
Standard 100-1977, Dictionary of Electrical and Electronic Terms, 2nd
ed.; however, some differences exist. For instance, IEEE Std 100-1977
defines a surge as a "transient wave of current, potential or power in
the electric circuit --- a definition broader than that used here.
Transient overvoltage is defined as "the peak voltage during the
transient condition resulting from the operation of a switching
device---a definition more restricted than that of the Guideline.

While the major purpose of the Guideline is to describe the en­vironment,
a secondary purpose is to lead toward standard tests, through an
application guide that will be prepared in the future. These standard
tests will provide a realistic evaluation of the surge withstand
capability of equipment connected to these power circuits. Of necessity,
the complex real situation must be simplified to produce a manageable
set of standards. One must recognize the unavoidably arbitrary character
of any standard and be prepared to accept an imperfect approach which
can simplify matters, rather than demand a perfect but unattainable
match between the actual situation and the standard.

**THE ORIGIN OF SURGE VOLTAGES**

Surge voltages occurring in low-voltage ac power circuits originate from
two major sources: load switching transients and direct or indirect
lightning effects on the power system. Load switching transients can be
further divided into transients associated with (1) major power system
switching disturbances, such as capacitor bank switching; (2) minor
switching near the point of interest, such as an appliance turnoff in a
household or the turnoff of other loads in an individual system; (3)
resonating circuits associated with switching devices, such as
thyristors; and (4) various system faults, such as short circuits and
arcing faults. Measurements and calculations of lightning effects have
been made to yield data on what levels can be produced, even if the
exact mechanism of any particular surge is unknown. The major mechanisms
by which lightning produces surge voltages are the following:

\(a\) A direct lightning strike to a primary circuit injects high
currents into the primary circuit, producing voltages by either flowing
through ground resistance or flowing through the surge impedance of the
primary conductors.

\(b\) A lightning strike that misses the line but hits a nearby object
sets up electromagnetic fields which can induce voltages on the
conductors of the primary circuit.

\(c\) The rapid collapse of voltage that occurs when a primary arrester
operates to limit the primary voltage couples effectively through the
capacitance of the transformer and produces surge voltages in addition
to those coupled into the secondary circuit by normal transformer
action.

\(d\) Lightning strikes the secondary circuits directly. Very high
currents can be involved, exceeding the capability of conventional
devices.

\(e\) Lightning ground current flow resulting from nearby
direct-to-ground discharges couples onto the common ground impedance
paths of the grounding network.

Fast-acting protection devices, such as current-limiting fuses and
circuit breakers capable of clearing or beginning to part contacts in
less than 2 ms, leave trapped inductive energy in the circuit upstream;
upon collapse of the field, very high voltages are generated.

Transient overvoltages associated with the switching of power factor
correction capacitors \[1\] have lower frequencies than the
high-frequency spikes with which this document is concerned. Their
levels, at least in the case of restrike-free switching operations, are
generally less than twice normal voltage and therefore are not of
substantial concern here, but should not be overlooked.

On the other hand, switching operations involving restrikes, such as
those produced by air contactors or mercury switches, can produce,
through escalation, surge voltages of complex waveshapes and of
amplitudes several times greater than the normal system voltage. The
severest case is generally found on the load side of the switch and
involves only the device that is being switched. While this situation
should certainly not be ignored, in such a case the prime responsibility
for protection rests with the local user of the device in question.
However, switching transients can also appear on the line side across
devices connected to the line. The presence and source of transients may
be unknown to the users of those devices. This potentially harmful
situation occurs often enough to command attention.

While the data have been recorded primarily on 120, 220/380, or 277/480
V systems, the general conclusions should be valid for 600 V systems. To
the extent that surge voltages are produced by a discrete amount of
energy being dumped into a power system, low-impedance, heavy industrial
systems can be expected to experience lower peaks from surge voltages
than 120 V residential systems, but comparable, or greater, amounts of
energy potentially available for deposition in a surge suppressor.

### **OCCURRENCE AND VOLTAGE LEVELS IN UNPROTECTED CIRCUITS**

**Rate of Occurrence Versus Voltage Level**

The rate of occurrence of surges varies over wide limits, depending on
the particular system. Prediction of the rate for a particular system is
always difficult and frequently impossible. Rate is related to the level
of the surges; low-level surges are more prevalent than high-level
surges. The relationship between the level and the rate of occurrence of
surges is partly caused by the attenuation of the surges as they
propagate away from the source of the surge and divide among paths
beyond branching points. Equipment at a given point will be subjected to
a relatively small number of high-level surges from nearby sources, but
to a larger number of surges from more remote sources.

Data collected from many sources have led to the plot shown in Fig. 1.
This prediction shows with certainty only a relative frequency of
occurrence, while the absolute number of occurrences can be described
only for an average location. The 'high exposure" and "low exposure"
limits of the band are shown as a guide, not as absolute limits, to
reflect both the location exposure (lightning activity in the area and
the nature of the system) and the exposure to switching surges created
by other loads.

The literature describes the frequency of occurrence vs amplitude of
lightning strikes, from the low levels of a few kiloamperes, through the
median values of about 20 kA, to the exceptional values in excess of 100
kA \[2\]. Clearly, a secondary arrester rated for 10 kA can protect
adequately in case of a mild direct strike, or of a more severe strike
divided among several paths to ground. However, a very high and direct
strike will exceed the capability of an ANSI-rated secondary arrester
\[3\].

The voltage and current amplitudes presented in the Guideline attempt to
provide for the vast majority of lightning strikes but should not be
considered as "worst case," since this concept cannot be determined
realistically. One should think in terms of the statistical distribution
of strikes, accepting a reasonable upper limit for most cases. Where the
consequences of a failure are not catastrophic but merely represent an
annoying economic loss, it is appropriate to make a trade-off of the
cost of protection against the likelihood of a failure caused by a high
but rare surge. For instance, a manufacturer may be concerned with
nation-wide failure rates, those at the upper limits of the distribution
curve, while the user of a specific system may be concerned with a
single failure occurring at a specific location under "worst-case
conditions." Rates can be estimated f or average systems, however, and
even if imprecise, they provide manufacturers and users with guidance.
Of equal importance is the observation that surges in the range of 1 to
2 kV are fairly common in residential circuits.

From the relative values of Fig. 1, two typical levels can be cited for
practical applications. First, the expectation of a 3 kV transient
occurrence on a 120 V circuit ranges from 0.01 to 1 per year at a given
location - a number sufficiently high to justify the recommendation of a
minimum 3 kV withstand capability. Second, the wiring flashover limits
indicate that a 6 kV withstand capability may be sufficient to ensure
device survival indoors, but a 10 kV withstand capability may be
required outdoors.

Fig. 1. Rate of surge occurrence vs voltage level.

**Timing of Occurrence**

Surges occur at random times with respect to the power frequency, and
the failure mode of equipment may be affected by the power frequency
follow current or by the timing. Consequently, surge testing must be
done with the ac voltage applied to the test piece.

Lightning surges are completely random in their timing with respect to
the power frequency. Switching surges are likely to occur near or after
current zero, but variable load power factors will produce a
quasi-random distribution. Some semiconductors, as shown in Appendix II,
exhibit failure levels that depend on the timing of the surge with
respect to the conduction of power frequency current. Gaps or other
devices involving a power-follow current may withstand this power follow
with success, depending upon the fraction of the half-cycle remaining
after the surge before current zero. Therefore, it is important to
consider the timing of the surge with respect to the power frequency. In
performing tests, either complete randomization of the timing or
controlled timing should be specified, with a sufficient number of
timing conditions to reveal the most critical timing.

**WAVESHAPE OF REPRESENTATIVE SURGE VOLTAGES**

**Waveshapes in Actual Occurrences**

***Indoor*** - Measurements in the field, measurements in the
laboratory, and theoretical calculations indicate that most surge
voltages in indoor low-voltage systems have oscillatory waveshapes,
unlike the well-known and generally accepted unidirectional waves
specified in high-voltage insulation standards. A surge impinging on the
system excites the natural resonant frequencies of the conductor system.
As a result, not only are the surges typically oscillatory, but surges
may have different amplitudes and waveshapes at different places in the
system. These oscillatory frequencies of surges range from 5 kHz to more
than 500 kHz. A 30 to 100 kHz frequency is a realistic measure of a
"typical" surge for most residential and light industrial ac line
networks.

***Outdoor*** - Surges encountered in outdoor locations have also been
recorded, some being oscillatory, others being unidirectional. The
"classical lightning surge" has been established as 1.2 x 50 μs for a
voltage wave and 8 x 20 μs for a current wave. Evidence has been
collected, however, to show that oscillations can also occur. Lenz \[4\]
reports 50 lightning surges recorded in two locations, the highest at
5.6 kV, with frequencies ranging from 100 to 500 kHz. Martzloff \[5\]
reports oscillatory lightning surges in a house during a multiple-stroke
flash.

Because the overriding concern here is the energy associated with these
surges, a conservative but realistic description of the surges can be
derived from the long-established specified duty of a secondary
arrester, as detailed below. While this specification is arbitrary, it
has the strength of experience and successful usage.

###### Selection of Representative Waveshapes

The definition of a waveshape to be used as representative of the
environment is important for the design of candidate protective devices,
since unrealistic requirements, such as excessive duration of the
voltage or very low source impedance, place a high energy require­ment on
the suppressor, with a resulting cost penalty to the end user. The two
requirements defined below reflect this trade-off.

***Indoor*** - Based on measurements conducted by several independent
organizations in 120 and 240 V systems (Appendix I), the waveshape shown
in Fig. 2 is reasonably representative of surge voltages in these power
circuits. Under the proposed description of a "0.5 μs - 100 kHz ring
wave," this waveshape rises in 0.5 μs, then decays while oscillating at
100 kHz, each peak being about 60% of the preceding peak.

> Fig. 2. The proposed 0.5 μs - 100 kHz ring wave (open-circuit
> voltage).

The fast rise can produce the effects associated with nonlinear voltage
distribution in windings and the dv/dt effects on semiconduc­tors.
Shorter rise times are found in many transients, but, as those
transients propagate into the wiring or are reflected from
discontinuities in the wiring, the rise time becomes longer.

The oscillating and decaying tail produces the effects of voltage
polarity reversals in surge suppressors or other devices that may be
sensitive to polarity changes. Some semiconductors are particularly
sensitive to damage when being forced into or out of a conducting state,
or when the transient is applied during a particular portion of the 60
Hz supply cycle (Appendix II). The response of a surge suppressor can
also be affected by reversals in the polarity, as in the case of RC
attenuation before a rectifier circuit in a dc power supply. The pulse
withstand capability of many semiconductors tends to improve if the
surge duration is much shorter than one microsecond. For this reason,
the first half-cycle of the test wave must have a sufficient duration.

***Outdoor*** - In the outdoor and service entrance environment, as well
as in locations close to the service entrance, substantial energy, or
current, is still available. For these locations, the unidirectional
impulses long established for secondary arresters are more appropriate
than the oscillatory wave.

Accordingly, the recommended waveshape is 1.2 x 30 μs for open-circuit
voltages and 8 x 20 μs for short-circuit current (impulse discharge
current) or current in a low-impedance device. The numbers used to
describe the impulse, 1.2 x 50 and 8 x 20, are as defined in IEEE
Standard 28 - ANSI Standard C62.l; Fig. 3 presents the wave-shape and a
graphic description of the numbers.

Fig. 3. Waveshapes for outdoor locations.

**ENERGY AND SOURCE IMPEDANCE**

**General**

The energy involved in the interaction of a power system with a surge
source and a surge suppressor will divide between the source and the
suppressor in accordance with the characteristics of the two impedances.
In a gap-type suppressor, the low impedance of the arc after sparkover
forces most of the energy to be dissipated elsewhere: for instance, in a
resistor added in series with the gap for limiting the power-follow
current. In an energy-absorber -suppressor, by its very nature, a
substantial share of the surge energy is dissipated in the suppressor,
but its clamping action does not involve the power-follow energy
resulting from the short-circuit action of a gap. It is therefore
essential to the effective use of suppression devices that a realistic
assumption be made about the source impedance of the surge whose effects
are to be duplicated.

The voltage wave shown in Fig. 2 is intended to represent the waveshape
a surge source would produce across an open circuit. The waveshape will
be different when the source is connected to a load having a lower
impedance, and the degree to which it is lower is a function of the
impedance of the source.

To prevent misunderstanding, a distinction between source im­pedance and
surge impedance needs to be made. Surge impedance, also called
characteristic impedance, is a concept relating the param­eters of a long
line to the propagation of traveling waves. For the wiring practices of
the ac power circuits discussed here, this characteristic impedance
would be in the range of 150 to 300 Ω, but because the durations of the
waves being discussed (50 to 20 μs) are much longer than the travel
times in the wiring systems being considered, traveling wave analyses
are not useful here.

Source impedance, defined as the impedance presented by a source of
energy to the input terminals of a device, or network" (IEEE Standard
100), is a more useful concept here. In the conventional Thevenin's
description, the open-circuit voltage (at the terminals of the network
or test generator) and the source impedance (of the surge source or test
generator) are sufficient to calculate the short-circuit current, as
well as any current for a specified suppressor impedance.

The measurements from which Fig. 1 was derived were of voltage only.
Little was known about the impedance of the circuits upon which the
measurements were made. Since then, measurements have been reported on
the impedance of power systems. Bull \[6\] reports that the impedance of
a power system, seen from the outlets, exhibits the characteristics of a
50 Ω resistor with 50 μH in parallel. Attempts were made to combine the
observed 6 kV open-circuit voltage with the assumption of a 50Ω/50 μH
impedance \[7\]. This combination resulted in low energy deposition
capability, which was contradicted by field experience of suppressor
performance. The problem led to the proposed definition of oscillatory
waves as well as high-energy unidirectional waves, in order to provide
both the effects of an oscillatory wave and the high-energy deposition
capability.

The degree to which source impedance is important depends largely on the
type of surge suppressors that are used. The surge suppressors must be
able to withstand the current passed through them by the surge source. A
test generator of too high an impedance may not subject the device under
test to sufficient stresses, while a generator of too low an impedance
may subject protective devices to unrealistically severe stresses. A
test voltage wave specified without reference to source impedance could
imply zero source impedance -one capable of producing that voltage
across any impedance, even a short circuit. That would imply an infinite
surge current, clearly an unrealistic situation.

Because of the wide range of possible source impedances and the
difficulty of selecting a specific value, three broad categories of
building locations are proposed to represent the vast majority of
locations, from those near the service entrance to those remote from It.
The source impedance of the surge increases from the outside to
locations well within the building. Open-circuit voltages, on the other
hand, show little variation within a building because the wiring
provides little attenuation. Figure 4 illustrates the application of the
three categories to the wiring of a building.

Fig. 4. Location categories.

Subcommittee 28A of the International Electrotechnical Com­mission has
prepared a Report \[8\], in which installation categories are defined.
These installation categories divide the power systems according to the
location in the building, in a manner similar to the location categories
defined in the Guideline. However, there are some significant
differences between the two concepts. First, the IEC categories are
defined for a "controlled voltage situation," a phrase that implies the
presence of some surge suppression device or surge attenuation mechanism
to reduce the voltage levels from one category to the next. Second, the
IEC report is more concerned with insulation coordination than with the
application of surge protective devices; therefore it does not address
the question of the coordination of the protectors but, rather, the
coordination of insulation levels --- that is, voltages.

Surges propagate with very little attenuation in a power system with no
substantial connected loads. Measurements made in an actual residential
system as well as in a laboratory simulation have shown that the most
significant limitation is produced by wiring flashover, not by
attenuation along the wires. Ironically, a carefully insulated
installation is likely to experience higher surge voltages than an
installation where wiring flashover occurs at low levels. Therefore, the
open-circuit voltage specified at the origin of a power system must be
assumed to propagate unattenuated far into the system, which is the
reason for maintaining the 6 kV surge specification when going from one
category to an adjacent category farther into the building.

Furthermore, source impedances are not defined in the lEC report. The
Guideline attempts to fill this need by specifying several levels of
source impedance, or of short-circuit current, for the various
categories.

# PROPOSED REPRESENTATION OF THE ENVIRONMENT

On the basis of the preceding discussions, the Guideline proposes to
reduce the infinite variety of actual conditions to three categories,
from the outside service drops to the long branch circuits and outlets.

For each category the most appropriate waveshape is indicated, an
open-circuit voltage for high-impedance loads, or a short-circuit
current for low-impedance loads. The tabulation that follows shows
open-circuit voltages and short-circuit currents for each of the three
categories. The energy deposited in a 500 V suppressor has been computed
and is shown for each of the categories.

The values shown in the table represent the maximum range, corresponding
to the "High Exposure" situation of Fig. 1. For less exposed systems, or
when the prospect of a failure is not highly objectionable, one could
specify lower values of open-circuit voltages with corresponding
reductions in the currents. IEC Category I, not represented in the
Guideline, would correspond to line cord-connected devices in this
context.

# CONCLUSIONS

The broad range of surge voltages occurring in low-voltage ac power
circuits can be simulated by a limited set of test waves, for the
purpose of evaluating their effects on equipment.

Field measurements, laboratory experiments, and calculations indicate
that two basic waves, at various open-circuit voltages and short-circuit
current values, can represent the majority of surges occurring in
residential, commercial, and light industrial power systems rated up to
600 V rms.

Exceptions will be found to the simplification of a broad guide­line;
however, these should not detract from the benefits that can be expected
from a reasonably valid uniformity in defining the environment. Other
test waves of different shapes may be appropriate for other purposes,
and the present guideline should not be imposed where it is not
applicable.

The Working Group is approaching the final phases of prepara­tion of the
Guideline document; comments are solicited from the engineering and user
communities. However, readers must recognize the unavoidably arbitrary
character of any standard and be prepared to accept an imperfect
approach, which can simplify matters and clarify the issues as well as
provide uniform evaluations of performances, rather than demand a
perfect but unattainable match between the actual situation and the
standard.

### 

### **ACKNOWLEDGMENTS**

The concepts presented in this paper have greatly benefited from the
informed questions and discussions by members of the Working Group on
Surge Voltage in AC Power Circuits Rated 600 V or Less, and from
interested reviewers; particular appreciation for effective critiques
from Catharine Fisher and Peter Richman is acknowledged. The data base
presented in Appendix I has been broadened by the contributions of the
Bell Telephone Laboratories and Landis & Gyr, Inc.

# REFERENCES

1\. "Switching Surges Due to De-Energization of Capacitive Circuits,"
AIEE Committee Report, AIEE Transactions, August 1 1957, pp. 562-564.

2\. Cianos, N. and E.T. Pierce, A Ground-Lightning Environment for
Engineering Usage, Stanford Research Institute, Menlo Park, CA 94205,
August 1972.

3\. Surge Arresters for Alternating-Current Power Circuits, IEEE
Standard 28-1974; ANSI Standard C62.1-1975; lEC Stan­dard 99-2.

4\. Lenz, J.E., "Basic Impulse Insulation Levels of Mercury Lamp Ballast
for Outdoor Applications," Illuminating Engrg., February 1964, pp.
133-140.

5\. Martzloff, F.D. and G.J. Hahn, "Surge Voltage in Residential and
Industrial Power Circuits," IEEE PAS-89, 6, July/August 1970, 1049-1056.

6\. Bull, J.H., "Impedance on the Supply Mains at Radio Frequen­cies,"
Proceedings of 1st Symposium on EMC, 75CH1012-4, Montreux, May 1975.

7\. Martzloff, F.D. and F.A. Fisher, "Transient Control Level Philosophy
and Implementation: The Reasoning Behind the Philosophy," Proceedings
2nd Symposium on EMC, 77CH1 224-5 EMC, Montreux, June 1977.

8\. Insulation Coordination Within Low-Voltage Systems Including
Clearances and Creepage Distances for Equipment, Internation­al
Electrotechnical Commission Report SC28A (Central Office) 5, to be
published in 1979.

# APPENDIX -- DATA BASE

*\[This format does not support the many oscillograms and tables of the
Appendix. See the pdf* *file\]*

A CONSENSUS ON POWERING AND GROUNDING

> **SENSITIVE ELECTRONIC EQUIPMENT**

Thomas S. Key, Member IEEE

Sandia National Laboratories

Albuquerque, NM 87185

François D. Martzloff, Fellow IEEE

National Bureau of Standards

Gaithersburg, MD 20899

**Abstract**---As sensitive electronic processing systems proliferate in
our facilities so do power-related problems. Efforts to alleviate these
problems have ranged from installing expensive power conditioning
equipment to applying special grounding techniques not found in
conventional safe grounding practice. Understanding of what is actually
going on has been lacking. We find power systems, modified from basic
practice to the extent of being unsafe, that continue to be plagued with
powering- and grounding-related problems. Out of this chaos we are
persuaded to study and understand the complexities of the problem and to
begin developing good practices. This is the objective of the IEEE
Working Group on Powering and Grounding Sensitive Electronic Equipment,
Standards Project P1100. We will introduce Project P1100, preview its
scope and technical content and, most importantly, invite participation
in this seriously needed consensus standard activity.

**INTRODUCTION**

Powering and grounding sensitive electronic equipment is a growing
concern for commercial and industrial power system designers. This
concern frequently materializes after start-up when electronic system
operating problems begin to occur. Grasping for power conditioning
equipment or magic grounding methods is a common response. In some cases
this has led to unsafe practices and violations of the National
Electrical Code without solving operating problems. Although good
information is available, there is presently no consensus on recommended
practice. This leaves responsible engineers to proceed from what they
already know or can readily obtain in the literature. Unfortunately,
there is conflicting information in the literature and, for most of us,
the technical particulars are somewhat foreign to our power system
design experience.

The concept of load and source compatibility is not new. The need to
provide power with a steady voltage and frequency has been recognized
since the inception of the electric utility industry. However, the
definition of \'steady\' has changed over the years, the greater
susceptibility of increasingly sophisticated electronic equipment to the
departure from 'steady' conditions. Some of the early concerns were
flicker of light bulbs due to voltage variations and overheating of
electomagnetic loads or interference of communication loads due to
voltage waveform distortion. Recognition of these problems led to the
development of voluntary standards which contributed significantly to
reducing occurrences.

More recently, transient voltage disturbances associated with short
circuits, lightning, and power system switching have emerged as a major
concern to manufacturers and users of electronic equipment. Today\'s
complaints about the quality of power are not easily resolved because
they involve both a multitude of different causes and a variety of
specific sensitivities in the affected equipment. Power system
designers, utility companies, load as well as source equipment
manufacturers, must cooperate with each other to find effective
solutions. As in the past, voluntary consensus standards are needed.

The issue of grounding, in particular how to deal with noise and safety
simultaneously, is complicated by philosophies advocated by people of
different backgrounds. Power-oriented engineers often differ in their
perception of common problems and solutions. One of the goals of the
proposed standard is to promote better understanding of the real issues
and to dispel some misconceptions on how to avoid or correct electronic
system grounding problems.

Since the earliest days of electric power, users have counted on
utilities to provide electricity that is as free as possible from
outages, voltage surges, and harmonic waveshape distortions. Reducing
such power line has always been a critical concern for utilities.
Recently, however, new sources of disturbances have begun to
proliferate, just as many pieces of equipment are becoming more
sensitive to these same power disturbances. Some of these disturbances
are generated by adjacent equipment, so that the supply should not be
blamed for the occurrence. These developments have presented utilities
and users with a new set of complex power quality issues that will
require wide-reaching cooperative efforts to be resolved.

A common practice applicable to power incompatibilities is to install
interface equipment between the raw utility power and sensitive loads.
Difficulties in assessing this need are: (1) the quantification of just
how much downtime is power-related, (2) the subjective nature of
estimating the cost of sensitive operation attributable to power. The
cost/ benefit aspects of the problem can be addressed from the technical
point of view in a standard, but detailed economic analysis and specific
decisions remain the prerogative of the user allocating the resources.
Focusing on the technical issues, dispelling misconceptions, and
recommending practices can assist the user in making an informed
economic decision.

With that goal clearly defined, the new IEEE Working Group, Project
P1100, was formed to develop a consensus standard that recommends
practices for powering and grounding sensitive electronic loads in
commercial and industrial power systems. The document is currently at
the first draft stage.

## POWERING ELECTRONIC SYSTEMS

Powering an electronic system is fundamentally the same as powering any
electrical system. Estimating the load, matching current and voltage
requirements, or planning for future growth involves the same basic
information. Similarly, designing an appropriate
[ele]{.underline}ctrical distribution system, selecting and coordinating
overcurrent protection, and assuring good voltage regulation makes use
of the same engineering practices. Even the principles of availability
and reliability can be applied to electronic loads in the same way as to
any other load.

An excellent reference library available for designing commercial and
industrial power systems of all types is the [IEEE Color
Book]{.underline} series. There are currently nine Color Books in the
Series providing recommended practices. The objective is to assist in
the design of safe, reliable, and economical electric power systems by
providing the consensus of knowledge and experience of the contributing
IEEE members. Project P1100 is intended to yield a new Color Book in the
series, directed specifically at powering and grounding sensitive
electronic equipment.

**The Duration of a Disturbance Is Key to Its Impact,**

Computers are just like motors or lights: when the power goes away, the
device quits, and when power is restored, it restarts. Of course, it is
frequently integrity of the process rather than the actual device that
we must concern ourselves with. If we lose power to one high speed
conveyor being fed by another high speed conveyor, we can expect a mess
somewhere on the factory floor. Likewise, a central processor
controlling a check printer with a stack of sequenced commands in
volatile memory will most likely be upset by the loss of power
continuity.

The duration of loss of power continuity is the key factor in predicting
if a process disruption will occur. A large freezer may be able to ride
through an outage of several hours before cooling loss. We are allowed
seconds to restore light in a hospital operating room. Data processing
upset may occur in tens of milliseconds, or in cycles of 60 Hz. ac
power. An outage is therefore defined differently by different users and
producers of electric power, sometimes\' creating an obstacle to
communication between these interested parties. Utility companies and
their power supply contracts will normally only address outages measured
in minutes. They do not consider perturbations lasting a few seconds or
less as the utilities responsibility. When customer equipment is more
critical or more sensitive than the norm, they consider it the
customer's problem. The special power quality and continuity
requirements of a number of commercial and industrial loads are
described in the [IEEE Orange Book]{.underline} \[1\].

Data processing equipment susceptibility to short duration (cycle to
cycle) breaks in power continuity not be overgeneralized. First, a
computer can ride through a short outage. It happens every cycle of the
ac power sine wave. Second computers should be no more sensitive to
steady-state voltage variations than any other load. American National
Standard C84.1 establishes steady-state voltage ranges that apply to all
equipment. Furthermore, harmonic distortion in the utility voltage has
not been shown to have any more impact on electronic loads than on
motors or relays. We conclude that if electronic loads have
susceptibilities to power-line disturbances, they also have tolerances
that may reduce the cost and effort required to protect them.

A profile of data processing equipment susceptibility (and tolerance) to
variations in the source voltage, Figure 1, has been published in an
IEEE \'Recommended Practice' \[1\], and a NBS \"Guideline\" \[2\].
Presented as a \"Typical design objective of power-conscious computer
hardware designers\", it is not a computer industry standard. However,
as a typical susceptibility profile, it does demonstrate the useful
feature of increasing equipment tolerance with decreasing duration of
voltage perturbation. As a practical matter, there are disturbances of
short than long duration. So, by comparing actual disturbance data to
this profile we begin to quantify our exposure to power-related
problems.

**Energy Analysis Is Useful In Diagnosing Power Problems**

We can interpret Figure 1 from an energy flow viewpoint on the right, we
have limitations related to the wrong energy level occurring in the
steady state. This limitation equates to a steady state voltage
regulation problem. For cycle to cycle time intervals, our concern
shifts to insufficient energy that occurs during an undervoltage
condition resulting from common overloads or short circuits. In
microsecond time domains, too much energy, in the form of a lightning or
switching event generated overvoltage, surfaces as a practical concern.

This analysis can facilitate defining power-related problems in a way
that leads to effective selection of power equipment or other
appropriate corrective action. The first step is powerline voltage
monitoring to determine site power quality. Once a site-specific power
quality profile has been established and energy-related problems
identified, one can proceed to single out appropriate power enhancement
measures. For example, if intermittent undervoltages or sags are
recorded, then interface equipment such as a motor-generator might be
effective in riding through these shortages of energy. Further
discussion of this method of diagnosis and prescription is found in
\[3).

The application of Figure 1 seems quite straight-forward; however,
solving a real-life power-related problem may not be. For one thing, the
tolerance to overvoltage of several hundred volts, indicated in Figure
1, assumes an assault at the input to the computer power supply. The
electronic equipment tolerance to overvoltages experienced in other
locations may be significantly less. Noise coupled into the electronic
system via many possible alternate paths, as compared to surges
conducted along the power line, can disrupt data at a 5-volt logic
level.

Related to the noise-coupling problem, is the attempt to apply Figure 1
in the presence of poor grounding or incorrect surge protecting of
equipment. These mistakes may allow internally generated power-related
problems that totally evade any power interface equipment installed, per
Figure 1, to protect the site from the outside world. At the same time,
such interface equipment will be adding cost and probably reducing
overall power system reliability.

A systems engineering approach is required to properly address all
aspects of the power- and noise-related, problems. In Project P1100, we
are attempting to present the best explanation possible of the myriad of
power enhancement products and at the same time maintain a systems
perspective- This perspective must include other critical elements of
the power system, i.e. grounding and surge protection details, and
installation procedures. We have found that grounding, discussed next,
is a key to noise-related problems.

## GROUNDING ELECTRONIC SYSTEMS

The subject of grounding is perhaps the most misunderstood, with the
result that a large portion of the problems encountered in power supply
applications originate from inappropriate grounding practices. An
indication of the complexity of this subject is the fact that it
occupies over five pages of the IEEE dictionary; no wonder
misconceptions still abound. The existence of this problem in electronic
systems can be explained by the different meanings attributed to the
term \'ground\' by the different specialists involved. Starting with the
60 Hz or power-frequency engineer, \'ground\' is synonymous with
\'earth\'; its function is to provide a low-impedance path for return of
power system fault currents to the generator. This low-impedance path
serves a safety role by limiting voltage differences during system
faults and by allowing sufficient fault currents to assure prompt
tripping of the source circuit breakers.

In this context, ground connections are generally large copper
conductors, offering low impedance to power-frequency current. Emphasis
is given to the resistance of the connection to earth\' -- that is, the
subjacent soil -- by appropriate dimensions and' number of driven rods
in the earth, of buried counter-poise conductors, etc. The safety
grounding system is passive and should not be called upon to carry rated
current except during intermittent anomalies of power system operation
such as short circuits. Occasionally, steady-state currents may be
present due to device leakage or to the nearby influence of strong
magnetic fields, for instance adjacent conductors of an arc furnace.
Nevertheless, the steady-state current in grounding conductors should be
relatively small when compared to phase conductor currents (NEC 250-21).

###### Both "Earthing" and "Referencing" Must Be Considered

Shifting now to the electronic engineer, designing his data processing
equipment, "ground" is synonymous to \'chassis\'. That is, the metal
enclosure of the equipment, sometimes symbolically concentrated into a
single shiny metal pad at the bottom of the cabinet to which all
connections to 'ground' are routed---and not always by the most direct
route. His data processing circuitry involves analog or pulse voltage
signals of generally less than 15 volts, or it involves current loops of
a few milliamperes.

These signals can be transferred in a balanced, ungrounded circuit or a
single-ended circuit with a common reference. Balanced circuits are
isolated from ground but their voltage with respect to ground (common
mode) is still significant to the operation and potential susceptibility
of the circuits. Single-ended circuits carry signals referred to a
common potential, most often that of the equipment internal chassis,
generally called 'reference'. Thus, in either case it appears that the
electronic engineer's concern is that his referencing system carries
signal currents that can become polluted by spurious ground currents
either through common connection points with the earthed system or by
common-mode noise coupling.

Now enters the systems engineer responsible for the installation of the
data processing system within one room of a building at best, or
distributed among several buildings at worst: to him, \'ground\' takes a
double meaning. The first is the concept of the power system engineer,
the second is the concept of the electronic engineer and, alas, they are
not the same. If only the first had been called \'earth\', and the
second called 'reference\', perhaps the designers would have coordinated
their two distinctive requirements ahead of time and much on-site misery
would have been avoided.

Instead, in the electronics engineer\'s case, the impedance of his
\'reference\' system includes a substantial inductive component because
of the high frequency of the signal and noise currents. The large
existing copper cables, suitable for earthing, are not suitable for
referencing. A new ground reference grid providing a large number of
different path links for the various noise frequencies will now have to
be incorporated into the system.

So we see, for electronic loads, we have both safety and noise to
concern ourselves with. Safe operation of an electrical or electronic
system depends on the integrity and low impedance of its
[earthing]{.underline}. Undisturbed operation of the same systems
depends on the geometry and intrinsic low impedance of its
[reference]{.underline}, regardless of the impedance between the
reference and the earth \[2\].

The significance of reference and insignificance of earth connection can
be illustrated by two examples: to prove its reality, consider that
sophisticated equipment aboard an electronic countermeasures airplane
are doing quite well, thank you, without an earth connection; back an
the ground we find an illusion held by the system operator, confronted
with interference and a referencing problem, when he contemplates and
sometimes implements \'better grounding\' by breaking up the concrete
floor of the computer room to install additional ground rods.

The solution to this operator\'s problem is not \'better grounding\',
but better referencing\--such as in the case, of the airborne electronic
system. On the ground level, the better referencing can be obtained by
establishing a \'ground grid\'. Here the major criterion is [low
impedance at high frequencies]{.underline} between any two points of the
ground grid. Recall that the safety ground system should provide low
impedance at low frequencies. In a computer room design, the 2\'x2\'
grid of a usual raised floor structure lends itself quite naturally to
providing such a good reference. There are or course a few electrical
design features that must be properly incorporated. References \[2\] and
\[4\] already provide guidance for implementing this solution, and
Project P1100 will extend the guidance to the status of a consensus
standard.

**Attempts at Noise or Surge Control Should Not Create Adverse Side
Effects.**

The first side effect is associated with the problem of circulating
currents in the ground and reference conductors. Without question, these
currents can inject parasitic signals into the data lines. This
injection is common-mode noise coupling caused by unavoidable shared
connection points between the power and the electronic equipment
chassis. The problem is real, the side effect is associated with how not
to solve it.

There have been a number of apparently successful remedies such as
sometimes obtained by opening up these 'ground loops\', by creating a
\'single point ground\', by establishing a 'dedicated/isolated ground\',
and finally, in the ultimate language contradiction, by installing a
\'floating ground\'. All of these concepts, motivated by steady-state,
low-level noise reduction theory, can and frequently do overlook the
potential of power frequency faults.

Attempts to decouple equipment chassis from earth ground for the purpose
of isolating and insulating often defeat the basic safety function of
earth ground. They ignore safety and hardware damage issues associated
with the relatively rare but potentially lethal situations occurring
during power system faults and lightning surges. They also violate the
National Electric Code as described in \[5\]; such practices should be
eradicated!

Continuity of the green wire or metallic raceway grounding system is not
incompatible with achieving effective noise, control. Simply apply the
principles of the ground reference grid discussed above and in \[2\].
Give careful attention to surge protection for both data and power lines
as presented below. Don\'t resort to tampering with safety aspects of
the grounding system to control noise. Finally, as a consulting
engineer, called upon to correct power- or noise-related problems,
beware of both the desire for and the existence of dangerous grounding
practices.

Another adverse side effect is associated with the configuration and use
of grounding conductors. It is the occurrence and conversion of what is
called 'common mode' and 'differential mode' in multi-conductor systems.
Initially defined in the context of communications circuitry, these two
modes have been applied to ac power systems that include phase, neutral,
and grounding conductors. Here a grounding conductor exists or is
implied by the presence of earthed bodies. As with 'referencing,' the
situation is confused by the blurring of boundaries between signal
processing technology and power delivery/system safety requirements.

Disturbances can occur in common mode but cures might be erroneously
proposed that address only differential mode disturbances, or vice
versa. Remedies to a differential mode surge can create a common-mode
disturbance. For instance, a frequently applied and very effective
method for common-mode noise elimination is the installation of an
isolation transformer. However, we should not expect this transformer to
reliably attenuate differential-mode noise \[6\]. Conversely, the
installation of a single protective device between the phase and neutral
conductors, at the end of a long branch circuit, will: (1) clamp the
voltage between these two conductors, and (2) create a large voltage,
akin to mode, between the neutral and grounding conductors.

The appropriate solution, discussed in detail in Reference \[7\] for the
case of a single-phase three-wire system, consists of providing an
additional surge-clamping device between the neutral and grounding
conductors. Project Pl100 will address the polyphase as well as the
single-phase situation.

With forethought, these side effects can be avoided. It is feasible to
design a system where noise problems are successfully resolved without
resorting to unsafe grounding practices. We have pointed out that a
reference grid system may be economically incorporated in a computer
room raised floor. Reference \[4\] describes how the reference grid
approach, when used with computer power centers (isolation transformers)
and surge suppression networks can successfully harmonize power and
signal grounding requirements. In Reference \[2\] detailed guidelines
are provided for computer room grounding. However, since these documents
do not constitute a consensus standard, one major goal of Project P1100
will be to establish a consensus opinion by describing good practices as
well as by citing erroneous practices that should be avoided.

###### SURGE PROTECTION

Power systems are exposed to external influences which can couple energy
into the circuits, causing a momentary overvoltage or overcurrent,
generally described by the term \'surge\'. Internal switching of loads
in these systems can also create these momentary events. Another
phenomenon, the discharge of electrostatic charges that have built-up on
the human body or objects, can also inject unwanted voltages or currents
into electronic circuits. Finally, another threat is related to nuclear
explosions effects, under the acronym of NEMP (Nuclear Electromagnetic
Pulse). The proposed standard will address the first two of these
surges, lightning- and switching-related surges.

Surges can have many effects on equipment, ranging from no detectable
effect to complete destruction. In general, electromechanical devices
withstand increasing voltage surges until breakdown occurs, while
electronic devices can have their operation up-set before hard failure
occurs. With increasing surge levels, progressively more intense upset
occurs, until breakdown takes place. If sensitive electronic data
processing equipment should be protect from even the upsetting levels,
it is axiomatic that damaging surges need to be dealt with before they
propagate beyond the service entry for the computer room \[7\] and
\[8\].

Definitions of the level beyond which transient over-voltages become a
threat depend on the type of victim equipment or process. Where
electromechanical devices can generally tolerate short duration voltages
of twice rating plus 1000 volts, few solid-state devices can tolerate
more than twice their normal rating. Furthermore, data processing can be
affected by fast changes with relatively small voltage amplitudes
compared to the hardware-damaging overvoltages.

**Lightning Surges Can Strike in More Ways Than One.**

Lightning surges on power systems occur in two modes: direct attachment
of the lightning path to the power systems conductors, and
electromagnetic coupling of energy into the power system conductors by
the radiation of a nearby lighting discharge.

Direct attachment injects the total lightning current into the system.
The current amplitudes range from a few thousand amperes to more than
200,000 amperes. However, the rapid change of current through the
impedance of the conductors produces a high voltage; most often this
high voltage causes secondary flashover to ground, diverting some
current even in the absence of an intentional diverter. As a result,
equipments connected at the end of overhead conductors are rarely
exposed to the full lightning discharge current.

Induction of surges by nearby lightning discharge is a less dramatic,
but more frequent event. The resulting surge characteristics are
influenced not only by the driving force---the electromagnetic
field---but also by the response of the power system---its natural
oscillations. This dual origin makes a general description of the
occurrence impractical, but nevertheless a consensus exists on what
representative threats can be expected in various physical
environments\[9\].

### **Switching Surges Can Be More Damaging Than Lightning**

Whenever a circuit containing capacitance and inductance is being
switched on or off, a transient disturbance occurs because the currents
and voltages do not reach instantaneously their final value- This type
of disturbance is inescapable and its severity depends on the relative
power level of the load being switched compared to the power system in
which the switching takes place Most of these disturbances involve the
of the response of the power system, just as in the case of induced
lightning surges, so that in practice the surges observed within a
building are similar in their diversity, regardless of their
origin---lightning or switching.

More complex circuit phenomena, such as current chopping and restrikes,
can produce surge voltages reaching ten times the normal circuit
voltage, involving energy levels determined by the power rating of the
elements being switched. These complex surges can have very destructive
effects, even on rugged equipment, and must generally be controlled at
the source rather than simply mitigated at the load \[9\].

[Effective Protection Techniques Have Been Developed]{.underline}.

Survival or undisturbed operation of the equipment can be achieved in
three manners: eliminating the cause of surges (for instance, eliminate
lightning, switching, etc.), producing equipment immune to any level of
surges, no matter how high, or, the obvious choice, finding the best
economic trade-off where moderate surge withstand capability is built
into equipment, and the worst surges occurring in the environment are
reduced, by application of suitable protective devices, to a level which
the equipment can tolerate.

Because the of the source of the surge is an energy transfer phenomenon,
involving a current, any attempt at blocking or
[restricting]{.underline} this current by a high impedance series path
will only produce higher surge voltages until breakdown occurs.
Breakdown allows current in an uncontrolled manner, generally through an
unwanted path. In contrast, a surge protective device, by
[diverting]{.underline} the current, offers a known, predictable and
therefore harmless path.

This diversion of major surge currents is best accomplished in two
stages. The first diversion should be performed at the entrance to the
building, typically by a conventional surge arrester, such as a
sparkover type device, rated for this duty \[10\]. Then, any residual
overvoltage, resulting from the action of the service entrance arrester,
can be dealt with by again diverting current with a secondary protective
device.

For this secondary protection, we recommend a clamping type solid state
device, installed at the power panel of the computer room, at the
terminals of a connected load, etc. Figure 2 illustrates this
coordination between two surge diverters and a series impedance.

**A Need for Integrated Surge Protection Is Recognized.**

An aspect of surge protection that might be overlooked is the need to
provide an integrated approach to the protection of the power and data
ports of an electronic system. A false sense of security might be
created when surge protection is installed in the power supply and at
the data entry and exit ports. However, unless the installation and
ground connection of these protective devices have been correctly
implemented, difficulties might still develop as a result of differences
in ground potential rise during operation of the protective devices.

As an Figure 3 shows the case of a computer powered by the building
supply on one side and interfacing with data lines from outside sensors
on the other side. The power lines are protected at the service entrance
and the data lines are protected at their entry point into the building.
A surge impinging on the data lines and correctly diverted to ground at
the entry point will unavoidably produce a rise in the potential at the
\'ground\' point where the data line protective device is connected, as
compared to the \'ground\' point where the power line protective device
is connected. The same difference of potentials would arise if the surge
impinged on the power supply port. Thus, the \'ground', potentials on
the power and data interface inputs at the computer cabinet will not be
the same, leading to upsets or damage. This phenomenon is frequently to
the dismay of the user who thought that adequate protection had been
implemented with the two devices installed at the entry points.

In such an instance where the entry points are far apart, the solution
consists in providing a secondary protective device for each port of
entry into the computer cabinet (or entry to the computer room where the
computer is installed on an equipotential plane or ground reference
grid), and assuring the same point of 'ground' connection is used for
these protective devices. While the qualitative aspect of this solution
is gaining recognition, the quantitative parameters still need to be
investigated. By the time Project P1100 nears completion, we expect that
measurements, now in progress at the National Bureau of Standards, will
contribute to the quantitative answer.

# STANDARDS PROJECT P1100

We have thus far reviewed the need and some of the key issues that
motivate us to recommended practices for powering and grounding
sensitive electronic loads. In so doing we recognize that there are
clearly many more details to address and many opinions and facts to
reconcile. The following section will layout how we are currently
proceeding in this effort. It is intended that enough detail BE provided
to encourage discussion and feedback to the Working Group.

## Approved Scope and Purpose of P1100

Project P1100 is titled \"Recommended Practice for Powering and
Grounding Sensitive Electronic Equipment (A Color Book)\" The IEEE
technical sponsor is the Power Systems Engineering Committee of the
Industrial Applications Society. A scope has been approved as follows:

> \"This project recommends design, installation and maintenance
> practices for electrical power and grounding (including both safety
> and noise control) of sensitive electronic loads such as computers,
> industrial controllers, and other electronic data processing equipment
> used in commercial and industrial applications."

## Status of Project P1100

The standards project authorization request (PAR) was submitted in June
1985 and approved by the IEEE Standards Board in September. A
\'strawman\' outline for eleven chapters was developed and chapter
objectives translated into a set of directives to chapter authors.
Internal and external review procedures have been established.
Preparation of a first draft is underway.

Meanwhile interest continues to grow. A number of tutorials have been
offered both inside and outside of IEEE. As an apparent offshoot of
deregulation, the industry is beginning to look at marketing a higher
quality electric service with power conditioning equipment incorporated
at increased electric energy rates. Still, there is no consensus
standard available as a reference for electrical engineers responsible
for the power system design. Help is needed in developing, writing, and
reviewing this standard.

[Proposed Chapters and Directives]{.underline}

1.0 INTRODUCTION - covers the purpose and background in much the same
way as in this paper.

2.0 SCOPE - as quoted in this paper.

3.  DEFINITIONS - this chapter provides definitions not otherwise
    available in IEEE Standards or as necessary to improve readability.
    The Chapter Chairperson is \"Provost Marshal\" with regard to use of
    undefined terms or acronyms in other chapters.

4.  NEED GENERAL NEED GUIDELINES -- this chapter is intended to identify
    the relevant codes and standards as well as the existing electrical
    environment that sensitive electronic equipment is typically
    subjected to in the field. Topics include coordination with other
    guidelines, electrical safety, power quality, grounding, surge
    protection, life-safety, and telecommunications systems
    considerations. These guidelines are established as a basis for the
    treatment of performance requirements and recommended practices in
    subsequent chapters.

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5.  FUNDAMENTALS - this chapter introduces the reader to the fundamental
    technical information necessary to understand and to apply
    recommended practices for design of a compatible and essentially
    hazard-free interconnection. Fundamentals not unique to sensitive
    electronic and/or electrical equipment will be treated very lightly,
    or only by reference to other IEEE Standards and appropriate books
    on recommended engineering practice. Fundamentals to be covered
    include power system quality, electronic data processing equipment
    power quality requirements, load and supply compatibility, grounding
    bonding and shielding, protection, and wiring practices.

6.  RECOMMENDED DESIGN/INSTALLATION PRACTICES - is the main message of
    this publication and is expected to be most difficult to gain
    consensus. Vagueness at this point would be a disservice to the
    reader. We intend to. put down on paper our collective engineering
    experience and judgment to pinpoint recommended practices. The
    proposed subjects are general discussion on performance and safety,
    60 Hz ac system, 400-480 Hz systems, and life-safety system
    interfaces and controls.

7.  NON-RECOMMENDED DESIGN/INSTALLATION PRACTICES \--is the chapter in
    which we very deliberately attack \"wives\' tales\" and raise
    \"warning flags,\" but are careful not to introduce any. new
    concepts or materials. Commonly observed non-recommended practices
    will be emphasized. The chapter is outlined by specific design topic
    to facilitate quick retrieval from the reference.

8.  SPECIAL MEASUREMENTS AND INSTRUMENTATION \-- presents information on
    special measurement requirements and on available equipment that are
    unique to investigating and diagnosing problems in power systems
    that serve sensitive electronic equipment. The proposed approach is
    to start with dc measurements of voltage, current, and power and to
    progress through the fundamental frequencies (60 and 415 Hz) to
    harmonic and higher frequencies, up to 300 kHz. RFI/EMI will be
    covered by reference only.

9.  SITE POWER ANALYSIS AND SITE SURVEYS - draws from the technical
    information base established in the previous chapters, and presents
    the practical aspects of problem diagnosis by an on-site engineer or
    technician. A section on interpreting and applying published power
    quality survey data is included; however, the chapter emphasis is he
    application of survey data from the user's own site.

10. SELECTION AND VERIFICATION OF EQUIPMENT AND MATERIALS - presents the
    myriad of available power enhancement equipment from a basic
    technology, performance, and functional point-of-view. A blend of
    manufacturer and user input is required. Manufacturers will be
    encouraged to provide generic rather than marketing details of
    equipment. How to verify equipment performance by testing is also
    covered.

11. CASE HISTORIES - is intended to provide explicit examples of
    real-world performance and/or safety problems that have been
    encountered in the [field.]{.underline} Examples are chosen that did
    not conform, in one or more ways, to specific recommended practices
    presented in this publication. Special care will be taken to ensure
    that the selected examples are representing key-points of Chapters 6
    and 7, rather than interesting, but, obscure ones.

12. APPENDIX (as required)

13. ANNOTATED BIBLIOGRAPHY

14. INDEX

[Coordination With Other Codes and Standards]{.underline}

As with most standards activities, there is a whole array of existing
and proposed standards that are to the technical scope. Careful
coordination is critical to ensure proper treatment and avoid
unnecessary overlap. Thus far we have identified or have been requested
to coordinate with the activities listed in Table 1.

# CONCLUSIONS

A consensus standard is needed for powering and grounding sensitive
electronic equipment. This standard should not only organize and present
recommended practices but also identify and dispel misconceptions and
discourage non-recommended practices. Ahead of us is a tough and
time-consuming job of sorting out various points of view and
coordinating various other related standards activities. It will be
several years before the task can be properly completed. This
introductory paper is intended to be the first of several preceding
publication of the consensus standard. The Project P1100 Working Group
will welcome comments on the concepts presented in this paper and
contributions to the final document.

###### REFERENCES

\[1\] IEEE Recommended Practice for Emergency and Standby Power Systems
for Industrial and Commercial Applications, [IEEE Orange
Book]{.underline}, Std 446-1980

\[2\] National Bureau of Standards, [Guideline on Power for ADP
Installations]{.underline}, Federal Information Processing Standards
Publication, FIPS PUB 94, Sep 21, 1983.

\[3\] T.S. Key, \"Diagnosing Power Quality-Related Computer Problems,\"
[IEEE Transactions on]{.underline} [Industrial
Applications]{.underline}, Vol. IA-15, no.4 , pp 381-393, July/August
1979.

\[4\] W.H. Lewis, \"Recommended power and signal grounding for control
and computer rooms,\" [IEEE Transactions]{.underline} [on Industrial
Applications]{.underline}, Vol. IA-21, No 6, pp. 1503-1516, Nov/Dec
1985.

\[5\] W.H. Lewis, \"Application of the NEC to the of sensitive
electronic equipment,\" [IEEE Transactions on Industrial
Applications]{.underline}, Vol. IA-22, No 3, pp. 400-415, May/Jun 1986.

\[6\] F.D. Martzloff, \"The propagation and attenuation of surge
voltages and surge currents in low-voltage ac power circuits, IE[EE
Transactions]{.underline} [Power Apparatus Systems]{.underline}, vol
PAS-102, pp. 1163-1170, May 1983.

\[7\] F.D. Martzloff and H.A. Gauper, Jr., \"Surge and High-Frequency
propagation in Industrial Power Lines,\" [IEEE Transactions on
Industrial Applications]{.underline}, Vol. IA-22, pp. 634-640,
July/August 1986.

\[8\] F.D. Martzloff, \"Coordination of surge protectors in low-voltage
ac power circuits,\" [IEEE Transactions Power Apparatus
Systems]{.underline}, vol PAS-99, pp. 129-133, Jan/Feb 1980.

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

\[10\] IEEE Standard for Surge Arresters for AC Power Circuits,
ANSI/IEEE C62.1-1981.

####### A STANDARD FOR THE 90S: 

####### IEEE C62.41 SURGES AHEAD

François D. Martzloff

National Institute of Standards and Technology

With each year that passes, we are relying more and more on electronics
in our lives, at home, at work, for travel, for defense\... the list is
endless. Reliability of these electronic systems is essential, and this
in a context of increased sophistication which often brings about more
susceptibility to disturbances. Thus, immunity to electromagnetic
disturbances, including surges in the power line, is a must.

Designers and users perform surge testing to verify that, indeed, their
equipment is immune to these surges. The question, however, is what
level of immunity must be achieved, since there are engineering
tradeoffs to be made, as well as economic considerations. Depending on
the type of equipment (its mission) and the location where it will be
used, a moderate or very high degree of immunity is appropriate. To
select the appropriate level of surge stress and to perform surge
testing in a manner that will yield valid results while ensuring safety,
reliable guidance is needed.

Ten years after its first publication as IEEE Standard 587, the Guide on
Surge Voltages in Low Voltage AC Power Circuits (now ANSI/IEEE
C62.41-1980) has undergone a major transformation into a Recommended
Practice format. From a guide proposing two basic waveforms to represent
typical surges, the document now proposes consideration of two standard
waveforms (the old friends of 1980) complemented by three additional
waveforms, one a fast burst, the others longer, high-energy surges.

## A History of IEEE C62.41

Actually, the occurrence of surges that led to the launching of a small
working group in 1966 to develop IEEE 587 have not changed much,
although the electronic equipment affected by surges as well as the
standard-writing group have undergone considerable changes. The initial
effort to provide guidance for designers on surges in low voltage
circuits was started by Dave Bodle \[1\], who persuaded a small group of
concerned fellows to seek a home in the IEEE Surge-Protective Devices
Committee (a body which, at the time, was mostly concerned with the high
voltage world of electric utilities). This pioneer group set out to
collect published data on surge occurrences and even circulated among
its members a set of six peak-reading surge counters donated by one
sponsor to add to its data base. These were the days before the
explosive development of disturbance monitors cum graphics. And so, IEEE
587 was born in 1980, with great expectations that it would be a useful
guide for designers and users of electrical and electronic equipment.

Alas, there were no other documents available to guide those users in
selecting severity levels from the choice proposed by IEEE 587. In
particular, the citation of 6 kV being a practical upper limit for the
occurrence of surges in 120-V circuits was soon misconstrued as implying
a requirement that all equipment should be designed to withstand 6 kV
surges. Product specification sheets began to state 'meets IEEE 587,'
forgetting the difference between a standard and a guide in IEEE
parlance. In the meantime, the guide was renumbered ANSI/IEEE C62.41, as
part of a family of surge-related documents \[2\] but the '587' label
has stuck and is even found in the model names of several commercial
surge generators.

In a first attempt to help users make sensible and correct decision on
surge testing, the IEEE working group developed a Guide on Surge
Testing - ANSI/IEEE C62.45-1987. The Guide provided information on how
to conduct reliable and safe surge tests ("Don\'t kid yourself, don\'t
kill yourself!"), also pointing out how to interpret the concepts of
locations categories proposed in the original document. However, the
questions and misuse by some continued, so the working group resolved to
update the guide.

Normally, IEEE procedures require a 5-year cycle of reaffirmation or
revision but the challenge of reviewing new data and developing
consensus on this subject stretched the work into ten years, culminating
in a Recommended Practice that was approved early in 1991 and is now
available from IEEE. From a group of 12 people in 1980, the working
group grew to 29 by 1990, reflecting the growing interest about surge
protection among users and manufacturers of electronic equipment.
Reconciling the different points of view from the enlarged group has
produced a new document that should receive even better acceptance than
the original 1980 version and, hopefully, result in fewer
misunderstandings.

## Toward a More Useful Standard

One of the first difficulties was to arrive at a satisfactory agreement
of what the word 'surge' means; to some a surge is a temporary increase
in the AC line voltage. That meaning is now replaced by the term
"swell," although a sizeable fraction of the engineering community will
continue to use the word surge with that meaning.

Next came the issue of noise versus surges (spikes, etc.). How big must
a voltage change be to become a surge? That issue was in fact not
resolved; instead, a conceptual figure was included in the document to
show the relationships among several parameters (see Figure 1) and thus
leave the bottom end of the range open to appropriate interpretation
depending on the circumstances. In addition, the single-value upper
limit of voltages proposed in the 1980 version has been replaced by a
table featuring three levels for each waveform, according to the
location category or the system exposure. The menu of waveforms proposed
in the 1991 version is new and, hopefully, improved, and includes the
following types:

-   The 0.5 μs - 100 kHz Ring Wave, defined in the 1980 version, as
    standard waveform.

-   The Combination Wave, 1.2/50 μs - 8/20 μs, also from 1980, as
    standard waveform.

-   The EFT Burst (5/50 ns), adopted from IEC 801-4, as additional
    waveform.

-   A new 10/1000 μs Wave, for high-energy stress, as additional
    waveform.

-   A new 5 kHz Ring Wave, for capacitor switching transient, as
    additional waveform.

The rationale for proposing standard and additional waveforms is rooted
in the acceptance of the 1980 waveforms as being representative and
useful, while recognizing that other waveforms may be encountered in
specific cases and should be recognized. However, the wish for complete
representation of all surges that may occur has to be tempered by
economics and engineering judgment; hence, the split between standard
(recommended) and additional (suggested). Figure 2 shows all five
waveforms, and Table 1 presents a summary of the voltage and impedance
values. The new waveforms are proposed in response to emerging concerns
on surge occurring in specific environments. Thus, a brief discussion of
these three new waveforms is in order.

## Additional Waveforms Address Emerging Concerns

The EFT Burst has been developed by Technical Committee 65 of the
International Electrotechnical Commission (IEC) to provide a screening
test for susceptibility to the fast transients that can be induced in
power as well as data lines by the multiple re-ignitions occurring
during the opening of a circuit by a contactor. While this type of
contactor is mostly found in industrial environments (the world of
TC65), other systems can have the same exposure (at least until the day
when all power switching will be done by bounce-free, restrike-free
solid-state relays). The catch, however, is that this test waveform was
proposed to evaluate immunity of equipment by a test procedure that
involves coupling the burst into the equipment under test by a
capacitance divider: the coupling capacitor and the internal capacitance
of the equipment under test. It does not mean that the 1-4 kV surges
involved in this test necessarily occur in the power systems; what it
means is that equipment that passes the high severity test will most
likely be immune to what the real world does to connected equipment. One
should not lose sight of this fundamental aspect of test standards; it
is impossible to duplicate all possible occurrences in one test, but if
a test can be developed so that equipment that passes the test has
better field performance than equipment that fails the test, then the
test is a valuable tool for reliable design.

The 10/1000 μs Wave has been proposed to provide a means to stress
equipment with high-energy surges, such as those that can occur during
major power-system fault clearing. The data base for that waveform is
somewhat limited, so a range of peak levels and source impedance is
proposed, to be selected according to the particulars of the situation.
As one check for reality, the energy deposition capability of this
waveform is such that small varistors (l4-mm diameter or less) in common
use - by the millions - could only withstand a few applications of that
surge. Thus, we know that such a high-energy surge does not occur very
often.

The 5 kHz Ring Wave has been proposed to represent the situation
encountered near large power-factor correction capacitor banks.
Switching transients in the range of 500 to 1000 Hz can occur, with
high-energy capability. In this case, the data base is rich in computer
simulations and anecdotal recordings but it is difficult to make an
accurate prediction for the general case because the actual transients
depend entirely on the local situation. It will be up to manufacturers
and users to agree on a compromise between conservative overdesign
wishes and economic viability of the design.

## Waveform Selection Supports International Harmonization Efforts

The waveforms presented in the new Recommended Practice document should
also be a positive step toward harmonization with international
standards. The Combination Wave is consistent with the conventional
'impulse\' typical of IEC surge testing; the EFT Burst represents the
adoption of an existing IEC Standard. Conversely, the 100 kHz Ring Wave,
long resisted by some of the IEC Committees, is beginning to gain a
foothold in the IEC community. The 10/1000 μs Wave could be an
alternative to the 100/1300 μs surge 'under consideration\' in some of
the IEC TC 77 surge immunity drafts. (This 100/1300 μs surge is a
varistor killer and, therefore, should not be considered beyond its
original scope of app1ication which is heavy industrial environments
where faults are cleared by fuses (5). The 5 kHz Ring Wave has yet to
gain international recognition.

To assist designers in making computer simulations, the Recommended
Practice document provides equations for the waveforms, and tolerances
are also specified. This detailed information might be better located in
the Guide on Surge Testing but it was included in the Recommended
Practice document until such time as a revised guide on surge testing
will include it (that revision has just been initiated, and it will
probably take another year before the revision is in print). *\[2004
note: It took 5 years!\]*

Last but not least, the new Recommended Practice document has three
appendices that offer tutorial discussions of the concepts used in the
document, provide information on the data base, and list almost 100
bibliographic citations, with brief notes on the contents of the papers.
Thus, readers of the Recommended Practice will have on hand a short
course on how to be prepared to deal with surges in low voltage AC
circuits.

> Francois D. Martzloff is a member of C62.41 working group, and has
> been involved in surge protection issues for more than two decades. He
> has been at the National Institute of Standards and Technology since
> 1985.

The author acknowledges the five-year effort in consensus building by
the members of the working group and other interested parties that made
possible the revision of IEEE 587 into a Recommended Practice.

### **REFERENCES**

1.  Bodle, D.W. et al. Characterization of the Electrical Environment,
    University of Toronto Press, 1976.

2.  C62: Complete Edition: A bound-book collection of all the guides and
    standards on surge protection, published periodically by IEEE.

3.  Martzloff, F.D. & Leedy, T.P. Electrical Fast Transients:
    Applications and Limitations,\" IEEE Transactions IA-26, Jan/Feb
    1990, pp 151-159

4.  Feninmore, C. and Martz1off, F.D. \"Validating Surge Tests by Field
    Experience: High-Energy Tests and Varistor Performance.\" Conference
    Record, IEEE/IAS Annual Meeting, Seattle, 1990.

5.  Meissen, W. Uberspannungen in Niederspannungsnetzen,
    Elektrotechnische Zeitschrift, vol. 104, 1983.

STANDARDS: TRANSNATIONAL ASPECTS

F. Martzloff, NIST, USA and A. Mendes, EDF/DER, France

**ABSTRACT** - Mass-production of electrical and electronic equipment
for the world market requires a system of standards of world-wide
applicability. The development of such standards is a complex task,
involving various national, regional, transnational, or international
organizations. This paper presents a review of the standards-writing
process, in particular in the area of Power Quality.

# The general need for standards

Mass production of electrical and electronic equipment for the world
market requires standard of world-wide applicability. Such standards are
reference documents that provide solutions to technical or commercial
problems in relations between contracting parties concerning products,
goods or services. Thus, a standard is a foundation to any contract.
Compliance with a standard is not necessarily mandatory, but it is
generally consid­ered as \'règles de l\'art\'. To make this
implementation mandatory, a law, regulation, ordinance, etc. is needed.
Examples are French government decrees, European Directives, and
ordinances in U.S. cities. A new aspect of the European Directives is
the position that electricity is a product, therefore subject to product
standards.

This position gives an added importance to the development of rational,
realistic, and cost-effective standards on Power Quality. These three
criteria for useful standards must be kept in mind at all stages of the
process of standards development. An unfortunate effect of selecting the
term \'Power Quality\' is its misinterpretation as a one-sided issue for
which the utilities would be solely responsible.

# National, regional, transnational, and international standards

There are some clear and some less clear character­istics that can be
identified to differentiate all the types of standards encountered in
international transactions. There is no universal \'standard\' that
regulates the development of these many standards. A simplified
classification might be as follows:

> National standards include several types:
>
> Voluntary consensus standards where a balance is established in the
> committee among the producers, users, and independent parties. Type:
> ANSI standards, Normes Françaises \...
>
> Industry standards, developed within one industry, where a balance is
> established among competitors.
>
> Type: NEMA Standards, PEG Standards, Specifications EDF, ERA
> Recommendations \...
>
> Regulatory standards:
>
> Developed and promulgated by government agencies within their
> jurisdiction. Type: MIL Standards \...
>
> Developed by independent organizations, adopted by national or local
> governments Type: UL, NFPA, OIML Standards \...
>
> Internal standards, perhaps more correctly called specifications,
> within one company, that can sometimes become de facto national
> standards.

Regional Standards are developed by a process similar to that of
national standards but shared among regional groups of nations. The need
to comply within that region can force multinational manufacturers to
adopt these regional standards, thereby making them de facto
international standards.

Type: CENELEC \...

Transnational standards fall in two categories:

> Standards developed by transnational organizations and adopted
> explicitly or by osmosis into local or national standards. Compliance
> with these standards might not be required, but their existence is
> recognized and influences the process of developing other standards.
>
> Type: IEEE Standards, Normes UNIPEDE \...

Internal standards developed by multinational firms, becoming de facto
standards within the market of that firm.

International standards are characterized by the fact that they are
developed by consensus among delegates from member countries, then
approved by national committees. These national committees in turn may
be appointed by a voluntary process or by government action, depending
on the country. The resulting standards may be formulated as
recommendations, but become de facto regulatory standards as purchasers
require compliance through their contractual agreements, or as
governments mandate compliance.

Type: IEC Standards, CCITT Standards ..

# Electromagnetic compatibility standards in the electrical industry

The performance of electrical equipment can often be described in fairly
simple terms. Therefore, the subject of ratings, dimensions, tolerances
is readily addressed by product standards developed by the manufacturers
or by the purchasers, working jointly or separately. However,
performance of equipment can be impacted by electromagnetic disturbances
and, conversely, the operation of equipment can emit disturbances that
impact other equipment. Avoiding electromagnetic interference (EMI)
became an important field of engineering, but all too often it has
become a process of correct­ing problems, rather than anticipating and
preventing them. The successful approach, both from the point of view of
sound engineering and from connotations of semantics, was to develop the
concept of Electromagnetic Compatibility (EMC).

The International Electrotechnical Commission (IEC) has developed a
hierarchy of standards to be observed by the various committees involved
in the area of EMC standards:

> Basic EMC Standards, providing general and fundamental concepts such
> as terminology, description of phenomena, test methods. etc.

Generic EMC Standards, providing specifica­tion for a limited number of
requirements and tests applicable to all products operating in a
particular environment.

> Product EMC Standards, providing specific requirements and test
> procedures dedicated to particular products.
>
> Product Family Standards, applicable to a group of similar products.

EMC standards are fundamental to the satisfactory operation of
electrical equipment. The issue of Power Quality may be considered as a
subset of the broader domain of EMC, so that it is useful to approach
the subject of Power Quality Standards along the same, well-developed
path of electromag­netic compatibility. That approach can be summa­rized
in one directive that can be applied to many other aspects of human
activities:

*\... thou shalt operate satisfactorily in thine environment, but thou
shalt not degrade it.*

An interesting aspect in the European context is the interpretation that
electrical energy is a product, therefore properly the object of
standards, hence the increased interest in power quality issues.

### **Power Quality Standards**

In general, power quality issues have arisen from several aspects:
increasing dependency on sophisti­cated electronic systems that may be
affected by the quality of their power supply, competition among energy
suppliers, and last but not least, the explosive development and
deployment of disturbance recorders with graphics capability that print
out records of disturbances for everyone to see.

From a handful of surveys of transient disturbances in the sixties and
seventies, we now witness a multitude of large scale monitoring
programs. An unresolved issue at this point, is the translation
(transformation) of objective measurements of electrical disturbances
into a subjective statement of I good power quality\' or \'poor power
quality\' - the statement that typical decision-makers desire, but that
engineers have difficulty in defining.

Defining standards for the quality of the electrical energy produced and
distributed by the utilities without considering the needs of the load
equip­ment would be the first mistake in standards development. The term
Power Quality has now gained too wide an acceptance to be changed, but
it fails to convey the concept of reciprocity between the parties. A
debate at a recent meeting of the IEEE Standards Coordinating Committee
on Power Quality pointed out that a more accurate description of the
Committee\'s scope would be Power Compatibility ­but the committee
resolved, with regrets, to go along with the entrenched usage.

A second mistake would be an attempt to enforce one-sided standards
based on narrow interests. International as well as national standards
bodies generally recognize this possible problem and make earnest
attempts at providing a balance of interests among the writers,
reviewers, and sponsors of product standards. The consequence of this
concern, however, is an agonizingly slow process in reaching sufficient
consensus to ensure acceptance of the standards. Even the top-down
approach taken by the European Community has met that difficulty in the
process, to wit the delay in application of the EMC Directive.

Satisfactory operation of electrical equipment requires an acceptable
quality of the delivered electrical energy, but agreeing on criteria of
what is acceptable is at the heart of the debate. The other important
requirement is that, in turn, the equipment connected to the power
system must not degrade the quality of that power system.

A power system is a dynamic entity, at every instant, phenomena occur
and produce disturbances that propagate throughout the system, impacting
the connected equipment as well as the elements of the power delivery
system. There is a wide range of phenomena, characteristics, coupling
and propagation modes, and consequences. The IEC Technical Committee 77
on Electromagnetic Compatibility is in the process of describing and
classifying the electromagnetic environment \[1\], \[2\]. These
documents provide guidance on the nature of the disturbances and
classify them in a limited number of types, making possible a rational
approach to emission control, withstand capability, and mitigation when
necessary \[3\].

As a universal phenomenon, electromagnetic disturbances can be defined,
described, and classified on a world-wide scale. However, when specific
disturbances occurring on specific power systems are concerned, then the
discussion must be carried among those sharing the same type of power
system. For instance, Europe uses 220 V, 50 Hz for residential and
commercial end-users; North American systems use 120/240 V or 120/208 at
60 Hz; Japan uses 100 V at 60 Hz in some regions. Thus, it should not be
surprising nor discouraging to have different standards evolve for these
different systems. Nevertheless, the basic principles should be held in
common and, therefore, a symposium such as this PQA 91 Confer-once
offers an opportunity to work toward commonalty where possible, all
under an EMC compatibility umbrella.

It is sometimes necessary to consider only national standards: the
nature of the electrical stresses are dependent upon the nature of the
networks, which are different among the countries and utilities. For
instance, in France or in the United States where the population density
is relatively low, the major part of the distribution system is built as
overhead lines: there will be many occurrences of voltage dips. On the
other hand, in a high-density country such as Holland where the
distribution system uses underground cables, there will be few voltage
dips. Another example of national differences is the different grounding
practices for the neutral, requiring corresponding dedicated standards.
An intermediate approach between national standards and international
standards is that of regional or transnational standards. For instance,
the countries of the European Community have sufficiently similar
practices, with a common market for electrical equipment to motivate
this approach.

### **Regional (transnational) standards**

As early as 1960, Europeans created CENELCOM (Comité Européen de
Normalisation Electrotechnique) with the task of developing European
standards. This committee has now been replaced by CENELEC (Comité
Européen de Normalisation Electrotechnique), the official standards
organization of the European Community. Leading the development of these
standards, several organizations contribute to the necessary database:
CIGRE (Conférence Internationale des Grands Réseaux Electriques), CIRED
(Congrès International des Réseaux de Distribution), IEEE (Institute of
Electrical and Electronics Engineers), UNIPEDE (Union Internationale des
Producteurs et Distri­buteurs d'Énergie Électrique).

For instance, UNIPEDE has recently proposed a description of the voltage
waveform \[4\]. This document describes the parameters characterizing
the voltage waveform and the disturbances that may appear at the point
of common coupling. Now, CENELEC is tasked with turning the UNIPEDE
document into a European Standard, which may then be used by European
utilities in the contracts with their customers. This standard will also
provide equipment manufacturers with the neces­sary information for
designing products with appropriate immunity levels.

# Nature of the equipment

The nature of the equipment involved has an influence on the concerns.
For instance, if wave­form distortion results from its operation,
questions arise on possible effects on revenue meters or on control
systems.

Electrical and electronic equipment may be classi­fied in two broad
categories:

> Small equipment, mass-produced, installed and used by anyone:
> appliances, electronic systems, with a load current of less than 16 A
> (Europe) or 12 A (USA, on 15 A branch circuits).
>
> Large equipment, produced in smaller number, custom-installed and used
> by professionals, with load currents above 16 A.

For each of these two, the type of appropriate standard will be
different:

In the first case, world-wide and comprehensive standards are necessary,
specifying emission limits and immunity levels. The IEC publications
series 555 are an example of such standards.

In the second case, Recommendations or Installa­tion Guides may be
sufficient. These documents may have an international basis,
complemented as needed by local requirements.

# Conclusions

Free circulation of electrical and electronic equipment requires the
observance of some rules. The most important, of course, involve safety,
which must not be placed in jeopardy by an insufficient level of
immunity to the disturbances occurring in the environment.

Regulatory agencies have added a requirement concerning the
electromagnetic environment, whereby the equipment shall not be the
source of objectionable emissions, while being capable of operating amid
a reasonable level of disturbances. The proliferation of new
technologies using higher frequencies, in particular in the 10-150 kHz
band, requires the development and implementation of rules concerning
the frequency spectrum and levels of emissions

In general; all these rules are promulgated through standards, acting as
reference documents generated by broad consensus or agreement among the
parties.

Specifications, regulations or directives can then refer to the relevant
standards. For instance, the European Directive will be more readily
accepted as its effective application is made easier and in a timely
manner. Unfortunately, the process of standards development remains
slow, and several more years will be required to reach a set of
generally-accepted emission limits, while there are practically no
standards concerning the immunity levels. By making this forum available
to many individuals involved in Power Quality issues, the process may be
clarified and even accelerated.

### REFERENCES

\[1\] IEC 77(Secretariat)103 - Description of the electromagnetic
environment.

\[21 IEC 77(Secretariat)108 - Classification of the electromagnetic
environment.

\[3\] IEEE C62.41-1991 - Recommended Practice on Surge Voltages in
Low-Voltage AC Power Circuits.

\[4\] DISNORM 12 - Definitions of the Physical Characteristics of
Electrical Energy Supplied by Low and Medium Voltage Public Systems.

POWER QUALITY WORK AT THE

INTERNATIONAL ELECTROTECHNICAL COMMISSION

François Martzloff

National Institute of Standards and Technology

## Abstract

The paper presents an update, including a brief historical background,
on the work to be undertaken at the International Electrotechnical
Commission (IEC) to address power quality issues. To be useful, this
work must take into consideration the three principal stakeholders,
namely the producers of electric power, the manufacturers of equipment
that use electric power, and the users of that equipment. Other
stakeholders include manufacturers of power quality monitors,
manufacturers of line conditioners, and power quality consultants. At
this time there are some differences of perceptions on how the work can
be accomplished to best serve the interests of all stakeholders.
Nevertheless, there is no disagreement on the first goal to be reached,
which is to catalyze development of compatible, comparable, and
consistent results in the measurement of power quality parameters.

###### Introduction

In a landmark 1996 decision, the Committee of Action of the IEC approved
a recommendation to undertake work on power quality issues as part of
the scope of Technical Committee TC77 on Electromagnetic Compatibility
(EMC). This decision, recommended by an Ad Hoc Group composed of power
quality experts from ten countries, marks an expansion of the scope that
will then reach beyond the purely technical issues generally addressed
by the EMC community. Power quality and EMC share many concerns, to the
point that each has at some time been described as being a subset of the
other. In addition to this fundamental aspect, other issues permeate any
discussion of power quality. It would be more accurate to draw a
multi-dimension diagram with many overlaps (see Figure 1). The Ad Hoc
Group considered three areas of contributions which an IEC Power Quality
Group could make, complementing the work currently done by existing
working groups or project teams of TC77:

\- Bringing order to the present chaos of uncoordinated methods of
monitoring power quality

\- Proposing a classification of power quality levels describing what
end-users can expect

\- Building bridges among producers and users of electric power, and
equipment manufacturers

Concerns have surfaced that undertaking such work might ultimately
result in the development and imposition of standards on the quality of
\"electricity as a product\" and create an adversarial relationship,
where for the moment the emphasis is on cooperation. There is a need to
reduce these concerns by defining more clearly the objectives and work
program of this new IEC activity.

## Power Quality in Other Organizations

The term \"Power Quality\" first appeared in the U.S. literature in the
late seventies used at first by the computer-user community in a
somewhat negative context, as it seemed to be associated with anecdotes
or complaints of malfunctions attributed - correctly or incorrectly - to
\"poor power quality.\" At the beginning, there was a tendency to took
for a culprit, the users blaming the electric power being supplied to
them, and the electric power supplier blaming insufficient immunity of
the equipment to unavoidable disturbances.

Even when a solution was indeed in sight, there remained among some
stakeholders some reluctance to assume the cost of correction, and
attempt to pass it on to the other stakeholder(s). The \"boundary\" of
the stakeholders was often defined as the revenue meter, as if electrons
would change their behavior when going through the current coil of the
meter.

Technically sound and economically viable solutions will depend on the
cooperation of three principal stakeholders:

\- Producers of electric power;

\- Manufacturers of equipment that uses electric power;

\- Users of equipment that uses electric power.

Perhaps not immediately obvious, but three other important stakeholders
in correcting power quality problems are:

\- Manufacturers of power quality monitoring instruments;

\- Manufacturers of line conditioning equipment;

\- Consultants called upon to solve power quality problems.

Considerable progress has been made since the early days in bringing the
parties together to seek mutually satisfactory solutions rather than
hunt for culprits. The PQA conferences held in the last several years
are a good indication of this change of mood and mode. We now hear the
word \"interface\" more often than the word \"boundary\" suggesting that
disputes are being replaced by constructive dialog. The term and concept
of \"System Compatibility\" have also become more visible 4, 5, 6, 7,
with the goals of the utilities defined as making their customers
satisfied and helping customers to be more competitive, rather than
merely supplying them with electric power.

Many electric utilities have instituted power quality programs in their
customer services, some as a defensive or reactive step, others as a
proactive and marketing strategy. Engineering societies have also
focused on practical, application-oriented power quality issues, while
initially the standards activities were slow in reacting to the growing
interest in those issues. Since then, several organizations have
established power quality programs for developing standards or
contributing to the development of standards, including the Canadian
Electricity Association (CEA)\', the European Committee for
Electrotechnical Standardization (CENELEC)\', the Electric Power
Research Institute (EPRI)\", the Institute of Electrical and Electronics
Engineers (IEEE)\", and the International Union of Producers and
Distributors of Electrical Energy (UNIPEDE) 12 . All of these
organizations have allocated substantial resources to address power
quality issues.

One of these issues in particular is the incompatibility found when
attempting to analyze and compare the results of power quality surveys
based on different definitions or measurement methods \", \", \". This
incompatibility is rooted on different definitions of disturbances, and
hence different algorithms in the software of power quality monitoring
instruments. Eliminating these incompatibilities is one of the prime
motivations for the proposed IEC work that will first focus on
measurement methods.

###### Power Quality vs. Voltage Quality

At the risk of oversimplification, one can identify two different
approaches to addressing power quality issues on the two sides of the
Atlantic Ocean. In Europe, attention seems to have focused on the
\"voltage quality\" while in North America, the concerns fell under a
broader umbrella of \"power quality.\" While the difference may seem to
be a mere linguistic subtlety between the U.K. English which is the
official English of the IEC and the U.S. English which is the unofficial
English of the IEEE, the words also reflect a difference in perspective.
In French, the second official language of the IEC, one finds the label
of \"qualit6 de la tension\" (tension = voltage), reflecting the
emphasis on voltage. Perhaps as a result of this difference of
perceptions, the few existing bilingual IEC documents on the subject
have not yet provided a satisfactory equivalent in the two languages

An anecdote can best illustrate this subtle perspective difference: in
what the U.S. community would recognize as a power quality pamphlet
influenced by the European Community, the untranslatable caption of a
cartoon from Electricit6 de France, \"Bien vivre avec sa tension\"
(Figure 2) proposes the double-entendre of learning to live with
\"tension\" - understood as the blood pressure of the end-user, or
\"tension\" - understood as the system voltage. Hopefully, there will
not be a triple-entendre where the word \"tension\" would refer to a
sag, or to strained relations among the three principal stakeholders,
resulting from concerns over the forthcoming IEC work on power quality
issues. The caption of Figure 2 is an attempt at providing in the power
quality context a culturally-equivalent rendition of the French for an
English-speaking audience.

Somewhat in contrast with the emphasis on voltage - but certainly not in
conflict - the U.S. perspective has included more than just supply
voltage in the power quality issues. An often-cited statement in power
quality articles is \"\... 83% of the alleged power quality problems are
actually end-user wiring problems\" and one article even shows a
screwdriver as \"the primary tool for solving power quality problems.\"
This broad perspective is also illustrated by an IEEE standard, part of
the IEEE Color Books series, on powering and grounding for sensitive
loads \" which is clearly related to power quality issues.

###### Satisfactory Operation vs. Voltage Quality

During the proceedings of the IEC Ad-Hoc Group meeting held in April
1996, interesting discussions took place among the participants on their
respective proposals for a definition of power quality - a necessary
prerequisite to undertaking work on the subject. A compromise consensus
emerged so that the group would be able to present a recommendation for
action where the terms would be defined. One of the proposals had
emphasized the voltage parameters, while another proposal had related
power quality to satisfactory operation of the user\'s equipment. The
resulting definition, cited below, still reflects these two points of
view:

> Power Quality - Set of parameters defining the properties of the power
> supply as delivered to the user in normal operating conditions in
> terms of continuity of supply and characteristics of voltage
> (symmetry, frequency, magnitude, waveform).
>
> Note 1: Power Quality expresses the users\' satisfaction with the
> supply of electricity. Power Quality is good if electricity supply is
> within statutory and any contractual limits, and there are no
> complaints from users, and vice-versa it is bad if the power supply is
> outside of limits and there are complaints from users.
>
> Note 2: Power Quality depends not only on the supply but can be
> strongly affected by the users\' selection of equipment and
> installation practices.

It will be one of the tasks (challenges?) of the group working on the
forthcoming documents to allocate appropriate attention to the two
points of view rather than to consider them as mutually exclusive.

## Forthcoming IEC Work on Power Quality

The approach now being considered by the IEC is to initially limit power
quality work to measurement methods, and perhaps even to a narrower
limit of characterization of voltage parameters. Starting with
measurement methods certainly is a necessity to get the work under way
and ensure that all parties speak the same language when discussing
power quality parameters. However, stopping there, useful as it may be
to catalyze compatible dialog between producer and consumer of electric
energy (power) will not be sufficient to fulfill the expectations of
equipment users. From all the fuss about power quality being addressed
at the IEC, they expect that more satisfactory operation of their
equipment will be facilitated by the commitment of resources now
envisaged by contributors to the IEC process, and that objective and
reliable guidance will be found in the new documents.

As mentioned in the Introduction, an Ad-Hoc Group of representatives
from several national or international organizations and committees
developed a recommendation to begin work on power quality, starting
first on measurement methods. This priority is a recognition of the
present uncoordinated efforts among dedicated, but isolated,
organizations which have produced incompatible or contradictory results
among power quality surveys conducted by different organizations. The
decision by the IEC Committee of Action to accept the recommendation
developed by the Ad-Hoc Group has now cleared the way for New Work Item
Proposals (NWIP), the method used by the IEC to launch the development
of new documents, to be submitted to the IEC National Committees for
approval.

As of the writing of this paper two NWIP proposals have been circulated.
One, originating from the French National Committee, has the title
\"Measurement Guide for Voltage Characteristics\" while the other,
submitted by the U.S. National Committee, has the title \"Power Quality
Measurements\" again reflecting the difference in perspective. The
French proposal somewhat mirrors the UNIPEDE 12 approach while the U.S.
proposal includes all the topics listed by the Ad-Hoc Group as well as a
reference to the IEEE Standard 1159 \". The French proposal concentrates
on low-frequency disturbance characterization, including power
frequency, voltage magnitude, voltage fluctuations, voltage dips,
harmonic voltages, and signalling voltages, but downplays transient
overvoltages (surges). It also makes several references to \"Compliance
with EN 50160\"11 which might be seen as leading to mandatory clauses.
The U.S. proposal includes a comprehensive list of disturbances,
suggests tutorial clauses on definitions and origins of disturbances,
and even the possibility of providing some tutorial material on remedial
or preventive actions. Both proposals follow the Committee of Action
decision that Technical Committee TC77 should be the principal
responsible committee for this work, in coordination with Technical
Committee TC8 (Standard voltages, current ratings and frequencies).

The officers of TC77 are on record as recommending that the two proposed
projects be merged into a single project since it is clear that both
proposals share the same goal of developing compatible, comparable, and
consistent results in the measurement of power quality parameters. The
responses from the National Committees will not be compiled before late
June 1997, but some responses will be known by the time of presentation
of this paper. Hopefully, the responses will be positive and the paper
presentation will include an update on the project planning.

###### Conclusions

· The first step has been taken at the IEC to start working on the
development of documents addressing power quality issues.

· The challenge will now be to proceed diligently to satisfy the needs
of end-users and not have the work stalled by the difficulties of
reaching consensus among many stakeholders.

· The decision to start with measurement methods will enable development
of a common language and build a working relationship among the
participants which should promote continuing progress toward technically
sound and cost effective solutions for the problems perceived -
correctly or incorrectly - as power quality problems encountered by
end-users in the equipment operation.

## Acknowledgments

Support for developing this paper, as well as support for participating
in the related IEC work, was provided by the author\'s agency, by EPRI,
by Delmarva Power, and by Pacific Gas & Electric. Gerald FitzPatrick and
Thomas Key provided helpful comments on the draft.

## References

I . Key, T. S., \"Diagnosing Power-Quality Related Computer Problems,\"
IEEE Transactions IA-15 No.4, July 1979.

2\. Goldstein, M. and Speranza, P.D., \"The Quality of U.S. Commercial
AC Power,\" Intelec Conference Proceedings, 1982, pp 28-33.

3\. Clemmensen, J.M. and Ferraro, R.J., \"The Emerging Problem of
Electric Power Quality,\" Public Utilities Fortnightly, November 28,
1985, Arlington VA.

4\. Gruzs, T., Key, T.S., Sitzlar, H.E., and Lai, J.S., \"Compatibility
at the Utility Interface: The UC Concept Applied to Surge-Protection
Systems,\" Proceeding, PQA\'91.

5\. Martzloff, F.D., \"Performance Criteria for System Compatibility,\"
Proceeding, IEEE APEC Conference, 1992, pp 287-292.

6\. Key, T.S., Sitzlar, H.E., and Moncrief, W., \"Electrical System
Compatibility Applied to End-use Equipment Characterization Projects,\"
Proceedings, PQA\'92.

7\. Key, T.S., Dorr, D.S., Hughes, M.B., and Stanislawski, J.,
\"Matching Electronic Appliances to their Electrical Environments,\"
Proceedings, PQA\'95.

8\. CEA 220 D 711 - Power Quality Measurement Protocol - Guide to
Performing Power Quality Surveys, Canadian Electricity Association, May
1996.

9\. EN 50160 \"Voltage Characteristics of Electricity Supplied by Public
Distribution Systems,\" November 1994.

10\. EPRI, Signature - A quarterly newsletter on power quality issues.

11\. IEEE Std 1100- 1992 \"Recommended Practice for Powering and
Grounding Electronic Equipment\".

12\. UNIPEDE \"Measurement Guide for Voltage Characteristics,\" May
1996.

13\. Martzloff, F.D. and Gruzs, T.M., \"Power Quality Site Surveys:
Facts, Fiction, and Fallacies,\" IEEE Transactions IAS Vol 24 No.6,
November/December 1988, pp 1005-1018.

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

15\. Martzloff, F.D., \"Surge Recordings that Make Sense: Shifting focus
from voltage to current measurements,\" Proceedings, ROMA\'96 EMC
Symposium, September 1996.

16\. IEEE Std 11 59-1995 \"Recommended Practice for Monitoring Electric
Power Quality"

## 

## THE TRILOGY UPDATE OF IEEE Std C62.41

#### François Martzloff

National Institute of Standards and Technology

**Abstract:** Progress report on the restructuring of two IEEE standards
concerned with surges in low-voltage ac power circuits into a Trilogy of
three documents. First a basic Guide describes the surge environment,
then a Recommended Practice proposes a limited set of representative
surge waveforms for test purposes, and finally a Recommended Practice
shows how to perform safe, repeatable and reliable surge tests on
equipment connected to these ac power circuits.

**1. INTRODUCTION**

Since 1980 when the seminal IEEE Std *587 Guide on Surge Voltages in
Low-Voltage AC Power Circuits* was first approved, the document has gone
through several revisions, while a companion, IEEE Std *C62.45 Guide on
Surge Testing for Equipment Connected to Low-Voltage AC Power Circuits*
was developed to provide guidance on test procedures. Experience in
applying the documents, and the availability of new information on the
subject led to a decision of performing a major update of the two
documents, mostly the C62.41. The purpose of this paper is to present a
progress report on the project and invite the International Conference
on Lightning Protection (ICLP) community in sharing common interests
about the occurrence of surges in low-voltage ac power circuits.

**2. HISTORY**

In 1991, the 1980 version of the IEEE 587 Guide (which had been renamed
IEEE/ANSI C62.4 1 soon after its original issue) was upgraded to a
Recommended Practice, with the addition of new recordings to the data
base, and the definition of "Additional Test Waves" to the seminal 100
kHz Ring Wave and Combination Wave (1.2/50 μs -- 8/20 μs).

Since 1991, the Recommended Practice remained unchanged, but new
information for the data base, and the perception of a need to describe
the scenario of a direct flash to the building --- not included in the
scope of the 1980-1991 versions --- have created a situation where a
mere update of the document would be insufficient.

Consequently, the IEEE Surge Protective Devices Committee and the
Standards Board of the IEEE have approved a new project, now known as
"The Trilogy" whereby the two documents, C62.41 \[1\] and C62.45 \[2\],
will be replaced by three separate, but related (and published
simultaneously) IEEE standards. The present C62.41-1991 will be split in
two, C62.41.1 and C62.41.2, while C62.45 will remain separate but better
connected to the two C62.41 documents.

**3. THE TRILOGY**

The identification of the three documents will be:

• C62.41.1-2000 -- IEEE Guide on the Surge Environment in Low-Voltage AC
Power Circuits

• C62.4 1.2-2000 -- IEEE Recommended Practice on Characterization of
Surges in Low-Voltage AC Power Circuits

• C62.45-2000 -- IEEE Recommended Practice on Surge Testing for
Equipment Connected to Low-Voltage AC

Power Circuits

To place these three documents of the Trilogy in perspective, note that
the IEEE generically refers to three types of documents as "standards":

***Guides,*** in which information is presented with no attempt to steer
the reader in a unique direction;

***Recommended Practices,*** in which several possible choices are
presented, and one is recommended as the first choice;

***Standards**,* in which a single approach is specified, with no
deviation allowed.

The last document of the Trilogy, C62.45 will not have major changes. It
will be an update to make it consistent with the recommendations of
C62.4 1.2, with the addition of some practical tips on how to perform
more reliable surge measurements. In contrast, the first document of the
1990s vintage, C62.41, is undergoing major restructuring. The purpose
and the contents of these three standards are summarized in the three
following Sections 4, *5,* and 6.

**4. GUIDE ON THE SURGE ENVIRONMENT**

**4.1 Data base**

The initial approach to a description of the surge environment was
limited to compiling the results of surge measurements made in the
field, either by systematic monitoring, or on the occasion of staged
tests, generally in connection with equipment failure investigations. As
the development progressed, it was recognized that additional
information on the surge environment can be gained by incorporating
other data. In its new structure as a Guide four elements will be
included into the data base:

1\. Recordings of surge events in the field;

2\. Numerical simulations and laboratory research;

3\. Inferences on the surge environment drawn from analysis of equipment
field failures;

4\. Discussion of the data base.

The 1980 and 1991 versions of C62.41 proposed the concept of "Location
Categories" as follows, in an effort to guide designers and users of
equipment toward a realistic perception of the surge threat depending on
the general location within a building, but not precise distances.

**4.2 Location Categories**

The concept of Location Categories was based on the fact that the
inherent inductance of the building wiring would reduce the
***current*** stress imposed by an impinging surge as distance from the
service entrance increases, while the ***voltage*** stress would not be
affected. The concept was illustrated in graphic form, showing buildings
where increasing distance from the service entrance were marked by
fine-line demarcations between the categories. Of course, electrons
flowing in the wiring were blissfully unaware of these demarcations, a
fact that was troublesome to some readers of the document. A possible
misinter­pretation of these fine-line demarcations might have
implications on the rating specifications of surge-protective devices
(SPDs) to be installed at a specific location.

To avoid this too-narrow interpretation the updated Guide will emphasize
that "boundaries" ***separating*** the categories should rather be seen
as "transitions" ***connecting*** the categories that overlap. The
graphic illustration of the three Location Categories A, B, and C will
show, rather than the fine lines of 1991, the amended concept and
representation with transition overlaps, as seen in Figure 1.

**Figure 1. The concept of Location Categories connected by transition
overlaps**

**4.3 The tale of two scenarios**

However, the concept of Location Categories was and remains implicitly
applicable only for surges impinging upon the building from the outside
or generated within. These were considered to be the vast majority of
surge events, and the more rare event of a direct flash to the building
was considered a special case, which was not addressed in the document.
The updated version will now include that situation, as described in
Section 5.

Given the increasing interest, and some of the undocumented perceptions
on what is involved in the scenario of a direct flash to a building, the
Trilogy is attempting to provide information presented in a manner that
will be useful and realistic. To emphasize the major difference between
common surge events and a less frequent direct flash, the surge
environment description of C62.41.1 is presented in two separate
scenarios:

***• Scenario I***: All surges impinging from the outside or generated
within the building, except for Scenario II

***• Scenario II***: Surges resulting exclusively from the dispersion of
the lightning current in the earthing electrodes

The concept of presenting the two scenarios has been well accepted among
the members of the IEEE Surge-Protective Devices Committee. One of the
pitfalls in applying this scenario might be an oversimplification made
in a well-intentioned attempt to simplify the complexity of the
dispersion of the lightning current among the available paths to
multiple earthing electrodes. Figure 2 shows an already very simplified
building wiring with extraneous metal which still suggests multiple
paths for the dispersion.

So far, few if any ***measurements*** have been reported in the
literature to document the details of the dispersion of lightning
current within a building \[3\]; \[4\]. However, several numerical
***simulation*** studies have been conducted \[5\]; \[6\]; \[7\], all
involving a certain degree of simplification \[8\]. This evolving
situation is closely monitored by the IEEE working group where the
Trilogy is being developed, to provide the latest consensus at the time
of balloting, but realizing that this consensus is an ever-evolving
goal.

**4.4 From database to representative waveforms**

In turn, the environment description of the C62.4 1.1 Guide will serve
as the basis for the definition of the waveforms given in the C62.41 .2
Recommended Practice, as described in the next section. The waveforms
that were proposed in the 1991 version will be maintained in the
description of Scenario I, but the definition of appropriate parameters
for Scenario II is still unresolved as of the writing of this paper.
Consensus might be reached among interested parties by the time of oral
presentation of this paper at the ICLP Rhodes, where the most recent
results of this process can be reported.

**5. RECOMMENDED PRACTICE ON CHARACTERIZATION OF SURGES**

**5.1 Purpose, proposals, and pitfalls**

The explicit purpose of this Recommended Practice is to propose a
limited set of test waveforms that can be used for subjecting equipment
to representative surge stresses as encountered in the low-voltage ac
power environment.

This set is ***a proposal,*** not a specification; it should be seen as
a menu from which equipment manufacturers and users can select stress
levels, as determined by the selected test waveform(s) and amplitude(s)
best suited for their own application.

The common pitfall, however, has been in the past that the purpose was
misinterpreted and the proposals were turned into equipment
specifications that were expected to be appropriate for all
applications. Continuing efforts in the redaction of the successive
versions of the document have been made, and appear to have reduced but
still not yet completely eradicated such misinterpretations.

The menu aspect of this Recommended Practice will be emphasized by
suggesting two types of test waveforms. First, a set of two "Standard
Waveforms" recommended for general applications; then a set of
"Additional Waveforms" recommended for special applications where they
appear appropriate.

**5.2 Standard Waveforms**

The original 1980 version proposed two representative waveforms, and
these have not changed since. The first waveform, labeled "0.5 μs ---
100 kHz Ring Wave" was constructed on the basis of the then novel
recognition that the traditional test waveforms used in high-voltage
laboratories might not be a good representation of the environment in
low-voltage ac power circuits. Even the limited field recordings
available at that time were showing oscillatory, high-frequency
waveforms rather than the textbook unidirectional impulses.

The second waveform, actually a combination of two stress types, was
proposed for subjecting equipment to a voltage stress (1.2/50 μs) when
the equipment would present a high impedance, or a current stress (8/20
μs) when the equipment would present a low impedance. This choice was
influenced by the wish of not denying the long experience gained with
those wavefonns. In contrast to the then prevalent test methods where
the current and voltage impulses were two separate tests, this second
waveform would be applied by a generator having the inherent capability
of delivering a voltage ***or*** a current stress according to the
impedance of the equipment under test. This new type of generator and
waveform became known as "Combination Wave."

**Figure 1 --- The concept of Location Categories connected by
transition overlaps**

**5.3 Additional Waveforms**

During the process of updating the 1980 vintage of the C62.41 Guide into
the 1991 version, several waveforms were considered by the working
group. The final proposal was to recommend considering a fast transient,
adopted from the IEC 801-4 (now IEC 61000-4-4), called EFT for
"Electrical Fast Transient," a 10/1000 μs Long Wave, and a 5* *kHz Ring
Wave. These waveforms were designated as "Additional Waveforms" to
emphasize that a test program should not be overburdened by unnecessary
tests when there was no compelling reason to include one or more of
these additional waveforms in the test regimen.

In the updating process for the Trilogy, the EFT and the Long Wave have
been kept as Additional Waveforms. In the 1991 version, the 5 kHz
waveform was intended to emulate capacitor switching surges. In the
laboratory, a conventional type of energy-storage surge generator could
produce that waveform superimposed to the power-frequency voltage.
However, it has been abandoned as more data became available on the
occurrence of capacitor switching surges, indicating that lower
frequencies, below 1 kHz, were more typical. Instead, the recommendation
is offered that specific studies be performed for installations where
large capacitor banks are being switched frequently.

**6. RECOMMENDED PRACTICE ON TESTING**

One of the outcomes of the Recommended Practice on Surge
Characterization is a set of tables indicating what types of surge test
waveforms are recommended for specific combinations of conductors at the
power port of equipment to be tested (phase, neutral, ground). To
illustrate the process, Table 1 presents a summary of these
recommendations for surge testing the ac power ports of equipment
(including surge protective devices, of course).

Now turning to the recommendations on actually performing the
recommended tests, in the 1980s and the early 1990s, guidance on surge
testing was offered in the format of an IEEE Guide. In the Trilogy, with
the experience accumulated in the use of the C62.45 Guide, augmented by
some anecdotal examples of observed questionable surge testing
procedures, the decision was made to elevate the C62.45 Guide to the
more compelling visibility and status of a Recommended Practice.

This enhanced version also will address issues raised by the shift from
analog to digital instruments and the resulting effects of aliasing,
insufficient resolution, and transducer saturation. Precautions for
avoiding artifacts will also be included in the recommendations.

**7. SCHEDULE AND RELATIONS WITH OTHER STANDARDS**

Efforts are being made to effect liaisons with the IEC Technical
Committees TC37 and TC8 1, as well as with other parties involved in
lightning studies. The effort has been difficult because the liaisons
were not optimized and the work was sometimes conducted by different
groups without sharing relevant information. It is one of the aims of
this paper to lower these barriers by presenting the subject within the
community of the ICLP participants.

The IEEE working group is hoping that the Trilogy will have matured
through the summer of 2000, in particular the consensus on how to turn
the agreed-upon Scenario II into one set of recommended test waveforms
that represent the environment. At the present time, IEC Publication
61643-1 \[9\] has been released, but it only specifies the types of
tests, without reference to the location and environment in which the
SPDs are to be installed.

**Table 1**

**Summary of recommended types of surge tests**

**8. SUMMARY**

The update of the two original documents, IEEE Std C62.41 and IEEE Std
C62.45*,* into a Trilogy will bring the following improvements to these
two previous documents, notwithstanding the fact that they served well
in the period of 1980 to 1999 (IEEE has filled over a thousand requests
for C62.41 since its first publication):

The new structure will provide readers with a more direct route to
fulfill their particular needs:

1\. A basic guide providing comprehensive data base and the rationale
for the simplification leading to the recommended standard and
additional test waveforms;

2\. A relatively terse description of the recommended test waveforms,
uncluttered by the data base;

3\. A straightforward and well-connected Recommended Practice on surge
testing methods.

The most significant changes in the Trilogy, compared to the earlier
versions of C62.41-1991 and C62.45-1992, are the following:

-   Separation of the database that was appended to C62.4 1 in the
    earlier versions, when enhancing acceptance and credibility of the
    proposals were deemed important elements. A Guide provides a
    comprehensive database, a Recommended Practice provides the standard
    and additional test waveforms.

-   Introduction of a Scenario II for the special case of a direct
    lightning flash to the building. Such a scenario implies higher
    stress levels for those surge-protective devices installed at the
    service entrance, compared with the stress levels suggested for
    usual applications.

-   Introduction of the concept of transition overlaps that act as
    interfaces between Location Categories, rather than the boundaries
    that previously separated these categories.

-   Removal of the earlier attempt to provide across-the-board waveforms
    for the case of capacitor switching, but instead make recommendation
    to perform case-by-case studies.

**9. ACKNOWLEDGMENTS**

The development of the IEEE C62 Trilogy update has been made possible
only with the technical contributions and moral support of my
colleagues, too numerous to list them all, from several
standards-writing groups, but who nevertheless deserve recognition for
their voluntary work.

Another beneficial factor that needs recognition is the growing trend
toward harmonization among standards-writing organizations, in spite of
their initial divergent positions.

**10. REFERENCES**

\[1\] IEEE Std C62.41- 1991 - *Recommended Practice on Surge Voltages in
Low-Voltage AC Power Circuits.*

\[2\] IEEE Std C62.45-1992 - *Guide on Surge Testing for Equipment
Connected to Low-Voltage AC Power Circuits.*

\[3\] Morris, M.E., Fisher, R.J., Schnetzer, G.H., Merewether, K.O., and
Jorgenson, R.E., "Rocket-Triggered Lightning Studies for the Protection
of Critical Assets," *IEEE Transactions IA-30,* May/June 1993.

\[4\] EPRI "Investigation of lightning entry into a secondary service
using rocket triggered lightning", *EPRI Report TR­110418,* April 1998.

\[5\] Birkl, J., Hasse, P., and Zahlmann, P., "Investigation of the
interaction of lightning currents with low-voltage

installations and their related threat parameters", *Proceedings, 23^rd^
International Conference on Lightning Protection,* Firenze, 1996.

\[6\] Mansoor, A. and Martzloff, F.D. ,"Driving high surge currents into
long cables: More begets less", *IEEE*

*Transactions PWRD-12,* No.3, July 1997.

\[7\] IEC 62066: 2002: *General basic information regarding surge
overvoltages and surge protection in low-voltage a. c. power circuits.*

\[8\] Mansoor, A. and Martzloff, F.D., "On the Dispersion of Lightning
Current after a Direct Flash to a Building,"

*Submitted for ICLP 2000,* September 2000.

\[9\] IEC 61643-1:1998 *Surge protective devices connected to
low-voltage power distribution systems - Part 1: Performance
requirements and testing methods*.

New IEEE Standards Foster Next-Generation System Compatibility

#### *By François Martzloff*

In November 2002, the Institute of Electrical and Electronics Engineers
(IEEE) approved a set of three standards that provide critical
parameters on the surge environment in low-voltage ac power circuits,
and suggest improved test methods for end-use equipment connected to
these circuits. When this standards trilogy is published in early 2003,
manufacturers and users of surge protective devices (SPDs) will have a
definitive set of documents to help them make more cost-effective and
technically sound design decisions regarding the compatibility of their
equipment with the surge environment.

The seminal IEEE Standard 587---Guide on Surge Voltages in Low-Voltage
AC Power Circuits---has gone through several revisions, including a name
change to C62.41, since it was first published in 1980. A companion,
IEEE Standard C62.45---Guide on Surge Testing for Equipment Connected to
Low-Voltage AC Power Circuits---was also developed to provide guidance
on test procedures.

IEEE 587/C62.41 and C62.45 served us well from 1980 to 1999. However,
with the availability of new knowledge on surge protection, and after
nearly 20 years of experience in applying the two standards, a major
update was needed. The newly developed standards provide a more direct
route to fulfilling the surge protection needs of users, and are
designed to promote greater harmony with the related standards of
international organizations.

The new trilogy consists of

-   IEEE Standard C62.41.1^TM^ 2002 -- Guide on the Surge Environment in
    Low-Voltage AC Power Circuits, which contains a comprehensive
    database describing the surge environment;

-   IEEE Standard C62.41.2^TM^ 2002 -- Recommended Practice on
    Characterization of Surges in Low-Voltage AC Power Circuits, which
    proposes a limited set of representative surge waveforms for test
    purposes; and

-   IEEE Standard C62.45 ^TM^ 2002 -- Recommended Practice on Surge
    Testing for Equipment Connected to Low-Voltage AC Power Circuits,
    which shows how to perform reasonable, repeatable, and reliable
    surge testing.

### **New Focus**

In developing the standards, IEEE focused on five key areas:
transitions, temporary overvoltages, multiple-port equipment problems,
scenarios, and harmonization. Because these factors can have significant
impacts on hardware selection and specification, they were debated
thoroughly by members of the working group and other interested parties
before a consensus was reached. Fortunately, the IEEE standard format
includes "normative" clauses, to emphasize important points, ***and
"informative" annexes, to provide perspective on less definitive
issues.***

### ***Transitions***

Earlier versions of C62.41 offered the concept of "Location Categories"
to help designers and users of equipment define surge threats by the
general location of the equipment within a building. Location categories
are based on the fact that the inherent inductance of the building
wiring reduces current stress from an impinging surge as the distance
from the service entrance increases, while voltage stress is not
affected. According to this concept, SPDs can be expected to have less
stress exposure as their point of use moves away from the service
entrance.

While the earlier standards did not specify precise distances, they
featured graphic representations with fine lines, or "boundaries,"
separating location categories. Because some users focused too narrowly
on these boundaries, the updated guide now uses the concept of
"Transitions" that connect rather than separate location categories, as
the graphic shows. These transitions leave some flexibility for
equipment manufacturers and users in selecting specific surge-withstand
values.

#### *[Temporary Overvoltages]{.underline}*

Although temporary overvoltages---which last seconds rather than the
microseconds of surges---might be seen as outside the scope of the surge
environment, their impact on SPDs can be devastating. For this reason,
IEEE added a description of their occurrence and mechanism to the
C62.41.1 guide.

#### *[Multiple-Port Equipment]{.underline}*

Most of today's electronic equipment contains multiple ports, with
connections to both the ac power supply and one or more additional
systems that must have a ground reference, such as phone systems,
television cable systems, and computer networks. Multiple-port equipment
is now the most common victim of surges. A surge on any of the connected
systems will cause a shift in ground reference potential to appear
across the equipment ports. Guide C62.41.1 alerts the engineering
community to this phenomenon---the most frequent source of insurance
claims---and supports the standardization of SPDs. Furthermore, IEEE has
just launched two projects for developing new standards addressing
performance and test methods of multiple-port SPDs.

#### Scenarios

In an effort to organize and present information in a way that will be
as useful and realistic as possible, the standards trilogy introduces
the concept of "Scenarios," which distinguish between two types of
surges. Scenario I describes surges coming from any source that impinge
upon an installation or are generated within the installation by load
switching. Scenario II covers surges that are associated with a rare but
possible direct lightning flash to a building, and with surge current
that exits the building via the service connection.

The concept of location categories applies only to surges in Scenario
I---those impinging upon a building from the outside or being generated
from within. These are considered to be the vast majority of surge
events. Guide C62.41.1 provides a surge environment description that
serves as the basis for defining the waveforms in Recommended Practice
C62.41.2.

The more rare event of a direct flash to a building in Scenario II was
considered to be a special case and not included in earlier documents.
Given the increasing interest in the ramifications of such an event, the
new standards address this situation. Definitions of appropriate
parameters for this scenario did raise some discussion in gaining
consensus, and therefore are proposed in an informative annex to allow
case-by-case applications.

#### Harmonization

In keeping with the transnational aim of IEEE standards, the new
standards were developed to harmonize with related documents from the
International Electrotechnical Commission (IEC). The IEEE working groups
established liaisons with IEC Technical Committees SC37A (Low-Voltage
SPDs) and TC81 (Lightning Protection), as well as with other parties
involved in lightning studies. These efforts will help to ensure greater
credibility and worldwide acceptance of both IEEE and IEC standards.

##### Expanded Scope

In earlier versions of the standard, surge environment descriptions were
limited to compilations of surge measurements in the field. The data
were gathered either by systematic monitoring or through staged tests
during equipment failure investigations. As development of Guide
C62.41.1 progressed, it became clear that more information on the surge
environment could be gained by incorporating other data. The standard
now includes additional data from recordings of surge events in the
field, numerical simulations and laboratory research, and inferences on
the surge environment drawn from analysis of equipment failures.

The proposed waveforms and associated stress levels in Recommended
Practice C62.41.2 required no major change during the updating process.
The waveforms should not be construed as specifications---a
misconception noted in the use of earlier versions of C62.41---but
rather as a menu from which equipment manufacturers and users can select
stress levels, as determined by the test waveform(s) and amplitude(s)
best suited to their own applications. The menu offers a set of two
standard waveforms for general applications and a set of two additional
waveforms for special applications.

The first standard waveform, the "Ring Wave," was constructed in 1980 on
the basis of the then-novel recognition that traditional test waveforms
used in high-voltage laboratories might not provide accurate
representations of the environment in low-voltage ac power circuits. The
second standard waveform, the "Combination Wave," defines two stress
types. It is used for subjecting equipment to voltage stress, when the
equipment presents a high impedance, or to current stress, when the
equipment presents a low impedance.

The additional waveforms are the "Electrical Fast Transient Burst,"
first developed within IEC for electromagnetic compatibility purposes
and adopted by IEEE in 1991, and the "Long Wave," which reflects field
observations of surge occurrences. The 1991 version of C62.41 also
included a 5-kHz ring wave to emulate capacitor-switching surges. This
wave was removed from the menu, as data on the wide range of
capacitor-switching surges made it clear that only case-by-case
applications would be reasonable.

Equipped with these waveforms, Recommended Practice C62.45 provides
information on instrumentation, considerations on tolerances in the
output of surge generators, and descriptions of test procedures,
including coupling of surges into test circuits. This enhanced version
addresses issues raised by the shift from analog to digital instruments
as well as the possible effects of aliasing, insufficient resolution,
and transducer saturation. It also includes precautions for avoiding
artifacts.

With the implementation of the new IEEE standards trilogy, designers and
users of next-generation devices will be well equipped to tackle the
surge environment of the future in low-voltage ac power circuits. Among
the benefits they will realize are more cost-effective use of resources
and greater harmony with the related standards of international
organizations.

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| ## François Martzloff                                                 |
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| ## April 2004                                                         |
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