+-------+----------------------------------------------------+--------+
| # Las | # Surge Protection Anthology                       | # Su   |
| t upd |                                                    | rges H |
| ated  | **Part 6 -- Tutorials, Textbooks, and Reviews**    | appen! |
| March |                                                    |        |
|  2004 | **Text of "System Compatibility" files**           |        |
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FOREWORD

This file contains the text part from four papers on the following
subjects:

-   Performance criteria for power system compatibility (1992)

-   Characterization of TVSSs from a system compatibility perspective
    (1992)

-   An important link in whole-house protection: Surge reference
    equalizers (1993)

-   Consumer power quality problems: Troubleshooting by telephone (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="0.875in" height="0.43333333333333335in"}

Performance Criteria for Power-System Compatibility

François D. Martzloff

National Institute of Standards and Technology

Gaithersburg, MD 20899

***Abstract*** - Power electronics create an opportunity for better
utilization of electric energy but can become a source of problems if
the electromagnetic characteristics (immunity and emissions limits) of
the equipment are not compatible with the characteristics (avoidable and
un­avoidable disturbances) of the power supply. Well-defined equipment
performance criteria can help end-users obtain better compatibility,
reliability, and cost effectiveness of the equipment - power supply
combination.

### I. INTRODUCTION

The ever-expanding application of power-electronics loads, the
increasing dependency upon information processing systems, and the
explosive development of power-system disturbance monitors (cum
graphics) have produced a new level of concern about the compatibility
of load equipment and power supply. Power-electronics loads are accused
of polluting power delivery because of their nonlinear characteristics
and the utilities are accused of delivering poor power quality.
Meanwhile, the rapidly growing number of users of power-system
disturbance monitors proudly display pictures of their 'glitch of the
month' (in the way senior engineers used to pull pictures of their
grandchildren out of their wallets) all to lament how bad the situation
has become It is time to take a fresh look at the situation and stop
pointing fingers; instead, available resources should be applied to
obtain better compatibility between hardware and software. Better
compatibility is also needed among the three partners irrevocably
involved, for better or for worse, in the power-electronics arena: the
equipment suppliers, the electric power suppliers, and the end-users.

A new term has emerged and gained popularity in recent years: Power
Quality. The basic need for satisfactory operation of equipment is well
perceived by all. However, depending upon the point of view of those
using this term, the interpretation of the term and the approach in
achieving its objective are different. A clear definition, accepted by
all interested parties, has yet to be developed.

It may be useful to look back and benefit from the experience gained,
long ago, in honing the concepts of electromagnetic compatibility
because the quest for power quality proceeds along the same path as the
broader topic of electromagnetic compatibility.

The performance of electrical equipment can often be described in fairly
simple terms. Therefore, the subject of ratings, dimensions, and
tolerances is readily ad­dressed by the product standards developed by
the manufacturers or by the purchasers, working jointly or separately.
However, performance of equipment can be adversely impacted by
electromagnetic disturbances and, conversely, the operation of equipment
can emit distur­bances that impact other equipment. Thus, avoiding
electromagnetic interference (EMI) became an important field of
engineering, but all too often it became a Pro­cess of correcting
problems rather than anticipating and preventing them. A more successful
approach, both from the point of view of sound engineering practice and
from the connotations of semantics, was the devel­opment of the concept
of Electromagnetic Compatibility (EMC). One way to look at power quality
issues would be to consider them as an interesting, dedicated subset of
EMC, limited to the area of low-frequency conducted phenomena, as
opposed to the \'dc-to-daylight\' domain of the IEEE/EMC Society. An
invitation for presenting a paper at this forum is an opportunity to
complement the usual power quality dialogue, limited to end-users and
electric utilities, by a three-way discussion that will include original
equipment manufacturers (OEMs).

# II. THE NEED FOR STANDARDS

Mass production of electrical and electronic equipment for the world
market requires standards of world-wide applicability. Such standards
are reference documents that provide solutions to technical or
commercial problems in the transactions between contracting parties
concerning products, goods or services. Standards act as a foundation to
any contract.

The development and implementation of power-quality standards is
presently incompletely coordinated, in spite of all the efforts to
provide coordination and liaison between the various standards-writing
bodies. As an example, the European Directives on EMC take the position
that electricity is a product, therefore subject to product standards of
quality \[1\]. However, the con­ditions for optimum compatibility between
the needs of equipment and the inherent characteristics of a power
supply are not yet defined.

Product standards have reached a state of development where equipment
survival in the field is adequately addressed, but the more subtle
immunity to unavoidable disturbances is not addressed, to wit blinking
clocks or industrial processes that shut down because their control
systems lack sufficient ride-through capability during momentary power
interruptions. Conversely, efforts to limit emissions of disturbances
into the power system caused by normal operation of the equipment have
faced a difficult challenge of achieving consensus, nationally as well
as internationally \[2\], \[3\].

### Power Quality Surveys and Electromagnetic Environment Characterization

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

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.
The IEEE attempts addressing these concerns with the steady development
of voluntary Guides, Recommended Practices, and Standards. However, the
process of consensus standards is all too often very slow, and sometimes
delivers only broad (generic) rather than specific documents because of
the lowest common denominator effect inherent in the consensus process.

Several national or international documents have been developed to
classify the characteristics and disturbances of power systems. For
instance, the normal steady-state conditions in U.S. power systems are
defined in ANSI C84.1-1989 \[4\]; surges are described in ANSI/IEEE
C62.41-1991 \[5\]; and an IEEE Guide is under devel­opment to describe
the range of disturbances \[6\]. On the international scene, the
variations in steady-state conditions and the types of transient
disturbances are addressed by the Technical Committee 77 (TC77) on
Electromagnetic Compatibility of the International Electrotechnical
Commission. Table I, excerpted from documents under consideration by the
TC77 shows the list of these phenomena that cause radiated as well as
conducted disturbances \[7\].

A useful development in designing for electromagnetic compatibility is
the recognition that equipment can be described in terms of several
generic ports (Figure 1) representing the path of entry or emission of
electro­magnetic disturbances \[8\] By breaking down the complex coupling
of the equipment to its environment, addressing compatibility issues
becomes more manage­able. However, one should not make the error of
presuming that these ports have no interaction, inside or outside the
equipment.

## Figure 1 -- Six ports of electronic equipment for entry or emission of electromagnetic disturbances

# Load Equipment Characteristics

An essential element of electromagnetic compatibility is the
characterization of load equipment - both its immunity levels and its
emission levels. The basic concept of compatibility, expressed in the
IEC defini­tion, is that "equipment should have a high probability .to
function satisfactorily in its lectromagnetic environ­ment without
introducing intolerable disturbances to anything in that environment."
\[7\].

While simple and easy to agree with in principle, this concept is
difficult to apply when the immunity and emission characteristics of the
load equipment are not available to the system designer. This
unavailability is results from either insufficient recognition of the
issue or reluctance by some OEMs to publish data that might be
misconstrued as a competitive weakness of their product. Actually, the
weakness in the overall situation is the lack of understanding and
cooperation among the three partners. Until such time as the usual
process of voluntary standards (typically in North America) or the
government-issued Directives (typically in Europe) impose full
disclosure of the immunity and emission characteristics of the
equipment, it will not be possible to design a system for predictable
and reliable power ­system compatibility.

### System Compatibility Performance Criteria

To remedy at least in part this undefined situation, System
Compatibility (SC) performance criteria have been developed by the Power
Electronics Applications Center (PEAC). This development is in response
to the growing need for ensuring equipment compatibility at the
interface between the utility and the end-user loads \[9\]. Load
equipment OEMs generally do not have a sufficient knowledge base or the
incentives to allocate their limited resources to research all aspects
of utility compatibility for equipment that may be installed by third
parties. Individual users may not have the appre­ciation of potential
problems and the leverage necessary to [bring]{.underline} about changes
in equipment design. Last but not least, Architectural and Engineering
firms (A&E), while understanding the potential incompatibilities, may
lack incentives or leverage to obtain redesign of load equipment or
reconfiguration of the power supply.

Therefore, the main purpose of these SC criteria is to facilitate
reconciliation of the inherent limitations of the power -System
environment with the characteristics of ever-changing electronic loads.
The SC documents will provide a uniform approach to system compatibility
until such time when the usual, slower standards development will have
caught up with the fast-changing technology.

The System Compatibility approach is based on a three-step process:

1.  Determine the electrical characteristics of the environment.

2.  Determine the immunity and emission charac­teristics of candidate
    load equipment.

3.  Identify the need, if any, of some interface between the environment
    and the equipment.

For the purposes of the SC process, the characteristics of the
environment can be obtained from environment description documents such
as \[5\], \[6\] or \[7\]. In the absence of sufficient documentation,
the immunity, emission, or mitigation characteristics need to be
determined by tests. To be consistent and fair, the tests must be
conducted according to a well-defined protocol, hence this development
of SC performance criteria. The tests can then demonstrate that specific
equipment is capable of operating in that environment, will not by
itself degrade the environment, and involves a minimum of undesirable
side effects.

These SC performance criteria tests are by necessity limited to the
major aspects of compatibility and do not purport to replace more
comprehensive tests performed by other parties, for instance those
required for design engineering, regulatory compliance, or customer
acceptance. The SC criteria have been developed from the point of view
of electric utilities in consultation with other interested parties,
including OEMs and end-users.

# III. THE SC DOCUMENT FAMILY[^1]

The SC performance criteria provide a timely step in the application of
power electronics equipment through objective testing for equipment of
interest to electric utilities. For instance, some utilities are
offering a comprehensive surge protection system to their custom­ers, or
are promoting energy savings through the use of electronic ballasts. To
ensure success of such offerings, the utilities need to assess the
performance of candidate devices offered by several OEMs. The test
results are presented within a context of broad compatibility, not as a
pass-fail judgment; expectations and results are presented to the
sponsoring utility for analysis and final decision.

By making these criteria available to industry, it is expected that more
consistent methods for evaluating power-system compatibility will be
achieved. Reaching this goal will be facilitated by the gathering of
applica­tion experience in the fast-evolving field of power electronics.
This experience will then provide the basis for the usual standards
development. The ultimate result will be more reliable and more
cost-effective application of power-electronics equipment in an
environment that is continuously evolving.

At the present time, several SC documents have been completed or are
near completion; it is envisioned that the concept could be expanded to
many more types of equipment. Table II shows the list of the major
catego­ries of documents under consideration, each to be subdivided into
specific devices. For instance, the Power Conditioning Equipment
category would include photovoltaic equipment, surge-protective devices,
uninterruptible power supplies, etc. Among those, the rationale for
documents in progress is briefly described in the following paragraphs.

# SC-110 - Surge-Protective Devices Used in Low-Voltage AC Power Systems

Surge-protective devices are applied in increasing numbers by end-users
and now by some utilities on the meter side of their secondary systems.
The surge current-handling capability of these devices ranges from 0.5
kA to 10 kA, with a large number of suppliers offering these devices for
installation at the service entrance or at receptacles within a
building. Many OEMs also include these devices in the power port of
their products. Some utilities now offer to their cus­tomers installing
surge-protective devices with a guaranteed protection. In such schemes,
a high-energy arrester is installed at the service entrance, combined
with protective devices connected next to the sensitive appliance
\[10\].

The voluntary standards development process has not kept pace with the
rapid development and application of these devices, in particular the
coordination of two devices installed within a short distance of each
other by uninformed end-users \[11\]. (Utilities offering the combined
protection are in a better position to obtain coordination among the
devices that they install, but still have no control over devices
installed within the premises by the occupant \[12\].)

Another aspect that has not been comprehensively addressed is the
failure mode of these devices; many test standards generally aim at
demonstrating a specific rating, with only a pass/fail criterion, and
the procedure does not go into failure mode determination. In con­trast,
SC-110 includes a test procedure to determine failure modes.

### SC-120 - Reference Equalizers Surge-Protective Devices for Power and Communications Systems [^2]

The increasing use of equipment that includes a power port and a
communications port, as defined in Figure 1, (cable TV receivers, smart
telephones, Fax machines, desk-top publishing systems, distributed
computer systems, industrial process control systems, etc.) has created
a new problem in surge protection. Appropriate surge-protective devices
correctly but independently applied to the two ports might not provide
adequate protection against the problem of differences in the voltages
appearing at the two ports during operation of one protective device.

To remedy this Situation, OEMs are offering a device that routes both
the power and the data connections through a single enclosure where the
protective devices for each port share the same ground reference.
Initially dubbed "local ground window" \[13\], a new generic name of
"Surge Reference Equalizer" is now proposed.

The SC-120 documentdescribes a test schedule that exercises the
protective devices of both the power port and the communications port
(telephone or cable TV), separately and in combination.

Another compatibility concern is raised by the in­crease in harmonic
currents produced by the new generation of power electronics. Possible
areas of concern include the overheating of transformers and neutral
conductors, interference associated with spurious zero-crossings, errors
in revenue meter accuracy, and improper power-system control. The
following are examples of SC documents addressing these concerns through
performance test criteria.

### SC-41 0 - High-Frequency Fluorescent Ballasts Used in Indoor Lighting Systems

The increasing emphasis on energy conservation and the development of
electronic ballasts have led some electric utilities to offer incentives
to their customers for using these ballasts. However, in the present
state of the market and standards development, these ballasts can create
compatibility problems for users as well as for utilities. Interest in
this issue is keen among both parties, hence the development of the
performance criteria document for this type of equipment.

### SC-610 - Adjustable Speed Drives Used in Commercial and Industrial Facilities

The accelerating trend in applying adjustable speed drive systems
provides a classic example of the race between an emerging technology
and the development of adequate compatibility. These devices produce
current harmonics (the emission aspect of EMC) and many are very
susceptible to power line disturbances (the immunity aspect of EMC). At
this stage of the development and application of these drives, it
appears that more effort is needed in addressing their electro­magnetic
(power system) compatibility.

SC-920 - Dry-Type Service Transformers Used in Commercial and Industrial
Facilities (k Factor Rating)

Here again, concerns about harmonic current effects have led to new
approaches in rating transformers exposed to these currents, by applying
a derating factor (\'k Factor\') reflecting the harmonic loading. These
concepts have not been fully explored and consensus on their general
applicability has not yet been reached.

Therefore, the "living document" nature of the SC criteria lends itself
well to addressing the compatibility and performance aspects of this
type of new, changing equipment. In such rapidly moving technologies,
the development of a corresponding SC document can address the need for
interim data. Availability of these documents will then give breathing
and reflection time for the development of appropriate standards and a
full consideration of the EMC issues.

# CONCLUSIONS

I The development of System Compatibility Perfor­mance Criteria was
undertaken as a contribution toward better operational compatibility at
the inter­face between end-users and electric utilities.

2\. These documents neither have nor seek the status of standards, but
they offer a shared medium to the three-partner community of end-users,
utilities, and original equipment manufacturers. This sharing of needs
and experience will improve the applications of load equipment, in
particular power electronics, until such time as voluntary or regulatory
standards can be fully developed.

3\. To that end, all three partners are invited to join in improving the
family of System Compatibility documents - a growing set of living
documents, not definitive standards - by review and constructive
comments addressed to the author of this paper.

# REFERENCES

\[1\] Martzloff, F.D., and Mendes, A., \"Standards: Transnational
aspects," Proceedings, First International Conference on Power Quality:
End-Use Applications and Perspectives, Gif-sur-Yvette, France, October
1991.

\[21 IEEE Draft P519, 1991 - Recommended Practice for Harmonic Control.

\[3\] IEC Std 555-2 - Disturbances caused by equipment connected to the
public low-voltage supply system, 1990.

\[4\] ANSI C84.1-1989 - American National Standard for Electric Power
Systems and Equipment Voltage Ratings.

\[5\] ANSI/IEEE C62.41-1991 - Recommended Practice on Surge Voltages in
Low-Voltage AC Power Systems.

\[6\] IEEE Draft P1250 - Guide on Service to Equipment Sensitive to
Momentary Voltage Disturbances.

\[7\] Draft International Standard 77(Secretariat)108: Classification of
Electromagnetic Environments, 1991.

\[8\] CENELEC prEN 50 082-2, Draft 1991 - Generic Immunity Standard.

\[9\] Key, T.S. and Sitzlar, H.E., "Utility compatibility performance
criteria for end-use equipment," Proceedings, Open Forum on Surge
Protection Application, NISTIR 4657, National Institute of Standards and
Technology, 1991.

\[10\] Maher, A.M., "Residential transient voltage surge suppression
program," Proceedings, First International Conference on Power Quality:
End-Use Applications and Perspectives, Gif-sur-Yvette, France, October
1991.

\[11\] Lai, J.S. and Martzloff, F.D., "Coordinating cascaded
surge-­protective devices," Proceedings, IEEE/IAS Annual Meeting, October
1991.

\[12\] Martzloff, F.D. and Leedy, T.F., "Selecting varistor clamping
voltage: Lower is not better!" Proceedings, Zurich EMC Symposium, 1989.

\[13\] Martzloff, F.D., "Protecting computer systems against power
transients," IEEE Spectrum, April 1990.

Characterization of Transient Voltage Surge Suppressors

**From a System Compatibility Perspective**

Raymond C. Hill Thomas S. Key

Research Center Power Electronics

Georgia Power Company Applications Center

Forest Park GA USA Knoxville TN USA

Francois D. Martzloff

National Institute of

Standards and Technology

Gaithersburg MD USA

Abstract - Transient voltage surge suppressors are characterized from
the point of view of electric utilities wishing to offer to their
customers a comprehensive surge­-protection plan. This plan involves a
surge arrester installed at the service entrance and one or more plug-in
suppressors installed within the premises, at the point of connection of
a surge-sensitive appliance. Complementary tests were conducted at two
laboratories to assess the compatibility of candidate devices with the
needs of the utilities and the end-users. Basic, fundamental tests of
protection performance and failure mode were performed for both
suppressors and arresters. Mechanical and environ­mental tests were per
formed on meter-base arresters. In addition to obtaining data on test
specimens, another outcome is the development of test protocols that can
be used for systematic and consistent testing of other candidate
devices.

BACKGROUND

The proliferation of electronics in residential power systems has
increased the need to protect sensitive electronic equipment from
damaging transient voltage surges. These surges can originate outside
the residence (lightning, power system switching) or inside (load
switching, faults). External sources are associated with greater
transient energy than internal sources. However, given the low tolerance
(immunity) of some loads, even these internal sources of surges should
not be ignored.

In answer to this need for surge protection, products have been
developed under the generic name of Transient Voltage Surge Suppressors
(TVSS). Some of these can be installed by the occupant of the premises,
typically as a plug-in device inserted between the wall receptacle and
the power cord of the equipment to be protected. Other TVSSs are
permanently-wired, typically installed at the service entrance panel or
as a modified wall receptacle. Both types have been available for some
time. Another type of service­-entrance protection has emerged, which is
incorporated into revenue-meter socket adapters. The protective socket
adapter plugs into a standard meter base, and the meter plugs into the
socket adapter.

Standards-writing groups are still in search of consensus on the names
that should be used for the different types of devices. The acronym
\'TVSS\' appears to be well entrenched in the U.S. usage to describe
devices installed on the load side of the main service disconnect (such
as in the Underwriters Laboratories Standard UL 1449) but is denied
international recognition. On the line side of the main disconnect, and
further upstream towards the utility distribution system, the term
\'secondary surge arrester\' has generally been used (although the IEEE
has not developed a definition of this term). The generic term
\'surge-protective device\' advocated by the IEEE has been condensed to
\'SPD\' in current drafts of the IEC. In this paper, we will
differentiate a plug-in suppressor from a service-entrance arrester.

Much testing has already been devoted to plug-in suppressors, but this
testing has generally been limited to a simple verification of the
protective function, without much consideration for their overall
performance in the system. There is even less information available on
the more recent service-entrance arresters. As an outgrowth of power
quality concerns, electric utilities have become interested in offering
surge protection to their customers. Currently, about 13 utilities have
launched programs of surge protection involving service-entrance
arresters as well as matching plug-in suppressors.

Such an extensive program cannot rely on simple verification of the
protective function, but requires an assessment of the overall system
compatibility. A longstanding approach to compatibility has been
developed by the engineering community of electromagnetic compatibility
(EMC), from which the surge-protection programs can benefit.

The basic EMC philosophy is expressed in the definition of EMC:
equipment should \"have a high probability to function satisfactorily in
its electromagnetic environment without introducing intolerable
disturbances to anything in that environment \[IEC International
Vocabulary 161\]. For SPDs, this philosophy can be expressed in simple
terms: Do the job of protection effectively, do survive in the process,
and do not introduce undesirable side effects.

When an electric utility provides a device for public use, it is
responsible not only for performance, but also for customer service and
safety. Hence, a device capable of operating with the high energies
available on the power system grid must be carefully chosen. The
electric utility must consider physical characteristics, mechanical and
electrical properties, and installation techniques.

On the other hand, plug-in suppressors are less exposed to high-energy
faults than the service-entrance arresters because the wiring impedance
reduces the available fault current. However, other compatibility issues
arise with these devices, such as the side effects of involving the
internal wiring of a building during the diversion of large surge
currents \[Martzloff, 1990\], or the coordination of cascaded SPDs \[Lai
& Martzloff, 1991\].

In response to these concerns, the characterization tests described in
this paper have been conducted on meter-base adapter arresters and on
plug-in suppressors. A process of interaction and iteration was involved
during the performance of the tests. First, tests were conducted
according to some preconceived test plan derived from existing industry
standards and defined in a draft test protocol. This protocol included a
list of expectations in the device performance, to be compared with the
test results. As a result of this comparison, the protocol was amended
to incorporate considerations emerging from observations made during the
tests.

SURGE-PROTECTION SCHEMES

Surge protection installed in the end-user premises can be implemented
by several approaches. The simplest would be to connect a single SPD at
the power port of selected pieces of equipment in the premises; each SPD
would be specified one at a time regardless of other equipment
protection. However, large surges originating outside the residence,
associated with lightning or major power-system events, are best
diverted at the service entrance. Surges generated within the premises
can be diverted by suppressors located close to the internal source or
close to the equipment in need of protection.

Figure 1 shows the principle of a two-stage protection scheme. The first
stage provides diversion of impinging high-energy surges through the
arrester, typically installed at the service entrance, or by a device
permanently wired at the service panel. The inductance of the premises
wiring inherently restricts the propagation of surges in branch
circuits. The second stage of voltage clamping is provided by a
suppressor of lesser surge-handling capability, which is typically
located close to the equipment in need of protection as an add-on,
plug-in device or which is incorporated within the equipment. This
second stage completes the scheme for surges of external origin as well
as for surges originating within the building.

Accordingly, different sets of surge-stress levels are applicable to the
first stage and to the second stage of the protection scheme. A
second-stage device, if provided with both a power port and a
communications port, is called a \'Surge Reference Equalizer\'. Possible
locations for the SPDs range from the secondary of the distribution
trans­former to the cord connection of equipment. Figure 2 shows the
various locations for installation of protective devices, starting at
the weather head and ending at the wall receptacles, including plug-in
TVSSs.

# ONGOING CHARACTERIZATION PROJECTS

Many organizations have recognized the need to characterize the
performance of the myriad of TVSSs offered by many manufacturers. From
time to time several trade magazines publish the results of surveys or
performance tests.

Underwriters Laboratories (UL) Standard 1449, which is the basis for UL
listing of TVSSs, plays an important part in the design of TVSS. While
the prime function of UL testing is to assess safety of products, the
case of TVSSs is different because UL considers that inadequate
performance. of a TVSS could present a safety hazard to downstream
equipment.

Now the electric utilities have taken an active role in characterizing
the performance of suppressors as well as arresters. Two complementary
programs are described in this paper, one conducted by Georgia Power,
the other by the Power Electronics Applications Center (PEAC). The PEAC
program has focused primarily on the electrical compatibility aspects.
Georgia Power has expanded the scope to include compatibility with other
environmental factors and utility concerns with service reliability,
mechanical durability, and safety.

# TEST PROGRAMS

The two characterization programs conducted by Georgia Power and by PEAC
have complementary and common elements for the service-entrance
arresters. For the plug-in suppressors, the work reported here has been
carried on by PEAC. Table I shows the principal tests conducted by the
two organizations. A noteworthy aspect of the program is that, unlike
some product evaluations conducted by consumer-oriented organizations,
the tests specimens are obtained with the full knowledge and cooperation
of the manufacturers.

This approach makes it possible to optimize the test program and, if
appropriate, suggest improvements in the design, rather than to perform
pass-fail tests without the benefit of manufacturer expertise and
involvement. Tests on undefined black boxes may appear desirable as a
generic, impartial, and uniform evaluation process. However, more useful
results can be obtained when the test takes into consideration the
expected behavior of the device.

# SERVICE-ENTRANCE ARRESTER CONCERNS

The arresters characterized in the two programs were meter-base types
because ease of installation is a primary interest to the utilities.
Meter-base extenders with built-in SPDs are the easiest for a utility to
retrofit on customer premises. The basic mechanical design of the
arresters is imposed by the application, configured as an adapter
inserted between the metter and its socket. Nevertheless, there are many
possible variations within that basic mechanical design. Likewise, the
basic protection function can be obtained through many possible
electrical designs. This degree of design freedom has two implications:
on the one band, it makes it necessary to assess the performance of
various brands, and on the other hand, it offers the opportunity to
optimize the design through the interaction between the testing
organizations and the manufacturers.

The Georgia Power Research Center and Power Quality Departments worked
together in this project Several tests were deemed necessary before any
device would be acceptable for residential use. Mechanical and
electrical tests were devised to assess performance. Specifications for
testing such a device were drawn up with reference to existing standards
and laboratory testing.

Of particular concern was an \"end-of-life\" test This test was devised
to determine the response to power-follow when a surge-suppressor
element fails in service. PEAC tests were performed by launching a
thermal runaway and observing the resulting failure of the device while
exposed to the normal line voltage. This approach met with limitations
of the duration of the available fault current in the indoor facility
(back-up breakers would trip before final clearing by the test specimen
could occur). The Georgia Power approach, on the other hand, was
conducted with less limitation on the duration of the available fault
current, but with a device first punctured by a separate, prior exposure
to a destructive level of over-voltage from a high-impedance source. The
two test methods should ultimately be revised to eliminate the current
limitation encountered at PEAC and the ambiguity of re-applying power to
a cold, pre-punctured varistor as tested by Georgia Power.

The specifications of a service-entrance arrester should include some
indication of arrester condition, ease of installation (including method
of grounding), environmental resistance, and safety. Several arresters
evaluated had neon-type indicator lamps. All lamps have a finite
lifetime, in most cases less than three years. The arresters of interest
will have a mean time before failure much greater than ten years.
Therefore, the use of indicator lamps is undesirable.

If a switch is added, then its mechanical life, water tightness,
possible physical abuse, and the extra step of having someone remember
(or care) to operate the switch and check the lamps, are all open to
question. One manufacturer has added a clear plastic window to the
bottom of the meter base extender that houses the surge-suppression
devices. When the protective fuses blow in the field or during a test,
the clear window properly clouded over. This change from clear to
clouded gives a noticeable indication of fuse operation and
corresponding failed surge-protector condition. Thus, there is an
opportunity for manufacturers to improve the concept and the design of
their indicators.

The meter-base adapters simply plug in behind the electric utility
meter. Grounding is accomplished by connecting a grounding pigtail to
the service neutral, a grounding lug or bole provided in the meter base,
or beneath a mounting screw in the meter base (the later method is still
in question). The Georgia Power Meter Department rejected any idea of
modifying the meter box to accept any of the surge-suppression devices
that had multiple pigtails to wire-in. Since the power company is not
allowed to work beyond the meter base, power distribution panel
installations at the residence were not considered. Where surges
entering the residence from the electric service are concerned, devices
located at the service entrance instead of the power-distribution panel
achieve better surge suppression.

Resistance to the environment should be considered. Susceptibility to
moisture ingress should be evaluated. Some device designs featured epoxy
encapsulation, 0-ring seals, or coating with a dry tar-ike substance.
Resistance to ultraviolet radiation is a necessity, because of the
sunlight exposure on the side of a house. Also, corrosion resistance is
a necessary test. Evaluation tests should include a \"salt-fog\" test
that will determine water tightness and corrosion resistance. The
flammability of any device should be investigated before installation in
the field.

Several mechanical properties of a service-entrance arrester must be
considered. These properties include impact resistance, thermal
withstand capabilities, and the ability of the meter-base extender jaws
to maintain sufficient pressure on the meter blades to prevent
overheating. If the meter-base extender jaws cannot maintain a low
contact resistance with the meter blades, then progressive contact
deterioration will further increase the resistance, leading to
overheating to the point that extensive damage may occur.

# GEORGIA POWER ELECTRICAL TESTS

To evaluate the electrical characteristics of the surge arresters,
Georgia Power performed four types of tests. These were: 1) nominal
varistor voltage, 2) surge withstand, 3) temporary overvoltage, and 4)
end-of-life failure mode.

# Nominal Varistor Voltage

Measurement of the nominal varistor voltage (the voltage across the
varistor with 1 mA dc flowing in the varistor) identifies the voltage
rating of the varistor used in each design. Changes in this voltage can
indicate the degradation of a device after testing. \'Ibis parameter was
measured according to the IEEE definition of varistor voltage
\[ANSI/IEEE C62.33-1982\]. By referring to varistor data tables, its was
apparent that the arrester manufacturers used devices with ratings as
low as 130 V and as high as 175 V.

# Surge Withstand

For the surge-withstand tests, two IEEE standards \[ANSI/IEEE
C62.41-1991; ANSMEEE C62.11-1987\] were consulted. ANSI/IEEE C62.41
defines the \'Combination Wave\' featuring an open-circuit voltage (OCV)
waveform of 1.2/50 μs with an inherent short-circuit current (SCI)
waveform of 8/20 us. For the \'Category C\' environment, the recommended
SCI amplitude is 10 kA. ANSI/IEEE C62.11 specifies a test of discharge
voltage at 1.5 kA and at 5 kA with an 8/20-μs wave, and a
current-withstand test of 10 kA with a 4/10-μs wave.

Two types of surge -withstand tests were performed. The first consisted
of the application of an 8/20-us current wave with increasing amplitude
until the device failed. One important unexpected event occurred during
testing of some of the devices. At some point, the clamping-voltage
level increased enough to cause internal arcing, usually on the printed
circuit board used to mount the varistors. When this occurred, the
device was considered to have failed because the power-follow available
at the service entrance would destroy the device. Available power-follow
currents at residential service entrances greater than 5 kA are
possible.

\'The second test was a multiple surge-withstand test, performed at a
level of 800 J per surge, with a modified cable fault locator
(\'thumper\'). Each arrester section was surged individually, with 120 V
ac applied before, during, and after the surge. The cable thumper was
modified to provide a Combination Wave, 13-kV OCV and 5.5-kA SCI. A
total of 100 surges at 6-s intervals was applied to the arrester. No
excessive change of nominal varistor voltage occurred.

# Temporary Overvoltage

Because of neutral and/or connector corrosion problems in the past,
which cause voltage shifts on the residential 120-V legs, the temporary
overvoltage (TOV) characteristic of the device was of importance. Tests
for TOV perform­ance were made at a point just below where thermal
runaway occurred. Although possible voltage shifts due to neutral or
connector corrosion vary in each case, the devices with the highest TOV
capability are often desirable.

The voltage step below which thermal runaway occurred was considered the
TOV capability point, provided that the device demonstrated thermal
stability for five minutes and constant standby current.

# End-of-Life Failure Mode

An \"end-of-life\" test was devised to determine the failure mode in
service. Similar to the fault current withstand test in ANSI/IEEE
C62.11, the metal oxide varistor is first punctured by overvoltage with
a lightly fused ac power supply. Then, full available fault current is
applied to the device at full rated voltage. The internal fusing of the
arrester must clear the fault without catastrophic failure of the device
or meter box housing and without phase-to-phase or phase-to-neutral
arcing. If phase-to-phase or phase-to-neutral arcing were to occur in
the field, then the high side transformer fuse would have to clear the
fault. Not only would the premises lose service power, but, because of
the long fuse curve of the high side fuse, the premises may sustain
extensive damage at the service entrance location.

The test circuit was fed by a 167-kVA distribution transformer with a
120/240-V low side. \'Ibis transformer fed a load-distribution center
with an 800-A main breaker. Wired from the main bus was a 200-A fused
disconnect equipped with two 200NLN Slow-Blow fuses. A 200-A meter box
was then wired to the fused disconnect.

For testing, the specimen arrester was then mounted in the meter socket
and the 800-A main breaker was used to energize the test specimen. The
fault current through the test specimen for this test configuration was
2.8 kA rms. A video recorder was used to record the arrester failure
mechanism, allowing a frame-by-frame postmortem of the end-of-life test.

# GEORGIA POWER MECHANICAL TESTS

# Impact Resistance

In view of the handling procedures for meter adapters, act resistance is
an important parameter. Two industry standards were consulted for test
techniques and impact force \[ASTM Std. D2444; ANSI/NEMA Std. TC
8-1978\]. Three different types of meter-adapter housings were
evaluated. One type was constructed of fiberglass materials, while the
other two were constructed of thermoplastic materials. In the tests, the
thermoplastic housing could withstand at least four times more impact
force than the fiberglass housings.

# Thermal Withstand

Two fiberglass and two types of thermoplastic meter adapter housings
were placed in an air oven and heated for two hours at temperatures of
600, 80\', 1000, and 125\'C.

At the end of each two-hour period, the devices were examined and flexed
by hand. AU but one of the thermo­plastic housings withstood the
elevated-temperature exposures without showing signs of deformation or
melting.

# Current Cycle Submersion

In the current cycle submersion test, the jaw and blade assembly samples
were inserted into meter base assemblies with double jaws. Meter blade
shorting bars were then inserted into the sample jaws. Then all the
assemblies were connected in a series loop. A computer-controlled,
constant ac current supply was used to drive current through the loop.

The samples were subjected to 50 load cycles consisting of a current-on
period of one hour and a current-off period of one-half hour. During the
current-off period, the loop was submerged in 4\'C water. At the end of
the current-off period, the loop was raised from the water and the
current applied for the next cycle. The temperature of the jaws was
measured at five-minute intervals during the current-on periods.

The contact resistance of the jaws is measured at the beginning of each
test, after every ten cycles, and at the end of each test. The jaw
temperature is also recorded with each set of resistance measurements so
that the resistance values can be corrected to 20\'C. The corrected
resistance values and jaw temperatures are used to evaluate the
performance of each jaw.

Two current levels, 200 A and 240 A, were used to evaluate the jaw and
blade assemblies. The procedure was derived from those described in UL
414 Standard, Section 15, on heating of meter jaws. The largest
application of interest is 200 A. After 50 load cycles at 200 A, the
shorting bars were extracted and then reinserted 13 times while the
meter jaws were still hot. Then, when the meter jaws were cool, the
shorting bars were extracted and reinserted another 12 times. After this
procedure, another 50 load cycles at 240 A were applied. It was found
that working the jaws as provided by the UL standard reveals some hidden
problems with some meter jaw designs.

# PEAC TEST PROGRAM

The tests at PEAC were performed on the basis of the test protocols
being developed simultaneously with the test program. At the conclusion
of the test programs reported here, two of these protocols reached
sufficient maturity to be released for comment by interested parties.
The first, identified as SC- 110, Surge-Protective Devices Used in
Low-Voltage AC Power Systems, covers all TVSSs test protocols. The
second, identified as SC-120, Surge Reference Equalizers Used in
Premises Power-Communications Systems, covers the test protocols used
for tests on the telephone port or on the cable TV port of these
devices.

PEAC TESTS ON METER-BASE ARRESTERS

PEAC tested four brands of meter-base arresters. All the brands used
metal oxide varistors (MOVS) as the surge-protective element. There were
substantial differences in the designs. The surge-protective elements
consisted of either multiple-paralleled 14-mm or [20-mm]{.underline}
radial-lead type MOVs, or single 40-mm MOV discs. The MOVs were
electrically connected by soldered or welded bonding, or by
spring-loaded contact.

The first type of design, used in two products, had the MOVs connected
between each line at the source-side of the meter and ground (Figure 3).
A second design included another MOV connected line-to-line at the
source-side of the meter. The third design used MOVs connected between
each line at the load-side of the meter and ground. The voltage ratings
of the MOVs used in the various brands included 130 V, 150 V, 250 V, and
275 V. Other significant design variations were fusing and failure
indication. Failure indication ranged from an inspection window, to
simple neon lights, to an audible alarm

# Initial Characterization Tests

The SC test protocol calls for a characterization that serves as a
baseline for assessing any change in the specimen during the test
sequence. The two principal tests in this initial characterization are a
determination of the nominal voltage (voltage at 1 mA dc) and a
verification of clamping action with a 100‑kHz Ring Wave.

# Clamping Voltage Results

Three samples of each arrester brand were surge tested with the
Combination Wave, 6-kV OCV, 5‑kA SCI. The clamping voltages for each
brand tested ranged from 420 V to 860 V for the line-to-ground surges,
and from 780 V to 1550 V for the line-to-line surges.

### **Durability Tests**

Three samples of each brand were subjected to 24 surges in each coupling
mode with the Combination Wave at 6-kV OCV, 1.25-kA SCI. The interval
between surges was sufficient to allow the samples to return to room
temperature. Two of three samples of one brand failed (short circuited
line-to-line) during the tests. All other samples withstood the
repetitive surges.

# Failure-Mode Tests

Samples of each brand were intentionally operated at a controlled
increasing voltage to initiate thermal runaway, thus causing device
failure. The line-to-ground voltage at which thermal runaway began for
the brands tested ranged from 170 to 345 V rms. Each brand was tested
with available 60-Hz short-circuit currents of 500 A, 1700 A, and 3600 A
rms. Results of the test ranged from no visible smoke, to some smoke
with sparks emitted, to heavy smoke and sustained burning.

When smaller diameter MOVs failed (short circuited), they blew apart and
cleared the circuit When larger diameter MOVs failed (short circuited),
they required the test setup overcurrent protection (not normally
present in residential ac power service entrance applications) to clear
the fault. Because of the nature of the indoor-facility test circuit,
those products with internal fuses in series with the MOVs did not blow
their fuses during any of the failure mode tests before the backup test
circuit breaker opened. Products with encapsulated (potted) MOVs tended
to prevent the failed MOVs from blowing apart sufficiently to clear the
circuit.

PEAC TESTS ON PLUG-IN TVSS

Two types of plug-in TVSSs were included in the PEAC characterization
project. The first type was the simple power-port TVSS, plug-in
construction. This device is inserted between the wall receptacle and
the power cord of an appliance. The second type was the surge reference
equalizer. This device combines into a single unit the protection of the
power port and the communications port, eliminating voltage shifts
between the reference \'grounds\' of the two ports, a recognized cause
of equipment failure.

# TESTS ON PLUG-IN POWER-PORT TVSS

Tests were conducted to determine surge clamping levels, durability,
tolerance to steady-state voltage variations, and device failure modes.
Other characteristics, such as consumer safety and packaging integrity,
that may be included in product safety listing agency test requirements
(such as UL 1449), were not evaluated as part of the tests conducted at
PEAC.

Three brands of plug-in TVSS products were tested. All used metal oxide
varistors (MOVS) as the surge-protective elements. The designs of the
products varied substantially. Figure 4 shows an example of the circuit
of a typical power-port TVSS. The products included various combinations
of single or multiple, parallel-connected 14-mm or 20-mm MOV discs.
These were connected line-to-neutral, line-to-ground, and
neutral-to-ground. Other designs included inductors and/or capacitors to
provide additional noise filtering. Some designs had two stages of MOVS,
one on the input side of the inductor, and one on the load side of the
inductor.

The voltage ratings of the MOVs used in the various brands were either
130 V or 150 V. One TVSS design used 130-V MOVs connected L-N and N-G
(Figure 4), and 150-V MOVs connected L-G. Some products contained no
fuses, while others had fuses and a circuit breaker. Failure indication
ranged from simple power-on lights to wiring diagnostics and MOV failure
detection.

Clamping Voltage Tests

Three samples of each brand were surge tested with the Combination Wave
at 6-kV OCV, 500-A SCI. The clamping voltages for each brand tested
ranged from 310 V to 400 V.

Three samples of each brand were also surge tested with the ANSI/IEEE
C62.41 100 kHz Ring Wave, 6-kV OCV, 200-A SCI. The clamping voltages
ranged from 90 V to 470 V for the line-to-neutral surges, and from 300 V
to 420 V for line-to-ground and neutral-to-ground surges. The low
line-to-neutral let-through voltages (90 V) were the result of an
additional 100-kHz filter in the product rather than MOV clamping.

Durability Test

Three samples of each brand were surge tested 24 times in each
connection mode with the Combination Wave at 6-kV OCV, 125-A SCI. All
samples withstood the repetitive surges without degradation, indicating
reasonable durability.

Failure Mode Tests

Samples of each brand were intentionally operated at a controlled
increasing voltage to initiate thermal runaway, thus causing device
failure. The voltage at which thermal runaway began for all brands was
approximately 180 V. Each brand was tested with an available
short-circuit current of 1700 A rms. Upon failure, one brand caused the
test setup branch breaker to trip. Another brand caused slight charring
of the cheesecloth wrapped around the units during the test to detect
potential fire hazard. All brands emitted some smoke when the MOV(S)
failed. Some product status lights did not indicate that the unit had
failed.

# PEAC TESTS ON SURGE REFERENCE EQUALIZERS

The objectives of these tests were to determine the electrical
performance of the communications port for a sampling of products on the
market today and to develop appropriate performance criteria. The Surge
Reference Equalizer (SRE) devices have two ports. The power port circuit
is similar to the circuit of the simple TVSS shown in Figure 4. Figure 5
shows the circuit of a telephone port SRE. Figure 6 shows the
installation of an SRE for a modem link to the telephone system.

The ac power ports of these devices were tested in accordance with the
SC-110 protocol, with typical results similar to those described in the
previous section on simple plug-in TVSSs. The communications ports were
tested, in accordance with the SC-120 protocol, to determine clamping or
let-through voltage performance, surge current handling capability, and
basic compatibility with the intended [communications]{.underline}
circuit (such as telephone wiring overcurrent protection and cable-TV
insertion loss). Other characteristics, such as consumer safety and
packaging integrity, expected to be included in product safety listing
agency tests (such as UL 1449), were not evaluated as part of the tests.

Three telephone port types and three cable TV (CATV) communications port
types of each brand were tested. A total of six 120-V single-phase
products were tested. There were substantial differences in the designs.
For telephone ports, most products used a multi-stage surge-suppression
circuit connected tip-to-ground and ring-to-ground. For the CATV port,
each product design was different. Two products had the CATV shield
solidly connected to the ac power ground; one connected the shield to
power ground through surge-protective elements. Most products relied on
a gas tube to provide CATV surge suppression. None of the products
provided any indication of the surge suppression circuit status (On/Off
or OK/Failed).

# Let-Through Voltage Tests

Samples of telephone port SREs were surge tested in each mode (Tip-Ring,
Tip-Ground, and Ring-Ground) with a surge of 10/1000 μs, 100-A and 200-A
SCI. These two test levels are based on telephone industry standards
\[ANSI/ElA/TIA 571\]. All three brands could withstand the 100-A surges,
but only one could withstand the 200-A surges. The let-through voltage
for the 100-A surges for each brand tested ranged from 230 V to 560 V.

Samples of CATV port SREs were surge tested in each available mode
(shield-center conductor, and shield-ground, if not solidly connected)
with the 100-kHz Ring Wave, 1-kV OCV, 33-A SCI. The let-through voltages
for each brand tested ranged from 60 V to 990 V for shield-to-center
conductor surges. The high let-through voltages were the result of the
turn-on delay of the gas tubes used in the products.

# Power-Cross Overvoltage Test

Each telephone port was subjected to a power cross overvoltage test,
based on industry standards \[UL 497A\], to determine the ability to
limit currents in the event of an accidental connection with power
lines. The products were subjected to two test conditions: 520-V rms
OCV, 40-A SCI for 1.5 s and 240-V rim OCV, 24-A SCI for 30 seconds.

Based on the UL 497A requirement, the products were expected to limit
the current to less than the damage level of normal telephone wiring
(simulated by a 0.6-A fuse), a safety requirement. All products failed
to limit the current sufficiently for both test conditions.

# Insertion Loss Tests

Any TVSS device inserted in the CATV circuit must not degrade the
intended signal (insertion losses) under normal operation. Additionally,
the device should not allow the intended signal to radiate
high-frequencies or allow ambient noise to interfere with the signal.
Each brand of CATV product was tested with a CATV broadcast signal and
insertion loss was measured. The products were also tested with weak
broadcast signals and weak CATV signals to evaluate qualitatively their
insertion losses. Two brands had less than I dB insertion loss while the
other brand had 3 dB insertion loss. None of the brands noticeably
degraded the observed TV reception.

# RELATED TOPICS

# Simulation Projects

The highly nonlinear response of MOVs defies intuitive circuit analysis
beyond a simple case with very few components. This situation leaves the
designer with the choice of testing with real components - ultimately,
the final test that cannot be avoided - or making a numerical
simulation. Several models for the varistor response, ranging from table
look-up to closed solutions, have been proposed by different authors. In
fact, there are so many models that citing a few presents the risk of
offending the other authors. The IEEE Surge-Protective Devices Committee
sponsors a working group devoted to the modeling of varistors.

# Low-Side Surges

Initially unexplained failures of distribution transformers had been the
subject of much research and controversy. Since the seminal paper
\[McMillen et al., 1982\], many papers have been published, resulting in
an increased awareness of the issue, now referred to as \'Low-Side
Surges\'. One of the conclusions that have been reached is that
improperly coordinated installation of SPDs at the service entrance may
be the cause of lightning-induced failures \[Dugan, 1992\].

This research led to a recommendation of providing a 480-V rated
arrester for 120/240-V service \[Marz & Mendis, 1992\]. When combined
with the concerns about excessively low clamping voltages selected for
TVSSs installed at the end of branch circuits or SPDs incorporated into
equipment, this situation leaves unanswered questions on the selection
of the appropriate voltage rating for the service entrance arrester
\[Martzloff & Lai, 1992\].

THE DEVELOPMENT OF SYSTEM COMPATIBILITY TEST PROTOCOLS

The need to assess system compatibility, as described in this paper, led
to the characterization projects involving tests focused on
compatibility concerns. This family of test protocols has the common
denominator of system compati­bility, hence their \'SC\' designations.
The SC documents will provide a uniform approach to system-compatibility
testing until the usual, slower standards development will have caught
up with the fast-changing electronic technology \[Key et al., 1992\].

Each protocol presents an introductory background, general guidelines,
and specific test guidelines. These test guidelines include a statement
of the rationale for performing the tests, define the purpose and test
procedure, and recite expected results. Three such protocols cover the
subject of TVSSs, as summarized below. Interested parties can obtain
copies from PEAC.

# SC-110: Surge-Protective Devices Used In Low-Voltage AC Power Systems

This test protocol applies to all low-voltage SPDs that may be installed
in end-user premises, as illustrated in Figure 2. In addition to the
principal tests performed by PEAC as described in this paper, this
protocol includes a number of optional tests that may be selected for
special cases. Recognition of the concerns about failure modes is an
important aspect of this test protocol.

# SC-111: Surge-Protective Devices for Meter-Base Service Entrance

This test protocol, still under development, is intended to complement
SC-110. The prime objective is to describe mechanical-environmental
tests specifically focused on the service-entrance application.
Electrical performance tests will also be included, similar to those of
SC-110, to have a single document for the meter-base arresters. Failure
mode, durability, and impact resistance, are important aspects for this
application. The menu of proposed tests under consideration includes the
following:

1\. Ultraviolet resistance - ASTM G53 - 1000 hours

2\. Salt-fog corrosion resistance - ASTM B 11 7 - 1000 hrs

3\. Flammability (self-ignition) - ASTM D1929

4\. Impact resistance - ASTM Std. D2444

5\. Thermal withstand - [\>]{.underline} 125oC for 2 hours

6\. Temperature rise - UL 414 Section 15

7\. Current cycle submersion - 50 cycles at 240 A

8\. Varistor voltage measurement

9\. Temporary overvoltage measurement

10\. Surge withstand to failure

11\. Multiple surge withstand

12\. End-of-life failure mode

**SC-120: Reference Equalizers Surge-Protective Devices for Power and
Communications Systems**

The increasing use of equipment that includes a power port and a
communications port (cable TV receivers, smart telephones, Fax machines,
desk-top publishing systems, distributed computer systems, industrial
process control systems, etc.), as shown in Figure 6, has created a new
problem in surge protection. Appropriate surge-protective devices
correctly but independently applied to each of the two ports might not
provide adequate protection against the problem of differences in the
\'ground\' reference voltages appearing at the two ports during
operation of one protective device.

The SC-120 document describes a test schedule that exercises the
protective devices of both the power port and the communications port
(telephone or cable TV), separately and in combination.

### **DISCUSSION**

There is a great variety of TVSS products on the market today; most use
MOVs as the basic surge-protective device. Within this common use of
MOVs, there is a great diversity in the selection of the voltage ratings
of the varistors incorporated by the TVSS manufacturers. One temptation
is to seek low surge clamping voltages. However, lower clamping voltages
are not necessarily better if they are accompanied by lower MOV ac rms
voltage ratings. Too low an MOV voltage rating leaves the MOV vulnerable
to high line voltage conditions and swells, increasing the likelihood of
premature failure \[Martzloff & Leedy, 1987; ANSI C84.1-1989; Davidson,
1991; Lagergren et al., 1992\].

Arresters installed on the line side of the service entrance circuit
breaker will be exposed to the available fault current in case of
failure. Typical levels of this fault current range from 3 to 10 kA rms.
It may be desirable to incorporate a fuse protection in the arrester
package to remove a failed arrester from the distribution system. Such
an arrangement raises the issue of designing a reliable indicator to
signal to the end-user that protection is lost.

The alternative would be to have the fuse in series with the service. In
that case, power to the premises would be interrupted, a situation that
may cause more complaints than a promptly recognized loss of surge
protection.

With plug-in TVSS products, unit overcurrent protection on the power
port is not mandatory if the product is designed for the rating of the
branch circuit outlet or overcurrent protection (15-A product for a 15-A
receptacle). The product, however, should be designed with fusing for
the MOVs or with other means to prevent a hazardous condition from
occurring when the MOV fails. For SRE devices, overcurrent protection on
the telephone port is a requirement for UL listing.

CONCLUSIONS

The characterization of TVSSs has provided an oppor­tunity to assess the
compatibility of these devices from the point of view of the utilities.
In the process, a set of test protocols for system compatibility has
been developed by an inter-action among SPD manufacturers, utilities,
standards-writing bodies, and, to some degree, end-users. From this, we
present several findings and calls for action:

1\. There is a wide range of products available for surge protection,
but all are not equal. A comprehensive product evaluation program would
be necessary to provide complete information. Work is beginning in that
direction, with the support of an increasing number of utilities.

2\. Test protocols are now available, enabling interested parties to
conduct or sponsor tests on an objective and consistent basis.

3\. SPD manufacturers still have an opportunity to improve their
products for greater compatibility. For instance, some designs were
found to leave unanswered questions on the reliability of failure
indication or fusing for protection against large fault currents.

4\. Individual end-users have little leverage to influence the process
of improving compatibility of products. However, the increasing interest
of utilities in providing surge protection to their customers will
increase this leverage above the critical mass.

5\. By making available a process whereby products can be tested and the
results communicated to the manufacturers, new possibilities are opened
for a cooperative mood that will result in improved products to the
satisfaction of all interested parties.

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ANSL?EIA/TIA-571-1991 - Environmental Considerations for Telephone
Terminals.

ANSI/IEEE C62.11-1987 - IEEE Standard for Metal-Oxide Surge Arresters
for AC Power Circuits.

ANSI/IEEE C62.33-1982 - Standard Test Specifications for Varistor
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ANSI/IEEE C62.41-1991 - Recommended Practice on Surge Voltages in
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ANSI/IEEE Std. TC 8-1978, Extra-Strength PVC Plastic Utilities Duct for
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IEC Pub 50(161) - International Electrotechnical Vocabulary

\- Chapter 161: Electromagnetic Compatibility, 1990. Dugan, R.C. -
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Distribution Transformers to Low-Voltage Side Lightning Surge Failure.
IEEE Transactions PAS-101, No. 9, Sept. 1982, pp 3457-3470.

UL 414 - Standard for Meter Sockets, fourth edition.

UL 497A - Standard for Safety - Secondary Protectors for Communications
Circuits. 1990

UL 1449 - Standard for Safety - Transient Voltage Surge Suppressors.
1985

**AN IMPORTANT LINK IN WHOLE-HOUSE PROTECTION:**

**SURGE REFERENCE EQUALIZERS**

+----------------------------------------+-----------------------------+
| François D. Martzloff                  | Marek Samotyj               |
|                                        |                             |
| National Institute of Standards and    | Electric Power Research     |
| Technology                             | Institute                   |
+----------------------------------------+-----------------------------+

**Abstract** - The increasing use of electronics in residential
applications has been paralleled by a realization that surge protection
may be necessary for this type of equipment Installing a
surge-protective device on the power-line port as well as on the
communications-line port of an equipment might appear sufficient to
ensure this protection. However, the normal operation of one of the
protective devices during a surge event can create differences in the
voltages of the references of the two ports. This difference in
voltages, applied across the equipment or across a communication link
between two pieces of equipment, can result in permanent damage as well
as upset. Equalizing these voltages can be achieved by proper routing of
the two lines through a single device, called Surge Reference Equalizer,
and thus avoid the risk of damage.

# The Problem

A new generation of smart electronics has emerged that involve
processing information obtained from communication networks: fax and
telephone answering machines connected to the telephone system,
television sets connected to a cable system, desk-top publishing systems
connecting several computers and printers, industrial process controls
with remote sensors and terminals, etc. This type of equipment generally
requires a metallic connection to the communications system, while being
powered through a connection to the local power system. This dual
connection introduces a risk of interference or damage to the equipment
because, during surge events, the two systems can have differences in
the voltage of the two systems reference points.

In the consumer world, damage is the greatest concern, upset may be
tolerable; in the commercial and industrial world, upset and its
consequences are already unacceptable. Understanding the topology of the
equipment and of its connections to the power and communications
networks, as well as the mode of propagation of surges in the two
systems, will help in defining appropriate solutions and avoiding
counter­productive situations.

A useful concept is to envision the relationship of any electrical
equipment to its electromagnetic environment by means of several
'ports\'. According to this concept, 'port\' means a point of access
where energy may be supplied or withdrawn. In the most general case, six
types of ports can be identified, as shown in Figure 1. The desirable
signals (including power) as well as undesirable signals can enter or
leave the equipment through these ports. Five of them involve metallic
connections, that is, cables (with the exception of fiber optics links).
The sixth is electro­magnetic coupling through the equipment enclosure,
directly into or out of the equipment inner circuits.

The general case of Figure 1 shows a separate 'earth port\'. In typical
situations, this port can be a distinct, direct connection to the local
grounding system, or it can be included in the connection of the other
ports, such as the equipment grounding conductor of the power line or
the shield of the cable TV connection. In computer-based systems, signal
cables usually include a 'signal reference\' conductor which is
connected to the equipment chassis and, therefore, ultimately to the
equipment grounding conductor of the power cord. Typical smart
electronics equipment have at least two ports, the ac power port and a
communications port.

In one scenario, a reasonably well-informed end-user might have provided
surge protection on both the power port and the communications port, yet
the equipment could be damaged by a difference in the reference voltages
developed during a surge event.

Figure 2 shows such an arrangement, where the telephone port of the Fax
machine is assumed by the end-user to be protected, thanks to the
Network Interface Device (NID) installed by the telephone company, and
the power port is also expected to be protected by the plug-in
surge-protective device installed by the surge-­conscious end-user. Such
a plug-in device is often called Transient Voltage Surge Suppressor,
TVSS for short in the U.S., but is now recognized by the acronym SPD by
the International Electrotechnical Commission.

If a surge impinges upon the building at the power or the telephone
port, the expected operation of the protective devices will divert the
surge current to ground ('protective earth\' in European terminology).
The voltage drop caused by the fast-changing surge current flowing in
the inductive ground connection of the protective device leaves the line
connection of the surge-carrying system at a voltage higher than that of
the system unaffected by the surge. A difference of voltage appears
across the two equipment ports during the surge event, in particular
during the rise time. This difference of voltage can cause an upset or
hard failure if the equipment has not been specifically designed for
that stress. Thus, separate, uncoordinated protection of each of the two
ports can still leave the equipment at risk.

Another scenario involves the voltage difference between the two chassis
(and thus the signal reference) of sub-units powered from different
branch circuits, as shown in Figure 3. In this scenario, a built-in SPD
or EM! filter has. been provided in each sub-unit by a prudent
manufacturer. The normal operation of the SPD or EMI filter during a
surge event causes a voltage drop in the conductor that returns the
surge towards the service entrance. Meanwhile, the chassis of the other
sub-unit, unaffected by the surge, remains at the voltage of the service
entrance reference. The result is that the two chassis assume different
transient voltages, and the data link reference conductor connected to
these two chassis will attempt to equalize the voltages, with possible
upsetting or damaging consequences to components in the line driver or
receiver circuits of the two sub-units.

The radical, well-known solution for this type of problem is to provide
a fiber optic communications link rather than a metallic connection.
This solution is frequently applied to solve problems in utilities,
industrial or commercial installations, but its relative complication
and present cost have kept it impractical for residential, consumer-type
applications. In .such cases, another solution is a Surge Reference
Equalizer. The generic name of this device has been introduced by a new
IEEE standard \[IEEE 1100\], giving recognition to a concept that has
emerged over the last several years.

The surge reference equalizer combines the protective function for both
system ports in the same enclosure. The device is plugged in the power
receptacle near the equipment to be protected, with the communications
system wires (telephone or data link) or the coaxial cable (\'IV) routed
through the enclosure. A common, single grounding connection equalizes
the voltages of the two paths that return the surge through the
grounding connection of the 3-prong power line plug, as shown in Figure
4.

Such a solution is particularly attractive as an element of 'whole-house
protection\' , a concept that has been recently introduced by some
electric utilities. In the whole-house protection scheme, some utilities
now offer an engineered, coordinated installation of SPDs to their
customers \[Maher, 1991\], instead of the do-it-yourself approach that
can lead to the situation illustrated by Figure 2. Several locations can
be considered for connecting these SPDs, as shown by the numbered SPD
locations in Figure 5. In the whole-house protection scheme, a two-step
approach is used: an SPD is installed by the utility at the service
entrance (location 2), and plug-in SPDs are supplied by the utility to
the consumer for insertion on the input ports to sensitive equipment
within the residence (location 6).

The objective of the two-step protection scheme is to divert most of the
impinging surge energy at the service entrance, and to complete the
protection at the point of use by a plug-in SPD. This second device can
then serve as surge reference equalizer, rather than serve only as a
TVSS on the power port.

Surge reference equalizers are now found in electronics and computer
stores, although neither the name nor the design have been standardized.
The intended function can be immediately recognized by the presence on
the enclosure of a power route - a male plug and one or more female
receptacles - and a communi­cations route - cable TV coax fittings,
telephone jacks, or RS232 connectors. Until the voluntary standards
process has fostered uniform characteristics *\[2004 note: 11 years
passed, still no standard\]*, the performance of these devices can vary
from one brand to another, although one could expect each manufacturer
to have made reasonable assumptions and tradeoffs in the design of the
product. An alert consumer who is considering on his own the purchase of
such a surge reference equalizer has no information on the performance
or side-effects of what the store-bought device offers. An engineered
scheme offered by the utilities can provide the leverage to obtain
devices with demonstrated performance.

**SYSTEM-COMPATIBILITY CRITERIA**

The rapid development and marketing of these surge reference equalizers
has left the process of voluntary standards development behind. At this
point, there is no available standard to assess the performance and
compatibility of these devices. For instance, the immunity level of the
input UHF circuitry of a TV receiver or recorder is not specified by
industry standards, leaving the designers of surge reference equalizers
in the dark as to what level of surge suppression they should provide in
their devices.

Fueled by the desire of electric utilities to provide enhanced power
quality .to their customers by supplying appropriate SPDs, the response
of EPRI has been to sponsor the development of test protocols for
assessing the system compatibility of these devices. The approach
consists in performing tests on devices proposed for installation in the
residential environment in accordance with a set of consistent and
objective criteria taking into consideration the surge environment, the
needs for protection of consumer electronics, and the need of the
electric utility for compatibility with its power delivery system.

In fact, the concept of providing test protocols for assessing
compatibility of equipment extends far beyond the specialized domain of
the surge reference equalizers discussed in the present paper. The Power
Electronic Applications Center (PEAC), sponsored by EPRI, is currently
developing a family of test protocols for equipment such as fluorescent
ballasts, adjustable speed drives, enhanced computer power supplies,
etc.

# TESTING FOR SYSTEM COMPATIBILITY

Tests for system compatibility of several surge reference equalizers
were performed at PEAC on devices proposed for a "Whole-House"
protection plan by an electric utility. The following brief review of
the test results illustrates the benefit of the program in identifying
adequate performance as well as needs for improvements in the
performance.

The tests were performed in accordance with the test protocol
\[SC-120\]. These tests include a determination of the clamping voltage
on both power and communications ports, an assessment of durability, and
checking for side effects. A unique aspect of the SC test protocols is
that while expected results are stated, the tests results are not
presented as pass/fail, but rather as a comparison between expectations
and results, leaving room for the sponsor to make a decision based on
the overall performance.

Two sets of candidate surge reference equalizers were tested at PEAC.
One set featured power port and telephone port protection, the other
power port and cable TV protection. For telephone-port devices, the
various designs were based on a multi-stage circuit connected between
each of the two conductors of the telephone cable and ground. For TV
-port devices, different design principles were apparent among the
manufacturers. Some had a solid connection between the shield of the TV
signal cable, others had this connection made through a
surge-suppressing component; all had a gas tube for protection between
the center conductor and the shield of the coaxial cable.

For the telephone ports, industry standards \[ANSI/EIA/TIA 571\], used
as the basis for the SC-120 protocol, specify a surge-handling
capability of 100 A and 200 A with a 10/1000 μs waveform. All devices
could discharge the 100 A surge, but only one could discharge the 200 A
without damage. The let-through voltages ranged from 230 V to 560 V,
levels that are compatible with immunity levels of typical telephone
equipment.

A regulatory requirement for telephone protectors is that in the event
of a power-cross (injection of power-frequency voltage on the telephone
wiring), the resulting power-frequency current must be limited or
interrupted before the telephone wiring in the residence overheats
dangerously. Surprisingly, this requirement was not satisfied. At this
point, the concept of system­ compatibility testing provides an avenue
for remedy rather than rejection: the tests are conducted with the
knowledge of .the manufacturers and deficiencies in performance can be
corrected by the manufacturer before they become an issue leading to
outright rejection of an otherwise attractive product.

The immunity levels of cable \'IV ports are not characterized by
published industry standards, and thus it is difficult to define
performance expectations for the devices intended to protect these
ports. The PEAC tests were performed to determine the clamping level
with an impinging surge of 1 kV peak, ringing at 100 kHz, and 33 A peak
available short circuit. The let-trough voltages ranged from 50 V to
1000 V, leaving open the question of adequate protection. Efforts will
be continued in obtaining the cooperation of the electronics industry in
defining the immunity levels of the TV port.

Functional and regulatory requirements for a TV-port device include
freedom from signal leakage and degradation through insertion loss or
interference. All devices were found satisfactory in this regard.

**Additional Remedies**

The problem of threatening voltage differences created along the return
path of a surge diverted at the end of a branch circuit can also be
reduced by other means. High-current surges on the power system
originating outside of the user\'s premises, associated with lightning
or major power-system events, are best diverted at the service entrance
of the premises. While such a protection is not mandated at present,
trends indicate growing interest in this type of surge protection.
Either the utility or the end-user may provide a high­-energy surge
arrester at the service entrance.

In such a scheme, external surges are diverted at the service entrance
and no longer flow in the building in search of a small protective
device installed at the end of a branch circuit. There are still surges
generated within the premises, but these have lower current levels and
can be diverted by protective devices located close to the internal
surge source or close to the sensitive equipment, for instance by the
surge reference equalizers. This possibility of dual protection raises
the issue of coordination of cascaded devices, an emerging concern in
the application of SPDs in the power system of end-user facilities \[Lai
& Martzloff, 1991\]. The clamping voltages of the service entrance
arrester and of the surge reference equalizer must be coordinated so
that the low-energy surge reference equalizer will not attempt to divert
large surges that the high-energy surge arrester is expected to
intercept.

**Conclusions**

The rapid expansion of smart electronics involving power and
communications connections creates the potential for disappointing
performance under surge conditions if adequate, coordinated protection
is not provided. Separate, uncoordinated surge protection of each of the
two ports still leaves the possibility of damage or upset.

A new type of device, the "Surge Reference Equalizer", offers a solution
to the problem, provided that the performance characteristics of the
device will be coordinated with the environmental stress and with other
surge-protective devices that may be installed on the systems.

System-compatibility tests performed on several proposed surge reference
equalizers show that their performance characteristics vary from
adequate to questionable (even unacceptable when regulatory safety
requirements were not satisfied). However, as a result of the basic
concept of the test program, these deficiencies in performance can be
recognized in time and corrective action taken before the devices are
broadly applied. In this manner, both the consumer and the electric
utility can be .confident in their expectation of effective protection
of the residential electronics.

**References**

ANSI/EIA/TIA 571-1991, Environmental Considerations for Telephone
Terminals, 1991.

IEEE Std 1100-1992, Recommended Practice for Powering and Grounding
Sensitive Equipment, 1992.

Lai, J.S. & Martzloff\' F.D., Coordinating Cascaded Surge-Protective
Devices, Proceedings, IEEE/IAS Annual Meeting, 1991.

Maher, M., Residential Transient Voltage Surge Suppression Program,
Proceedings, PQA 91, First International Conference On Power Quality,
1991.

SC-120, Test Protocol for System Compatibility of Surge Reference
Equalizers Used in Premises Power-Communication Systems, Power
Electronics Applications Center, Knoxville TN. Draft, 1992.

**Consumer Power Quality Problems:**

**Troubleshooting by Telephone**

PROJECT 99-05

Prepared by

National Rural Electric

Cooperative Association

Cooperative Research Network

4301 Wilson Boulevard

Arlington, Virginia 22203-1 860

and

Francois D. Martzloff

National Institute of Standards and Technology

100 Bureau Drive

Gaithersburg, Maryland 20899

CRN

COOPERATIVE RESEARCH NETWORK

> [www.crnweb.org](http://www.crnweb.org/)

The National Rural Electric Cooperative Association (NRECA) is the
national service organization of more than 900 rural electric systems.
These cooperatively owned utilities own and operate about 44% of the
miles of distribution lines in the nation to provide power to less than
10% of the The National Rural Electric Cooperative Association (NRECA)
is the national service nation\'s people, primarily in the sparsely
populated, rural areas of 46 states.

NRECA was founded in 1942 to unite rural electric systems in a way that
would permit them to develop the services and support needed to properly
serve rural America. NRECA is on of the largest, rural-oriented
cooperative organizations in the United States.

The Cooperative Research Network, a service of NRECA that was used to
support this project, was created to conduct studies and carry out
research of special interest to rural electric systems and their
consumers.

> **CONTENTS**
>
> Foreword ix
>
> Executive Summary xi
>
> Section 1 Disturbances and Remedies 1
>
> Introduction 1
>
> The Nature of Disturbances 2
>
> Too Much Voltage 2
>
> Not Enough Voltage 12
>
> Other Power-Line Disturbances 16
>
> System Interactions 18
>
> Section 2 Questions to Ask 23
>
> Customer-Owned Offenders 23
>
> How to Use the Worksheets 24
>
> Identifying Residential and Commercial Appliance Categories 24
>
> Worksheet EDE: Electronic, dual, external 29
>
> Worksheet EDI: Electronic, dual, internal 30
>
> Worksheet ES: Electronic, simple 31
>
> Worksheet HE: Heat, electronic 32
>
> Worksheet HM: Heat, mechanical 33
>
> Worksheet ME: Motor, electronic 34
>
> Worksheet MM: Motor, mechanical 35
>
> Worksheet PLC: Power line conditioning 36
>
> ILLUSTRATIONS
>
> FIGURE PAGE
>
> 1.1 Sine wave of an AC voltage supply. 2
>
> 1.2 A surge induced by lightning on an AC voltage. 3
>
> 1.3: Typical voltage on a distribution bus during capacitor bank
> energizing. 4
>
> 1.4: Example of a customer\'s bus voltage during utility capacitor
> switching. 5
>
> 1.5 A lamp and a rabbit-ear TV are examples of single-port appliances.
> 6
>
> A computer with a telephone modem connection is an example\
> of a two-port appliance. An ordinary house offers many examples\
> of both single-port and multiple-port appliances.
>
> 1.6 A typical TVSS with power and telephone protection. 7
>
> 1.7 A meter-base arrester installed by the utility. 7
>
> 1.8 Relative energy deposited in the suppressor by a typical
> high-energy 9
>
> surge for various combinations of 250-volt (H), 150-volt (M), and\
> 130-volt (L) ratings, as a function of separation distance.\
> 1.9 Division of surge current in a cascade of two 150-volt devices: 11
> 9
>
> is the current in a 40-mm-diameter arrester and 1, is the current in\
> a 20-mm-diameter suppressor, with 10-meter separation for the\
> same 3000-ampere surge as in Figure 1.8.
>
> 1.10 A voltage swell lasting eight cycles. 10
>
> 1.11 Unequal line voltages caused by an open neutral. 11
>
> 1.12 A very brief outage (top) and a very long outage (bottom). 13
>
> 1.13 A sag lasting 10 cycles with the line voltage reduced to 55% of
> normal. 13
>
> 1.14 The original CBEMA curve (top) and the updated ITIC curve
> (bottom). 15
>
> 1.15 Noise superimposed on an AC voltage. 16
>
> 1.16 An AC voltage distorted by harmonics. 16
>
> 1.17 Commutation notches on an AC voltage. 17
>
> 1.18 Power and telephone services enter the house at opposite ends. 18
>
> A personal computer is connected across the two systems.\
> 1.19 Voltage and current recorded with telephone and power services 19
>
> entering at opposite ends of the house.\
> 1.20 Mitigation obtained by inserting a surge reference equalizer in
> 19
>
> both the power line and the telephone line.\
> 1.21 Shifting reference potential can be remedied by inserting a surge
> 21
>
> reference equalizer on the communications and power lines (here,
>
> the appliance is a TV and the communications line is a TV cable,\
> but a PC with a telephone modem connection presents the same\
> problem). In the ideal situation, the communications and power lines\
> enter the house on the same side, and the SRE is most effective.
>
> TABLE PAGE
>
> 2.1 Home-Based Disturbances, Causes, and Remedies 23
>
> 2.2 Categories of Equipment Victims 25

**FOREWORD**

Customer service representatives have a tough task when they have to
respond to calls from consumers who are having problems with an
appliance. \"My television won\'t work. What\'s wrong?\" \"My computer
lost its memory. What did the co-op do to cause this?\" Complaints may
be couched in vague terms, and the caller may tend to blame the electric
cooperative.

This manual was commissioned by the Cooperative Research Network to
address these kinds of complaints. Written with the help of an expert in
household and small-business electricity problems, it provides a series
of worksheets that guide representatives through a question-and-answer
session with a caller, leading the caller from the general to the
specific with the goal of finding the exact source of the problem (which
often is not attributable to the cooperative).

Service representatives can use the work-sheets in conjunction with the
manual's simple explanations of the nature of disturbances and how to
prevent or cure their effects to diagnose specific problems. On the
basis of the diagnosis, the representative can tell the consumer what to
do or can call in the cooperative\'s repair service to handle the
problem. if the cause of a particular problem proves elusive, the
representative can refer it to a specialist.

The manual should help representatives work more effectively and
efficiently. It should help cooperatives avoid unnecessary service
calls. And it should help consumers get quick solutions to their
problems, whether utility-related or not.

> Martin E. Gordon, P.E.
>
> Senior Program Manager
>
> Cooperative Research Network

**EXECUTIVE SUMMARY**

When an electricity consumer has a problem with an appliance\--a light
bulb that flickers, a television that \"burns out,\" a motor that
overheats, for example-a natural tendency is to complain to the electric
utility, in actuality, many such problems are not the fault of the
electric utility, and indeed may be beyond the control of the electric
utility.

How does an electric cooperative, with limited customer-service
resources, handle such complaints? How can it efficiently separate
problems that it can fix from those that are beyond its control, and
perhaps recommend cures or preventive measures to consumers for the
latter problems? This manual suggests a way: It provides worksheets for
customer service representatives to guide them through a dialogue with a
customer calling for help. By following the guidance, a representative
can ask the right questions, get at the root of a problem, and then
decide on an appropriate action: send a repair crew, tell the customer
how to fix the problem, or, for a problem that resists immediate
solution, call in an expert in the field.

> The manual is organized in two parts:
>
> Part 1 reviews the nature of disturbances that can occur in the power
> supply to customers-disturbances such as voltage surges, lightning
> strokes, voltage swells, outages, brownouts, voltage sags, noise,
> harmonics, unbalanced phases, and interaction between the power system
> and a telephone or cable TV system. A customer service representative
> can learn in this part how the disturbances originate, how they affect
> electrical equipment, and what can be done about them.
>
> Part 2 helps the customer service representa­tive troubleshoot over the
> telephone. It contains worksheets, eiGht in all, covering the major
> categories of equipment-heaters, motors, and electronics of various
> types. Each worksheet is a blueprint for a question-and -answer
> session with a customer, designed to arrive at the cause of the
> customer\'s problem and a possible cure. By applying the simple theory
> in Part I and following the step-by-step instructions, the
> representative should be able to diagnose many problems and decide
> whether intervention by the coopera-tive is warranted.

The manual stresses a crucial fact: that problems with equipment
connected to both an electric power system and a communication
system-televisions with cable connections or personal computers with
modem hookups, for example-can be caused by either system. Such problems
are compounded when the two services enter at opposite ends of the
building., physical separation of the entry point magnifies the
disturbances. Such disturbances should never be blindly attributed to
\"power line surges\"-, often the communication link can be at fault,
especially when it is improperly installed, as sometimes happens with
cable connections.

Scattered throughout Part I are short case histories drawn from ordinary
experiences-a chandelier that inexplicably flickers, motor controllers
that shut down when the electric utility adjusts its power factor. With
such experiences and simple electrical theory as background, customer
service representatives should be able to analyze many of the problems
posed by disturbances and find a solution for the consumer, or know when
to call in expert help.

# 1 DISTURBANCES AND REMEDIES

In This Section: Introduction; the nature of disturbances; too much
voltage; not enough voltage; other power-line disturbances; system
interactions

## Introduction

Many people believe that upsets or damage to electrical equipment can be
blamed on disturbances caused by the power distribution system or by
lightning. However, such a belief is an incorrect generalization; many
times the problem is in the equipment itself, not the power system. This
manual can help cooperatives\' customer service representatives
distinguish between equipment-related and system-related problems, and
either suggest a solution the customer or alert the dispatcher that the
cooperative\'s assistance is needed. The manual presents in simple terms
the principles underlying unwanted upsets and damage and offers remedies
for them.

This first part of the manual gives an overview of the disturbances that
can occur in the power supply to the customer. It briefly describes the
origins of the disturbances and explains which disturbances are
avoidable, which are unavoidable, which are predictable, and which are
entirely random occurrences. The first part is organized in four
sections. The first two are concerned with the most frequent but brief
disturbances-too much or not enough voltage (energy). The third section
addresses less frequent disturbances that are almost permanent, such as
noise, harmonics, notches, and voltage unbalance. The fourth and last
section describes the possible interaction between the power system and
a communications system, which is believed to be the cause of many
failures that are often misinterpreted as caused by a \"power line
surge.\"

The second part of the manual is formatted as a collection of worksheets
that suggest interactions between the customer service representative
and the customer reporting a problem.

An important fact is that upset or damage to equipment that involves a
communications system can also be caused by disturbances on the
communications system and should not blindly be attributed to \"power
line surges.\" Ways to prevent this kind of upset or damage do exist,
but some are beyond the control of the customer and the distributing
utility. It is a matter of recognizing the situation and selecting a
technically correct and cost-effective remedy. There may be cases where
the risk or consequences of such damage or upset might be low, compared
to the cost of prevention. Therefore, the choice of protecting or not
protecting should be made thoughtfully, not left to neglect or
ignorance. Armed with this knowledge, customer service representatives
as well as customers will be guided toward a satisfactory resolution.

### The Nature of Disturbances

Electric power is delivered to customers in the form of an
alternating-current (AC) voltage

that the utility strives to keep as constant as possible (Figure 1.1).
However, disturbances can and

will occur in this voltage, in the form of either too much or not
enough. In turn, the energy

consumed by the load-what the utility sells-is related to the voltage at
which it is delivered.

The AC voltage follows a sinusoidal pattern, with a complete cycle
occurring 60 times per

second\--engineers call that a 60-hertz (Hz) AC voltage. This smooth
waveform can be distorted

under steady-state conditions, or have a transient overvoltage or
undervoltage.

Some disturbances are brief\--from millionths of a second (microseconds)
to thousandths

of a second (milliseconds). Other disturbances can be long, lasting from
seconds to hours in the

worst cases of service interruption.

### Too Much Voltage

Too much voltage can be the result of a normal or abnormal utility
operation, or the effect of an external influence. Under normal
operating conditions, the steady-state voltage is controlled by the
utility within a narrow band. Deviations from this band are rare, and
the utility can readily correct them, if informed of their occurrence,
by acting on voltage regulators and tap changers.

On the other hand, there are momentary (transient) disturbances that
occur under the typical operating conditions of a power system. There
are two types of transient excessive voltage that can occur under normal
circumstances, although by themselves they would be described as
\"abnormal\":

> 1\. A surge is an overvoltage that can reach thousands of volts,
> lasting less than one cycle of the power frequency, that is, less than
> 16 milliseconds.
>
> 2\. A swell is longer, up to a few seconds, but does not exceed about
> twice the normal line voltage.

A third type of excessive voltage, a temporary overvoltage, is not a
part of normal operation, but is associated with a fault in the power
system. Temporary overvoltages can last a much longer time, and
generally do not disappear until the fault is cleared.

### SURGES

**Types and Origins of Surges**

Surges have been blamed as the cause of equipment upsets or damage under
many names: power surges, spikes, glitches, impulses, and so forth. In
this report, the term surge is used, with the understanding that it
means events lasting less than one cycle of the power frequency.

> The two major causes of surges are

· Lightning\--an obvious and well recognized event (Figure 1.2)

· Load switching\--a type of event that includes major power system
operations as well as simple and seemingly benign switching by the
customer Next to outages, surges are the type of disturbance most
frequently perceived by customers as the source of their problems, and
therefore merit a detailed examination.

***Lightning Surges.*** There are four types of lightning surges,
described here in order of severity. The first, rare but traumatic, is a
direct lightning stroke to the building. Unless special protection
systems have been provided (lightning rods in plain language, air
terminals in protection jargon) with proper down-conductors and
grounding, damage to the structure and equipment can be substantial. Of
course, such an event cannot be blamed on the utility. Few residential
customers go to the expense of installing a lightning protection system.
Instead, they make an intuitive risk analysis: A typical lightning
protection system can cost thousands of dollars, while the probability
of a direct stroke (outside of known areas of high lightning activity)
is about once every 200 years for a detached home.

The second type of lightning surge occurs when a nearby stroke, and the
resulting flow of current in the earth, elevates the potential of the
ground references of the building, including the power system neutral
that is bonded to ground at the service entrance. This situation is
called ground potential rise. Meanwhile, the power supply phase
conductors, which are referred to ground through the secondary winding
of the distant distribution transformer (whose neutral is grounded
there) remain essentially at the ground potential of that distant
transformer. A large difference of potential can then occur between the
neutral and the phase conductors at the service entrance of the
building. That difference of potential appears to be a surge delivered
by the, utility connection, but has nothing to do with the utility
operations.

The third type of lightning surge is produced by the radiation of
electromagnetic fields associated with a lightning strike at some
distance from the building. Such a surge involves low energy but can
still produce upsets and even damage in sensitive electronic circuits.
The severity of these surges depends mostly on distance. Nearby strikes
are rare but may have severe effects, distant strikes are more frequent
(increasing with the area of collection, that is, with the square of the
distance) but less severe. Again, these surges cannot be blamed on the
utility, but some customers might believe that they came from the
utility connection and attempt to place the responsibility on the
utility.

The fourth and last type of lightning surge is one that actually arrives
on the service drop of the utility, as a result of a direct stroke to
some element of the distribution system. A surge induced in the utility
distribution circuits by a nearby stroke, just like the third type
discussed above, can also appear at the service entrance. In contrast to
the first three types, this fourth type is truly an excessive voltage
delivered by the utility to customers. However, the general practice
among utilities is to provide surge arresters on their systems, so that
the residual surge that can appear at a customer\'s service entrance is
somewhat limited. The rare exception would be a direct stroke to the
pole or service drop, where the utility surge arrester would not
intervene before a surge heads for the service entrance.

***Switching Surges.*** There are two types of switching surges:

\- Those that result from normal switching of a load on or off by a
customer or the utility

\- Those that are incidental to an intended operation aimed at clearing
a fault-a short circuit or severe overload.

Switching Surges from Normal Operations. The first type of switching
surge (\"normal\" surge) occurs whenever a load-any type of load-is
being switched, either within the distribution system or within the
customer\'s installation. Therefore, these can occur quite frequently.
Those associated with the switching of a local load, especially if it is
an inductive load such as a motor, are generally short (a few
microseconds) and do not involve a large amount of energy. However,
there is another source of potentially large switching surges when
capacitor banks are switched for power-factor correction. These can
occur at random if the power-factor correction bank is controlled by the
instantaneous state of the system, or they can occur at fixed times in
the day if the capacitor bank is switched on and off by a timer.
Capacitor switching surges from the utility have been found troublesome
in installations where the customer also has some power-factor
correction capacitors: Magnification of the surges can occur. (See box,
\"Capacitor Switching Surges.\")

**Capacitor Switching Surges**

Capacitor banks have long been accepted as a necessary part of efficient
electric power systems. Switching capacitor banks on and off is
generally considered a normal operation for a utility system, and the
transients associated with switching are generally not a problem for
utility equipment. The low-frequency transients, however. can be
magnified in a customer\'s facility (if the customer has low-voltage
power-factor correction capacitors) or result in the nuisance tripping
of power-electronic devices such as adjustable-speed drives. Actually,
capacitor energizing is just one of the many, switching events that can
cause transients on a utility system, but, because of their regularity
and impact on power system equipment, they quite often receive special
attention.

There are a number of transient-related concerns that are generally
evaluated when distribution shunt capacitor banks are applied to a power
system. However, these considerations are related to the system design
rather than its operation, and the customer has no control over them.
Remedies will essentially be to learn how to live with these unavoidable
transients. When they originate from the switching of a large capacitor
bank, it is unrealistic to expect that the typical surge suppressor has
the energy-handling capability to absorb them.

**Characteristics of Energizing an Isolated Capacitor Bank.**

Energizing a capacitor bank results in an immediate drop in system
voltage toward zero, followed by an oscillating transient voltage
superimposed on the fundamental power frequency waveform. The peak
voltage magnitude depends on the instantaneous system voltage at the
instant of energization, and can rise to 2 times the normal system
voltage under worst-case conditions.

Ordinarily, though, other components of the system help to keep the
voltage rise to 1.2 to 1.8 times the normal value, and the transient
oscillates at frequencies from 300 to 1,000,000 Hz. Figure 1.3 shows an
example, recorded in the field, of a transient created by energizing a
capacitor bank.

Transient overvoltages caused by capacitor switching are generally not a
problem for utilities because their peak magnitudes are usually just
below the level at which surge protective devices (SPDS) begin to
operate. However, these transients will often be coupled through
step-down transformers to customer loads (Figure 1.4). where they can
affect power-quality-sensitive customer equipment, such -as computers.

If the customer uses capacitors for- the correction of power factor on
the low-voltage side, higher transient overvoltages can rise even
higher. This effect---"voltage magnification\"\--occurs when a transient
oscillation, initiated by the energization of a utility capacitor bank,
excites a resonant circuit in the low-voltage system (the circuit is a
combination of the inductance of the step-down transformer and the
capacitance of the customer\'s power-factor correction bank). The result
is a higher overvoltage at the lower voltage bus. The worst
magnification occurs when the following conditions exist:

The size of the utility\'s switched capacitor bank is more thin 10 times
larger than the customer\'s customer bank.

The frequency- of the energizing oscillation is close to the resonant
frequency of the circuit formed by the step-down transformer and the
customer's power-factor correction capacitor bank.

The customer\'s load has relatively little resistance (this is typical
of industrial plants where motors represent the major part of the load).

Ordinarily, these transient switching overvoltages might simply damage
low-energy surge-protective devices or cause a nuisance trip of
power-electronic equipment. Nevertheless, incidents have been reported
of complete failure of end-user equipment.

## Switching Surges from Fault-Clearing

The second type of switching surge, far less frequent, occurs when a
system fault is cleared, either by the opening of a circuit breaker or
the operation of a fuse. The latter can generate high surges if the fuse
is located at the end of a long cable, in which the fault current can
store substantial energy in the cable inductance.

The magnitude of these fault-clearing surges can reach several times the
normal system voltage, and their duration ranges from hundreds of
microseconds to a few milliseconds.

**Effect of Surges on Equipment**

**Upset versus Damage**

Surges impinging on equipment can cause upsets or permanent damage, with
consequences ranging from barely noticeable to total destruction or
consequential damage.

Among upsets, there are several possibilities:

\* Barely noticeable, with self-recovery: a click in a sound system or a
flash on a video screen

\* Permanent and noticeable, requiring, manual reset: blinking, clocks
and VCRs

\* Permanent but not readily noticeable:data corruption

There are also several kinds of damage:

\* Damaged components, repairable at a service shop

\* Damaged components that are too costly to repair

\* Obvious and irreparable damage requiring complete replacement of the
equipment

\* Damage such as internal equipment fire that could set other objects
afire

Insurance statistics provide information on the relative frequency of
damage among insured appliances. It is significant that video equipment
is at the top of the list, and the discussion of multiple-port equipment
damage under \"System Interactions" at the end of Part 1 will explain
why. A poll is a connection between a piece of equipment and the outside
world. The line cord of an appliance is a power port. The modular
telephone jack on a fax machine, or the UHF connector at the back of a
TV set is a communications port. In the modern home, both one-port and
multiple-port appliances abound (Figure 1.5), and the same situation
exists in commercial and industrial installations. When the time comes
to understand the origin of the surge suspected to have caused damage to
an appliance, it is important to determine if the appliance is a
single-port or a multiple-port type.

Many appliances are still single-port equipment, in spite of the trend
to provide sophisticated controls: a simple kitchen range is a
single-port appliance, but a range controlled by a smart-house computer
system is a two-port appliance. A TV set with rabbit-ear antenna is a
single-port appliance, but the same set with a roof antenna or cable TV
connection becomes a two-port appliance.

**Multiple-Port Equipment**

More and more electronic equipment in homes and businesses requires a
communications link, hence a communications port in addition to the
usual power supply connection, the power port. Examples of such two-port
appliances include fax machines, telephone answering machines, personal
computers with modem or printer connections, and cable-connected TV
receivers and VCRs.

A possible problem is that although each of the power and communications
systems may include a scheme for protection against surges, the surge
current flowing in the surged system causes a shift in the voltage of
its reference point while the other, nonsurged, system reference point
remains unchanged. The difference of voltage between the two reference
points appears across the two ports. Depending on the nature of the
appliance and its immunity, this difference of voltage may have some
upsetting or damaging consequences. The problem is so important that it
is discussed in more detail in \"System Interactions\" at the end of
Part 1.

**Remedies Against Surges**

**General Approach**

At first glance, it would seem that if surges could be prevented from
happening, many problems could be prevented. However, lightning cannot
be eliminated. (There are some yet unproved schemes to dissipate the
charges in a cloud and thus prevent lightning strokes.) Similarly,
switching surges that occur in the utility system cannot be eliminated
by the time they arrive at a customer\'s service entrance. Therefore,
the general remedy is to install (insert) surge-protective devices at
one or more points of a customer\'s installation.

## Surge-Protective Devices: What\'s in a Name?

The devices that can protect against surges are called surge-protective
devices, or SPDS, by engineers, but that might sound too much like
jar­gon to most customers. The name that seems to stick in the general
public is surge suppressor, which many manufacturers use for their trade
designation, with a variety of catchy trade-marked names. The
Underwriters Laboratories chose to call them transient voltage surge
suppressors (TVSSs), and that name or acronym generally appears next to
the UL sign on the product. In the utility industry, the generic name
used in the transmission and distribution parts of the system is surge
arrester.

Actually a surge cannot be suppressed nor arrested; the correct word to
describe what happens is diverted. What these protective devices do is
simply divert a surge to around, where it can do no harm. So a name that
makes sense would be surge diverter, but it was not picked. The consumer
industry has settled on TVSS, while the utilities stay with the
long-used word arrester and use it for the more rugged devices that a
utility installs at the service entrance.

The surge protection schemes for residential customers are these:

\- Insert a TVSS for each sensitive appliance (Figure 1.6)

\- Accept the offer (if made) from the utility to provide the
\"whole-house protection\" (Figure 1.7)

Wholehouse protection consists of a protective device at the service
entrance complemented by TVSSs for sensitive appliances within the
house. The service entrance protection is an adapter inserted by the
utility between the revenue meter and its base. Variations exist, such
as a separate box connected to the meter base box.

With whole-house protection-that is, an arrester at the service entrance
and one or more TVSSs inside the building\--the issue of \"cascade
coordination\" arises. The concern is that, if the various protective
devices are not selected with due consideration, the stress of incoming
surges may not be shared according to the capability of each device.
(See box, \"Cascade Coordination.\") This is a concept that the
residential customer should not be expected to assess; it is the
utility\'s responsibility to consider it and offer an integrated,
coordinated package of service entrance protection and TVSSs.

### Cascade Coordination

Cascading surge-protective devices is a concept whereby two (or more)
protective devices are connected at two (or more) different points of a
power system. The "upstream" device (the one closest to the utility's
distribution system) is the first line of defense; it is designed to
divert the bulk of an impinging surge. The "downstream" devices (those
closest to the equipment to be protected) are intended as a final stage,
diverting any remaining surges, including those generated within the
customers wiring.

Successful coordination of casccaded devices is achieved when the
heavy-duty upstream device does indeed divert the bulk of the surge,
instead of letting the downstream devices attempt to divert an excessive
amount of the surge current. In keeping with the terminology of this
manual, the upstream device will be referred to as an arrester, while
the lighter duty,. downstream devices will he referred to as
suppressors. The basic and critical parameters for successful
coordination of the arrester/suppressor cascade include the relative
voltage damping of the devices, their electrical separation through
wiring inductance. and the actual waveform of the impinging surge.

A well-designed cascade arrangement maximizes the benefit of surge
protection with a minimum expenditure of hardware. Another benefit of a
cascade is the diversion of large surge currents at the service
entrance, so that they do not flow in the building, and side effects are
thus avoided.

It is one thing to design a cascade based on optimum coordination where
all the parameters are under the control of the designer. Such an
opportunity exists in utility systems implemented under centralized
engineering. It is an altogether different challenge to attempt, after
the fact, coordinating the operation of surge-protective devices
connected to the power system by diverse and uncoordinated (and
uninformed) users.

Promoting a coordinated approach may come too late for the de facto
situation in which millions of suppressors are in service with a
relatively low clamping voltage. This situation will impose an upper
limit to the clamping voltage of a candidate retrofitted arrester.
Therefore, close attention must be paid to the selection of the relative
clamping voltage of the devic4es, in view of the conflicting
requirements for performance under surge conditions---a successful
cascade---and reliably withstanding temporary power-frequency
overvoltages. Nevertheless, coordination still may be possible if the
available tradeoffs are understood. In the future, well-informed users
could avoid the pitfalls of poor coordination or the disappointment of
implementing protection schemes that cannot provide the hoped-for
results.

An illustration of the effect of the relative voltages and device
separation on the energy-sharing between two devices appears in Figure
1.8. The figure shows a plot of the percentage of the total energy
dissipated in the suppressor, as a function of the distance separating
the two devices. for various combinations of clamping voltages. In the
plot, H, M, and L correspond respectively to a high (250 V). medium (150
V). and low (130 V) voltage rating, in a 120-V rms circuit application.
In the designations H-H. H-M, H-L, etc., the first letter is the rating
of the arrester and the second letter is the rating of the suppressor.

Figure 1.9 shows an example of a coordinated scheme where the current in
the suppressor is indeed small compared to the current in the arrester.
This encouraging result can serve as the basis for the selection of the
two devices in a scheme that a utility can offer to its customers as an
integrated package.

The active element in most surge protective devices is one or several
disks of metal oxide varistor (MOV) that perform the current diversion
function. The surge diversion capability of arresters and suppressors
increases with their diameter. A typical cascade might consist of a
40-millimeter-diameter arrester and a 20-millimeter-diameter suppressor,
described as a 40-mm/20-mm cascade.

Although the reality of having many millions of 130-volt suppressors
installed on 120-volt systems makes a well-coordinated cascade difficult
or perhaps unattainable, at least in the near future, a cooperative can
still take certain steps to improve coordination in a protection system.
As a compromise, a cascade with equal voltage ratings for the arrester
and the suppressor can offer successful coordination, if the impinging
surges are relatively short. The coordination of a simple cascade of an
arrester and a suppressor of equal voltage rating, both connected
line-to-neutral, is slightly improved by the larger diameter of the
arrester. However, an unfavorable combination of tolerances for the two
devices can wipe out the improvement---for example, if the arrester
clamping voltage is at the upper end of the tolerance band and the
suppressor is at the lower end of the tolerance band, effectively making
the suppressor the lower device hence the one that will have to divert
most of the surge.

In large business or industrial installations with internal feeders,
subpanels, and fairly long branch circuits, the question of cascade
coordination is more complex than for a simple residence. It should be
assessed by the specialist responsible for the electrical installation.

**SWELLS**

**Origins of Swells**

The disturbance called a swell is a brief increase in the line voltage,
typically less than 20 or 30%, associated with load rejections and
sluggish voltage regulation response. The AC voltage sine wave remains
essentially undistorted, but its amplitude is increased for a few cycles
or a few seconds (Figure 1.10).

**Effect of Swells on Equipment**

Swells lasting only a few cycles are unlikely to cause any damage, and
only the most sensitive electronic equipment might experience a
momentary disturbance. On the other hand, swells lasting more than a few
cycles can cause a trip-out of protective circuitry in some
power-electronic systems. Variable-frequency drives (also called
adjustable-speed drives) often include an overvoltage sensor in their
electronic control, which can cause a trip of the system, with or
without restart. The safety issue of automatic restart versus mandated
manual-only restart is well known among plant engineers.

### Remedies against Swells

For the residential consumer, there is no concern about damage and only
a small likelihood of some upset of an electronic appliance. A user of
variable-speed drives (these are beginning to appear in residential
heating and air-conditioning systems) might experience a trip-out during
a swell. That possibility raises the question of ability to withstand
swells, to be taken up with the vendor of the variable-speed drive.

There is no device that can suppress a swell the way a suppressor
\"suppresses\" a surge; the remedy must be inherent immunity of the
equipment. Thus, there is little that the user\--residential or
industrial\--can do short of requesting the vendor to provide
appropriate designs for the equipment.

### TEMPORARY OVERVOLTAGES

### Types and Origins of Temporary Overvoltages

Temporary over-voltages are abnormal disturbances, at the power
frequency, that occur under the usual (normal or abnormal) operating
conditions of a distribution system. The principal causes are system
faults over which the utility has little or no control (animals, storms,
vehicle collisions) and a troublesome situation of a lost (open) neutral
connection in the service drop to customers, in particular the
residential 120/240-V three-wire systems.

### Distribution System Faults

Overvoltages on the distribution system originate from a variety of
system faults such as line-to-ground insulation failure within the
distribution transformer. Overvoltages caused by system faults can reach
2.5 times the normal voltage. Depending on the settings of the
protective schemes, it can take as long as 5 seconds to clear the
circuits.

A rare but possible system fault occurs when the same pole carries two
systems at different voltages and a collision, high wind, or ice causes
one set of conductors to fall onto the other. This scenario will produce
overvoltages proportional to the difference of the two system voltages.

**Open Neutral**

An open neutral situation can occur as a result of corrosion in
underground service drops, falling branches or ice on three-conductor
overhead service drops, and even a loose connection of the neutral in a
service panel. Service drops with aluminum neutral conductors are more
prone to this type of fault.

Utility engineers can report many anecdotes about that type of
disturbance.

As the box \"When a Neutral Opens\" explains, what happens is that if
the loads on the two sides of he 120/240-V customer installation are not
balanced, the side with the lightest load experiences a large increase
from 120 V, theoretically almost up to the full 240 V.

## When a Neutral Opens

Open neutral connections in 120 240 V customer installations can occur
several circumstances including:

\* When corrosion of an aluminum underground service reaches an acute
stage

\* When the neutral wire of a separate-conductor service drop is broken
by falling branches or icing

\* When an intermittent loose connection exists in the service panel

(Note that all of the above are "when" clauses---not "if and
when"---because all of these circumstances are somewhat likely to occur
at some point; it is only a matter of probability and frequency of
occurrence.)

In typical installations, the two halves of the power supply, on each
side of the center-tap neutral connection, are seldom exactly balanced,
and sometimes are highly unbalanced. If the installation neutral becomes
disconnected from the utility neutral voltages V1 and V2 appear on each
side of the now disconnected installation neutral (see Figure 1.11). The
only remaining connection is the two lines, L1 and L2, across which the
full 240-V supply is maintained.

The potential at the midpoint between the two loads Z1 and Z2 will be
somewhere between the potential of L1 and L2, in inverse proportion to
the values of Z1 and Z2. If, for instance, Z2 is much lower than Z1, a
TVSS connected on the L1 side will experience a severe overvoltage (as
will the equipment represented by Z1). However, while most equipment has
some tolerance for a moderate over-voltage, TVSSs, in particular those
that claim low clamping voltage, are quite sensitive to that condition.
The situation is probably the cause of most reported catastrophic
failures of TVSSs.

Some publications on power quality include an illustration of a
screwdriver (presumable intended to tighten loose connections) with a
caption that reads "the most useful power-quality tool"!

### Effects of Temporary Overvoltages on Equipment

Overvoltages, whether a result of distribution system faults or open
neutrals, can be quite destructive for equipment if allowed to last more
than a few cycles (in which case they might fall in the category of
swells). Power equipment is designed to survive these overvoltages:
transformers are likely to saturate, providing some voltage reduction on
the secondary. Distribution arresters are generally selected for their
ability to survive temporary overvoltages. However, many consumer-type
TVSSs are likely to fail during a temporary overvoltage \[see box,
\"Lower Is Not (Necessarily) Better\"\]. In fact, the major cause of
TVSS failures is a temporary overvoltage, rather than an unusually large
surge.

**Lower Is Not (Necessarily) Better!**

The fundamental purpose of a surge protective device is to reduce the
stress imposed on load equipment when Surges occur on the AC power
system. Surge protective devices (SPDs) do this by diverting the current
of an impinging surge to ground through a low impedance. The effect is a
Substantial reduction of the impinging voltage surge.

An SPD is a voltage divider in which the voltage on its low side (the
side connected to the load) becomes lower as the surge current
increases, \"clamping\" the voltage impressed on the load.

Before the proliferation of SPDS, made possible by the development of
metal-oxide varistors (MOVs), the perception existed that the threat of
surges was the voltage they can develop at the terminals of a load.
Thus, people thought that clamping that voltage to a low level was
desirable and, intuitively but erroneously, the lower the better. This
perception was reinforced by the decision of the Underwriters
Laboratories to require manufacturers of TVSSs (UL Standard .1449) to
show the clamping voltage of their product on the package, picking from
a list of discrete steps starting with 330 V for 120-V applications.
This UL requirement triggered a downward \"auction\" among manufacturers
who wanted to be in the 330-V category. overlooking the undesirable side
effects of such a tight clamping.

Actually most load equipment is more robust to surges than TVSS
manufacturers imply by offering these low clamping voltages. For
instance, a 500-V clamping voltage would be quite adequate for
protecting equipment. Furthermore-the point of the axiom \"Lower is not
better!\"-a TVSS clamping at 500 V would not respond to most swells or
temporary overvoltages, a characteristic that is highly desirable. Such
a passive situation would help in retarding the aging process of MOV\'s.
More important, it certainly would reduce the incidence of the
catastrophic failures that are periodically reported in trade magazines.

Some manufacturers have responded to the argument by offering guarantees
or no-questions-asked replacement. Nevertheless, failure of a TVSS from
a temporary overvoltage might still be a traumatic experience for a
homeowner. Those few manufacturers who subscribe to the \"Lower is not
better\" philosophy should be rewarded by being chosen when consumers go
through the quandary of trying to select from the multitude of TVSSs
offered on the shelves.

**Remedies against Temporary Overvoltages**

The nature of temporary overvoltages makes it difficult if not
impossible to prevent them, and therefore they must be accepted as a
probable, but hopefully rare, event. Surges can be diverted because the
energy levels to be absorbed in the diversion are limited. In contrast,
a temporary overvoltage involves the full power of the system, and no
device can absorb that level of energy. As noted above, some equipment
can be designed to withstand the overvoltages, but that decision is
beyond the control of a utility.

#### Not Enough Voltage

**OUTAGES**

Outages represent the worst type of disturbance for the operations of a
customer. They can have a duration as short as a few cycles, the typical
situation when the breaker of a feeder trips out on a fault and the
fault is cleared, with automatic reclosing (Figure 1.12). Other outages
can be much longer, as when the distribution equipment suffers a major
fault (downed lines, catastrophic failure of transformers or
switchgear).

Outages rarely damage equipment directly. Indirectly, of course,
industrial processing equipment (for metals, plastics, textiles,
semiconductor devices, and so forth) shut down by an unscheduled outage
can suffer damage. The material under process is not only ruined but can
also jam the equipment, with painful and time-consuming cleanup
operations.

Less dramatic consequences or cessation of operation can range from
inconvenience to loss of revenue. Individual consumers also can suffer
from loss of power needed for heating, air conditioning, and food
refrigeration. One utility, with a mixture of seriousness and
facetiousness, used to describe the severity of outages by the number of
claims filed for spoiled freezer loads of frozen raspberries!

The obvious remedy against outages at the customer level is to provide a
standby source of power, either a storage battery or an engine-generator
set. The battery-power approach, generally called an uninterruptible
power supply (UPS), is a very popular remedy. It is applied at all power
levels, from the small package favored by reliability-conscious computer
users, to a building-wide system where loads are segregated into
essential and nonessential. There are various types of UPS offered by
manufacturers in a highly competitive market, each with performance
characteristics aimed at minimizing or avoiding altogether the momentary
disturbance when power is transferred from the utility to the standby
source.

For large industrial loads, schemes of dual feeders with an automatic
transfer switch have been applied successfully by mutual agreement
between the customer and the utility. Such an approach is justified when
the financial and operational cost of an outage justifies the investment
in a dual feeder system. Pessimists have noted, however, that when an
installation depends on two feeders, it might be subjected to twice as
many sags because each feeder carries a likelihood of sags.

**SAGS**

Power quality engineers call "sag" an event when the line voltage is
reduced for a few cycles to a level of less than 80% of the normal
voltage (Figure 1.13). This type of disturbance can trigger upset or
shutdown of control circuits. Sags rarely cause equipment damage but are
the cause of many complaints of malfunction.

Sags have their source in faults in a feeder that cause a large current
to be drawn in the feeder, hence a voltage drop in the bus from which
other feeders draw power. Many power quality engineers consider sags as
a major cause of equipment malfunctions---but rarely, if at all, of
damage. Upsets affect primarily the information technology equipment.
Also affected are simple power devices controlled by a magnetic motor
starter, which can drop out and stop a process.

Field studies of sag-related disturbances in processing equipment have
revealed that the source of the problem can be s simple relay in the
control system, rather than a major disturbance in the power equipment.
In such cases, a very effective remedy is to provide the control system
with a UPS, or even with a simple constant-voltage transformer that can
ride through most sags.

**BROWNOUTS**

In periods of high demand where the system capacity is reached and would
be exceeded, utilities resort to the scheme of deliberately reducing the
voltage by a few percent. The effect is a reduction of the power
consumed by most loads with some exceptions in the case of process
controls that include a voltage regulating scheme that defeats the
objective of the brownout.

### SUSTAINED UNDERVOLTAGES

A very severe brownout might cause overheating of compressor motors, and
some people believe that domestic refrigerators therefore should be
disconnected when the lights are very dim. This perception needs
clarification, and utility engineers should quantity the risks involved.

Another damaging consequence might be the failure of some electronic
voltage regulators built into computer-based equipment (generically
called \"information technology\" equipment). Such equipment has an
intermediate regulating stage that can become overloaded and overheat
when attempting to compensate for the voltage reduction. Anecdotes have
been circulated, and the phenomenon has been demonstrated in the
laboratory, but is confined to isolated cases. It is recounted here as a
yet another hint that equipment failures should not blindly be
attributed to surges.

### CHARACTERISTIC CURVES

The information technology industry has developed a characteristic curve
describing the tolerance of equipment to undervoltages (mostly sags) and
overvoltages (mostly surges). That curve, well known to power-quality
specialists as the CBEMA curve, has recently been updated and is now
called the ITT curve (for the Information Technology industry Council).
See box, \"The CBMA Curve.\"

### FLICKER

When light sources (mostly incandescent but also some fluorescent) are
supplied from a power line in which repetitive sags occur, a Bickering
effect is produced that humans find annoying. The correct term to
describe the behavior of the power supply is voltage fluctuation, but
flickering is often used to describe the quality of the power, even
though it is only the effect, not the cause.

Voltage fluctuations can be considered repetitive sags of low amplitude
(the human eye can detect light output variations caused by a fraction
of a percent fluctuation in the voltage, when the fluctuations occur at
rates ranging from a few seconds to about 20 per second). Typical
sources are arc furnaces (not too many around) and welding machines (arc
and resistance spot welding).

There is no remedy that the customer can apply when the fluctuations
come from an intermittent load of a neighbor. (Be sure that the skillet
or flat-iron is not on!) If the complaint sounds serious, the only
remedy is for the utility to investigate where the intermittent load is,
and negotiate a solution with the offender. Power quality specialists
are acquainted with a variety of solutions, but each is to be applied
case by case.

**The Case of the Flickering Chandelier**

In one anecdote. a customer complained of flickering lights to the
electric utility. which installed a strip-chart recorder the service
entrance in response (.as if that could detect small fluctuations!). Of
course. None detected. It turned out that the customer had left an empty
electric skillet on while supper was being enjoyed in the dining room.
In that vintage-era house, the skillet (1500 watts on a 14-AWG wire) and
the chandelier were on the same branch circuit. The flicker was caused
by the thermostat of the skillet cycling on and off. Flickering candles
on the d ining room table may be romantic. but a flickering chandelier
is declared annoying.

**The CBMA Curve**

In the 1ate 1970s. computer manufacturers and users reached a consensus
on the power quality (use of the term had just started) that would be
necessary to ensure undisturbed operation of computers. The concept\--as
a design goal, not a specification\--was first proposed as relevant to
mainframe computers and presented in the form of a double curve showing
a lower limit and an upper limit for acceptable mains voltage, or, in
other words, the tolerance of equipment to power supply variations. This
chart became known as the CBEMA curve and was soon considered\--perhaps
not an appropriate extension\--as applicable to some electronic
equipment other than computers, and was cited in several standards. The
original curve was a challenging consensus-building effort. It was a
committee agreement on what people thought the equipment could stand. It
was not thoroughly tested or verified at that time. Although the
power-supply technologies of business equipment have improved, some
manufacturers are still reluctant to incorporate them into their
products because of competitive market constraints.

In the 1990s, increasing interest in solving power quality problems let
to extensive research in the tolerance of various equipment to power
supply disturbances, in particular sags. Changing technology- in
computer equipment---now classified as information technology equipment
(ITE) also led to a revision of the limits, and a revised curve was
issued in 1996 by the Information Technology Industry Council (ITIC),
together with an application note (Figure 1.14).

Updates to this information may be found at the Web site
<http://www.cbema.org/itic/site_map/index>

**Other Power-Line Disturbances**

Other disturbances, less frequent than the "too much" and "not enough"
just described, can also occur as the result of the operation of the
distribution system and interactions with customer loads. These
disturbances include noise, harmonics, notches, unbalance, and carrier
signals.

**NOISE**

The term noise is loosely used to describe small disturbances (a few
volts at most) at high frequencies (note the plural). See Figure 1.15.
The sources of noise include chattering relays (a short-duration event)
and coupling of radio frequencies from a nearby broadcast antenna (a
quasi-permanent situation).

In keeping with Federal Communications Commission (FCC) requirements,
most domestic equipment has a filter in the power cord that limits the
emission of high frequencies back into the power cord. Industrial
equipment has similar FCC requirements, but less stringent. By
reciprocity, this filter also limits the penetration of line-conducted
noise into equipment; this fact is worth keeping in mind when
considering the purchase of a TVSS making claims of adding noise
filtering to its prime mission of surge protection.

**HARMONICS**

Harmonics are currents and voltages at frequencies that are multiples of
the fundamental 60-Hz waveform (Figure 1.16). They are the result of
normal operation of certain loads, called non-linear because impedance
is not constant or because they draw currents that are not proportional
to their impedance. This type of load is becoming more widespread as
consumer electronics proliferate and as new, sophisticated power-control
schemes aimed at improving efficiency are built into some major
appliances. The presence of large harmonics is readily visible in the
voltage waveform. Small, but potentially objectionable, harmonics
require a more sophisticated instrument, such as a power-quality
monitor, to detect and quantify them.

**Effect of Harmonics on Equipment**

As a result of the increase in occurrence of harmonics, the subject has
become a hot topic (pun intended) because the effect on equipment can be
severe overheating. The problem starts because nonlinear customer loads
generate currents at harmonic frequencies. (In the jargon of the
applicable standards, this is called harmonic emission.) There are
several undesirable results from this situation:

> 1\. Effective (root mean square, or RMS) currents in conductors are
> increased, in particular in the neutral of three-phase systems. These
> increased currents can cause overheating because the wiring
> installation, done in accordance with earlier versions of the National
> Electrical Code (NEC R, trademark of the National Fire Protection
> Association), made no provision for that situation.
>
> 2\. The harmonic currents circulate in the delta-connected secondary
> of wye-delta transformers but not in the primary side, therefore
> primary overcurrent protection is not effective and the secondary can
> be severely overheated.
>
> 3\. If the harmonic currents are not filtered out or canceled at the
> point of common coupling (as they are in 2 above), the currents flow
> in the utility distribution system and cause a voltage distortion in
> the supply of adjacent loads, proportional to the current and the
> utility system impedance. In other words, systems with relatively low
> available short circuit capacity will experience more voltage
> distortion for a given nonlinear load than systems with high capacity.

### Remedies against Harmonics

Remedies against harmonics are essentially compromises in a range of
extremes. One such compromise is to control harmonic emission by
mandating limits for each and every piece of equipment, the approach
presently taken by some European countries. Another approach, which has
gained acceptance in the United States, is a voluntary compromise where
limits for harmonic emissions at the point of common coupling are only
recommended.

Consumers have practically no control over the harmonics that their
equipment can generate, but the perception in the United States is that,
for the moment, they do not pose problems. This laissez-faire attitude
might change if harmonic-generating loads such as electronic ballasts
and variable frequency drives for heating and air conditioning were to
become a larger portion of the total consumer load.

In commercial and office buildings with older wiring and a large amount
of information technology equipment, supplied single-phase from a
three-phase system with shared neutral, harmonics can cause overheating
problems. Later versions of the NEC recognized the problem and have
mandated larger ampacity for shared-neutral conductors.

Industrial customers are more concerned about harmonics because some of
their loads can have a significant emission. Remedies include the
providing filters as a retrofit option. As of 2001, the issues are still
the subject of much debate, and should be reviewed by power-quality
specialists before expensive and possibly counterproductive measures are
implemented.

### NOTCHES

"Notches" can be created in the supply voltage when large
power-electronic drives in adjacent loads cause a momentary short
circuit between the phases that power the drive, each in turn. These are
called commutation notches and occasionally cause some interference with
other loads that use the 60-Hz power frequency as a controlling signal
(Figure 1.17).

In a sense, notches may be considered as a special case of harmonic
emission, and the remedies, if interference is noted, are similar to
those mentioned for harmonics in general.

### UNBALANCE

Voltage unbalance between phases occurs when a three-phase system
supplies single-phase loads that draw unequal currents. Three-phase
loads supplied under those conditions can be adversely affected, with
overheating of motors in particular as a symptom. Variable-frequency
drive systems have a tendency to magnify the problem by skipping some of
the six half-cycles that are expected, each in turn, to deliver power to
the drive. Thus, a severe current unbalance can result from a moderate
voltage unbalance.

The remedy for this situation is under the control of the end user and
is simply to reassess the allocation of single-phase loads from the
three-phase system.

### CARRIER SIGNALS

Occurrences of interference from carrier signals have been described in
anecdotes. These are isolated cases for which case-by-case remedies have
been developed by power-quality specialists.

##### System Interactions

#### THE PROBLEM

A special kind of surge problem is that of an interaction between the
power system and a communications system, as briefly mentioned in the
beginning section of this part, \"Surges.\" This case merits special
attention because it can be misinterpreted as being caused by the
utility power supply, Furthermore, the problem can arise even if both of
the systems have been provided with surge protection, leaving a customer
thus afflicted puzzled or disappointed. The effect of this interaction
is to shift the reference potentials of the two ports during a surge, as
explained in the box \"Shifting Reference Potentials.\"

Shifting Reference Potentials

To illustrate the problem of shifting reference potentials, a laboratory
replica of a residential wiring system was used to make measurements
during surge events produced by- injecting a surge into the wiring. In
Figure 1.18 a modem-equipped PC is connected by its power port to a
branch circuit, and by its modern port to the telephone service of the
house. For a worst-case scenario the power telephone services enter the
house at opposite ends.

An open loop is formed by the copper pipe or ground conductor used as a
bonding conductor. the equipment grounding conductor of the branch
circuit feeding the PC, and the telephone wires from the network
interface device (NID) to the PC. If a surge impinges on the external
telephone plant, it is diverted by the NID via the copper pipe to the
common grounding point of the house. at the power service entrance. The
surge current in the copper pipe creates a changing magnetic flux
-around the pipe, which induces a voltage in the loop. This voltage will
appear between the two PC ports if they are separated by a high
impedance (of unknown surge voltage withstand capacity). With the
telephone wires routed away from the copper pipe\--which can be expected
in residential wiring\--a large loop is formed, embracing the flux
produced by the surge current in the copper pipe.

Figure 1.19 shows the recording obtained in the laboratory replica of
residential wiring. For a rate of change in tile Surge current of 75
A/uus (amperes per microsecond). typical of standard test waveforms, a
peak of 4.3 kV is induced in the loop and appears between the two ports.

A relatively simple retrofit solution is to equalize the difference of
voltage between the two systems by a device designed for the purpose and
inserted in both communications and power links just before they enter
the appliance. This device, defined in IEEE Standard 1100-1992 as a
\"surge reference equalizer,\" is commercially available as a unit
featuring a plug and receptacle for the power link, as well as a pair of
telephone jacks or TV coaxial fittings for the communications link. By
way of illustration of a surge reference equalizer's effectiveness,
Figure 1.20 shows a reduction of voltage from 4.3 kV down to 200 V,
obtained by inserting typical surge reference equalizer in the power and
telephone lines at the point of connection of the PC.

A smaller loop would exist if the telephone and power service entered at
the same end of the house, the recommended practice. With such a
configuration, a reduction in the voltage difference of about 75% of the
large loop value was found in the cited test series, still justifying
the provision of a surge reference equalizer for good protection.

Some appliances that require little power are often equipped with an
intermediate power supply integrated with the plug, and feeding a
low-voltage DC or AC to the main part of the applicance. If properly
designed, this intermediate power supply, by acting as an isolator, will
assume the stress that would otherwise appear across the ports of the
main part of the two-port appliance.

Of course, the problem would be eliminated if the communications link
were to use fiber optics. That solution is increasingly used in business
and industrial environments, but the technology and marketing for fiber
optics have not yet reached the consumer applications.

The root of the problem is the grounding practices of the two
utilities\--power and communications, either telephone or cable-which
are not always coordinated. In some cases, the prescriptions of the
National Electrical Code are not followed. During a surge event, the
normal, intended, expected operation of one of the surge protectors
causes the surge current to flow to the grounding electrode of the
installation. This current induces a voltage in the circuits of the
installation, which appears across the two ports of appliances, and
shifts the reference potentials of the two utilities. If the two
utilities enter at opposite ends of the house, the problem is more
acute. To check whether this undesirable (and difficult to correct)
situation exists, a customer in a single-family residence just has to
look at the outside of the house.

A case history has been documented in which the two services not only
entered at opposite ends of the house, but also did not have their
ground references bonded-not even remotely (see box, \"The Case of the
Cozy Cabin\"). That was a clear violation of the NEC, which the cable TV
utility did correct when notified. However, it is a hint that many
installations nationwide might have the same deficiency. Insurance
statistics indicate that the largest number of claims for \"lightning
damage\" is for video equipment. It is likely, even if not conclusively
recorded, that most of these incidents involve the two-port
configuration.

### The Case of the Cozy Cabin

A good example of a situation that fosters system interaction occurred
in a small house in a rural setting\--a cozy cabin\--where the power and
cable TV services entered at opposite ends of the cabin, precisely the
scenario described in the box \"Shifting Reference Potentials.\" This
installation had come to the attention of a power-quality engineer
because two failures of a TV set occurred within a few months.

Examining one of the sets, the engineer found that a flashover had
occurred at the input of the TV signal. where an isolating gap separates
the cable TV ground from the set chassis, which is ultimately connected
to the power system ground via the power cord. The engineer performed
laboratory tests after cleaning the carbonized flashover path Linder
conditions simulating the configuration of the cozy cabin, and indeed a
flashover was observed at the insulating gap when the shift in
potentials reached 2.5 kV. That level is well below the 4.3 kV found in
the study described in \"Shifting Reference Potentials.\" System
interaction was clearly the cause of failure.

This case history helps to confirm allegations that cable TV
installation practices prevailing in many residential situations might
be in violation of the U.S. National Electrical Code. This violation is
made even more hazardous by the separation of the service entrances.
Therefore, one of the first questions that should be answered when
inquiries are made on possible causes for damage to a TV or VCR is
whether the two services enter at the same end or opposite ends of the
house and whether the cable TV service is bonded to the power ground. If
the bonding is clearly missing, the cable company should be requested to
correct the violation. Even if the services enter at the same end of the
house, providing a surge reference equalizer just in the back of the TV
set would be good insurance against another incident.

###### REMEDIES AGAINST SYSTEM INTERACTIONS

Fortunately, industry has recognized the problem and offers a line of
devices specially designed to protect against those special, but
prevalent, surge problems. This type of device can be recognized easily
because it has (1) an input line cord with output power receptacles and
(2) two telephone modular jacks (or video coax connectors) to insert in
the telephone connection (or video cable connection). The proper
engineering term for this device is surge refer­ence equalizer (SRE), but
here again, popular usage has not adopted the engineering jargon and the
device is often called simply a surge suppressor, with added words to
draw attention to the two-port system.

To place the operation of a surge equalizer in perspective, visualize
the two ports of the equipment and their ground references, as in Figure
1.21. During a surge event on one system, there is a transient unbalance
between the two input references, which can be made worse when the
service entrances are at opposite ends. Inserting an SRE just behind the
TV set almost re-establishes a balance between the two ports. The ideal
situation would be to first have the two services on the same side, and
as a finishing touch, still provide an SRE.

**2 QUESTIONS TO ASK**

In This Section: Customer-owned offenders; how to use the worksheets;
identifying residential and commercial appliance categories- Worksheet
EDE: electronic, dual, external; Worksheet EDI: electronic, dual,
internal; Worksheet ES: electronic, simple; Worksheet HE: heat,
electronic; Worksheet HM: heat, mechanical; Worksheet ME: motor,
electronic; Worksheet MM: motor, mechanical-, Worksheet PLC: Power line
conditioning

This part of the manual is intended to facilitate the interactions
between a customer and a cooperative\'s service representative in
tracking down the cause of malfunction or damage and offering remedies
when possible. Hopefully, this procedure will serve the common interests
of both parties, but, as a note of caution, not all problems can be
solved over the telephone, and in some cases it might be necessary to
call in a power quality specialist to study the problem and identify
possible solutions, just as some medical problems can be described over
the telephone to the family doctor and a suitable prescription be picked
up at the local pharmacy, but other problems require a visit to the
doctor\'s office and even a referral to a specialist.

While the main thrust of the manual is the effect of the utility supply
on equipment-with the equipment characterized as \"victim\"-there are
also cases of disturbed equipment that are associated with the
customer\'s own operations where some other equipment can be
characterized as a troublemaker or \"offender.\" These offenders are
listed in Table 2.1, for a quick check that the reported problem does
not fall in that category, so that the dialogue can then focus on the
suspected interaction between the utility power supply and the equipment
problem.

**Customer-Owned Offenders**

Some appliances generate disturbances that can cause a malfunction of
other appliances in the same installation, or even in neighbors\'
installations. These disturbances are not attributable to the utility,
but an uninformed customer might still make it a subject of complaint to
the utility. Table 2.1 describes typical disturbances, their causes, and
possible remedies.

**How to Use the Worksheets**

The procedure of troubleshooting consists of the following steps:

1\. Obtain from the customer a description of the victim equipment, and
categorize the type, using Table 2.2, a list of appliances likely to be
found in residential and small-business installations.

2\. Turn to the diagnostic worksheets corresponding to the type of
victim equipment identified in step 1. The worksheets are structured in
three parts:

> a\) History and symptoms
>
> b\) Tentative diagnostics and remedies
>
> c\) Disposition of case

3\. Obtain from the customer as much background information as possible,
using Part A of the worksheet as a script for the dialogue.

4\. Reviewing the information thus obtained, ask further questions as
appropriate according to Part B of the work sheet.

5\. Present to the customer a tentative diagnostic and possible remedy
(some problems might be beyond simple remedies).

**Identifying Residential and Commercial Appliance Categories**

For the purpose of narrowing the tentative diagnosis, Table 2.2 lists
several categories of equipment victims. To allow good understanding
between the customer and the service representative, it will be useful
to pin down, early in the dialogue, what is the specific appliance
category to be discussed. When the category is thus pinned down, the
\"script\" for the dialogue can be found in one of the eight work sheets
at the end of the manual. The customer representative should photocopy
blank work sheets and keep a supply of them to be filled in as the
dialogue progresses, then file them for future reference or additional
review. For easy reference to the corresponding work sheet, the
categories identified by the table are associated with a code that
appears in bold type on the top right corner of the work sheet.

**MOTOR-DRIVEN APPLIANCES AND HEATING APPLIANCES**

For each category (motor-driven or heating), there can be two or more
types, depending on the type of control used:

> Mechanical control (on-off, rotary, etc.\--no sophisticated keypad or
> other electronic control)
>
> Electronic control (keypad, display, etc.)

These different controls influence the tentative diagnosis,
Consequently, motor-driven and heating appliances are divided into four
kinds, with the following codes in Table 2.2:

> 1\. Motor, mechanical: MM
>
> 2\. Motor, electronic: ME
>
> 3\. Heat, mechanical: HM
>
> 4\. Heat, electronic: HE

**ELECTRONIC (COMMUNICATIONS) APPLIANCES**

This generic category includes telephones, audio and video equipment,
and personal computers. Here again, two types must be recognized:

> 1\. Appliances with a simple, one-link connection to a power system
> (or to a telephone system for simple sets).
>
> 2\. Appliances with a dual connection to both power and communication.
> Such appliances can be subdivided further into two types:
>
> a\) Appliances that are powered as well as linked to an external
> communication system such as telephone line, rooftop antenna, cable
> TV, or satellite dish. The exposure of this type of appliance is
> significant because surges of external origin can come in through
> either the power line or the communication link. They can be caused by
> system disturbances or by remote lightning strokes.
>
> b\) Appliances that are powered as well as linked to an internal
> communication system, such a garage door opener, burglar alarm,
> intercom, thermostat, or computer-controlled appliance. The exposure
> of this type of appliance, even though it involves two systems, is
> lower than that of systems with external links. Disturbance or damage
> associated with the internal communication links is limited to the
> rare case of a very close lightning stroke inducing a voltage in those
> internal links.

The absence of a communication link or the type is a link is present,
will influence the diagnosis. The types of electronic appliances can be
assigned these codes in Table 2.2 *\[see pdf file for the tables\]*

*The next page is an example of the contents of a work sheet. The
handbook contained several of these, addressing the questions relevant
to the type of appliance. See the pdf file of this handbook for the
complete set of the work sheets in their actual layout designed for
filling-in the sheet by the customer service representative while on the
telephone*

**[Worksheet EDE]{.underline}**

**[Electronic, dual, external]{.underline}**

A. HISTORY AND SYMPTOMS

Appliance identity Similar problem in neighbor\'s home?

O Name of customer O Yes

O No

O Appliance in question O Don\'t know

[O]{.underline} Where located in building? Power system conditions:

O Approximate age? Years O Apparently normal

Symptoms O Problem occurred in conjunction with

O Quit working during normal operation A utility outage?

O Would not start when turned on Other incident?

O Smoke came out Describe:

O Acrid smell

O Blinking displays O Don't know

O Other System interaction

Has that condition happened before? O Proper bonding of power system and

O Previous repair history communications system? (Y/N)

O Did not report it O Surge reference equalizer installed? (Y?N)

O Reported it but no action

O Suggested action failed Other information and remarks by customer:

O Don\'t know

Weather at the time of the problem

O Blue sky

O High winds

O Ice storm

O Distant thunder

O Local lightning

O Don\'t know

B. TENTATIVE DIAGNOSIS AND REMEDY

Diagnosis Remedy

System interaction (most likely). See under A. Install surge reference
equalizer.

End-of-life burnout. (How old is equipment?) Replace.

Mechanical switch failure Repair

Surge on the power line Was there a surge reference equalizer? If yes,

a temporary overvoltage is likely. If no, install

surge reference equalizer

Temporary overvoltage Repair if appliance is expensive, or replace

C. DISPOSITION OF CASE

+-----------------------------------------------------------------------+
| ## François Martzloff                                                 |
+-----------------------------------------------------------------------+
| ######## END OF FILE "Text System Compatibility"                      |
+-----------------------------------------------------------------------+
| ## April 2004                                                         |
+-----------------------------------------------------------------------+

[^1]: ***2004 Note:*** The documents listed under this section were
    cited as in-progress examples and were subsequently either brought
    to completion and made available to EPRI-PEAC stakeholders, or were
    discontinued.

[^2]: ***2004 Note:*** At the time this paper was published, a draft
    SC-120 had been developed and disseminated among several interested
    parties by the Power Electronics Applications Center (PEAC) that
    eventually became EPRI-PEAC. However, insufficient available data on
    the performance of the protective functions and the actual need for
    protection of the input ports caused the project to be discontinued.