Characterization of Transient Voltage Surge Suppressors

From a System Compatibility Perspective

 

Raymond C. Hill 

Research Center

Georgia Power Company

Thomas S. Key

Power Electronics

Applications Center

François D. Martzloff

National Institute of

Standards and Technology 

Reprint from Proceedings, PQA’92, Atlanta GA September 1992

Significance

Part 6: Tutorials, textbooks and reviews

Part 7: Mitigation techniques

A comprehensive review of test programs (up to 1992) of surge-protective devices,

including service-entrance SPDs and downstream SPDs.

Tests performed at Georgia Power facilities for surge withstand capability, TOV

withstand, failure modes, and mechanical tests.

Test performed at the Power Electronics Applications Center (PEAC) on meter-base

arresters, plug-in TVSSs (power port and communications port) and surge-reference

equalizers.
Characterization of Transient Voltage Surge Suppressors 

From a System Compatibility Perspective 

Raymond C. Hill 

Research Center 

Georgia Power Company 

Forest Park GA USA 

Thomas S. Key 

Power Electronics 

Applications Center 

Knoxville TN USA 

Abstract - Transient voltage surge suppressors are 

characterized from the point of view of electric utilities 

wishing to ofler to their customers a comprehensive surgeprotection plan. This plan involves a surge arrester 

installed at the service enlrme and one or more plug-in 

suppressors installed within Me premises, at the point of 

connection of a surge-sensitive appliance. Complementary 

tests were conducted at nvo 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 performed 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 intemal 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 thc 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 serviceentrance 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. 

t Technology Administration, U.S. Depaament of Commerce 

Contributions of the National Institute of Standards and Technology 

arc not subject to U.S. Copyright 

Franpis D. Mactzloff 

National Institute of 

Standards and Technology t 

Gaithersburg MD USA 

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 serviceentrance 

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 compatibiity 

(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 1611 *. 

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. 

* Citations are listed alphabetically at the end of this paper. 
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 highenergy faults than the serviceentrance 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, 19901, or the coordination of cascaded 

SPDs [Lai & Martzloff, 19911. 

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. 'Ihis 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 pr@ection. 

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. 

Impinging 

\ surge 

- 

T Restrict T I 

Figure 1 

Two-stage surge-protection scheme 

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 a performance 

tests. 

LEGEND 

0 Secondary arrester at transfotmer 4 Permanently wired, bad side 

1 Arrester at weather head 5 Permanently wired receptacle 

2 Meter-base adapter amster 6 Plug-in NSS 

3 Permanently wired, line side 

Figure 2 

Possible locations for arresters and suppressors 
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 sewiceentrance arresters. For the plug-in 

suppressors, the work reported here has been carried on by 

PEAC. Table 1 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 lolowledge 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, 

imparial, and uniform evaluation process. However, more 

useful results can be obtained when the test takes into 

consideration the expected behavior of the device. 

SERVICEENTRANCE 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 meter 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 

hand, 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. 

Table 1 

Principal Characterization Tests Performed 

I OFTEST 

11 ARRESTERS PLUG M PHONE CATV I lV&i I SRE' I SRE* 1 

DURABILITY IWWI 

IMPACT 

LET-THROUGH N/A 

POWER CROSS N/A PEAC WA 

INSERTION LOSS N/A N/A PEAC 

1 SURGE REFERENCE EQUALIZER FOR TELEPHONE 

SURGE REFERENCE EQUALIZER FOR CABLE TV 

GP: TESTS BY GEORGIA POWER 

PEAC: TESTS BY PEAC I ** N/A: NOT APPLICABLE TO MIS TYPE OF DEVICE I 

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 obsetving 

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 overvoltage 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 serviceentrance arrester should 

include some indication of arrester condition, ease of 

installation (including method of grounding), environmental 

resistance, and safety. Several arresters evaluated had neontype 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 

tightuess, 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 cleac 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 hole 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 wirein. 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 powerdistribution 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, O-ring 

seals, or coating with a dry tar-like 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 "saltfog" 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 serviceentrance 

arrester must be considered. These properties include impact 

resistace, thennal withstand capabilities, and the ability of 

the meter-base extender jaws to maintain sufficient pressure 

on the meter blades to prevent overheating. If the meterbase 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. 'Ihis parameter was measured 

according to the IEEE deffition of varistor voltage 

[ANSIAEEE C62.33-19821. 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 

[ANSIAEEE C62.41-1991; ANSVIEEE C62.11-19871 were 

consulted. ANSVIEEE C62.41 defines the 'Combination 

Wave' featuring an opencircuit voltage (OCV) waveform of 

1.U50 p with an inherent short-circuit current (SCI) 

waveform of 8/20 p. For the 'Category C' environment, 

the recommended SCI amplitude is 10 kA. ANSIIIEEE 

C62.11 specifies a test of discharge voltage at 1.5 kA and at 

5 kA with an 8120-p wave, and a current-withstand test of 

10 kA with a 4/10-p wave. 

Two types of surge-withstand tests were performed. The 

first consisted of the application of an 8120-p 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 maled 

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 andlor connector conrosion 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 thennal 

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 ANSIfiEEE C62.11, the metal oxi& varistor is first 

punctured by overvoltage with a lightly fused ac power 

supply. Then, full available fault current is applied to the 

&vice 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-toneutral 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 1201240-V low side. This transformer 

fed a loaddistribution 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 post-mortem of the 

end-of-life test. 

GEORGIA POWER MECHANICAL TESTS 

Impact Resistance 

In view of the handling procedures for meter adapters, 

impact resistance is an important parameter. Two industry 

standards were consulted for test techniques and impact 

force [ASTM Std. DW, ANSIJNEMA Std TC 8-19781. 

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 60°, 80°, 100°, and 125OC. 

At the end of each two-hour period, the &vices were 

examined and flexed by hand. All but one of the thennoplastic 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 computercontrolled, 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 currentan 

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 conected 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 'Ihen, 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 Wig 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 LowVoltage AC Power Systems, covers all TVSSs test protocols. 

The second, identified as SC-120, Surge Reference Equalizers 

Used in Premises Power-Communications System, 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 surgeprotective element. There were substantial differences in the 

designs. The surge-protective elements consisted of either 

multiple-paralleled 14mm or 20-mm radial-lead type MOVs, 

or single 40-mm MOV discs. The MOVs were electrically 

connected by soldered or welded bonding, or by springloaded contact. 

The fast 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 ~0~ected between 

each line at the load-side of the meter and ground. The 

voltaga 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. 

Fm utility L1 L2 

Figure 3 

Internal connections of MOVs in the meter-base arresters 

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 nonnally 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. 

Roducts with encapsulated (potted) MOVs tended to prevent 

the failed MOVs from blowing apart sufficiently to clear the 

circuit. 

PEAC TESTS ON PLUG-IN mss 

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. 'Ihis 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 WSS 

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 powerport TVSS. The products included various combinations of 

single or multiple, palallel<~~e~ted 14mm or 20-mm 

MOV discs. These were connected line-to-neutral, 

line-to-ground, and neutral-to-ground. Other designs 

included inductors andlor 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. 

Figure 4 

Typical circuit of a power-port, plug-in TVSS 

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 

Time 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. 

'Ihree samples of each brand were also surge tested with 

the ANSIhEEE 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 ftre hazard. All brands emitted 

some smoke when the MOW) 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. 

TELEPHONE LINE '9 gPowgrowid 

Fuse 

Figure 5 

Typical circuit for a telephone port SRE 

\ 

Ground 

rod 

1' Metal water pipe I 

Figure 6 

Surge Reference Equalizer for telephone link 

TEE 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 fastchanging electronic technology 

[Key et al., 19921. 

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 117 - 1000 hrs 

3. Flammability (self-ignition) - ASTM Dl929 

4. Impact resistance - ASTM Std. D2444 

5. Thermal withstand - 2 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 lime voltage conditions and swells, increasing the 

likelihood of premature failure [Martzloff & Leedy, 1987; 

ANSI C84.1-1989; Davidson, 1991; Lagergren et al., 19921. 

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, standardswriting bodies, and, to some degree, end-users. From this, 

we present several fidings and calls for action: 

1. There is a wide range of products available for surge 

protection, but all are not equal. A comprehensive productevaluation 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. I~dividual end-users have little leverage to influence the 

process of improving compatibility of products. However, 

the iuaeasing 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. 

IEC Pub 50(161) - International Electrotechnical Vocabulary 

- Chapter 161: Electromagnetic Compatibility, 1990. 

Dugan, R.C. - Low-Side Surges: Answers to Common 

Questions. Cooper Power System Bulletin SE9001, 1992 

Key, T.S., Sitzlar, H.E., and Moncrief, W.A. - Electrical 

System Compatibility Applied to End-use Equipment 

Characterization Project. Proceedings, PQA'92 (This 

conference). 

Lagergren, E.S., Parker, ME., Schiller, S.B., and Mattzloff, 

FD. - The Effect of Repetitive Swells on Metal-Oxide 

Varistors. Proceedings, PQA'92 Ois conference). 

Lai, J.S. and Martzloff, FD. - Coordinating Cascaded SurgeProtective Devices. Proceedings, IEEEIAS Annual Meeting, 

October 1991. 

Martzloff, F.D. - Coupling, Propagation, and Side Effects of 

Surges in an Industrial Building Wiring System. IEEE 

Transactions IA-26, MarchIApril 1990, pp. 193-203. 

Martzloff, F.D. and Leedy, T.F. - Selecting Varistor 

Clamping Voltage: Lower is not Better! Proceedings, 1989 

EMC Zurich Symposium, pp 137-142. 

Marz, M.B. and Mendis, S.R. - Protecting Load Devices from 

the Effects of Low-Side Surges. Proceedings, IEEUICPS 

Conference, May 1992. 

McMilen, CJ.. Schoendube, C.W., and Caverly, D.W. - 

Susceptibility of Distribution Tmsforma 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 - Secondaly Protectors for 

Communications Circuits. 1990 

UL 1449 - Standard for Safety - Transient Voltage Surge 

Suppressors. 1985 

REFERENCES Raymond C. Hill received a BEET from Southern Technical 

ANSI ~12.7-~987 - Requirementsfor warrhour sockets. lnbjitute in 1973 and his Professional Engineer license in 1983. 

He has worked for Western Electric and Florida Power 8 Light ANSI C84.1-1989 - American National Standardfor electric before joining Georgia Power. For the last 13 years, he has 

power system and equipment - Voltage Ratings (60 Hertz). been with the ~eojgia Power Research ~ente; where he is 

ANSI/EI--571-1991 - Environmental Considerationsfor responsible for high-voltage and high-current testing. He has 

Telephone Terminals. taught courses sponsored by Georgia Power and Georgia Tech 

on high voltage testing techniques. 

C62.1 - IEEE for Thomas S.Key received an MS, EE from Rensselaer Polytechnic Surge Arresters for AC Power Circuits. Insthute in 1974. Before ioining PEAC in 1989, he managed 

ANSVlEEE C62.33-1982 - Standard Tea Specifications for power system design applicat$ns for renewable sources of 

Varistor Surge-Protective Devices. energy at Sandia National Laboratory. At PEAC, he is Manager 

of Power Quality, responsible for power quality research and C62.41-1991 - Recomnended Practice On Surge testing. He has contributed many papers to the IEEE, and led Voltages in Low-Voltage AC Power Circuits. the development of a new IEEE 'Color BOOK on powering and 

ANSINEMA Std. TC 8-1978, Bra-Strength PVC Plastic grounding sensitive electronics. 

Utilities Duct for Underground Instal2ation. Francois D. Martzloff, a native of France, received an MS. EE 

ASTM std. D2444 - I~~~~~ ~~~i~~~~~ ofmmplastic pipe at ~eorgia Tech in 1952 an4 twenty years later, an MS, IA at 

and Fittings by Means of a Tup (Falling Weight). Union College. After 29 years with GE, he joined the National 

Institute of Standards and Technology in 1985. As an IEEE 

Davidson, R. - Suppression Voltage ratings on UL Listed Fellow, he has contributed a number of papers and led the 

Transient Voltage Suppressors. Proceedings. Forum on Surge development of severalstandards on surge characterization and 

Protection Application, NISTIR-4657, August 1991, pp 89-92. surge testing.