Significance:

Part 5 – Monitoring instruments, laboratory measurements, and test methods

The three impulse generators described in this report were investigated a possible candidates for producing the

transient waveform just then adopted for testing the emerging ground-fault circuit interrupters (GFCI) that were

found to be susceptible to the oscillatory transients that had been found to be the most frequent type of transient on

ac power lines (See “Res&Ind surges” in Part 3). 

The third approach was eventually adopted as recommended test circuit in UL standards concerned with GFCI

misoperation, and its waveform became the basis of the IEEE “Ring Wave” promulgated with IEEE Std 587 -1980. 

TM

A packaged design suitable for bench-top use was then implemented (See “TCL Generators” in this Part 3) and

several units were built for GE Corporate R&D, GE operating departments, and the Underwriters Laboratories.

It should be noted that at that time, the perceived threat was the low energy-delivery capability of these oscillatory

transients, not the higher energy-delivery capability of what became known as the “Combination Wave”. 
General Elactric Company 

Corporate Resoarch and Development 

Schenectady, New York 

High-Voltage Impulse Testers 

TECHNICA L INFORMATION 

SERIES 

\UTHOR 

Howell, EK+ 

Martzloff, FD 

I 

IRlGlNATiNG 

:OMPONENT CORPORATE 

RESEARCH AND OEVELOPMEN Physics & Electronics Engineering Laboratory SCHENECTADI,N.Y. - 

iUYMARY Design tests on various electronic appliances require 

to subject the test sample to voltage spikes superimposed 

to the 120 volt a-c line voltage. 

This report discusses three types of surge generator 

circuits which can be used to produce these test impulses, 

and gives a recommendation for a simple test circuit 

which can be easily built by other organizations, thereby 

promoting uniform performance criteria. 

The test wave shape has the rise time of a 500 kHz 

oscillation, followed by ringing at 100 kHz. The first 

peak is adjustable from 0 to 8 kV; the second is 60% of 

the first. 

SUBJECT 

impulse test circuits 

+General Electric Circuit Protective Devices Products 

Department, Plainville, CT. 

NO 

75CRD039 DATE 

March 1975 IITU 

(EY WORDS 

GE CLASS , 

surge voltages, transients, spikes, impulse, 

test equipment 

INFORMATION PREPARED FOR 

Additional Hard Copies Available From 

Microfiche Copies Available From 

RD-54 W70) 

Corporate Research 8 Development Distribution 

P.O. Box 43 Bldg 5, Schenectady , N.Y. ,12301 

Technical Information Exchange 

P.O. Box 43 Bldg. 5, Schenectady , N.Y., 12301 
HIGH-VOLTAGE IMPULSE TESTERS 

E. K. Howell and F. D. Martzloff 

I. INTRODUCTION 

The high-voltage impulse generators described 

in this report have been developed by several individuals for the purpose of simulating transient overvoltages as they occur on residential or industrial 

low-voltage a-c power circuits (120 or 220 volts). 

Each circuit was developed on the basis of certain 

objectives, and consequently the designs are quite 

different. An evaluation and comparison has been 

made, from the point of view of producing a simple 

and economical system limited to generating the 

proposed "typical" surge wave shape on a 120 volt 

single-phase circuit. (1-3) 

The objective of this test circuit is to superimpose on a 120-volt, 60 Hz power line a wave shape 

having a rise time to first peak of a 500 kHz'wave. 

followed by a damped ringing at 100 kHz in which 

each successive peak should be about 60% of the 

preceding peak amplitude, the amplitude of the first 

peak being adjustable from 0 to 8000 volts. The 

source impedance for the high-voltage wave should be 

50 ohms. 

The three circuits are the following: 

1. General-purpose ignitron switch generator, 

suitable for 20 kV, 20 kA pulses. 

2. Specialized generator with low-voltage SCR 

switch and step-up pulse transformer. 

3. Relay-type switch and resonant circuit 

(recommended circuit). 

11. GENERAL-PURPOSE CIRCUIT 

This circuit is assembled from available laboratory components, with an ignitron switch built especially for the purpose. (4) The circuit schematic is 

shown in Fig. 1. The switch is SW; the energy 

storage element & can be a line (cable) or capacitor 

bank, charged by the high-voltage supply HVDC. 

The surge is produced across the matching impedance 

R by discharging the cable when the switch is fired. 

4 

Fig. 1 Schematic diagram of surge generator. 

Manuscript received February 7, 1975. 

The surges developed by this circuit can be 

coupled into an a-c power supply, with a suitable 

filter inserted between the bench supply and the receptacle where the device under test will be connected. 

and where the surge is injected, in a shunt mode; 

that is, directly across the a-c terminals (Fig. 2). 

This shunt mode allows very fast rise time for the 

pulse, typically 50 to 100 nsec in the absence of deliberate sloping network. Furthermore, the source 

impedance of the surge can be readily adjusted as 

desired by controlling the parameters (cable characteristic impedance, or surge impedance of a capacitor 

bank). 

In fact, the very flexibility of the circuit becomes 

a handicap in this case (too complicated for routine 

testing to a specific wave shape), and together with 

the relatively high cost and inability (as designed) to 

produce repetitive pulses, this makes this approach 

less attractive than the two others. On the other 

hand, when experimentation is the object, the flexibility of this circuit is a great asset. 

111. THYRISTOR SWITCH AND STEP-UP 

PULSE TRANSFORMER 

This circuit was designed with the specific objective of producing spikes on the a-c line, with the 

further aim of avoiding a high-voltage switch and the 

need for a filter. The surge is to be injected in 

series with the a-c line by a coupling transformer 

acting as a step-up pulse transformer. Figure 3 

shows the schematic diagram of the circuit. Energy 

is stored in capacitor C. at about 500 volts. The 

thyristor discharges the capacitor through the primary of TI and the pulse is coupled across inductance 

L by the coupling capacitor Ca. C4 and C3 serve. 

respectively, to bypass the a-c line and to control 

the ringing frequency. 60 Hz power is supplied through 

the isolating transformer Ta. 

The difficulty in this circuit, when fast rise times 

are desired, is to control the inductance of the TL 

primary loop, which must be in the order of 0. 2 )IH 

or less for the rise time desired in this case. While 

the components for this circuit are of special design. 

a supplier was identified who could produce them for 

interested users. However, the relative complication 

of the circuit, the cost of the high current SCR required, made this approach less attractive than the 

third circuit. which will now be described in detail. 

IV. RELAY-TYPE SWITCH WITH RESONANT 

CIRCUIT 

The basic schematic diagram of the tester is 

shown in Fig. 4, and the relay control circuit is 

given in Fig. 5. Photographs of the waveforms are 

shown in Figs. 6 through 10. 
(50) IGNITRON 

I----------I 

I FUNCTION I SWITCH I GENERATOR I 

USED AS 

TRIGGER &--+-- 3 r ------- 4 5 

Spike at outlet - Spike fed back into power supply 

(Minimum RC) 

6 kV crest 

10~s first loop 

- 60 Hz trace with spike 

- expanded spike (50us/div) 

- zero trace with scope pickup 

Fig. 2 Surges developed by the general-purpose circuit can be coupled into an a-c power supply. 
500 VDC 

TEST 

RECEPTACLE 

Fig. 3 Schematic circuit of test circuit with series injection by pulse transformer. 

- ------- I 

CR-I LI 1 

: 

CRO TRIGGER 

CONTROL OUTPUT 

JND 

+ CI - -025uF. lOkV, (Gudeman, 2 x -01 + RI - 22~1, 1~. cornp. 

-005) R2 - 12n, 1W. Comp. C2 - -01PP. 10kV. (Plastic Capacitors, 

Inc. ) R3 - 1.3Mn (12 x 1lOKn. l/2W) 

C3 - 4pF. 40W R4 - 47- (10 x 4.71Cn. 1/2W) 

LI - 15UH (32 turns, X23 wire, 0.7" dia. R5 - 200n' 'I2" 

Air Core ) CR-I - Relay, 2 N.O. poles in series 

L2 - 70vH (28 turns, #23 wire. 2.6" dia. GE CR2790 E 100 A2 

Air Core) 

* Gudeman GC 2455103M37 - -01~~ 

Gudeman GC 245S502M37 - -005pF 

Plastic Cap-Inc. OF100-103F - .01vF 

Fig. 4 Basic impulse generator circuit. 
Fig. 5 Relay co~ 

WA U. 

CRO GATE 

INPUT 

m 

I + 

60 Hz CI 

!:I 

50 VA 

DI,D2 - IN5060 

SC'R1 - GE C122B 

CR-1 - Relay GE CR 2790 E 100 A2 

TI - Triad N4S X 

- 

D 2 CR-I 

-- 

SCR l 

ltrol circuit for impulse generator. 

Vert: 2 kV/div Hor: O.2ps/div 

Fig. 6 Impulse rise - no load. 

Vert: 2 kV/div Hor: O.Zps/div 

Fig. 7 Impulse rise - 50 ohm load. 

Vert: 2 kV/div Hor: 2ps/div 

Fig. 8 Ringing wave - no load. 

Vert: 2 kV/div Hor: 2ys/div 

Fig. 9 Ringing wave - 50 ohm load. 
In principle, a d-c voltage is stored on capacitor 

Cl. At about the 70 degree point on the 60 Hz supply 

wave, a pair of relay contacts are closed to connect 

C1 to the Line Output terminal by way of.a waveshaping network L1, R1. C2. R2, and L2. A large 

capacitor, C3, prevents transmission of the wave 

back into the power system. Figure 10 shows the 

pulse superimposed on the 60 Hz, 120 volt line (contact bounce produced two subordinate trailing pulses). 

The 500 kHz rise characteristic is obtained by 

the series resonance of L1 and the capacitance of C1 

and C2 in series. Component values are selected to 

make JLIC approximately 50 ohms, and R1 mas 

selected to provide heavy damping for a smooth transition to the following wave. Figure 6 shows the rise 

time. open-circuit, and Fig. 7 with 50 ohm load. 

The 100 kHz damped ring results from the parallel 

resonance of L2 with the parallel capacitance of C1 

plus C2. Again, is about 50 ohms. The series 

damping resistor R2 was selected to produce the 

decay to 60% amplitude between successive peaks. 

Figure 8 shows the ringing wave on open circuit, and 

Fig. 9 shows the same wave when loaded by 50 ohms. 

A comparison of first-peak amplitudes shows that the 

source impedance is approximately the desired 50 

ohms. Approximately 8 kV d-c charge on Cl is required to produce an open-circuit peak of 6 kV on the 

output terminal because of the charge transferred to 

C2. 

Vert: 2OOV/div Hor: 2ms/div 

Fig. 10 Impulse superimposed on 120 volt line 

voltage - output of impulse tester. 

At low voltages, the relay contacts behave normally, but at high voltages they can no longer be considered as contacts but rather as a moving spark gap. 

In Figs. 8 and 9 disturbances in the sinusoidal shape 

occur as current in the plasma reverses in each halfcycle. The introduction of heavy metal ions into the 

plasma, such as by use of a mercury relay, can reduce the extent of such waveform distortions; however. 

it is considered that these distortions do not materially . . 

tests. 

Laboratory tests with this circuit used a storage 

CRO with delayed sweep and single sTKreep capabilities. 

The main sweep gate output was used to trigger the 

relay control circuit, and the main sweep was triggered from the 60 Hz line such as to produce the 

high-voltage surge at the desired point of line voltage. 

Main sweep duration was about 20 msec. The delayed 

sweep was first delayed 1 msec, then triggered by 

the output from divider R4, R5 at the start of the highvoltage rise time. Since the charging time constant 

on C1 is 0.033 second, the test can be repeated 

within 0, 5 second. 

It should be emphasized that this is an experimental design to illustrate a concept, not a product 

design. There are no operator-safety provisions 

shown, and only "qualified persons" must be allowed 

to operate the apparatus. The component values are 

approximations taken for ready availability and ease 

of construction. The performance does show, however, that the proposed test waveform can be produced by a relatively simple, inexpensive method. 

ACKNOWLEDGMENTS 

The general-purpose ignition switch and its control circults were developed by R.N. Bushman as 

part of the laboratory equipment used in transients 

investigations at Corporate RBiD. 

The SCR/pulse transformer circuit and magnetic 

components was designed by H. W. Lord, especially 

for the purpose of producing the spikes on the a-c 

line voltage. 

REFERENCES 

F. D. Martzloff and G. J. Hahn, "Surge Voltages 

in Residentlal Power Circuits. " IEEE Trans. 

Power Apparatus and Systems, PAS-89. No, 6 

1049-1056 (July-Aug. 1970). 

J. E. Lenz, "Basic Impulse Levels in Mercury 

Lamp Ballasts for Outdoor Application, " Illum. 

Eng. 133-140 (Feb. 1964). 

"IEEE Guide for Surge Withstand Capability 

(SWC) Tests, " American National Standard, 

published by the Institute of Electrical and Electronics Engrs., Inc.. Nos. IEEE Std. 472-1974 

and ANSI C37-90a-1974. 

"Ignitron Switch for Surge Generator, " General 

Electric Publication GEI-45105, Corporate R&D 

Schenectady, N. Y.