)

S'
NBSIR 79-1933

EVALUATION OF A MULTIMEGAVOLT

IMPULSE MEASUREMENT SYSTEM

r^et' <^cc - e^CU«N,

use,

lavq

Robert E. Hebner, Jr. David L Hillhouse

Randolph A. Bullock

October 1 5, 1 979

Issued November 1 979

Prepared for: Bonneville Power Administration

Portland, Oregon

U.S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

I. Introduction 1 II. Apparatus 7

11. 1 Divider Design, Construction and Calibration 7

II. 1. a Introduction 7

II.l .b 1 MV Divider 8

1 1. 2 Ramp Generator 21

1 1. 3 Step Generator 29

III. Computer Analysis Outline 31

111.1 Introduction 31

1 1 1. 2 Program Description 33

IV. Experimental Measurements 39

IV. 1 Introduction 39

IV. 2 Step Response of NBS-1 43

IV. 3 Step Response of BPA-R 43

IV. 4 Step Response of Combination of NBS-1 and BPA-R 45

IV. 5 Ramp Response of the Combination of NBS-1 and BPA-R 47

IV. 6 Step Response of BPA-C 49

IV. 7 Step Response of the Combination of NBS-1 and BPA-C 55

IV. 8 Ramp Response of the Combination of NBS-1 and BPA-C 57

V. Duhamel's Integral Calculations 57

VI. Conclusions 64

VII. References 65

Appendix 1 Listing of Software Used for Data Analysis 67
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I. INTRODUCTION

The accepted techniques for measuring the high voltage pulses used

for testing power system apparatus in the United States are described in

the voluntary standard issued by the Institute of Electrical and Electronic

Engineers, "High Voltage Testing Techniques," IEEE-4. This document is

essentially the same as International Electrotechnical Commission Publication

60-3.

The basic assumptions underlying this standard are sumnarized in a

publication^ by the International Research Group Renardieres on Impulse

Measuring Systems (IRR-IMS group). Basically, it is assumed that the

measuring system can be modeled as a two terminal pair network. The

relationship between the input and the output is

[ 1 ]

where V is the voltage, I is the current, the subscripts i and o refer

to input and output respectively and s is the Laplace operator. Formally,

the matrix A is represented as

V^. (s)

li (s) = [A]

Vo (s)

^0 < = >
- 2

-

All ^21

[ 2 ]

The voltage transfer function, H(s)» is defined as the voltage ratio when

the output current is zero, i.e..

It should be noted that in some cases, e.g., capacitor dividers with a

resistor in the low impedance element, A-ji (s) may not be defined at

zero. In this case, to represent the ratio as a single real number, All

must be frequency independent over the frequency range of interest. The

assumption of frequency independence over the range of frequencies of

interest is implicit because the divider must attenuate equally all frequencies

contained in the input signal.

H(s) = Vq(s)/V.(s) = 1/A^i(s) [ 3 ]

The divider ratio, N, is then defined as

N = A^^(o) = [A^^(s)] [ 4 ]

i
- 3

-

These fundamental considerations highlight two important facets of

the calibration of impulse measurement systems:

- determination of the divider ratio — a single

real number by which output voltage is multiplied

to determine the input voltage, and,

- verification that the transfer characteristics of

the system are frequency independent over a

sufficiently-wide frequency range so that this

single real number is valid for the waveform to

be measured.

The divider ratio can be measured using a variety of techniques which are

generally, but not exclusively, based on comparison of the input and

output voltages at a single frequency or a series of discrete frequencies.

The frequency dependence of A-j-j (s) is generally determined in the time

domain by measuring the response of the system to a voltage step.

Obviously, the frequency dependence can also be measured in the frequency

domain by performing measurements throughout all frequency ranges of

interest. Because these latter measurements are difficult and time

consuming^ time domain measurements are generally performed.

The purpose of this investigation was to determine experimentally

the adequacy of measurements of the response to a voltage step in large

scale, practical measurement systems. There are valid technical reasons
- 4-

to question measurement accuracy in such systems. These are based on the

fact that a practical measurement system is not well -correlated with

the model outlined above. Obvious discrepancies include the following

items

- The measurement system is not an ideal two-terminal

pair network. The constraint of current equality in

the input terminal pairs and in the output terminal pairs

cannot be easily realized, particularly because of ground

currents which cannot always be confined to specified paths.

- Inductive and capacitive couplings among the pulse generating

circuit, the measuring circuit beyond the divider terminals,

and the divider itself introduce signals in addition to

those specified at the terminals of the divider. (An unusual

phenomenon in this category is the cavity resonance of the

2 entire high voltage hall. This resonance, however, was not

observed in this investigation).

- It is not technically feasible to apply a voltage step directly

between two widely separated input terminals. Leads, therefore,

must be used to connect the terminals to a step generator.

Because the lead geometries are different in the tests of the

step response and the measurements of high voltage transients,

the entire divider circuitry is modified. The significance of

lead effects must be determined.
-5-

- The relatively small signals encountered in the determination

of the step response may be contaminated by extraneous

electro-magnetic interference.

These problems have long been recognized and a considerable amount of

effort has been devoted to verifying that measurements with uncertainties

of the order of a few percent can be performed. An area where inaccuracies

of a few percent are difficult to attain is the measurement of impulses

which are chopped on the front. As a demonstration of this exception,

IEEE-4 describes a technique to correct the crest value of a frontchopped impulse in those cases in which the response time of the measuring

system is more than 5 % of the risetime of voltage pulse. Unfortunately,

range of applicability of this correction is poorly documented. This

fact is emphasized, as this is the only correction for which the standard

explicitly suggests agreement between the parties involved before the

correction is applied.

The approach taken in this investigation was to verify that all of

the parameters in Duhamel's integral (also referred to as the convolution

integral could be measured with sufficient accuracy to guarantee

that corrections based on the measured response to a step would permit

meaningful measurements of the voltage waveform. Duhamel's integral

can be expressed as

0

[ 5 ]
- 6-

where x is an integration variable, 0'(x) is the time derivative of the

unit step response, V^. is the input voltage, the output voltage, and

N is the divider ratio as defined in Eq. 4. This equation dictates the

measurement program -- the input and output voltage, the divider ratio

and the step response each must be measured.

Measurements of the divider ratio, the step response and the output

voltage are conventional in a modern, high voltage test laboratory. It is

assumed that the input can be determined from these three measurements.

To verify this assumption, the input is also measured using a second

divider which introduces only negligible distortion in the applied

waveform. To provide evidence that the characteristics of this second

divider are appropriate for the desired measurement, two low voltage

checks are performed. First a low voltage (100-1000 V) ramp, having

about the same time-to-crest as the high voltage pulse, is applied to

the divider under test. The input and output voltages are measured with an

oscilloscope. Using the same experimental setup, the test is repeated

using the second divider to measure the input voltage. Comparison of

these results provides information with which to judge the validity of

the approach.

It should be noted that the low voltage tests using two dividers are

technically difficult. The output voltages typically range from

0.01-0.1 V peak. Electromagnetic interference and ground impedance

make measurements at this level challenging in an industral high

voltage laboratory.
-7-

This test protocol was originally developed and employed with

mixed success by the IRR-IMS group for an experimental session in the

summer of 1976 at the high voltage laboratory of Electricity de France.

Section II of this report describes the design, construction and

testing of the resistor dividers, the ramp generator, and the step generator.

The software used to evaluate the measurements is given in Section III.

Section IV presents the results of tests performed at the high

voltage laboratory of the Bonneville Power Administration. Section V

summarizes the data analysis results. Finally, Section VI summarizes

the results of the measurements and suggests possible implications.

II. APPARATUS

II. 1 Divider Design, Construction, and Calibration

II. 1. a Introduction

The basic design of the impulse divider had been developed by other

5 workers. In principle, the high impedance element is a non-inductive

resistor having a resistance of approximately 10,000 U. The resistance

distribution along the resistor is chosen to match approximately the

capacitance distribution, which is controlled primarily through the

choice of the size and position of the divider's guard ring(s). Two

dividers were constructed — one designed to measure standard lightning

impulses up to about 350 kV peak and the other designed to measure

standard lightning impulses up to approximately 1 MV peak. During the
- 8

-

high voltage tests, it was only necessary to use the larger divider, so

only it will be described in detail. The remainder of this subsection is a

description of the design, construction, and calibration of this divider.

Il.l.b 1 MV Divider

A photograph of the completed 1 MV divider is shown in Fig. 1. The

high impedance element consists of three discrete resistors. Each

resistor is nominally 1 meter long and 5 cm in diameter. To obtain a

somewhat non-uniform resistance distribution, which approximately matches

the capacitance distribution, the three resistors were designed to have

nominal resistances of 2500 3500 Q, and 4000 It should be noted

that a computer program has been developed to optimize the design of

resistor dividers.^ Because of the availability of design information

for dividers of this size, however, it was not judged necessary to incur

the expense of duplicating that program. The resistors were wound using

resistance wire that had a resistance of 26.2 J^/m. To obtain a noninductive resistor, two nominally equal windings were used, wound in

opposite directions one on top of the other and connected in parallel. Each

winding consisted of more than 1000 turns; the exact number of turns

depended on the desired resistance.

The resistors were wound using a lathe, so the actual resistance

was determined by the available pitch settings. The completed resistors

had values of 2729 Q, 3483 Q, 3945 Q.
-9 -

Fig. 1 The resistor divider, NBS-1 , rated at one million volts.
- 10-

The divider's low impedance element has a nominal resistance of

1 and consists of two 2-J2 pieces of resistance wire connected in

parallel. Each of the Z-Q. resistors is twisted to minimize its inductance.^ With this low value of resistance, the effect of low-side

capacitance (e.g., from cables or the measuring instrument) was judged

to be negligible. This judgement is based on the maximum frequency

which can be generated in the high voltage circuit, This frequency

4 can be estimated as

^ 4(h"

"H7r

’

where c is the speed of light, hg is the height of the generator, and h^

is the height of the front capacitor. To calculate f„,„, it was assumed

hr = Z hr which in general should overestimate f In Fig. 2, the

maximum frequency is superimposed on a plot of the calculated magnitude

of low side impedance versus frequency (using the conservative assumption

that low side capacitance is 1000 pF (equivalent to about 10 m of coaxial

cable)). It should be emphasized that this plot does not constitute

proof of measurement accuracy. It does, however, indicate that the

design of the divider low-side is probably adequate for the measurement

of the voltage pulses in a wide range of measurement applications.
11 -

U)

(ui) JO)8J8uao ^ « CM

00

NX

in 9

3

O’ _ O ^ w

O)o

eo

CM

(U) z

Fig.

2

Low-side

impedance

(solid

line)

as

a

function

of

freguency

and

theoretical

maximum

frcguency

(dashed

line)

as

a

function

of

generator

height.
- 12 -

The design of the guard ring was done experimentally. The size was

estimated from experience with other dividers of the same physical

dimensions and voltage ratings. Low voltage tests were performed to

document the relationship between the size of the guard ring and the

response to a voltage step.

The divider was calibrated by four different methods, consisting of

three low-voltage measurements:

- step-response

- dc voltage ratio

- resistances (plus calculation)

and one high voltage measurement:

- comparison with an electro-optic Kerr system, of

the measurement of the peak value of a high voltage

impul se.

A typical low-voltage step response is shown in Fig. 3. Average

step height from such oscillograms with an applied voltage of 135.5 V was

12.30 mV, from which a divider ratio of 10590:1 was obtained. The

uncertainty of this method was about ±1%, primarily attributable to

errors in resolving the spacing of the traces on the photographic record.

By digitizing the entire oscillogram and correcting for all distortion

in the oscilloscope screen and photographic reproduction, it is, in

principle, possible to reduce this uncertainty — perhaps by as much as

a factor of ten. In this case, the only correction applied was for

errors in the vertical gain of the oscilloscope. For the position on

the screen of the response shown in Fig. 3, this correction was negligible.
Applied Voltage: 135.5 V

Vertical Scale: 5 mV/Div

Horizontal Scale: 200 ns/Div

Fig. 3 Typical step response of NBS-1 .
-14-

Non-negl igible distortions were observed, however, for trace positions

significantly higher or lower on the screen.

To check the overall performance of the divider, the response time

was measured using five different values of the damping resistor (R^ in

Fig. 5). These data are shown in Fig. 4. From a least-squares linear

fit, the equivalent input capacitance^ was found to be 95.8 pF with a

standard deviation of 5 pF.

Measurement of the dc voltage ratio was performed using two digital

voltmeters. Typical results are presented in the following table.

TABLE 1: DC VOLTAGE RATIO

V in 0

(volts) (volts) Ratio

60.20 0.00567 10620

74.12 0.00698 10620

99.90 0.00940 10630

127.28 0.01198 10620

151.46 0.01425 10630

175.21 0.01649 10630

The resistances which must be measured in order to calculate the

ratio are shown in the circuit of Fig. 5. In this figure, Rj^ is the

'

damping resistor, R^^ is the divider high-side resistor, is the low- I

side resistor, R.j. is the terminator resistor at the input to the oscilloscope,]

R^ is the resistance of the center conductor of the coaxial cable

i connecting the divider with the oscilloscope and R

2

is the resistance of

the shield of that cable. From this circuit,

!
-15-

Fig. 4 Response time of NBS-1 as a function of damping resistance.
H

L

Fig. 5 Equivalent circuit of NBS-1 with damping

resistor and cable termination.
-17-

V. /V

0 i\/\) (R^ + R2 + Rt)/Rj> [ 6 ]

where

= R|_ II (R, + Rg + Ry) , [7]

and

R = + Rn +

T L H

[ 8 ]

The measured values were

R = 10360

T

R^ = 0.977

^1 R

2

Rj ~ 50.34

R^ = 50.26 .Q .

[ 9 ]
-18-

Calculations from these measurements yield a divider ratio of 10620:1, which

agrees with Table 1 values.

The test circuit for the simultaneous measurement of the high

voltage pulse using both an electro-optic Kerr system^ and the divider

is shown in Fig. 6. The pulse transformer provides an approximately

rectangular pulse with a full-width at half maximum of about 6 ys. To

perform an accurate measurement of the divider low-side peak voltage, a

suppressed-zero technique is used. The response of the Kerr cell is

shown in Fig. 7. The peak voltage applied to the cell is determined

from the equation:

I/I^ = sin^ (ff(V/V^)/2) [ 10]

where I/I^ is the relative transmittance of the Kerr system, V is the

applied voltage and is a constant determined by the cell geometry and

the properties of the electro-optic fluid.

Dividing this voltage by the measured peak of the divider output yielded

a divider ratio of 10560:1, within 0.7% of the low voltage values discussed

earlier. The applied voltage was approximately 150 kV peak during these

tests. During the development and testing of various configurations of

the low impedance element of the divider, a series of high voltage tests

was performed using both the square wave and a 1.2 x 50 ys standard j

i
Fig.

6

Test

circuit

for

high

voltage

calibration

of

NBS-1.
- 20 -

Fig. 7

Vertical Scale: 50 mV/DIv

Horizontal Scale: 1 (is/DIv

Typical response of Kerr system to high voltage pulse

-n 1-0 IS

maximum transmittance of the system whilp the minimum. syscem wmie
- 21 -

lightning impulse. The choice was determined by convenience and availability

of pulse sources, because it was assumed that the rates of change of both

waveshapes were sufficiently slow that the measured ratio would be

independent of pulse shape. While no systematic investigation of this

assumption was performed, a spot check indicated that the divider ratios

measured using the two waveforms differed by only about 0.1%.

The results of the four determinations of the divider ratio are

^ shown in the following table:

I TABLE 2: SUMMARY OF DIVIDER RATIO DETERMINATIONS

Measurement Method Ratio Deviation Fr

dc voltage 10620:1 +0.2

resistance 10620:1 +0.2

step response 10590:1 -0.1

comparison with Kerr system 10560:1 -0.4

II . 2 Ramp Generator

i

I

A voltage ramp with a nominal slope of 500 V/us, chopped after

' approximately 1 ys {^^21 volts), is required for the low-voltage

calibration of the high voltage divider. The circuit used to generate

' I

i

j this ramp is shown in Fig. 8. It is essentially a modification and

optimization of an earlier circuit used in unpublished experiments at

I Electricity de France. Voltage, V, is furnished by a conventional lowI current dc power supply. Capacitor, C, which serves as an "infinite"

' source during ramp generation, is charged slowly through resistor, R,

I which also serves to limit the power supply current after the circuit

! fires. Switching gap, G-| , is adjusted to break down when voltage V-j
- 22 -

G

CO

d>

JC

GC

3

Q.

3

o

A

A/W-’AAAi

O

o

If

o

(0 0)

v> 0)

oW E

o o

>

LU

LO

a> >»

£1 O) o> r*) U) cn $ a. X "o o 3

>

a. C/)

00

CT!

Ramp

generator

circuit.
-23-

equals the desired value, usually about 10 kV. G-| consists of two

2.5 cm brass spheres, operating in air. L, C-j , R.| , and Rj^ act to

generate and shape a ramp voltage across C-j after G-j fires. Gap G^,

similar in construction to G-j , chops the ramp at the desired voltage

Output voltage is applied directly to the divider under test, and

to a storage scope (not shown) via two cascaded 10:1 attenuators.

Once placed in operation, the circuit functions as a relaxation

oscillator, with a period determined by RC, V and the setting of gap G.j

.

The scope is triggered by a 30 cm diameter loop antenna placed 20-30 cm

from gap G.|

.

The response of the elemental circuit of Fig. 8 is easily calculated.

With the valid assumption that the time constant RC is much larger

than the ramp time, that C is much larger than C.j , and that G.j fires

instantaneously, output voltage is

\

(cos bt + ^ sin bt)]/(R-, + R-)

b

' ^

[ 11 ]

and ramp slope is

pQ

=

^1q_= V-| R^ q (e "^^sin bt)/b(R.j + R^)

dt

[ 12 ]
-24-

where ~ \

a = p/2

and

p

= (R^/L) + (1/R2C^),

q

= (R.J + R

2

)/R

2

LC-|

Equations (11) and (12) are valid until G

2

fires, after which the response is

of no interest beyond the fact that collapses very rapidly,

i.e., is truly "chopped".

The response of the circuit of Fig. 8 is shown in Fig. 9 for

V = 8.5 kV. This calculation is useful in ascertaining appropriate

component values to be used in the initial design of the circuit.

However, at these speeds stray capacitances and inductances play very

important roles in determining the shape of the final wave. These stray

parameters are never well known. Furthermore, their inclusion in the

basic circuit creates an intolerably complicated and tedious analytical

situation. Therefore, after the analytical first cut, design of the

circuit was primarily experimental, consisting of varying the physical

size, location and orientation of the circuit parameters, and observing
- 25 -

CM

00

d

tf> d

d

d

M

(sH/a) adois

(A) aBe^iOA

cn

C71

Calculated

response

of

ramp

generator

circuit.
-26-

the effects of these changes on the waveform. It may be noted in passing

that the waveshape is much more sensitive to the size and orientation of

the inductor than to any of the other parameters.

The efficiency of this design procedure is demonstrated by comparing

Figs. 10a and 10b. The former shows a typical wave early in the design

process, the latter the output wave of the final circuit. In Fig. 10b,

with applied voltage V-j ^ 8.5 kV, peak ^ 525 volts, chop time ^ 1.02 ys, and the slope near the peak ^ 520 V/ys. The wave is clean and

the chop is sharp 150 volts in 30 ns). This is close to the design

goals.

The final circuit layout is shown in Fig. 11. The open, "breadboarded"

layout on a large ground plane was found to be the simplest means of

controlling strays and pick-up in order to optimize the waveform. Component

descriptions are as follows:

Component Values Description

R

C

C

L

R

1

«h

5 M ^

0.75 yF

0.1 yF

2 7 yH

3.0 ^

9.3 Q.

Rated 1 mA steady-state, > 20 kV

flashover

Two 1.5 yF, 5 kV capacitors in series

Four 0.1 yF, 5 kV capacitors in series-parallel

35 turn air core solenoid, wound on 3.8 cm OD X 23 cm plastic form

6 turn, handwound, #24 resistance wire on 1.6 cm OD X 7.6 cm form

7 turn, handwound, #30 resistance wire on 1.6 cm OD X 7.6 cm form

Gnd Plane

1.1 ^ 1 turn, handwound, #30 resistance wire on

1

6 cm OD X 5 cm form

2.5 cm brass spheres in hardwood frame,

air gap screw-adjusted

Similar to G-j , except sphere

diameter = 1.90 cm

30 X 45 X 0.16 cm aluminum sheet, mounted on plywood base.
-27-

t 100 V

—*\ p^0.2|iS

Fig. 10 Upper photo (a) shows output of generator as first

constructed. Lower photo (b) shows output with

component location and orientation optimized.
-28-

Fig. 11 Ramp generator.
-29-

II. 3 Step Generator

The step generator is a conventional circuit based on a commercial lyavailable mercury-wetted-contact relay (Fig. 12). A dc power supply

provides a bias voltage through a current limiting resistor to a normally

open contact of the relay. For the tests performed during this work,

the dc voltage level is typically between 100 V and 150 V. A digital

voltmeter is used to record accurately the voltage on the normal ly-open

contact. When a pulse is applied to the coil of the relay, the normal lyopen contact is "instantaneously" shorted to the grounded contact. No

attempt is made to determine accurately the actual risetime of the

step. Using this generator, however, response times of measurement

systems as short as 20-25 ns have been measured. This provides an upper

bound on the risetime of the step.

Two operational constraints on this generator should be emphasized.

One is the occasionally overlooked fact that for resistor dividers the

magnitude of the voltage step must be determined at the relay side of

the current-1 imiting resistor which is between the dc power

supply and the relay. For capacitor or series RC dividers, however, the

voltage at the power supply is the voltage step.

A second operational difficulty is the fact that the step generator,

in order to simulate the high voltage measuring circuit, is usually at

least the height of the divider away from the divider base. It is,

however, necessary that the ground terminal of the relay remain at the

same potential as the base of the divider. Because high voltage laboratory
- 30 -

To dc

Power Supply ^

To Pulse

Generator

o

AAAr

To Divider

Under Test

Fig. 12 Step generator circuit.
-31-

grounding systems are designed to accommodate high voltage, high current

signals, it is sometimes necessary to make special provisions to insure

accurate measurement of the response of the system to a low voltage, low

current step.

III. COMPUTER ANALYSIS OUTLINE

III.l Introduction

The coding required to perform the actual integration is a small

fraction of the total program which is required.

First, data are converted to digital form for use by the computer.

This is done in either of two ways:

1. Direct conversion using a transient recorder (very fast A/D

converter with memory), or,

2. Indirect conversion using oscillographs for recording and

subsequent digitizing by means of a graphics tablet with

a computer interface.

Next, the digital image of the waveform is converted to a standard

format for use by the software. Data from the transient recorder or

graphic tablet is entered into computer memory via an interface link.

The data, once in memory, is converted from (X,Y) pairs of coordinates

back into time-referred voltage values. After the various data conversion

steps are performed, there are many options for dealing with the data

sets in computer memory.
In addition to removing dc offsets and correcting algebraic signs i

iif of all waveforms, the step response of the divider under test must be 'j

'i normalized to a positive unit-step in order to perform the Duhamel's Integral^

computation.

To obtain accurate results, the data are smoothed, using a polynominal i?

fitting subroutine called SMOOTH. After these adjustments, a calculation

^

of the system output is performed through application of Duhamel's ^

Integral to the measured input wave and step response. ,A

After calculation of the theoretical output, the measured output ,|

is compared using CORRELATE, which calculates the average error and its

standard deviation as well as instantaneous percent error. The waveforms

j involved may also be printed for plotting or further inspection. |

. I'

I

i, The program is structured as a small main program handling filing,

j

|i input/output, all operator functions, and subroutine control, with most

of the numerical work handled by small subroutines. This configuration was ''j i

found to be quite efficient as well as very easy to debug, maintain, and

expand. All permanent data are stored as integers in the main-program '!

I in one of 12 columns. Each column has a capacity of 600 data points and

a two-column work space is held in common. This limits access to main ,

data storage while allowing free access to workspace.

i

I To conserve limited minicomputer-core space, as well as execution

time, all data are held in 1/2 word integer format rather than full-word i

floating-point despite the loss of accuracy. Thus, each column of data
-33-

• must have a scale-factor to reconstruct the real value of each data

‘ point. The sample interval and number of samples is read in at the

'I pi beginning of a run, and remains constant. The operation of the control

section is interactive, i.e., as each task is finished, control returns

to the operator to select the next task. A string of control commands

I'

.j! may also be prerecorded on a floppy disc for unattended "batch" processing.

I

I j

!' III. 2 Program Description

1 1

|; The program listing is given in the Appendix of this report. The

r

j purpose of this section is to provide a functional description of the

I various tasks performed by the software to clarify the considerations

!i that went into the data analysis.

I

'

The main program and all essential subroutines are written in

Fortran V. The code is specifically intended to be used on a 16-bit

g

' Interdata minicomputer. It would require minor modifications to be used

|; with different computers.

I

t

t !

i

|: The subroutine organization is shown in Fig. 13. A brief functional

I' J

description of each of the tasks follows listed by mnemonic and grouped

; by activity.

List of Tasks by Mnemonic and Function

i J

Utility (Input/Output)

I RE [a] Read data directly from a mass storage file into memory

.i by indicated operand column

_i|

pi WR [a] Write data to a mass storage file, on logical unit OU,

from column a

.M
-34-

(/» <uc.3 ^ ca O —1 —

a; _! <c _i C u _J

>><_3

O <C LU

<-1 ' U_ <_} <1 o:

«« </1 LU LU LU LU < > 1— LO H- 0

-J

Q 2: 0 <c

LU 0 < -J >- LU OL 21 (_} 2 0 CO o: A A 4^
-35-

RL Read file label from logical unit, lU

WL Write file label on logical unit, OU, after rewind

WR [a] Write filemark on logical unit a

RF [a] Rewind logical unit a

Control and Miscellaneous

LA [a] Label column a (using a 12 character alphanumeric label)

CP [ab] Copy data and labels from column a to column b

lU [a] Set input logical unit to a

OU [a] Set output logical unit to a

LU List units; display values of lU and OU and list all

numbers assigned by the operating system

uni t

PA Pause into the operating system with easy return

KI Kill run - returns control to main program entry point;

permits change in operating parameters without destroying

data memory

EN End run - close all mass storage files, next logical

assignments and return to the operating system

uni t

Data Input Routines

TA [a] Tablet data input; reads data in graphics table format,

corrects (X,Y) pairs for rotation and scaling, generates

a constant-sample-interval data set compatible with main

program data array, and stores this in column a. Due to

the nature of the input medium and the whole process,

great care must be exercised in retracing the scope trace

to provide data for this operation. For calibration of

the graphic tablet output in terms of photograph_ divisions

,

a special procedure is followed: the corners of a

2 cm X 2 cm square from anywhere in the graticule is

entered, along with six points along some "baseline",

preferably a "ground-line" trace. This is done both

before and after data are entered. Data are separated

from calibration marks by a pair of points in the same location (before and after data).
-36-

This routine automatically scales and corrects the

input data for minor trace (baseline) rotation with

respect to the tablet axes, gives error messages for

unusual conditions, allows for interactive "data-saving"

patches during a run, e.g., if it cannot find the proper

scaling numbers, or to correct minor errors made at the

tablet, uses subroutine XYVDT to convert X,Y pairs to a compatible data set for the rest of the program, and it assumes no pulseshape for operation.

SK [a] Skip 'a' data sets (graphics tablet format) on logical unit

lU

XY [a] Reads (X,Y) coordinate pairs from control terminal, converts

to standard data set to store in column a. Generates a standard, compatible data set using time and voltage scaling,

same as TA (tablet) routine but without leading and trailing

automatic scaling, rotation numbers. Input time and voltage

scales must be in units of seconds/nib or volts/nib, where

1 nib is the resolution of the table output. It provides a chance to correct errors after data are entered. It also

allows observation of the data when the run is finished.

8 8

MI [a] Reads data from a Biomation 8100 Transient Recorder via MIDAS

interface, stores data in column a

FP Reads data from a transient recorder until the first peak

is observed. Prints out the true peak value and the position,

virtual risetime and rate-of-rise of impulse.

Data Analysis Routine

PO [abc] If columns a,b represent the voltage and the current in a waveform, column c (output) will represent instantaneous

power.

IM [a] Uses subroutine NEARST to locate peak (single maximum

value)

Searches before and after an apparent peak to insure

that the true peak has been located, calculates the

value of the peak and its location in time.

Calculates the virtual risetime which is defined as 1.67 times the time interval between the points

which are 30% and 90% of the peak value on the rise

of a voltage pulse and as 1.25 times the time interval

between the points which are 10% and 90% of the peak

value on the rise of a current pulse.
-37-

Calculates the virtual rate of rise which is the ratio

of the peak value and the virtual risetime.

Calculates the virtual origin which is a time defined

as the time at which the voltage waveform reaches

30% of its peak value minus 0.3 times the virtual

risetime for a voltage wave and, for a current wave,

as the time at which the current waveform reaches

10% of its peak value minus 0.1 times the virtual

risetime.

Calculates the virtual fall time which is defined as the time interval between the virtual origin and the

time at which either the voltage or current waveform

returns to a value of 50% of the peak after the peak

has been reached.

SM [ab] Fits the data in column a to a third order polynominal,

five points at a time, creating column b (non-destructive).

CO [abc] Calculates the average percent difference and standard

deviation between data in columns a and b and stores

instantaneous error in column c.

PI [abc] If an input waveform is in column a and a step response in

column b, this subroutine uses Duhamel's integral to

calculate an output waveform which is in column c.

rJO [a] If column a contains a step response, it will be normalized

to a positive unit step by altering the scale factor and

assuming average of last five data points represents 1. This routine can be used to eliminate dc offsets from a waveform or to normalize the response of a Kerr system.
-38-

Auxiliary Subroutines

ROTSCA -- Corrects for rotation and scaling of (X,Y) coordinate

data from graphics tablet (used by TA).

XYVDT — Converts (X,Y) coordinate data set into constant-sampleinterval data set for TA and XY routines.

NEARST -- Finds the nearest data point in a column of data to the

specified value, returns its location and error.

FIXDTA -- Fits any floating-point data set into an integer column,

finds best scale factor.

RELESE -- Releases interface driver for subsequent use.

MIDAS -- Interface driver, sends one line of commands, one line of

data.

CONURT -- Converts interface ASCII output to 16-bit integer,

reconstructs transient recorder output.

WAIT — Interrupts operating system, waits for operator to press

'RUN' button on front panel of CPU.

CLOSE -- Closes all mass storage files.

SYSTEM — Allows a FORTRAN program to execute operating system

instructions by passing them through this routine as

a character string.
-39-

READ 1 — Reads one character from logical unit 5 and returns to

IV. EXPERIMENTAL MEASUREMENTS

IV. 1 Introduction

A series of measurements was performed in the high voltage laboratory

of the Bonneville Power Administration (BPA), Vancouver, Washington. During

these measurements, the primary measurement devices were three high voltage

dividers. One was the resistor divider, rated at one million volts, which

was described earlier. For convenience of notation, this divider is

referred to as NBS-1.

The second divider was a resistor divider owned by the Bonneville

Power Administration. This divider, which is referred to as BPA-R, is

approximately 6.5 m tall and consists of counterwound resistor sections

in a porcelain enclosure. Either one of two low-side resistances could

be selected. Measured resistance values for this divider are presented

in Table 3.

program without carriage return.

TABLE 3: MEASURED RESISTANCES DIVIDER BPA-R

Value from earl ier

BPA data

Value measured

using BPA bridge

during test period

High Impedance Element 11630 11616 Q

I Low Impedance Element #1 43.88 44.05

1

i Low Impedance Element #2 14.64 $7
-40-

The third divider referred to as BPA-C, is a mixed (RC) divider

approximately 15 m high and rated at 4.5 MV, shown schematically in

Fig. 14. The high impedance element consists of a number of identical

resistor-capacitor units in series, each unit consisting of a 2250 pF

capacitor and a 50 resistor (these values were provided by the manufacturer

and not reverified as a part of this investigation). The series capacitance

had been measured by the BPA staff to be 433.43 pF. The primary components

of the low impedance element are a resistive and capacitive element

bolted to the base of the divider, a cable — with impedance matching

series resistor R located at the divider — to connect the divider to

the oscilloscope, and the cable termination located at the input to the

oscilloscope.

The capacitance at the base of the divider C^, has a value

0.9641 yF. The resistance R^ is zero, a modification which was apparently

performed after the original construction of the divider. The individual

resistors which originally constituted this resistance were still in

place but had been shunted by soldered pieces of wire. The cablematching resistor had a value of 50.48

The terminator is a series of switch-selectable circuits, three of

which are shown in Fig. 14. Switch position (1) permits direct connection

of the cable to the oscilloscope input. Position (2) applies a terminator

as shown. The remaining switch positions select other terminatorattenuator combinations. All terminators were designed to have nominal

equivalent single series RC elements of 0.95 yF and 50
- 41 -

0

Q.

OO

0)

o H o

cn

Mixed

divider

(RC)

with

cable

termination.
-42-

The divider ratio for a variety of divider terminator settings was

determined at low voltage from the capacitance ratio. The calculated

values are given in Table 4 along with the ratio determined from the

step response at the one setting at which step response measurements

were performed.

TABLE 4: BPA-C DIVIDER RATIO MEASUREMENTS

Nominal Ratio Ratio from Capacitance

Measurements

Ratio from StepResponse

2000 2334 —

4000 4636 4570

8000 9272 —

10000 11115 —

14000 16191 —

20000 23197 —

Table 4 shows that all the calculated ratios and the one ratio

determined from the step-response are significantly different from the

corresponding nominal ratios. This may be due to a modification of the

divider's low-side after its manufacture. The difference between the

ratio determined from capacitance measurements and that determined from

the step-response (1.4%) is within the combined uncertainties of the two

measurements.

During the two one-week test periods the following measurements

were performed:

- step response of NBS-1

- step response of BPA-R

- step response of the combination of NBS-1 and BPA-R
-43-

- ramp response of the combination of NBS-1 and BPA-R

- step response of BPA-C

- step response of the combination of NBS-1 and BPA-C

- ramp response of the combination of NBS-1 and BPA-C.

! Each of these measurements are described individually in the following

I sections.

j IV. 2 Step Response of NBS-1

The step-response of NBS-1 was measured in both BPA indoor highI voltage laboratories. The response time and divider ratio were consistent

with those measured at NBS.

I IV. 3 Step Response of BPA-R

Step response measurements with various values of damping resistor

are shown in Fig. 15. Note that for low values of the damping resistor

two types of oscillation are apparent. One is a lower-frequency oscillation — about 4 MHz -- attributable to a resonance between the lead

inductance and divider capacitance which the damping resistor of higher

value removes. The higher frequency oscillation -- about 30 MHz -- is

apparently intrinsic to the divider.

i

i

I

In an effort to insure that the measured response was the true

response to a voltage step and not due to an error in the design and/or

I

I

construction of the test circuit, a variety of checks were made. A number

j of different configurations of the connections of the various devices to

j the ground mat were attempted. As a general observation, changes in the
Fig. 15 Typical step responses of BPA-R .
-45-

ground configuration produced slight changes in the high frequency

oscillations, but no change yielded a substantive improvement. In

addition, the following steps were taken:

- the stranded high voltage lead was replaced by a solid

high voltage lead;

- tests were made in which the location of the cable connecting

the divider to the oscil loscope was changed;

- an isolation transformer, provided by BPA, was used to separate

the oscilloscope from the power system ground;

- an isolation transformer was used to separate the ground of

the dc power supply from the power system ground.

None of these adjustments produced a significant modification of

the high frequency oscillations.

IV. 4 Step Response of the Combination of NBS-1 and BPA-R

One of the measurements performed was the simultaneous recording

of the same waveform using the two different dividers. One purpose

of these tests was to insure that the signal in one measuring circuit

did not influence the response of the other measuring circuit. Using

the circuit shown in Fig. 16, the following measurements were performed:
- 46 -
-47-

- the step response of NBS-1 with BPA-R disconnected

from the step generator, i.e., the measurement

circuit was open at the step generator, and the

BPA-R measurement loop was grounded at the step

generator;

- the step response of BPA-R with MBS-1 open and with

NBS-1 grounded at the step generator;

- the simultaneous step responses with both measurement

systems connected to the step generator.

No difference in the step response was discernible in any of the

configurations. This was the anticipated result.

IV. 5 Ramp Response of the Combination of NBS-1 and BPA-R

The same sequence of measurements outlined above was performed with

the step generator replaced by the low-voltage ramp generator. The

significant result of these measurements is shown by the photographs in

Fig. 17. These photographs show a simultaneous measurement of the same

ramp using NBS-1 and BPA-R. Note the high frequency oscillations in the

measurement using BPA-R. It is assumed that these are due to the same

source as the high frequency oscillations in the step response. From
-48-

Simultaneous

Measurements

NBS-1

5 mV/Div Vertical

200 ns/Div Horizontal

BPA-R

100 mV/Div Vertical

200 ns/Div Horizontal

Fig. 17 Input ramp (upper photo) and response

of BPA-R (lower photo).
-49-

the response of NBS-1, it can be seen that the ramp is chopped approximately

1.2 ys after the pulse is initiated. The oscillations in the BPA-R

measurement system, therefore, persist into the time domain relevant for

tests on power system apparatus. Information provided by the staff of

BPA indicated that these oscillations are also apparent during high voltage

tests using a standard lightning impulse and so are not merely an artifact

of the low voltage calibration procedure.

Because the oscillations are apparently intrinsic to the BPA-R

measurement system, and because they persist throughout the time domain

of interest for these tests, it was concluded that this measurement system

was inappropriate for the ±3% accuracy desired in these tests. For that

reason the remainder of the experimentation and analysis was performed

using BPA-C.

IV. 6 Step Response of BPA-C

The step response of BPA-C was measured in the outdoor test area.

The experimental arrangement is shown in Fig. 18. Measurements were made

using damping resistors having values of 0, 61, 103, 141, 184, 269, and

451 A plot of the response time vs. damping resistance is shown in

Fig. 19. The slope of the least-squares fit to the data points indicates

that the input capacitance of the divider is 780 ± 40 pF. The input

capacitance was also measured using a capacitance bridge. In the square

loop arrangement — the arrangement in which the step response was measured

the input capacitance was 820 pF. If the high voltage lead is run along a
15m
-51-

Fig. 19 Response time of BPA-C as a function

of damping resistance.
-52-

diagonal of the original square loop, the input capacitance is 790 pF.

Because the disagreement between the input capacitance as determined

from the step response and as measured using bridge techniques is

somewhat larger than anticipated, it was judged to be prudent to

attempt to identify the source of the difference.

An examination of the step response data. Fig. 20, shows that there

is a difference between the level at which the step was triggered and the

position of the zero line as evidenced by a vertical gap of about 5 mV

between the base line and the start of the step trace. An investigation

of the circuit indicated that there is a 60 Hz signal with peak-to-peak

amplitude of approximately 6 mV appearing on the oscilloscope screen with

no input signal applied to the divider. Fig. 21a. If everything is

left in the same physical location but the divider low-side is electrically

disconnected from the divider high-side, the signal amplitude is reduced

to about 3 mV peak-to-peak. Fig. 21b. If the low-side is reconnected to

the divider, but the ground connection is broken, the peak-to-peak

amplitude of the 60-Hz signals is 3 mV, Fig. 21c. From these data, it

is inferred that approximately equal signals are coming from

the divider and from pick-up in the low-side and connecting cables.

There are a variety of 60-Hz sources in the vicinity of the outdoor

laboratory including a non-interruptabl e 13.8 kV supply line about 18-20 m

from the divider.

As a result of this investigation, it was concluded that it was not

feasible to perform a low-voltage calibration of the divider in the

outdoor test area, so the divider was moved inside the high voltage

laboratory
-53-

Rq=184Q

10 mV/Div Vertical

500 ns/Div Horizontal

Fig. 20 Typical step response of BPA-C during outdoor tests.
-54-

10 mV/Div Vertical

5 ms/Div Horizontal

Fig. 21 Output of divider with no input (a); output with

only the divider low-side and cable connected to

the oscilloscope (b); output with shield of cable

open-circuited at divider.
-55-

The physical arrangement of the divider in the laboratory is shown

in Fig. 22. In this configuration, the measured input capacitance was

790 pF. In the indoor laboratory, the 60-Hz signal was negligible and

to within experimental uncertainty the response time of the measuring

circuit was the product of the input capacitance of the divider, as

measured by the capacitance bridge — and the value of the damping

resistor. This result indicates that the low-voltage measuring system

is behaving in a manner consistent with the theoretical model used for

system calibration.

IV. 7 Step Response of the Combination of NBS-1 and BPA-C

Before BPA-C was moved into the indoor laboratory, step responses

were recorded in the outdoor test area using the measurement circuit

shown in Fig. 18. Again the following measurements were performed:

- step response of BPA-C with NBS-1 grounded and "open"

at the step generator;

- step response of NBS-1 with BPA-C grounded

and "open" at the step generator;

- simultaneous responses of both NBS-1 and BPA-C to the

same voltage step.

As before, no interaction between the two circuits was observed.

As described in the previous section, the induced 60-Hz signal in the

system made this data unsuitable for quantitative analysis. Because both
-56-

Fig.

22

Experimental

arrangement

for

indoor

step-response

measurements

of

BPA-C.
-57-

these data and the measurements taken using NBS-1 and BPA-R indicated

no interaction between the circuits, this set of measurements was not

repeated in the subsequent indoor tests. Step responses of the dividers

in the high voltage laboratory were, of course, measured and are shown

in Fig. 23.

IV. 8 Ramp Response of the Combination of NBS-1 and BPA-C

Ramp responses were obtained using both high and low voltage ramps.

These responses were used to perform the calculations described in the

next section of this report.

The low voltage ramp measurements were identical to those performed

using NBS-1 and BPA-R, described above. Typical data showing the ramp

measured with NBS-1, BPA-C and directly measured using a low-voltage

attenuator are shown in Fig. 24.

The circuit for the measurement with the high voltage ramp is shown in Fig. 25.

A conventional Marx generator applied a high voltage pulse to a sphere gap.

The voltage across the sphere gap was measured using both NBS-1 and

BPA-C. High voltage damping resistors were constructed and were used

in each measuring circuit. The high voltage ramp responses of the two measuring

systems in the high voltage configuration using the high voltage

damping resistors are shown in Fig. 26.

V. DUHAMEL'S INTEGRAL CALCULATIONS

To verify that the measuring system is well characterized, it is

necessary to insure that Duhamel's Integral computation of the output waveform predicts the measured waveform.
-58-

IS!

mmm

step Response

BPA-C

Vertical: 10 mV/Div

Horizontal: 500 ns/Div

Step Response

NBS-1

Vertical: 10 mV/Div

Horizontal: 200 ns/Div

Fig. 23 Step responses of BPA-C and NBS-1

inside high voltage laboratory.
-59-

Low Voltage Ramp

Measurements

BPA-C

Fig. 24 Ramp measured with BPA-C, NBS-1 , and directly

from generator (simultaneous measurements)-
High

Voltage

Laboratory

Building
-61-

W8S388

wmzmnmm

iraiiiii

Ramp Response

BPA-H

Vertical: 20 kV/Div

Horizontal: 1jjs/Dlv

RflBfln

nlSiiMiii

NBS-1

Vertical: 20kV/Div

Horizontal: 1|is/Dlv

g. 26 Typical ramp responses of BPA-C and NBS-1

(simultaneous measurements) .
-62-

Data from three different experimental set-ups are summarized in

Table 5. The first set of data was taken with a low voltage ramp measured

simultaneously using the divider BPA-C and a low-voltage attenuator. The

Duhamel's Integral calculation used the step response of BPA-C, measured

in the experimental configuration, and the directly measured waveform to

calculate the output waveform from BPA-C. Measured and calculated

outputs are compared in columns 2-4.

The second set of data presented is the result of a simultaneous

measurement of a low-voltage ramp using NBS-1 and BPA-C. In this case

it is assumed that the waveform as measured by NBS-1 is the input to

BPA-C. The comparison between the calculated and measured outputs is

shown in columns 5-7.

The final set of data is the result of a simultaneous measurement

of a high-voltage ramp using NBS-1 and BPA-C. Again it is necessary to

assume that the output waveform from NBS-1 is the input waveform to

BPA-C. These results are presented in columns 8-10.

The magnitude of the average difference obtained is within expected

experimental uncertainty. Each calculation required four measurements --

the step response of each divider and the ramp response of each divider.

The step response was needed both to determine the divider ratios and to

perform the integration. The ramp was recorded and digitized for the

integration and transcription of results. The accuracy of recording and

transcription is estimated to be of order ]%, so an average difference

of less than about 2 % is probably coincidental.
TABLE

5:

DUHAMEL'S

INTEGRAL

CALCULATIONS

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-64-

VI. CONCLUSIONS

The data presented indicate that, under the conditions of this

test, a Duhamel's Integral calculation is valid for a 4.5 MV divider.

From this it can be inferred that the measured response of this divider to

a low voltage step provides sufficient information about the transfer

function of the measurement system to predict the response to the specific

pulses used in this test.

Although this is a significant first step, more work remains to

completely characterize the measuring system. Specific individual

investigations which would be desirable include:

- measurements of higher voltage, faster ramps where

the higher time rate of change of the current

may provide more significant coupling between

the voltage generating circuit and either of the two

measuring circuits;

- development of methods to evaluate the transfer

functions of the measurement systems outdoors

in situations where the 60-Hz signals make low

voltage measurements unfeasible;

- development of more convenient calibration methods

which will permit rapid recal ibration of the

measurement system in each configuration used in an

industrial laboratory.
-65-

The necessity to develop fast, convenient, accurate methods to evaluate

measurement system behavior cannot be overemphasized. A change in divider

location or in lead configuration significantly changes the divider ratio.

For large dividers, such as the one tested here, variations of the ratio

of several percent can occur for the measurement of the peak value of a

standard lightning impulse. For faster pulses, even very small changes in

the circuit configuration may have significant impact on the divider ratio.

It is, therefore, necessary to verify the magnitude of the ratio in each

configuration of the measurement circuit.

The low-voltage step response method used here (presented in the standard

IEEE-4), although proven to be correct in this application, requires very

accurate low voltage measurements under adverse circumstances. Routine

application of the technique, therefore, requires experienced, highly

trained measurement specialists. Until improved calibration methods are

proven to be accurate, industrial high voltage laboratories will be forced

to develop specific training programs for laboratory staff or tolerate

unspecified, but probably significant, measurement errors.

VII. REFERENCES

1. IRR-IMS Group, "Facing UHV Measuring Problems," Electra, No. 35,

pp 157-254, July 1974.

2. R. Malewski, D. Train and A. De Champlain, "Cavity Resonance Effect

in Large HV Laboratories Equipped with Electromagnetic Shield,"

IEEE Trans. Power App. Sys., Vol . PAS-77, pp 1863-1871, 1977.
- 66 -

3. F.A. Fisher, "Transient Response of Impulse Voltage Dividers,"

AIEE Trans. Common. Electron., Vol . 77, pp 411-420, 1958.

4. A. Greenwood, "Electrical Transients in Power Systems," WileyInterscience, New York, pp 27-31, 1971.

5. See, for example, F.C. Creed and M.M.C. Collins, "The Measurement

of Short-Duration Impulse Voltages," AIEE Trans., pp 621-630, 1963.

6. R. Malewski and S. Maruvada, "Computer Assisted Design of Impulse

Voltage Divider." IEEE Trans. Power App. Syst. , Vol. PAS-76,

pp. 1267-1274, 1976.

7. R.E. Hebner, R. Malewski, E.C. Cassidy, "Optical Methods of Electrical

Measurement at High Voltage Levels," Proc. IEEE, Vol. 65,

pp 1524-1548, 1977.

3. Certain commercial equipment, instruments, or materials are identified

in this paper in order to adequately specify the experimental

procedure. In no case does such identification imply recommendation

or endorsement by the National Bureau of Standards, nor does it

imply that the material or equipment identified is necessarily the

best available for the purpose.
- 67 -

APPENDIX 1

LISTING OF SOFTWARE USED FOR

DATA ANALYSIS
1NTEGER>k

2

Nft(bO0.l2)

RErtL

DV(12)

.DRTE(5).XNftnE(5),C0LftBL(

12.3)

COMMON

/SCRRT/UORK(600)

IMPLICIT

INTEGER>k2

(I-N)

- 68-

(Ss

S)LU

CJ

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t

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BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR -79-1933

Z, Accession No..

4. TITLE AND SUBTITLE

Evaluation of a Multimegavolt Impulse Measurement System

5. Publication Date

tzstloR Code

7. AUTHOR(S)

R.E. Hebner, D.L. Hillhouse, and R.A. Bullock

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rSfreer, City, State, ZIP) 13. Type of Report & Period Covered

Bonneville Power Administration

Portland, Oregon 97202 14. Sp^sc^ng €k)de

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200^word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here,)

The calibration of a 4.5 MV impulse divider was evaluated by measuring both the

input and output waveforms and the response of the divider to a low voltage step.

The measured output was compared to an output calculated from the step response

and the measured input waveform using Duhamel's Integral. The validity of the

approach for this large measurement system was demonstrated for the specific

waveforms studied.

17. KEY WORDS fsix to twelve entriea; alphabetical order; capitalize only the lirat letter o{ the first key word unleaa a proper name;

aeparated by aemicolona)

Divider; Duhamel's integral; high voltage; impulse; pulse measurements,

response time; step response; transients

Ts. AVAILABILITY [Xl UnlimiteT

I I For Official Distribution. Do Not Release to NTIS

I

; Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- ^ Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

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UNCLASSIFIED

21. NO. OF

PRINTED PAGES

101

22. Price

$ 6 . 50

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