NBS

PUBLICATIONS

NBSIR 84-2987

A1110M 0S2S2S

Outline of CCVT Calibration

Procedure, EPR1-NBS Prototype

System--Supplement to EPR1

Report EL-690 (Field Calibration

System for CCVTs, April 1978)

David L. Hillhouse

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Gaithersburg, MD 20899

August 1 984

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U.S. DEPARTMENT OF COMMERCE

MATinwAL 3UREAU OF STANDARDS

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84-2987

1984

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NBSIR 84-2987

OUTLINE OF CCVT CALIBRATION

PROCEDURE, EPRI-NBS PROTOTYPE

SYSTEM-SUPPLEMENT TO EPRI

REPORT EL-690 (FIELD CALIBRATION

SYSTEM FOR CCVTs, APRIL, 1978)

David L. Hillhouse

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Gaithersburg, MD 20899

August 1 984

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

TABLE OF CONTENTS

Page

Abstract 1

1. INTRODUCTION ...... 1

1.1 Calibration Before Going to The Field 1 1.2 Field Calibration of Operating CCVTs 2

2. DETAILED CALIBRATION PROCEDURES 2

2.1 Calibration Before Going to The Field 2 2.2 Field Calibration of Operating CCVTs A 2.3 Recalibration after Return from The Field . 6

3. PRECAUTIONS 6

4. REFERENCES 6

i i i
LIST OF FIGURES

Page

Figure 1. Measurement 1 — Voltage integrity, divider module 7

Figure 2. Calibration of standard capacitor 8

Figure 3. Measurement 3 — Calibration of standard divider 9

Figure 4. Measurement 4 — On-line calibration of CCVT 10

Figure 5. Coaxial Choke Test Circuit 11

i v
OUTLINE OF CCVT CALIBRATION PROCEDURE,

EPRI-NBS PROTOTYPE SYSTEM—SUPPLEMENT

TO EPRI REPORT EL-690 (Field Calibration

SYSTEM FOR CCVTs, April, 1978)

David L. Hillhouse

ABSTRACT

This report contains, in outline form, the step-by-step procedure for

use of the EPRI-NBS Prototype Field Calibration System for Coupling

Capacitor Voltage Transformers (CCVTs) in the calibration of CCVTs in

the substation. It was prepared for the use of EPRI (Electric Power

Research Institute) personnel at Waltz Mill, PA, where the system now resides. It is a supplement to the EPRI final report (EL-690, April,

1978) on the project in which the system was developed.

Keywords: calibration; CCVT; EPRI; high voltage; prototype; substation

1. INTRODUCTION

This report outlines the most important steps to be taken in the field

calibration of CCVTs in the substation. It does not cover all the details of

these procedures. Such details are more fully documented in the references

given at the end of the report.

GENERAL NOTE: This report is a supplement to the final report [1] on the

development and testing of this calibration system. Reference [1] should be

studied carefully before attempting to follow the procedures outlined below.

The overall philosophy requires that the system must be calibrated at home

before proceeding to the field; then recalibrated at the site. Following this,

the test CCVTs are calibrated against the system, and the system calibration is

repeated afterward for closure. Upon return home, the initial calibration of

the system is repeated to gain assurance of overall stability.

1.1 Calibration Before Going to The Field

Calibration before going to the field consists of three steps, the first of

which is optional, as follows:

Measurement 1 (OPTIONAL). Check of the voltage integrity of the transfer

standard divider at 25% overvoltage, using the truck-mounted resonant power

supply.

Measurement 2. Low-voltage calibration of the truck -mounted compressed gas

standard capacitor.

Measurement 3. One-hundred-ki 1 ovolt calibration of the modular standard

divider, using the truck-mounted resonant power supply.

Numbers in brackets refer to the literature references listed at the end of

this report.

1
1.2 Field Calibration of Operating CCVTs

Field calibration of operating CCVTs consists of six steps, one of which is

optional

:

Measurement 1. Same as Measurement 1 above.

Measurement 2. Same as Measurement 2 above.

Measurement 3. Same as Measurement 3 above.

Measurement 4a. Check of the coaxial choke system in the signal cables.

Measurement 4. On-line calibration of the substation CCVTs.

Measurements 2 and 3. Repeat for closure.

The procedure for recalibration of the system after return from the field is

identical to that outlined in Section 1.1 for pre-cal i bration

.

2. DETAILED CALIBRATION PROCEDURES

NOTE: FOR FURTHER DETAILS, SEE ESPECIALLY Sections 6-2, 7-5, and Appendix D of

reference [1].

2.1 Calibration Before Going to the Field

Measurement 1 (OPTIONAL) . Check of the voltage integrity of the modular

transfer standard divider.

Step (1) Connect the circuit as shown in figure 1, making sure to

short out two of the three modules (500 kV conf i guration )

.

Step (2) Turn on the current comparator bridge and detector power

supplies, adjust the detector for lew gain. Introduce some noise by, e.g., inserting an ungrounded "antenna" into the

detector input terminals, tune the detector for maximum 60 Hz

output.

Step (3) Turn on the 100 kV resonant power supply, adjust input voltage to

about 10% of full scale, resonate the circuit per the

manufacturer ' s operating instructions, contained in his manual.

Step (4) Obtain a preliminary bridge balance (ratio of approximately 80:1)

by alternately adjusting first the ratio and then the quadrature

circuit for detector minimum. Increase detector gain as balance

is approached.

Step (5) Once preliminary balance is obtained, increase voltage to 100 kV

(120% of rated voltage per module).

Step (6) Rebalance the bridge, monitor for five minutes (time is

arbitrary), record the results. Comparison with earlier data

should show little shift over a period of months, and negligible

five-minute drift.

2
Step (7) Reduce the voltage to zero, shut off power, short a different pair

of modules, repeat steps (3) through (6).

Measurement 2 . Low-voltage calibration of the truck-mounted 200 k V compressed

gas standard capacitor.

Step (1) Connect the circuit as shown in figure 2.

Step (2) Turn on the bridge and detector power supplies, adjust detector

for low gain. Introduce some noise, by, e.g. , inserting an ungrounded "antenna" into the detector input terminals, tune the

detector for maximum 60-Hz gain.

Step (3) Turn on the 250 V transformer power supply, adjust to full

voltage.

Step (4) Obtain a preliminary bridge balance (ratio of approximately 10:1)

by alternately adjusting first the ratio and then the quadrature

circuit for minimum. Increase detector gain as balance is

approached.

Step (5) Obtain final bridge balance, record the results. Typical values

might be:

Ratio = 1 .00191

Multiplier = 10

Phase Angle = 0.005 mi 1 1 i radi ans

.

This represents the comparison of a 1000.00 pF reference standard

capacitor with the nominally 100 pF compressed gas capacitor —

value above is 1000.00/(10 x 1.00191) = 99.809 pF.

Step (6) Reduce voltage to zero, turn off the power, secure for safety [2],

Measurement 3 . One-hundred-kilovolt calibration of the modular transfer

standard divider, using the truck-mounted resonant power supply.

Step (1)

Step (2)

Step (3)

Step (4)

Step (5)

Step (6)

Connect the circuit as shown in figure 3 (500 kV configuration).

Turn on the bridge and detector power supplies, adjust the

detector for low gain. Introduce some noise, tune the detector

for maximum 60-Hz output.

Turn on the 100 kV resonant power supply, adjust the input voltage

to about 10% of full scale, resonate, the circuit.

Obtain a preliminary bridge balance (ratio of approximately 250:1

for 500 kV configuration) by alternately adjusting first the ratio

and then the quadrature circuit for detector minimum. Increase

detector gain as balance is approached.

When preliminary balance is obtained, increase voltage to 100 <7.

Rebalance the bridge (there will have been a small shift due to

divider voltage dependence), record the results. Typical values

might be:

3
Ratio = 0.49775

Multiplier = 500

Phase angle = 2.60 milliradians.

As the mathematics in [1] will show, the standard divider (SD)

ratio is obtained from a combination of the Measurement 2 and

Measurement 3 values, as follows:

SD Ratio = (10 x 1.00191 ) (500 x 0.49775) = 2493.50.

SD Phase Angle = 2.60+0.005 = 2.65 milliradians.

Step (7) Reduce the voltage to zero, turn off the power, secure for

safety [2].

2.2 Field Calibration of Operating CCVTs

The first three measurements below are identical to those in Section 2.1.

Measurement 1 (OPTIONAL) . Check of the voltage integrity of the modular

transfer standard divider.

Measurement 2 . Low-voltage calibration of the 200 kV truck-mounted compressed

gas standard capacitor.

Measurement 3 . One-hundred-kilovolt calibration of the modular transfer

standard divider, using the truck-mounted resonant power supply.

Measurement 4a . Check of the coaxial choke system (fig. 5)

NOTE: A discussion of the theory of Measurement 4a will be found in Appendix 6

of reference [3], The choke test circuit is located on top of the bridge. It

performs, by means of switches and a slightly different technique, the test

shown in figure 18, Appendix A-6, reference [3]. The voltages of concern are

V , between grounds G1 and G2, and V 92 , between grounds G2 and G3, figure 16 of

the same reference. These voltages must be cancelled in order to avoid

significant error in Measurement 4.

Step (1) Connect the circuit for CCVT calibration, as shown in figure 4,

EXCEPT DO NOT MAKE the plugboard connections 1-9 and 2-7, as called for on page D-16 of reference [1], shown also as open

circuits on figure 5 of this report.

Step (2) With the center conductors of the standard divider (SD) and test

piece (TP) signal cables shorted to shield at the divider and in

the control house, respectively,

(a) Plug a DVM into the choke test circuit output.

(b) Select the SD choke with the standard divider position of the

choke selector switch.

(c) With the function selector switch in the choke selector

position, readthe "choke-in" voltage on the DVM (should be no more than a few millivolts if choke is working

correctly )

.

4
(d) With the function selector switch in the choke ronitor

position, read the "choke-out" voltage by the same means (may

be 0.1 to 0.5 volts in a typical substation).

(e) Select the TP choke with the test piece position of the choke

selector switch, repeat the above procedure.

(f) Place the function selector switch in position 4.

NOTE: The choke out position of the function selector switch can also be used

to monitor the full line voltage (approximately 120 volts) when the system is in

operation.

Measurement 4 . On-line calibration of the substation CCVTS.

Step (1) Connect the circuit as shown in figure 4, carefully following the

safety procedures outlined in Sections 3 and 4 of reference [2].

Step (2) Turn on the bridge and detector power supplies, adjust the

detector for low gain. Introduce some noise, tune the detector

for maximum 60-Hz output.

Step (3) Instruct the control house to connect and identify the low side of

a test piece (CCVT).

Step (4) Balance the bridge (ratio of approximately 1:1 for a 500 kV,

. three-module divider) by alternately adjusting first the ratio and

then the quadrature circuit for detector minimum. Increase

detector gain as balance is approached.

Step (5) Record the results. Typical values may be:

Ratio = 0.98989

Multiplier =1.0

Phase Angle = 0.44 mi 1 1 i radians

.

The CCVT ratio is obtained by combining the data from Measurements

2, 3, and 4. Using the values from Measurement 2, Step (5) and

Measurement 3, Step (6):

CCVT Ratio = (10 x 1 .00191 )x (500 x 0.49775)

(1 .0 x 0.98989) = (10 x 500 x 1.0) x (1.00191 x 0.49775 x 0.98989) = 2*68.29.

CCVT Phase Angle = 2.60+0.005+0.44 = 3.09 mi 1 1 i radians

.

Step (6) Switch control house connections to another CCVT, repeat Steps (3) through (5) above.

Step (7) Disconnect from the high voltage bus, carefully following

Section 5 of reference [2], Repeat Measurements 4a and 4 for

another phase.

5
Measurement 2 and 3. Repeat for closure.

At the end of each day, and at the end of the test, the divider is recal i brated,

in order to correct for any drift in its values (primarily due to self-heating).

2.3 Recalibration after- Return from the Field

Repeat the calibration outlined in Section 2.1 (Calibration Before Going to the

Field).

3. PRECAUTIONS

Be sure to perform the ground voltage checks called for in for in Section 2.2,

Measurement 4a, at least once for every change of phases.

Use the same standard divider cable for all measurements. This cable forms part

of the divider low-side capacitance, so that it changes the value of a 2500:1

ratio (500 kV) by approximately 0.01% per meter of cable length.

4. REFERENCES

[1] Hilhouse, D. L., Petersons, 0., and Sze, W. C., A Prototype Field

Calibration System for Coupling Capacitor Voltage Transformers (CCVTs),

EPRI Final Report No. EL-690 (April 1978).

[2] Hillhouse, D. L., Guide for Safe Operating Procedures. . .During the Field

Calibration of CCVTs, NBSIR 81-2192, (Feb. 1981).

[3] Hillhouse, D. L., Petersons, 0., and Sze, W. C., A Simplified System for

Calibration of CCVTs in the Substation, NBS Technical Note 1155,

(May 1982).

[4] Hillhouse, D. L., Petersons, 0., and Sze, W. C., A Prototype System for

On-Site Calibration of Coupling Capacitor Voltage Transformers (CCVTs),

IEEE Transactions on Power Apparatus and Systems, Vol. PAS-98,

(May/June 1979), 1026-1036.

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1- PUBLICATION OR

REPORTINGNBSIR ad-298

7

in j. Or jan. ReportNo. 3- Publication Oat»

August 1984

4- TITLE AND SUBTITLE

OUTLINE OF CCVT CALIBRATION PROCEDURE* EPRI-NBS PROTOTYPE SYSTEM—SUPPLEMENT TO

EPRI REPORT EL-690 (Field Calibration System for QCVTs, April 1978)

5- AU-THOR(S)

Da.vid L- HilThouse„ Physicist

PERFORMINGORGANlZAT10f*(/f joint or other thamNBS- see- instructions)

NATIONAL BUREAU 0 R STANDARDS

DEPARTMENT 0 F COMMERCE

WASHINGTON. D\C. 20234.

T. Contract/ Grant Nov

I. Type of Report & Period Coverec

3. SPONSORING ORGANIZATION NAME AN 0 COMPLETE AQORESS (Street, City. State-. ZIP

)

10- SUPPLEMENTARY NOTES

i I Document describes, a computer program: SF- 1 85. FIPS Software Summary, is attached. 11— ABSTRACT (A 200-word or less factual summary of most si gnifican t information. If document includes a si gmficant

bi bliograohy or I i terature- survey. mention- it here/

This report contains,- irr outline fornr, the step-by-step procedure for use of the

EPRI-NBS Prototype Field Calibration System for Coupling Capacitor Voltage

Transformers (CCVTs) in the calibration of CCVTs in the substation. It was

prepared for the use of EPRI (Electrie- Power Research Institute) personnel at Waltz

Mill, PA* where the system now resides.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key

calibration; CCVT; EPRI; high voltage; prototype; substation

words Ov semicolons)

13. AVAILABILITY

14. NO. OF

i y ) Unlimited

1 I For Official Distribution. Do Not Release co NT1S

PRINTED PAGES

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