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ANSI/ e5izEi9 IEEE Standard for High-Potential-Test Requirements for Excitation Systems for Synchronous Machines

EEE Std 421 B-1979 (Reaffirmed 1984)

Published by The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, NY 10017, USA

.June 1, 1979 SH07344

Authorized licensed use limited to: UNIV ESTADUAL PAULISTA JULIO DE MESQUITA FILHO. Downloaded on February 10,2011 at 11:20:27 UTC from IEEE Xplore. Restrictions apply.

ANSI/IEEE Std 421B-1979 (Reaffirmed 1984)

An American National Standard

IEEE Standard for High-Potential-Test Requirements for

Excitation Systems for Synchronous Machines

Sponsor

Power Generation Committee of the

IEEE Power Engineering Society

Approved December 15,1977 Reaffirmed June 14,1984

IEEE Standards Board

Approved July 21, 1981

American National Standards Institute

@ Copyright 1979 by

The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, NY 10017, USA

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise,

without prior written permission of the publisher.


Approved December 15,1977

IEEE Standards Board

William R. Kruesi, Chairman Irvin N. Howell, Jr, Vice Chairman

Ivan G. Easton, Secretary

William E. Andrus Jean Jacques Archambault Mark Barber Edward J. Cohen Warren H. Cook Louis Costrell R. L. Curtis David B. Dobson

R. 0. Duncan Charles W. Flint Jay Forster Ralph I. Hauser Joseph L. Koepfinger Irving Kolodny Benjamin J. Leon Thomas J. Martin

Donald T. Michael Voss A. Moore William S. Morgan William J. Neiswender Ralph M. Showers Robert A. Soderman Leonard W. Thomas, Sr B. W. Whittington


Foreword

(This Foreword is not a part of IEEE Std 421B-1979, IEEE Standard High-Potential-Test Requirements for Excita- tion Systems for Synchronous Machines.)

The IEEE Working Group on High-Potential Testing of the Excitation Systems Subcommittee of the Power Generation Committee was activated in February 1969. The subcommittee recognized the need for a standard because of obsolete conflicting standards and changes in excitation-system equipment. Excitation systems no longer consist only of a rotating machine and a simple voltage regulator, but have developed into various types of systems with many regulating loops. The application of semiconductors and other new components in modem excitation systems of increased size and complexity required new guides for high-potential testing. A new standard would ensure more consistent testing of equipment.

Members of the IEEE Working Group of the Excitation Systems Subcommittee of the Power Gen- eration Committee which prepared this standard are:

D. H. Miller, Chairman

A. A. Berthe G. M. Cotzas T. L. Dillman T. K. Essandoh

D. I. Gorden P. R. H. Landrieu J. R. Mather J. R. Michalec


Contents

SECTION PAGE

1 . Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 . Standards References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 . High-Potential Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 TypeofTests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4 . Frequency and Waveshape of Test Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 . Duration and Application of Test Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6 . Measurement of Test Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Standard Test Voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Exciter Output Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

7 . Temperature a t which Tests Shall be Made . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

8 . 8.1 8.2 Allothercircuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

9 . Revision of American National Standards Referred to in This Document . . . . . . . . . . . . . . . . . . 9

APPENDIX Appendix A Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Appendix B Technical Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fig B1 High-Potential Test Voltages (Comparison of Various Standards) . . . . . . . . . . . . . . . . . . 12 APPENDIX FIGURE


IEEE Standard for High-Potential-Test Requirements for

Excitation Systems for Synchronous Machines

1. Scope

This standard applies to high-potential testing of complete excitation systems and their components for synchronous machines. The components of the excitation system are de- scribed in IEEE Std 421-1972, Criteria and Definitions for Excitation Systems for Syn- chronous Machines. Also included are auxiliary devices that are exposed to excitation system stresses. Examples of such auxiliary devices are temperature indicators, transducers, meters, etc. This standard does not cover the synchronous-machine field winding or field circuit breaker and discharge resistor. This standard supplements existing standards for components used on excitation systems: ANSI C19.3-1973, Industrial Control Apparatus - General; ANSI C19.4-1973, Industrial Control Apparatus - Enclosures; ANSI C19.5-1973, Industrial Con- trol Apparatus - Switching or Controlling De- vices; ANSI C19.6-1973, Industrial Control Apparatus - Control-Circuit Devices and Assemblies; ANSI C19.7-1973, Industrial Con- trol Apparatus - Controllers and Controller As- semblies; ANSI C34.2-1968 (R1973), Practices and Requirements for Semiconductor Power Rectifiers; ANSI C37.18-1968 (R1975), Re- quirements for Field Discharge Circuit Breakers for Rotating Electric Machinery; ANSI/IEEE C57.12.00-197 3, General Requirements for Distribution, Power, and Regulating Trans- formers; ANSI/IEEE C57.12.90-1973, Test Code for Distribution, Power, and Regulating Transformers; and NEMA ICs1970 (R1975), Industrial Controls and Systems.

2. Standards References

The following standards publications are referenced in this standard.

ANSI C19.3-1973, Industrial Control Appara- tus - General

ANSI C19.4-1973, Industrial Control Appara- tus - Enclosures

ANSI C19.5-1973, Industrial Control Appara- tus - Switching or Controlling Devices

ANSI C19.6-1973, Industrial Control Appara- tus - Control-Circuit Devices and Assemblies

ANSI C19.7-1973, Industrial Control Appara- tus - Controllers and Controller Assemblies

ANSI C34.2-1968 (R1973), Practices and Re- quirements for Semiconductor Power Recti- fiers

ANSI C37.18-1968 (R1975), Requirements for Field Discharge Circuit Breakers for Rotating Electric Machinery

ANSI C50.10-1977, General Requirements for Synchronous Machines

ANSI/IEEE C57.12.00-197 3, General Require- ments for Distribution, Power, and Regulating Transformers

ANSI/IEEE C57.12.90-1973, Test Code for Distribution, Power, and Regulating Trans- formers

IEEE Std 4-1978, Standard Techniques for High-Voltage Testing

IEEE Std 95-1977, Recommended Practices for Insulation Testing of Large AC Rotating Machinery with High Direct Voltage

IEEE Std 421-1972, Criteria and Definitions for Excitation Systems for Synchronous Ma- chines

NEMA ICs1970 (R1975), Industrial Controls and Systems


IEEE Std 421B-1979

3. High-Potential Tests

IEEE STANDARD FOR HIGH-POTENTIAL-TEST REQUIREMENTS

5. Duration and Application of Test Voltage

3.1 General. High-potential tests, as used here- in, are those tests required to establish the adequacy of the various insulations of the excitation-system components to withstand the voltage stresses imposed during normal or transient conditions. Transient conditions include faults, asynchronous operation, or other unusual operation. I t is the responsibility of the manufacturer to design and test for the worst case stress.

3.2 Type of Tests. High-potential tests fall under two categories: acceptance and service tests.

3.2.1 Acceptance. Acceptance tests at standard test voltage shall be made on all circuits after final assembly at the factory. Rotating equipment shall be tested after all functional testing is complete. Controls and other equipment shall be tested before functional testing. Acceptance tests made in the field during installation shall be conducted at 75 percent of the standard test voltage.

3.2.2 Service. Service tests can be made at any time after installation to verify the integrity of insulation. The voltage applied during service tests shall not exceed 65 percent of the standard test voltage.

NOTE: Users are cautioned to follow the manufac- turers’ recommendations for protecting semiconductor components when performing high-potential tests.

The test voltage shall be applied continuously for a period of 60 s. The test voltage shall be successively applied to each electric circuit with all other electric circuits and metal parts grounded. [See ANSI C19.3-1973 through

(R1975), Industrial Controls and Systems.] Interconnected polyphase windings may be considered as one circuit.

ANSI C19.7-1973 and NEMA ICS-1970

6. Measurement of Test Voltage

The test voltage shall be measured by avolt- meter. The voltmeter shall derive its voltage directly from the test voltage, through a voltage divider, through an auxiliary ratio transformer, or by means of a voltmeter coil placed in the testing transformer. The voltmeter shall indicate the rms voltage or, if direct voltage is used, the voltmeter shall indicate the peak voltage [See ANSI C19.3-1973 through ANSI C19.7-1973, IEEE Std 4-1978, and NEMA ICS- 1970 (R1975).]

7. Temperature at which Tests Shall be Made

High-potential tests shall be conducted at ambient temperature [(See ANSI C19.3-1973 through ANSI C19.7-1973 and NEMA ICS- 1970 (R1975).]

4. Frequency and Waveshape of Test Voltage

8. Standard Test Voltages The frequency of the test voltage shall be 25

to 60 Hz, and the shape of the wave shall be a sine wave with a deviation factor not greater than 10 percent with the equipment under test connected to the test apparatus. As an alter- nate to the preceding, direct voltage (dc) may be used, in which case the peak test voltage shall be 1.7 times the rms value of the corres- ponding alternating voltage. [See IEEE Std 4- 1978, Standard Techniques for High-Voltage Testing, and IEEE Std 95-1977, Recommended Practices for Insulation Testing of Large AC Rotating Machinery with High Direct Voltage.]

8.1 Exciter Output Circuit. For exciters rated 350 V dc or less, the ac rms test voltage shall be 10 times the rated output voltage of the exciter, but with a minimum of 1500 V. For exciters rated more than 350 V dc, the ac rms test voltage shall be 2800 V plus two times the rated output voltage of the exciter. The exciter output circuit includes armature windings of rotating machines, commutators, brushes, rectifier circuits, transformer windings, and all components not isolated from the exciter output.

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FOR EXCITATION SYSTEMS FOR SYNCHRONOUS MACHINES IEEE

Std 421B-1979

The synchronous-machine field winding is not included as it is covered by ANSI C50.10- 1977, General Requirements for Synchronous Machines. Field discharge circuit breakers and discharge circuits shall be tested as required by ANSI C37.18-1968 (R1975), Require- ments for Field Discharge Circuit Breakers for Rotating Electric Machinery. The exciter rated output voltage (for determination of the test voltage) shall not be less than the voltage required at the associated generator field terminals when the generator is operated at rated kilovolt-amperes, rated power factor, and rated voltage with the generator field winding at normal operating temperature.

8.2 All Other Circuits (electrically isolated from the exciter output circuit)

8.2.1 For circuits rated above 60 V or above 60 VA, the ac rms test voltage shall be 1000 V plus twice the rated voltage.

8.2.2 Circuits rated at 60 V or less and 60 VA or less need not be given a high-potential test.

9. Revision of American National Standards Referred to in This Document

When the American National Standards referred to in this document are superseded by a revision approved by the American National Standards Institute, the revision shall apply.

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Appendixes

(These Appendixes are not a part of IEEE Std 421B-1979, IEEE Standard for High-Potential-Test Requirements for Excitation Systems for Synchronous Machines.)

Appendix A Background

For many years the only existing standard concerning excitation-system high-potential testing was ANSI C50.5-1955, Rotating Ex- citers for Synchronous Machines (withdrawn). This applied to dc commutator-type exciters which were disappearing from new application.

Other standards used as guides for high- potential testing were ANSI C50.10-1977, which covered the high-potential-test requirements of the synchronous-machine field winding, but never completely agreed with ANSI C50.5-1955. ANSI C19.1-1959, Indus- trial Control Apparatus (withdrawn), could have been used to cover an excitation control;

however, in 1969 it was somewhat outdated. NEMA ICS-1970 (R1975) is very similar to

There were other standards on transformers, field circuit breakers, and similar components, but nothing to apply to modem circuits using semiconductor signal and power components.

More instrumentation and protection was being connected to the synchronous-machine field circuit. This indicated a need for special components that were built and tested to withstand the voltage and power levels involved. The considerations were both reliability and safety .

ANSI C19.1-1959.

Appendix B Technical Considerations

The standard test voltages are listed by circuits because high-potential testing applies voltage stress from circuit to circuit, or from circuit to ground, and is a test of the integrity of insulation - where little current flows unless there is a test failure. High-potential testing is an overvoltage test. Other dielectric tests may include insulation resistance, power factor, etc. The standard test voltage levels are based on what is considered good design prac- tice for this type of equipment. For the exciter output circuit the worst case stress is usually due to the induced voltage from the synchronous-machine field winding caused by asynchronous operation. It is the responsibility of the manufacturer to design and verify that the equipment will withstand the voltage

levels that result for the worst case condition. Where generator field circuit breakers and

discharge circuits are used for rapid deexcita- tion, they are not to be considered part of the exciter output circuit. Field circuit breakers and discharge circuits should be high-potential tested per ANSI C37.18-1968 (R1975), which specifies the same test voltage as ANSI C50.10- 1977 for the main field winding. Thus if a generator field circuit breaker is used, the input side of the circuit breaker will be tested per this standard, while the output side of the circuit breaker will be tested per ANSI C37.18- 1968 (R1975).

The standard was written to agree with existing standards as much as possible. The test voltage for the exciter output circuit was chosen as

11


IEEE Std 421B-1979

7000

5000

8

a

a v, 1000

2000

+

0 0 I O 0 200 300 400 500 600 700 800 900 1000

EXCITER RATED OUTPUT DIRECT VOLTAGE

Fig B1 High-Potential Test Voltages

(Comparison of Various Standards)

an extension of ANSI C50.5-1955, but is less than the test voltage required by the synchronous-machine field winding per ANSI C50.10-1977 (see Fig Bl). The reasoning for choosing a test voltage lower than ANSI C50.10-1977 (for rated voltages above 350 V dc) is that experience indicates that higher test voltages are not necessary and would impose an unnecessary cost penalty on users. In addi- tion, synchronous-machine field windings are subjected to higher mechanical and thermal

stresses and, therefore, should be subjected to a more strenuous high-potential test.

All other circuits, rated at 60 V or less and 60 VA or less (low-voltage and low-power circuits), are exempt from high-potential testing because voltage stresses and transients that may occur during testing can damage semiconductors, integrated circuits, and similar components. At the low operating voltage level of these signal circuits, testing of the insulation is not critical.

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