DOWEI

Contents

1.Overview 11

1.1Scope 11

1.2Purpose 11

2.Normative references 12

3.Definitions 12

4.General requirements 13

4.1Service conditions 13

4.2Effect of air density on flashover voltage 14

4.3Frequency 15

4.4Effect of altitude on temperature rise and effect of ambient temperature on permissible loading 15

4.5Basic impulse insulation levels, dielectric tests, and outdoor instrument transformer creepage distance and wet test 16

4.6Temperature rise 19

4.7Capacitance and dissipation factor requirements 20

4.8Classification of tests 20

4.9Construction 22

5.Accuracy classes for metering 25

5.1Basis for accuracy classes 25

5.2Expression of transformer correction factor at 0.6 power factor (lagging) of metered load 26

5.3Standard accuracy classes 26

5.4Limiting values of ratio correction factor and phase angle for standard accuracy classes 27

6.Current transformers 30

6.1Terms in which ratings shall be expressed 30

6.2Standard burdens 30

6.3Accuracy ratings for metering 30

6.4Accuracy ratings for relaying 32

6.5Continuous thermal current rating factors based on 30 °C average ambient air temperature 34

6.6Short-time current ratings 34

6.7Secondary winding-induced voltages 35

6.8Nameplates 36

6.9Terminals 36

6.10Application data 36

6.11Routine accuracy tests 39

7.Voltage transformers 40

7.1Terms in which ratings shall be expressed 40

7.2Standard burdens 44

7.3Accuracy ratings 45

7.4Thermal burden ratings 45

7.5Nameplates 46

7.6Terminals 46

7.7Short-circuit capability 46

7.8Application data 47

7.9Induced voltage test 47

7.10Routine accuracy tests 47

8.Test procedures applicable to instrument transformers 47

Ratio and phase angle measurement and calculations 48

8.2Impedance, excitation, and composite error measurements 49

8.3Polarity 52

8.4Resistance measurements 53

8.5Dielectric tests 55

8.6Partial discharge measurement 57

9.Test procedures applicable to current transformers 59

9.1Ratio and phase angle measurement and calculations 59

9.2Demagnetization 63

9.3Impedance measurements 64

9.4Polarity 65

10.Test procedures applicable to voltage transformers 66

10.1Ratio and phase angle measurement and calculations 66

10.2Impedance measurements 68

10.3Polarity 69

11.Type test procedures applicable to instrument transformers 70

11.1Short-time characteristics 70

11.2Temperature rise tests 72

11.3Impulse tests 75

11.4Partial discharge measurement 77

11.5Wet voltage withstand tests 78

11.6Ground shield check—72kV class and above 79

12.Type test procedures applicable to current transformers 79

12.1Short-time thermal rating of current transformers 79

12.2Current transformer temperature rise tests 80

12.3Inter-turn overvoltage test 80

13.Type test procedures applicable to voltage transformers 81

13.1Short-circuit thermal capability of voltage transformers 81

13.2Voltage transformer temperature rise tests 82

Annex A (informative) Bibliography 83

Annex B (normative) Bushing-type current transformer (BCT) and special purpose window type current transformers 86

B.1Introduction 86

B.2Scope 86

B.3General requirements 86

B.4Continuous thermal ratings 88

B.5Short-time ratings 90

B.6Dielectric consideration 90

B.7Construction 90

B.8Routine tests 92

B.9Type tests 93

B.10Installation 93

B.11Field tests 94

B.12Bushing linear coupler (BLC) 94

1.Overview

1.1Scope

This standard is intended for use as a basis for performance and interchangeability of equipment covered, and to assist in the proper selection of such equipment. Safety precautions are also addressed.

This standard covers certain electrical, dimensional, and mechanical characteristics, and takes into consideration certain safety features of current and inductively coupled voltage transformers of types generally used in the measurement of electricity and the control.

1.2Purpose

The purpose of this standard is to provide the performance requirements for electrical system and test interchangeability of current and inductively coupled voltage transformers. These transformers are for both indoor and outdoor application.

This standard covers the requirements for Class 1 instrument transformers. For instrument transformers of a nominal system voltage of 115 kV and above if Class 2 is required refer to IEEE Std C57.13.5™.1

2.Normative references

The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so each referenced document is cited in text and its relationship to this document is explained). For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies.

IEC 60270, High-voltage test techniques—Partial discharge measurements.2

IEC 61869-2, Instrument Transformers—Part 2: Additional Requirements for Current Transformers. IEEE Std 4™, IEEE Standard for High-Voltage Testing Techniques.3, 4

IEEE Std 693™, IEEE Recommended Practice for Seismic Design of Substations.

IEEE Std C37.04™, IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers.

IEEE Std C37.09™, IEEE Standard Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Basis.

IEEE Std C57.12.00™, IEEE Standard General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.

IEEE Std C57.12.90™, IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.

IEEE Std C57.13.5™, IEEE Standard of Performance and Test Requirements for Instrument Transformers of a Nominal System Voltage of 115 kV and Above.

IEEE Std C57.13.6™, IEEE Standard for High-Accuracy Instrument Transformers.

IEEE Std C57.19.00™, IEEE Standard General Requirements and Test Procedure for Power Apparatus Bushings.

3.Definitions

For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause.5

class 1 instrument transformer: An instrument transformer that is constructed and tested in accordance with this standard.

class 2 instrument transformer: An instrument transformer that is constructed and tested in accordance with IEEE Std C57.13.5™.

gapped core: A core where the magnetic core has an intentional gap filled with non-magnetic material.

indoor voltage transformer: One that, because of its construction, shall be protected from the weather.

prescribed extinction voltage: The minimum voltage at which the reference partial discharge intensity shall be met when the voltage applied to the transformer is gradually decreased without interruption from the power frequency withstand voltage or pre-stress voltage value during the partial discharge test.

partial discharge inception voltage: The lowest voltage at which partial discharges exceeding a specified level are observed under specified conditions when the voltage applied to the test object is gradually increased from a lower value.

Table 2 —Basic impulse insulation levels and dielectric tests

Table 3 —Creepage distances for porcelain insulators

Bibliography

Bibliographical references are resources that provide additional or helpful material but do not need to be understood or used to implement this standard. Reference to these resources is made for informational use only.

[B1]  Arnold, A. H. M., “Current-transformer testing,” Journal of the IEE, vol. 74, pp. 424444, 1934.

[B2] Arnold, A. H. M., “Precision testing of current transformers,” Journal of the IEE, vol. 68, pp. 898905, 1930.

[B3] ASTM D117-1996, Standard Guide for Sampling, Test Methods, Specifications, and Guide for Electrical Insulation Oils of Petroleum Origin.

[B4] Bousman, H. W., and Ten Broeck, R. L., “A capacitance bridge for determining the ratio and phase angle of potential transformers,” AIEE Transactions, vol. 62, pp. 541545, Aug. 1943.

[B5] Brownlee, A. L., “A primary method of measuring the ratio and phase angle of current transformers,” AIEE Transactions, vol. 69, part 1, pp. 459460, 1950.

[B6] Buchanan, J. H., “Design, construction, and testing of voltage transformers,” Journal of the IEE, vol. 78, pp. 292316, Mar. 1936.

[B7] Clothier, W. K., and Medina, L., “The absolute calibration of voltage transformers,” Proceedings of the IEE, vol. 104A, pp. 204214, June 1957.

[B8] Glynne, A., “The use of a simple AC potentiometer for the precision testing of instrument transformers,” Journal of the IEE, part 11, no. 21, pp. 177181, June 1944.

[B9]  Harris, F. K., Electrical Measurements. New York: John Wiley and Sons, Inc., 1952.

[B10] Harris, F. K., et al., “An international comparison of voltage-transformer calibrations to 350 kV,”

IEEE Transactions on Communication and Electronics, vol. 83, pp. 1319, Jan. 1964. [B11] IEEE Std C57.98™, IEEE Guide for Transformer Impulse Tests.

[B12] Kusters, N. L., and Moore, W. J. M., “The compensated current comparator: A new reference standard for current-transformer calibrations in industry,” IEEE Transactions on Instrumentation and Measurement, vol. IM-13, pp. 107114, June/Sept. 1964.

[B13] Kusters, N. L., and Petersons, O., “A transformer-ratio-arm bridge for high-voltage capacitance measurements,” IEEE Transactions on Communications and Electronics, no. 69, pp. 606611, Nov. 1963.

[B14] Kusters, N. L., “The precise measurement of current ratios,” IEEE Transactions on Instrumentation and Measurement, vol. IM-13, pp. 197209, Dec. 1964.

[B15] Miljanic, P. N., Kusters, N. L., and Moore, W. J. M., “The application of current comparators to the calibration of current transformers at ratios up to 36 000/5 amperes,” IEEE Transactions on Instrumentation and Measurement, vol. IM-17, pp. 196203, Sept. 1968.

[B16] Petersons, O., and Anderson, W. E., “A wide-range high-voltage capacitance bridge with one ppm accuracy,” IEEE Transactions on Instrumentation and Measurement, vol. IM-24, no. 4, pp. 336344, Dec. 1975.

[B17] Petersons, O., “A self-balancing current comparator,” IEEE Transactions on Instrumentation and Measurement, vol. IM-15, nos. 1 and 2, pp. 6271, Mar./June 1966.

[B18] Petersons, O., “A self-balancing high-voltage capacitance bridge,” IEEE Transactions on Instrumentation and Measurement, vol. IM-13, no. 4, pp. 216224, Dec. 1964.

[B19] Silsbee, F. B., “A shielded resistor for voltage transformer testing,” NBS Scientific Papers, vol. 20, pp. 489514, 1926.

[B20] Silsbee, F. B., Smith, R. L., Forman, N. L., and Park, J. H., “Equipment for testing current transformers,” NBS Journal of Research, vol. 11, pp. 93122, July 1933.

[B21] Souders, T. M., “A wide range current comparator system for calibrating current transformers,”

IEEE Transactions on Power Apparatus and Systems, vol. PAS-90, no. 1, pp. 318323, Jan./Feb. 1971.

[B22] Sze, W. C., “Comparators for voltage transformer calibrations at NBS,” NBS Journal of Research, part C, Engineering and Instrumentation, vol. 69C, no. 4, Oct./Dec. 1965.

[B23] Zinn, E., “Fundamentale Bestimmung der Fehler von Hochstspannungswandlern durch ein Summierverfahren mittels Teilern aus Kapazitat und Widerstand,” Archiv fur Electrotechnik, vol. 44, pp. 147156, 19581960.

Useful material covering instrument transformers17

[B24] AIEE Committee on Protective Devices, Current Transformer Subcommittee, “Current- and potential-transformer standardization,” AIEE Transactions, vol. 61, pp. 698706, Sept. 1942.

[B25] ANSI/NCSL Z540.3, Requirements for the Calibration of Measuring and Testing Equipment.

[B26] Arnold, A. H. M., “Dielectric admittances in current transformers,” Proceedings of the IEE, vol. 97, part II, pp. 692698, 1950.

[B27] Arnold, A. H. M., “The effect of capacitance on the design of torodial current transformers,”

Proceedings of the IEE, vol. 97, part II, no. 60, pp. 797808, Dec. 1950.

[B28] Arnold, A. H. M., “Leakage phenomena in ring-type current transformers,” Journal of the IEE, vol. 74, pp. 413-423, 1934.

[B29] Davis, R., “The design and construction of a shielded resistor for high voltages,” Journal of the IEE,

vol. 79, pp. 10281034, 1931.

[B30] Dunfee, B. L., and Moore, W. J. M., “An international comparison of current-ratio standards at audio frequencies,” IEEE Transactions on Instrumentation and Measurement, vol. IM-14, pp. 172177, Dec. 1965.

[B31] Foley, A. H., “A direct reading high-voltage capacitance bridge,” AIEE Transactions, vol. 69, part II, pp. 692698, 1950.

[B32] Hague, B., Instrument TransformersTheir Theory, Characteristics and Testing. London: Sir Isaac Pitman and Sons, Inc., 1936.

[B33] IEEE Std C57.13.1™-1981, Guide for Field Testing of Relaying Current Transformers. 18

[B34] IEEE Std C37.235™, IEEE Guide for the Application of Rogowski Coils Used for Protective Relaying Purposes.

[B35] ISO/IEC 17025:2005, General Requirements for the Competence of Testing and Calibration Laboratories.

[B36] Kusters, N. L. and Moore, W. J. M., “The development and performance of current comparators for audio frequencies,” IEEE Transactions on Instrumentation and Measurement, vol. IM-14, pp. 178198, Dec. 1965.

[B37] McGregor, M. C., et al., “New apparatus at the National Bureau of Standards for absolute capacitance measurement,” IRE Transactions on Instrumentation, vol. I-7, nos. 3 and 4, pp. 253261, Dec. 1958.

[B38] Miljanic, P. N., “Capacitive error in current comparators,” IEEE Transactions on Instrumentation and Measurement, vol. IM-13, pp. 210216, Dec. 1964.

[B39] Moreton, S. D., “A simple method for the determination of bushing-current-transformer characteristics,” AIEE Transactions, vol. 62, pp. 581585, Sept. 1943.

[B40] NEMA SG4, Alternating Current High-Voltage Circuit Breakers.

[B41] Park, J. H., “Accuracy of high-range current transformers,” NBS Journal of Research, vol. 14, pp. 367392, 1935.

[B42] Pfuntner, R. A., “The accuracy of current transformers adjacent to high-current buses,” AIEE Transactions, vol. 70, part II, pp. 16561662, 1951.

[B43] Settles, J. L., Farber, W. R., and Conner, E. E., “The analytical and graphical determination of complete potential transformer characteristics,” AIEE Transactions, part III, pp. 12131219, 1960.

[B44] Silsbee, F. B., “A study of the inductance of four terminal resistance standards,” United States Bureau of Standards Scientific Papers, no. 281, pp. 375422, 1916.

[B45] Silsbee, F. B., “Notes on the design of four terminal resistance standard for alternating currents,”

NBS Journal of Research, vol. 4, pp. 73107, Jan. 1930.

[B46] Silsbee, F. B., “Precautions against stray magnetic fields in measurements with large alternating currents,” AIEE Transactions, vol. 48, pp. 13011306, Oct. 1929.

[B47] Weller, C. T., “A 132 kV shielded potentiometer for determining the accuracy of potential transformers,” AIEE Transactions, vol. 48, pp. 790807, July 1929.

[B48] Woods, C. A., Jr., and Bottonari, S. A., “Overcurrent performance of bushing-type current transformers,” AIEE Transactions, vol. 59, pp. 554560, Sept. 1940.

[B49] Zocholl, S. E., Analyzing and applying current transformers, Schweitzer Engineering Laboratories, Inc., 2004.