GOST-21023-1975-ENG.pdf
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1、 USSR STATE STANDARD POWER TRANSFORMERS METHODS OF MEASURING PARTIAL DISCHARGE CHARACTERISTICS DURING POWER FREQUENCY VOLTAGE TESTING GOST 21023-75 Official Edition English Version Approved by Interstandard STANDARDS PUBLISHING HOUSE Moscow 21023-75 1 UDC 621.314.222.6.019.3:006.354 Group E69 USSR S
2、TATE STANDARD POWER TRANSFORMERS Methods of measuring partial discharge characteristics during power frequency voltage testing GOST 21023-75 Date of Introduction 01.01.77 This Standard applies to power oil transformers (including auto-transformers) of voltage classes 220 kV and above and establishes
3、 the methods of measuring the partial discharge characteristics during insulation tests with power frequency voltage. This Standard does not apply to the transformers which are in operation. (Amended Wording, Amendment Nos. 1, 3 and 4). 1. GENERAL PROVISIONS 1.1. Measuring of partial discharge chara
4、cteristics is carried out to determine, that in insulation of the tested transformer, when testing under normalized voltage, there are no partial discharges, whose intensity exceeds the value established by the Standard or Specifications for the transformer. Official Edition Reprinting is prohibited
5、 Standards Publishing House, 1975 Standards Publishing House, 1997 Revised Edition with Amendments -,-,- 21023-75 2 1.2. Determination of the maximal value of apparent charge during effect of test voltage is obligatory when measuring partial discharge characteristics. Carrying out the additional mea
6、suring of partial discharge average current as well as their intensity in microvolts is allowed. 1.3. Measuring of partial discharge characteristics shall be carried out for completely assembled transformer. When preparing the transformer for tests with measurement of partial discharge characteristi
7、cs its active part shall be subjected to the technological processing established by the Standard or Specifications for the transformer. 2. MEASURING DEVICE FOR PARTIAL DISCHARGE CHARACTERISTICS 2.1. Device for measuring of partial discharge characteristics (hereinafter referred to as measuring devi
8、ce) shall be connected through coupling capacitor to a linear terminal of the highest voltage winding of transformer tested phase, and besides to a linear terminal of average voltage winding in the auto-transformer. When two or three phases of the transformer are tested simultaneously, the measuring
9、 device shall be connected through coupling capacitor to the linear terminal of highest voltage winding of each tested phase. The schematic circuit of installation for measuring partial discharge characteristics is given in figure 1. Connection of the measuring device to terminals of all windings of
10、 tested transformer is allowed (for example, when locating the partial discharges). Inductance coil whose inductance value is taken from the following condition shall be connected to grounding of a neutral in parallel with the measuring device: l f Z L 2 10 where Z stands for the input resistance of
11、 measuring device; fl stands for the lower limiting frequency of measurement. -,-,- 21023-75 3 N o t e s : 1. The inductance coil connected to grounding of a neutral in parallel with the measuring device can be used as a measuring element; in this case l 2 10050 f L = 2. Cross-section of winding wir
12、es of the inductance coil shall be sufficient for flowing a current of test frequency without coil heating during all test period of time. Schematic circuit of installation for measuring of partial discharge characteristics MI is the measuring instrument (or set of measuring instruments); Zm is the
13、resistance of a measuring element; MC is the measuring cable; c is the capacity of input or individual coupling capacitor; Cin is the capacity on an input of the measuring device (total capacity of input measuring plate and measuring cable); 0 is the capacity of calibration capacitor; G is the calib
14、ration generator; is the protection device; F is the fuse Figure 1 (Amended Wording, Amendment No. 1). MI Zm ZmZm MC MC MC CinCinCin CcCcCc F FF G 21023-75 4 2.2. An input of the highest or average voltage of the tested transformer equipped with measuring plate shall be used as the coupling capacito
15、r. A separate capacitor may be used as the coupling capacitor. A value of apparent charge of the partial discharges in insulation of the coupling capacitor for the test voltage reduced to value of the apparent charge of partial discharges in insulation of the tested transformer shall not exceed 50%
16、of the value normalized by the Standard or Specifications, but shall not be more than 10-10 C. A value of capacity of the separate coupling capacitor shall be established on condition of ensuring a reliable measurement of the minimum value of partial discharge apparent charge normalized by the Stand
17、ard or Specifications, but shall not be less than 30 pF. 2.3. The coupling capacitor can be used in combined circuit of measuring the partial discharge characteristics and test voltage if it is determined that it has not an influence on results of measuring the partial discharge characteristics. The
18、 combined circuit of measuring the partial discharge characteristics and test voltage is given in Appendix 1 as an example. 2.4. Measuring components shall comply with the requirements of GOST 20074. A dissipation power of measuring component shall be sufficient for flowing a current through it unde
19、r test voltage. (Amended Wording, Amendment No. 3). 2.5. The general requirements for the circuit and measuring device shall be specified in accordance with GOST 20074. The measuring device shall be broadband with upper passband frequency not more than 400 kHz. Irrespective of the fact which readout
20、 or recording devices for apparent charge the measuring device is equipped with, usage of an oscilloscope is recommended that allows to distinct types of partial discharges as well as partial discharges due to interferences. 21023-75 5 In case the direct readout instruments (peak voltmeters) are use
21、d to measure an apparent charge, the error due to frequency of partial discharge pulses in a frequency range from 100 Hz to 10 kHz shall be within the permissible limits. The lower passband frequency of high-pass filter shall not be more than 50 kHz. An attenuation factor of the high-pass filter at
22、frequency of 1 kHz shall not be less than 50 dB, and not less than 60 dB at test voltage frequency. Use of narrow-band measuring device which shall have a frequency passband from 8 to 10 kHz and upper boundary frequency of adjustment not more than 400 kHz is allowed. When using the narrow-band measu
23、ring device, a check of attenuation of the partial discharge pulse in a transformer winding is obligatory. Measurement may be carried out unless this attenuation at device adjustment frequency exceeds 10 dB. (Amended Wording, Amendment Nos. 1, 2, 3 and 4). 3. PREPARATION FOR MEASUREMENT 3.1. Calibra
24、tion of installation for measuring the partial discharge characteristics 3.1.1. Calibration shall be carried out for each tested phase of the transformer before beginning of tests and after them. Carrying out the complete calibration for one phase only is allowed if measurement of the partial discha
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