Current transformers

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Annex 3. Standards for testing electrical equipment and apparatus for electrical installations of consumers

Current transformers

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Encyclopedia of radio electronics and electrical engineering / Rules for the technical operation of consumer electrical installations (PTE)

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K, M - are produced within the time limits established by the PPR system.

Name of the test	Type of test	Test norms	Directions
20.1. Insulation resistance measurement:	K, M
1) primary windings		No limitation	Produced for transformers with voltages above 1000 V with a megohmmeter for a voltage of 2500 V
2) secondary windings		Must be at least 1 MΩ with circuits connected to them	Produced with a megohmmeter for a voltage of 1000 V. For current transformers TFN-220 kV, in the presence of an output from the screen of the secondary winding, the insulation resistance between the screen and the secondary winding is also measured
20.2. Measurement of the dielectric loss tangent tgδ of winding insulation	М	Limit values tgδ insulation windings of current transformers with paper-oil insulation are given in table. 27 (Appendix 3.1). Measurements are made at a voltage of 10 kV	Produced: for current transformers with a voltage of 110 kV and above - with unsatisfactory indicators of the quality of the oil poured into them for current transformers with a voltage of 35 kV - during repair work in cells (at connections) where they are installed
20.3. Power frequency overvoltage test:	М
1) insulation of primary windings;		The values of the test voltage are given in table. 5 (Appendix 3.1). Test duration for current transformers with porcelain external insulation - 1 min., with organic insulation - 5 min. Current transformers with a voltage of more than 35 kV are not tested with increased voltage	It is allowed to test instrument transformers together with busbars. In this case, the test voltage is taken according to the standards adopted for electrical equipment with the lowest level of test voltage. High voltage testing of current transformers connected to power cables 6 - 10 kV is carried out without busbars along with cables according to the standards adopted for cables
2) isolation of secondary windings		Produced with a voltage of 1000 V for 1 min.
20.4. Removal of characteristics of magnetization	К	The characteristic is removed when the voltage on one of the secondary windings rises until saturation begins, but not higher than 1800 V. If the winding has branches, the characteristic is taken on the working branch Only three control points are allowed to be taken. Differences from the values measured at the factory, or from those measured on a serviceable current transformer, of the same type as the tested one, should not exceed 10%	The measured characteristic is compared with the typical magnetization characteristic or with the magnetization characteristics of serviceable transformers of the same type as the tested one.
20.5. Turn ratio measurement	К	The deviation of the measured coefficient from the passport or from the measured one on a serviceable transformer, of the same type as the tested one, should not exceed 2%
20.6. DC winding resistance measurement	К	The deviation of the measured resistance from the nameplate or from that measured on other phases should not exceed 2%	When comparing the measured value with the nameplate data, the measured value must be adjusted to the factory temperature
20.7. Transformer oil tests	М	Oil from current transformers 110 - 220 kV is tested according to the requirements of Table. 6 (Appendix 3.1), paragraphs 1 - 3 once every two years	The frequency of oil sampling in excess of "normally permissible" should be set faster
20.8. Tests of built-in current transformers	М	Built-in current transformers are tested according to 20.1, 20.3.2, 20.5,20.6, 20.7, XNUMX
20.9. Thermal imaging control	М	Manufactured in accordance with established standards and manufacturer's instructions

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