Power transformer AC withstand voltage test standard and precautions
1) Check the test wiring to ensure correctness. The tested transformer shell and non-pressurized winding should be grounded reliably. The gas protection should be put into operation. The overcurrent and overvoltage protection in the test circuit should be set correctly and reliably.
2) When the transformer is subjected to the AC withstand voltage test, it must be carried out after the insulating oil is at a standstill and the air bubbles are sufficiently escaped. Otherwise, it will cause discharge during the withstand voltage test, which makes it difficult to judge. 3-10kV transformer oil needs to be static for more than 5h, 110kV and below transformer oil is static for 24h; 220kV transformer oil is static for 48h, and 500kV transformer oil is static for 72h to avoid undue insulation breakdown when withstand voltage.
3) All venting parts such as bushings and inlet holes of oil-immersed power transformers should be fully vented to avoid lowering the insulation strength due to residual air, resulting in breakdown or discharge.
4) During the test, the boosting speed should be uniform. When the voltage rises above 40% of the test voltage, the test voltage should be increased by 3% per second; the step-down should be rapid, but avoid suddenly shutting off the power above 40% of the test voltage. .
5) The AC power frequency withstand voltage test of the three-phase transformer does not have to be phase-separated, but the three-phase lead-out end of the same-side winding must be short-circuited before testing, otherwise the insulation of the transformer winding may be damaged.
6) AC withstand voltage is 1 min. If discharge or breakdown occurs, immediately step down and cut off the power.
7) Keep an eye on the indicator during the pressurization, observe and monitor the transformer under test, protect the sound and phenomenon of the ball gap, and analyze the relevant signs such as corona or discharge.
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