Analysis of discharge phenomenon in an UHV converter transformer during factory test

摘要

The UHV HY converter transformer failed to pass the valve side AC withstand voltage test during the factory test because of the partial discharge exceeding the test requirements, it is preliminary judgement that the discharge comes from the tank wall and the discharge type is shallow discharge by ultrasonic positioning. Through product disassembly, it is confirmed that there is no abnormality in the windings, but surface discharge was found on the paperboard covering the aluminum plate of the electric shield of the oil tank, and there is bulge on the edge of the aluminum plate installation hole shield cap. The electric field simulation model including winding, aluminum plate, paperboard, oil gap and bulge was established to find out why partial discharge occurred. The calculation results show that the existence of wedge oil gap will greatly distort the local electric field intensity and lead to the partial discharge of bulge part. It is analyzed and confirmed that the conductor partial bulge and wedge oil gap caused by improper assembly are the technical reasons of the partial discharge exceeding standard in the factory test. Based on the above analysis conclusion, the quality control of production process in the factory has been strengthened, and the corresponding product process documents have been updated, these measures put an end to the recurrence of similar defects from the source, and ensure the quality of converter transformers.