Study on Insulation Diagnosis Method for Transformer Based on Transmission Characteristics Under Nanosecond Pulse

Based on the nanosecond pulse impact test of a real-type transformer, the variation law of the transformer's transient transfer characteristics was obtained. By analyzing the differences of the transfer characteristics in a specific frequency band under different accumulated pulse numbers, an insulation assessment function of the transformer under the cumulative effect of nanosecond pulses was constructed based on the transfer characteristics. The research results show that the current transfer characteristics reflect the cumulative deterioration degree of the transformer insulation most sensitively, and the transfer ratio constantly decreases with the increase of the accumulated pulse number. Through fitting, the insulation assessment function of the transformer under the nanosecond pulse effect can be obtained. Finally, the accuracy and effectiveness of the method were verified by conducting five different accumulated impact tests on a distribution transformer of the same type.