The DC magnetic bias of transformer will happens when DC current enters into the winding through the neutral point of transformer

causing such problems as increase of reactive power consumption and noise of the transformer.In recent years

capacitive DC isolation devices are installed on transformers in areas where DC bias is serious in Ningxia grid so to avoid the above problems.The device

however

has operation with disease phenomena.For avoiding reoccurrence of such phenomena and in view of investigation and analysis on the fault of capacitance blocking device of transformer

the reason of the fault is found out by equipment inspection at site

theoretical calculation and experimental lab verification as well as in combination of structure of the device itself and the countermeasures for such fault is proposed.The analysis result has great significance in improving safe and reliable operation of capacitance blocking device of transformer.