Reason Analysis on Over-standard Dielectric Loss of 220 kV Capacitor Voltage Transformer

Dielectric loss value(tanδ)all exceed the standard in the handover test of a 500 kV substation in term of the same batch of 220 kV capacitor voltage transformer.In order to find out the reason,the transformers are returned to factory test.Reasons for the differences in field test and factory test is analyzed.At the same time,manufacturers proposed improvement for solving that.