Study on Charge Behavior in Transformer Oil/Pressboard Composite Insulation System by Optical Measurement of Electric Fieid

Abstract

We measured an electric field in transformer oil/pressboard composite insulation system under dc voltage application using Kerr electro-optic measurement system. When a pressboard was inserted between two parallel-plane electrodes, the electric field between the pressboard and the cathode decreased monotonously with time. On the other hand, the electric field between the pressboard and the anode increased with time, reached a maximum value and then fell down. We discussed this phenomenon by charge accumulation model and potential distribution considering the difference in charge accumulation rate on the pressboard between positive and negative charges.
In this paper, discussion results were described based on experiment with pressboards changing its thickness, location and number.