Kerr electro-optic field measurement in palm oil fatty acid ester transformer insulation system

A palm oil fatty acid ester (PFAE) has good insulation performance, excellent cooling ability and superior biodegradability. Recently, investigations for application of PFAE to power transformers have been started. In this paper, the electric field in PFAE was measured in situ by using Kerr electro-optic method under dc voltages application. At first, Ken-constant of PFAE was identified. Then, electric field strength E and its temporal change were measured in several PFAE / pressboard (PB) insulation systems. Electric field E in PFAE showed the capacitive distribution at the moment of dc voltage application, and decreased rapidly with time and finally the resistive field distribution was obtained. The transition time of the capacitive distribution to the resistive one and the value of E in PFAE were different from those in mineral oil. Their differences were discussed with the charge behavior in liquids, based on electro-chemical properties of the oil.