Experimental Research On Transformer Oil-paper Insulation Under Low Temperature

Power transformer is the most important equipment in power system,and the oil-paper insulation is used in big power transformers.The safety of the oil-paper insulating transformers is related to the security and stability of power grid directly.The high temperature properties of oil-paper insulation were forcused by a lot of scholars in world,due to the high temperature aging determined transformer reliability and operational life.Recently,the insulation failure occurred in low-load transformer or standby transformer under extremely low temperature in the northeast of China.So,studying the low-temperature properties of oil-paper insulation to ensure the safe operation of transformer in extremely cold area has great economic and social benefits.In order to study the insulation property of oil-paper under low temperature, the thermal insulated bushings was developed with the helped by cable insulation technology at first.And then fix it on the cover of low temperature fridge.So as to construct an experimental platform, which can simulate reality low temperature condition.This article focuses on the AC dielectic properties and dielectic strength with different rates of oil-papers in oil-paper insulation.The experiment shows that the loss factor of oil-paper insulation system decreases first,then rises and show the trend.And the higher moisture of oil-paper insulation is the larger the loss factor will be. However, the relative dielectic constant monotonously rises as the temperature decreases.The AC breakdown voltage declines two times.It maybe relates to the precipitation of water from oil and the extrusion from paper. According to the expriment results, it can be inferred that transformer insulation fault is closely related to moisture content in extremely low temperature.In order to make sure the safe operation of oil-paper insulation transformer in extremely low temperature,the moisture content in insulation must be strictly limited.