Study On The Infuluence Of Local Overheating On The Discharge Characteristics Of Oil-paper Insulation

Power resources have become an indispensable and important energy source in modern society.The effective and safe production,transmission and use of power resources are related to the normal operation and stable development of the whole society.Transformer is one of the key equipments in the power system,but various problems will inevitably occur during the operation.Relevant investigations show that the transformer fault caused by local overheating occupies a large proportion in various fault problems.In recent years,as the capacity of transformers increasing the problem of local overheating has become more prominent.The high temperature causes the deterioration rate of the insulating material to be accelerated,resulting in a shortened life and ultimately a breakdown accident.The problem of overheating is worthy of our attention due to the universality and the seriousness of potential hazards.The problem of local overheating on insulation should be studied in detail.In this paper,we refer to the research methods of the influence of temperature on the insulation of oil-paper insulation,and design and build a discharge test platform that can simulate the actual overheating inside the transformer.Through the collation and analysis of the discharge patterns collected in the multiple sets of interturn discharge test,it is found that the changes of discharge pattern form under different test conditions have the same regularity to some extent.According to this feature and combined the change of the characteristic quantity,the oil-paper interturn insulation discharge process can be divided into six stages,which are the initial stage,the horizontal development stage,the vertical development stage,the stabilization stage,the pre-breakdown stage and the breakdown stage.Carry out the discharge test of the oil-paper interturn insulation samples under normal oil temperature 40? and local overheating temperature 80?,100?,120? and 140?.The partial discharge detector is used to collect the relevant discharge data during the test.Through the comparative analysis of the test data under different temperature conditions,it can be concluded that with the local hot spot temperature increasing,the initial discharge voltage and the breakdown voltage decrease,and the velocity of discharge development become faster,the average duration of the test become shorter.Besides,the average discharge capacity,the maximum discharge capacity and the pulse repetition rate become larger as the increase of the test temperature,but the change trend is unchanged.In addition,under the condition of non-overheating and overheating of medium and high temperature,discharge tests on the insulation samples treated with accelerated thermal aging for 250 hours and 500 hours are carried out.Comparing the discharge parameters of samples with different aging degree under the same test temperature,we can get some conclusions.With the deepening of the aging degree,the initial discharge voltage and the breakdown voltage are reduced,and the velocity of discharge development is accelerated,and the average duration of the test is shortened,besides,the values of the average discharge capacity,the maximum discharge capacity and the pulse repetition rate are all increased.