Study On Gas Generating Characteristic In Different Signal Energy Level And Signal Energy Entropy Feature Of Air-Gap Discharge In Oil-Paper Insulation

Power transformer is one of the most significant and key electrical equipment in power system, its severe failure will induce the damage of transformer itself and raise the outage of power network, which causes significant economic losses. Statistics show that 80% of transformer failures are induced by insulation fault, partial discharge is one of main reasons to cause insulation age and damage inside transformer. Oil-immersed paper insulation is the common insulation way of power transformer, the gap discharge is one of the modes for partial discharge in oil-immersed paper insulation, and its developing process is a long-term and complicated dynamic state. Thus, conducting the research work on the discharge features of developing process for the gap discharge and the characteristic parameters for reflecting developing process of gap discharge, which is significantly meaningful to divide the entire developing process, to understand the variation of discharge status, to provide criterion for online diagnosis of cracking stages inside oil-immersed paper insulation, and to avoid the discharge failure.The model of gap discharge according to CIGRE Method II and emulated test platform are established in this paper, lots of gap discharge experiment are performed based on constant voltage method and pulse current method. The energy variation and distribution characteristic of gap discharge during discharge process is studied deeply, and the energy "entropy" is proposed as the new characteristic parameter of the gap discharge developing process. According to the "step" features of new characteristic parameter, the entire developing process of gap discharge can be divided into several stages. Correlation analysis is carried out for variable relevance of new characteristic parameters in different stages based on dissolved gas, gas production characteristic of air gap and energy of discharge signal. In final, threshold recognition method using the threshold features of new characteristic parameters is developed for online identification of the entire developing process of air gap discharge. The main of innovation achievements this paper is as follows:The component content of dissolved gases in oil is correlation with discharge signals energy during the developing process of air-gap discharge, and the gas characteristic in different energy level shows different developing characteristic; the alternative variation of electronegative gases has impact on the forms of discharge inside the air-gap, which leading to local energy distribution mutation of discharge signals.This paper studies the developing variation of crystallinity degree in oil-paper insulation during the developing process of discharge based on the energy band theory of high polymer, and the change of crystalline region make an impact make an impact on energy level; as the developing of discharge, the average electrical strength of oil-immersed paper insulation presents the increasing trend when degree of crystallinity is increased.The developing characteristic of energy "entropy" during the entire discharge process has mutation and a threshold, and the entire trend of this characteristic is constantly towards to 0. The mutation of energy "entropy" is regarded as identifiers to divide the entire process of air gap discharge into four stages, i.e. the initial stage, the stable stage, the developing stage and the warning stage. Different discharge stages correspond to different discharge status. The discharge signal has variable energy level under different discharge status, and there is an order of magnitude difference between the energy "entropy" of different stages.The "step" characteristic of energy "entropy" changes with the transformation of different discharge forms inside the gar gap. Spectrum analysis of C 1s for oil-immersed paper insulation shows that variable stages develops with the generation of new groups. In addition, with the transformation of different stages, the threshold range of energy "entropy" gradually decreases with the trend of an order. The dissolved gas shows that the partial high energy discharge emerges in the middle and late stage of stable discharge, and the degradation of oil-paper insulation begins. With the consumption of electronegative gases in the air gap, the volume of gases presents the trend of alternative decrease- increase variation.According to the threshold features of new characteristic parameter in different status, an identification method for developing stages of air gap discharge based on Threshold judgement is proposed and presented. The analysis of degree of crystallinity, average electrical strength and dissolved gas for samples shows the feasibility of the method, which provides a new idea for on-line identification of discharge state.