Study On Electric Field And Temperature Distribution Characteristics In Valve Side Bushing Of Converter Transformer

UHV transmission is the fundamental solution to the development of energy and electric power in China.In recent years,HVDC transmission has been widely used in our country because of its advantages of large capacity and long distance transmission.Valve side bushing of converter transformer is a key component in HVDC system,and its performance is directly related to the safe and stable operation of HVDC system.The complex form of the working voltage and the heavy current in the DC project lead to the frequent failure of the bushing.In this paper,the distribution of electric field and temperature in bushing at working is analyzed by means of simulation and experiment.By simulating the typical fault of casing.The discharge and electric field distribution characteristics and of fault bushing are studied.These results can provide reference for founding the weak insulation areas and studying the mechanism of fault generation and development in the bushing.Based on the actual size of the dry SF6 valve bushing of converter transformer,a simulation model of the bushing is established by using the finite element simulation software INFOLYTICA.The electric field of the bushing under the excitation of DC,AC and polarity reversal is calculated.The distribution characteristics of electric field and voltage are analyzed,and the optimization function of aluminum foil for the electric field of capacitor is researched.In view of the fact that the current level of HVDC transmission project is further improved,and the overheating problems of the bushing becomes more and more serious.In order to master the working conditions such as the working current,temperature and so on,the spectral characteristics of the current which bushing bears are calculated by SIMULINK.And the temperature of converter transformer oil in peak load period was investigated by field measurement,in this paper.A large current test platform is designed to simulate the operating environment of the bushing,and the temperature rise test was carried out on the test bushing.According to develop the test procedures and place the temperature probe into the different place of the bushing,the temperature results of different measuring point is obtained.On the basis of this,the variation of the thermal state of test bushing and the temperature characteristic of converter transformer bushing is researched.Aiming at the bushing failure in operating experience,four kinds of typical faults,such as the breakdown of capacitance plates,the metal particles fault,the air bubbles fault and the cracks fault,are designed and manufactured.Under the laboratory condition,the partial discharge test under DC was carried on the four kinds of bushing model.The relationship between the number of discharge and the magnitude of the discharge is studied.In the end,the electric field distribution characteristics of four kinds of typical faults are analyzed by means of electric field simulation,and this research provides a guidance for the study of the generation and development of DC bushing faults.