Influence Of Temperature On Partial Discharge UHF Characteristics Of GIS Defects

Partial discharge detection is the most effective way to discover the potential danger of insulation.Currently,UHF method is usually adopted by on-line partial discharge of Gas Insulated Switchgear(GIS).But partial discharge is affected by many factors.The operation conditions of GIS are complex,the working current,ambient temperature,sunshine,high energy ray and other factors will affect the results of partial discharge detection,and it may even be the internal reason for the detection of misreporting in the on-line monitoring.In order to diagnose the intensity level and severity of the partial discharge,it is necessary to consider the effect of operating conditions on the partial discharge.Considering that the influence of temperature on the electrical properties of insulation materials are very significant,and the final effect of load current,ambient temperature and sunshine factors all cause the temperature change in GIS.Therefore,Research is carried out in this paper,aiming to find out temprature's influence on the typical GIS partial discharge.In order to investigate temparature's influence on the typical GIS partial discharge model,this research analyzes the current literature on the distribution of inside and outside temparature of GIS in different site operation conditions,and simulates the environment temparature which the partial discharge defect is in.First of all,A test platform is built based on a temparature control box and a transformer to conduct experiments in the laboratory.Three types of typical defects are designed.That is protrusion discharge,surface discharge and void discharge.A UHF partial discharge detector is applied to collect data at different temparatures.Short-term tests and long-term constant voltage to beakdown tests are conducted respectively at different temparature.As for the short-term test,a short-term(300s)constant voltage is impressed,discharge initial voltages at different tempratures,discharge frequency in a single cycle,mean value of discharge amplitude and the distribution of discharge time interval(?t)are analyzed.Moreover,Apriori algorithm is used to calculate distribution of discharge amplitudes,phases and frequency.As for the long-term constant voltage to breakdown tests,the erosion of solid insulations after breakdown are observed and compared,discharge initial voltage,discharge time,mean value,maximum value and standard deviation of discharge amplitude with time throughout the course are obsreved,also,the changing trend of cumulative amplitudes in 100 cycles with time throughout the course are obsreved.The typical discharge phases are dignosed by inflection points.And Apriori algorithm is used to calculate the distribution of amplitudes,phases,frequencies in each stage.Then,the relations among site on-line UHF discharge data,temprarature and load tendency are revealed.The initial voltage of discharge,mean value of discharge,maximum value of discharge,and cumulative frequencies of discharge changing with time are analyzed,moreover,they are compared with laboratory conclusions.Finally,based on experimental results,this thesis attempts to make explanations on temparature's influence on partial discharge with the help of Fermi-Dirac Statistics,Trap Theory and the Thermionic Emission Theory.Finally,A linear correction method is used to modify the effect of temperature on the partial discharge.The discharge amplitude and discharge number at different temperature are corrected to 20 ?.The results show that laboratory short-term and long-term tests data are consistent with site operation discharge data.When the temperature rises,initial voltage of discharge decreases,the number of discharge in single cycle increases,the discharge interval(?t)decreases,mean value of discharge amplitude decreases,the protrusion discharge phase contracts,the surface discharge phase broadens,the void discharge phase shifts towards right.Fermi-Dirac Statistical Distribution Theory,Trap Theory,and Thermionic Emission Theory are proved to explain temperature's influence on partial discharge effectively.In the end,the linear correction equation can be used to modify the discharge amplitude and the discharge number of single wave from different temperature to 20 ?.