Research On Dielectric Loss Characteristics Of High Voltage SF6 Current Transformer Based On Finite Element Theory

SF₆ current transformers have excellent electrical performance and reliable insulation withstand strength,and have been widely used in power systems.During the operation of SF₆ current transformers,their reliability can be reduced due to the influence of operating time and environment.At the same time,dielectric loss factor is an important parameter index that reflects the insulation performance of SF₆ current transformers.The change of dielectric loss factor is an effective method to judge its internal insulation status.Therefore,the study of dielectric loss has strong theoretical significance and application promotion value.In this paper,the influence of the wiring method and the humidity of SF₆ gas on the electric field distribution and distributed capacitance of the SF₆ current transformer was studied through simulation,and a test platform was built to study the dielectric loss change of SF₆ current transformer under different temperature,different humidity,different voltage,and different wiring methods.The main contributions of this paper were as follows:（1）The relationship between the dielectric loss of the SF₆ current transformer and the measured voltage was studied:With the increase of the measured voltage,the dielectric loss of the SF₆ current transformer with intact insulation basically remains unchanged.When the measured voltage is slightly greater than the rated operating voltage,The dielectric loss has increased.For SF₆ current transformers whose insulation may be degraded,high-voltage methods need to be considered for dielectric loss measurement.（2）The relationship between the dielectric loss of the SF₆ current transformer and different wiring methods was studied:The measured value of the dielectric loss of the SF₆ current transformer with the positive connection method is higher than that of the reverse connection method.The positive connection method is more sensitive and effective for measuring the dielectric loss of SF₆ current transformers.In order to ensure the insulation performance of the equipment on site,it is recommended to use the positive connection method for testing as much as possible.（3）The relationship between the dielectric loss of the SF₆ current transformer and different temperature and humidity was studied:With the increase of temperature and humidity,the dielectric loss of SF₆ current transformer increases,and the change in dielectric loss value caused by humidity changes is more obvious.The reason of the phenomenon is the increase in humidity makes the equipment absorb the moisture in the air,or the formation of tiny water droplets on the surface causes the dielectric loss to increase.When evaluating the dielectric loss of the SF₆ current transformer,it is necessary to comprehensively consider the influence of the temperature and humidity of the site environment.This article used Ansoft Maxwell software to build a simulation model,which was verified by building a test platform.Furthermore,the effects of applied voltage and operating conditions on dielectric loss are studied by experiments.The test results showed the influence of the forward connection method and the reverse connection method on the dielectric loss:the reverse connection method would increase the dielectric loss value in terms of capacitance distribution and electric field intensity distribution compared with the forward connection method;with the increase of the humidity of SF₆ in the SF₆ current transformer,the maximum electric field strength and distributed capacitance would increase,which would increase the dielectric loss of the SF₆ current transformer.The method can effectively solves the problem that the current on-site cannot diagnose the insulation defects of its solid insulation parts,and strengthens 110kV Technical supervision of SF₆ current transformer.