Research On The Insulation State Detection Method Of Power Capacitor Based On Time Domain Dielectric Response

Power capacitor is widely used in power system and is one of the most basic components.It plays the role of filter,carrier and high frequency protection in power grid.Power capacitors suffer from high electrical strength and environmental impact,such as harmonic current,over-voltage,over load,high temperature,etc.,which will cause thermal aging,chemical aging,electrical aging and other internal dielectrics,and reduce their insulation performance.In order to ensure the stable operation of the power capacitor in the normal operation of the power system,it is of great significance to study the aging state detection method of its oil film insulation.Firstly,this paper introduces the principle of polarization depolarization current method,and studies the influence of polarization voltage,polarization time,depolarization time and test environment temperature on the measurement results.The oil film insulation samples of power capacitor are developed.The aging samples of oil film insulation are obtained by heat and electric aging treatment in different periods.Secondly,the polarization depolarization current method is used to test the aging samples of oil film insulation in each aging period to obtain the depolarization current data,and then the extended Debye equivalent circuit is used to simulate the oil film insulation of the samples,and the matrix beam algorithm is used to obtain the low-frequency dielectric loss and DC conductivity of the tested samples in each aging period.Finally,this method is applied to a batch of power capacitors which are retired after being put into operation to verify the feasibility of the method.Through the above experiments and data analysis,it is concluded that the polarization depolarization current curve will be affected by the change of polarization voltage value.With the increase of polarization voltage,the polarization depolarization current curve also shows an upward trend,but the two insulation parameters of DC conductivity and 0.1Hz dielectric loss only change slightly,and the phenomenon of polarization depolarization time change is similar to that of polarization voltage.The change of test temperature has great influence on polarization depolarization current curve and two insulation parameters.With the increase of aging degree of oil film,the polarization depolarization current curve has an upward trend,and the DC conductivity and 0.1Hz low-frequency dielectric loss also show an upward trend with the increase of aging period.In addition,the higher the heat aging temperature,the faster the aging of oil film insulation.The experimental results show that the setting of polarization depolarization time is different for power capacitors with different capacitance values.Based on the polarization depolarization current method,the aging state of oil film insulation can be detected under different aging cycles,but the capacitance value of its electrical parameters can not be measured.Therefore,as a lossless detection method,polarization depolarization current method can accurately detect the aging state of oil film insulation structure of power capacitor.