Development Of High Frequency Current Sensor Based On Ni-Zn Ferrite Soft Magnetic Material

The proportion of power cables used in power transmission and distribution systems is increasing,and the reliability of power cables has an important impact on the safe and stable operation of the power grid.Partial discharge is the main cause of power cable failure.Timely and effective detection of partial discharge in power cables is of great significance for finding potential faults and preventing power failures.High frequency current method is the most promising method for detecting partial discharge of cable.The performance of high frequency current sensor has an important influence on the effect of partial discharge detection.The development of high frequency current sensor with high sensitivity and wide frequency band is beneficial to the detection of weak partial discharge signals.High frequency current sensor of traditional core materials such as permalloy,amorphous alloy and Mn-Zn ferrite and the highest working frequency can only reach 10MHz,it has become increasingly difficult to meet the actual demand.Ni-Zn ferrite with high permeability,low coercivity and high working frequency characteristics,is suitable as a core material of high frequency current sensor with high sensitivity,wide frequency band.In this paper,the factors affecting the performance of the high frequency current sensor are studied,including the line diameter,the number of turns,the integral resistance and the magnetic properties of the core.The mathematical model of the average transmission impedance,the maximum transmission impedance and the parameters of the high frequency current sensor is established.According to the mathematical model,the parameters of the high frequency current sensor to achieve the best performance are selected and the high frequency current sensor is made.We used the developed high-frequency current sensor to detect partial discharge in power cables.The partial discharge models of four kinds of power cables were tested by pulse current method and high-frequency current method respectively.The discharge phase spectrum of two detection methods is obtained,and the distribution characteristics of the two kinds of test methods are compared.The research results show that the traditional HF current sensor design methods are mostly based on formula deduction and experimental correction,which can not quantify all parameters,and can not predict transmission impedance performance when selecting high frequency current sensor parameters.According to the mathematical model of the transmission impedance and parameters of the high frequency current sensor,it is found that the parameters have different effects on the transmission impedance of the high frequency current sensor.The high frequency current sensor based on the mathematical model is excellent in transmission impedance,up to 15.33 mV/mA.Its performance is superior to the HFCT-39 high frequency current sensor of Italy TECHimp company,and its performance is far beyond the KHLS-100K/60N high frequency current sensor of China KeHai company,reaching the top level at home and abroad.In addition,the laboratory test results show that,in addition to the spear ground insulation defect,the pulse current method and the high-frequency current method are basically consistent with the phase of the discharge signal.The other three kinds of defects are all measured by the high-frequency current method,and the pulse current method is lagged behind the discharge signal.The amount of discharge measured by the two methods is also different.The sensitivity of pulse current method to the insulation defects of different power cables is also different.