Development Of A Micro Current Sensor Based On Zero Flux Principle

On line insulation monitoring of high voltage power equipment is an important technical means to ensure safe operation of power system,also,high precision micro current sensor is an important tool to realize on-line monitoring of power system.Current sensor is involved electrical protection,electrical energy measurement or control and other related fields,and responsible for signal acquisition,is an important part of the online monitoring system.Therefore,the accuracy and reliability of the current sensor is directly related to safe operation of the power system.Current sensors are generally installed in the high voltage field,they are susceptible to strong magnetic field interference,its working environment is very bad.In the insulation monitoring of power line or equipment,because the magnitude of the measured current varies from a few to a few tens microampere,ordinary small current sensor is difficult to meet the demand.Therefore,it is of great significance to develop a kind of high precision,sensitive,micro current sensor which is suitable for the on-line monitoring of the insulation condition of electrical equipment.In this paper,based on the principle of zero flux a micro current sensor with accuracy of 0.2 is developed.The main contents of this thesis are as follows:Primarily,this paper adopted single turn cored current sensor as the research object.According to the principle of electromagnetic induction,the equivalent circuit of electromagnetic current sensor was established and the error formula was deduced,came a conclusion that the excitation current is the main cause of measurement error.According to the error formula,the influence factors of the influence error were analyzed from the core structure parameters,the secondary load impedance,the number of secondary winding turns and the core material of the current sensor.The induction part of the current sensor was designed.In order to further reduce the error,current sensor need add external compensation.Firstly,this paper introduced two methods of active compensation and passive compensation.On this basis,the overall compensation scheme based on zero flux principle was designed.In this scheme,the active electronic circuit compensation method is combined with the passive compensation method of the three winding parallel impedance to make the magnetic core reach the state of zero flux,which makes the error reduce to minimum.In order to verify the correctness of the compensation scheme,a micro current sensor model with zero magnetic flux compensation was established based on Simulink,and the model was compared with the traditional current sensor.The simulation results show that the error of the micro current sensor with zero flux compensation is reduced compared with the traditional current sensor,and the measurement accuracy is improved.The hardware compensation circuit and signal processing circuit were designed.The function of the compensation circuit is to transform the induction voltage processing into the compensation current to compensate the phase amplitude of the output current.Signal processing circuit is used to condition the secondary side of the weak signal to facilitate the subsequent processing and detection.This paper toke LabVIEW as the software platform,the error measuring program of the micro current sensor was designed.The program can achieve data acquisition,digital filtering,waveform display,amplitude error and phase error measurement function.Through laboratory test,the program is stable,reliable,interactive and rich in display content.The experimental platform was built in the laboratory environment,and the hardware and software of the micro current sensor were tested.The experimental results show that the micro current sensor can measure the power frequency current of ?A~mA,and the compensation scheme can effectively reduce the measurement error and improve the measurement accuracy.The whole system has stable operation and achieves all the design targets.