Research On The Measurement Of Capacitance Current In Distribution Network Based On High-frequency Signal Injection Method

The precise measurement of capacitance current in distribution network is the prerequisite and basis for automatic compensation of automatic tuning arc suppression coil,is also the important parameters of the inhibition of TV occuring ferromagnetic resonance and the basis for line selection. This paper mainly studies on measuring technique of neutral point ungrounded system capacitive current based on signal injection method.The traditional signal injection methods include three-frequency method, dual-frequency method(phaser method),single-frequency method,frequency sweep method,the comprehensive method and so on. These methods have the advantages of simple operation,high security and have been widely adopted. But they all have varying degrees problems: frequency selection with difficulty,relatively small measuring range, fussy and complicated calculation,lack of stability and so on. To solve these issues and based on the conclusion obtained from the error analysis,combining with the actual measurement experience,this paper presents a high-frequency signal injection method. It has advantages of greatly simplified calculation,enlarging the measuring range,and without the problem of frequency selection with difficulty.This paper combines theory,simulation and experimentation to study on the high-frequency method.Firstly,we do error analysis of the traditional signal injection methods and arrival at a conclusion:bigger the difference between the two injected frequencies is, the smaller the error is;the lower the low frequency in a reasonable range,the better. Secondly both the selection of high frequency(HF) and low frequency(LF) is analyzed in detail,combining with relevant simulation. Finally,The high-frequency method theory is proposed,with the HF set to 5000 Hz,ignoring the effect of TV leakage resistance and capacitance to ground of the system,while the LF set to 20 Hz directly if the resonant frequency of the system was not found after a frequency sweep from 200 Hz to 17 Hz. HF method has advantages of sweep frequency and fixed frequency. To find the most suitable frequency,low capacitance systems could use frequency sweep,combined with the characteristics of the grid itself. High capacitance systems could use the frequency of 20 Hz to reduce the error at lower.A series of experiments on TV parameters,which plays a decisive role that in the simulation and the experiment,was done,including the excitation parameters,leakage resistance,and the leakage inductance. According to the TV parameters got from the experiment result to calculate,we set the simulation module parameters and build simulation model to do simulation analysis of high-frequency method. Finally,the experimental platform is built in the laboratory to simulate the capacitance current measurement of 10 kV power system not charged. Simulation analysis and experimental results show that high-frequency method has the advantages of simple operation,accurate measurement,wide application range and the like.