Capacitance Current Measurement Of Medium Voltage Distribution Network Based On Signal Injection Method

The medium voltage distribution network generally adopts the non-effective grounding method in which the neutral point is not grounded and the neutral point is grounded via the arc suppression coil.The capacitance current value is the basis for judging the single-phase grounding hazard of the medium voltage distribution networ,k and the configuration of the arc suppression c.oil.The traditional method of measuring the capacitive current on the primary side by using the asymmetric of the distribution network is less safe and complicated to operate.With the large number of cable lines put into operation,the symmetry of the system is getting higher and higher,it leads to the measurement error of the traditional capacitive current measurement method becoming larger.The secondary side injection signal measurement capacitance current way is a simple and safe method of capacitance current measurement that does not depend on the asymmetry of the power grid,the key technol'ogy of this method is studied in the paper.In this paper,the calculation of cable electrical parameters and the analysis of frequency characteristics are firstly carried out in the measurement frequency band of the signal injection method.The actual cable parameters and the variation of cable parameters with frequency are obtained.Secondly,the impedance frequency characteristics of the potential transformer are tested,and the linear transmission frequency band of the transformer is found.The intensity and frequency of the signal injected by the signal injection method are determined by simulation.Thirdly,the frequency characteristics of the medium voltage distribution network system are studied,The zero sequence frequency characteristic curves of the actual medium voltage distribution network system and the pure capacitance system are obtained by simulation and calculation,and compare the frequency characteristic curves of the two,It is proved that the actual medium voltage distribution network can be equivalent to the correctness of a pure capacitance at the measurement point,which proves that the grid capacitor current can be measured by the signal injection method.Finally,three methods of measuring the capacitance current of the grid by three-frequency method,phasor method and sweeping method are given.The principle analysis and error analysis of these three methods are also given,and their applicable conditions are also given.And through the simulation of the actual medium voltage distribution network model,the accuracy and range of the three-frequency method and the frequency division method for measuring the capacitance current of the grid are given.