Fault Location Method Based On Pulse Injection At Low Voltage Side Of Distribution Transformer

Distribution network is the key part connecting the transmission network and users for electricity distribution.Ensuring its stable and secure operation can improve the quality and robustness of electricity supply.The environmental disturbance can easily affect the network’s secure and stable operation,and most outage time of power users is as a consequence of the distribution network fault.Therefore,searching out the fault point and eliminating the fault in time after the fault taking place are important for ensuring the normal production and people’s life.The traveling wave method is more efficient on account of being less affected by the inherent parameters of the system comparing with other fault location methods.So the traveling wave method is widely used in fault location technique of power grid.According to the origination of traveling wave,the methods can be divided into passive and active technique.The precision of passive technique is related to the magnitude of traveling wave generated by fault,so it will be susceptible to the phase angle of voltage when fault takes place.While active technique is not affected by the phase angle and always injects signal at the high voltage side,the signal injection may threaten people’s security.In addition,the injecting location mostly locates in the main station,so it has trouble in monitoring the fault in the multi branch or at the end of the distribution line.Therefore,injecting pulse at the low-voltage side of the distribution transformer,and the pulse is used as fault location signal after the transmission of the distribution transformer,it has many advantages such as simple injection,variable injection location and more relative security.The fault location method is based on pulse injecting at the distribution transformer’s low voltage side.Then establish the high frequency model suitable for two kinds of distribution transformers and carry out the low voltage injection test.Finally the fault location method of pulse injection at the low voltage side is proposed.Based on the low-frequency electromagnetic transient model of distribution transformer,the high frequency model of distribution transformer is proposed.The fault injection strategy are proposed by using the established transformer model.According to the transmission line model of medium voltage power grid,the propagation characteristics of pulse signal and the refraction and reflection of pulse signal when encountering different impedance are researched.Based on the multipath propagation model in the distribution line,the characteristics between any two points can be obtained,and the pulse response of the injection point can be obtained when the injecting signal is pulse.By comparing the two pulse responses before and after the fault occurs,the fault characteristic signal is extracted and the calculation formula of fault distance is proposed.The distance from multi-point to fault point can be calculated by multi-point injection,and the fault location algorithm is able to be proposed by comparing with the structure of distribution network.The impedance characteristics of the distribution transformer can be measured under different conditions by using the impedance analyzer,and the transformer model parameters can be calculated.The model is established in simulation software by using the calculated parameters,and the model is verified in frequency domain and time domain according to compare the simulation and experiment results.The influence of different pulse width,pulse waveform,injection mode and transformer type on the injection signal of high voltage side is compared and analyzed,and the optimal injection parameters are selected.The simulation is carried out after establishing the fault location model based on pulse injection.The influence of different factors on the accuracy of fault location is studied by changing the fault distance,fault resistance and fault types.The results demonstrate that the fault location method proposed in this paper is accurate and valid.A platform of fault location method based on pulse injection is built in the laboratory and the test is carried out after the fault point is set artificially.The results demonstrate that the proposed method can find fault location precisely.Finally,the fault distance experiments at different points are carried out in the distribution network model.The distances from multiple points to fault point is able to be obtained by analyzing fault signals.Then combines the distances with the grid topology,the fault location is finally determined.The above research work can accurately find the fault location after the distribution network fault occurs,eliminate the fault quickly and make sure of the power grid’s stable operation and people’s ordinary work and life.