Positive sequence current differential protection based on least square method for distribution network with distribution generation

A positive-sequence current differential protection scheme based on the least square method for the distribution network with distribution generation connected is proposed in the paper. By comparing the similarity of the positive-sequence current waveforms at both ends of the line, it is judged whether there is a fault or not. Firstly, the fault characteristics of the distribution network with inverter interfaced distributed generator (IIDG) are analyzed, and the fault characteristics of the distribution network are obtained when a metallic short circuit and fault with high resistance occur. According to these fault characteristics, a differential protection scheme based on the least square method is proposed. The instantaneous sampling value of the positive sequence component of the current is used in the criterion. And the residual square sum of each instantaneous value of the positive sequence current at both ends is calculated. The sum of squares of residuals in the half of the cycle is integrated, and the integrated value is used as the criterion. The simulation results show that the differential protection can operate under the situation of common fault types, transition resistance, and normal load levels etc. This scheme can adapt to the distribution network with poor communication conditions, and quickly and accurately remove faults.