Optimal allocation of voltage sag monitors in multi voltage grades distribution network based on improved MRA method

Abstract

In order to capture all the fault points of voltage sag in distribution network, based on improved MRA method, an optimal allocation method of voltage sag monitors in multi voltage grades distribution network is proposed. All buses in the system are classified according to the voltage grades. When the fault point is located at different voltage grades of the system, the corresponding zero sequence impedance matrix will be different under the conditions of single-phase earth fault or the two-phase earth fault. This paper constructs different zero sequence impedance matrix based on the fault lines of different voltage grades, which overcomes the shortage of traditional optimal method of building the only zero sequence impendence matrix and improves the precision of calculation. As for transformer that is not YNyn connection mode and will not pass zero-sequence component, in this paper, by using the symmetrical component method in short circuit calculation, the zero sequence component is eliminated, and the amplitude expression of voltage sag is modified, which improves the accuracy of the algorithm. The proposed method is simulated with a distribution network which contains four voltage levels. The optimal allocation by proposed method is compared with that by the traditional method, the results show that traditional method applied to the distribution network exists monitoring blind spot, the proposed method can be used for the optimal allocation of the distribution network.