Optimal placement of voltage sag monitors based on fault location principle

Voltage sag is one of the most serious power quality problems confronted by both customers and power supply companies, and on-line monitoring is an effective way to record and analyze voltage sag in the whole network. With the consideration of limited costs, it is impossible to place monitoring devices on each bus in a network. In the traditional method, the placement scheme of voltage sag monitors are determined based on a given voltage threshold, But in engineering the threshold is difficult to select. In the improved method, monitor reach area method and fault location principle are combined to establish fault observability matrix for voltage sags, then optimal monitoring scheme can be obtained using 0-1 linear programming. In the optimal monitoring scheme, the fewest monitors are needed to observe voltage sags and their fault locations in the whole network. Based on the improved placement scheme, if a fault occurs at any position in the whole network, then fault position can be located. Therefore, voltages at non-monitored buses can be easily and accurately determined based on short-circuit calculation. The proposed method had been applied to the IEEE 30-bus test system, simulation results had verified the correctness and effectiveness of the new method. Compared with the traditional method, in the improved method the fault position of voltage sag can be determined more accurately, magnitude of voltage sag at non-monitored buses can be obtained more accurately with fewer monitors, and there is no need to consider the selection of voltage threshold. Therefore, the proposed method can meet the practical application better.