Voltage sags are unavoidable and cause serious harm to sensitive loads. Reasonable configuration of limited monitors can reduce monitoring costs and provide data support for sag management and reduction of sag hazards. Therefore, the optimal configuration of sag monitors is of great significance. Aiming at the traditional method that ignores the inconsistency of the degree of sag damage in different areas, an optimal configuration model of sag monitor considering the reliability of monitoring in sag sensitive areas and the location of phasor measurement unit (PMU) is proposed. The model takes sag observability as a constraint, takes the smallest number of monitors and covers the widest range of sag sensitive areas as the goal, and further configures PMU to assist in monitoring voltage sags. In addition, the Zeroin method is proposed to improve the accuracy of the exposed area calculation. The IEEE-30 system simulation shows that the proposed method can ensure the minimum number of monitor and high redundancy coverage of sensitive loads, ensuring its economic benefits. The proposed method overcomes the difficulty of balancing the monitoring cost with the monitoring capability of sensitive areas.

Reasonable placement of limited monitors is beneficial to reduce the cost of monitoring for voltage sags assessment. However, existing methods only consider the observability of voltage sags, leading to information loss. To capture all the voltage sags and the corresponding fault positions in distribution network, a multistage optimal placement approach of power quality monitors considering voltage sag and fault position observability is proposed. The initial requirement of voltage sag monitoring, that is, voltage sag observability is ensured by monitoring reach area method. Then, based on a simple fault location method, the fault location observability index is proposed for describing monitoring effects for fault position observability. A series of placement schemes with different costs and monitoring effects are given, which is convenient for engineers to choose the proper placement scheme according to the budget and demand. The simulation results carried on the IEEE 69-bus system show that the proposed approach can is correct and available.