Formulation and Visualization of Bus Voltage-Var Safety Regions for a Power System

This letter studies formulations on the safety regions of the voltage and reactive power (Volt/Var) of each bus in a power system by nonlinear network decomposition and proposes visualizations of these regions for operators to monitor the Volt/Var safety of the system. Unlike the conventional approach that searches for boundaries of such regions by a large number of repeated power flow calculations, the proposed method takes an analytical approach so as to avoid repeated calculations. Firstly, the power network is decomposed into a set of two-bus channels, where a complex-valued index is introduced to represent the Volt/Var status with each channel. Then, by using a scalable holomorphic embedding method, the trajectories of the indices of all channels are obtained, which together predict Volt/Var safety of the entire system under prospective operating conditions. Next, boundaries of the Volt/Var safety regions are derived and visualized to monitor the margin information of voltage stability and control. Finally, the effectiveness of the proposed method is validated on the IEEE 14-bus system in detail.