Cutset-angle Based Wide Area Thermal Security Region and Its Application in China Southern Power Grid

This paper presents a novel methodology for constructing wide area thermal security region (WATSR) to monitor the wide area thermal security of bulk power system under N-1 criterion by utilizing wide area measurement system. A general cutset angle for large-scale inter-area power system is defined and developed as a measurement to assess the system thermal security so as to construct WATSR in cutset-angle space. WATSR consists of all stable operating points under N-1 criterion, while its boundary is a complete set of all the critical points. In this paper, the boundary of WATSR is represented via its piecewise approximation with a set of hyperplanes to enhance the calculating speed. Hyperplanes are described as a set of linear equalities, which are convenient to be determined. And, because coefficients of a hyperplane can indicate the sensitivities between various control parameters, it is beneficial to power system online security assessment and control strategy optimization. A two-step algorithm is given to apply WATSR to online monitoring for bulk power system. The first step is offline calculation. The aim of this step is to determine a minimum set of hyperplanes to properly describe the boundary of WATSR. A hyperplane is a sub-segment of the security region boundary and normally corresponds to a certain constraint. The second step is online matching. Data retrieved from wide area measurement system are used to determine the relative constraints given by the hyperplanes. And then, the stability of the system can be quickly and accurately determined by the assistance of WATSR result. Once the power system turns to critical, WATSR can help the operators to optimize their control strategy. The methodology of WATSR has been successfully implemented in the China Southern Power Grid, which is known as one of the largest alternating current/direct current parallel transmission system in the world. Feasibility and effectiveness of the presented method have been validated through intensive analyses in China Southern Power Grid. Copyright (c) 2014 John Wiley & Sons, Ltd.