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This paper presents a concept, method, and implementation of utilizing phasor measurement unit (PMU) information to monitor the wide-area security of a power system. The close dependency of major transmission paths requires an approach that takes that interaction into account while establishing operational transfer capability, and evaluates grid reliability and security on a system-wide basis. Thus, the concept of wide-area security region, which considers all essential constraints, including thermal, voltage stability, transient stability, and small signal stability, is proposed. This approach expands the idea of traditional transmission system nomograms to a multidimensional case, involving multiple system limits and parameters such as transmission path constraints, zonal generation or load, etc., considered concurrently. In this paper, the security region boundary is represented using piecewise approximation with the help of linear inequalities (so called hyperplanes) in a multidimensional space, consisting of system parameters that are critical for security analysis. The goal of this approximation is to find a minimum set of hyperplanes that describe the boundary with a given accuracy. Offline computer simulations are conducted to build the security region and the hyperplanes can be applied in real time with phasor information for on-line security assessment. Numerical simulations have been performed for the full size Western Electricity Coordinating Council (WECC) system model, which comprises 15 126 buses and 3034 generators. Simulation results demonstrated the feasibility and effectiveness of this approach, and proved that the proposed approach can significantly enhance the wide-area situation awareness for a bulk power system like WECC.Index Terms-Operating transfer capability, real time security assessment, security margin, wide-area dynamic security region.

This paper presents a way to derive power oscillation damping control strategies for Flexible AC Transmission (FACTS) devices, and derives these laws for the four major types of FACTS devices using an energy function (Lyapunov) method. All controls rely only on locally measurable information, and are independent of system topology, implying structural uncertainty need not affect power oscillation damping control --strategies. Keywords:-FACTS, power oscillation damping] energy function methods 1 Introduction FACTS devices are increasingly being used as cost effective measures to increase power system transmission capability, to improve first swing margin, to actively damp oscillations, and to help stabilize weakly coupled systems in the event of critical faults [5], [6]. This paper presents a new method for designing power swing damping control strategies for FACTS devices, and derives these laws for thyristor controlled series capacitors (TCSC), static VAR compensators (SVC), static condensers (STATCON), and thyristor controlled phase shifting transformers (TCPS). Previous approaches have either assumed a particular control strategy (and then demonstrated the stability of the system [3]), or have chosen an a priori set of variables to estimate (and then to control based upon inferred values of these variables [4]).The present approach introduces a structure preserving energy function in which each FACTS device in the system is identified with a specific term. Taking the derivative of this energy function, it is easy to see how to choose parameters within the FACTS devices to ensure that each term of the derivative is negative semidefinite, and hence that each term contributes to system stability. This strategy identifies both the control variables, and control laws as a function of these variables. Important aspects of the approach are:

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