Optimum Load-Shedding Policy for Power Systems

The now classical problem of optimlum dispatching miimizes the cost of production and transmission of electrical power to meet a specified demand under normal operating conditions. It appears logical and desirable to utilize and extend the methodology of optimum dispatching to problems encountered during abnormal operating conditions. This paper, as a first step in that direction, discusses a systematic approach toward minimizing the curtailment of service in a power system after a severe fault. The problem of minimizing load curtailment under a given set of emergency conditions is formulated as a problem of static optimization, subject to operational and equipment constraints. First, a feasible steady-state solution is obtained for the postfault network configuration. Starting from this initial feasible solution, the optinum (minimum curtailment) is approached by a gradient technique. An efficient computational procedure is based on the Newton-Raphson technique for solving the power flow equations, and the Kuhn-Tucker theorem for the optimization. The analytical results are verified on a 26-node example problem. Two typical emergency situations are considered: the loss of generation and the loss of an interconnection tie line. The same optimization procedure and the computed dual (Lagrangian) variables can be utilized for computer programs involving optimum service restoration, generation reserve scheduling, and system expansion studies.