Economic dispatch solution of an electric power network with optimum selection of generator bus voltages and transformer turns ratios

Abstract

A prime objective in a large electrical power network is that of scheduling the generation at various generating plants to supply the existing network loads and transmission losses while minimizing the total cost of generation and keeping the network voltages, power, and reactive voltamperes within practical operating limits. To achieve this objective, an optimum solution is obtained by modification of the generator power schedule, the magnitude of voltage held at generator and L-T-C busses, and the off-nominal turns ratio of the transformers instead of only rescheduling the generator powers as previous methods have done. The necessary condition for an optimum modification, which will minimize the total cost of generation and keep the network voltage, power, and reative volt-amperes within practical operating limits is established by using transformations of the fundamental bus voltage equations and the method of Lagrangian multipliers. The sufficient conditions for these equations were not proven, but the results obtained from the examples given show that a minimum is achieved within given engineering based constraints. The demonstration of the method was made on a newtwork used as a standard for literature on load flow analysis and on an operational power network. The method in its present form requires too much digital computer time to obtain a solution; therefore, it can not be considered for use in an automatic generator power dispatching system. It does, however, furnish valuable information which has not been available before for planning additions to a network and for determining the best operating procedure for a network.