.RGE-SCALE POWER S YSTEMS

This paper presents a method for an optimal op- eration of large-scale power systems similar to the one utilized by the Houston Lighting and Power Company. The main objective is to minimize the system fuel costs, and maintain an acceptable system performance in terms of limits on generator real and re- active power outputs, transformer tap settings, and bus voltage levels. Minimizing the fuel costs of such large-scale systems en- hances the performance of optimal real power generator allocation and of optimal power flow that results in an economic dispatch. To handle the large-scale systems of this nature, the idea of decomposing the problem into the real power optimization prob- lem and the reactive power optimization problem is introduced. The control variables are generator real power outputs for the real power optimization problem and generator reactive powei outputs, compensating capacitors and transformer tap settings for the reactive power optimization. The gradient projection method (GPM) is utilized to solve the optimization problems. It is an iterative numerical proce- dure for finding an extremum of a function of several variables that are required to satisfy various constraining relations with- out using penalty functions or Lagrange multipliers among other advantages. Mathematical models are developed to represent the sensitivity relationships between dependent and control variables for both real- and reactive-power optimization procedures; and thus eliminate the use of B-coefficients. Data provided by the Houston Lighting and Power Company are used to demonstrate the effectiveness of the proposed procedures.