Transmission Losses and Economy Loading by the Use of Admittance Constants

In order to operate a power system at optimum economy, the production costs and transmission losses must be coordinated. A straightforward derivation of the co-ordination conditions is given. A widely adopted method of finding transmission penalty factors used so-called "B-constants." These constants are not easily modified to consider changes in the transmission system or deviation from "base-case" system conditions. By starting with the equilibrium equation of a power system written in terms of admittance constants, a concise expression for the total losses of a power transmission system which does not neglect shunt paths to neutral or the effect of off-nominal turns ratios is developed. Following this same approach, an easily modified, approximate expression for the penalty factor is formed. Any errors incurred by using this approximate penalty factor are small when compared with the inaccuracy of the original data on production costs. Several test cases on hypothetical systems are given. The generation schedules for economic dispatch, using approximate penalty factors, compare quite favorably in actual hourly costs with the costs of schedules obtained by exact penalty factors.