Calculation of transmission losses from a planning viewpoint

An analytical technique based on statistical methods is developed to evaluate the expected difference in the transmission losses, in a defined study area, between two overall systems that use two different 500 kV line configurations that are technically and environmentally acceptable. A study area is carefully chosen so that essentially all the difference in IR loss between any two alternatives occurs in that study area. The annual load duration curve of the entire system is used to define the annual generation schedule pattern of the study area. AC load flows are performed on a reduced system that has all of the study area represented. Using power conservation equation and Maclaurin series, the interface flow is eliminated from the study area loss function. The load-duration curve, which is a reliability function, is expressed as a continuous function of the study area load demand. This function is used to derive the probability density function of the study area load demand. The annual expected value of the difference in the study area losses between two alternatives is evaluated using the above probability density function and the derived loss function. Calculated values show very good agreement with those obtained with load flow studies