ABSTRACT
Power flow on transmission networks is calculated using linear mathematical models for transmission lines, transformers, and shunt or series reactances, but nonlinear electrical descriptions for generation and load at the buses. There are two main sources of the nonlinearity. First, the power demand on the transmission network from distribution and subtransmission connections is closely modeled by constant real and reactive power, so if terminal voltages increase, the current demand decreases, and vice versa. A second reason for the nonlinear problem is that generating plants normally operate at a regulated voltage level and fixed real power injection. Reactive power flow on the transmission network results in higher current flows, and hence higher transmission line losses. Electric utilities have line compensation banks, that is, buses with shunt capacitors or inductors to regulate reactive power. An on-line power flow is a periodically executed program in the digital computers that are monitoring and controlling the power system.
