Linear Var Flow Methods for Security Assessment
К.R. Padiyar, T. L. Jose · Electric Machines & Power Systems · 1986
In this paper, an investigation of various approximations for the solution of reactive power flow equations, suitable for security assessment, is presented. When the loads are assumed to be a combination of constant current and constant impedance types, the power flow equations can be decoupled exactly. The reactive power flow equations become linear with parameters which are functions of phase angles. Hence, once the phase angles are known, voltage magnitudes can be computed exactly without iterations But approximations are required to simplify computations for on-line application. Various approximations and the factors that influence the accuracy of the solutions are investigated.lt is shown that iterative linear power flow (ILPF) and fast decoupled load flow (FDLF) methods (for voltage computations) can be derived from one set of approximations. Case studies of a 30 bus system is presented to compare the accuracy of various approximations. The results indicate that a major factor influencing the accuracy of the solution is the variability of conductance to susceptance ratio in a system. A new method is presented which gives very accurate results with moderate computing effort.