Implicit generator and SVC modelling for contingency scheduling of reactive power dispatch

In the paper, CIGRE models of generating units are used for contingency scheduling of reactive power. These models are based upon the capability curves and the reactive power margin at each automatic voltage regulator (AVR) state (normal operation, threshold or loss of voltage control after AVR reaches the limits), rather than on the commonly used PV or PQ representation for generators in load flow. These models, in effect, add a supplementary generator node behind a reactance for each machine, which simulates the behaviour of the generator AVR at each state. The models are not detailed enough to allow the simulation of transient effects but are adequate to represent the system during a slow change under steady-state operation. The salient advantage of the proposed implicit method is to preserve the factorised triangulated nodal admittance matrix used for the fast decoupled load flow [B'] and [B"] for each state. This is achieved by calculating new injected powers and voltages at generating nodes and using these values for updating the solution during iteration for the final load-flow results. Simple illustrative cases for the explicit and implicit generation reactance modelling are presented. The injected power and voltage correction techniques are also used for static VAr compensator (SVC) representation, and a numerical example is given. The method was used for contingency analysis of a 620 busbar, 66 generating unit system. The technique proved to be reliable and efficient.