Application of an optimisation method for determining the reactive margin from voltage collapse in reactive power planning

Power system reactive power planning requires the computation of the reactive power margin from the point of voltage collapse in the steady-state in order to quantify the adequacy of the level of installed reactive power plant. This reactive margin is the difference between the maximum reactive load distributed across selected power system nodes and the reactive load at the planned system operating point. The margin can be estimated by applying an optimisation method using the total reactive load as the objective, with the load flow equations as equality constraints, whilst including system limits such as generator reactive capability limits as inequality constraints. This paper describes a full AC formulation of the optimisation problem. It is solved using an interior point implementation of the Newton method developed for the optimal power flow. This avoids potential difficulties in identifying the binding inequality constraints