Optimisation of static-capacitor installations and switching schedules in distribution systems

In distribution systems, static-capacitor banks are installed to reduce energy losses and to achieve voltage correction. The determination of the sizes and locations of the capacitor installations is formulated as an optimisation problem in the paper. The objective function is taken to be the sum of the annual cost of energy loss and the annual cost of additional capacitor installations. To schedule switching operations, the year is divided into a number of periods based on seasonal variations in the cost of energy and in the load requirements during the year, and the day is divided into a number of intervals based on the hour-to-hour variations in the cost of energy. The load currents are assumed to remain constant within each interval. The method of solution consists of first minimising the annual cost of energy loss alone, by quadratic programming, and then minimising the total annual cost by a step-by-step iterative procedure. The method takes account of the discrete nature of the capacitor installations and supplytransformer tap settings. The solution yields the optimum capacitor installations together with the optimum capacitor switching and transformer tap-changing schedules.