Reactive Power Optimization For Urban High Voltage Power Systems

The purpose of reactive power optimization is to reduce the active power loss and to improve the voltage quality in power networks by adjusting the reactive power devices. In substations of a urban power system, there are shunt capacitor sets connected to the low voltage buses. The reactive power optimization for urban high voltage power systems can be carried out by adjusting shunt capacitor sets and transform taps.When only one system operating state is considered for the reactive power optimization, the constructed objective function can be the minmized active power loss, the equation constraint is composed of the nodal power balance equations, and the inequation constraint will be consisted of the constraints of breach power, nodal voltage, reactive power compensation capacity and the transformer taps. In practical application, the heuristic sensitivity approach is used to reduce the computational time. By using the sensitivity values of active power loss to nodal reactive injections, the reactive compensation effects of all buses are ordered, from which the adjustment scheme for capacitor sets is obtained by repeated accurate load flow computation. Voltages at the medium and low voltage buses are satisfied by adjusting transformer taps. Computed results will provide the active power losses, shunt capacitor states and transformer tap values.When the system operating states in a period of time is considered for the compositive reactive power optimization, load data in the next 24 hours are obtained from the on-line load forecasting function, shunt capacitor states and transformer tap changers in the next 24 hours are determined. The optimal objective is to minimize the compositive costs, while cost of adjusting control devices and other security operation constraints are also considered. The optimization procedure is composed of two stages of static and compositive optimization. In the static stage, shunt capacitors are ordered by the reactive sensitivities and states are determined in static. In the compositive optimization stage, device states in 24 hours are coordinated. Computed result gives out the adjusting scheme in 24 hours, including the total compositive economic index, capacitor set states and transformer tap values at every...