Synchronized and soft switching of capacitor banks in distribution systems

Abstract

Reactive power unbalance in an electrical network causes unnecessary voltage drops and reduces the total amount of active power that can be transmitted by the lines. One of the most economical methods to improve both the voltage quality and the transmission capacity is to provide reactive power support by installation of shunt capacitors. This is true for all system voltage levels and for most types of loads in both utility and industrial networks. However, the switching of a capacitor bank results in overvoltages close to as well as far away from the capacitor bank. The transient voltage from switching of one capacitor bank can even be magnified in overvoltage at capacitor banks at other locations. The voltage and current transients generated during the energization of shunt capacitor banks have become recognised as serious problems in modern electrical networks. The concerns include both power quality issues for voltage sensitive customers and excessive stresses on power system equipment. The transient inrush currents may also cause disturbance and damage to telecommunication systems. This paper deals with newly developed practical methods to avoid or minimise the transients from switching of shunt capacitor banks.