Mitigation of capacitor bank switching transients by using SVCs in large plants instead of capacitor bank and circuit breaker

Industrial plants generally make use of large induction motors which are the heavy consumers of reactive power. These motors sometimes cause the reduction of power factor and make the plants use capacitor banks to improve the power factor. Switching on capacitor banks to a circuit generally causes the increase of the voltage in the feeding bus and will also bring severe inrush current. This situation disrupts feeding power quality in the plant and will sometimes bring several damages and problems for the plant. In this article, while analyzing and studying switching transients of capacitor banks applied for power factor correction in industrial plants, their substitution with static var compensators (SVCs) have been considered and the capability of these compensators in reducing transient problems is analyzed. Then having considered a sample case, the model simulation is done using Matlab/Simulink software, and voltages and transient currents generated when correcting power factor are studies once by using capacitor bank and circuit breaker and once by using SVC. Inrush currents, over-voltages and FFT analysis has been obtained in each two cases.

I. Introduction

Nowadays, most industrial plants (for example cement plants) make use of large induction motors for their products. Induction motors receive great reactive power from network for their proper function. In one hand, reactive power consumption cause the reduction of voltage of feeder bus in the plant, and on the other hand, it causes the reduction of power factor of the whole plant. The reduction of power factor of the plant or in other word, the increase of the plant consumed reactive power leads to the congestion of the transmission line connected to the plant and occupies the capacity of the said line. Therefore, regional electricity departments usually make large industrial plants to supply their required reactive power in the same place. To this end, generally, large plants try to provide their required reactive power by using capacitor banks in the entrance and do not allow power factor come lower than the predetermined limit.