Metodologias para mitigação de interferências no sistema de proteção de banco de capacitores de média e alta tensão

Abstract

There are many types of protection for capacitor banks, like simple star, double star and H bridge. Burning of capacitive elements results in actuation of protection, due to variations in unbalance voltage and unbalance current previously set in the relay.But not only internal failures can cause sensibilization of protection, external system interferences cause variation of impedance between phases of equipment, resulting in false operation of protection system. Capacitance of capacitor units is a characteristic intrinsically linked to geometry of elements that composes the capacitor, but it varies with ambient temperature. Therefore, large capacitor banks when exposed to non-uniform shading present variation of capacitance and, as consequence, variations in unbalance voltage and unbalance current. The phenomenon of non-uniform shading can be observed mainly in Static Var Compensation (SVC) and Fixed Series Compensators (FSC), basically because of the size of its capacitor columns that favors partial shading of capacitor units. This study presents several aspects of balancing of capacitor banks, as well as clarifications about interference of external factors in the detection of failures of capacitor units. The simple geographical position of the capacitor bank can result in constant operational disturbances and, as consequence, increase of financial cost linked to unavailability, team displacement/mobilization and unnecessary repairs. Therefore, the results obtained in this study will help detecting interferences in the protection system of the capacitor bank, as well as alternatives to reduce external influence in the protection system. It will also analyze the principal factors impacting in the natural unbalance if the capacitor bank, increasing equipment reliability and operability of the equipment of reactive power compensation.