Resumo:
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.
