Capacitor Bank Balancing

High voltage (HV) capacitor banks are constructed using combinations of series and parallel capacitor units to meet the required voltage and kvar requirements. These capacitor banks utilize protective relays which will trip the bank when problems are detected. Most commonly, these relays will be applied in some form of unbalance protection that relies on equivalent sections of the bank having nearly identical capacitances. In reality, equivalent bank sections rarely have identical capacitances. This unbalance within a healthy capacitor bank is known as inherent unbalance. This paper explains the concept of capacitor unbalance and its causes. It then discusses practical levels of unbalance and how to balance an unbalanced capacitor bank.