parallel capacitors is a kind of reactive power compensation equipment, usually high-voltage centralized compensation is used to compensate the reactive power on all circuits and transformers on the power supply side of the low-voltage busbar of the substation. In use, it is often combined with on-load tapping transformers to improve the power quality of the power system . Its functions are:
1. Compensate the reactive power of the inductive load of the power system.
2. In order to improve the power factor, improve the voltage quality, reduce the line loss, and increase the output power of the system or transformer.
3. Improve bus voltage quality, reduce power loss, improve power supply quality, and achieve the purpose of stable operation of the system.

Commonly used shunt capacitors can be divided into single iron shell type, box type, assembly type, semi-closed type, dry type and gas-filled type according to their different structures. The parallel capacitor bank is only allowed to operate at 1.1 times the rated voltage for a long time. When the steady-state voltage of the power supply bus rises, the over-voltage protection should act, and the time limit will be signaled or tripped. When the overvoltage protection acts on the signal, it can be without delay.