Power capacitor protection

1. The capacitor bank should adopt appropriate protection measures, such as balanced or differential relay protection or transient overcurrent relay protection. For capacitors of 3.15kV and above, separate fuses must be installed on each capacitor. The rated current of the device should be selected according to the characteristics of the fuse and the inrush current when it is turned on. Generally, the rated current of the capacitor is 1.5 times to prevent the capacitor tank from exploding.

2. In addition to the forms of protection indicated above, the following protections may be made when necessary:

(1) If the voltage rise is frequent and long-term, measures should be taken to increase the voltage by no more than 1.1 times the rated voltage;

(2) Protect with a suitable current automatic switch so that the current does not rise more than 1.3 times the rated current;

(3) If the capacitor is connected to the overhead line, a suitable lightning arrester can be used for atmospheric overvoltage protection;

(4) In a high-voltage network, when the short-circuit current exceeds 20A, and the short-circuit current protection device or fuse cannot reliably protect the ground from short-circuit, a single-phase short-circuit protection device should be used.

3. Correct selection of the protection mode of the capacitor bank is the key to ensure the safe and reliable operation of the capacitor. However, no matter which protection method is adopted, the following requirements should be met:

(1) The protection device should have sufficient sensitivity, and the protection device can operate reliably regardless of the internal failure of a single capacitor in the capacitor bank or the damage of some components;

(2) It is possible to selectively remove the faulty capacitor, or to check out the damaged capacitor after the capacitor bank power supply is completely disconnected;

(3) The protection device must not malfunction when the capacitor is stopped and the grounding or other fault occurs in the power system;

(4) The protection device should be easy to install, adjust, test and operate;

(5) Less power consumption and lower operating costs.

4. The capacitor is not allowed to be equipped with an automatic reclosing device, and the phase reaction is equipped with a pressureless release automatic trip device. It is mainly because the capacitor discharges for a certain period of time. When the switch of the capacitor bank trips, if the switch is reclosed immediately, the capacitor is too late to discharge. In the capacitor, there may be a charge opposite to the polarity of the reclosing voltage, which will cause the switch to be closed. A large inrush current is generated instantaneously, causing the capacitor casing to expand, inject and even explode.