One reason for this is the overcurrent caused by the higher harmonics of the grid
When the harmonic current in the power grid into the capacitor, it will be superimposed on the high-voltage capacitor's fundamental current, so that the operating current increases, but also make high-voltage capacitor on the fundamental voltage RMS voltage increases. If the capacitor capacitive reactance with the system to match the inductive reactance, will produce a higher harmonic generation of the role of amplification and over-current over-voltage, causing the capacitor internal dielectric partial discharge, the capacitor drum belly, fuse group explosion and other failures.
Second, the capacitor operating voltage is too high
The operating voltage of the high voltage capacitor can reflect the voltage of the bus system of the substation and directly affect the life and output function of the capacitor. The active power loss of the high voltage capacitor is mainly composed of dielectric loss and conductor resistance loss, and the dielectric loss accounts for more than 98% of the total active power loss of the high voltage capacitor. Pr = Qctgδ = ωCU2tgδ · 10-3 Where Pr is the active power loss of the high-voltage capacitor; Qc is the reactive power of the high-voltage capacitor; tgδ is the voltage of the high-voltage capacitor Ω is the grid angular frequency; C is the permittivity of the high-voltage capacitor; U is the operating voltage of the high-voltage capacitor.
As the operating voltage increases, the active power loss of the high-voltage capacitor will increase rapidly, and then the speed of the temperature increase will increase, and the high-voltage capacitor can not be used in high-voltage capacitor, Free increase, leading to reduced insulation life of the capacitor. In addition, due to high voltage capacitor continuous operation of the over-voltage is generally set at 1.10 times the rated voltage, when the capacitor is in over-voltage operation for a long time, will lead to capacitor over-current damage; Voltage protection device.
Third, the operating temperature is too high
If the capacitor is in a high electric field and high temperature operation for a long time, it will cause the dielectric medium aging and dielectric loss increase, which will lead to rapid heating and capacitor heating inside the capacitor is the capacitor Life, or even lead to thermal breakdown of the capacitor. According to regulations, if the ambient temperature exceeds 30 ℃, the capacitor shell temperature exceeds 50 ℃, should open the ventilation device cooling, when the ambient temperature exceeds 40 ℃, should immediately stop the capacitor operation. Therefore, in order to prevent the capacitor from operating temperature is too high and damage, should set the temperature monitoring device at any time to monitor the operating temperature of the capacitor, and the use of forced ventilation to improve the capacitor cooling conditions, .
The fourth reason, over-voltage generated by circuit breaker operation
Capacitor circuit breaker using vacuum circuit breaker, when the circuit breaker is closed, the circuit breaker contacts may occur bounce phenomenon and over-voltage. Although the resulting over-voltage peak is low, the impact of the capacitor is not large, but because the capacitor switching in the number of times a year or more, and the circuit breaker may lead to break-down capacitor overvoltage, it must take Effective protection measures to limit the over-voltage generated by the operation of the circuit breaker.
The fifth reason, the capacitor connected bus voltage loss
If the capacitor suddenly loses its voltage during operation, it may lead to instantaneous trip on the power supply side or main transformer disconnection. If the capacitor is not removed when the power supply is switched on or the standby power supply is automatically put into service, the capacitor may be damaged due to overvoltage. In addition, when the substation lost voltage recovery does not remove the capacitor, may have a resonant over-voltage, the transformer or capacitor damage. Therefore, the capacitor should be set up voltage protection device to ensure that the capacitor in the bus after the loss of reliable operation, but also in the bus voltage back to normal after the reliable access.