Effect of improper temperature and voltage on film capacitors

In the case of breaking the capacitor bank, if the circuit breaker is severely punctured, a loop phenomenon will occur in the circuit, and several times the operating overvoltage will occur at the terminals of the capacitor. Under such a high operating overvoltage, strong partial discharge and dielectric damage occur inside the film capacitor, and even capacitor breakdown occurs. Thus the quality of the circuit breaker used to switch capacitors is closely related to the actual service life of the capacitor. In order to prevent excessive inrush current and overvoltage, the capacitor (group) should be discharged in time after the capacitor is retracted from the network. The residual voltage on the capacitor should not exceed 10% of its rated voltage before the capacitor is put back into operation on the grid.

The relationship between the service life of the film capacitor and the ambient temperature:

Each capacitor's label is marked with its temperature category, for example: "-40/A", which means that the capacitor can be put into the grid at a low ambient temperature of -40 °C. The high ambient temperature for continuous operation of this capacitor is: Ih average high temperature is 40 °C, 24h average high temperature is 30 °C, and annual average high temperature is 20 °C. This is because at a low temperature, the viscosity of the impregnating agent inside the capacitor increases, the internal voltage decreases, and the capacitor's power resistance decreases.

Operating at temperatures below its allowable low temperature is likely to cause partial discharges inside the capacitor, thereby accelerating its electrical aging and reducing the actual life of the capacitor. On the other hand, if the film capacitor is operated for a long period of time above its high allowable temperature, it will accelerate the thermal aging of the capacitor. Therefore, on the one hand, it is necessary to select a capacitor whose temperature category is compatible with the actual operating environment temperature. On the other hand, in the installation and use of the capacitor, special attention should be paid to the ventilation, heat dissipation and radiation problems of the capacitor under actual working conditions, so that the capacitor is The heat generated during operation can be dissipated in time, and every effort is made to reduce the temperature of the medium inside the capacitor under high temperature conditions in order to extend the actual service life of the capacitor.