​Some factors can cause the failure of electrolytic capacitors, such as extremely low temperature, capacitor temperature rise (welding temperature, ambient temperature, AC ripple), high voltage, instantaneous voltage, VHF or reverse bias; Among them, the temperature rise is the most important factor affecting the working life (LOP) of electrolytic capacitors.

The conductivity of the capacitor is determined by the ionization ability and viscosity of the electrolyte. When the temperature decreases, the viscosity of electrolyte increases, so the ionic mobility and conductivity decrease. When the electrolyte is frozen, the ion mobility is so low that the resistance is very high. On the contrary, too much heat will accelerate the evaporation of electrolyte. When the amount of electrolyte is reduced to a certain limit, the life of capacitor will be terminated. When working in high cold area (below - 25 ℃), heating is needed to ensure the normal working temperature of electrolytic capacitor. For example, outdoor UPS is equipped with heating plate in Northeast China.

Capacitor is easy to be broken down under overvoltage condition, but surge voltage and instantaneous high voltage often appear in practical application. In particular, China has a vast territory and complex power grids. Therefore, the AC power grid is very complex, which often exceeds 30% of the normal voltage. Especially for single-phase input, phase deviation will aggravate the normal range of AC input.

The test results show that the commonly used 450V / 470uf105 ℃ imported ordinary 2000h electrolytic capacitor, under the voltage of 1.34 times of the rated voltage, after 2 hours, the capacitor will leak liquid and gas, and the top will burst open. According to statistics and analysis, the failure of PFC output electrolytic capacitor of communication switching power supply close to power grid is mainly due to power grid surge and high voltage damage. The voltage selection of electrolytic capacitor is generally two-stage derating, and it is reasonable to reduce it to 80% of the rated value.