一、Common failure modes of aluminum electrolytic capacitors
When a capacitor fails, the materials, structure, manufacturing process, performance and use environment of various capacitors are different, and the failure mechanism is also different. Common failure modes of aluminum electrolytic capacitors: leakage, burst, open circuit, breakdown, deterioration of electrical parameters, etc.
二、Failure modes and their causes
①Poorly sealed aluminum electrolytic capacitors;
②Problems with the mechanical seal process;
③If the aluminum electrolytic capacitor is sealed with a rubber plug, it may cause liquid leakage due to aging and cracking of the rubber because it is used for too long.;
④For installation problems, general manufacturers will consider the problem of liquid leakage. They will clearly stipulate in the enterprise standard that vertical installation is required, while some companies use horizontal installation, etc.
2、Deterioration of electrical parameters
①Decrease in capacitance and rise in loss
The capacitance of aluminum electrolytic capacitors declines slowly at the early stage of the work, which is caused by the working electrolyte constantly repairing and thickening the anodic oxide film during the load。
②Increased leakage current
Increased leakage current often leads to failure of aluminum electrolytic capacitors. The process level is low, the oxide film is damaged and stained seriously, the working electrolyte formulation is not good, the raw material purity is not high, the chemical and electrochemical properties of the electrolyte are difficult to stabilize for a long time, the aluminum foil purity is not high, and the impurity content is high. These factors are all May cause excessive leakage current failure.
The breakdown of the aluminum electrolytic capacitor is caused by the rupture of the anodized aluminum dielectric film, which causes the electrolyte to directly contact the anode. The aluminum oxide film may be locally damaged due to various materials, processes or environmental conditions. The oxygen ions provided by the working electrolyte under the action of an external electric field can re-form the oxide film at the damaged site, so that the anodic oxide film can be filled and repaired. However, if there are impurity ions or other problems in the damaged part, and the filling and repairing work cannot be perfected, micropores will be left on the anodized film, and may even become penetration holes, causing the aluminum electrolytic capacitor to break down.
Aluminum electrolytic capacitors may experience open-circuit failure during long-term operation in high-temperature or hot-humid environments. The reason is that the anode lead foil is subject to electrochemical corrosion and breaks. For high-voltage large-capacity capacitors, this failure mode is more.
The aluminum electrolytic capacitor has too large AC components in the working voltage, or there are many problems with the oxide film medium, or there are harmful anions such as chloride and sulfate, so that the rate of gas produced by electrolysis is faster when the leakage current is large. The longer the time, the greater the leakage current, the more gas in the shell, the higher the temperature. The pressure difference between the inside and outside of the capacitor metal shell will increase with the increase of working voltage and working time. If the seal is good and there is no explosion-proof measures, the increase in air pressure to a certain degree will cause the capacitor to burst.
Aluminum electrolytic capacitors burned out, usually caused by the following reasons:
①Aluminum electrolytic capacitors with positive and negative poles reversed are capacitors with positive and negative poles. If the positive and negative poles are connected incorrectly when the aluminum electrolytic capacitor is installed, the capacitor will burn down.;
②The withstand voltage is not enough. When the voltage exceeds the withstand voltage of the aluminum electrolytic capacitor, the phenomenon of capacitor burnout will also occur;
③Substandard quality The aluminum electrolytic capacitors produced by some manufacturers are unqualified, which may also cause the capacitor to burn out, etc.