In judging whether the filter electrolytic capacitor is damaged or not, it can be judged as damaged when the electrolytic capacitor appears the following forms: appearance explosion, aluminum shell bulge, plastic jacket cracking, electrolyte outflow, safety valve opening or being pressed out, cracking of the top part of the small capacitor, serious corrosion of the connecting post, deformation and falling off of the cover plate, indicating that the electrolytic capacitor has been damaged. If the multimeter is used to measure open circuit or short circuit, the capacity is obviously reduced and the leakage is serious.

The causes of electrolytic capacitor damage are as follows:

(1) The quality of components is not good (large leakage current, large loss, insufficient withstand voltage, containing impurities such as chloride ion, poor structure and short service life).

(2) The rectifier bridge before filtering is damaged, and the alternating current enters the capacitor directly.

(3) The partial resistance is damaged, and the uneven partial voltage causes a capacitor to break down first, and then other capacitors also break down.

(4) The capacitor is not installed properly, such as the outer insulation is damaged, the shell is connected to the undesired potential, and the electrical connection and welding are poor, resulting in poor contact, heating and damage.

(5) Poor heat dissipation environment, so that the capacitor temperature rise too high, long time and damage.

The following points should be paid attention to when replacing the electrolytic capacitor:

(1) It is better to choose the same model as the original one to replace the filter electrolytic capacitor. When the same model can not be obtained at the moment, the following points must be paid attention to: the withstand voltage, leakage current, capacity, overall dimension, polarity and installation method should be the same, and the type that can withstand large ripple current and long service life should be selected.

(2) In the process of replacing the electrolytic capacitor, the electrical connection (screw connection and welding) shall be firm and reliable. The positive and negative electrodes shall not be wrongly connected. The clamp used for fixing shall be firm and shall not damage the external insulation of the capacitor. The partial voltage resistance shall be connected as it is, and the resistance value shall be measured to make the partial voltage uniform.

(3) For electrolytic capacitors that have been placed for more than one year, the leakage current value shall be measured, which shall not be too large. Before installation, the DC current shall be applied for aging, and the DC current shall be lowered first. When the leakage current is reduced, the voltage shall be increased. Finally, at the rated voltage, the leakage current value shall not exceed the standard value.

(4) Because the size of the capacitor is not suitable, and when the replacement capacitor can only be installed in other positions, it must be noted that the bus from the inverter module to the capacitor cannot be longer than the original bus, and the area surrounded by two + and – buses must be as small as possible, and it is best to use twisted pair. This is because the extension of capacitor connected bus or the surrounding area of + and – bus will cause the increase of bus inductance and the rise of pulse Overvoltage on the power module, which will cause damage to the power module or overvoltage absorbing device. In the case of no alternative, the surge absorbing capacitor with high frequency and high voltage is added to the inverter module with short wires to help absorb the overvoltage of the bus and make up for the harm caused by the extension of the bus connected by the capacitor.

Editor in charge: LQ

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