(1) With the ×1Ω or ×10Ω block of the pointer multimeter, the amplitude of the pointer swing caused by the charging and discharging of the capacitor during the measurement process is compared with the good capacitance, and the capacitance is roughly judged, and the capacity is reduced. At the same time, the leakage resistance value of the capacitor can be measured. When the black meter is connected to the positive pole, the measured resistance value (after the needle is stabilized) is large, and should be hundreds of kilohms; when the red meter is connected to the positive pole, the measured value is measured. The resistance value is small and should be in the order of tens of kiloohms. If the resistance value is small, it means that the capacitor has a large leakage current and the quality is deteriorated. If the amplitude of the hand swing is too small compared with the measurement result of the normal capacitance, the capacity is reduced; if the positive and negative leakage resistance values are too small (or zero), the capacitor has been seriously leaked or short-circuited. Both indicate that the capacitor has deteriorated and must be replaced.
(2) Using a dedicated digital capacitance meter to detect the capacitance, compared with the nominal capacity, the error should generally be within 15%. If the capacitance is too small, the capacitor is out of capacitance and needs to be replaced.
The cause of damage to the Electrolytic capacitor is as follows.
1) The capacity reduction of the Electrolytic Capacitor is caused by the long service life and the high ambient temperature, which causes the internal electrolyte to gradually evaporate and dry up, and finally fails due to the capacity shrinkage. For inverters with a service life of more than three years, it is necessary to detect the capacitance value of the capacitor when it is suspected that the fault is related to the capacitor.
2) If the capacitor is damaged in a short period of time, it may cause the power supply voltage at both ends of the capacitor is too high (caused by the power supply voltage is too high or the load motor is overheated) and the quality of the capacitor itself is poor. Pay attention to the inverter itself. (The component quality is poor) and the external environment (high supply voltage or load motor reverse power generation). When the rectifier module breaks down, the AC voltage appears across the capacitor, causing the reverse leakage current to increase. The capacitor itself becomes an energy-consuming component like a resistor device, causing burnout and bursting. In the event of a capacitor burst failure, it cannot Ignore the detection of the rectifier module.
In the actual circuit, because the storage capacitors are connected in series, the capacitor has a voltage equalizing resistor connected in series (also provides a discharge function after power failure). When there is an open circuit, the voltage across the capacitor rises, and the capacitor may be exceeded. The safe work area is damaged. In the event of a capacitor damage, you should also pay attention to the inspection of the voltage equalization resistor.
3) Some capacitors are good with a multimeter or digital capacitance meter. However, after installation, after applying 530V DC voltage, heat and cracking are caused by leakage, which is caused by poor quality, insufficient withstand voltage and serious leakage.
4) The “hidden failure” of the electrolytic capacitor means that the measurement does not cause any problem. The general detection method is powerless, but the capacitor cannot be used normally. During operation, the electrolytic capacitor is subjected to large current charging and discharging shocks of several hundred Hz for a long time, which may cause contact resistance of the electrode lead due to oxidation. This "contact resistance" does not affect the measurement result during the measurement. The capacitance is still normal and there is no leakage. However, if it is connected to the circuit, the capacitance will decrease due to the decrease of the charging and discharging currents, and the voltage of the DC link will fall, and the inverter will not work normally. If there is no problem in detecting the current limiting resistor and the charging contactor and the rectifier module, it is necessary to introduce the maintenance focus into the "normal performance" capacitor.
