What happens if film capacitors are used incorrectly

    Film capacitor quality detection

    Method 1

    1. Connect the capacitor to the power supply. If the multimeter pointer does not swing at the moment of connection, it means that the capacitor is faulty or broken. If the needle keeps indicating the power supply voltage but does not swing, it means that the capacitor is short-circuited. If the needle swings normally but does not return to zero, it means that the capacitor is leaking. Because the higher the voltage value indicated, the greater the leakage.

    2. The auxiliary DC voltage used to measure a small-capacity capacitor cannot exceed the withstand voltage of the capacitor being measured, so as to avoid capacitor breakdown and damage due to measurement. To accurately measure the capacity of a capacitor, a capacitance bridge or Q meter is required. The above simple detection method can only roughly judge the quality of the pressure gauge capacitor.

    3. For fixed capacitors with large capacity, the resistance range (R×1000) of the multimeter can be used to measure the two electrodes of the capacitor to see the swing of the needle. The larger the swing, the larger the capacitance of the capacitor. If the test rod keeps touching the capacitor lead, the needle should point to near ∞, otherwise, it indicates that the capacitor has leakage. The smaller the resistance value, the greater the leakage, and the worse the quality of the capacitor.

    4. When checking the quality of capacitors, for electrolytic capacitors with lower withstand voltage, the resistance range should be set to R×100 or R×1K, connect the red test lead to the negative terminal of the capacitor, and the black test lead to the positive terminal. At this time, the multimeter pointer will swing and then return to zero or near zero, which means that the quality of the electrolytic capacitor is qualified. The larger the capacity of the electrolytic capacitor, the longer the charging time, and the slower the pointer swings.

Method 2

In the absence of special instruments, the quality of capacitors can be tested and judged using the resistance range of a multimeter. Fixed capacitors with large capacity (above 1μF) can use the resistance range (R×1000) of a multimeter to measure the two electrodes of the capacitor. The needle should swing in the direction of small resistance and then slowly swing back to near ∞. Then exchange the test rods and try again to see the swing of the needle. The larger the swing, the larger the capacitance of the capacitor.If the test rod keeps touching the capacitor leads, the needle should point near ∞, otherwise, it indicates that the capacitor has leakage. The smaller the resistance value, the greater the leakage, and the capacitor is of poor quality. If the needle does not move at all during measurement, it indicates that the capacitor has failed or is open-circuited. If the needle swings but cannot return to the starting point, it indicates that the capacitor has a large leakage and is of poor quality.

Method 3

The capacitor of the test circuit must be cut off first, and then the high-voltage capacitor is released first, and then the filter capacitor after rectification (or other circuits with large resistance at both ends) and other circuit designs are measured in the circuit. If the capacitance cannot be determined in the circuit measurement, it can only be removed for measurement.

Method 4

The capacitance of electrolytic capacitors is usually measured with the R x 10, R x 100 and R x 1K of the multimeter. The red and black pens are connected to the negative pole of the capacitor (the capacitor should be discharged before each test), and the quality of the capacitor can be judged by the needle swing. If the needle swings to the right and then slowly returns to the left, the capacitor is usually good.If the needle does not swing after the swing, it means that the capacitor has been disconnected. If the needle is placed back to a certain position after the needle swings, it indicates that the capacitor has leaked. If the needle does not swing, it means that the capacitor electrolyte has dried up and lost capacity.

Film capacitor usage errors and solutions

At low temperatures, the viscosity of the impregnating agent inside the capacitor increases, the internal voltage decreases, and the capacitor's electrical resistance decreases. The heat generated by the capacitor during operation can be dissipated in time, reducing the dielectric temperature inside the capacitor, and thus extending the actual service life of the capacitor.

When disconnecting a capacitor bank, if the circuit breaker has a severe breakdown, the capacitor terminals will experience a high multiple operating overvoltage of 3, 5, 7 times, etc., and strong partial discharge and dielectric damage will occur inside the capacitor, leading to capacitor breakdown. The quality of the circuit breaker used to switch capacitors is closely related to the actual service life of the capacitor. The national standard stipulates: Use a circuit breaker suitable for switching capacitors, and the circuit breaker will not have a severe breakdown that may cause excessive overvoltage during the disconnection operation.

Therefore, in order to prevent excessive inrush current and overvoltage, the capacitor should be discharged in time after being removed from the network. Before the capacitor is put into operation again in the grid, the residual voltage on the capacitor should not exceed 10% of its rated voltage.