Insulation resistance and precautions for film capacitors

1. Insulation resistance of film capacitor

The insulation resistance of a film capacitor refers to the ratio of the voltage applied across the capacitor to the leakage current, that is, R = U / IL. R is the insulation resistance, U is the voltage, and IL is the leakage current of the film capacitor. There may be many people who don't know what is the leakage current of the film capacitor. When the leakage current of the film capacitor applies the rated DC working voltage to both ends of the film capacitor, we will see that the change of the charging current for charging the capacitor starts to be very large, and the current will follow. Decline with time, reach a relatively stable state when it reaches a certain value, and the magnitude of this current is called leakage current.

Therefore, the capacitance of the film capacitor is C=Q/U, Q is the charge amount, and U is the voltage applied across the capacitor. Combined with the above formula, R = Q / (C * IL) can be obtained, so we can know that the larger the capacitance of the film capacitor, the smaller the insulation resistance, the smaller the capacitance of the film capacitor, and the greater the insulation resistance.

2. Note on film capacitors

(1) When maintaining the film capacitors in peacetime, check the items in time. For example, check whether it is under the correct current and voltage during the use of the product, and the indication of the relevant current voltmeter. During the inspection process, the appearance of the product is guaranteed to be intact, without any cracks or leakage. Check the product for abnormal heating and avoid problems during the operation of the product. Check whether there is flashover on the outside, complete connection, and do not let go of any small details during the inspection;

(2) The impedance of the film capacitor is inversely proportional to the frequency, and as the frequency increases, the loss also increases. Measures should be taken to limit the harmonics and inrush currents in the circuit. Film capacitors must always produce heat. Pay special attention to ventilation and cooling. After the reactive power compensation device is installed, during the test run, the system should be tested and over-voltage, over-current, oscillation, harmonics, etc. should be taken in time. The normal operation of the capacitor is very necessary.