Capacitance leakage Capacitance medium cannot be absolutely non-conductive. When DC voltage is applied to the capacitor, there will be leakage current in the capacitor. If the leakage current is too large, the capacitor will be damaged by heat.
Except electrolytic capacitor, the leakage current of other capacitors is extremely small, so the insulation resistance parameter is used to express its insulation performance. However, due to the large leakage of electrolytic capacitor, the leakage current is used to represent its insulation performance (proportional to the capacity). When the rated DC working voltage is applied to the capacitor, it will be observed that the charging current changes greatly at first, then decreases with time, and reaches a relatively stable state at a certain final value, which is called leakage current.
Its calculation formula is: I = kcu (μ a); Where k is the leakage current constant in μ a (v μ f), I is the leakage current, C is the capacitance, and U is the voltage.
There are four kinds of leakage currents, namely, semiconductor component leakage current, power supply leakage current, capacitor leakage current and filter leakage current.
The leakage current is still I = 0.02× Cu! The unit of calculation is uA. But the leakage error of the machine itself may exceed the calculated value. The aging test time is 40 degrees for 2 ~ 4 hours, and there are various DC waves. I = 0.02× 50V× 0.1uf = 0.1ua. Your leakage test is to measure DC leakage.
The leakage current of power filter is defined as the current from the filter housing to any end of AC incoming line at rated AC voltage.
If all the ports of the filter are completely insulated from the shell, the value of leakage current mainly depends on the leakage current of the * * * mode capacitor CY, that is, mainly depends on the capacity of CY.
Because the leakage current of filter is related to personal safety, all countries in the world have strict standards for it: for 220V/50Hz AC power supply, the leakage current of noise filter is generally required to be less than 1mA.
Extended data:
The failure modes of capacitors mainly include: open circuit, short circuit, structural damage, function loss, parameter change, poor contact and so on. Among them, open circuit mode accounts for about 60%, short circuit mode accounts for about 20%, and others account for about 20%.
In practical application, open circuit is not the main failure mode, but short circuit is the main failure mode of ceramic capacitors and tantalum capacitors, and short circuit is mainly characterized by excessive leakage current. All faults are caused by the inherent defects and improper use of capacitors, so solving the leakage problem of ceramic capacitors and tantalum capacitors is to improve the inherent reliability and use reliability of capacitors.
The loss of capacitance has a great relationship with leakage and the temperature of the environment! ! ! Detection method of fixed capacitance A. Detection of small capacitance below 10pF Because the capacity of fixed capacitance below10pf is too small, a multimeter can only be used to qualitatively check whether there is leakage, internal short circuit or breakdown.
In the case of capacitor leakage leading to failure, in order to improve the reliability of capacitor use, corresponding measures are taken from the perspective of inherent reliability and operational reliability, technical guidelines and standards are formed, and capacitor manufacturers with quality assurance are selected to reduce the occurrence of quality problems.
References:
Baidu encyclopedia-leakage current