Leakage current refers to the current formed between mutually insulated metal parts in electrical equipment, or between live parts and grounded parts, through the surrounding medium or insulation surface, when no fault voltage is applied. According to the US UL standard, leakage current includes the current that can be conducted from the accessible parts of household appliances, including capacitive coupling current. Leakage current consists of two parts: one is the conduction current I1 through the insulation resistance; the other is the displacement current I2 through the distributed capacitance. The capacitive reactance of the latter is XC=1/2pfc, which is inversely proportional to the power frequency. The distributed capacitance current increases with frequency, so leakage current increases with the power frequency. For example, when using thyristor power supply, its harmonic components increase the leakage current. 



    If a programmable leakage current tester is used to assess the insulation performance of a circuit or a system, this current should include not only all currents flowing into the ground (or conductive parts outside the circuit) through insulating materials, but also currents flowing into the ground through capacitive components in the circuit or system (distributed capacitance can be regarded as capacitive components). Longer wiring will constitute larger distributed capacitance, increasing leakage current, which should be particularly noted in ungrounded systems. 



    The principle of measuring leakage current is basically the same as measuring insulation resistance. Measuring insulation resistance is actually also a leakage current, but it is expressed in the form of resistance. However, formal measurement of leakage current applies AC voltage, so the leakage current component includes the capacitive component current.



During the withstand voltage test, in order to protect the test equipment and test according to the specified technical indicators, it is also necessary to determine a maximum current value allowed to flow through the device under test (insulating material) without damaging it, under the highest electric field strength. This current is also usually called leakage current, but this method is only used in the above specific occasions. Please note the difference. 



    The programmable leakage current tester is actually the current flowing through the insulation part of an electrical circuit or equipment when there is no fault and under the action of applied voltage. Therefore, it is one of the important indicators to measure the insulation performance of electrical appliances, and it is also the primary indicator of product safety performance. 



    Limiting leakage current to a very small value plays an important role in improving product safety performance. 



    The programmable leakage current tester is used to measure the leakage current of electrical appliances that is unrelated to operation, flowing through insulation or distributed parameter impedance from the working power supply (or other power sources). Its input impedance simulates the impedance of the human body. 



    The leakage current tester mainly consists of impedance conversion, range conversion, AC/DC conversion, amplification, and indicating devices. Some also have overcurrent protection, audible and visual alarm circuits, and test voltage adjustment devices. The indicating devices are divided into analog and digital types.



    The so-called touch current, simply put, refers to the current flowing through the metal touchable parts of the equipment, through the human body to the grounded part or touchable parts. In this regard, when testing, we must use a human body simulation circuit, connect a voltmeter in parallel, and use different human body simulation circuits according to different product safety standards.



Leakage current is divided into four types: semiconductor component leakage current, power supply leakage current, capacitor leakage current, and filter leakage current.



Chinese name: 漏电流; English name: Leakage Current



1 Semiconductor component leakage current



2 Power supply leakage current



3 Capacitor leakage current



4 Filter leakage current



1. Semiconductor component leakage current



A very small current flowing through the PN junction when it is cut off. When D-S is set to forward bias and G-S is reverse biased, after the conductive channel is opened, current will flow from D to S. But in reality, due to the existence of free electrons, the free electrons attach to SiO2 and N+, causing leakage current in D-S.



2. Power supply leakage current



In switching power supplies, to reduce interference, according to national standards, an EMI filter circuit must be provided. Due to the EMI circuit, when the switching power supply is connected to the mains, there is a small current to the ground, which is the leakage current. If not grounded, the computer case will have a voltage of 110 volts to the ground, and touching it will give a tingling sensation, and it will also affect the computer's operation.









Note: The above information and technical parameters are compiled and published by Yangzhou Darui Electric Co., Ltd.