Knowledge on Leakage Current Measurement
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Written by: usergirl
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Date: Sat, 31 Dec 2011 |
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High-quality electrical products have to go through various safety specification tests, including hipot test, insulation resistance test, grounding resistance test, leakage current test, etc. Among all these tests, leakage current test is the most complicated part. By leakage current test of products, abnormal leakage current can be examined. Leakage current tester is the commonly used measurement equipment for leakage current test.
What is Leakage Current Test?
Leakage current test actually includes three different kinds of tests. Two of them are to test the earth leakage current value and shell leakage current value separately. They are generally applied in products which have grounding metal shell. The third kind of test is component leakage current test, which is mostly applied in medical equipments. All the ac electronic load above are to ensure that the products can be used safely without bringing danger.
Operation of Leakage Current Test
In the recent years, leakage current test is demanded in safety specification of many products, no matter in the designing or producing process of products. In the designing process of products, the design engineers of the product can have access to the important information about the integrity of the products by leakage current test. So they can design the product better to satisfy the demand of safety standard. The products will be tested in rated voltage or 1.1 times of input rated voltage, which is the same condition of practical use or breakdown. In the earth leakage current test, the test of ground lead of the measured equipment can give out the current value of System Neutral. In the shell leakage current test, the current values from different points on the shell of the measured equipment to the System Neutral are examined.
In the leakage current test, the tested current can be used to calculate the approximate value set for the current tripping in the hipot test. It's only an approximate value, because component deviation of different measured equipments can cause minor difference in the leakage current value. In calculating the stated value of leakage currents, the most important thing is to know the basic difference between the hipot test and leakage current test. That is, most leakage current testers offer switch test of L/N, but they only examine the leakage current value from a current-carrying component to the measured shell at the same time. However, hipot test examines the leakage current value between two current-carrying components at the same time. Therefore, the leakage current value showed by hipot test is comparatively higher. An effective rule-of-thumb method is to set the tripping current of hipot test at 20% to 25% of the results of this formula. (Voltage of hipot test ÷ Voltage of leakage current test) ×Examined current of leakage current＝Approximate current value of hipot test.
Although hipot tester and leakage current test can both examine the insulating strength of the measured equipment, the testing process and result of the two tests have some key differences. Hipot test is operated by high voltage when the insulating system of all the current-carrying components in the measured equipment is cut out. Leakage current test (touch current) is operated by stimulating the impedance of human body with testing equipments when the current is still on.
I studied power supply for many years, manufactured electrical safety tester. Now focused on ac electronic load research.
Source: Knowledge on Leakage Current Measurement
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