DC leakage current measurement and DC withstand voltage test methods and characteristics

　　Due to the limitation of insulation resistance measurement, there are items to measure leakage resistance in insulation test. The equipment used to measure the leakage current is more complex than the megger. Generally, it is tested with high-voltage rectifier equipment. Due to the high test voltage, it is easy to expose the weakness of the insulation itself. Use a micro ampere meter to directly measure the leakage current, which can be monitored at any time with high sensitivity. The relationship between voltage and current, current and time can be used to judge the insulation defects. Therefore, it belongs to non-destructive test.

　　The voltage is added to the insulator in stages to control the voltage. When the voltage increases, the weak insulation will have a large leakage current, that is, a lower insulation resistance.

　　The wiring and principle of DC leakage current test and DC withstand voltage test are the same, and they are mostly carried out synchronously in the field test. Its principle is the same as that of insulation resistance measurement. The difference is that the power supply used for leakage current measurement or DC withstand voltage test mostly adopts adjustable DC high voltage device - DC high voltage generator, and the current flowing through the test object is measured directly with microammeter.

　　DC leakage current test and DC withstand voltage test are often carried out simultaneously with the same set of DC high voltage generator.

　　Test method: apply high voltage and measure current. The DC high voltage generator can adjust the required high voltage, and the micro ampere meter can accurately measure the leakage current.

　　Test features:

　　(1) The test voltage is high and can be adjusted at will.

　　When measuring the leakage current, the corresponding test voltage is applied to the tested equipment with a certain voltage level. This test voltage is much higher than the rated voltage of the megger, so it is easy to expose the weakness of the insulation itself. Because some defects or weaknesses in insulation can be exposed only under high electric field strength.

　　(2) The test voltage is stable, the micro ampere meter directly measures the leakage current, has high sensitivity and good repeatability under the same test conditions.

　　To convert, we must first know the voltage added to the tested equipment. Although the specified voltage value is engraved on the nameplate of the megger, the actual voltage added to the tested equipment is not necessarily this value, but related to the insulation resistance of the tested equipment. When the insulation resistance of the tested equipment is very low, the voltage acting on the tested equipment is also very low. Only when the insulation resistance tends to infinity, the voltage acting on the tested equipment is close to the nameplate value. This is because when the insulation resistance of the tested equipment is too low, the internal resistance voltage drop of the megger will significantly reduce the voltage on the "line" terminal.

　　(3) During the leakage current test, the relationship curve between leakage current and pressurization time and the relationship curve between leakage current and applied voltage can be made to judge the insulation condition. Under the action of DC voltage, when the insulation is damp or defective, the current decreases slowly with the pressurization time, and the final steady-state value is also large, that is, the insulation resistance is small.

　　(4) The test instrument DC high voltage generator is portable and suitable for field test.

　　DC withstand voltage test is the same as DC leakage current test, but its function is different

　　High DC withstand voltage test voltage and long time -- test the insulation strength;

　　The DC leakage current test voltage is relatively low -- check the insulation condition.