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AC withstand voltage test is an external AC test voltage applied to the insulation of electrical equipment. The test voltage is higher than the rated working voltage of the equipment and lasts for a certain period of time (usually 1 minute). AC withstand voltage test is a test that best meets the actual operating conditions of electrical equipment and is an important means to avoid insulation accidents. Therefore, the AC withstand voltage test is a decisive test among various insulation tests.

Wiring principle for AC withstand voltage test

The wiring for the AC withstand voltage test should be determined according to the requirements of the test object (voltage, capacity) and the existing test equipment conditions. Usually, high-voltage complete sets of equipment (including high-voltage test transformers and test transformer control boxes/sets) are used for testing. The wiring diagram for the AC power frequency withstand voltage test is shown in the following figure.

The voltmeter connected to the measuring coils P1 and P2 in the figure belongs to the low-voltage side measurement, which can be converted to the high-voltage side through the transformation ratio. The voltmeter connected between C1 and C2 belongs to the high-voltage side measurement, which is a commonly used method on site. It can avoid the impact of the increase in terminal voltage of the tested equipment due to capacitive current.  

Test methods for series resonance, parallel resonance, and series parallel resonance

For large generator sets, transformers GIS、 The AC withstand voltage test of large capacity test samples such as cross-linked cables requires large capacity test transformers, voltage regulators, and power supplies. It is often difficult to achieve on-site testing, even with experimental equipment, requiring the use of large vehicles, cranes, etc., which is laborious and time-consuming. In this case, on-site tests can be conducted using series resonance, parallel resonance, or series parallel resonance methods depending on the specific situation. Series parallel resonance can be achieved by adjusting inductance, as well as by adjusting frequency or capacitance. But most of the experiments are conducted on large capacitance equipment on site, so the capacitance is determined, and resonance compensation is generally carried out by adjusting inductance or frequency.