How to choose suitable testing equipment for cable AC withstand voltage test

The AC withstand voltage test is the most effective and direct method to identify the insulation strength of a cable, and is an important part of the preventive test. In addition, because the cable AC withstand voltage test voltage is generally higher than the operating voltage, the cable has a larger safety margin after passing the test. Therefore, the AC withstand voltage test is an important means to ensure the safe operation of high-voltage cables.

What test equipment will be used in the AC withstand voltage test of general cables? This article EP Hipot Electric teaches you how to choose the appropriate cable AC withstand voltage test equipment.

1. AC Series resonance test device

The AC withstand voltage test of the cable generally uses series resonance, . The capacity and voltage are calculated according to the voltage level, maximum cross section, and length of the cable, which is especially suitable for long cable distance requirements. The AC withstand voltage test of the cable requires high capacity and low voltage, and there are many components of series resonance. It consists of excitation transformer, variable frequency power supply, high voltage reactor, capacitive voltage divider, compensation capacitor, etc., which are carried on site for testing. There are a lot of equipment, inconvenient, and high cost. It is mainly used for AC withstand voltage test of main transformers, GIS, cables, generators, transformers and other equipment with voltage levels of 10kV, 35kV, 110kV, 220kV and above. If there are many test products, consider series resonance, a more comprehensive set of AC withstand voltage equipment, which can not only be used for AC withstand voltage of cables, but also for AC withstand voltage of various equipment such as transformers, GIS, generators, transformers, etc. hipot testing.

Variable Frequency AC Resonance Test System

2. VLF AC withstand voltage device

If it is only for the withstand voltage test of the cable and no other tests, it is recommended to use the VLF High Voltage Tester EPVLF. It is a simplified version of the series resonance, and there is no need to bring a bunch of equipment for the field test.

The VLF AC withstand voltage device is only for the AC withstand voltage test of cables of 35kV and below, and the AC withstand voltage test of the generator. Its distance is limited. For example, for a cable of 35kV 300 square meters, it is no problem to make 2 kilometers. It only requires about 1 kilometer, 10kV cable, 16 square meters of 7 to 8 kilometers, no problem, 270 cable 2 to 3 kilometers; the AC withstand voltage of the generator depends on whether it is a thermal power generator or a hydroelectric power generator or a thermal power generator Generally within 120MW, hydro generators generally within 80MW, 10Kv cables generally choose ultra-low frequency AC withstand voltage devices of 30kV, 35kV cables generally choose ultra-low frequency AC withstand voltage devices of 80kV, calculated according to the cable test voltage, such as 10kV cables Voltage, there is a 6kV cable, his phase voltage is 6kV, his test voltage is equal to 6 divided by the root number 3 and then multiplied by 3 equals 10.39kV, the highest is not more than 11kV,

Of course, the 10kV cable also has a voltage of 15kV. The maximum test voltage does not exceed 27kV, so we can use a 30kV VLF Hipot Tester EPVLF-30kV. The voltage can also be selected according to the on-site cable voltage. There are 30kV, 40kV, 50kV, 60kV, and 80kV specifications.

3. Power frequency withstand voltage test device

There is also called AC Hipot Test Set, which is the power frequency withstand voltage test device. It is currently the most frequently used test device in the electric power industry, and many electric power test colleagues have seen it.

The power frequency withstand voltage test device AC Hipot Tester is composed of a testing transformer and operating box, mainly AC withstand voltage test, DC as auxiliary, plus a battery, discharge rod, micro-ammeter can do DC withstand voltage test , If you don’t want to buy a DC high voltage generator, you can use the power frequency withstand voltage test instead.

What is the relationship between the power frequency withstand voltage test device and the cable AC withstand voltage test? The point is here. Generally, if the customer specializes in the AC withstand voltage test of the cable, our preferred equipment is the series resonance and VLF AC withstand voltage device, but for a very small number of customers, we can also recommend the power frequency withstand voltage to help customers save money. For example, in some wire and cable factories with a relatively small cross-sectional area of cable voltage, the maximum test voltage of the cable does not exceed 5KV, the maximum cable is 6 square meters, and the size is about 500 to 1000 meters. This can be equipped with power frequency withstand voltage and capacity Make it bigger, the voltage is 5kV, the price is not high, and it is economical. Equipped with series resonance and VLF AC withstand voltage devices, the price is a bit expensive. The power frequency withstand voltage test device is more in line with the factory test and will not be used to run long-distance cables. The power frequency withstand voltage test device can be based on site requirements. Customize suitable capacity and voltage.