What are the commonly used instruments for AC withstand voltage testing of power cables

1. Frequency conversion series resonance withstand voltage test device

Usually, series resonance method is used during the AC voltage withstand test of cables. This method can calculate the required capacitance and voltage based on parameters such as voltage level, cross-section, and length of the cable. This method is particularly suitable for situations where longer cable distances need to be tested. When conducting AC voltage withstand tests, the cable needs to have a high capacity requirement and a low voltage requirement. In addition, it includes multiple series resonant components, and the required equipment includes excitation transformers, variable frequency power supplies, high-voltage reactors, capacitor voltage dividers, compensation capacitors, etc. These devices need to be carried on site and are commonly used for AC withstand voltage testing of high-voltage main transformers, GIS, generators, transformers, cables, and other equipment such as 10kV, 35kV, 110kV, and 220kV. If multiple devices need to be tested on site, series resonance testing equipment can be considered. This equipment is relatively comprehensive and can be used not only for AC voltage withstand testing of cables, but also for AC voltage withstand testing of various equipment such as transformers, GIS, generators, and transformers.

2. Ultra low frequency and high voltage generator

If we only need to test the voltage resistance of the cable without conducting other tests, we can recommend using an ultra-low frequency high-voltage generator. This generator is a simplified version of series resonance, which is very convenient to use and does not require carrying a large number of devices during on-site testing. This testing instrument is specifically suitable for the AC withstand voltage test of cables with a voltage of 35kV and below, as well as the AC withstand voltage test of generators. However, there are certain limitations to its testing scope. For example, for a 300 square meter specification of 35kV cables, this testing instrument can test a distance of about 2 kilometers and generally requires a testing distance of no more than 1 kilometer. For the 16 square meter specification of 10kV cables, the testing distance can reach 7 to 8 kilometers, and for testing 270 cables, the testing distance is 2 to 3 kilometers. The AC withstand voltage of thermal generators and hydroelectric generators is different. The AC withstand voltage of thermal generators is generally below 120MW, while that of hydroelectric generators is generally below 80MW. To test the voltage resistance of 10kV and 35kV cables, we need to use an 80kV ultra-low frequency generator. According to the calculation method of cable test voltage, for example, for a 10kV cable, its phase voltage is 6kV, and its test voltage is 6 divided by the root sign 3 and then multiplied by 3, which is 10.39kV. Its maximum voltage should not exceed 11kV. 10kV cables are not limited to voltages of 10kV, but can also be applied to voltages of 15kV. During the experiment, its maximum test voltage will not exceed 27kV. For this, we can use a 30kV ultra-low frequency generator for coordination, or choose the corresponding voltage specifications based on the actual voltage of the cable on site, which may be 30kV, 50kV, 80kV, etc.

3. DC high-voltage generator

The DC high-voltage generator adopts a high-frequency voltage doubling circuit, applies the latest PWM high-frequency pulse width modulation technology, closed-loop adjustment, and adopts voltage feedback, greatly improving voltage stability. Using high-performance high-power IGBT devices and driving technology, and adopting special shielding, isolation, and grounding measures according to electromagnetic compatibility theory. The DC high-voltage generator has achieved high quality, portability, and can withstand rated voltage discharge without damage. It has the characteristics of high output power and small size, with reliable overvoltage, overcurrent, and zero position closing protection functions, and with 0.75 times voltage switching function. Mainly applicable to the power sector, industrial and mining, metallurgy, steel and other enterprise departments, conducting DC withstand voltage tests or DC leakage current tests on high-voltage electrical equipment such as zinc oxide lightning arresters, power cables, transformers, circuit breakers, generators, etc.

4. Power frequency withstand voltage test device

There is another communication testing equipment that needs to be introduced to everyone, which is the power frequency withstand voltage testing device, which is currently one of the most commonly used testing equipment in the power industry. Many colleagues engaged in power testing will use it. The equipment mainly consists of a test transformer and a power operation box. Its main purpose is to conduct AC voltage withstand tests, as well as auxiliary DC voltage withstand tests. Just add a silicon stack, electric rod, and microampere meter to complete the DC withstand voltage test. If you do not want to purchase a DC high-voltage generator, you can use a power frequency withstand voltage test instead.

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