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At present, more and more XLPE cross-linked polyethylene insulated power cables are replacing the original oil filled paper insulated power cables both internationally and domestically. However, due to the large capacity of the test subjects and the limitations of the testing equipment, the direct current withstand voltage test method has been used for a long time in the testing methods for cross-linked cables before they are put into operation. In recent years, with the construction and renovation of urban and rural power grids, there have been more and more XLPE cross-linked cables. The cables are put into operation only after DC withstand voltage testing, and there are also cases of cable or cable head breakdown under operating voltage. So, everyone is exploring new experimental methods. Due to the large capacitance of cables, traditional power frequency test transformers are bulky and bulky, and high current working power sources are not easily available on site. Therefore, series resonant AC withstand voltage test is generally adopted. Selection of Communication Voltage Test Methods

Power cables generally have a relatively large capacitance and exhibit a capacitive load under AC test voltage. Long power cables require AC test equipment and test power sources with large capacity. In order to achieve the purpose of testing with a smaller capacity test power supply, Cui Yong generally uses the following resonance methods for testing. The test after installation and laying emphasizes the AC withstand voltage test. In recent years, consensus has been reached both domestically and internationally that AC testing methods should be given priority for the voltage withstand test of cross-linked cables. The test of high-voltage cables will change the original selection order of "DC method, AC method" to "AC method, DC method", emphasizing the priority of using AC test methods.

1. Ultra low frequency 0.1Hz withstand voltage test

Due to the large capacitance of the XLPE cable being tested, the capacity of the test transformer required for power frequency testing is also very large, resulting in bulky testing equipment that is not suitable for on-site use. Using 0.1Hz as the test power supply, theoretically the capacity of the test transformer can be reduced to 1/500, and the weight of the test transformer can be greatly reduced, making it easier to move to the site for testing. At present, this method is mainly used for testing medium and low voltage cables. Due to the low voltage level, it cannot be used for testing high voltage cables of 110KV and above.

2. Oscillatory voltage test

The oscillation voltage test is to charge a cable with a DC power supply, and then discharge a series resistor and reactance through a discharge ball gap to obtain a damped oscillation voltage. This method is superior to DC withstand voltage testing, but still not as effective as power frequency testing.

3. Resonant voltage withstand test

The adjustable inductance type resonance test system can meet the withstand voltage requirements, but due to its large weight and poor mobility, it is mainly used for experimenters.         

The frequency conversion resonance test system not only meets the voltage resistance requirements of 110kV VLPE cables, but also has the advantages of light weight and good mobility, making it suitable for on-site testing.

Conclusion:

1. DC withstand voltage test cannot simulate the operating conditions of high-voltage cross-linked cables, the test effect is poor, and it has certain harmfulness. It is not suitable for on-site completion acceptance test.

2. AC voltage withstand test is an effective means of on-site inspection of the laying and accessory installation quality of cross-linked cables. The load of the variable frequency resonant device meets the requirements of IEC and international standards, and can meet the on-site AC withstand voltage requirements of 110KV and 220KV high-voltage cross-linked cables through the series and parallel connection of reactors.