By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as AC/DC voltage withstand test device). Next, we will share with you an introduction to cable AC voltage withstand test.
Cable AC withstand voltage test for XLPE cross-linked cables
The AC voltage withstand test of cables is currently being replaced by an increasing number of XLPE cross-linked polyethylene insulated power cables both internationally and domestically, replacing the original oil filled paper insulated power cables. However, due to the large capacity of the test subjects and the limitations of the testing equipment, the direct current withstand voltage test method is still used in the testing methods for cross-linked cables before they are put into operation. In recent years, many research institutions both internationally and domestically have shown that direct current testing can cause varying degrees of damage to XLPE cross-linked polyethylene cables. Special testing equipment should be used for AC voltage withstand testing of power cables, and it is recommended to use the HTXZ series resonance testing device to test the AC voltage withstand test of cables.
The benefits of AC voltage withstand test for cables
Some research perspectives suggest that XLPE structures have the ability to store and accumulate unipolar residual charges. If the DC residual charges cannot be effectively released after DC testing, adding AC voltage peaks to the DC residual charges after operation may cause cable breakdown. Some domestic research institutions believe that in the DC withstand voltage test of cross-linked polyethylene cables, due to the space charge effect, the actual electric field strength in insulation can be up to 11 times higher than the working electric field strength of cable insulation. Cross linked polyethylene insulated cables can cause serious insulation damage even if they pass the DC test without breakdown. Secondly, due to the difference in field strength distribution between the applied DC voltage and the operating AC voltage. DC testing cannot truly simulate the overvoltage that cables can withstand under operating conditions, and effectively detect defects in the cables and cable joints themselves and construction processes. Therefore, the use of non DC methods for conducting voltage withstand tests on cross-linked cables is increasingly receiving attention. At present, ultra-low frequency power supplies (VIFs) have been used for voltage withstand tests on medium and low voltage cables abroad. However, due to the low voltage level of these VLFs, they cannot be used for testing high voltage cables of 110kV and above. This method has also been used for low voltage cables in China, but due to the testing equipment, it has not been widely promoted. In recent years, due to the renovation of urban and rural network construction, XLPE cross-linked cables have become more and more common, and cables are only put into operation after DC voltage withstand tests. Cases of cable or cable head breakdown under operating voltage also occur from time to time. Therefore, we are exploring new testing methods.
Frequency of AC withstand voltage test for cables
Due to the large capacitance of cables, traditional power frequency test transformers are bulky and large, and high current working power series resonances are not easily available on site. Therefore, series resonant AC withstand voltage test equipment is generally used, which can significantly reduce the input power capacity, reduce weight, and facilitate use and transportation. Initially, inductive series resonant test equipment (50Hz) was mostly used, but it has the disadvantages of poor automation and high noise. Therefore, frequency modulation (30-300Hz) series resonant test equipment is now mostly used, which can obtain higher quality factors, (Q value), and has the advantages of automatic tuning, multiple protections, low noise, flexible combination, etc. Based on relevant technical data at home and abroad, selecting a suitable test frequency range is a relatively important issue. In this regard, according to current domestic and foreign terminology, we can summarize it into three categories: the first category is a wider frequency range of 30-300Hz, 20-300Hz, 1-300Hz, the second category is a power frequency range of 45-65Hz, 45-55Hz, and the third category is 35-75Hz.