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How the cable AC voltage withstand test?

Information Source:Henan Huadong Cable Co., Ltd  Release date:2014-03-18

Because the capacitance of cable is larger, the power of traditional heavy, large, power supply and a large current is not obtained easily in the field. Therefore, generally by the series resonance AC voltage withstand test 'AC voltage withstand test device. The input power supply capacity can be significantly reduced, light weight, easy to use and transport. At the beginning of the adjustable series resonant equipment (50Hz), but has the disadvantages of poor degree of automation, noise and etc.. Now most of the frequency modulated (30-300Hz) series resonant test equipment, can get high quality (Q value), and with automatic tuning, multiple protection, and low noise, flexible combinations (single weight is reduced) etc.. Comprehensive domestic and foreign relevant technical data, select the appropriate test frequency range is a very important problem. In this regard, there are some different views and formulation. On the current domestic and foreign references, we sum up can be divided into 3 categories: first for a wide range of frequencies of 30-300Hz, 20-300Hz, 1-300Hz; second for the frequency range, 45-65Hz, 45-55Hz; third is close to the power frequency, 35-75Hz.

(1) first kinds of wide frequency range
CIGRE twenty-first, 09 working group released the "test guidelines", suggested that the frequency range of 30-300Hz. But in fact the lower frequency is equivalent to better. IEC60840 and IEC62067 draft standard (2001 and 2000) provided by 20-300Hz.
Some foreign manufacturers design series resonance reactor, in special cases also have the lowest frequency is 25Hz or 20Hz. Of course, frequency is low, the subjects of cable length (capacitance) can increase. But the reactor core and amplification, an increase in weight. Individual data display, AC test 1-300Hz has the equivalent AC test, which shows the frequency of application may have a lower limit, for example, less than 20Hz or even 0.1Hz is also feasible. Further show that in such a frequency range, voltage distribution and dielectric properties of the medium inside insulation is same.
The working frequency is more than 300Hz is appropriate? The data reported that, with the increase of frequency, reduce the loss of series resonant reactor and the excitation transformer, but consider the subjects of polarization heat capacitance medium frequency is higher than 300Hz, so it is not desirable.

(2) for the frequency range second
International industrial frequency mainly refers to 50Hz and 60Hz two, the IEC standard on the industrial test frequency range high voltage insulation is 45-65Hz, rated power of 50Hz in china. GB/T16927.1-1997 provides frequency test, the frequency range of 45-55Hz.
Think the test voltage power cables must also be frequency, this tends to be more conservative point of view. To solve this problem should focus on the transfer and preventive test aims to discover the ability to set the insulation defects. At different frequencies as long as the internal insulation medium voltage distribution are the same, and the same basic insulation failure detection ability, can achieve the purpose of testing. So even if the power frequency range wider frequency is acceptable. In the mid 90's to frequency range selection of AC voltage withstand test 'AC withstand voltage test right, do a lot of research work, carefully. The frequency in the range of 30-300Hz, there was no significant difference between the breakdown of insulation defects inside several typical rubber cable. This should be credible, it has been widely used. Analysis of breakdown characteristics of the good at different frequencies, the main reason is the fine structure of the coaxial insulation, insulation materials, a single, relatively pure electric field distribution is reasonable, rules. Therefore, under different frequency voltage distribution of the same structure, forming a wide frequency range of test conditions. The frequency of the pressure test is equal to the DC voltage zero oil paper insulated cable, its actual effect is very good, for decades without doubt.

(3) third is close to the frequency, 35-75Hz
Foreign had normal XLPE (cross-linked polyethylene) cable insulation breakdown test samples, carried out at different frequencies. The results show that when the frequency is 35-75Hz breakdown voltage are at 95% confidence level. So at some point in favour of test voltage frequency best selected in 35-75Hz, is close to the operating voltage and frequency of 50Hz. Notably, the test results are normal on the dielectric breakdown test. The test voltage of the handover and preventive test value is low, the insulation weakness it only breakdown defective (mechanical damage, water tree, terminal or connector box stress iron cone construction or material error, etc.), entirely inadequate to cable insulation breakdown of normal. The two test purposes and working mechanism are not the same. Breakdown characteristics of "there seems to be no need to normal insulation 35-75Hz extension" applied to the detection of insulation defects.

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