Vlf Cable Test Voltage

Additional equipment for testing major cables very low frequency vlf high voltage test set for xlpe cables.

Vlf cable test voltage. A list of field test voltages from 5 kv to 69 kv can be found in ieee 400 2. Vlf testing of cables is supported in iec 60502 up to 35 kv and in ieee 400 2 up to 69 kv. The vlf test can be used in a number of ways. As higher voltage vlf equipment is developed standards may be adapted to increase the voltage level for application.

Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device. Dc high voltage test set for paper lead cables. Vlf testing is performed with an ac hi pot at frequency ranging from 0 01 to 1 hz. The device under test must withstand a vlf very low frequency ac voltage for a preset testing time without flashover.

Task steps 5 1 on site risk assessment prior to performing this activity any hazards associated with prerequisite tasks at the worksite shall be identified and assessed. Unlike with dc voltage testing very low frequency is not destructive to good insulation and does not lead to premature failures. While other wave shapes are available for testing of cable systems recommended test voltage levels have not been established. In the first step a go no go statement is sufficient.

How long should a vlf test last. A typical modern vlf test set has an output rating of 33kv peak sinewave 23kv rms and is capable of accommodating an output load of 0 5µf at 0 1hz i e. Ac is the standard used to transmit power worldwide usually at a frequency of 50 or 60 hertz. Acceptance test voltages are generally 2 5 3 times the line to ground system voltage.

Vlf ac test voltages with cosinerectangular and the sinusoidal wave shapes are most commonly used. The most commonly used commercially available vlf ac voltage test frequency is 0 1 hz. This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus. While supplies to railways and aircraft may use 162 3 of 400hz it is still a sinusoidal voltage waveform.

Vlf cable testing is the cutting edge technology for proof testing of fully operating medium voltage cables and the detection of faulty ones. Vlf testing can be classified as a withstand or diagnostic test meaning it may be performed as a proof test for acceptance or as a maintenance test for assessing the condition of cable. A typical 15 kv medium voltage cable in usa has an insulation thickness of 0 22 5 6 mm and therefore during a vlf test time of 30 minutes all defects within the cable should grow to failure. A channel tree growth rate with a 3u 0 test voltage at 0 1 hz vlf sinusoidal on field aged xlpe cables is 10 9 12 6 mm per hour mm h.