While other wave shapes are available for testing of cable systems recommended test voltage levels have not been established.
Vlf cable test voltage.
In the first step a go no go statement is sufficient.
Additional equipment for testing major cables very low frequency vlf high voltage test set for xlpe cables.
The most commonly used commercially available vlf ac voltage test frequency is 0 1 hz.
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Unlike with dc voltage testing very low frequency is not destructive to good insulation and does not lead to premature failures.
Vlf cable testing is the cutting edge technology for proof testing of fully operating medium voltage cables and the detection of faulty ones.
While supplies to railways and aircraft may use 162 3 of 400hz it is still a sinusoidal voltage waveform.
Acceptance test voltages are generally 2 5 3 times the line to ground system voltage.
Designs and manufactures industry leading high voltage test equipment for proof testing diagnostic testing high voltage breakdown testing and preventative maintenance testing.
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.
Vlf testing of cables is supported in iec 60502 up to 35 kv and in ieee 400 2 up to 69 kv.
Output voltages are determined from the ieee 400 2 guide choosing rms or peak depending on the output waveform.
The vlf test can be used in a number of ways.
A list of field test voltages from 5 kv to 69 kv can be found in ieee 400 2.
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.
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.
As higher voltage vlf equipment is developed standards may be adapted to increase the voltage level for application.
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.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
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.
Dc high voltage test set for paper lead cables.
The device under test must withstand a vlf very low frequency ac voltage for a preset testing time without flashover.
Vlf ac test voltages with cosinerectangular and the sinusoidal wave shapes are most commonly used.
Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device.
