As higher voltage vlf equipment is developed standards may be adapted to increase the voltage level for application.
Vlf cable test voltage.
Vlf testing is performed with an ac hi pot at frequency ranging from 0 01 to 1 hz.
The vlf test can be used in a number of ways.
The device under test must withstand a vlf very low frequency ac voltage for a preset testing time without flashover.
While other wave shapes are available for testing of cable systems recommended test voltage levels have not been established.
Dc high voltage test set for paper lead cables.
In the first step a go no go statement is sufficient.
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.
Vlf testing of cables is supported in iec 60502 up to 35 kv and in ieee 400 2 up to 69 kv.
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.
Acceptance test voltages are generally 2 5 3 times the line to ground system voltage.
The most commonly used commercially available vlf ac voltage test frequency is 0 1 hz.
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.
How long should a vlf test last.
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Additional equipment for testing major cables very low frequency vlf high voltage test set for xlpe cables.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
Unlike with dc voltage testing very low frequency is not destructive to good insulation and does not lead to premature failures.
Designs and manufactures industry leading high voltage test equipment for proof testing diagnostic testing high voltage breakdown testing and preventative maintenance testing.
Output voltages are determined from the ieee 400 2 guide choosing rms or peak depending on the output waveform.
Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device.
A list of field test voltages from 5 kv to 69 kv can be found in ieee 400 2.
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.
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.
Ac is the standard used to transmit power worldwide usually at a frequency of 50 or 60 hertz.
