Very low frequency is the preferred method over 60hz for two reasons.
Vlf cable test report.
At a typical vlf frequency of 0 1hz it takes 600 times less power to test the same cable compared to 60 hz.
Cable length size 250m 500m 1000m 2000m 11kv or less mω 400mm2 250 125 60 30 185 240mm2 300 150 75 37 35mm2 500 250 125 62 22kv or more mω.
It is not a diagnostic test.
Working at heights poles ladders swms002.
Connecting a vlf test instrument to a cable refer to ieee 400 2 for safety guidelines.
The vlf test instrument should be solidly grounded before connecting up any cables.
It is an ac stress test.
If a vlf test is too low in voltage and or too short in duration more harm than good may result.
Subsequent work by the cdfi has shown there to be no significant change in the efficacy of a vlf test conducted over the frequency range 0 1 to 0 01 hz when the ieee 400 2 voltages and times are used.
Vlf cable testing is the cutting edge technology for proof testing of fully operating medium voltage cables and the detection of faulty ones.
There are no leakage current readings to take.
When comparing this figure to power frequency ac or 0 1 hz vlf cos rectangular the tree growth rate is only 2 2 5 9 and 3 4 7 8 mm h.
Hv cable commissioning test report page 2 of 2 form sp0407c01 ver 10 ergon energy corporation limited abn 50 087 646 062 1 sheath test criteria new hdpe sheaths.
That is the point of vlf testing.
But my cable might fail during the test precisely.
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.
The increased load capability in field applications in which 60 hertz is too bulky and expensive making it nearly impossible to test a cable of considerable length.
In the first step a go no go statement is sufficient.
The device under test must withstand a vlf very low frequency ac voltage for a preset testing time without flashover.
This report concluded there is no distinguishable difference between failure rates on test for the common vlf test frequencies of 0 05 hz and 0 1 hz from data obtained through laboratory.
The hv test lead outside shield conductor is connected to the concentric neutral ground point of the cable under test.
Once partial discharge is triggered in a defect under the test.
Dc leakage currents tell little about the cable quality a cable either holds the test voltage or fails.
Vlf cable testing makes use of ac voltages in a frequency range of 0 01.
The main conductor of the hv test lead is then connected.
If a cable can t hold 2 3 times normal voltage.
The vlf cable testing time varies from 15 to 60 minutes.
Ieee 400 2 establishes some suggested test voltages and times.
When vlf withstand testing cable the proper test voltage and time duration are critical for the success of the test.
