Hipot result judgement.. 2

[powerjunx]

hello folks!

i am going to use a hipot to test the burried cable from the transformer to the load - an induction motor.

my question is how do i judge the result or evaluate it for the suitability or wholeness of the cable underneath?
my boss told me that it is all about only on PASS OR FAIL judgement but he cant give a further detail, is there a standard procedure - a mathematical calculation perhaps - for evaluating the results?

i am greatful to accept your comments, folks!

thank you!!

yours,
fbjavier

 

[busbar]

An applicable reference may be IEEE Std 400-2001, …Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems
Scope: This Guide lists the various field test methods that are presently available or under development to perform field tests on insulated, shielded power cable systems rated 5 kV through 500 kV. A summary of advantages and disadvantages of the methods will be included. Users should avail themselves of th technical papers that are included as References and in the Bibliography before deciding whether to perform a test and which test to utilize. In making such decisions, consideration should be given to the performance of the entire cable system, including joints, terminations, and associated equipment.
It may be obtained at shop.ieee.org

 

[jbartos]

Suggestion: Visit

http://www.emersonprocess.com/home/...tfacts/maintenancefacts0310_hipot-testing.pdf

http://www.ecmweb.com/ar/electric_putting_hipot_pasture/

etc. for more practical info useful to know in addition to IEEE Std 400-2001

 

[QCE]

AC Test will be pass fail.
DC Test will give you a leakage current number that can be compared to a standard listed above.
So your boss is correct if you only have a AC High Potential test set.

pass fail - means if it doesn't fail it passes

 

[alehman]

DC hipot maintenance testing is the subject of considerable debate and has been discussed previously in this forum. Basically, it is not recommended for aged (>12 months or so) XLPE cable. It is questionable for EPR cable as well. DC hipot is still used for acceptance testing but is becomming less favored.

Those concerns aside, there are no "standard" or pass/fail DC leakage values. There are far too many variables and environmental influences to standardize leakage values. As with AC, DC hipot tests are pass/fail. What you are looking for is stable or declining current. If leakage current begins to increase during the test period, the test fails.

 

[alehman]

I would add that if large differences are seen between identical cables (phases), consider re-test or failing high leakage cables.

 

[rbulsara]

In addition to what ahelman others said above:

One good reference would be look at test results of 'passed' (or even failed) cables of the tests done in the past the same or similar cables.

The graph of the leakage current vs. time should taper off and become almost constant after 1 minute or so. If it keeps rising it is a failure.

 

[powerjunx]

thanks alot guys!
id really appreciate much your comments.