Medium Voltage Series ckts.

What does the Client's procedure state?

What does the local electrical code state?

What does the test equipment manufacturer's instruction leaflet say?

Wait a minute here. Do I understand you correctly? You are going to be applying a megger to a 12 kilometer long cable and you do not know how long to apply this instrument to a part of the power grid. So instead of asking your supervisor this question or reviewing the written test procedure, you ask us how long you should be doing this test.

Well I think that you should not be doing this test at all. Power grid cable testing is not something anyone unsupervised and not authorized should be doing.

Is this an airport series lighting cable?

Yes, sir the cable that we r going to use are series cables use to power runway lighting,taxiway lighting,etc.

I think you should be taking three readings: One immediately after the resistance value appears to stabilize, another 60 seconds later and one more 10 minutes later. This will allow you to calculate RTG (Resistance To Ground), PI (Polarization Index) DA (Dielectric Absorption) and leakage current. Taking the same readings every few months will help you determine the health of you cables as they age.

Resistance to Ground and among parallel cables is slowly caused by water/moisture seepage. Physical damage to underground cable can also be caused by transport system is also a very serious problemat some places.

Cable fault detectors need to be installed and as soon as something serious is detected, immediate remedial action is to be initiated.

It is also good thing to do complete quality test at regular interval that may span few months. Immediate problems can happen so installing an automatic alarm is all worth.

Recently our engineers reported damage to airstrip cable by trucks during rail and perhaps they may have cables thru soft ground as well.

Dear Engineer, i got your question. First thing you need to do is that perform Hypo test. I hope it will give you a good result. If you didn't get a good result then perform megger test. The result is a display containing a series of nine(9) if you are getting two 9 i.e, 99 or three nine i.e, 999 then assume that the cable is good. If short circuit is displaying the n the cable is damaged.