Cable Hipot Before Megger or Megger Before Hipot?

Hipot first. The stress of the test can damage insulation - the Megger test will catch it.

Thank you both;

The normal Megger test is about 5 or 10 kV DC, would applying this voltage cause a damage to the cable or detect the fault on aged cables? In the post case, the megger test did not detect a fault since it is below the service voltage of the cable, although it is DC.

Enjoy helping others

why not PD test - it will help you to locate problem when megger just confirm tt IR is not well.

True! An IR Test may not damage the cable insulation as the test voltage is less than the rated voltage of the cable. But, the Hi-Pot test voltage is definitely much more than the rated voltage of the cable. (To be exact, 125% to 150% of the rated cable voltage will be the AC Hi-Pot Test Voltage and the DC Hi-Pot test voltage will be 1.7 times the AC Test Value). So, there is a possibility that this high voltage will definitely cause damage the cable insulation, particularly, if the insulation is already weak.

Seems like the best approach is to follow electricalexpert65's good advice and limit the applied voltage to whatever margin (10%?) above cable rating you would expect the cable to experience in your planned application.

Sometimes testing only confirms our worst fears. Buy the way all the advice you have receive is good advice, but I keep reading your inquiry.

First if you have had a trip why not just ohm it out and see if you have a fault with that?

Second take a real good look at your system how well has it been maintained, is everything well maintained? As long as you are down has all the equipment been cleaned and repaired? What else could cause the line to trip out? Personally, I would walk through a commissioning checklist and have the inspectors sign off before I reactivated a possible 69KV line.

Now to address you question. There are many companies who keep a Megger around as standard test equipment. So in order to avoid cost you might try to check the line with that. To my knowledge a Megger will not do any significant damage to a 69 KV power line or its equipment.

Hi pot testing is a different story. It is an expensive piece of equipment and you need certified testers to operate it and it is not something a lot of companies have laying around just because they may need it someday. If you decide to Hi pot the line, it will find any faults even if that is not what caused the original trip. You say in your question that this line has 3 splices in it already, the Hi pot will probably fail them.

So if you decided to Hi pot the cables I don't see need to run the Megger next.