Underground Feeder 500mcm Cable Fault

You've discovered the schedule and secret plan of the mole men, in their quest for world domination.

On a more serious note, what tests have you done on these feeder lines? Maybe the services are at 105% of designed capacity already and this is just a slow failure. Maybe you really do have a mole problem. The adolescent young critters after being kicked out of the nest scamper across an uninsulated termination. BANG! Vaporized mole leaves a black, sooty stain on your black insulation and darkened underground bunker. Yeah, I guess that would be hard to see. Maybe you've been real lucky and the failure remelted the insulation so that the short is gone. No, that's even less likely than a mole.

I know that you're baffled about what your problem might be. So you don't know what information is relevant. But right now we don't know if you're talking about the conditions outside of McMurdo Station or Tripoli Libya.

It is not clear which relay trips ( overcurrent or earth fault? instantaneous or delayed time?). Sometimes it may happen that due moisture ingress at terminations electric tracking may occur to ground and earth fault relay may trip due to this . Again for old cables speciallay PILC cables, the joints ( end termination and straight through joints) filled with liquid insulations say, PIB oil, due ingress of moisture( due to fine crack developed in leadsheath dome), this trip may occur. Best way to detect this type of fault, is Hi Pot test. If the cables fail to pass the Hi Pot test, the cable fault location work to be taken up to locate the fault. Specially for this type of fault, SIM method coupled with Surge Generator,TDR may be deployed to prelocate the fault. After prelocation, pinpointing of may be done with deployment of Surge Generator,and sound cum magnetic amplifier with test probe.