for phase-to-ground fault,ypu can pinpoint the location by a voltage detector:injecting dc pulse in the phase line and use the portable detector on the surface of the ground.when you pass the fault point,the detector will show a different voltage--in direction.
btw,for a long cable,you can use...
for large cap like yours,you need do 2 tests:
1.insulation test,use meg meter.
2.capacity test,apply voltage(from 0 to full rate),read the current and caculate its capacity.
!when apply voltage be sure current in a limited value.
!after test,don't forget discharge the cap.
torontoele