Under Ground Cable Protection

On critical loads you generally want to keep your protection schemes as simple as possible, and will sometimes provide redundant feeds..

We have in the past installed line differential relaying with simple 50/51 overcurrent protection, depending on the breaker configuration.

If you are feeding the load direct without a downstream incoming circuit breaker then simple overcurrent (50/51) will be sufficient.

Thanks a lot ekiechle for your valuable comment. Please advise me further considering the following:

The feeders are already protected by O/C and G/F relays.The cables in this case have many T- Offs in the manholes and the cable ducts are filled with saline water. There are frequent Gound Fault failures of the cable.The down time and cable damage are to be avoided. Is pilot wire protection a feasible remedy? will it trip the feeder without causing cosiderable damage to the feeder, with minimum impact on the system?

Let me get this straight. You have a 13 kV cable in a raceway system filled with salt water, and you have multiple taps? How are the taps protected? Sounds like it is time to pull in a new cable. Pick one rated for submarine use. Then Fuse the mother and forget the relays.