davva
Marine/Ocean
- Sep 27, 2004
- 99
What would be the best way to protect a feeder for earth fault for the following arrangement.
A ship (totally isolated, IT insulated neutral) is to supply power to the shore. On shore there will be an isolating transformer (either star or delta primary) and a solidly earthed star secondary for the shore power system.
The feeder I refer to is the umbilical that will cross from the ship to the shore. The two power systems cannot be intentionally bonded, i.e. the ship must not be bonded to the shore.
An isolating transformer will also be installed on the ship for the feeder to keep the ship's insulated earth network from being effected by earth faults on the umbilical (even though it can survive the first earth fault).
I was considering a transformer with a solidly earthed star connected secondary on the ship side and an armoured cable that would only be bonded to earth at the ship side (insulated from earth at the shore side). Then use earth fault protection at the ship side.
Maybe also add use of differential protection in the above scheme (but would prefer not to run interposing CT wires across the ship to shore).
Another thought was to use an unearthed secondary on the ship side and just use a core balance CT (again armoured cable earthed on at the ship). However the CBCT or the protecting circuit breaker may not detect a high impedance line-to-line fault in the umbilical (hot spots on the cable are a concern due to hazardous area).
Would distance protection be a useful method. I've never used it before so don't know the pros and cons.
Thoughts on the above are appreciated.
A ship (totally isolated, IT insulated neutral) is to supply power to the shore. On shore there will be an isolating transformer (either star or delta primary) and a solidly earthed star secondary for the shore power system.
The feeder I refer to is the umbilical that will cross from the ship to the shore. The two power systems cannot be intentionally bonded, i.e. the ship must not be bonded to the shore.
An isolating transformer will also be installed on the ship for the feeder to keep the ship's insulated earth network from being effected by earth faults on the umbilical (even though it can survive the first earth fault).
I was considering a transformer with a solidly earthed star connected secondary on the ship side and an armoured cable that would only be bonded to earth at the ship side (insulated from earth at the shore side). Then use earth fault protection at the ship side.
Maybe also add use of differential protection in the above scheme (but would prefer not to run interposing CT wires across the ship to shore).
Another thought was to use an unearthed secondary on the ship side and just use a core balance CT (again armoured cable earthed on at the ship). However the CBCT or the protecting circuit breaker may not detect a high impedance line-to-line fault in the umbilical (hot spots on the cable are a concern due to hazardous area).
Would distance protection be a useful method. I've never used it before so don't know the pros and cons.
Thoughts on the above are appreciated.
