The main advantages of Insulated neutral ship’s system are:
– Continuity of service on a ground fault
– Ground fault currents can be kept low
The main disadvantages of Insulated neutral ship’s system are:
– High level of insulation may be necessary.
– High transient over – voltages may occur
– Grounded circuit detection may be difficult
In the latest edition of lEC 60092- 502 TANKERS both insulated and earthed distribution systems are permitted, however, systems with a hull return are not permitted. Return via the ship’s construction is only acceptable in limited systems, such as diesel-engine battery start systems, intrinsically safe systems and impressed-current cathodic protection systems, outside any hazardous area.
Most main electrical power systems on ships, in the range from 400V to 690V, will have an insulated neutral.
It is, however, important that a ground-fault is detected and cleared as quickly as possible. This is to avoid a large short-circuit current on a second ground-fault, which can be in excess of the 3 – phase fault current for which the equipment is rated, which can do damage beyond repair.
Hazardous areas will also have an insulated neutral power supply system, as the flashover from a faulted cable in a grounded system, which may cause an explosion, is too high.