Neutral rated voltage - IEC 80005

[simonfr]

Im trying to understand the text in IEC 80005

The standard considers that the standard rating cables are 6/10(12)kV. Fine all good
But then the standard considers that the Neutral cables are considered to be 1.8/3(3.6)kV.

Now, if we are using say 10kV, the corresponding neutral voltage for the cable doesnt tally, as the phase to neutral voltage will be 5.8kV surely? Therefore the neutral cable insulation capabilities are mismatched?

Greater understanding is much appreciated

Thanks

 

[RRaghunath]

The neutral cable from the shore to ship is connected to the hull of the ship and hence is as good as at ground potential.
In case of SLG fault on the ship, the star point of the transformer on shore may have increased potential equal to L-G voltage of the system.
This will be the case for the cable between the star point and the NGR.
But, the cable to ship (from NGR) is directly connected to the hull of the ship and hence the specification of 1.8/3kV for this cable does make sense.

R Raghunath

 

[simonfr]

If the ship - and the shore power system - is an IT system. The 'shore' supply neutral point shall be earthed via high resistance.
The vessel generation may be 3 phase + neutral, with the neutral bonded to the hull 'earth' via high resistance also.

Connect both shore and ship cabling, to provide power - 3 phase + neutral - with the protective insulation monitoring active.

Does the neutral insulation reduced voltage statement still apply?


I have a shore to ship power design given to me - where shore power shall be supplied by a 'shore' transformer - 3 phase + neutral, star point earthed via NER.
The supply sends to the vessel 3ph+N (full sized conductors) and a 'token' earth at 10mm2 for an insulation monitoring earth 'reference point'.
The vessel is 3Ph + N, the vessel neutral is earthed via NER also to the hull.
Supply umbilical 10mm2 earth cable bonded to the vessel hull.
Protection system from shore to ship via insulation monitoring (IT system).