Generator High Resistance Grounding connection

[ctpt]

This is for an offshore installation, IEC world.
There are 4 gas turbine generators (4x33%) connected to a 6.6kV switchboard.
The generators are high resistance grounded (20A per generator). It is a 3 Ph, 3 wire system
Now regarding the connection of the resistors to the installation structure, client wants that there shall be two connections from the resistor (ground side) for neutral grounding. One cable should be connected directly to the nearest structure and the other cable shall be connected to the ground bar (PE) of the 6.6kV switchboard. The PE bar is of course grounded at either end. The following clause of IEC-61892-2 is taken as reference for proposing this arrangement by client.

5.7.2 Earthing resistors shall be connected to the unit's structure or hull. In addition earthing resistors shall be connected together on the structure/hull side of the resistor, where to also the protective earthing (PE) conductor of the distribution system shall be connected.

Is it the correct interpretation of IEC? What we are having is that the generators are resistance grounded individually and also connected to a common PE bar thus forming a common grounding point for all the parallel generators.
Frankly speaking, I have not seen this kind of arrangement before.

Advise and guidance is requested.
Thanks a lot in advance.

 

[juleselec]

On an offshore platform, anything connected to the metallic structure of the topside is more or less earthed. But this doesn't necessarily mean that all earthing points are equi-potentially bonded. So usually there are interconnections to prevent circulating earth currents.

From what I've seen on offshore platforms, all of the earth bars are typically interconnected by cables and also connected to the structure. The main earth bar usually has some connections to two (or more) of the jackets or part of the sub-structure.

So for NERs, it's not odd to connect them all to a common earth bar that other protective earths are also connected to. Actually, this is common practice in my experience.

 

[7anoter4]

I think all 4 generators are connected to a common switchgear with a Grounding Bus [so they have a common grounding bus].
If the grounding resistor is enclosed then the enclosure shall be grounded to the near-by structure grounding in order to
mitigate the touch voltage. The grounding cable provide a low resistance return path from the faulted device[motor or else] to the
generator neutral point through the Grounding Bus.