Neutral Grounding

[prakashv]

Kindly look into the following and advise, as I think, it is an unsafe practice.


I have noted the following on an OFFSHORE PETROLEUM PROCESS PLATFORM being constructed with three Gas Turbines, each rated for 17.2 MVA, 11KV, 3Ph, Star connection with NGR (Neutral Grounding Resistor).

As the construction is almost completed, the main switchboard for the turbines, feeders, 11kV/415V transformers, sub distribution boards and associated installations are being commissioned by feeding a temporary 11kV power supply generated by a portable generator rated for 1,25 MVA, 415V and transformed by a step-up transformer rated for 1.5 MVA, 415V/ 11kV (delta/ Star).

The step-up transformer is connected though one of the main the incomers, after disconnecting the cables of the turbine. However, star point of the step-up transformer is not grounded, even though the Main Power System and associated monitoring/ protection system are arranged for “Resistance Grounding”.

 

[bennie]

Re: Neutral Grounding

The resistance grounding is to limit ground fault current between the generator and the primary of the main transformer. This is the one place in the system that can not utilize overcurrent devices.

Many generating plants are directly connected to the primary winding of the main transformers. This is due to the magnitude of current.
The paralleling is done on the high voltage bus, with less current present.

The resistance grounding of the generator, has no effect on a ground fault on the secondary of the main transformer. The main transformer essentially isolates the generator, from the rest of the system.

 

[prakashv]

Re: Neutral Grounding

I was asking the suitability about the operation without connecting the neutral to the ground, either solid or resistance. Please read my post

Thanks

 

[bennie]

Re: Neutral Grounding

Sorry, I thought I did read it.
You are asking "why the secondary of the transformer is not grounded"?. The reason is...It is not grounded.

What is the actual voltage? 11 KV is non standard.