grounding of 1MW,600V, induction generator

[JLuc]

Hi all,

I was wondering what is the common practice for the grounding of induction generator (1MW, 600V in my case). The generators are ordered with the neutral out. So what should we do with it?

If it is let floating, we will need to add some kind of ground fault detection system somewhere (generator side of step-up transformer is delta).

Thanks in advance for your answers.

JL

 

[dpc]

What is the generator connected to? If it is a standby or emergency generator, the grounding should match what is done for the normal power source, generally.

The main options: solidly grounded and high-resistance grounded. Ungrounded is not recommended, if there any other option.

 

[JLuc]

Generators are connected to the grid, via a 600 / 25000Y/14400 V , delta-Y transformer. (delta on 600V side)

 

[dpc]

I would high-resistance ground the generator. This will greatly limit the damage to the stator core for a generator ground fault while avoiding common problems associated with ungrounded systems.

 

[edison123]

JLuc

Are you sure the winding is wye connected ? Just yesterday, I repaired a 690 V, 950 KW ABB wind induction generator (bearing failure and shaft damages) and the winding was delta connected. And I didn't see any ground terminal. 1 MW at 600 V is a lot of current for a wye connection.

 

[digitrex]

But these are Induction generators. I think the step-up transformer should be Dy type so that the 600V wye side can be grounded.

 

[TurbineGen]

I agree with DPC. High impedance grounding (such as that done with a small local transformer and resistor bank) greatly reduces fault currents to a few Amps. Your protection scheme will need to be designed for this as well.

The Delta-WYE transformer isolates ground faults between the generator and the transformer.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[JLuc]

We plan to use two Multilin 369 to protect both generators.

We will high-resistance ground them. The Multilin 369 doesn't have the 59N function, but it has a 50G/51G protection that can be used with 50:0.025 CTs (pick-up level can be adjusted from 0.25 to 25.00 A).

Do you see any problems with this protection scheme?

Thank you