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DER: Connecting to 4 wire system at the same voltage

DER: Connecting to 4 wire system at the same voltage

DER: Connecting to 4 wire system at the same voltage

(OP)
I have a 13.8kV 3 phase generator that I'm connecting to the utility as part of a DER project.
So I've been pouring over the interconnection requirements documents from several local utilities and all of them show a transformer between the generator and the utility.

What if my generation is at the same voltage as the utility?
If the utility is 13.8kV, 3 phase, 4 wire connection, and my generation is also 13.8kV, how do I go about determining the grounding requirements for my three phase generator?
Typically I put an NGR on the generator neutral or transformer neutral (depending on configuration) and call it a day.
But if I put a NGR on the generator neutral and I'm connected to 3 phase, 4 wire utility connection, I'm basically bypassing the NGR no since the fault current won't be limited to 5A?

The NGR will still protect my generator, but does it wreck things on the utility side?

RE: DER: Connecting to 4 wire system at the same voltage

If you connect the generator directly to the utility, there is no way you can control fault current magnitude in case of fault in generator. It means the generator will need to be scrapped in case of a fault in the generator as there is every likelihood of core damage rendering it irreparable.
The idea of having HRG for generator is to limit the fault current magnitude in case of stator fault and thus limit the damage generator being an expensive equipment.
The transformer can be 1:1 ratio in your case.

RE: DER: Connecting to 4 wire system at the same voltage

Generally, it is advisable to have a transformer (even if it is 1:1 ratio) between the generator and the grid to act as a buffer for lightning impulse traveling waves which could destroy the directly connected generator winding. I have seen a few such cases and adding a 1:1 transformer eliminated such generator winding failures. The generator windings are not designed for lightning impulses unlike the transformer which has a large volume of oil and insulation to take on such direct hits.

As for synching, the neutrals are not synched to the grid. It's only 3 phases and their sequence that matter. Your generator protection, whether via NGR or a NG transformer, can be maintained as it is. Utility side protection is their problem.

Muthu
www.edison.co.in

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