Good morning, I have a Synchroniza

[mher1]

Good morning,
I have a Synchronization Panel connecting 4 generators together (415 Volts) onto the same bus.
After the bus we are going to step the voltage up to 33 KV.
Is it advisable to use a step down transformer and reverse connect (for step up)?
What kind of Neutral grounding has to be adopted?

 

[krisys]

Your question is not clear.

Nevertheless, synchronizing at 415V level may be more economical. But your 415V switchboard ratings (both continuous and short circuit ratings) are adequate there is no problem. Otherwise unit transformers may be used. But these are generally used for the larger generators (say larger than 10MW).

 

[mher1]

As explained the Synchronization of 4 generators will be on the LV side.
Then we need to step up the voltage to 33 KV.
In the absence of an step up transformer, we are planning to use a step down transformer and connect backwards to step up the voltage.
However, we are trying to study the implications of such a choice specially when it comes to Neutral Earthing and the Vector Group of the transformer.

 

[ScottyUK]

Normally a zig-zag or inter-star transformer would be used as the earthing transformer. This winding type has specific properties which make it well-suited to system earthing duty.

 

[waross]

The vector group may not be important.
If the generators have neutrals, consider impedance grounding or direct grounding each generator.
Delta on the generator side and wye on the high side is a good connection for a generator.
It distributes unbalances and single phase loads across all three phases rather than loading one phase only. This reduces heating of the rotor.
How will the transformer be energized?
If the transformer can be energized from the high side you should have no problems (other than the normal transformer inrush).
If you will have to do a "Black Start" or if you will have to energize the transformer from the generator side, you may have to start the first gen-set and bring the speed and voltage up with the transformer connected.
I prefer a star:delta bank of off the shelf for grounding as opposed to a special order and possibly a special build Zig-Zag transformer.
The Zig-Zag is proven technology. It does the job well.

Bill
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"Why not the best?"
Jimmy Carter