Why not star star generator transformer?
Why not star star generator transformer?
(OP)
Hi There,
I am reviewing this Transformer spec prepared by one of the consultants for connecting a 50 MW wind farm to the 132kV grid. Basically it is a 12/132kV connection. They have specified star-star connection with both sides solidly earthed (Yn0Yn0). I thought the best way to connect generator transformer is star delta (Ynd11 - where Delta is 12kV) for all the reasons such as it reduces third harmonic and reduces costs (less copper in delta winding) etc...But what I am not sure is that if we go with star delta then how do u limit the fault current on the LV side? Is it necessary to always put neutral earth resistors on LV? Any reason to not connect star star?
Regards.
I am reviewing this Transformer spec prepared by one of the consultants for connecting a 50 MW wind farm to the 132kV grid. Basically it is a 12/132kV connection. They have specified star-star connection with both sides solidly earthed (Yn0Yn0). I thought the best way to connect generator transformer is star delta (Ynd11 - where Delta is 12kV) for all the reasons such as it reduces third harmonic and reduces costs (less copper in delta winding) etc...But what I am not sure is that if we go with star delta then how do u limit the fault current on the LV side? Is it necessary to always put neutral earth resistors on LV? Any reason to not connect star star?
Regards.






RE: Why not star star generator transformer?
Did you ask your "consultant" why he chose star/star ?
RE: Why not star star generator transformer?
Can you please explain that if we will have delta on the LV side then we would require earthing transformer, won't it make it more expensive? In that case isn't it just better to have tertiary connection (As u suggested)?
Also, consultant suggested that the star star is chosen so that both sides could be earthed via NER because he considers that this calls for maximum protection.
RE: Why not star star generator transformer?
RE: Why not star star generator transformer?
F1 is on the utility line.
F2 is on a different utility feeder connected to the same substation.
F3 is at the generator bus.
Breaker 1 is on the utility feeder at the substation.
RE: Why not star star generator transformer?
RE: Why not star star generator transformer?
What you are looking at is the stepup from the collector system to the transmission system.
On the other hand, you may not have been given very much information on the wind farm, where you would not have known much about the collector system.
Some of these people are not very forth coming with information.
RE: Why not star star generator transformer?
The neutral still swings though. :)
RE: Why not star star generator transformer?
RE: Why not star star generator transformer?
You must be aware of neutral swings on a wye primary.
This may be avoided by;
A> Connecting a solid neutral back to the GSUs if the GSUs have a wye secondary.
B> Using a transformer with a delta tertiary winding.
C> Using a transformer with a three legged core.
Bill
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"Why not the best?"
Jimmy Carter
RE: Why not star star generator transformer?
davidbeach - there are turbine mfgs. supplying directly at 12,000 volts.
Y-Y with delta tert may be the best configuration for this application. Impedance grounding would not normally be recommended for such a connection without additional protection for faults on the 132kV system and backfeed isolation.
RE: Why not star star generator transformer?
RE: Why not star star generator transformer?
I'd second that thought. Perhaps the GSU is located withing the tower as part of the package. Most Wind Turbines I've seen and installed have a 1500 - 3000 kVA oil filled transformer installed on a pad next to the bas of the tower.
I can't understand why the expense, and lost space in the nacille to have a 12kV rated gen set.