GE Frame 9 Gas Turbine

[obewan9043]

I have a GE Frame 9 Gas Turbine producing 125 MW at 11kv 50hz. I have step up transformer to 132kv to supply to the utility My problem is when I ran the SKM IEC short circuit analysis on the one line, my 6000 VAC bus is 155Ka and my 380 VAC bus il 2345 ka. Is there a way to reduce this short circuit? Thank you.

 

[AMBMI]

Suggestion: please purchase anotherr calculation software ;-)
Seriously: have you checked that you inserted the right input values? I wonder which kind of transformer is feeding your 6 kV bus....

 

[Gianoli]

More info is required before anyone can could even speculate about his problem. What is feeding the 6000 VAC bus? Transformer(s)? If so, what size and impedance ? Are sychronous machines present on the bus ?

 

[obewan9043]

Thank you for answering guy. I'm using the typical force air transformer from the software. I do not have any loads connected to the buses now

Voltage Rating %R %X
11:132kv 120 Mva 1 6.9282
11:0.6kv 500 kva 1 6.9282
11:0.38kv 500 kva 1 6.6282

 

[AMBMI]

Something strange in the Zcc value of the 120 MVA transformer: I think that you should get a value close to 20%
In any case the max short circuit you should have at 0.6 kV is
0.5/(0.6*SQRT(3)*0.07) = 6.87 kA

 

[waross]

We seem to have a discrepancy between 600V and 6000V.
No matter.
The available fault current at 600V will be 6.87 kA
The available fault current at 6000V will be .687 kA
The maximum transient fault current may approach 200% of these values.
If the transformer has a convection cooling rating, ONAN, the P.U. values will be based on these ratings.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alex68]

Typical impedances for IEC transformers are:

500 kVA Vsc = 4%
132 MVA Vsc = 12...13%

So please review your calculation with these values.

Alex

 

[7anoter4]

Hi obewan9043
It is difficult to understand your problem due to lack of some data.
First of all you need a generator. If your turbine is 125 MW you need a 150 MVA generator with 13-14% xd". Also you need an Unit Auxiliary Transformer. If you intend to supply from this transformer the start induction motor ,the excitation and the compressor and if you intend to use for example oil instead of gas probably some 17-20 MVA would be necessary . If you intend to supply from this UAT also the HeatRecoverySteamTurbine you'll need another 5-7 MVA. So ,let say, a 25 MVA 8% will be ok.
If a Generator CB will be provided the GE gas turbine may start using this UAT.
Else you will need a Reserve Auxiliary Transformer connected directly to the Utility 132 KV Grid. In this case the short circuit current will be a little higher.
If the Utility System 132 kV may be provided with a 50 kA CB then the System Short circuit will be 11431.5 MVA .
In the first case [ supply from UAT] the short circuit current I"sc on the Generator terminals may be 132 kA ,on the 6.3 kV bus bar 27.5 kA, on the 600 V bus bar 7.4 kA and on the 380 V about 12.5 kA.
Best Regards