Hello everyone.

I am very confused about apparent power rating of GE 9FA Gas turbine static starter (LS2100e 14 MVA). My question is an isolation transformer takes power from a 6.6 KV bus to feed this LCI. But the transformer rating is 2MVA. But the LCI rating is written as 14 MVA. How is it possible? Anyone kindly explain me?

Thanx in advance..

 

In few words: Duty Cycle?

Regards
cww

 

generator duty cycle S1

Thanks
CWW

 

CWW

Which duty cycle? please?

 

niazbibiyana,

Your questions are best directed to GE for the most proper and concise answers. As the manufacturer and supplier they are in the best position to clarify any questions and resolve any issues.

 

The starter circuit need not be rated for the 100% value because it does not run long or often.
Much like a car starter, it puts out a lot of power for a short time.
Run continuously it would be a problem.
Google duty cycle.

Regards
cww

 

CSA

I got your point. I asked them, but he was unable to answer me. That's why I am asking here. I just wanted to know the basic thing. Transformer rating is 2 MVA but LCI rating is 14 MVA. How was that possible!

Thanks

 

Mr. Curt

But when LCI goes to desired load (when It has to drive the alternator as synchronous motor for a short time), the supply transformer should go to overload and to be tripped. Right?

Thanks

 

You are not factoring the link reactor into the overall operation.

The recovery time.

 

The LCI 14MVA rating is for maximum output, Which the unit does not require to start the gas turbine (as to why the XFMR rating is much lower). And the LCI XFMR relay will only trip based on the settings in the relay. For example for an "phase" pickup it would normally be at close to rated CT value of 5A x the multiplier setting. For a better understanding of the MVA actually being used, on the next start up you can check the current output of the LCI (on the keypad) and also look at the protective relay (main screen). Also, look at your relay settings to see what would actually cause a trip. This should help give you a better understanding of what is going on.

Hope this helps.

 

The link reactor Ac/Dc is used to filter the output.

 

Apparently not, I'm fairly sure the designers knew what they were doing, and again. short time.

The ratings for transformers are largely dependent on heating and the difficulty of getting it out of the transformer. For a short time you can output almost any current the doesn't melt the windings or badly saturate the core. This makes things like welders practical when used with a reasonable duty cycle.

If you had to have a 200 Amp continuous rated transformer the welder would be a lot heavier. The heating corresponds to the average current. Motor ratings are applied the same way. They determined that that transformer could handle that duty cycle without overheating or other issues. I'm not an expert on that or similar machines, but since the transformer hasn't blown up, it's OK in the application regardless of it's continuous duty rating.

Regards
cww

 

Don't forget about crank cool and off line water wash. We could be on the LCI for many hours for either of these evolutions. Not sure about the size of our transformer. as stated above, GE has the sizing worked out.

 

Hello:

In a 9 FB with LS2100e (LCI) the name plate of the isolation transformer is HV winding 8,75 MVA/ LV1 winding 4,375 - LV2 winding 4,375 MVA.

 

Niazbibiyana... it is analogous to sizing an auto-transformer for motor starting.

Simply put, it is sized to accommodate RMS value of kVA x time (or Amps if V is constant) during the starting period!

Are you are interested the calculation detail?

Regards,
Phil Corso

 

Thsnx Jade,

I calculated the data during GT start up. The total MVA rating of transformer was = 1.73( root over of 3) * 6600 (supply voltage) * 1800 (RMS value of current) * .8 *.8 . Which is exceeded its rating 2 MVA. I am confused.
.. Can you tell me more detailed ?

 

Thanx Phil Corso,

Yes ., I am interested. Can you show me details. I also don't understand. If 2 MVA isolation transformer is enough to supply that power, So, why don't we use the 8 MVA LCI? Why should we use 14 MVA LCI?

It will be highly appreciated, if you kindly show me details.

[email protected]

 

Hello:

To be precise, In a 9 FB with LS2100e (LCI)
the name plate:
Isolation transformer 8,75 MVA
LS2100e PWR OUT 7,8 MW.

 

Niazbibiyan...

I'm unable to connect with you via Boxbe. So my first question to you is... Are you familiar with calculation to determine motor starting or acceleration time?

Phil Corso

 

Hello niazbibiyana:

You could put nameplate to isolation transformer and LCI.

Thank you