90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
(OP)
We are evaluating whether 90MVA, 66/33 kV Tranformer switching is possible with one 43.5MVA Gas turbine Generator connected to 66kV busbar.The question is whether one 43.5 MVA Generaor will be able to withstand the switching inrush current of the 90MVA transformer(inrush is 5.3 times of I fl as per document)
Request your expert opinion on this





RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
To limit the inrush current, the transformer should be switched with no load on secondary.
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
A loaded secondary reduces available volt-seconds and can reduce saturation, which reduces inrush. If you are lucky, that reduction will win over the increased current caused by the load. Did you run it in ETAP or some other trustworthy simulation program?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
On PRC comment, I forget to mention GTG is having a 55MVA transformer before connecting it to the 66kV bus, which is softstarts along with Generator. 90MVA transformer is distribution transformer from the BUS. We have 3 other STGs of 42MW capacity connected in 66kV bus. We are looking for restart after black out. until now we had another power source for black out re-start. This power source will be discontinued shortly. Just to add is we are currently experiencing voltage dip up to 11% while energising 90MVA transformer with 3 Generators online.
Skogsgurra: We would like to have a preliminary assessment before engaging a consultant.
Power0020: Can you please confirm about your point of view , if you have the similar experience. it will be helpful if you can explain a bit more as most of the engineers have opinion that Generator can Trip due to the high reactive inrush current requirement.
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
You'll find that the AVR will boost the field as it tries to recover the severe transient depression. It may hit the over-excitation limiter which in some installations is an instantaneous trip and in others is a delayed trip. You will quite possibly see the AVR then swing onto the under-excitation limiter as it tries to suppress the resultant overshoot. Your AVR topology will make a big difference to how the machine behaves: a 2-quadrant (regenerative) rectifier connected via sliprings can actively suppress the field by feeding the excess energy back into the source, but a brushless machine can't do this and has to rely on the resistance of the rotor to dissipate the stored energy over a time determined by the rotor R-L time constant, during which time the UEL may well be operational. Normally this isn't a trip, just a warning that the machine is operating near the stability limit, which isn't the best place to be especially if you are going to be adding large blocks of load.
Can you arrange the system transformer to be softly energised at the same time as the GSU transformer? It may require modification to switching interlocks, and you probably don't have synchronising capability other than at the GSU transformer breakers but in a blackout this probably doesn't matter too much.
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
Regards
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
The saturation check function in generator protection relay should block the trip signal, the only concern here is the UV setting on generator.
RE: 90MVA, 66/33 kV Tranformer switching with one 43.5MVA Gas turbine Generator connected to 66kV busbar
Why not using a transformer controlled switching to mitigate the inrush current?
Please, find attached a paper on controlled switching of a 100 MVA, 230/138 kV transformer in which is showed the success of this strategy.
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...