Can we replace One different make single phase GT with others make Single make GTs.

what do you mean by GTs?

Sure, as long as the characteristics (mechanical, electrical) are the same... Whatever it is that you mean by GT.

I suggest you re-phrase your question to be less ambiguous and avoid acronyms since they are not used all over the world equally. Title your question short, and elaborate more details below it. No doubt it makes sense to you since you are working on this issue, but the other persons reading this groups question have no idea what you are doing, so you need to be more specific. In that way you'll get more chance to find the answer you are looking for.

Maybe you meant AT as in Auto-Transformer in a single pole application where one pole is defective and you want to find out if a spare pole from another substation but different manufacturer can be used to replace it...

Is he realy talking about a single phase gas turbine?

More than likely he means three single phase transformers being used as a GSU (Generator Step Up) transformer. The answer is, only if they are all very closely matched and you have a staff who understands what precautions to take.

Alan

It should be fine if the new one has equal or higher capacity than the old one, and with the same primary voltage class level, ratio and impedance (built under the same standard).

Wei, It's important that the core and tank be as identical as possible; material, magnetic properties, thickness, form; etc. Any differences will manifest themselves as an imbalance and result in zero sequence components where none were expected.

Alan

Alan, you are right. I thought the impedance and capacity could limit the winding and core materials used, and primary voltage could limit the insulation level (under the same standard), and impedance and ratio could limit the zero sequence components. So in this case the taps of the single transformer should be properly selected and to avoid difference of the primary phase voltages to cause the zero sequence components.