Autotransformer Question

These are: 132/220 kV auto-transformers.

Regards,

Please keep any not relevant information for yourself.

No homework..... It would be 50 MVA in 3 phases...The current would be tripled...

Is input MVA equals to output MVA in autotransformer? is 150 MVA in parallel with 150 MVA make it 300 MVA auto-transformer rating for our case of 132/220 kV step up auto-ransformer?

Regards,

Do your own research....

https://en.wikipedia.org/wiki/Autotransformer

No, input MVA is not equal to output MVA for any transfo, the input carries the magnetising current as well as the transformed secondary current.

Transformers are rated [what is written on "Rating Plate"] by the output MVA. For transfos of MVA size, magnetising current is around 5% of full load: but for "plug-top" transfos rated 1VA, no-load VA may be twice the output VA.

I cannot see your arrangement. I suppose that each phase has two 50 MVA transfo in parallel. That is 100 MVA per phase. With 3 phases, that makes 300 MVA.

There is an assumption here that the paralleled transfos are so similar in impedance and voltage ratio that any circulating currents due to small difference of terminal voltage on-load do not affect the rating. A purchase of 2 or more transfo to operate in parallel must make it clear they are to operate in parallel, unless the whole specification includes ratio & impedance tolerances (& loss due to circulating currents) OK for parallel operation.

Since a 3 phase system is not made to be used as single phase, a 3 phase transfo (or group of transfos, operating as one) is rated by its 3 phase capacity, which is the total power it can deliver to a consumer.

Yes, the 6nos single phase auto transformers will be 2nos three phase banks of 150MVA rating each. You are right.