breaker selection.

[SauravWest]

DearSirs,

I have a 4 MVA transformer with subtransient reactance of 8%. The SC MVMA will be 50 MVA and short circuit current delivered will be 2624 Amps and rated current will be 210 Amps.



Now, I have to select circuit breaker of 11 kV.

a) with 25 percentage margin also, the rated current: 400 Amps.

b) SC current of breaker will be 8 kAmps.

Is the above calculation correct?

Regards,

 

[jghrist]

Is the 11 kV the secondary? If so, the calculations seem OK

 

[Parchie]

The question is whether you can secure a 400A MV breaker in the market! The ones I knew were 1,200A's.

 

[cranky108]

Not that I know about 11kV, or EU standards, but typically you would buy a standard size breaker with a capacity larger than what you need. Also be sure the interrupting is much higher than what you need, it will ensure a longer contact life over many operations.

600 and 1200 amp rating are typical here. Maybe 800 also, for distribution applications.
Maybe a recloser for a small station.