Transformer Overloading-Inrush

[harbee]

I have a 7.5 MVA, 46kV-4.16 kV transformer that feeds (2)-1200 HP motor and 1500 kVA worth of auxiliary loads (Overall load~3900 kVA). I am upgrading one of the 1200 HP motor to 1600 HP. At worst case condition, having 1200 HP running and 1600 HP starting the kVA at inrush is around 11000 kVA. Do you the transformer will handle this load ?. This increase in kVA will be for fraction of seconds until the 1600 HP motor reaches steady state. Does NEC or IEEE explains any such conditions ?

 

[jghrist]

The transformer will handle the load, but the real question is will the voltage drop during starting be excessive? This depends on source impedance, transformer impedance, feeder impedance, and the sensitivity of other equipment to voltage dips.

 

[sajuthomas]

Transformer will handle the load. But one thing there is a chance of inter trip if your differential protection relay is not properly adjusted