A 200kW Genset feeding a Step-up / Step-down circuit

[MCTRONIC]

At our site, we have two 70 hp motors that are feed from a "Step up/Step-down" conception in order to reduce voltage drops. The "Step-up" is done by three single phase transformers (347/2400V 167kVA) connected as a three phase transformer (600/4160V 500kVA). The step down is done by three single phase transformers (347/2400V 167kVA) connected as a three phase transformer (4160/600V 500kVA). I was thinking of buying a 175kW genset that would feed the loads when power losses occurs. But I was wondering if the inrush of the transformers (12 times nominal current at 0.1sec) would mean that I'd have to oversize the genset in order for it to handle the inrush of the transformers. Would I have also to oversize the genset's protection (breaker) as well ?

Please help me.

A junior engineer.
MCTRONIC

 

[dpc]

If the transformers are connected to the generator when the generator field is applied, you can gradually build voltage to them along with the generator and eliminate the big inrush.

If not, you'll have to make sure the generator breaker can pass the inrush current, but it shouldn't be necessary to increase generator size. Voltage will dip, but come back.

The transformer inrush current may not be as high as you think since it will be greatly limited by the generator impedance and voltage drop.

 

[waross]

You could use a modified transfer switch for the transformers.
Usually the generator contactor closes when power is available from the generator which is too late. If you break out the control circuit and use a UPS to close the contactor and connect the transformers to the generator before the engine is started you should have a well behaved system. Use a second transfer switch for other loads.
respectfully