Advantages of 2 transformer system

[Cloud]

Hello.

We have a 2 service transformer design.
1. Primary 24kV, Secondary: 230V- LV use, 130VAC (L-N) for heating and cooling coils.
2. Primary 24kV, Secondary: 460V- direct 460VAC to be used by motors.

My question is, what is the advantage of having 2 systems? independent aspect? code?
I'm thinking of suggesting to use only 1 rating of SST that can cover 2 systems, say with secondary at 400VAC but concern about if it can supply the 460VAC.

Need your take on this.
Thanks!

 

[Julius Right]

It depends on rated voltage of the receiver -the lighting and cooling coils rated voltage is-probably-230 and 130 V. If the motor rated power is more than-let's say-200 hp and is located far from the transformer it is recommended a higher voltage. In this case the current will be less and the voltage drop will be less. The permissible voltage drop-mainly at D.O.L.start -depends also on transformer rated power and short-circuit impedance of the transformer.
However, if you would provide all the receivers for 400 V-the induction motors-and 240 V single-phase, lighting and other, you could use a single system of 400/240 like all around IEC World.

 

[Cloud]

Thank you for the response. I think it is more convenient to change the motor ratings to 400 since it is just on the design stage.

 

[kwired]

400 volt systems are not common in the US and typically only exist when supplying foreign made equipment. Much of this equipment also comes from places that run at 50 instead of 60 Hz.

Off the shelf NEMA general purpose motors are going to be least expensive primarily because they are the most readily available if you are in North America - but your application may or may not need closer examination as to how suitable those may be. Those off the shelf NEMA motors will be 115, 208, 230 or 460 volt rated.

400 volt 50 Hz motor can be run on 480 volt 60 Hz because the V/F ratio is the same, but will run at a faster speed then it does at 50 Hz.

 

[Cloud]

Thanks kwired. You're of great help as always.