I am designing a new project which contains medium voltage chiller motors.
The power supply voltage at the beginning of the project will be 3 phase 11 kV, 60 Hz. But in future, within couple of years the voltage will be changed to 13.8kV, 60 Hz. The transformers will be dual voltage (11-13.8 kV). But I am not sure about the availability of dual voltage motors. Could anybody advise me in this regard?.

Hello magdy El Kady

Welcome to the forum.

It is possible to get a motor would with a tapped winding, so you could get a star configured motor would to provide both voltages, however, in doing so, you will be reducing the winding area on the lower voltage setting and therfore increaseing the copper losses in the stator.
Another alternative is to get a larger motor for the higher voltage and run it on the lower voltage. The motor rating would need to increase by the voltage increase so that at the lower voltage it was not overloaded. i.e. increase th motor size to 126% of that required and rated at 13.8KV and you should be OK.

Best regards,

Thanks Marke for your response.

I would like to ask if the dual voltage (11-13.8 kV) motor is a standard manufacturer product or an expensive costume made one. Some of my colleagues advised that such dual voltage motor is not available and difficult to be produced.

I want also to high light that the motor is 2 MW rating. It will be provided with reduced voltage starter, either autotransformer or solid state soft starter. Rated voltage of all equipment will be 15 or 17.5 kV, so they can work on both 11 and 13.8 kV. The autotransformer for motor starting will have dual voltage primary winding. The setting of the relays will be modified upon changing the supply voltage to 13.8 kV. I think also that the soft starter (if used) can work on 13.8 kV through proper setting, but I need a confirmation about this issue as well.

Well it is possible to make the motor, in star configuration, but finding somewone to do it is another problem. There is a compromise in efficiency due to the winding window, and probably it would be wound on a larger frame to accomodate this.
Best to talk to the motor manufacturers about what they are prepared to do.
Best regards,

Another possibility would be to use a step down transformer with a VSD - 13.8kV to 6.6kV. You would need a standard 6.6kV motor. This would mean that when using the 11kV input, the motor would provide full rated torque up to ~47Hz (@ 5.2kV). I think that this would be a more expensive option. BTW, what is the application?
I don't know if there any soft starters available to run at 13.8kV.

Hello magdy El kady,

Soft starters are available for operation on 13.8kV supplies and beyond.

Although I cannot personnaly assist you with the supply of one, you could try:

http://www.benshaw.com

or

http://www.motortronics.com

Hope this helps.

Regards,
GGOSS