Power output of a 3x460V motor running on VFD limited at Vout=400V 1

[winflex]

Dear motor & drive experts,

I am designing a test stand using components available in the US (3x460V@60Hz)that will run in Australia(3x400V@50Hz). There are several ~10hp motors on the stand that drive centripetal pumps. The motors are controlled using VFDs, so frequency is not an issue. For qualification I will set the maximum output voltage of the VFDs at 400V to simulate the conditions in Australia. The motors will be running at frequencies varying from 53.3Hz to 73.3Hz, meaning that they will run at constant power, variable torque.

I am trying to figure out by how much I should de-rate the motor nameplate hp. Assuming constant winding resistance, would it be appropriate to de-rate motor power by 1-(400/460)=13% ?
Also, how important is is to specify inverter duty motors?

Thank you for your input!

 

[DickDV]

Assuming the motor will be in a constant hp range from 50 to 73.3Hz, then the hp throughout that range will be equal to the hp at 50hz.

The hp at 50hz will be 50/60 of the nameplate hp at 60hz assuming you program the drive for constant V/hz ratio from 0 to 50hz equal to 480/60=8.00. Then limit the output voltage to 400V and the output frequency to 73.3hz.

 

[rhatcher]

Good answer DickDV.

 

[sibeen]

If you're designing this for Australian conditions perhaps you should be setting the maximum output voltage to 415 volts. Although the relevant Australian standards state that the normal voltage is 400 volts there is the get out that it is 400V +10% -6%. These standards were changed to 230/400 volt to be in line with International/European standards, in reality the voltage didn't move from 415 V.