Re rating a Synchronous Machine

[magneticted]

We have a 9MW 4P 6.6Kv 60hZ Synchronous Motor, and we are thinking of using this on another plant where the frequency is 50 hZ. We know we will have to rate the motor for a lower power, but is this feasable. What are the issues we have to think about

 

[asekhar]

FAQ237-1224: Motors: Changing between a 50 and 60Hz supply, gives detailed analysis of this.

You would require to derate it for power & voltage to avoid cooling issues.

Additionaly probably you will need to find out the critical speed of the motor, incase it falls near the new rpm (in this case it is unlikely).


Anand Sekhar

 

[ScottyUK]

Well, it will be a 7.5MW machine at 50Hz assuming that delivered torque remains the same. You should check the auxiliaries such as the field regulator and the control gear are capable of operation at the lower frequency. Lubrication may behave differently at the lower speed - this will almost certainly be a white metal bearing and oil wedge formation relies on shaft rotation. Not my field of expertise but something to check.


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If we learn from our mistakes I'm getting a great education!

 

[motorspert]

Bringing a motor like that down in speed shouldn't be a problem, as long as the voltage comes down pro-rata ie to 5.5kV not a problem in France, but I suspect you wont have the voltage available and may not want to have a specially made transformer.

What is the rated power factor? usually its unity, but if not you may be able to run at a lower power factor.

I dont see any probems mechanically, unlikely to be near the critical speed and the bearings will be fine.

Where is it? Can u get ot to a repair shop and test it, see what it will do? Iknow one in the Uk that will do that for you and rewind if necessary