Help needed interpretting Motor Data

skyfox

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Nov 2006
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Good Day All,


Motor has the following Spec.


380-480V: 50Hz 0.2 kW 3,000 RPM
460V 60Hz 0.24 kW 3,600 RPM.


This is a motor driving a cooling fan to cool another motor. (attached to the other motor housing)


Question: Can this motor be safely operated at 400VAC 60Hz?

It is a constant speed operation. Switched on when Main motor's temperature rises and then shuts off after it cools down. Triggered from Main motor's Thermistor.




Thanks-
 
The motor is rated for 60hZ so there isn't any problem there. You will be running it at a lower voltage, for a constant load that would increase the current required to hold speed. But you have a fan and the load on that falls as the cube of the speed, so the fan will run a bit more slowly and so be less efficient at cooling your main motor.


It is a long time since I did motor theory, I hope my memory is still at the right voltage!!
 
will depend on how heavily loaded the fan is (how much air its moving), my first thought is 60V is bit too low from nameplate voltage.


bench test it and put a clamp meter in one of the phases and check the current load. the fan needs to be connected to the motor when you do this and no restriction of air on inlet or outlet of fan.


if current is too high then maybe an inverter will recify the issue and set it up for V/F to nameplate of motor, its small kW so an inverter will be cheap.
 
Odd, where do you have a 400V 60Hz supply system ?
If you are in the US, why not simply run it at 460V 60Hz ?

Anyway, running at with DOL start at 13 % below nominal voltage will mean that its torque characteristic will be reduced by 25%.
(400V/460V)² = ~0.75
So basically the motor is derated 25%.

As BryanG says, because the fan will run at a sligthly lower speed, it will require somewhat less torque to turn. But the reduced load curve of the fan will not exactly even out the lower motor torque.

So maybe the motor can run the fan OK. For a 0.24kW motor I think it will be OK.
The small motor probably do not have an integral thermistor.
But you can measure the current when it operates. For the overload of a motor, it is allways the motor current that matters. If the motor current isnt more than the name plate, it will be OK.

The fan in the small motor (and the fan that it drives) will operate at a sligtly lower speed. But probably not so much that it derates the motor further.
 
There are a small handful of countries that operate at 400V / 60Hz. Not too many but they do exist.

The blower motor will run at a slower speed but not for lack of trying. It will attempt to run at the speed appropriate for the 60 Hz supply. Any speed less than that goes into slip. Since the motor is underfluxed at 400V/60Hz you would expect increased slip. But as has been stated, as the speed drops off in a fan application the torque requirement drops off fairly quickly so it is likely you will be fine.

Another clue that you will probably be OK is allowable voltage range for 50Hz operation. In that case the motor is likely overfluxed at voltages greater than 380V. This additional flux producing current causes more motor heating than you would expect given the torque requirement. The motor was designed to deal with this additional heating so it is probably going to be just fine if there is a little additional heating due to underfluxing and increased slip.

Keith
 

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