60hz to 50Hz... and the motor sped up???

[lownox]

Yesterday, we were testing a filtration unit with a fractional HP PSC motor. Oddly (to me) it is labeled 220V 60Hz. The rated RPM is 1050. So we ran this motor in our unit at the rated voltage using a variac. We were measuring RPM, current, and air flow through our filter as the motor is driving a small blower wheel.

We have a 50Hz generator set and decided to run the motor with that. Keep in mind we are not motor people, so we were not maintaining V/Hz ratios or anything. We ran at 220 50Hz and this is were things get ODD.

The recorded RPM went UP as well as the airflow! It is as if the motor got more powerful using the voltage from this generator.

My question is... How is this possible?

Let me know if there is anything else about this scenario that would help you answer this question. This one has us stumped.

Steve

 

[LionelHutz]

It sounds like the motor stalled before even reaching the 50Hz speed when operated at 60Hz but was able to reach full 50Hz speed when operated at 50Hz.

You increased the V/Hz ratio which can increase the magnetic field in the motor and make more torque.

The fan produces is squared load compared to speed and at 60HZ the motor has a large torque dip at part speed which it could not get past to accelerate the fan further.

Maybe a combination of the above.

 

[edison123]

What was the recorded RPM ?

Muthu

http://www.edison.co.in