Reply to "High Vibration Problem at Raw Mill Motor"

John from PA posted:
How much else in the way of pertinent info may be in error?

By the way, in your calculation (see below) the "120" is line frequency so unless you have a 60 Hz source, the result of the calculation should be 8.33 RPM.  But your motor speed of 995 agrees with a 6-pole motor on a 50 Hz supply.

Speed(RPM) = 120 f(Hz) / P(Poles)
So Fluctuation in speed will be 120*0.5/6=10 RPM

Dear Sir,

That mistake was due to some miss-understanding. There will be no other error in the provided information.

I think 120 is a constant in the formula (not Lf) whereas f(hz) is the line frequency. So to calculate the fluctuation of RPM, I used maximum fluctuation of frequency.

ac-motor-synchronous-speed

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