Is it possible vibration may appear on line frequency(50 HZ)?and what is the reason of this?

We experienced a high vibration on motor with exciter even RPM 69 during startup upto 500 microns.

Dominant peaks are 50Hz and 100 Hz.

Then electrical department replaced some diaodes in exciter of the motor,now motor is running ok.

But i want to know that why  dominant vibration was on 50HZ(line frequency)?even motor speed is 1500 RPM,


Line FrequencyLF


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Original Post

One of your spectrum notes says "0" RPM. Is this correct?

Even when not running it has a 50 Hz Peak in it?

Sounds like the VFD Rectifiers (if that is the type system you are using) are somehow "Leaking" Line Frequency through into the motor.

I saw this  some 30 years ago but do not remember exactly what was wrong, but the electrician fixed it rather quickly.

If it is there when not running, there is something really bad wrong.

If you have a motor that normally is fed by a DC supply by a exciter or being a DC motor and your rectifier system fail and resulting in that you feed AC instead it will end giving LF related vibrations and if that is on even when the motor is not running/rotating it will vibrate with LF related frequency. I have once had that, vibrating when not running/rotating until excitation turns off, slightly freeky. Olov

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