- something is exciting your motor from the side of the gearbox / planetary gearbox, 50 teeth for sun gear sounds a low number, you also have to check the planetary teeth rotation speed
- or there is some electric fault weakness on the motor but I don't understand how is it possible that the line frequency is fluctuating?? OK, rotation frequency, but line frequency should be constant at 50 Hz
Actually, in my experience 50 on the sun would be quite high for a raw mill application. In general when shock loads are high, then the pitch gets "course" which lowers the number.
As a reference to a typical drive and the associated vibration analysis, see http://www.vibration.org/Prese...0Sept%205%202006.pdf.
Is this a multiple stage gearbox and do we know (for sure) is it a planetary arrangement (as opposed to a sun or solar arrangement).