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Torsional mode frequency and supply vibration

Torsional mode frequency and supply vibration

Torsional mode frequency and supply vibration

(OP)
Hello,

I am making a design of a blower. The impeller is rigidly coupled to the motor. Shall I design the system torsional natural frequencies to be above  motor supply frequency (60Hz)? What about 2 x supply(120Hz) ?

Many thanks!

-S

RE: Torsional mode frequency and supply vibration

Some ideas on torsional excitation:

120hz is an important torsional exciting frerquency since it exists for single phase motors or unbalanced 3-phase motors.

I don't think 60hz is particular important.  During DOL start, there is torque oscillation at a frequency (1-s)*60hz... but should not remain at 60hz for long.

I would think running speed and 2x running speed may be good to avoid.  Possibly number of blades times running speed also.

Vfd could make life more complicated.
 

=====================================
(2B)+(2B)'  ?

RE: Torsional mode frequency and supply vibration

(OP)
Thanks Pete for your quick informative post.

Actually, the case here is inverter driven 3-phase motor, so life is complicated :) Sorry not mention that in my 1st post.

But anyway, you think that 1x supply is not that significant excitation as 2x supply? Resonance would be there but with a smaller amplitude?

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