Torsional mode frequency and supply vibration

[MS0000]

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

 

[electricpete]

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.


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(2B)+(2B)' ?

 

[MS0000]

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?