RBPF line : an aerodynamic problem ?
RBPF line : an aerodynamic problem ?
(OP)
Hi,
I have a noisy squirrel-cage induction machine with a 115 dB line at Rotor Bar Pass Frequency (f*Zr/p where f is fundamental current frequency, Zr number of rotor bars, and p number of pole pairs) in off-load sinusoidal running conditions.
That sharp peak decreases to 90 dB when using the external cooling fan... which suggests that noise comes from a purely aerodynamic problem.
A possible explanation is that rotor teeth rise too much above rotor bars, which makes the rotor act like a fan with Zr blades. As the motor is open, this noise would easily radiate out of the motor.
Is that a well-known noise problem in induction machines ? Does this phenomenon have a name ? Have you ever met such a problem ?
Thanks for you answers,
I have a noisy squirrel-cage induction machine with a 115 dB line at Rotor Bar Pass Frequency (f*Zr/p where f is fundamental current frequency, Zr number of rotor bars, and p number of pole pairs) in off-load sinusoidal running conditions.
That sharp peak decreases to 90 dB when using the external cooling fan... which suggests that noise comes from a purely aerodynamic problem.
A possible explanation is that rotor teeth rise too much above rotor bars, which makes the rotor act like a fan with Zr blades. As the motor is open, this noise would easily radiate out of the motor.
Is that a well-known noise problem in induction machines ? Does this phenomenon have a name ? Have you ever met such a problem ?
Thanks for you answers,






RE: RBPF line : an aerodynamic problem ?
Blows air on the outside of the motor or the inside?
Is this a vfd fed machine?
Traditionally, RBPF is number of bars times running speed. This differs from your f*Zr/p by a factor of (1-s). Can you clarify.
RBPF wtih 2*LF sidebands is a very common pattern in vibration resulting from electromagnetic effects.
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RE: RBPF line : an aerodynamic problem ?
This is a vfd fed machine, but tests were run in sinusoidal supply (provided by an alternator).
Sorry, I forgot the slip as test were run in off-load case, the noisy frequency is f(1-s)Zr/p.
I know that RBPF line usually comes from electromagnetic effects, but as I said, the variation of 25 dB when switching on the fan clearly shows that the problem is not magnetic.
Tests have been run at several different frequencies, and RBPF line systematically decreases with the fan. It increases with speed at constant flux, which also indicates that it comes from an aerodynamic problem...
RE: RBPF line : an aerodynamic problem ?
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