Stiff-enough stator design for 6 pole motor - Modal frequency analysis
Stiff-enough stator design for 6 pole motor - Modal frequency analysis
(OP)
Hi,
I am engineering a 6-pole motor. Now, I am making FEA modal analysis of the stator frame. From literature and experiment I know that in 2 pole machines the stator frame oval shaped modal frequency is kept sub-critical compared to 2 x supply frequency. That is because the 2-pole excitation does have the same oval shape as that oval mode shape, therefore, the resonance would be for real for sure. How is it with machines with more poles: 4, 6, 8... and so on. Electro-magnetic excitation is divided into smaller forces per pole(6-merlon star in 6-pole machine) so probably the vibration response is smaller and so on. Shall I keep stator oval shape modal frequency still sub-critical compared to 2 x supply frequency in 6-pole machine? All the experiences about the design of 4-pole and on machines are really appreciated! I hope you got my point.
Thanks,
S
I am engineering a 6-pole motor. Now, I am making FEA modal analysis of the stator frame. From literature and experiment I know that in 2 pole machines the stator frame oval shaped modal frequency is kept sub-critical compared to 2 x supply frequency. That is because the 2-pole excitation does have the same oval shape as that oval mode shape, therefore, the resonance would be for real for sure. How is it with machines with more poles: 4, 6, 8... and so on. Electro-magnetic excitation is divided into smaller forces per pole(6-merlon star in 6-pole machine) so probably the vibration response is smaller and so on. Shall I keep stator oval shape modal frequency still sub-critical compared to 2 x supply frequency in 6-pole machine? All the experiences about the design of 4-pole and on machines are really appreciated! I hope you got my point.
Thanks,
S






RE: Stiff-enough stator design for 6 pole motor - Modal frequency analysis
The force wave from the fundamental has P poles and time frequency 2*LF.
If you have eccentricity, the spatial order of the force wave can get shifted by one compared to the mmf wave... so 4-pole motor may have 3-pole and 5-pole force shape at twice line frequency. But not 2-pole.
You can also get shapes that have P+/-|R-S|, but those are not at 2*LF frequency (they are near RBPF).
I don't see any reason why the 2-pole mode shape would need to be separated below twice line frequency on a 4-pole or 6-pole motor.
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(2B)+(2B)' ?
RE: Stiff-enough stator design for 6 pole motor - Modal frequency analysis
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(2B)+(2B)' ?
RE: Stiff-enough stator design for 6 pole motor - Modal frequency analysis
Sorry, I did confuse mode freq and excitation. For sure 2xLF excitation is kept below mode shape - not another way :) Especially because this is variable speed machine.
I am not fluent in those shortcuts, can you explain: |R-S| and RBPF ?
RE: Stiff-enough stator design for 6 pole motor - Modal frequency analysis
R = Number of rotor bars
S = Number of stator slots
RBPF = Rotor Bar Pass Frequency
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(2B)+(2B)' ?