Rotor Bar Cracks in a Motor
Four rotor bar cracks in a motor are analyzed using a high-resolution 500 Hz spectrum, revealing a classic pattern of impact clusters at pole pass frequency and repetitive impacts at running speed.
CLASSIC CASE FOR CRACKED ROTOR BAR.
The pictures below are for 4 crack points in the motor rotor bar. The classic pattern is shown at high resolution 500 hz spectrum, which is (1x) plus harmonics, and clear sidebands equal to pole pass frequency.
The high resolution spectrum cleary shows the very small difference between the rotating speed harmonics and the sidebands.
The waveform here is telling a very interesting story:
1- The cluster of impact is repeated with constant frequency equal to pole pass frequency.
2- At each cluster, there are repetitive impacts equally spaced with frequency equal to running speed.
Additional Images
