The additional heat generated from the added current will also further increase the rate of insulation degradation in the stator. All emax test results indicated broken rotor bars in the motor. After motor changing, there is no fp sideband appearing around 1x harmonic running speed. You can see the stainless steel retatining rings of this 2pole rotor in this image.
Diagnosing broken rotor bars in a twopole motor reliable plant. Fpole sidebands surrounding running speed harmonics. Vibration analysis report of brokencracked rotor bar. Vibration analysis report of brokencracked rotor bar cbm connect. Rotor surface cracks are normal under extreme driving conditions. The rotor bar passing frequency rbf peak can increase in amplitude, and there will be 2xlf. Figure 1 fft showing advanced broken cracked rotor bar symptoms. Diagnosing rotor bar issues with torque and current. Top 3 causes of broken rotor bars electrical apparatus. Rotor bar cracked after the motor was dismantled, we inspected the rotor and found the rotor was cracked. Loose rotor bars may give similar symptoms and also will show vibration at rotor bar passing frequencies. Detecting cracked or broken rotor bars in you electric motors.
Regardless, the presence of broken rotor bars precipitates deterioration in other components that can result in timeconsuming and expensive fixes. Hence, operators must follow manufacturers guidelines and restrict the number of starts per hour as recommended. This results in an unbalance and a strong 1 times running speed vibration as well as the side bands related to slip frequency. Broken rotor bars precipitate deterioration in other components as well and can result in timeconsuming repairs and loss of motor efficiency. The broken bars also lead to deterioration elsewhere that can lead to expensive repairs of the entire motor core. This bending causes bar fatigue and eventually bar cracks. Broken rotor bars rarely cause immediate failures, especially in large multipole slowspeed motors. Amplitude at 1x rpm is relatively unimportant it will fluctuate greatly as the hot spots being generated cause the rotor to bow unpredictably. The motor wont be able to build accelerating torque so it may not even start. Cracked rotor bars electric motor rotor repair heco inc. The combination of thermal expansion and centrifugal forces also cause the bars to bend at the end of the rotor slot.
However, if there are enough broken rotor bars, the motor may not start as it may not be able to develop sufficient accelerating torque. In the event such a fault occurs the overcurrent protection must act instantaneously to trip the motor and protect the stator. A visual inspection found 22 of 51 rotor bars were broken or cracked see figure 5. Do you suspect that you have a cracked rotor bar in your electric motor.
Worst case it will cause the rotor to warp or more bars to crack. Broken rotor bars really become an issue when there are several of them. The motor was sent to the motor shop, where it was disassembled. Getting the rotor back up and running machine design. Cracked rotor bars or cracked rotor bar shorting ring connections are a major source of problems for many electric motors, and detecting them can require the use. Detecting broken rotor bars prevents catastrophic damage. Here are tips on how to find the problem, fix the rotor, and get the motor running again. Overview of rotor bar failures primary impact on the motor. The proper clearance must be present or bowing may occur causing out of balance problems. During routine emax testing in june 2003, motor engineer enrique. The motor was pulled and a ric test was performed, which also indicated a rotor anomaly figure 4. Rotor bars of 2pole 3600rpm electric motor rotors are subjected to high stresses caused by repeated starting, thermal expansion and.
When a rotor bar is cracked or broken, resistance in this bar rises. Advanced problems will exhibit a humming or pulsing sound and feel. The presence of broken bars will cause an increase in overall motor losses and a decrease in motor efficiency. Significant is the number of and size of the sidebands.923 1548 279 633 1355 489 721 1242 852 1131 690 207 699 354 887 1401 1360 500 914 1488 250 392 1491 840 449 73 332 363 564 291 1339 555 1074 146