Cracked or broken rotor bars

I just dont understand how a broken rotor bar would generate this spectrum. Studies have shown that many of the failures of machines such as electric motors result from failures in their bearings. A defect in the rotor bar of an induction motor causes the modulation of the stator current. I turned around and determined it was comming from the wheel. Resistance of broken bars is very high in comparison with the value of healthy rotor bars. Investigation of broken rotor bar faults in threephase squirrelcage induction motors 481 broken bar broke n bars a b c fig. Slip freq sync speed rpm actual 1495 1488 7rpm or 0. Past efforts on broken rotor bar diagnosis have been focused on vibration analysis and. Broken cracked rotor bars is one of the commonly encountered induction motor faults that may cause serious motor damage to the motor if not detected timely.

Detecting broken rotor bars using vibration analysis. You could be putting yourself and your motor in serious danger. The following figure is the broken rotor bar setting screen as it appears in 8 series setup software program. One person taps the bars and the other monitors bar movement. Likely vibration spectral pattern for an electric motor with cracked or broken rotor bars bearing faults. Early detection of broken rotor bars is essential to keeping a machine from having to undergo costly repairs. Spectral analysis of motor current was firstly used to detect a broken rotor bar through the. Figure 1 shows the photographs of a rotor with broken bars and a broken end ring segments that we have manufactured. Growler test a growler is an electrical device used for testing insulation of a motor for shorted coils. Another phenomenon that cannot be looked over is the induced rotor current. Around the supply line frequency peak, which is 60hz, the currents show up as side bands. Vibration analysis report of brokencracked rotor bar cbm.

Detecting broken rotor bars in induction motors with model. Dec 24, 2017 dont take any foolish risks when it comes to your large machinery. Professionals who maintain motors need to be able to answer the following questions. Broken rotor bars and eccentricity are common faults in squirrel cage induction motors. 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 of specialized rotor testing equipment. Diagnosing rotor bar issues with torque and current signature. I am asking out of curiosity what to do when a motor has been diagnosed with damaged bars. A broken rotor barbars interrupts the flow of current and consequently distorts the rotor magnetic field. Detection of broken rotor bars in threephase squirrelcage. When a rotor bar is cracked or broken, resistance in this bar rises. The rotor bar effect on the lower sideband amplitude when a broken bar is present within the rotor, current cannot flow through it, and therefore, it can no longer add its share of torque to the rotors load burden. I am looking for a method and explanation to detect broken rotor bars using vibration.

Here are some methods to help detect cracked or broken rotor bars. Rbpf etc in many motors and also with additional inputs from mcsa. Analysis of induction motor with broken rotor bars using. Most rotor breaks take the form of cracks, usually around the base of the disk where it joins the hub. Rotor bar problems the electrical problem that is most effectively diagnosed and monitored through vibration analysis.

Broken or cracked rotor bars, and shorted laminations, will cause heat variations that are easily identified with the infrared camera. This paper presents a modelbased fault detection approach for induction motors. Loose rotor bars may give similar symptoms and also will show vibration at rotor bar passing frequencies. With broken rotor bars in the motor there is an additional, backward rotating magnetic field produced, which is rotating at the slip speed with respect to the rotor. The impact of broken rotor bars to the stator current can be determined by analyzing in the frequency domain this approach to detect rotor bar failures is typically called a motor current signature analysis mcsa. The main faults of induction motors are broken rotor bars, winding faults, and mechanical faults. Past efforts on broken rotor bar diagnosis have been focused on current signature analysis. Methods of detecting cracked rotor bars in electric motors. Do you suspect that you have a cracked rotor bar in your electric motor.

Often, however, failure occurs due to fracture of bars caused by fatigue. Diagnosing broken rotor bars in a twopole motor reliable plant. When your rotor bar is broken, thats a serious sign of trouble. But identifying faults in rotor bars correctly need serious analysis involvement. Past efforts on broken rotor bar diagnosis have been focused on vibration analysis and current signature analysis using spectral analysis.

With a broken rotor bar, the amplitude of the beat increases with load. Detecting broken rotor bars prevents catastrophic damage. As the rotor rotates at high radial speed, broken rotor bars can lift out of the slot due to centrifugal force and strike against the stator winding causing a catastrophic motor failure. The rotor bar passing frequency rbf peak can increase in amplitude, and there will be 2xlf. The existing condition monitoring techniques are incapable of positively detecting a cracked or single bar problem during operating conditions. Broken rotor bars are one of the most severe induction motor faults. Diagnosing rotor bar issues with torque and current. Broken, cracked rotor bars, bad joints between end rings and rotor bars and end ring problems have unique and easily recognizable symptoms. If it is a cracked rotor do not drive again until those are replaced.

These forces behave like a mechanical umbalance of the rotor causing the hi 1x running speed vibration. Catastrophic failures provoked by broken bars or cracked end rings in fabricated rotors. Vibration analysis report of brokencracked rotor bar. Evaluation of the detectability of broken rotor bars. The amplitudes of these sidebands are related to the number of broken bars and motor loads. This results in an unbalance and a strong 1 times running speed vibration as well as the side bands related to slip frequency. A cracked rotor bar can also cause localized heating of the rotor which causes uneven expansion and rotor bowing. Other occasional rotor problems include warping, heatchecking, and rotor bluing, which happens when a rotor has been subjected to high heat. Vibration and current analysis used to diagnose motor rotor bar problem.

The major rotor squirrel cage rotors faults are cracked or. Broken rotor bar is one of the commonly encountered induction motor faults that may cause serious motor damage to the motor if not detected timely. The most common faults are openings or shortings of one or more of the stators phase windings 2, broken rotor bars or cracked rotors endrings 3, static or dynamic airgap irregularities 4, and bearing failures 5. Detection of broken rotor bars in threephase squirrel. Furthermore, it explores nonconventional techniques, which can assist in detection of broken rotor bars. They can be caused by thermal stresses due to thermal overload and unbalance, hot spots or excessive losses, sparking. Cracked motor rotor bars caused vibration of motor, gearbox, and plant floor.

In this paper broken rotor bars are modeled by using matlabsimulink tool. The motor was sent to the motor shop, where it was disassembled. Brokenrotorbar diagnosis for induction motors iopscience. Broken rotor bars rarely cause immediate failures, especially in large. Using motor current signature to detect the number of. Often, a machine with a broken bar will keep working, making it hard to know when its time for repairs.

Monitoring and diagnosis of failures in squirrelcage induction motors due to cracked or broken bars. Pdf monitoring and diagnosis of failures in squirrelcage. From the spectrum we can see 1x harmonic running speed with pole pass freq sideband. A growler consists of a coil of wire wrapped around an iron core and connected to a source of alternating current. The most common and accurate method is the current spectrum test. Hence, operators must follow manufacturers guidelines and restrict the number of starts per hour as recommended.

This stops the current flow in broken bar and additional current starts flowing in the bars next to. Can you have another rotor built ahead of time assuming you have sufficeint motor data. Razik abstract in this paper, a new technique to detect broken rotor bars in polyphase induction machines is presented. Failure diagnosis of squirrelcage induction motor with. The backward rotating magnetic field speed produced by the rotor due to broken bars and with respect to the rotor is. A broken rotor must be replaced as soon as possible to protect the driver and all around him. Broken rotor bars precipitate deterioration in other components as well and can result in timeconsuming repairs and loss of motor efficiency. Again along the thinking above would this then be at rbpf with 2xfline sidebands as every time a rotor bar passes a loose winding in the slot the magnetic forces cause the winding to lift and drop and the rate of the number of rotor bars. Therefore, it is possible to detect early evolution of broken rotor bars as compared to conventional currentbased method.

A growler is applied to a rotor that has been separated from the stator and frame of the motor. High currents generate high heat which expands the bars, the joint between a bar and an end ring fractures, in cast rotors porous. Rotor bars break because of thermal, magnetic, residual, dynamic, and mechanical stresses kliman and stein, 1992, nandi et al. Figure 1a shows a rotor with one broken bar drilled at the center of the rotor, and fig. The results demonstrate that matlabsimulink model can be used for educational purposes. Amplitude at 1x rpm is relatively unimportant it will fluctuate greatly as the hot spots being generated cause the rotor to bow unpredictably. Will loose rotor bars be at rbpf or wspf my thinking is if you have a loose rotor bar every time it passes a winding slot the magnetic force causes the rotor bar to lift and drop at the rate of the number of slots.

Read on to learn about 5 ways you can detect a broken rotor bar. Was not previously detected by motor shop because not tested under load. Detection of broken rotor bars in induction motors using. The change in lower sideband is specifically due to the broken bar, whereas changes in the upper sideband are due to consequent speed variations. Using motor current signature to detect the number of cracked. Often, the only way to discover if there is a problem is through testing. It can be caused by thermal stresses due to thermal overload and unbalance, hot spots or excessive losses, sparking.

The stator windings receive currents induced by the rotor. Rotor asymmetry the rotor rotating offcenter, both static and dynamic. Broken rotor bar detection by power and current based fft. Worst case it will cause the rotor to warp or more bars to crack. This chapter describes a new diagnosis approach, the rootmusic rm method, for identification of the progressive cracking in the rotor of induction motors.

Pdf proposed fault diagnostics of a broken rotor bar. Bearings are composed of four basic components, namely cage, balls or rollers, inner race and outer race. Aug 14, 2015 in the video we discuss the symptoms of a busted brake rotor, hear a car with a broken rotor, and remove the wheel to see what to look for. The growler induces current flow in the heal thy rotor bars, but in the cracked or broken bars there is less or no current flowing. All emax test results indicated broken rotor bars in the motor. Diagnosis of the broken rotor bars faults by rootmusic method. Figure 5 some of the broken rotor bars found using online and offline tests. Many of these tests need to be done in an electric motor repair shop. Pdf evaluation of the detectability of broken rotor bars. The presence of broken bars will cause an increase in overall motor losses and a decrease. Broken fabricated rotor bars may be detected by tapping on the bars from one end ring to the other with a hammer and screwdriver. Diagnosing rotor bar issues with torque and current signature analysis.

Broken bars can cause sparking, a serious concern in hazardous areas. The frequencies and amplitudes of the broken rotor bar brb fault. Rotor winding monitoring induction motors iris power. Diagnosis of the broken rotor bars faults by rootmusic. To confirm this will be fpole sidebands surrounding running speed harmonics. This method works best with two people performing it. For determination the number of broken rotor bars in squirrelcage induction motors when these motors are working, this study presents a new method based on an intelligent processing of the stator. Everything ive read indicates to look for pole pass freq around turning speed or multiples of turning speed. These imbalances show up as 1st and 3rd sidebands around the.

The rotor faults can be observed as harmonics in stator current. This method is fine for a few cracked bars, but other bars may be fatigued and will break after a short time. The presence of broken bars will cause an increase in overall. In such cases uneven bar stress is then unavoidable. In the video we discuss the symptoms of a busted brake rotor, hear a car with a broken rotor, and remove the wheel to see what to look for. You may not notice any immediate repercussions of a bar thats damaged. With a resistive fracture, currents are diverted to adjacent bars increasing the current in these bars and causing localized hot spots. Brokencracked rotor bars is one of the commonly encountered induction motor faults that may cause serious motor damage to the motor if not detected timely. When rotor bars fail, and the motor is accelerating and running at full speed, you may hear a distinctive beat frequency noise, the volume or amplitude modulating.

Current signature analysis motoring detects rotor cage winding faults in induction motors including broken rotor bars, cracked shorting rings and unequal air gaps. In the process i found a broken sway bar connector. It was determined that bad braze joints between the bars and end rings from a rotor repair performed in 2001 caused the broken and cracked rotor bars. I purchased a new set of pads and started to change the pads. Actually the spectrums you show doesnt have enough resolution to see broken or cracked rotor bars. Broken rotor bar fault detection in induction motors using. Fpole sidebands surrounding running speed harmonics. Secondly, normally we get ppf, rbpf etc in many motors and also with additional inputs from mcsa. Investigation of broken rotor bar faults in threephase.

How can an instrument 100 to 1,000 feet or more away from the motor provide information about the condition of the rotor. Advanced problems will exhibit a humming or pulsing sound. Nov 30, 2012 when rotor bars fail, and the motor is accelerating and running at full speed, you may hear a distinctive beat frequency noise, the volume or amplitude modulating. Figure 1 fft showing advanced broken cracked rotor bar symptoms. Posted on december 24, 2017 december 7, 2018 by brian james. Many faults appear gradually, and sometimes it can be very. These conditions will most often occur on the spectrum analyzer when the motor has at least a 60% load.

Past efforts on broken rotor bar diagnosis have been focused on current signature analysis using spectral analysis and wavelet transform. Broken rotor bar fault detection in inverterfed squirrel. Sep 23, 2017 early detection of broken rotor bars is essential to keeping a machine from having to undergo costly repairs. Loose or broken bars will respond much differently from tight sound bars. Savings a catastrophic failure of this motor would have resulted in a more expensive repair and the high costs associated with an unplanned outage. A broken rotor bar will cause the stator current to increase or decrease. Getting the rotor back up and running machine design.

The motor was pulled and a ric test was performed, which also indicated a rotor anomaly figure 4. Proposed fault diagnostics of a broken rotor bar induction motor fed from pwm inverter. Windings drive broken end rings broken rotor bars bearingrelated eccentricityrelated figure 1. Jul 26, 2018 do you suspect that you have a cracked rotor bar in your electric motor. The reasons for rotor bar and endring breakage are many. Root cause it was determined that bad braze joints between the bars and end rings from a rotor repair performed in 2001 caused the broken and cracked rotor bars. Significant is the number of and size of the sidebands. The single phase rotor test is looking to see if there is any alternation in amp draw. Troubleshooters guide to vibration september 01, 2007.

A new approach to detect broken rotor bars in induction. Does anyone have expirience with repairing rotor bars cracked broken in large motors. From time to time, a brake rotor can break, creating an immediate threat to motoring safety. Increased accuracy detection of cracked or broken rotor bars during runtime by an enhanced power based fft detection. Advanced problems will exhibit a humming or pulsing sound and feel. Most rotor breaks take the form of cracks, usually around the base of the disk where it joins the hub section. We discovered that our 99 mercury mountaineer had bad rotors. A visual inspection found 22 of 51 rotor bars were broken or cracked see figure 5. Field investigation of gearbox vibration due to cracked motor.

Electromagnetic force unbalance, due to variations in rotor current, is commonly caused by broken or cracked rotor bars, broken, cracked or poorly brazed end ring joints, highresistance endring joints or shorted or loose rotor laminations. A new approach to detect broken rotor bars in induction machines by current spectrum analysis g. The babbitt in the motor bearings was also damaged. However, if there are enough broken rotor bars, the motor may not start as it may not be able to develop sufficient accelerating torque. Secondary effects created by broken rotor bars that impact a motor. Condition monitoring methods, failure identification and. Broken rotor bars rarely cause immediate failures, especially in large multipole slowspeed motors.