Motor rotor bar crack

Single phase power is applied to the motor, the rotor rotates slowly, and an analog meter is used to monitor one phase looking for fluctuations in amp draw. Growler test a growler is an electrical device used for testing insulation of a motor for shorted coils. Rotor testing with mce pdma a leader in electric motor. Loose rotor bars may give similar symptoms and also will show vibration at rotor bar passing frequencies. The bars on the failure in june were at the end ring connection point and appeared to be from fatigue. Fpole sidebands surrounding running speed harmonics.

How resistance is important in understanding electricity. It looks to me as if the bar directly under the crack has migrated more toward this end over repeated cycle. Rotor bar broken fault is one of the common faults of the submersible motor. Condition monitoring of electrical machines abb machsense. The apparent lengths of the cracks were in the range of 1020 mm and were easily visible with the naked eye.

Utilising rotor bar crack detection equipment and automated tig welding and undercutting equipment our quality processes are second to none. This creates a warping of the rotor bar and a significant thermal expansion equal to many tons of axial pressure. The rotor can be visualized as a large rotating electromagnet with north and south poles. The use of motor current signature analysis mcsa for motor fault detection such as broken rotor bar is now well established, however the detection of mechanical faults related to the driven system is a more challenging task. Rotor bar test motor current reliability solutions. We have the capability to rewind and vacuum pressure impregnate vpi both epoxy and silicone resins and our ac motor test rig can dynamically test all ac railway traction motor specifications. Rotor bike components crafts products with a specific intention. Rotor asymmetry the rotor rotating offcenter, both static and dynamic, could cause the rotor to rub against the stator winding leading to rotor core. The number of winding slots will be between about 25 and 100. The condition of the rotor bars in an induction motor can be measured by performing a highresolution frequency analysis on the input current to the motor the presence of a defective rotor bar will cause the motor torque to be reduced slightly every time a pole of the rotating magnetic field passes by it. Thermal expansion of the copper or aluminum can change the severity of the defect.

These methods are based on the detection of sidebands around the supply frequency in the stator current signal. A cracked rotor bar can also cause localized heating of the rotor which causes uneven expansion and rotor bowing. The rotor was rebarred by a rotor rebar facility, after about four months of service it failed again. Its rotation is due to the interaction between the windings and magnetic fields which produces a torque around the rotors axis. This results in an unbalance and a strong 1 times running speed vibration as well as the side bands related to slip frequency. Movement is reduced by forming a depression in a portion of a rotor bar of the rotor cage. Failure analysis of brass rotor bars sciencedirect. Brokenrotorbar diagnosis for induction motors jinjiang wang 1, robert x. Now when the rotor heats, there is a relative push upwards by this bar and downwards by its two neighbors. In this paper, broken rotor bar brb fault is investigated by utilizing the motor current signature analysis mcsa method. Regional sales manager at industrial motor services in richmond, virginia. Rotor bar cracked after the motor was dismantled, we inspected the rotor and found the rotor was cracked. Recently there has been a growing interest for the detection of gear faults by mcsa.

How to repair crack rotor bar for induction motor cr4. Diecasting rotor crack is divided into two kinds of cold crack and hot crack. Rotor surface cracks are normal under extreme driving conditions. This scenario results in localized heating of the rotor, causing it to warp. As soon as a crack develops, the resistance of that bar increases, increasing its heating, and consequently worsening the crack. The figure below shows a deep bar cage rotor with deep and narrow bars. Other occasional rotor problems include warping, heatchecking, and rotor bluing, which happens when a rotor has been subjected to high heat. Ger4212 ge generator rotor design, operational issues. 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. Most rotor breaks take the form of cracks, usually around the base of the disk where it joins the hub section. Squirrel cage rotor testing easa convention 2003 moscone convention center san francisco, ca june 30, 2003. The deep bar rotor in an induction motor is used to obtain high rotor resistance at starting and low rotor resistance at the running condition. At the same time, the adjacent rotor bars experience increased currents because of the reduced current in the broken bar.

The displacement of rotor bar material deforms an adjacent portion of. Ac induction motor image courtesy of ieee introduction an ac induction motor converts electrical energy into mechanical motion. Broken rotor bars also create some secondary effects that. Formation of the depression displaces rotor bar material adjacent to the depression. Amplitude at 1x rpm is relatively unimportant it will fluctuate greatly as the hot spots being generated cause the rotor to bow unpredictably. First, the total mass of the induction motor rotor bars must be sufficient to handle the heat generated by the high currents during a transient start condition. During startup, very high temperatures will develop around the crack or open bar causing potential damage to the rotor core as well as the stator insulation. This leads to cracks in the joint between the bars and the shortning rings. Submersible motor rotor bars broken fault analysis based. Why faradays research is revolutionary to start the era of electrical engineering.

Root cause ac motor failure analysis with a focus on shaft failures austin h. A method for reducing the movement of a rotor cage relative to a rotor core in a rotor assembly, such as found in a squirrel cage ac induction motor. The resultant assembly is sturdier and less noisy than a coppercage rotor. Vibration analysis report of brokencracked rotor bar. The electrical effect of the broken or cracked rotor bar is an increase in the rotor circuit impedance and. Broken rotor bars rarely cause immediate failures, especially in large multipole slowspeed motors. Figure 5 some of the broken rotor bars found using online and offline tests. A lot of time is wasted on diagnosis when a rotor bar issue is not obvious. In order not to affect the production efficiency of submersible motor, the fault should be detected in time. Broken rotor bar detection by power and current based fft. 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.

This motor failed due to open rotor bars after several years of service in june. Advanced problems will exhibit a humming or pulsing sound and feel. Fault diagnosis and detection in industrial motor network. When a crack appears the resistance in the bar increases, which in turn increases the heating and thereby enlarge the crack. An accurate assessment of condition and remaining life can also be made with online current analysis. Diagnostics of rotor and stator problems in industrial.

A bar with a high resistance connection will have less current flowing through it and will not expand at the same rate. As the rotor temperature decreases or under external force, the crack will expand. The rotor is a moving component of an electromagnetic system in the electric motor, electric generator, or alternator. Root cause ac motor failure analysis with a focus on shaft.

A bar may be assumed to be made up of a number of narrow layers connected in parallel. In industrial environment, induction motor is very symmetrical, and it may have obvious electrical signal components at different fault frequencies due to their manufacturing errors, inappropriate motor installation, and other influencing factors. Conversely, a generator converts mechanical motion into electrical energy. How to know the number of rotor bars in induction motor. Second, the number of induction motor rotor bars and thus slots must be slightly different from the number of stator slots to minimize both electromagnetic and acoustic noise. The initial diagnoses, however, can easily be made with vibration data. Broken, cracked rotor bars, bad joints between end rings and rotor bars and end ring problems have unique and easily recognizable symptoms. Rotor influence measurements are popular in some circles or motor circuit analysis. Besides a simple visual inspection, below is a summary of the most common methods of detecting cracked rotor bars as.

Such fluctuations are indicative of a cracked rotor bar. Please give your expert opinion on the photos below. This differential expansion and non symmetric heating results in severe stress and an eventual crack. Keep in mind as a motors rotor begins to lose bars it also reduces the motors ability to meet full load requirements. In summary, the 869 offers current based analysis, but also a more advanced power based approach for broken rotor bar detection. Are there any signs of movement between rotor and shaft or bar and lamination. An experimental investigation on broken rotor bar in three phase induction motor by vibration signature analysis using mems accelerometer. Loose rotor bars extremely unusual and never found in cast rotors.

Is the lubrication system as intended or has there been lubricant leakage or deterioration. The use of copper for the conductor bars and end rings of induction motors in place of aluminum results in attractive improvements in motor energy efficiency. Chris says that a standard motor repair practice should include a rotor bar and stator slot count when the equipment is serviced. Cold crack is characterized by the rotor end ring surface or the guide bar has penetrated or not penetrate the crack elongated slit, the crack is not oxidized. Do you suspect that you have a cracked rotor bar in your electric motor. In really simple terms, there are a couple of factors. An experimental investigation on broken rotor bar in three. When offline its about the only way to detect rotor issues unassembled.

Rotor bar problems are infrequent, in most applications. It gives motor designers greater latitude and makes better use of the slots by filling them completely. Automated slip detection vibration data gives mechanical condition and confirms findings of mcsa abb consider rotor design and construction of motor which give an unique index to estimate the fault severity. As illustrated in figure 4, the magnetic flux that radiates from the rotor follows the magnetic circuit across the air gap, through the stator core and then back across the air gap into the rotor to complete the loop. Detecting broken rotor bars prevents catastrophic damage. The current also becomes larger in the other rotor bars as the current has been reduced in the broken bar. In case of a crack in bars, the cracked bar will overheat because of which bar may break.

Another test for detecting a cracked rotor bar is the singlephase rotor test, and for this test the motor remains assembled. From our original q rings to our unprecedented dualsided power meter, 2inpower, we apply technology to help you become a stronger, faster, and moreefficient cyclist. However, if there are enough broken rotor bars, the motor may not start as it may not be able to develop sufficient accelerating torque. Overview of rotor bar failures primary impact on the motor. Thus, the surrounding bar will carry higher currents and are subjected to larger thermal and. Hence, operators must follow manufacturers guidelines and restrict the number of starts per hour as recommended. Rotor bar test motor current finds rotor bar defects in ac motors.

Gao, and ruqiang yan2 1 department of mechanical engineering, university of connecticut, storrs, ct, usa 2 school of instrument science and engineering, southeast university, nanjing, china email. I have one type of hoist motor, the rotor is conical in shape, it is a 2 poles motor and we need to run a lot with jog. Bars in an ac rotor carrying the current induced in the rotor by the stator. Broken rotor bar is one of the commonly encountered induction motor faults that. 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. Methods of detecting cracked rotor bars in electric motors. The frequency, then, is the number of windings slots x rpm winding slot pass frequency or wspf. Because of this, a cast rotor should maintain its balance indefinitely whereas a welded, brazed or.

Additionally, chris adds that a nameplate should be attached on the motor with the data as well as in the standard repair report. Broken rotor bars precipitate deterioration in other components as well and can result in timeconsuming repairs and loss of motor efficiency. Here are some methods to help detect cracked or broken rotor bars. 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. Sidebands around electrical line frequency, spaced at the number of poles times the motors slip frequency, indicate a rotor bar defect. The online and offline analysis in our case studies use a battery of standard electrical tests including current signature analysis csa and. A power based fft algorithm provides the following benefits.

As a loose rotor bar passes a winding slot, the magnetic force causes it to momentarily lift and then drop. If the motor can run, the electrom itig surge tester is the quickest and simplest way to detect a rotor issue. Both ends near the brazing zones demonstrated upright throughthickness edgecracks running transversely across the bar, which can be observed in fig. After motor changing, there is no fp sideband appearing around 1x harmonic running speed. Before reading about these different tests, please check out our last few articled on electric motor theory and rotor bar cracks. Significant is the number of and size of the sidebands. Rotor bars were found cracked while thermal processing brazing or shrinkage fitting was attained. Furthermore, it explores nonconventional techniques, which can assist in detection of broken rotor bars.