Pdf a new criterion for rotor broken bar fault diagnosis. Authority us united states prior art keywords rotor slots conductor bars conductor core prior art date. An electric motor consists of an iron rotor wheel mounted on a shaft, supported by bearings at each end, spinning within a multi-coil cage of wire called a stator. An electric motor be definition products magnetic flux. Using the proposed oxidation models, the rotor bar and end ring faults in progress can be. An electric motor is an electrical machine that converts electrical energy into mechanical energy. In some induction motors, what is called the deep bar effect, or distribution of rotor currents due to eddy currents, is taken advantage of. The current is induced in the rotor from the electrical field in the stator. Squirrel cage induction motors suffer from numerous faults, for example cracks in the rotor bars. When the rotor is stationary or turnin g slowly the frequency of rotor currents is relatively high, the currents crowd to the top of the rotor bar and the resistive part of impedance is relatively high. Ther away from the stator a rotor bar or part of a bar is. In case of fully closed slots the rotor bars are force fit into the slots from the sides of the rotor. Rotor for electric motor download pdf info publication number us2781465a. 750 Lessons in this case study include a demonstration that the load does not impact the relative relationship between peak voltage and current frequencies while tr ending a fault.
Of rotor bars x rotational frequency each of these frequencies is identified in the spectra shown in figures 8 and. 762 If the sidered as introducing an unbalance of problem can be simplified by neglect-3 fig. The rotor bars are placed in slots and at both ends of the rotor these bars are short circuited with a ring. Two manufacture technologies, nonmagnetic high-temperature resistant ceramic adhesive and electrical discharge machining edm, are applied to. When an electric motor starts, the rotating magnetic stator field is going to apply alternating forces very rapidly to each rotor bar and the forces diminish. Response modeling of the rotor bars is being used to guide the design of the slot pattern in the. An alternator rotor is made up of a wire coil enveloped around an iron core. For example, a 4-pole motor with 48 stator slots and 57 rotor bars could de-velop a cusp with only one open bar, whereas the same motor with 5 bars might not develop a cusp until 3 bars have failed. Current goes up and down, it creates a rotating field. Select specific electric loading ac ampere conductors per meter of air. The axial currents in the rotor bars will interact with the radial flux wave to produce the driving torque of the motor, which will act in the same direction as the rotating field, the rotor being dragged along by the field.
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. Angular speed of the stator magnetic motive force in electrical radians per second. Rotor bar width to depth geometry now depends on what torque-speed. Electric motor repair shops have been using techniques such as growler testing, single-phasing, infrared, vibration and/or dye testing as methods used through the repair process. Physics; 2018 1th international scientific conference on electric power. Single broken rotor bar during a medium voltage induction motor operation. Rotor bar 5 overload, locked rotor, vibration shaft/coupling 2 mechanical, overload unknown 10 no root cause determined. The 3-phase set of currents, each of equal magnitude and with a phase. In a spectrum of motor current, this modulation creates pole pass sidebands around the line frequency peak 60 hz in north america. The rotor bars in the figure are quite large and are placed near the surface of the rotor. Unfortunately, a failure in the squirrel-cage rotor bar is bound to happen. Motor phase a with respect to inverter dc-link middle-potential point. 1 and ieee, 5 percent of motor failures happen because of problems in the rotor cage 1. Any small unbalance in the magnetic or electric circuit of motors is reflected in the axially transmitted fluxes. 1faculty of electrical engineering, university of montenegro, 81000 podgorica. Other hand, if the rotor bars are placed deeper into the rotor surface, there will be more leakage and the rotor reactance x2 will be larger. 245 Damage to the rotor laminations is another defect that can be catastrophic to the motor. 2007 different procedures for diagnosis of rotor fault in closed loop induction motors drives. The rotor circuit is shorted and current flows in the rotor conductors.
The basic idea of an electric motor is to generate two magnetic fields: rotor magnetic field and stator magnetic field and make the stator field rotating. And at times, it would mean that its time for an electric motor overhauling to figure out what is the main reason behind the failure. Consideration of the equations representing the electrical supply circuit of the. Investigation of broken rotor bar faults in three-phase squirrel-cage induction motors 47 im s ii b n dn e 2blv2 l 2 60 1 where b im is the amplitude of the fundamental component and theith harmonic component,eiis the effective value of voltage induce d by the fundamental air-gap flux and the ith harmonic air-gap flux,dis the inner diameter of the stator core,nsis the. A torque spectrum showing slip frequency peak and two multiples is shown in figure 10. The rotor will induce currents, appearing as side bands around the 60 hz supply line frequency, back in. If the motor can be disassembled, the rotor bars can be counted. This is the same setup as used in a single-phase test. 887 It consists of a group of individual electro-magnets arranged in such a way that they form a hollow cylinder, with one pole of each magnet facing toward the center of the group. Types of induction motors, one with wound type rotor, also called slip-ring motor and another one with squirrel-cage rotor.
In motor electrical energy efficiency would save 20. 19 Loose rotor bars are a common failure mode of electric motors. About press copyright contact us creators advertise developers terms privacy policy. The rotor and stator are separated by an air gap which allows free rotation of the rotor. But, sideband frequency f rb of rotor bar didnt occur at this motor. We specialize in aluminum rotor casting using pure and alloyed aluminum. The studies 2 3 show that approximately -10 of induction motor failures are rotor-related. For example, figure 725ais a photograph of a rotor lamination showing the cross section of the bars in the rotor. Aeng006-4-1-electrical machines and drives induction motors school of engineering torque. For example, a 4-pole motor with 48 stator slots and 57 rotor bars could develop a cusp with only one open bar, whereas the same motor with 5 bars might not. The electrical effect of the broken or cracked rotor bar is an increase in the rotor circuit impedance and, therefore, the stator impedance as well. Rotor should maintain its balance indefinitely whereas a welded, brazed or wound cage.
820 During the operation of an induction motor, many types of faults can be avoided, involving electrical and mechanical faults. Induction motor for the healthy rotor, and broken bars. Stator failure when broken rotor bars can lift out of the rotor slot due to. This is called a cage induction motor or a squirrel cage motor. Of the rotor to the two sides of the coil, and the rate of change of magnetic a number of broken bars can be con- flux in the direction of the force. This invention relates to squirrel cage asynchronous motors. When this happens, the chances of rotor locking decreases and the motor runs much quieter. Resistance bars on the outer cage of a double cage rotor will affect the. Plant electric motors can be achieved by early detection of any developing. As the motor heats up, the copper bar expands more quickly than the steel laminations. Exists and the only indication you have is rotor bar pass frequency and a gut. Assuming a linear magnetic system, the electrical motor.
An induction motor or asynchronous motor is an ac electric motor in which the electric current in the rotor. Cracked rotor bars electric motor rotor repair2018-4-26. Offline detection of broken rotor bars in ac induction motors. Procedure for determining rotor bar count without motor disassembly 1. Rotor bar failures are not common in properly applied systems. While monitoring current, slowly increase voltage and slowly rotate the motor shaft until. Austin hughes, bill drury, in electric motors and drives fifth edition, 201. Clarkson university, on leave from the department of electrical engineering. Ikemi, development of high-power and high- efficiency motor for a newly developed electric vehicle, sae. 5 One of the most difficult motor faults to diagnose accurately in the ac induction motor is the broken rotor bar fault.
Key words: induction motor, copper rotor bars, efficiency, losses, energy saving. Surveys by the electric power research institute epri see. Merely of a number of bars imbedded in the rotor slots and connected at both ends by means of end rings. The stator is in the stationary electrical component. The flux generates a magnetic field in the air gap between the stator and the rotor and induces a voltage which produces current through the rotor bars. Safety how youtube works test new features press copyright contact us creators. Pdf detection of broken rotor bar faults and effects of. The rotor is the most stressed component of a three phase ac induction motor. Depending on the mechanical and electrical properties desired, rotor bars may be made of. This manual covers squirrel cage rotor motor where the rotor consists of a set of non-insulated bars that are interconnected by short-circuiting rings. We custom manufacture cast rotors and bar rotors that are designed to be high-performance, precision motion control components. President success by design rotor testing evaluating the condition of electric motor rotors is not a new concept. St ator l minations stator laminations are c5 rated and are accurately. 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 action of the rotating flux and the current produces a force that generates a torque to start the motor. To improve process reliability in critical motor applications, new on-line predictive diagnostic tools for broken rotor bar detection on large ac motors are. We note that slip is essential to this mechanism, so that it is never possible for the rotor to catch-up with the field, as there would then be no rotor. 678
The fundamentals of ac electric induction motor design and application by edward j. Abstract three phase squirrel cage induction motors. Electrical conductivity: in an induction motor, the higher the electrical conductivity of the rotor, the greater the efficiency of the motor under normal. Electric motors to match the actual demand of the application thereby reducing motor energy consumption by typically 20 to 50 percent. The broken-rotor-bar single-phase electrical model of an induction motor. Designing for many rotor bars also decreases harmonics in the rotor air gap flux density distribution, but can cause saturation in the rotor teeth and can. In this paper the rotor bar fault diagnosis problem for a particular. 580 The repairers of electric induction motors must note. Scim are continuously subjected to electrical, thermal, mechanical and environmental stresses in any. Typical induction motor rotors the magnetic field generated in the stator induces an emf in the rotor bars.
A defect in the rotor bar of an induction motor causes the modulation of the stator current. Electrical conductivity: in an induction motor, the higher the electrical conductivity of the rotor, the greater. The cage does not need to be insulated from the rotor iron. The left sideband 1-2nsf is due to electrical or magnetic rotor asymmetry caused by broken rotor bars. Electrical motors work, and by simplifying the explanations to suit the intended. The most accurate and reliable test for cracked rotor bars would be the induction motor current analysis, also known as the current spectrum test. 806 Simple diagnostic methods for detecting damaged rotor. Google has not performed a legal analysis and makes no representation as to. As electric motors use a major fraction of industrial energy. Rotor bar frequency calculation rotor bars in electric motor broken rotor bar detection.
The rotor will constantly be turning to align its magnetic field with that of the stator field. Although unknown rotor bars data, it is possible to find the rotor bar frequency. Uncouple the motor from the load so the shaft turns freely. Most electric motors operate through the interaction between the motors magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motors shaft. Rotor eccentricities 14,15, and rotor electrical asymmetry due to broken rotor bars brb or end-ring segments 16,17. For an induction motor, torque is also proportional to the product of flux per stator pole and the rotor current. In which the conductors do not fill the slots completely, may lose its balance in time. , cmrp success by design reliability services hello and. Cage induction motors sponsored by epri and performed by general electric. Replace 40hp, 15 year old motors instead of rewinding. A rotor assembly is provided in which a solid rotor ring is formed at either end of a stack of laminated discs, the solid rotor rings yielding improved electrical and mechanical characteristics in a low weight assembly. 198 Different rotor bars type, lower in iron loss, total loss and. Motor torque, load torque and selection of motors contents 2. Measurements of stator voltage, stator current, stator excitation to be specific about failure monitoring, this paper studies frequency, and rotor velocity are taken over a small range of the detection of broken rotor bars in induction motors. Motors, the electric power is conducted directly to the armature i. Thermal expansion the laminations are made of steel, while the rotor bar is made of copper. Electric motors can be powered by direct current dc sources, such as from batteries, or rectifiers.
For larger motors, the squirrel cage is made of copper, aluminum, or brass bars welded or brazed to end rings of a similar material. In this case st udy a 400 0 hp motor without starting restrictions is followed through to rotor bar failure. This type of design is called the national electrical manufacturers association. Motors, the rotor does not receive electric power by. 711 Broken rotor bars can lead to catastrophic and severe damage to a 41 bearing-related 37 stator-related 10 rotor-related 12 other. Offers high-performance squirrel cage rotor castings available as raw castings or machined on a shaft. To detector is evaluated experimentally using one stator and three rotors from. Use a variac to apply voltage to a single phase of the motor. Legal status the legal status is an assumption and is not a legal conclusion. An ac motor has two basic electrical parts: a stator and a rotor as shown in figure 8. Polyphase motors have rotor bars shaped to give different speed-torque. A defect in the rotor bar of an induction motor causes the. And power and are used to detect broken rotor bars, bearing. Test results of induction motor broken rotor bar fault. In turn, a current is produced in the rotor bars and shorting ring and another magnetic field is. To detect broken rotor bars, spirit to that discussed in 5. Its change in dimension is primarily lengthwise and will cause movement of the ends of the bar in the slots.
Teco-westinghouse motor company synchronous machines. This current circulates in the bars of the rotor and the magnetic field generated by it reacts with the stators field. During the start-up process, the outer most section of many rotor bar designs can heat up as much as 300. Abstract to analyze the performance of electrical machines, theory of reference have been effectively used. Rotor amortisseur windings are fabricated copper or copper alloy bars brazed to copper resistance ring segments. The rotor consists of a series of bars which are welded together at either end. Rotor bars and slots are sized to assure tight bar construction, thus eliminating bar vibration. The motor is subjected to will manifest itself as an electrical signal in. Evaluating induction motor rotor bars with electrical signature analysis howard w penrose, ph. In this test, the motor is placed under 50 - 100 load. Motor current signature analysis defective rotor bar problem modulation of the electrical line current occurs in an ac induction motor with a defective rotor bar. In order to improve the starting performance of squirrel-cage induction motors, the so-called skin effect becomes very serious, which causes a highly uneven distribution of rotor-bar currents. 163 For the energisation of induction motor im, the constant frequency supplies or adjustable speed ac drives are mostly preferred.