Number Of Rotor Slots Research Articles

Determination of rotor slot number of an induction motor using an external search coil

This paper describes determination of the number rotor slots of an induction motor from the induced emf in an external search coil. This information is needed in prediction of motor speed from the external search coil induced voltage. The approach is based on identifying saliency harmonics and rotor slot harmonics, via FFT analysis of the external search coil emf. The proposed approach is tested on an induction motor driven by the mains supply. The experiments are repeated with a PWM supply. It is shown that the method works well in both cases and the number of rotor slots of the test machine is accurately predicted. .

The impact of different stator and rotor slot number combinations on iron losses of a three-phase induction motor at no-load

The electromechanical characteristics of induction motors depend on the used stator and rotor slot combination. The correlation between the usage of different stator and rotor slot number combinations, magnetic flux density distributions, no-load iron losses and rated load winding over-temperatures for a specific induction motor is presented. The motor's magnetic field was analyzed by traces of the magnetic flux density vector, obtained by FEM. Post-processing of FE magnetic field solution was used for posterior iron loss calculation of the motor iron loss at no-load. The examined motor stator lamination had 36 semi-closed slots and the rotor laminations had 28, 33, 34, 44 and 46 semi-closed slots.

Experiments and Considerations Relating to the Loss Separation of a VR Vernier Motor

Recently, various types of vernier motor have been developed. The variable-reluctance vernier motor (VRVM) is a three-phase reluctance motor whose stator has slots and distributed three-phase windings. The rotor is a slotted iron core without windings. The relationship between S, R, and P is S = R ± P, where S and R are the numbers of stator and rotor slots and P is the number of poles. The rotor of the VRVM moves at a sub-multiple of the angular velocity of the stator mmf. The multiplying factor is P/R. The authors previously reported that a VRVM can be analyzed as a three-phase reluctance motor, and obtained the voltage equations on the γ−δ axis and an expression for the torque. However, the loss separation of a VRVM is not yet clear. In this paper, the iron loss of VRVM is analyzed by the finite element method and compared with experimental values.

Estimation of the number of rotor slots and rotor speed in induction motors using current, flux or vibration signature analysis

Effective condition monitoring of induction motors requires knowledge of the number of rotor slots and the rotor speed. These were primarily obtained in the literature by multiple measurements and using design knowledge of the motor under test. Furthermore, the earlier studies have mainly concentrated on stator current analysis. This paper investigates the use of the stator current, axial flux and vibration signals in order to provide accurate rotor speed and rotor slot number estimation by utilising the eccentricity harmonics, slip frequency, rotor frequency and rotor slot passing frequency. The proposed methods are examined using an extensive series of measurements on a 2.2 kW squirrel-cage and a 5 kW wound-rotor induction motor over a wide range of loading conditions.

Speed Estimation of Induction Motor Drive Using d-Axis Slot Harmonics and Parameter Identification Method

This paper describes a rotor speed estimation technique of an induction motor, which utilizes slot harmonics on the d-axis caused by permeance variation across the air gap. The frequency of the slot harmonics is a multiple of the actual rotor speed, and is proportional to the number of rotor slots. In order to extract the slot harmonics, a novel adaptive band-pass filter incorporating coordinate transformation is proposed, which is effective to estimate the rotor speed from 400 to 2000r/min. This rotor speed estimation is applied to a field-oriented controller as well as a speed controller. In addition, performance improvement is carried out by compensating a motor parameter mismatch. Feasibility of the proposed technique is confirmed through several tests, using a prototype experimental setup.

Losses, torques and magnetic noise in induction motors with static converter supply, taking multiple armature reaction and slot openings into account

A system of n complex equations, for which n=14, … , 30 suffices, is used to determine the n unknown stator—and rotor current harmonics for each of the given terminal voltage harmonics. Correct superposition of harmonics yields the air-gap field, losses, torque and radial force. As an illustrative example, the systems of simultaneous equations are solved for an eight-pole squirrel-cage motor with different numbers of rotor slots. Parasitic effects such as supplementary losses, synchronous torques, magnetic noise or line-current harmonics depend highly on the slot number difference Z1−Z2 and on winding connections. Owing to the voltage distortion of the static converter, copper losses increased by 61%. In the case of parallel winding branches, equalising currents with 511 Hz and 37% magnitude occurred, which increased the copper losses by 152%. With Δ-connected windings, circulating currents with a magnitude of 33% have been detected, thus increasing the losses by 21%. Rules to avoid these additional losses are given. Parasitic synchronous torques are increased and emerge at additional speeds. Asynchronous dips in the torque–speed curve because of voltage harmonics are of minor importance, even for large supply voltage harmonics. The accurate determination of radial force waves enables the prediction of core vibrations and the magnetic noise, even at resonance frequency. It has been found by experiments that sound radiation of an oscillating sphere or cylinder seem not to be equivalent to that of an induction motor.

Speed Sensorless Estimation of AC Induction Motors Using the Fast Orthogonal Search Algorithm

This paper presents a method of estimating the speed of an induction motor using a measurement of the stator current. Speed-induced current harmonics are identified in the stator current using the fast orthogonal search (FOS) algorithm. The frequencies of these estimated harmonics are in turn used to estimate the speed of the motor given the number of rotor slots in the motor. Several optimizations of the FOS algorithm are presented to allow for real-time performance on an embedded digital signal processor. Experimental results of speed estimates on a 1/4 horsepower motor are presented to verify this approach.

Rotor-position estimation for induction machines at zero and low frequency utilizing zero-sequence currents

This paper considers the position and speed estimation at low- and zero-frequency operations in standard delta-connected cage induction machines (IMs). A rotor-slot detection technique is used, where test vectors are injected during the pulsewidth-modulation (PWM) periods and the resulting zero-sequence-current derivatives (ZSCDs) are measured using a nonintegrating Rogowski coil. The rotor slotting in a near-standard 30-kW symmetric IM is utilized for rotor-position tracking. The rotor-slot number was selected to yield a measurable position-dependent ZSC. Experimental results show the variation of the measured current signals with rotor position and how these are used for tracking of the rotor position.

Analysis of HB Type Vernier Motor

Direct drive motors are used as actuators in numerous applications in which they must rotate at low speeds with high torque and low torque ripple. Recently, various types of vernier motor have been developed. The HB type vernier motor is one of them. The structure of rotor is the same as HB type stepping motor. Our model of HB type vernier motor has a winding as field system in the rotor, but stator has three-phase windings. Relationship between S, R and P is S ± P/2=R/2, where S, R and P are the numbers of stator and rotor slots and the number of poles. The rotor of the vernier motor moves at a sub-multiple of the angular velocity of the stator mmf. The multiplying factor is P/R.As a result of analysis, the voltage equation on the γ-δ axis of HB type vernier motor is equal to general synchronous machine. The tests were performed on the trial motor. The calculated pull-out torque agreed well with the measured values. Our model of HB type vernier motor is equivalent with the PM type vernier motor which has permanent magnets in the rotor. The result of this analysis is useful for the design of both types of vernier motor.

Asynchronous Torque Characteristics of VR Type Vernier Motor

Recently, various types of vernier motor are developed. The VR type vernier motor is a kind of three-phase reluctance motor, and its stator has slots and distributed three-phase windings. The rotor is slotted iron core without windings. Relationship between S, R and P is S = R±2, where S and R are the numbers of stator and rotor slots per pair of poles, and the number of poles P is two. The rotor of the vernier motor moves at a sub-multiple of the angular velocity of the stator mmf. The multiplying factor is P/R.Authors had reported that the VR type vernier motors are analyzed as a three-phase reluctance motor, and have obtained the voltage equations on the γ-δ axis and expression of the torque.However, the asynchronous characteristics of the vernier motor are not clear yet. In this paper, the asynchronous characteristics of the vernier motors are analyzed with the symmetric components transformation and the commutator transformation. The voltage equations on the symmetrical co-ordinates and asynchronous and synchronous torque expression at steady state condition are obtained.The tests were performed on the trial motor. The calculated asynchronous torque has agreed well with the measured values.

Pattern Recognition-A Technique for Induction Machines Rotor Broken Bar Detection

A pattern recognition technique based on the Bayes minimum error classifier is developed to detect broken rotor bar faults in induction motors at the steady state. The proposed algorithm uses only stator currents as input without the need for any other variables. First rotor speed is estimated from the stator currents, then appropriate features are extracted. The produced feature vector is normalized and fed to the trained classifier to see if the motor is healthy or has broken bar faults. Only a number of poles and rotor slots are needed as preknowledge information. Theoretical approach together with experimental results derived from a 3 hp ac induction motor show the strength of the proposed method. In order to cover many different motor load conditions data are obtained from 10% to 130% of the rated load for both a healthy induction motor and an induction motor with a rotor having four broken bars.

Detection of Rotor Slot and Other Eccentricity-Related Harmonics in a Three-Phase Induction Motor with Different Rotor Cages

Detection of rotor slot and other eccentricity-related harmonics in the line current of a three-phase induction motor is important both from the viewpoint of sensorless speed estimation as well as eccentricity-related fault detection. It is now clear that not all three-phase induction motors are capable of generating such harmonics in the line current, however. Recent research has shown that the presence of these harmonics is primarily dependent on the number of rotor slots and the number of fundamental pole pairs of the machine. While the number of fundamental pole pairs of a three-phase induction motor usually is within one to four (higher pole pairs are generally avoided due to increased magnetizing current), the number of rotor slots can vary widely. The present paper investigates this phenomenon further and obtains a hitherto nebulous theoretical basis for the experimentally verified results. Detailed coupled magnetic circuit simulation results are presented for a four-pole, three-phase induction motor with 44, 43, and 42 rotor slots under healthy, static, dynamic, and mixed eccentricity conditions. The simulation is flexible enough to accommodate other pole numbers also. These simulations are helpful in quantifying the predicted harmonics under different combinations of load, pole pair numbers, rotor slots, and eccentricity conditions, thus making the problem easier for drive designers or diagnostic tools developers. Data from three different induction machines-namely, a four-pole, 44-bar, 3H; a four-pole, 28-bar, 3HP; and a two-pole, 39-bar, 100 HP motor-have been used to verify the results experimentally.

The Effect of Rotor Design on Rotor Slot Harmonics in Induction Machines

This paper looks at the effect of different rotor designs on rotor slot harmonics (RSH) in induction-motor, line-current, spectra. The magnitude and the frequency of the rotor slotting harmonics for a number of different rotor designs have been obtained experimentally to identify which of the motor design parameters have significant effect on these harmonics. A computational model has also been developed using the mmf-permeance technique incorporating the effect of saturation, skew, slot-openings, static eccentricity, and the number of rotor slots on these harmonics. The model has been validated using the experimental data. This enables the effect of rotor design changes to be investigated over a wider range of variation than is possible experimentally. The model also facilitates an understanding of the reasons why design changes have the effect they have.

Analysis on Noise of Automotive Alternator Considering the Number of Stator Slots

Noise of automotive alternators can be classified into mechanical noise, aerodynamic noise and electro-magnetic noise. which is the same as for electric motors. Previous studies show that the elect ro-magnetic noise takes a maw peak at the rotating frequency multiplied by the number of stator slots. It has not been proved clearly so far, however, that the major peak is wholely due to the stator slots. On the contrary it is well known that noise of motors. which has a mechanism similar to the alternator except that the number of stator slots in automotive alternators is in gene\integer multiple of that of rotor segments, is closely related to the number of rotor slots. Therefore, the statement that only the stator slots is the source of the major peak in the noise spectrum of alternators is suspicious although not easy, to show theoretically, that the statement is incorrect. In this paper. effects of the stator slots on the noise in an automotive alternator are experimentally investigated by intentionally modifying the number of stator slots in such a way that the number of the states is not an integer multiples of the rotor slots. It is shown that both the stator slots are not so much influential as the rotor slots and claimed that the major peak in the noise spectrum of conventional alternators is due to superposition of a component caused by the stator and a higher harmonic component caused by the rotor

Reduction of electromagnetic force harmonics in asynchronous traction motor by adapting the rotor slot number

The harmonics in electromagnetic force are a source of mechanical vibration and audible noise in an asynchronous traction motor. This paper describes an approach to reduce the force harmonics by changing the rotor slot number. Both the radial and tangential forces acting on the stator teeth are calculated by Maxwell stress tensor and their time harmonics are examined by the discrete Fourier decomposition. As a result, the optimal slot number of the rotor to reduce or eliminate the specific force harmonics is determined.

COMPREHENSIVE METHOD FOR TRANSIENT MODELING OF SINGLE PHASE INDUCTION MOTORS INCLUDING THE SPACE HARMONICS

ABSTRACT In this paper a method which enables the simulation of single phase induction machines during transient as well as steady state is presented. The approach, based on the winding functions, makes no assumption as to the necessity for sinusoidal MMF and therefore include all space harmonics in the machine. The parameters of the model are directly calculated from the geometry and winding layout of the machine. The results are shown to be in good agreement with the solution obtained by a conventional d-q model for symmetric conditions. However, the developed method is then extended to include the effect of skewing of the rotor bars. Furthermore, the effect of stator and rotor slot numbers on the single phase induction motor start-up is explored.

Comparative assessment of the noise and vibration of centrifugal and induction pumps

case [21. Increasing requirements to lower the vibration and noise of production equipment dictate use of precision methods during fabrication; this significantly increases its cost. Conversion from the centrifugal to the induction scheme [3], which is an asynchronous electric motor with a liquid impeller enables us to eliminate the discrete components of pump vibrations. Such a pump (see Fig. 1) consists of stator 1 made of standard sheets; three-phase winding 2 is situated in the stator slots. Impeller 3 is built of slotless disks pressed onto shaft 4. The fluid flows along helical channel 5, and to protect it from the stator packet and impeller, the latter are enclosed with plastic or nonmagnetic high-resistance steel casings. The helical partition between individual spirals of the channel between inlet and outlet is made of a nonmagnetic low-resistance alloy. The fluid in the channel is placed in motion by pondermotive forces that develop due to interaction between the magnetic field of the stator and the eddy currents induced by the field. The pump is reversible; reversal is accomplished by reversing the ends of the winding. In the vibration spectrum of a pump fabricated in accordance with the scheme under consideration there are no discrete frequencies caused by rotor imbalance, nor blade frequencies of the impeller. Such harmonics as rotor and combination harmonics caused by a different number of stator and rotor slots are also absent. Only stator slot harmonics are retained; yes, and these may be significantly attenuated by use of a packet with closed slots. To lower nonslot harmonics of the motor, it is better to use sine windings [4], the most adaptable to production of which are shortened windings [5], although they are more sensitive to circuit asymmetry than the full windings. The magnetomotive force (MMF) of the full sine windings of each phase contain only basic and slot harmonics:

Comparison of two optimization techniques for the design of a three‐phase induction motor using three different objective functions

AbstractTwo optimization techniques, the simplex and Hooke‐Jeeves methods, are employed for optimum design of a 3.75 kW three‐phase induction motor. Three different objective functions, efficiency, cost and cost‐efficiency are used for this study. The obtained results are mainly compared in respect with their objective functions, but other design details have been also pointed out. Effects of stator‐ and rotor slot numbers and shape and the size of step in the search routine upon the optimum design are examined and discussed.

Effect of the stator slot opening on the electromagnetic vibration in a squirrel‐cage induction motor

AbstractField harmonics produce a radial electromagnetic force in a squirrel‐cage induction motor with a particular number of rotor slots corresponding to the number of poles. The radial force causes vibration and acoustic noise.In this paper, a simplified equation for the radial force at no‐load is introduced, and the relation between the width of the stator slot opening and the radial force is discussed quantitatively. The field harmonic component produced by the interaction between the fundamental magnetomotive force due to the stator current and the pulsation of air‐gap permeance dominates for the radial force.Furthermore, the vibration of the stator core due to the radial force is calculated under a simple assumption. The calculated results are verified by experiments.

Effect of the Stator Slot Opening on the Electromagnetic Vibration in a Squirrel-Cage Induction Motor.

The field harmonics produce a radial electromagnetic force in a squirrel-cage induction motor with a particular number of rotor slots corresponding the number of poles. The radial force causes vibration and acoustic noise.In this paper, a simplified equation for the radial force at no-load is introduced and the relation between the width of the stator slot opening and the radial force is discussed quantitatively. The field harmonic component produced by the interaction between the fundamental magnetomotive force due to the stator current and the pulsation of air gap permeance dominates for the radial force.Furthermore, the vibration of the stator core due to the radial force is calculated under a simple assumption. The calculated results are verified by experiments.