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Subject Name:EE1001 - SPECIAL ELECTRICAL MACHINESUnit - 1

1. What is a Synchrono us Reluctance Motor?

It is the motor driven by reluctance torque which is produced due to tendency of the salient pole rotor poles alignthemselves with synchronously rotating field produced by stator.

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2. What are the types of synch. Reluctance Motor?

Cageless, Line-start, radial type and axial typeEditCommentAdd to print

3. State the pr inciple of o perat ion of Sync h. Reluctance Motor .

When a piece of magnetic material is located in a magnetic field, a force acts on the material tending to bring itinto the most dense portion of the field. The force tends to align the specimen of material in such a way that thereluctance of the magnetic path that lies through the material will be minimum.Edit

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4. State any advantages o f Synch . Reluctance Motor .

Can operate from PWM A.C.InvertersLower torque rippleSimple and rugged constructionHigh speed capabilityEditCommentAdd to print

5. Wri te any fou r appl icat ion of Synch. Reluctance Motor

Recording instruments, timing devices, in spinning mills, film material making and fibre manufacturing equipmentEdit

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6. Define torq ue angle.

When load is increased lightly, the rotor momentarily slows down, causing the rotor to lag the rotating field. Thisangle is called torque angle.EditCommentAdd to print

7. What is Vernier Motor?

A Vernier Motor is an unexcited reluctance type Synchronous motor which has the feature of high torque at lowspeed. This feature is based on the principle of vernier or magnetic gearing such that a small displacement of therotor produces a large displacement of axes of maximum and minimum permeance.Edit

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8. Define reluctance torq ue.

In synchronous reluctance motor, the torque which is produced at critical speed due to the tendency of the salientrotor poles to align themselves with synchronously rotating field produced by stator is known as reluctancetorque.EditCommentAdd to print

9. What is meant by f lux concentrat ing and flux focusing ?

In a 6 pole magnetized synch. Rel. Motor, the design is such that the magnet pole area exceeds the pole area atthe air gap producing an air gap flux density higher than that in the magnet. This arrangement is known as fluxconcentrating and flux focusingEditComment
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10. What are the factors to be considered w hi le designing a verneier motor?

Air gap permeance should have same number of stator polesNumber of stator and rotor slots should be such that N1=N2+PEditComment

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11. What are the appl icat ions of Vernier mo tor?

Direct drive applications, high torque at low speed applicationEditCommentAdd to print

12. When does a PM Synchron ous mo tor operates as a Synch ronou s Reluctance moto r?

If the cage winding is included in the rotor and the magnets are left out or demagnetized, PM Synchronous motoroperates as a Synchronous Reluctance motor

Subject Name:EE1001 - SPECIAL ELECTRICAL MACHINESUnit - 2

1. What is a stepper motor?

A stepper motor can be consider as a digital electromechanical device where each step command pulse(electrical pulse) input results in a movement of the shaft by a discrete angle called step angle of the motor. So instepper motor, the input is in the form of programmed energization of the stator winding and the output is thediscrete angular rotation.EditCommentAdd to print

2. Name the di f ferent types o f stepper m otor .

1. Variable reluctance stepper motor2. Permanent magnet stepper motor3. Hybrid stepper motor.EditCommentAdd to print

3. Define slewin g.

The stepper motor may be operated at very high stepping rates i.e., 25000 steps per second. The operation ofstepper motor at high speeds is called slewing.EditCommentAdd to print

4. What is a slewing rate?The maximum rate at which the motor can step unidirectionally is called slewing rate.EditCommentAdd to print

5. What is synchronis m in stepper motor /

It is the one- to-one correspondence between the numbers of pulses applied to the stepper motor controller andthe number of steps through which the motor has actually moved. i.e., The output shaft rotates such that one stepbeing taken each time a command pulse is received.EditCommentAdd to print

6. What is var iable reluctance stepper m otor?

The stepper motor in which the reluctance of the magnetic circuit formed by the rotor and stator teeth varies withthe angular position of the rotor is known as variable reluctance (VR) stepper motor The direction of rotation ofthe VR stepper motor. is independent of the polarity of the stator current.
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7. What is Permanent Magnet Stepper Motor?

The stepper motor in which the rotor poles are permanently magnetized is known as Permanent magnet StepperMotor.


8. What is Hybr id Stepper Motor?

The stepper motor which combines the feature of both variable reluctance and permanent magnet steppermotors is known as hybrid stepper motor.EditCommentAdd to print

9. What is meant by micro stepping in stepper moto r?

The mode of operation of the variable reluctance stepper motor in which the step angle is very small is known asmicro stepping. It is also called as mini stepping.Edit

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10. What are the di f ferent types of d r ive circui ts for stepper mo tor?

Resistance driveDual voltage driveChopper drive

11. What is meant by power dri ving circui t?

The output from the logic sequence generator signals are the low level signals which are too

weak to energise stepper motor windings. The circuit using power semiconductor switching

devices in order to increase the voltage, current and power levels of the logic sequence output

is known as power drive circuit.

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12. What is logic sequencer?

The logic sequencer generates the programmed logic sequences required for the operation of

stepper motor.

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13. What i s lead angle?The angle of difference between the phase to be de energized to bring the stepper motor to

the position of equilibrium and energisation of next phase winding to start the motor during

closed loop operation is known as lead angle. The relation between the rotor's present

position and the phase to be excited is specified in terms of lead angle.

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Unit - 3
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1. What is a Switched Reluctance Motor?

It is electromagnetic and electrodynamic equipment that converts electrical energy into mechanical energy. Theelectromagnetic torque is developed in SRM due to variable reluctance principle.EditCommentAdd to print

2. State the pr inciple of o perat ion of Switch ed Reluctance Motor .It develops an electromagnetic torque due to variable reluctance principle. When air gap is minimum, thereluctance will be minimum. Hence inductance will be maximum. So the rate change of inductance is zero. Whenthe reluctance varies, there will be a change in inductance. So when a particular stator winding of SRM is excited,the rotor pole comes in alignment with that stator pole and thus the rotor rotates.EditCommentAdd to print

3. What is rotor posi t ion sensor?

The motor shaft of SRM carries a rotor position sensor that gives the information about the position of the rotorwith reference to the reference axis to the controller. The controller compares the 8information from the rotorposition sensor with the reference speed signal and then suitably turns on and off the concerned powersemiconductor device of the switching circuit such that the desired phase winding is connected to the d.c.supply.Edit

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4. What is the need for s haft posi t ion s ensor fro SRM?

For commutation (i.e.) the turning on and turning off of various semiconductor devices in the switching circuitry isinfluenced by the signals obtained from the rotor position sensor. For speed control of the motor, it is necessaryto use the rotor position sensor.EditCommentAdd to print

5. Speci fy the funct ion of control ler circui t in SRM.

The controllers gets the signal from the rotor position sensor, reference speed signal and signal from the outputof power semiconductor circuit and then suitably turns on and turns off the concerned phase winding of the SRM.Edit

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6. Write down the instantaneous torq ue equation of SRM.

= change in Instantaneous inductance with respect to change in rotor position sensorEditCommentAdd to print

7. State the need for no n- l inear analysis of s witched reluctance m otor .

Machine with linear magnetic characteristics means that it has constant magnetic permeability and no magneticsaturation. In practice, the switched reluctance motor which follows variable reluctance principle operates with itsmagnetic material in saturation. As saturation tends to increase the size of the variable reluctance machines for agiven output, the non-linear analysis is required.EditCommentAdd to print

8. Define energy ratio in SRM.

Energy ratio is defined as the ratio of mechanical energy transferred to the sum of mechanical energy transferredto the sum of mechanical energy transferred and the stored energy.EditCommentAdd to print

9. What are the two typ es of current con trol techniques?

Hysterisis type current controlVoltage-PWM type current controlEditCommentAdd to print
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10. What is m eant by dwel l in SRM?

Dwell means conduction period.

Unit - 4

1. What is Bru shless PM D.C.Motor?

It is similar to salient pole D.C.Motor except that there is no field winding on rotor and is provided by PM. It

reduces losses. Complexity in construction is reduced.EditCommentAdd to print

2. Give the meri ts of PMBLDC Motor com pared to conv ent ional motor .

No field winding no field copper lossHigher efficiencySize is smallPossible for very high speedEditCommentAdd to print

3. What are the types o f PMBLDC squ are wave D.C.Motor?

1800 pole arc PMBLDC square wave1200 pole arc PMBLDC square waveEditCommentAdd to print

4. State the pr incip le of op erat ion of PMBLDC.

When D.C. supply is given to the motor, the armature winding draws current. This current sets up an emf which isperpendicular the main MMF set up by the PM field. Hence a force is experienced by the armature conductorsaccording to Flemming's left hand rule. As it is in the rotor, a reactive force develops a torque in the rotor. If thisdeveloped torque is more than the load torque and frictional torque, the motor start rotating.EditCommentAdd to print

5. Define magnetic rem anence.The magnetic flux density which persists in magnetic materials even though the magnetizing forces arecompletely removed.EditCommentAdd to print

6. Define coerciv ity forc es.

The demagnetizing force which is necessary to neutralize completely the magnetism in an electromagnet afterthe magnetizing force becomes zero.EditCommentAdd to print

7. How the PMBLDC Motors are classi f ied?

BLPM square wave motorBLPM sine wave motorEditCommentAdd to print

8. Define energy prod uct and maxim um energy pro duct of Permanent Magnet.

The absolute value of product of flux density and field intensity at each point along the demagnetization curve iscalled energy product.EditCommentAdd to print

9. When does the demagnetizat ion occur in PMBLDC Motor?

During normal operation of motor when the torque and back emf are constant, if the field flux level becomes low,

then demagnetizing occurs.EditComment
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