SYNCHRONOUS RELUCTANCE MOTORS (SyRM)

SYNCHRONOUS RELUCTANCE MOTORS (SyRM)

Topics: Constructional features  - Types - Axial and Radial flux motors - operating principles -variable Reluctance motors  - Voltage  and  Torque  equations  -  phasor diagram  - performance  characteristics  -  Applications.

  CONSTRUCTION OF  SyRM :

     Discuss in detail about the construction and working of synchronous reluctance motor with neat diagram.                                                                             (8 Mark)    (Nov / Dec: 2017)
     Describe the constructional details and working principle of synchronous reluctance motor.
                                                                                                         (13 Mark) (Nov / Dec: 2018)
     Explain with neat diagram, the construction, working principle and types of synchronous reluctance motor                                                                       (16 Mark) (Nov / Dec: 2016)
1                                                                                                      (16 Mark) (Apr / May: 2018)                                          

The Synchronous reluctance motor (SyRM) consists of two main parts

     1. Stator                 2. Rotor 

STATOR:

  ü The stator has armature core, made up of ferromagnetic steel sheets.

      ü The core is laminated to minimize the eddy current loss.

  ü Semi-closed slots are provided along the inner periphery of the armature.

  ü The slot carries three-phase distributed type winding.

  ü The windings are wound for the required number of poles.
    
    

       ROTOR:

ü  In Sy R M the rotor should be constructed in such a way that, the inductance should be maximum along direct axis and minimum along the quadrature axis.

ü  Because, the developed reluctance torque is proportional to the  difference between direct axis Synchronous Inductance ( Lds)  and quadrature axis synchronous inductance (Lqs)

                                    i.e) difference between Lds & Lqs should be high as possible.

Classify the different types of synchronous reluctance motor. 

                                                                                                2 Mark: (Nov / Dec: 2017)

         For achieving maximum value of the difference, the different types of rotors are:

Ø  Segmental Rotor

Ø  Axially laminated Rotor

Ø  Radially laminated Rotor.

1  1.SEGMENTAL ROTOR:

ü  This structure is obtained by scooping out (remove (or) take away) iron material in the             quadrature axis

2. AXIALLY LAMINATED ROTOR:

ü  Here instead of scooping out the iron material in the quadrature axis, flux barriers consisting of thin sheets of non-magnetic material like brass or aluminium are introduced in the path of the quadrature axis flux.

ü  The d-axis flux moves smoothly and along the flux barriers.

ü  The q-axis flux flows across the barriers in the quadrature axis.

ü  So direct axis synchronous inductance (Lds) is not affect much. But the quadrature axis inductance is considerably reduced due to flux barriers.

ü  Thus higher (Ld – Lq) is obtained.

3. RADIALLY LAMINATED ROTOR:

ü  In radially laminated type, the assembled core is then put into liquid aluminium both under pressure.

ü  The constructional details of the radially laminated rotor for two-pole and four-pole motors are shown in fig.

WORKING OF SyRM:

ü  When a three-phase SyRM is supplied with three phase balanced voltage, the balanced three phase current flows through the windings. These current establishes sinusoidally varying magnetic field.

ü  This mmf is called Rotating Magnetic Field.

ü   The rotating field has a speed 120F/P  rpm. This is called synchronous speed.

ü  The stator poles induce opposite poles on the rotator (i.e..south pole on rotor part 1 and north pole on rotor part 2)

ü  So the rotor is attracted by stator poles. Hence, the rotor moves together with rotating magnetic field in the same direction.

ü  SyRM starts as an induction motor and reluctance pulls the rotor in synchronism with the stator field.

PHASOR DIAGRAM AND TORQUE EQUATION OF SyRM

            Draw the steady state phasor diagram of synchronous reluctance motor.

                                                                                                                   Mark: (Nov/Dec-2018)

            Draw and explain the speed-torque characteristics of synchronous reluctance motor.

                                                            16 Mark: (Apr/May-2018, Nov/Dec-2016, Nov/Dec-2017)

                     Explain the phasor diagram and characteristics of synchronous reluctance motor.

       

                   Draw the steady state phasor diagram of synchronous reluctance motor and derive the              expression for torque of synchronous reluctance motor.

           

           Draw and explain phasor diagram with characteristics of synchronous reluctance motor.

     Neglecting armature resistance, the phasor diagram is given by,

      From phasor diagram,

                                                                                                                                                           

   For understanding only,

       Torque – Angle characteristics:

              Draw the torque-angle characteristics of synchronous reluctance motor.

6                                                                                                              2 Mark: (Nov/Dec-2018)

        Torque – speed characteristics :

     Advantages of SyRM :

                 Mention any two advantage of synchronous reluctance motors.

                                                                                       2 Mark: (Apr/May-2019, Nov/Dec-2016)

v No electromagnetic losses.

v Mechanically strong.

v Cheaper than PM and conventional synchronous motor.

v Higher Efficiency.

v Reliable.

     Applications of SyRM:

                               Mention some applications of synchronous reluctance motor. 2 Mark: (Nov/Dec-2018)

  v Pumps, conveyers.

  v Wrapping and folding machines.

  v Postioning of control rods in nuclear reactors.

  v Synthetic fiber manufacturing companies.

                                                            Questions

      1.      Define ‘Reluctance torque’ with reference to synchronous reluctance motor.

2                                                         2 Mark: (Apr/may -2018, Nov/Dec-2016, Nov/Dec-2018)

         Ans:

                The tendency of the salient rotor poles to align them-selves with the synchronously rotating field produced by the stator (in the minimum reluctance position) is known as reluctance torque.

        

2                           

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