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                   B.Tech. DEGREE EXAMINATION
                                         ECE & EI
                                     III SEMESTER
                           ELECTRICAL MACHINES
                     (Effective ECE from the admitted batch 2007–08 onwards)
                      (Effective EI from the admitted batch 2008–09 onwards)

Time: 3 Hours                                                                   Max.Marks: 60
Instructions:      Each Unit carries 12 marks.
                   Answer all units choosing one question from each unit.
                   All parts of the unit must be answered in one place only.
                   Figures in the right hand margin indicate marks allotted.
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1. a) Derive the expression for induced emf in a DC generator                                     6
    b) A 6-pole dc generator has a lap-connected armature with 480
       conductors the resistance of the armature circuit is 0.02Ω.
       With an output current of 500A from the armature, the
       terminal voltage is 230V when the machine is driven at
       900 rpm. Calculate the useful flux per pole                                                6
2. a) What is the aim of Swinburne’s test? Write down the procedure
      to conduct the Swinburne’s test with a neat diagram           6
    b) A dc generator has an armature emf of 100V when the useful
       flux per pole is 20mwb and the speed is 800 rpm. Calculate the
       generated emf
       i) with the same flux and a speed of 1000 rpm
       ii) with a flux per pole of 24mwb and a speed of 900 rpm                                   6
3. a) Explain the constructional details of transformers                                          6
   b) A 230/110V 1- Transformer takes an input of 350 VA at no
      load and at rated voltage. The core loss is 110W. Find
      i) the iron-loss component of no-load current
      ii) the magnetizing component of no-load current and
      iii) no load power factor                                         6
4. a) Write short notes on Auto-Transformer                             6
   b) When a 100KVA, 1- Transformer was tested, the following
      results were obtained
      On open circuit the power consumed was 1300W and on short
      circuit at full-load current the power consumed was 1200W.
      Calculate the efficiency of Transformer on full load and ½
      full load when working at unity power factor                      6
5. a) Explain the constructional details of any one rotor of 3-
      induction motor                                                   6
   b) A 240V 3-phase 6-pole 50Hz Induction Motor consumes a
      power of 2KW at no load and at rated voltage and frequency.
      At full load ship of 3% the power input to the rotor is 50KW
      and the stator ohmic loss is 2.5KW. Neglect copper loss at no
      load. If the stator core loss and the mechanical losses are
      assumed equal, then at a ship of 3%, calculate
      i) rotor ohmic loss ii) shaft power                               6
6. a) Explain any one starting method of 3-phase Induction Motor        6
   b) The power input to the rotor of 220V, 50Hz, 3 phase, 6-pole
      Induction motor is 100KW. It is observed that rotor emf makes
      120 complete cycles per minute. Calculate (i) slip (ii) rotor
      speed (iii) mechanical power developed (iv) speed of the stator
      field w.r.t. the rotor                                            6
7. a) Explain main constructional features of cylindrical rotor type
      Alternator                                                        6
   b) A 4-pole AC machine has a 3-phase winding wound in 36 slots
      with nil span of 1400. Calculate i) Pitch factor
      ii) Distribution factor                                            6
8. 3-phase, 16-pole Alternator has a star connected winding with 144
   slots and 10 conductors per slot. The flux per pole is 30mwb,
   sinusoidally distributed and the speed is 375 rpm. The winding is
   chorded by one slot. Find the no load phase and line emfs.           12
9. a) Briefly explain the Double Revolving Field Theory                  6
   b) Write short notes on Split Phase 1- Induction Motor                6
10. a) Briefly explain capacitor run 1- Induction Motor                  6
   b) Briefly explain shaded pole 1- Induction Motor                     6

                                                             [4,6/III S/110]

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