Electrical Machines
For a 3 - Φ, 4 pole, 50 Hz IM rotating at full load speed of 1440 rpm, calculate speed of rotor field with respect to rotor structure and stator structure respectively?

 1440, 1500.
 60, 1440.
 50, 1500.
  60, 1500.

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Electrical Machines
Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

 1, 2, and 3
 1 and 3
 2, 3 and 4
 1, 2 and 4

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Electrical Machines
Torque angle of a synchorous machine operating from a constant voltage bus is usually defined as the space angle between

 Stator mmf wave and resultant flux density.
  Rotor mmf wave and stator mmf wave.
 Stator mmf wave and resultant mmf wave.
 Rotor mmf wave and resultant flux density wave.

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