91. Compare the per pole permeance of direct and quadrature of a salient pole synchronous machine
    

1. 1. Direct axis permeance is more than quadrature axis permeance

   
   
   

   2. Quadrature axis permeance is more than direct axis permeance

   
   
   

   3. Direct and quadrate axis permeances are equal

   
   
   

   4. Quadrature axis permanence is zero

   
   
   

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   NA

   Correct Option: A

   NA

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92. d = direct axis, q = quadrature axis, E_f = excitation emf. In a salient pole synchronous machine
    

1. 1. I_d and I_q are both in phase with E_f

   
   
   

   2. I_q is in phase with E_f and I_d at 90° to E_f

   
   
   

   3. I_q is at 90° to E_f and I_d is in phase with E_f

   
   
   

   4. I_d and I_q are at 90° to E_f

   
   
   

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   NA

   Correct Option: B

   NA

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93. In a cylindrical rotor synchronous machine, the phasor addition of startor and rotor mmf is possible because
    

1. 1. two mmfs are rotating in opposite direction

   
   
   

   2. two mmfs are rotating in same direction at different speeds

   
   
   

   3. two mmfs are stationary with respect to each other

   
   
   

   4. one mmf is stationary and the other mmf is rotating

   
   
   

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   NA

   Correct Option: C

   NA

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94. Fifth harmonic component of the induced voltage in 3-phase ac generator can be entirely eliminated by using a winding pitch of
    
    

1. 1. 2/3

   
   
   

   2. 4/5

   
   
   

   3. 5/6

   
   
   

   4. 6/7

   
   
   

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   Coil span factor for n_th harmonic,
   

   kc = cos	1	n∊
   	2

   
   where, ε is angle by which the coil is short of full pitch.
   

   ∴  kc = cos	1	× 5		1 −	4		π = 0
   	2				5

   
   Thus fifth harmonic component gets eliminated by using a coil pitch of 4/5.

   Correct Option: B

   Coil span factor for n_th harmonic,
   

   kc = cos	1	n∊
   	2

   
   where, ε is angle by which the coil is short of full pitch.
   

   ∴  kc = cos	1	× 5		1 −	4		π = 0
   	2				5

   
   Thus fifth harmonic component gets eliminated by using a coil pitch of 4/5.

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95. During a disturbance of a synchronous machine, the rotor swings from A to B before finally setting down to a steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point (s)
    

1. 1. A and B

   
   
   

   2. A and C

   
   
   

   3. B and C

   
   
   

   4. only at C

   
   
   

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   NA

   Correct Option: D

   NA

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