1. Diverters are used only in
(A) shunt motors
(B) series motors
(C) either of these
(D) none of the above
Ans: (B) series motors
Explanation:
Diverters are used only in series motors for speed control, these are not used in shunt motors. Since, shunt field winding resistance is very high, if we connect a diverter across shunt field winding, total current will flow through the diverter and almost short circuit the shunt field winding. This will increase the motor speed to a very high value. Therefore diverters are not used in shunt motors.
2. Which of the following starter is sufficient to start the DC series motor ?
(A) 3 point starter
(B) 4 point starter
(C) 2 point starter
(D) all of the above
Ans: (C) 2 point starter
Explanation:
3. Total core loss is also called as -------------?
(A) Eddy current loss
(B) Hysteresis loss
(C) Magnetic loss
(D) Copper loss
Ans: (C) Magnetic loss
Explanation:
As iron loss is proportional to flux density or flux, it is also called magnetic loss. The total core loss or magnetic loss consists of eddy current loss and hysteresis loss.
4. Maximum efficiency will occur, when copper loss is_______to iron loss?
(A) greater than
(B) less than
(C) equal to
(D) any of the above
Ans:(C) equal to
Explanation:
Condition for maximum efficiency is, copper loss = iron loss or variable losses is equal to fixed losses.
5. A DC series motor is accidentally connected to single-phase ac supply voltage. The torque produced will be
(A) pulsating and unidirectional
(B) steady and unidirectional
(C) oscillating
(D) none of the above
Ans: (A) pulsating and unidirectional
Explanation:
In DC series motor, the AC currents through the field and armature winding will be unidirectional by commutator and brushes. So torque will be unidirectional but pulsating due to AC.