1. The armature of DC machine is laminated in order to reduce
- hysteresis losses
- copper losses
- frictional losses
- eddy current losses
Answer: 4
2. The yoke of a DC machine is generally made of
- silicon steel
- cast steel
- soft iron
- cast steel
Answer: 4
3. If field current is decreased in shunt dc motor, the speed of the motor
- increases
- decreases
- remain same
- none of the above
Answer: 1
As a shunt field current If decreases, φ also decreases and the speed rises as speed is inversely proportional to flux
4. In Ward-Leonard system, the lower limit of the speed imposed by
- armature resistance
- field resistance
- residual magnetism of the generator
- none of the above
Answer: 3
In Ward-Leonard method of speed control, the lower limit of speed is imposed by residual magnetism of the generator.
Also Read
Resistance in series/parallel connection
5. Ward-Leonard control is basically a _________________________ control method.
- armature resistance control
- field control
- armature voltage control
- field diverter control
Answer: 3
Ward-Leonard speed control method consists a motor with a constant excitation and applying a variable voltage to its armature to provide the required speed. Hence it is armature voltage control method.
6. In a DC Machine, the current flow in a armature circuit is
- pulsating DC
- pure DC
- AC
- none of the above
Answer: 3
7. As the armature reaction effect increases, the main flux of DC machine is
- increases
- decreases
- remain same
- none of the above
Answer: 2
8. In DC machines, slot wedges are generally made of
- cotton
- fibre
- impregnated paper
- silicon steel
Answer: 2
9. Eddy current loss will depends on
- flux density
- frequency
- thickness
- all of the above
Answer: 4
10. Hysteresis loss will depends on
- f
- f²
- f³
- f1.6
Answer: 1
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