01․ Commutator pitches of duplex and simplex lap windings are respectively
Commutator pitches of duplex winding is 2 and Commutator pitches of simplex winding is 1. It is defined as the distance between two ends of same armature coil are connected. So, difference in duplex winding are 2 as there are two turns in the duplex winding.
02․ The emf induced in the dc generator armature winding is
The emf induced in the dc generator armature winding is AC, but we need DC current from DC generator, so to convert this AC current to DC current mechanical rectifier called as commutator is used.
03․ Commutator in DC generator is used for
Commutator is used as mechanical rectifier in DC machines. It converts AC armature current in to DC current.
04․ A DC generator without commutator is a
Commutator is used to convert AC current into DC current. If commutator is not present, then it will acts as an AC generator with huge losses.
05․ In DC machine yoke offers
In case of DC machines yoke is used to
- Mechanical protection to the machine
- Flux path completion.
06․ In a dc machine 72 number of coils are used. Find the number of commutator segments required?
In DC machines, Number of coils = Number of commutator segments
07․ In DC generators brushes are used for
In case of DC generator the brushes need to collect current with minimum sparking, which is known as successful commutation.
08․ which of the following type of brush and their application is/are correct
These are the different applications for different types of brushes in DC machines.
09․ Which of the following bearings and their uses are correct
These are different applications of different bearings. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, as contact area is very small, so if the ball bearing is overloaded, the balls can deform or squish the running bearing. So it has to be used for small rating machines.
Since the roller is a cylinder, so the contact between the inner and outer race is not a point but a line. This spreads the load over more area, allowing the bearing to handle much greater loads than ball bearings. Hence it is used for large machines.
10․ Which of the following windings are necessary in case of all dc machines?
In case of all DC machines we must use closed winding. Lap and wave windings are used based on the requirement of voltage and current levels, but winding of all DC machines is closed winding. It is never short pitched.
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