Electrical Machines Viva Questions and Answers: Part-1

Electrical Machines Viva Questions and Answers

[1] How to reverse the direction of rotation of dc motor?
To reverse direction of rotation of dc motor, either direction of main field produced by the field winding is reversed or direction of the current passing through the armature is reversed.
By changing the direction of current passing through the field winding,the direction of the main field can be reversed.

[2] What are the functions of yoke? what is the choice material for the yoke?

1. It serves the purpose of outer most cover of the dc machine. so that the insulating material get protected from the harmful atmospheric environmental like noise, dust and various gases like SO2, acidic fumes etc.
2. It provides mechanical support to the poles.
3. It forms a part of the magnetic circuit.
4. It provides a path of low reluctance for magnetic flux.
5. It is prepared by using cast iron. For large machines, rolled steel, cast steel, silicon steel is used which provides high permeability.

[3] Why generators are operated in parallel?

The generators are operated in parallel to get,

1. Continuity and reliability of service without interruption
2. Maintenance and repair will be easy
3. Efficient operation of each generator
4. Increase in plant capacity

[4] Why pole shoe has been given a specific shape?

• It is necessary that maximum area of the armature comes across the flux produced by the field winding. 
• Pole shoe enlarges the area of armature core to come across the flux, which is necessary to produce larger induced emf. To achieve this, pole shoe has been given a particular shape.

[5] What are the basic components required for generator action to exits?
A generating action requires following basic components to exits,

1. The conductor or a coil
2. The flux
3. The relative motion between conductor and flux

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