Interview Questions - Electrical Machines

State the Faraday’s law of electromagnetic induction.
Faraday’s Law of electromagnetic induction states that whenever a current carrying conductor cuts the
magnetic flux, a dynamically induced emf gets generated in the conductor.

How are DC machines classified? 
The DC machines are classified as DC motor and DC generator.

What is the function of a DC generator?
The DC generator is a dynamic DC machine which generates electrical energy from mechanical energy
using Faraday’s law of electromagnetic induction.

State the functions of commutator or specify the role of commutator in DC generator.
The functions of commutator are:
(i) Through the brushes, it provides a connection between the rotating armature conductor and stationary
external circuit.
(ii) The alternating current induced in the armature conductor is converted into unidirectional current
in a DC generator.

Mention the types of excitation in DC machine. Or What are the different methods of excitation
of generator? 
The different methods of excitation of DC generator are: (i) Self excitation and (ii) Separate excitation.

What is self excited generator? How does it get excited?
If a separate DC source is not required for excitation, it is called self excited generator. Here, the required power for exciting the field winding is obtained from the power developed in the armature of
the DC generator.

State the emf equation of a DC machine stating the meaning of each term.
The emf equation of a DC machine is ⲫZNP/60A
where ⲫ is the flux per pole, Z is the number of armature conductors, N is the speed of the machine
in rpm, P is the number of poles in the machine and A is the number of parallel paths.

What is stepper motor?
A stepper motor is a special type of synchronous motor designed to rotate through a specific angle for
each applied electrical pulse.

What are the different types of stepper motor?
The different types of stepper are variable reluctance, permanent magnet and hybrid stepper motor.

List the applications of stepper motor.
The stepper motors are used in
  • Computer peripherals like printer, disk drive etc., X-Y plotter, scientific instrument and machine tool
  • Quartz-crystal watch
  • Many supporting roles in the manufacture of packaged foodstuff, commercial end product and even in the production of science fiction movies

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