Generators and Transformers

What is Generator?

A generator is a mechanical equipment which converts mechanical form of energy into electrical energy. Generators find application in agricultural and industrial production. The most widely used principle for the construction of generator is based on the law of electromagnetic force.

What is the Working Principle of Generator?

It consists of a rectangular coil with a number of copper wires wound over an iron core. The coil is called the armature. It is used to increase the magnetic flux. A strong permanent magnet is placed and the armature is rotated between the magnets where the magnetic lines are perpendicular to the axis of the armature. There are two slip rings connected to the arms of the armature. They are used to provide movable contact. Two metallic brushes are connected to the slip rings to pass current from the armature to the slip rings. The current is passed through a load resistance, which is connected across the slip rings.

Working Principle of Generator

At different time intervals, the position of the armature keeps changing. When the magnetic field lines are perpendicular to the coil, the coil is rotated in the magnetic field and the induced e.m.f produced increases. This happens in this position because of the number of intercepting magnetic field lines maximum.

What are the Types of Generators?

Following are the types of generators:

AC Generators

What are AC generators?

AC generators are also known as alternators which converts mechanical energy into electrical energy in the form of alternating current. Kilo volt-amperes is the unit used for rating AC generator.

What is the Working Principle of AC Generator?

The working principle of AC generator is based on the electromagnetic induction. The armature rotates between the poles of the magnet which is perpendicular to the magnetic field. As there is a changed in the flux produced by the armature, emf is induced producing electric current with the help of galvanometer, slip rings, and brushes. The flow of alternating current through the galvanometer can be observed when the galvanometer oscillates between positive and negative poles.

What are the Types of AC Generators?

There are two types of AC generators:

  • Synchronous generators
  • Induction generators

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What are the Advantages of AC Generators?

Advantages of AC generators are:

  • The time spent on maintenance is very less as there are no brushes.
  • When compared to DC generator, the size of A generators are small.
  • Minimal amount of losses are there.
  • The breakers used are relatively smaller when compared to DC generators.

FAQs on AC Generator

Q1. What happens when the number of turns are increased in AC generator?
Ans: As the number of turns increase, emf will also increase for AC generator.

Q2. Name the parameter on which the emf of AC generator depends.
Ans: Emf of AC generator depends on the length of the rotating wire.

Q3. What is the use of armature in AC generator?
Ans: Armature is used for producing output voltage.

DC Generator

What is DC generator?

A DC generator is used for converting mechanical energy onto direct current electricity.

What is the Working Principle of DC Generator?

The working principle of DC generator is based on Faraday’s laws of electromagnetic induction. When a conductor is placed in the varying field, an emf is induced in the conductor. The magnitude of the emf induced can be calculated with the help of emf equation of DC generator. The circulation of induced current takes place within the closed path. With the help of Fleming’s right hand rule, the direction of induced current can be determined.

Emf equation of DC generator is given as:

\(Eg=\frac{P\phi NZ}{60A}\)

Where,

  • P is the number of field poles
  • Φ is the flux produced per pole in Weber
  • Z is the total number of armature conductors
  • A is the number of parallel paths in armature
  • N is the rotational speed of the armature in rpm

What are the Types of DC Generators?

Following are the types of SC generators:

  • Permanent magnet DC generator
  • Separately excited DC generator
  • Self excited Dc generator
    • Series wound generator
    • Shunt wound generator
    • Compound wound generator

What are the Advantages of DC Generators?

Following are the advantages of DC generator:

  • Cable cost will be less as there is no shielding from radiation.
  • The fluctuations in the generator can be reduced by constant arrangement the coils.
  • The operating characteristics of DC generator depends on the field winding.

FAQs on DC Generator

Q1. When can two DC generators can be operated simultaneously?
Ans: When the dropping voltage characteristics of both the DC generators are same then the two Dc generators can be operated simultaneously.

Q2. What is the use of lap winding in DC generator?
Ans: Lap winding is used for maintaining low voltage and high current in DC generator.

Q3. Define critical resistance in DC generator.
Ans: Critical resistance is defined as the resistance offered by the field.

What is a Transformer?

You must have heard about transformers, do you know what is the main purpose of a transformer?
Transformers are used for the transmission of electrical energy. A transformer works on the principle of mutual induction. At a different voltage level, transformers can change the electrical energy of a given voltage.

Working Principle of Transformers

It consists of two coils named as Primary coil and a Secondary coil which is wound on a soft iron core. The soft iron core is laminated to minimize eddy currents. The alternating current is applied across the primary coil and the output is obtained across the secondary coil.

What are the Types of Transformers?

There are two types of transformers:

  • Step-up Transformer
  • Step-down Transformer

Step-up transformer converts a low voltage into a high voltage. The number of turns in the primary coil is less than the number of turns in the secondary coil, i.e. \(N_p~<~N_s\). Step-down Transformer converts a high voltage when current decreases into a low voltage when current increases. The number of turns in the primary coil is greater than the number of turns in the secondary coil, i.e. \(N_p~>~ N_s\).

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According to Faraday’s law of electromagnetic induction, the induced e.m.f is given by:

\(e\) = \(-\frac{dϕ}{dt}\)
\(e_p\) = \(-\frac{dϕ_p}{dt}\)
\(e_s\) = \(-\frac{dϕ_s}{dt}\)

By using the above equations, we get,

\(e_s\) = \({N_s}{N_p}~e_p\)

The ratio \({N_s}{N_p}\) = \(k\)

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