Free Charges and Bound Charges

Introduction

AC generator is a primary device for the production of alternating current AC. It works on the principles of Faraday’s law and electromagnetic induction. The phenomenon of electromagnetic induction has been technologically used in various forms, but the most important and widespread use of electromagnetic induction is that of the generation of alternating current. The modern AC generator with the typical output capacity of 100 MW is a highly evolved machine. This machine was invented by Nikola Tesla. 

Transformers are the devices that work on the principle of mutual induction and are responsible for the transformation of altering voltage from higher to lower or lower to higher values. 

AC Generator

An AC generator is used for the purpose of conversion of mechanical energy to electrical energy. This electrical energy is in the form of alternating current, which is stored in a load or directly used. Here we will discuss the function and the parts of an AC generator.

Working of an AC Generator

An AC generator works on the principle of Faraday’s law of electromagnetic induction, which states that the EMF or voltage is generated in a current-carrying conductor in the presence of a uniform magnetic field, this can be obtained either by rotating armature coil in a static magnetic field or by rotating the magnetic field around the stationary coil. The generated electromotive force (EMF) depends on the number of turns the armature coil has, the magnetic field strength and the speed of the rotating magnetic field. 

When the armature coil rotates between the poles of the magnet, the rotation is perpendicular to the magnetic field, this leads to a change in the magnetic flux linked to the armature. Due to the change in flux, the electric current flows through the Galvanometer (a device used to detect small magnitudes of current flowing through to a circuit, whereas the device used to detect larger magnitudes of current is called Ammeter) and the slip rings and brushes the movement in Galvanometer indicates the presence of current. 

When the coil is mechanically rotated in the magnetic field using external force, the rotation causes a change in magnetic flux through the coil. Hence, the electromagnetic force is induced in the coil. To make the rotation easier, the ends of the coil are connected to an external circuit by means of slip rings and brushes. 

The changing flux is represented by,

Φ(t)=B⋅A(t)=BAcos(ωt)

 Here,  

B=  magnetic field

A=  area of cross section

ω = angular speed of the coil

t=   time

Φ = Magnetic flux

 E= – N Δϕ/Δ(t)

E = Induced EMF

N=  number of turns in the rotating coil

E=−NBAωsin(ωt)

 The above equation represents the maximum value of EMF that can be produced in the generator.

Transformer

A transformer works on the principle of mutual induction and is responsible for the transformation or breaking of alternating voltage from one value to another. There are two types of transformers:

1. The step-up transformer is used to decrease the output current and the voltage.
2.  The step-down transformer is used to increase the output current and the voltage.

 In simple language, a transformer performs the function of controlling voltage and hence helps in the easy transmission of alternating current. The transformer was primarily pictured by Michael Faraday in 1831. 

Parts of Transformers

1. Core: This is the support to the transformer and is responsible for or providing a low reluctance path to the flow of magnetic flux. On this core, winding or coils of wire is done.

• The core is composed of soft iron for the sake of reduction of the losses.
•  The diameter of the core is proportional to the losses.

1. The primary and the secondary coil: The coils are wrapped around the core of the transformer, these coils are made up of copper to minimise the losses as copper is highly conductive. There are two types of coils:

•  Primary coil: In this coil, the input is given (Np= number of turns of the primary coil).
•  Secondary coil: The output is received in this coin (Ns= number of turns of the secondary coil).

1. Insulation: Insulation is important to separate the primary coil from the secondary coil and  so it’s mutual induction. The insulation can be provided by insulating oil, insulating tape, insulating paper or wood-based lamination.

Working of Transformers

A transformer works on the principle of Faraday’s law of electromagnetic induction and mutual induction. The two coils that are the primary coil and the secondary coil are separated by the laminating material and are found on the transformer core. 

 When an alternating current, AC, is passed through the primary coil, the input coil creates a change in magnetic flux. As stated by Faraday’s law of electromagnetic induction, the change in magnetic flux induces an EMF and an AC produced in the secondary output coil through the means of mutual induction. 

Ep = – Np dΦ/dt

Es = -Ns dΦ/dt

Ac voltage obtained across secondary  = Vs = Es = Ns

Ac voltage obtained across primary          Vp    Ep    Np

Vs = (Ns/ Np) Vp

Is = (Np/Ns) Ip

Where Vp is the Primary Voltage

Vs is the Secondary Voltage

Np is the Number of Primary coil

Ns is the Number of Secondary coil

Ep is EMF induced across primary coil

Es is EMF induced across secondary coil

Φ  is the Flux Linkage

Conclusion 

An AC generator converts mechanical energy into electrical energy, contrary to an electric motor, which converts electrical energy into mechanical energy. The former works on the principle of electromagnetic induction, whereas the latter works on the principle of a moving coil galvanometer that is armature when moves in a magnetic field exert a couple force on the armature because the armature rotates.

Transformer transfers electric energy from one alternating-current circuit to more circuits either by increasing or decreasing the voltage