AC generator and transformer

An AC generator is a primary device for producing 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 critical and comprehensive use of electromagnetic induction is the generation of alternating current. Initially invented by Nikola Tesla, the modern AC generator with the typical output capacity of 100 MW is a highly evolved machine. 

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 to convert mechanical energy to electrical energy. This electrical energy is in alternating current, stored in a load, or directly used. Here we will discuss AC Generator parts and functions.

PARTS OF THE AC GENERATOR

An AC generator consists of the following parts-

• A pair of strong magnets, with a North and South Pole

• The magnetic field produces a magnetic flux which is changed by the moving armature coil
•  The moving armature coil leads to voltage, called AC voltage

•  An armature coil

• In this coil, the voltage is produced
• The coil consists of wires having N number of turns

• Two slip rings and two carbon brushes

• The slip rings are electrical connections responsible for or transferring the power to and fro from the rotor of an AC generator.

•  A load or a battery to store the produced alternating current

•  Rotor and Prime mover

• Prime mover is the energy source used to move the armature coil mechanically
• The rotating component of the AC generator is called the rotor

WORKING OF 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 in a static magnetic field or by rotating the magnetic field around the stationary coil. The generated EMF electromagnetic force 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 of which is perpendicular to the magnetic field,  it changes the magnetic flux linked to the armature. Because of the change in flux of the electric current, which flows through the Galvanometer, slip rings, and brushes, the movement in the Galvanometer indicates the presence of current. 

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

E = Induced EMF

N= number of turns in the rotating coil

E=−NBAωsin(ωt)

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

TRANSFORMER- 

A transformer works on mutual induction and is responsible for transforming alternating voltage from one value to another. There are two types of transformers – The step-up transformer, which decreases the output current, and the step-down transformer, which increases the output current.

To put it simply, the transformer performs the function of controlling voltage and hence helps in the easy transmission of alternating current. Michael Faraday primarily pictured the transformer in 1831. 

PARTS OF TRANSFORMERS 

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 off 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

The primary and the secondary coil- The coils are wrapped around the transformer’s core. These coils are made up of copper to minimise the losses since copper is highly conductive. There are two types of coils-

• Primary coil: Denoted by NP (number of turns essentials of the primary coil). It is here that the input is given. 
• Secondary coil: Denoted by NS (number of turns of the secondary coil). It is here that the output is received.  

It is important to note that the presence of insulation is crucial to separate the primary coil from the secondary coil; insulating oils, insulating tapes, insulating papers, or wood-based lamination is used for the same. 

WORKING OF TRANSFORMERS 

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’s 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 Is 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

IS  current through the secondary coil

IP  current through the primary coil

NP  is the Number of Primary coil

NS  is the Number of Secondary coil

EP  emf induced across the primary coil

EP  emf induced across the secondary coil

Φ  is the Flux Linkage

The above relations are based upon the following three assumptions-

• Primary current and resistance are small
• Tiny flux links both the primary and secondary coil
• The secondary current is small

In actual transformers, small energy losses occur due to the following aspects-

• Flux Leakage- some amount of flux is always leaked, as there is no complete transfer of flux from primary to secondary
• Resistance of the coils- because of resistance and heat dissipation, some energy is lost
• Eddy Currents- the alternating magnetic flux leads to the production of Eddy Currents in the iron core and causes heating. This loss can be minimised if laminated iron core is used
• Hysteresis- because of repeated reversion of alternating current and magnetic field, the core gets magnetised, leading to the expenditure of energy in the core in the form of heat.
  

  Conclusion 

  An AC generator converts mechanical energy into electrical energy, contrary to an electric motor which converts electrical energy into mechanical energy,  Former works on the principle of electromagnetic induction. In contrast, the latter works on the principle of moving coil galvanometer, that is, when moving in a magnetic field, exert a couple of forces on the armature because the armature rotates. Transformers transfer electric energy from one alternating-current circuit to more circuits by increasing or decreasing the voltage.