Electrical Machines

An electrical machine is the apparatus that converts energy from one domain to another domain. We are mainly concentrating on three domains namely - electric domain, magnetic domain and mechanical domain.

Electro-magnetic System: When the energy is in electrical domain, and is converted to magnetic domain, or when the energy is in magnetic domain, and is converted to electrical domain,  this type of system is called electromagnetic system.

Electro-mechanical system: When the energy is in electrical domain, and is converted to mechanical domain, or when the energy is in mechanical domain, and is converted to electrical domain, this type of system is called electromagnetic system.

Electric machines can be mainly divided into three according to the type of conversion namely - Transformers, Generators, Motors.

TRANSFORMERS

A transformer is a static electrical machine that converts alternating current from one voltage level to another level (higher or lower), or to the same level, without changing the frequency. A transformer transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying electric current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction. Here energy in electrical domain is first converted to magnetic domain and again converted back to electrical domain. Transformer may be single phase or three phase according to the required application. There are 2 types of transformers:

Step-up transformer

Step-down transformer

GENERATORS

An electric generator is an electrical machine that converts mechanical energy to electrical energy. A generator forces electrons to flow through an external electrical circuit. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. The source of mechanical energy, the prime mover, may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy. Here energy in mechanical domain is first converted to magnetic domain and then converted to electrical domain.

The two main parts of an electrical machine can be described in either mechanical or electrical terms. In mechanical terms, the rotor is the rotating part, and the stator is the stationary part of an electrical machine. In electrical terms, the armature is the power-producing component and the field is the magnetic field component of an electrical machine. The armature can be on either the rotor or the stator. The magnetic field can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. Generators are classified into two types, AC generators and DC generators.

MOTORS

An electric motor converts electrical energy into mechanical energy. The reverse process of electrical generators, most electric motors operate through interacting magnetic fields and current-carrying conductors to generate rotational force. Motors and generators have many similarities and many types of electric motors can be run as generators, and vice versa. Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. Here energy in electrical domain is first converted to magnetic domain and then converted to mechanical domain. They may be powered by direct current or by alternating current which leads to the two main classifications: AC motors and DC motors.

Basic Laws

Joules Law
The heat produced by a current I flowing through a resistance R for a time t, is proportion to I2Rt or, Heat =( I2Rt) / J, where J = 4.2 Joules / cal. 

Ampere’s Rule
This rule gives the direction in which a magnetic needle deflect when placed near a current carrying conductor. Imagine a person swimming in the direction of the current, facing the magnetic needle. Then the direction of deflection of the north pole of the needle will be towards his left side.
 
Coulomb’s Law
The force between two electric charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.
 
Ampere’s right hand rule
This gives the direction of magnetic field around a current carrying conductor. Imagine that the wire is gripped in the right hand with the thumb pointing along the wire in the direction of current. Then the direction of the fingers will give the direction of the magnetic field. 

Maxwell’s cork-screw rule
This also gives the direction of the magnetic field around a current carrying a conductor. Imagine that a right-handed corkscrew is driven in the direction of the current flow. Then the direction of the magnetic filed due to the current will be the direction of rotation of the head of the screw.
 
Laws of Parallel Currents
1. Two parallel conductors attract each other if the currents through them flow in the same direction and repel each other if the currents through them flow in the opposite direction.
2. The force between two such parallel conductors is proportional to the product of the of the current strengths and to the length of the conductors considered and varies inversely as the distance between them.
 
Faraday’s Laws of Electromagnetic Induction
1. Whenever the magnetic flux linked with the circuit changes, an EMF is always induced in it.
2. The magnitude of the induced EMF is proportional to the rate of change of flux linkage.
 
Lenz’s Law
The electro-magnetically induced current always flows in such a direction as to oppose the very cause which produces it.
 
Fleming’s Left- hand Rule (for motor-action)
This gives the direction of force on a current carrying conductor placed in a magnetic field. Hold the left hand with forefinger, middle finger and thumb at right angles to one another. If the forefinger represents the direction of the field and the middle finger that of the current, then the thumb gives the direction of the motion of the conductor.
 
Fleming’s Right - hand Rule (for generator -action)
This gives the direction of induced current in a conductor, which is moved in a magnetic field. Hold the right hand with forefinger, middle finger, and thumb at right angles to one another .If the forefinger represents the direction of the field and the thumb that of the conductor motion, then the middle finger gives the direction of the induced current.
 
Kirchhoff’s Laws 
1. In an electrical network, the sum of the currents entering a junction is equal to the sum of the currents leaving the junction.
2. The algebraic sum of the potential differences around a closed circuit is zero.
 
Maxwell’s Law
1. Any two circuits carrying current tend so to dispose themselves as to include the largest possible number of lines of force common to the two.
2. Every electro-magnetic system tends to change its configuration so that the exciting circuit embraces the largest number of lines of force in a positive direction.
 
Hall Effect
 It states that if a magnetic field is applied perpendicular to a metal plate, which carries a current, then a transverse voltage is set up in the plate perpendicular to both the current and the magnetic field. This transverse voltage is known as Hall Voltage.

Seebeck Effect
When two dissimilar metal wires are joined at the ends to form two junctions (Thermo couple) and when these junctions are kept at different temperatures, an EMF is produced in the circuit. This is called Seebeck Effect.

Peltier Effect
When an electric current is passed through a thermo-couple, then heating is produced at one junction and cooling at the other junction.

ELECTRICAL ENGINEERING

Electrical Engineering is a field of engineering that deals with the study and application of electricity generation, transmission, distribution and consumption of electrical energy for the benefit of mankind.

Electrical Energy is the only form of energy, which can be easily converted to any another form of energy. Electrical energy is basically very clean, environmental friendly and economical to transport. We can setup generating stations where resources are available. Also, this generated energy can be transmitted to the desired load present at any locations economically as compared to other sources of energy. For this reason, electrical energy has a great significance in the modern world.

Now, there are many ways for generating electrical energy. Around 70 to 75% of electrical energy is produced from fossil fuels. Rest of the energy is produced from hydel energy, wind energy, tidal energy, nuclear energy and solar energy. Although major portion of energy is produced from fossil fuels like coal, we are more interested in renewable sources.