Fundamentals of electrical engineering

1) Generation of electrical energyGenerator basically converts mechanical energy to electrical energy

Fuel energy Mechanical energy electrical energy

Fuels used in generators are

Solid fuels – wood, husk, coal, graphite – thermal power stations

Liquid fuels – diesel/petrol/ kerosene - diesel power station

Gaseous – LPG, CNG - gas power station

Water – Hydro electric power stationPotential energy to kinetic energyM g H = 1/2 M V2

Nuclear - Atomic power station

Unconventional energy sources are1. Solar heat2. wind power3. tidal power ( see tidals)

Important terms in electrical engineering

Current – Amperes - flow of electrons

Voltage - Volts - potential difference (pressure)220 in India 50 Hz frequency110 in US and UK 60 Hz frequency

Resistance - Ohms - resist to flow of electrons

Electrical power - Watts - current resistance

Energy - Watt hour - watt hours

Capacitance - Farads - to store electrical energy- capacitor is used.

Ohm’s law: Ohm’s law : The ratio of potential difference (v) between any two points of a conductor to the current (I) flowing between them is constant, provided the temperature of the conductor does not change. Where R is the resistance of the conductor between the two points.

V/I = constant = R

General A/C power supply single phase: Two wires one phase one neutral

Three wires one additional earthing

Power = √3 V I COSФ

COSФ is called power factor and its value should be 0.8 or more for the efficient use of electrical power

Three phase (Delta connection): Three wires (all phases) and one optional earthing

VL = VP, I L = √3 I p

Power = √3 VL I L COSФ

Three phase (star connection): Four wires (Three phases and one neutral) and one optional earthing

VL = √3 VP, I L = I p

Power = √3 VL I L COSФ

In the short circuit the resistance will become zero then the current flow will become infinite. It leads to burning of the circuit and or apparatus.In the closed circuits only one will get shock that is the reason often birds doesn’t get shock on electrical poles.Earthing does not require any sleeve as it does not have any resistance.

Faradays laws of electromagnetic induction

I L

I p

VL

Vp

1. Whenever a conductor cuts magnetic flux an e.m.f is induced2. The magnitude of the induced e.m.f is equal to the rate of change of flux-linkages.

Series circuits - same current flows through each circuit component

V=V1+V2+V3, R=R1+R2+R3 and V1=VxR1/R ……..

Parallel circuits - same voltage is supplied through each circuit component

I=I1+I2+I3, 1/R=1/R1+1/R2+1/R3 and I1=V/R1

Short and open circuitsWhen two points of a circuit are connected together by a thick metallic wire, they are said to be short circuited.

Effect: 1) No voltage exist across it 2) Current through it is very large

N

Direction of current

Direction of movement

S

R1 R3R2

V

V

R1

R3

R2

When two points of a circuit are broken or disconnected it is said to be open circuit. When any switch is off then that circuit is called open circuit.

Effect:1) resistance between two points is infinite2) there is no flow of current 3)

Fuse wires:A fuse is a safety device which is connected in a circuit to protect the electrical apparatus from the dangerous effects of a short circuit and from an overload.The actual fuse is metal wires made of easily melting material usually tin and leads alloy for small currents and copper for large currents.

Earthing:Earthing or connecting to earth means that the metallic casing of electrical apparatus in an installation are connected to the general mass of earth by an earth plate. Earthing should be designed so that in the event of the insulation becoming defective, the earthing wires will convey the fault current to earth.

Power factor - Ratio of True power (W) to Apparent power (VA) and represented by COSФ

Real electrical load contains resistance (Ohms) in combination of impedance (farads), and capacitance. Because of these components current lagging and leading happens and it reduces effective power transmission thus power factor came in to the picture.

Resistance same time

Impedance current lagging

Capacitance Current leading

Difference between AC and DC

Alternate current: single-phase 220 V three-phase 440 V

V I

I

V

IV

Time

Current / Voltage

Direct current: 1.5, 3, 6, 12, 24 Volts

A/C DC

We cannot store

small size (generation)

components

Wave from I, V are in sinusoidal

Transmission loss are less

High load motors, plumbs and

heaters are only operated by A/C

A/C will be produced by

conversion of mechanical every to

electrical power

capacity of A/C power (Units) are

represented in KW, KVA

there be a P.F. (power factor)

the current in the different sections will

be obtained by the vector sum of currents

and voltages

we can store

big size components

straight line

transmission loses are more

electronic equipment, PCBs,

small motors are operated by

D/C

chemical energy and A/C energy

can be converted to D/C energy

capacity of D/C power will be

represented in ampere hours

(AH)

there wound be any power factor

the current and voltage in the

different sections will be

algebraic sum

Resistance (conductance)

It may be defined as the property of a substance due to which it (induce) opposes the flow of electricity through if.

Poor conductors: bakelite, mica, glass, rubber, poly vinyl chlorideGood conductors: - silver, copper, aluminumGood insulators: paper, cotton, sweater, ceramics

Generator (Motor)An electrical generator is a machine which converts mechanical energy into electrical energy. This energy conversion is based on the principle of the production of induced e.m.f. Basic essential parts of an electrical generator are (i) a magnetic field (ii) a conductor.

The most extensively used A.C. motors are induction motors.

LED (Light Emitting Diode)

It is a junction diode emits light or exhibit electro luminescence by the appreciation of electrostatic field. This is because when a free electron recombines, it may fall all the way from unbound or higher level to its ground state, releasing a photon of a wavelength corresponding to the energy level difference associated with this transition.

Capacitor

A capacitor essentially consists of two conducting surfaces separated by a layer of an insulating medium called dielectric. The purpose of a capacitor is to store electrical energy. The property of a capacitor to store electricity may be called its capacitance.

Suppose we give a coulomb of charge to one of the two plates of capacitor and if a p.d of V volts is established between the two, then its capacitance is

Relays:

A relay is a magnetically operated switching device used for a wide range of control application. It consists of an electromagnet assembly which moves in armature to open or close one or more sets of normally open and or normally closed contacts Faradays laws of electromagnetic induction

Transformers:It is a device to step up or step down the voltage level. Current in primary sets-up magnetic field (flux) in core which in turn induces voltage across secondary. The secondary voltage is proportional to primary voltage in the same ratio as number of turns. Current are inversely proportional as turn ratio.

Principle: All transformers work on the principle that a current changing in one coil induces an e.m.f. in neibeighbouring.

Circuit breakers: A circuit breaker is simply switching device which provides automatic interruption of current flowing through it when current conditions are abnormal (both overload and short circuits conditions) without causing damage to itself. These are thermal type, magnetic air circuit breakers, oil circuit breakers, vacuum type etc.There are many advantages of transmitting and generating electrical energy high voltage, standard generation voltage is 11 KV in IndiaEarth wire carries current only during an earth fault. While neutral wire carry current whenever there is unbalanced situation of power there phase, 4-wire supply system.Indian electricity rules: The minimum size of cable for light circuit for copper 1/1.12 and for aluminum 1/1.4 diameter.Not more than 10 points should be connected on one light circuit.

Board of trade unit and 1 KWH – 1 BOT unit.

LCD (Liquid Crystal Displays)

The molecules in an ordinary liquid normally have random orientations. In liquid crystals the molecules are oriented in a definite crystal pattern. When an electric field is applied to liquid crystal, the molecules which are align themselves perpendicular to the field. When not activated the liquid crystal is transparent. When activated the molecular turbulence causes the light to be scattered in all directions so that the activated area appears bright.