Unit 1_Electric Circuits and Electrical Installations.ppt

Basic electrical components and circuits

1. UNIT 1 – Electric Circuits and Electrical
Installations
Circuit components – Resistor, Inductor, Capacitor - Network
reduction techniques - series, parallel, series parallel - Voltage and
Current sources- Kirchoff’s Laws – Domestic wiring and earthing-
Protective devices- Fuse, MCB- estimation of energy consumption.

2. Electrical Symbols

3. Basic Electrical Quantities
Electricity:
The invisible energy that constitutes the flow of electrons in a closed circuit to do
work is called electricity.
•Charged Body
Every substance or body is electrically neutral as all the atoms of the body contain
equal number of electrons and protons. A body is said to be charged positive or negative if it
has deficit or excess of electrons from its normal due share, respectively.
Unit of charge
Practical unit of charge is Coulomb (symbol C)
1 coulomb = charge on 628 x 10
16
electrons
•Free Electrons
The valence electrons that are loosely attached to the nucleus of the atom and can be
easily detached are called free electrons. They move from one atom to the other at random in
the metal itself.

4. Basic Electrical Quantities
•Electrical Potential
The capacity of a charged body to do work is called electric potential. The measure of electric
potential is the work done to charge a body to one coulomb and is given by
Electric Potential = Work done / Charge or V = W/Q
Unit: joule/coulomb or volt.
•Potential Difference
The difference in the electric potential of the two charged bodies is called potential difference.
Unit: volt
•Electric Current
When an electric potential difference is applied across the metallic wire, the loosely attached
free electrons start drifting towards the positive terminal of the cell..
The magnitude of flow of current at any section of the conductor is the rate of flow of the
electrons, that is , charge flowing per second and is expressed as
I = Q / t
Unit: ampere (A).

5. Basic Electrical Quantities
•Electrical Energy
When a potential difference V (Volt) is applied across a circuit, a current of I (Ampere)
flows through it for a particular period (t second). A work is said to be done by the
moving stream of electrons (or charge) is called Electrical Energy and is given by
V= Work done / Q
Work done or Electrical Energy is expanded as VQ = VIt (since I = Q/t)
Work done = I
2
Rt = (V
2
/R) * t
Unit : Watt Hour(WHr)
•Electrical Power
The rate at which work is being done in an electrical circuit is called electrical power.
Electrical power = Work done in an electrical circuit / Time
P = VIt / t = V I = I
2
R = V
2
/ R
Unit : Watt (W)

6. Networks and circuits
Interconnection of two or more simple circuit elements is called an electric
network. A Network contains atleast one closed path, it is called an electric circuit.
Network Circuit

7. •Branch
A part of the network which connects the various points of the network with one another is
called a branch. A branch may contain one or more elements. AB, BC,BE and CF are the
various branches.
•Junction Point
A point at which three or more branches meet is called a junction point. Point B and E are the
junction points in the network.
•Node
A point at which two or more elements are joined together is called a node. A, B, C, D, E and F are
the nodes of the network.
•Mesh
A mesh is a loop that does not contain other loops. All meshes are loops. But all loops are not
meshes. ABED and BCFE are the mesh of the network.
•Loop
A loop is any closed path of branches. ABED, BCFE and ABCFED are the loops of the network.
Networks and circuits

8. R, L ,C Parameters
•Resistors
The opposition offered to the flow of electric
current or free electrons is called Resistance.
The relation among voltage, current and
resistance is given by the Ohm law:
R = V /I
Resistance is measured in ohms (symbol W) after Georg Simon Ohm. The SI definition
of ohm is: “the ohm is the electric resistance between two points of a conductor
when a constant potential difference of 1 volt, applied to these points, produces in
the conductor a current of 1 ampere.
A wire is said to have a resistance of one ohm if one ampere current passing through it
produces a heat of 0.24 calorie (or one joule).

9. R, L ,C Parameters

10. Factors affecting Resistance
•Resistance
R l/a or R =
∝
ρ 1/a
Where ρ (‘Rho’ a Greek letter) is a constant of proportionality called resistivity of the wire material.
•Resistivity
The resistivity of a wire is given by the relation ρ = R a / l. The resistance offered by one meter
length of wire of given material having an area of cross-section of one square metre is called the
resistivity of the wire material.
ρ = R a / l = Ω m
2
/ m = Ω - m Unit: ohm metre in SI units.
R, L ,C Parameters
•Ohm’s Law: Ohm’s law states that the current flowing
between any two points of a conductor (or circuit) is directly
proportional to the potential difference across them,
provided physical conditions i.e., temperature do not change.
I V or V / I = constant
∝
This constant is called resistance (R) of the conductor.
Where:I is the current (amperes)
V is the potential difference
(volts)
R is the resistance (ohms)

R
V
I
V
I R
+ -
Ohm’s Law

11. Capacitor
•The capacitance expresses ability to accumulate an electrical energy in the form of electric
field. Capacitance is the basic required property of capacitor. The simplest capacitor consists
of two isolated conductive plates. The general relation among current, voltage and capacitance
C is given by:
•The unit of measure capacitance is farad (symbol F) after Michael Faraday. The SI definition
is: “the farad is the capacitance of a capacitor between the plates of which there appears a
potential difference of 1 volt when it is charged by a quantity of electricity of 1 coulomb”.
R, L ,C Parameters

12. Inductor:
It is the property of the substance which stores energy in the form of electromagnetic field. It’s
symbol is ‘L’. The inductance is ability to accumulate electrical energy in the form of magnetic
field. Inductance is fundamental property of inductor. The simplest inductor is a coiled wire
optionally equipped with a core. The general relation among current, voltage and inductance L is
given by:
•The unit of measure inductance is henry (symbol H) after Joseph Henry. The SI definition is:
“the henry is the inductance of a closed circuit in which an electromotive force of 1 volt is
produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per
second”.
R, L ,C Parameters

13. R, L ,C Parameters
VOLTAGE-CURRENT RELATIONSHIPS

14. Voltage and Current Sources

15. Independent sources:
If the voltage of the voltage source is completely independent of current and the
current of the current source is completely independent of the voltage, then the
sources are called as independent sources.
Dependent sources:
The special kind of sources in which the
source voltage or current depends on
some other quantity in the circuit
which may be either a voltage or a
current anywhere in the circuit are
called Dependent sources.
There are four dependent sources:
a. Voltage dependent Voltage source
b. Current dependent Current source
c. Voltage dependent Current source
d. Current dependent Current source
Voltage and Current Sources

16. •Ideal & Practical sources:
1.An ideal voltage source is one which delivers energy to
the load at a constant terminal voltage, irrespective of
the current drawn by the load.
2.An ideal current source is one, which delivers energy
with a constant current to the load, irrespective of the
terminal voltage across the load.
3.A practical current source is also assumed to deliver a
constant current, irrespective of the terminal voltage
across the load connected to it.
4.A Practical voltage source always possesses a very small
value of internal resistance r. The internal resistance of a
voltage source is always connected in
series with it & for a current source; it is always
connected in parallel with it.
Voltage and Current Sources

17. Voltage and Current Sources

18. Voltage and Current Sources

19. Voltage and Current Sources

20. Voltage and Current Sources

21. Voltage and Current Sources

22. Kirchhoff's Laws
Kirchhoff's First Law – The Current Law, (KCL)
•It states that the “total current entering a junction
or node is exactly equal to the current leaving the
node”.
•In other words the algebraic sum of ALL the
currents entering and leaving a node must be
equal to zero.
•The term Node in an electrical circuit generally
refers to a connection or junction of three or more
current carrying paths.
•The current flowing towards the junction is
considered positive and the current flowing away
from the node or junction is considered negative.

23. Kirchhoff's Second Law – The Voltage Law, (KVL)
•Kirchhoff's Voltage Law or KVL, states that in any
closed loop network, the total voltage around the loop
is equal to the sum of all the voltage drops within the
same loop.
•In other words the algebraic sum of all electromotive
forces (emfs) and potential drops (voltages) around
any closed loop in a circuit is zero.
Kirchhoff's Laws

24. Network Reduction Techniques
•A network is a collection of interconnected electrical components. In
general, the electrical networks are made to exchange the energy between
different elements .These electrical networks can be constructed either by
using Resistors or Inductors or Capacitors or combination of these
elements. Network analysis is the process of finding the voltage response
or the current response for any element in the network by using the
available techniques.
 Series Connections
 Parallel Connections
 Series Parallel Connections

25. Resistors in series
•When some conductors having resistances R1, R2 and R3 etc. are joined end-on-end, they are said to be
connected in series.
•It can be proved that the equivalent resistance or total resistance between points A and D is equal to the
sum of the three individual resistances.
Network Reduction Techniques

26. Resistors in Parallel
Three resistances, as joined in the figure are said to be connected in parallel.
Network Reduction Techniques

27. Inductors in Series
Let M = coefficient of mutual inductance
L1 = coefficient of self-inductance of 1st coil
L2 = coefficient of self-inductance of 2nd coil
i) Let the two coils be so joined in series that their ii) When the coils are so joined that their fluxes (or m.m.fs) are
additive i.e., in the same direction.fluxes are in opposite directions
Inductance L
T
= (L
1
+M) + (L
2
+M) = L
1
+L
2
+2M Inductance L
T
= (L
1
-M) + (L
2
-M) = L
1
+L
2
-2M
Network Reduction Techniques

28. Inductors in Parallel
Network Reduction Techniques

29. Capacitors in Series and Parallel
•C1, C2, C3 = Capacitances of three capacitors
•V1, V2, V3 = p.ds. across three capacitors.
•V = applied voltage across combination
•C = combined or equivalent or joining capacitance.
•In series combination, charge on all capacitors is the same but p.d. across each is different.
Network Reduction Techniques

30. Resistors in Series-Parallel Combination
I = V / R
EQ
 
= 5 / 10 = 0.5 A
R
EQ
 = R1 + Rp = 4
+ 6 = 10 Ω.
R
p
 = (R
c
 × R
d
) / (R
c
 + R
d
)
= (12 × 12) / (12 + 12)
= 6 Ω.
Rd = R2 + R3 = 4 + 8 =
12 Ω.
Rc = R4 + R
b
 
= 10 + 2 = 12 Ω.
R
b
 = (R
a 
× R
5
) / (R
a
 + R
5
) = (4 ×
4) / (4 + 4) = 2Ω.
Ra = R6 + R7 = 2+2 = 4Ω
Network Reduction Techniques

31. Inductors in Series-Parallel Combination
Network Reduction Techniques

32. Capacitors in Series-Parallel Combination
Network Reduction Techniques

33. Protective Device - FuseProtective Device - Fuse
A short piece of wire, inserted in series with
the circuit, which melts when
predetermined value of current flows
through it and breaks the circuit is called a
fuse. It is used to protect circuits from over
current, overload and make sure the
protection of the circuit.
The time required to blow out a fuse
depends on the magnitude of excessive
current. Larger the current, smaller is the
time taken by the fuse to blow out. Hence
fuse has inverse time current characteristics.

34. Types of Fuses
Protective Device - FuseProtective Device - Fuse

35. DC Fuses
1. 
CARTRIGE FUSES
The fuse element is encased in a glass envelope that
is terminated by metal caps.
2. AUTOMOTIVE FUSES They come in ‘blade’ form (a transparent plastic
envelope with flat contacts) and are colour coded according to rated current.
3. RESETTABLE FUSES They contain carbon black particles embedded in
organic polymers. Normally, the carbon black makes the mixture conductive.
When a large current flows, heat is generated which expands the organic
polymer. The carbon black particles are forced apart, and conductivity
decreases to the point where no current flows.
 
4.SEMICONDUCTOR FUSES
 
The power dissipated by a semiconductor
increases exponentially with current flow, and hence semiconductors are used
for
 
ultrafast fuses. These fuses are usually used to protect semiconductor
switching devices that are sensitive to even small current spikes.
5. OVERVOLTAGE SUPPRESSION 
Sometimes voltage spikes can be
harmful to circuits too, and often an overvoltage protection device is used with
a fuse to
 
protect against both voltage and current spikes.
Protective Device - FuseProtective Device - Fuse

36. AC FUSES :
HIGH VOLTAGE FUSES : These fuses are used in high voltage AC transmission lines
where voltages can exceed several hundreds of kilovolts.
 
1.Expulsion Fuses: 
These fuses are filled with chemicals like boric acid that produce gases on
heating. These gases extinguish the arc and are expelled from the ends of the fuse. The fuse
element is made of copper, tin or silver.
2.HRC (High Rupture Current) fuses: HRC fuses are cartridge type fuses consisting of a
transparent envelope made of steatite (magnesium silicate). The fuse is filled with quartz
powder (and in the case of a liquid-filled HRC fuses, a non-conducting liquid like mineral oil)
that acts as an arc extinguishing agent.
Protective Device - FuseProtective Device - Fuse

37. LOW VOLTAGE FUSES:
 
These fuses are used in the relatively low
voltage distribution networks.
1.Cartridge fuses: 
They are very similar to cartridge DC fuses. They consist
of a transparent envelope surrounding the fuse element. They can be plugged
in (blade type) or screwed into a fixture (bolt type).
2. Drop out fuses: 
They contain a spring-loaded lever arm that retracts when
a fault occurs and must be rewired and put back in place to resume normal
operation. They are a type of expulsion fuse.
3. Rewireable fuses: 
They are a simple reusable fuse used in homes and
offices. They consist of a carrier and a socket. When the fuse is blown, the
carrier is taken out, rewired and put back in the socket to resume normal
operation. They are somewhat less reliable than HRC fuses.
4. Striker fuse: 
These fuses are provided with a spring-loaded striker that
can act as a visual indicator that the fuse has blown and also activate other
switchgear.
5. Switch fuse: 
A handle that is manually operated can
connect or disconnect high current fuses.

Protective Device - FuseProtective Device - Fuse

38. Protective Device - MCB (Miniature Circuit Breaker)

39. Protective Device - MCB

40. Domestic Wiring

41. EARTHING

42. EARTHING - TYPES
Equipment Earthing:
The following equipments used in the power system have to be earthed:
1. All the metal frames of motor, generators, transformers and controlling equipment
2. The steel tower or pole carrying overhead conductors
3. Earth terminal of all 3-pin outlet sockets
4. In case of concentric cables, the external conductor that is armouring of such cables
System Earthing:
A proper system has to be adopted while earthing. Two earth connections are applied to
improve the reliability. In factories and substation where more than one equipment is to be
earthed, parallel connections should invariable be used. For proper earthing of heavy power
equipment, double earthing has to be adopted.
Methods of Earthing
1) Plate Earthing
2)
 Pipe Earthing
3) Rod Earthing
4) Earthing through the Water mains
5) Strip or Wire Earthing

43. EARTHING - TYPES

44. EARTHING - TYPES

45. EARTHING - TYPES

46. POWER RATING OF BASIC HOUSE HOLD EQUIPMENTS
EQUIPMENT WATTS EQUIPMENT WATTS
CFL Bulb - 40 Watt Equivalent 11 Desktop Computer (Gaming) 500
CFL Bulb - 60 Watt Equivalent 18 Printer 100
Coffee Machine 1000 DVD Player 15
Dishwasher 1200-1500 TV - LCD 150
Laptop 100 TV - Plasma 200
Halogen LAMP - 40 Watt 40 Satellite Dish 25
Ceiling Fan 120 Stereo Receiver 450
Incandescent 50 Watt 50 Video Game Console 150
Incandescent 100 Watt 100 Smart Phone - Recharge 6
Water Heater - Electric 4500 CFL Bulb - 40 Watt Equivalent 11
Well Pump - 1/3 1HP 750 CFL Bulb - 60 Watt Equivalent 18

47. Estimation of Energy Consumption
•Energy= Power * time, 1 Unit of Energy = 1000WHr.
•If the cost of 1 unit is considered 5 /Unit then the bill for this application will be 136.7 × 5
₹
= 687.5.
₹