Chapter 3 covers electromagnetic fundamentals, focusing on magnets, magnetic fields, and electric machines, including transformers, generators, and motors. It explains the principles of magnetism, the construction and function of transformers, including their efficiency and various types, and the interactions within electric machines. The chapter further illustrates key concepts, such as electromagnetic induction and the application of transformers in voltage conversion and electrical isolation.

1. Chapter 3:
Electromagnetic
Fundamentals

2. Table of contents
3.1
3.3
3.2
3.4
Elaborate
magnetic
field
Explain type
of
transformer
Explain
electric
machines
Elaborate the
principle of
the
transformer

3. Magnetic
Field
3.
1

4. What is MAGNETS ??
A magnet is a metal or rock
that can attract objects
containing iron, nickel, cobalt
or a mixture of these metals
Magnetism is the force exerted by magnets
when they attract or repel each other.
Magnetism is caused by the motion of
electric charges. Every substance is made up
of tiny units called atoms. Each atom has
electrons, particles that carry electric
charges.
MAGNETS MAGNETISM

5. Characteristics of magnetic materials
The magnetic field
exists in the area around
the magnet and the
space is filled with
magnetic flux
The magnetic flux is the
circle of magnetic field
lines
The magnetic poles
consist of a north pole
and a south pole
1 3
2

6. Magnetic field concept
A magnetic field is the area surrounding
a magnet where magnetic forces act.
The magnetic field cannot be seen but its
effect can be observed using iron powder
and a compass.
magnetic field lines move
from the north pole to the
south pole of the magnet

7. Magnetic force lines/ magnetic
flux
The direction of magnetic field lines can be determined using a compass.
The magnetic field deflects the needle on the compass.
Stronger magnets have closer magnetic lines of force.

8. Magnetic force lines/ magnetic
flux
It is a circle of lines of magnetic force that surround
the magnet.
The direction of the magnetic field can be
determined by placing several compasses around
the magnetic bar.
The compass needle will show the direction out of
the north pole and the direction in to the south pole

9. Magnetic Fields And Magnetic Poles
MAGNETIC FIELD is the space that surrounds a magnet where the space is filled with
magnetic flux.
The magnetic poles swing freely, the north pole will always point north and the south
pole will always point south.

10. A magnetic field shows that the same magnetic poles repel
each other

11. A magnetic force field shows that different magnetic poles
attract

12. SAME MAGNETIC
POLES
DIFFERENT MAGNETIC
POLES

13. ELECTROMAGNETIC
An electromagnet (electromagnet) is a magnet
whose magnetic field is produced by the flow of
electric current.
The magnetism of an electromagnet is temporary
(temporary magnet), which can be magnetised
(magnetised) and demagnetised (demagnetised).
A simple electromagnet can be formed by winding
20 turns of insulated copper wire on a soft iron core
like a soft iron nail.
The iron nail will become a magnet when the switch
is turned on.

14. Electric
Machines
3.2

15. What Is An Electrical Machine?
An electrical machine is a device which converts
mechanical energy into electrical energy or vice versa.
Electrical machines also include transformers, which do
not actually make conversion between mechanical and
electrical form but they convert AC current from one
voltage level to another voltage level.

16. Types of Electrical Machines
The electric machines are of three main types,
transformer, generator, and motor.
Electrical Transformer: In the transformer, both
input and output are electrical power.
Electrical Generator: In a generator, the input is
mechanical power and the output is electrical
power.
Electrical Motor: In a motor, the input is electrical
power and output is mechanical power.

17. Electrical Transformer
Transformers do not actually make
conversion between mechanical and
electrical energy, but they transfer
electric power from one circuit to
another circuit.
They can increase or decrease (step-
up or step-down) the voltage while
transferring the power without changing
the frequency, but with the
corresponding decrease or increase in
the current.
Input power and output power of an
electrical transformer should ideally be
the same.

18. Electric Generator
An electric generator is
an electrical machine
which converts
mechanical energy into
electrical energy. A
generator works on the
principle of electromagne
tic induction
AC Generator (converts
mechanical energy into
Alternating Current (AC)
electricity)
DC Generator (converts
mechanical energy into
Direct Current (DC)
electricity)

19. Electrical Motor
A motor is an electrical machine which
converts electrical energy into
mechanical energy.
When a current carrying conductor is
placed in a magnetic field, the
conductor experiences a mechanical
force and this is the principle behind
motoring action.
1. AC motors: (i)Induction motors and
(ii) Synchronous motor
2. DC motors: (i) Brushed DC motor
and (ii) Brushless DC motor

21. Types of Electical Motor
AC Motor DC Motor Special Purpose
Motor

22. Transformer
3.3

23. What Is A Transformer ?
Transformers do not actually make
conversion between mechanical and
electrical energy, but they transfer
electric power from one circuit to
another circuit.
They can increase or decrease (step-
up or step-down) the voltage while
transferring the power without changing
the frequency, but with the
corresponding decrease or increase in
the current.
Input power and output power of an
electrical transformer should ideally be
the same.

24. Transformer Symbol
(a) Air core (b) Iron core
(d) Multiple secondary
(c) Center tapped transformer

25. THE BASIC TRANSFORMER
•Source voltage is applied to the primary winding
•The load is connected to the secondary winding
•The core provided a physical structure for placement of windings and a
magnetic path so that the magnetic flux lines are concentrated close to
the coils
•Typical core materials are : air, ferrite and iron

26. TRANSFORMER
BASICS
▪ When an AC voltage is applied in a
coil, the electromagnetic field
expands, collapses and reverses as
the current increases, decreases
and reverses.
▪ When two coils are placed very close
to each other, the changing magnetic
field produced by the first coil will
cause an induced voltage in the
second coil because of the mutual
inductance between the two coil.
HOW???

27. ▪ When two coils are placed very
close to each other, the
changing magnetic flux line
produced by the first coil will
cut through the second coil.
The two coils are said to be
magnetically linked or
coupled. As a result, a voltage
is induced.

28. TRANSFORMER BASICS
The parts of an ideal transformer

29. BASIC PRINCIPLES
 The transformer is based on two principles:
 first, that an electric current can produce a magnetic field (electromagnetism), and
 second that a changing magnetic field within a coil of wire induces a voltage across the ends of
the coil (electromagnetic induction).
 Changing the current in the primary coil changes the
 magnetic flux that is developed.
 The changing magnetic flux induces a voltage in the secondary coil.
 Current passing through the primary coil creates a magnetic field.
 The primary and secondary coils are wrapped around a core of very high magnetic permeability, such
as iron, so that most of the magnetic flux passes through both the primary and secondary coils.

30. TRANSFORMER CONSTRUCTION
 The transformer consists of core, surrounded by at least two series
of coils.
 The core is used as to aid in linking the flux from the primary
coil to the secondary coil.
 Dots are used in diagrams of transformers to indicate the current
polarities for the windings.
 Dotted terminals have the same polarity.

31. (a) Voltage are in phase (b) Voltage are out of
phase
Dot Notation

32. THE FUNCTION
▪ Function of a transformer:
▪ To transfer current, voltage and power from one series of
windings (coils) to another.

33. INDUCTION LAW
• Taking the ratio of the two equations for Vs and Vp
gives the basic equation for stepping up or stepping
down the voltage

34. IDEAL POWER EQUATION
 If the secondary coil is attached to a load that allows current to flow,
electrical power is transmitted from the primary circuit to the
secondary circuit.
 Ideally, the transformer is perfectly efficient; all the incoming energy
is transformed from the primary circuit to the magnetic field and into
the secondary circuit. If this condition is met, the incoming electric
power must equal the outgoing power:-

35. IDEAL TRANSFORMER EQUATION
giving the ideal transformer equation
Transformers normally have high efficiency, so this formula
is a reasonable approximation.

36. For an ideal transformer, the PPrimary is equal to the PSecondary, or
the power input is equal to the power output.
Pout = Pin VsIs
= VpIp Is/Ip =
Vp/Vs
Efficiency of transformer,
IDEAL TRANSFORMER EQUATION

37. TURN RATIO
A useful parameter for ideal transformers is the
turns ratio defined as
n =
Nsec
N pri
Nsec = number of secondary windings
Npri = number of secondary windings
Most transformers are not marked with turns ratio,
however it is a useful parameter for understanding
transformer operation.

38. STEP-UP TRANSFORMER
• A transformer that has more turns on the secondary
than the primary side of transformer will increase the
input voltage.
– This is called a step-up transformer.
– Nsec > Npri
– ŋ > 1
– Symbol
Npri Nsec

39. DC ISOLATION

40. STEP-DOWN TRANSFORMER
• A transformer that has more turns on the primary
than the secondary side of the transformer will
decrease the input voltage.
– This is called a step-down transformer.
– Nsec < Npri
– ŋ < 1
– Symbol
Npri Nsec

41. REFLECTED LOAD

42. TRANSFORMER POWER RATING & EFFICIENCY

43. NON IDEAL TRANSFORMER
 An ideal transformer has no power loss; all power applied to the primary is all
delivered to the load. Actual transformers depart from this ideal model. Some
loss mechanisms are:
 Winding resistance
 Hysteresis loss
 Core losses
 Flux leakage
 Winding capacitance
 The ideal transformer does not dissipate power. Power delivered from the source is
passed on to the load by the transformer.
 The efficiency of a transformer is the ratio of power delivered to the load (Pout) to
the power delivered to the primary (Pin).

44. POWER LOSSES
Iron or core losses
•The magnitude of these losses is quite small.
This losses due to eddy current and hysteresis
loss in it.
Copper losses
•Is the energy loss in the windings when the
transformer is loaded.
Total copper loss, Pc = I 2R + I 2R
p p s s

45. TYPE OF TRANSFORMER
• Several types of transformer:
– Center tapped transformer
– Multiple winding transformer
– Auto transformer

46. CENTER TAPPED TRANSFORMER

47. MULTIPLE WINDING TRANSFORMER

48. AUTOTRANSFORMER

49. TRANSFORMER APPLICATION
– Step-up or step-down voltage and current.
– Isolation device
» electrical isolation. Electrical isolation can be used to improve
the safety of electrical equipment.
» DC isolation. Coupling transformers can be used to block DC
signals from reaching the secondary circuit.
– Impedance matching for max power transfer

50. SPECIAL TRANSFORMER
APPLICATIONS
 Autotransformers
• Use in low-voltage applications since has only one winding.
 Induction Circuit Breaker
• Use to shut off the current in a circuit, thus prevent fires
• cause by a short in an electrical device.
 Lighting Ballast
• Use to start the lamp by producing the necessary voltage and limits
current thro the lamp.
 Coupling Transformer
• Isolates each section of the amplifier – so individual amplifier
characteristics will not interfere with others

51. EXAMPLE 1
A transformer has 800 turns on the primary and a turns
ratio of 0.25. How many turns are on the secondary?
Solution
n = Ns / Np
NS = Np x n = 800 x 0.25 = 200 turns

52. EXAMPLE
2
A doorbell requires 0.4 A at 6V. It is connected via a
transformer whose primary coil contains 2000 turns
to a 120V AC line. Calculate:-
(a) NS
(b) IP

53. SOLUTION 2
a)
b)

54. EXAMPLE 3
The voltage ratio of a single-phase, 50Hz transformer is
5000/500V at no load. Calculate the number of turns in each
winding if the maximum value of the flux in core is 7.82mWb.

55. SOLUTION 3
Ep=Vp=5000V, Es=Vs=500V, Øm=7.82mWb
Ep = 4.44 f Øm Np
Np = Ep / 4.44 f Øm = 5000 / (4.44 x 50 x 7.82m)
= 2880 turns

56. EXAMPLE
4
A single transformer is connected to a 660V supply. The
voltage/turn of the transformer is 1.1V. The secondary voltage
of the transformer is found to be 440V. Determine the
following:-
a)Primary and secondary turns
b)Cross-section of the core if the maximum flux density is 1.4T

57. SOLUTION 4
Voltage/turn=1.1V, Vp=660V, Vs=440V, Bmax=1.4T
i) Np = Vp / 1.1 = 660 / 1.1 = 600 turns
Ns = Vs / 1.1 = 440 / 1.1 = 400 turns
ii) Ep = 4.44 f Øm Np Øm = Bmax
A
A = Vp / 4.44 f Bmax Np
= 660 / (4.44 x 50 x 1.4 x 600)
= 35.39 x 10-4 m2 = 35.39cm2

58. EXAMPLE
5
a) Illustrate the parts of an ideal transformer.(5m)
b) Identify the importance of the core material. (3m)
c) A 50 kVA, single-phase transformer has 500 turns on the primary and
100 turns on the secondary. The primary is connected to 2500V,
50Hz supply. Calculate the following :- (9m)
i) The secondary voltage on open circuit
ii) The current flowing through the windings on full load
iii) The maximum value of flux
d) A single phase ideal transformer contains 3000 circumferences at
primary coil and 800 circumferences at secondary coil. Primary coil
is connected to 240VAC, 50Hz supply. Calculate:- (8m)
i) Secondary voltage
ii) Current on secondary coil if the current on primary coil is 5A.
iii) Transformer power on primary and secondary coils

59. SOLUTION 5(a)
a)

60. SOLUTION 5(b) & (c)
b) The importance of the core material is to reduce
losses of eddy current. The losses in transformer are
constant but not affected by load changes
c)

61. SOLUTION 5(c)
c)

62. SOLUTION 5(d)
d)