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Mechanical and Electrical
Systems
SAB 2032/SAM 3012
(Sistem Mekanikal dan Elektrikal)
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Mechanical and Electrical System
SAB 2032/SAM 3012
Lecturer: Dr. Khurram Kamal
Dept. of Electrical Engineering
(Faculty of Electrical Engineering/FKE)
P07-405, Phone: 07-5536-192
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Objective:
To give basic information about electrical
principle, electrical machinery, distribution
system, wiring and protection
Mendedahkan Pelajar kepada Bekalan Elektrik,
Mesin Elektrik, Sistem Pengagihan, Pendawaian
dan Perlindungan
Lecture hours: 14 hrs (electrical part)
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Syllabus and Lecture Plan
1. Power Supply (AC and DC)  4 hrs
1.1 Current, Voltage, Power and their relationships
1.2 Single and Three Phase System (star and delta)
1.3 Source of Supply, Transmission and Distribution
2. Electrical Machinery (Transformer and Three Phase
Induction Motor)  6 hrs
2.1 TransformerPrinciple of operation and application,
Rating, Losses and Efficiency
2.2 Induction Motor Principle of operation and
application,Synchronous speed, Rotor speed and
sleep, Rating and starting circuits.
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3. Electrical Distribution and Wiring  4 hrs
3.1 Wiring system, Types and size of cables
3.2 Protections and Grounding
3.3 Electrical Load (Estimation)
3.4 Substation, Switchboard and Distribution Board
3.5 Symbols and Single line diagram
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Marking Total 50%
1. Task
: 10%
2. Test
: 15%
3. Final Exam : 25%
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Familiarization with electricity
Electric shock
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Electrical Engineer design systems objective:
 To gather, store, process, transport, and present
information
 To distribute, store, and convert energy between
various form
Manipulation of energy
interdependent
Manipulation of information
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Basic Electrical System
■ Electricity is a form of energy
■ Examples of energy source – hydro, coal, wind, nuclear
■
■
■
and solar
Electrical systems permits us easily to transmit energy
from a source of supply to a point of application
Electrical engineering is the profession concerned with
systems that produce, transmit and measure electrical
signals
Examples of electrical systems – power system,
communication system, computer system, control
system and signal processing system
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…Basic Electrical System
1. The source - to provide energy for the electrical system,
eg. Battery, generator, socket outlet
2. The load - to absorb the electrical energy supplied by
the source, eg. Lamps, air-cond
3. The transmission system - conducts energy from the
source to the load, eg. Insulated wire
4. The control apparatus - permits energy to flow or
interrupts the flow, eg. switch
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…Basic Electrical System
■ Example of Electrical System
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…Basic Electrical System
■ Example of Electrical System
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1. Power Supply (AC and DC)
Electricity is the movement of free electrons in a
material toward an area of positive (+) charges.
The conduction of those electrons is determined by
the type of material. Some conduct well, while other
materials prevent the movement of electrons.
Electricity can take the form of static electricity, direct
current (DC) electricity, or alternating current (AC)
electricity.
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What are free electrons?
What determines the conduction of electricity?
What are the different types of electricity?
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Free electrons
Most electrons are bound in orbit around atoms. But in many
substances, there are electrons that are not connected to any
atom and are roaming freely throughout the material. These
electrons may have been knocked free in the creation of ions
or may be the result of a collision of a high energy particle,
such as from radioactive materials or cosmic rays.
Electrons have a negative (-) electrical charge and protons have a
positive (+) charge. Atoms with an excess of electrons are called
negative ions and those that are missing electrons in the shells or
orbits are called positive ions.
An electric force field causes particles with opposite charges to
attract each other. A buildup of opposite charges creates an
electric potential. Release of the potential energy results in the
movement of free electrons, which is called electricity.
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Valence electrons are the electrons contained in the outermost, or
valence, electron shell of an atom. Valence electrons are important in
determining how an element reacts chemically with other elements: The
fewer valence electrons an atom holds, the less stable it becomes and
the more likely it is to react.
Proton charge= 1.602 x 10-19 Coulomb
Elec. charge= -1.602 x 10-19 Coulomb
This helium (He) model displays two valence electrons
located in its outermost energy level.
Helium is a member of the noble gases and contains
two protons, neutrons, and electrons.
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Solid metals are good conductors of electricity,
because electrons are allowed to move freely
throughout the material. Copper and gold are some
of the best conductors of electricity. Although iron is
a good conductor, iron oxide (rust) is not.
In the solid state, the atoms of metals are held in place
and only vibrate. This allows free electrons to roam about
the material.
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Free electrons among metal atoms
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In semiconductors—such as materials used in computer chips—the
electrons have limitations to their movement, such as only being allow
to move in one direction or in one plane.
Nonconductors inhibit the movement of electrons within the material.
But they often do allow electrons and ions to collect on their surfaces.
Examples of nonconductors or electrical insulators are:
Plastic, Rubber, Glass, Most metal oxides (like rust), Air, Oil, Pure,
de-ionized water
Gases are not good conductors of electricity because of the distances
between atoms. Electrons have difficulty moving through gases, unless
the gas is ionized or heated to higher temperatures.
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Conductivity (Ohm. m)
Silver
1.59×10−8
Copper
1.68×10−8
Gold
2.44×10−8
Aluminium
2.82×10−8
Tungsten
5.60×10−8
Nickel
6.99×10−8
Brass
0.8×10−7
Iron
1.0×10−7
Tin
1.09×10−7
Platinum
1.1×10−7
Lead
2.2×10−7
Manganin
4.82×10−7
Constantan
4.9×10−7
Mercury
9.8×10−7
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Nichrome
1.10×10−6
Carbon
3.5×10−5
Germanium
4.6×10−1
Silicon
6.40×102
Glass
1010 to 1014
Hard rubber
approx. 1013
Sulfur
1015
Paraffin
1017
Quartz (fused)
7.5×1017
PET
1020
Teflon
1022 to 1024
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Insulator Materials
Material
Air (vacuum)
Teflon
Paper
Oil
Mica
Glass
Ceramic
Dielectric constant
1.0
2.0
2.5
4.0
5.0
7.5
1200
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Types of electricity
Common types of electricity are static electricity, direct current (DC)
electricity, and alternating current (AC) electricity.
Static electricity
Static electricity is the collection of free electrons on the surface of a
material, giving it a negative (-) charge. Atoms on the surface of another
material that have lost one more of their electrons are called positive (+)
ions.
Often the electrons are pulled from the atoms on one surface and allowed
to collect on the surface of another material. Static electricity is caused by
rubbing the two different materials together.
Since opposite charges attract, there is a tendency for the electrons to
attract toward the positive ions, resulting in static electricity.
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DC and AC electricity
In a metal or other conducting material, electrons will flow from an area of an
excess negative (-) charges to an area of positive (+) charges. This flow of
electrons through the conductor is electricity.
If the opposite charges are constant, such as with the terminals in a battery, the
current is called direct current or DC electricity, because it is going one direction.
If the terminals constantly switch their polarity from (+) to (-) and back again, the
direction of the electrons alternates and is call alternating current or AC electricity.
This is the type of electricity that comes from the outlets in most homes.
DC can be created by a battery or DC generator. AC requires an AC generator
for its creation.
DC is used in many devices that do not require high voltages for their
operation, such that batteries are used for power. AC can be used in higher
voltages. It has the advantage of being able to have its voltage easily changed
to a higher or lower level. AC is required for many electronic devices.
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Conclusion
Electricity is the movement of free electrons in a material. It moves the
best though metals.
Static electricity is the collection of electrons and positive ions on the
surface of a material--usually a non-conductor.
Direct current electricity moves in one direction and usually is created in
batteries. Alternating current electricity is most commonly used in homes
and can have its voltage changed to suit the need.
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Electric Current
Electric current is the rate of charge flow past a given point in an electric
circuit, measured in coulombs/second which is named amperes.
In most DC electric circuits, it can be assumed that the resistance to current
flow is a constant so that the current in the circuit is related to voltage and
resistance by Ohm's law.
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Voltage
Voltage is the electrical potential energy and is measured in volts.
A good analogy is to think of a water hose. There is water pressure or potential
energy on the other side of the faucet or outlet valve. Once you open the faucet,
the pressure causes the water to rush through the hose.
The unit symbol for volts is V, as in 110V.
Current
Current indicates the amount of electrons passing through the wire and is
measured in amperes or amps for short. For some reason, they use I to
indicate current instead of a different letter. The unit symbol for amps is A, as in
2.0A.
Electrical current is similar to the rate of water flowing through a hose.
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Resistance
Electrical resistance can be thought of as the "friction" on the
movement of electrons in a wire. Resistance is measured in ohms,
and the unit symbol for it is the Greek letter omega, Ω. Thus 3 ohms is
often written as 3 Ω.
Most devices in an electrical circuit can be considered resistors,
including light bulbs and electric motors. Even the wire itself provides
some resistance. Just as you get some heat from friction, electrical
resistance also results in heat. That is why the light bulb filament gets
hot and glows.
Following the water hose analogy, resistance is similar to the
friction inside the hose.
But also, the resistance increases with a narrower hose, just like a
thin copper wire has more electrical resistance than a thick wire.
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Electrical Quantities & Units
■ Electric Charge, Q
– Energy exists at proton and electron
– Unit - Coulomb (C)
– 1 C - electrical quantity when 1 Ampere current flows
for 1 second in a conductor
■ Current, I
–
–
–
–
Rate of charge flows
I = Q / t Ampere (A)
1 A = transfer of 1 C charge in 1 s
DC and AC
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… Electrical Quantities & Units
■ Energy, W
– Capacity for doing work
– Unit - Joule (J)
■ Voltage, V @ E
–
–
–
–
Potential between 2 points in a circuit
Energy needed to transfer 1 unit charge
V = W/Q Joule/Coulomb @ Volt (V)
1V = Energy needed to transfer 1 C charge through
an element
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… Electrical Quantities & Units
■ Power, P
Rate for doing work
P = W / t Joule/s @ Watt (W)
1 W – Power used when 1 A current flowing through a
potential of 1 V
P = VI = (W/Q)(Q/t)
■ Resistance, R
All conductors have their own resistance
To limit the flow of current in a circuit
Unit – Ohm () – Element with resistance of 1  will allow 1 A
to pass through if 1 V voltage is applied across the element
R = 0 Ω – short circuit (large current flow)
R =  - open circuit (no current flow)
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… Electrical Quantities & Units
No
Quantity
Symbol
Unit
Formula
1
Charge
Q
Coulomb, C
Ixt
2
Current
I
Ampere, A
Q/t
3
Voltage
V
Volt, V
W/Q
4
Energy
W
Joule, J
Pxt
5
Power
P
Watt, W
W/t
6
Resistance
R
Ohm, Ω
V/I
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Capacitance
C
Farad, F
Q/V
8
Inductance
L
Henry, H
Φ/I
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Frequency
F
Hertz, Hz
1/t
10
Impedance
Z
Ohm, Ω
V/I
11
Admittance
X
Ohm, Ω
V/I
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Ohm's Law for Electrical Circuits
Ohm's Law states that in a simple electrical circuit, the
voltage equals the electrical current times the resistance.
(The current flowing in a circuit is directly proportional
to the voltage applied and inversely proportional to the
resistance at a constant temperature).
V = IR
where:
V is the voltage in volts
I is the current in amperes or amps
R is the resistance in ohms
IR is I times R
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…Basic Electrical Laws – Ohm’s Law
■ V=IR
V
I
R
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Example:
How many amperes of current are in the circuit below?
100 V
R
Vs
20 Ω
Using Ohm’s law: I =
Vs
R
=
100 V
20 Ω
= 5A
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…Basic Electrical Laws – Ohm’s Law
Examples:
1. An electric bulb uses 0.5 A of current with voltage
generated being 120 V. Determine the value of
resistance.
2. If a current of 0.5 A flows through resistor of 15 Ω,
calculate the voltage drop across the resistor.
1. Ans; R = V/I = 120/0.5 = 240 Ω
2. Ans; V = IR = 0.5 x 15 = 7.5 V
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…Basic Electrical Laws – Ohm’s Law
More Examples:
3. (i) For the circuit shown,
determine current flowing and
power absorbed by the resistor
if the resistance is 1 kΩ and
voltage across it is 10 V
I
+
+
V
R
Vs
(ii) If the current flowing through
the circuit is 3A and power
absorbed is 72 W, determine
the resistor value and voltage
across it.
-
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Voltage, Current and Resistance
Direct current or DC electricity is the continuous movement of
electrons from negative to positive through a conducting material such
as a metal wire. A DC circuit is necessary to allow the current or steam
of electrons to flow. In a circuit, the direction of the current is opposite
the flow of electrons. DC electricity in a circuit consists of voltage,
current and resistance. The flow of DC electricity is similar to the flow
of water through a hose. Batteries and DC generators are the sources
to create DC electricity.
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DC Power
The electric power in watts associated with a complete electric circuit
or a circuit component represents the rate at which energy is
converted from the electrical energy of the moving charges to some
other form, e.g., heat, mechanical energy, or energy stored in electric
fields or magnetic fields. For a resistor in a D C Circuit the power is
given by the product of applied voltage and the electric current :
P = VI
Power (watts) = Voltage (volts) x Current (amperes)
Power consumed = kilowatt hours (kWh) x charge (dollars, RM, etc)
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Calculating your electric bill
Computer : 500 watts (12 hours)
TV : 400 watts (5 hours)
Lighting : 3 x 15 watt = 45 watts (6 hours)
Others : 100 watts (2 hours)
P = VI
Power consumed :
(500 x 12) + (400 x 5) + (45 x 6) + (100 x 2) = 8470 wh = 8.47kWh
Electric bill per month : 8.47 kWh x RM 0.218/kWh x 30 = RM 55.50
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DC Circuit Water Analogy
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Voltage-Pressure Analogy
A battery is analogous to a pump in a water circuit. A pump takes in water at low
pressure and does work on it, ejecting it at high pressure. A battery takes in charge at
low voltage, does work on it and ejects it at high voltage.
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Current-Flow rate Analogy
Connecting a battery to an appliance through a wire is like using a large pipe for
water flow. Very little voltage drop occurs along the wire because of its small
resistance. You can operate most appliances at the end of an extension cord
without noticeable effects on performance.
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