# Mechanical and Electrical Systems

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Mechanical and Electrical Systems
SAB 2032/SAM 3012 (Sistem Mekanikal dan Elektrikal)

Mechanical and Electrical System
SAB 2032/SAM 3012 Lecturer: Dr. Khurram Kamal Dept. of Electrical Engineering (Faculty of Electrical Engineering/FKE) P07-405, Phone:

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)

Syllabus and Lecture Plan
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.

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

Marking Total 50% 1. Task : 10% 2. Test : 15% 3. Final Exam : 25%

Familiarization with electricity
Electric shock

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

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

…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

…Basic Electrical System
Example of Electrical System

…Basic Electrical System
Example of Electrical System

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.

What are free electrons?
What determines the conduction of electricity? What are the different types of electricity?

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.

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= x Coulomb Elec. charge= x 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.

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.

Free electrons among metal atoms

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.

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

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

Insulator Materials Material Dielectric constant Air (vacuum) Teflon Paper Oil Mica Glass Ceramic

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.

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.

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.

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.

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.

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.

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

… Electrical Quantities & Units
Energy, W Capacity for doing work Unit - Joule (J) Voltage, E Potential between 2 points in a circuit Energy needed to transfer 1 unit charge V = W/Q Volt (V) 1V = Energy needed to transfer 1 C charge through an element

… Electrical Quantities & Units
Power, P Rate for doing work P = W / t 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)

… Electrical Quantities & Units
No Quantity Symbol Unit Formula 1 Charge Q Coulomb, C I x t 2 Current I Ampere, A Q/t 3 Voltage V Volt, V W/Q 4 Energy W Joule, J P x t 5 Power P Watt, W W/t 6 Resistance R Ohm, Ω V/I 7 Capacitance C Farad, F Q/V 8 Inductance L Henry, H Φ/I 9 Frequency F Hertz, Hz 1/t 10 Impedance Z 11 Admittance X

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). 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 V = IR

…Basic Electrical Laws – Ohm’s Law
V=IR V I R

Example: How many amperes of current are in the circuit below? R 100 V
Vs 20 Ω I = Vs R = Using Ohm’s law: 100 V 20 Ω 5 A

…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

…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 (ii) If the current flowing through the circuit is 3A and power absorbed is 72 W, determine the resistor value and voltage across it.

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.

Power (watts) = Voltage (volts) x Current (amperes)
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)

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

DC Circuit Water Analogy

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.

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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