GEGA1006-005

Lecture 12 – Electricity

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 Lecture Schedule

Serial Time Events

No.18 20/10/2023 Electricity
No.19 24/10/2023 Light
No.20 27/10/2023 Wind power
No.21 31/10/2023 Water energy
No.22 03/11/2023 Nuclear power
No.23 07/11/2023 GP4
No.24 10/11/2023 GP5
No.25 14/11/2023 GP6
No.26 17/11/2023 GP7
No.27 21/11/2023 battery
No.28 24/11/2023 Solar energy
No. 29 28/11/2023 review
No. 30 TBD Final Exam

2023/10/28 2
 Outline

1. What is electricity?

2. How to generate electricity?

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Electricity

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 Electricity
Electromagnetic induction Electric Engine
電磁感應

Faraday
Alternating current Alternating current

Edison Tesla Westinghouse

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 Electricity

Typhoon - Hato (2017-08-23)

https://www.hk01.com

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 Electricity
➢ Electricity provides lighting, cooling and heating, powers home appliances,
communication/internet, shower heaters, computers, mass transport trains and
numerous other machines.
➢ Comfortable and enjoyable modern life would not be possible without electricity.

Household electricity consumption http://www.youtube.com/watch?v=20Vb6hlLQSg 5:18

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 Electricity
• Electricity is convenient, safe and “clean” to the end-user. It is the most desirable
form of energy.
• We just pay the bill and let the power stations to take care of generating and
transmitting electricity to us.
• The voltage of 230 V (volts) in Macau reverses directions 50 times a second.
𝑉 𝑡 = 230 sin 2𝜋50𝑡 volt

2
Rms voltage= 𝑉
2 𝑝𝑒𝑎𝑘

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 Electric power system

• An electric power system is a network of electrical components deployed to

supply, transfer, store, and use electric power.

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 Basics about electricity
Electric Charges
There are two kinds of electric charges in all materials
• Negative charges are the type possessed by electrons （電子）
• Positive charges are the type possessed by protons （質子）

• Charges of the same sign repel one another

• Charges with opposite signs attract one another

同性相斥，異性相吸

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 Basics about electricity

Quantization of Electric Charges

- The electric charge, q, is an integral multiple of a fundamental unit of charge e,
thus q = N e, e = 1.6x10-19 C
- For an electron: q = –e , for a proton: q = +e

http://www.youtube.com/watch?v=XiHVe8U5PhU 9:27

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 Insulators and conductors
• Electrical insulators are materials in which all the electrons are bound
to atoms.
- The electrons cannot move freely in the material.
- Examples of good insulators include glass, rubber and wood.

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 Insulators and conductors

atom in a
conductor

• Electrical conductors are materials in which some of the

electrons are not bound to the atoms, they are free to move.
- These electrons are relatively free to move in the material.
- Examples of good conductors include copper, aluminum,
silver and gold.

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 Insulators and conductors
• To conclude,
what is the main difference of the insulator & conductor?

• Insulator (I): • Conductor (C):

non-conducting materials conducting materials

✓ The ability of electrons to move

freely within the materials…

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 PIA-1
• Select the insulator & conductor…

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 PIA-2

ways to generate the electric charges in

our daily life???

Triboelectrification…
摩擦生电

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 Basics about electricity
The electrical Current
• It is the charge flow in materials and is the amount of electricity that flows in the
circuit.
➢ Current (I) is measured in Coulombs per second or amperes or amps (A).
➢ The more current, the higher the amps.
➢ It is pushed and pulled by voltage.
➢ It produces heat.

Current (I) is actually a rate quantity, to

define how fast the charges (Q) passing
through a cross-section within the time (t).

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 Basics about electricity
The Circuit
◼ The path a current takes.
◼ It must be a complete loop.
◼ An incomplete circuit will not conduct electricity.

Lightning is current flowing

through air

The electrons, the charge carriers in an

electrical circuit, flow in the opposite
direction of the electric current.

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 Basics about electricity
The Voltage
• Voltage (V) is electromotive force. It is the force or push on electrons in the
circuit.
– It is referred to as potential difference.
– Has the potential to do work but does nothing by itself.
– It’s measured in volts (V).

Note: The number of electrons is the same

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 Basics about electricity
Resistance

• In life, resistance is the opposition to intended directions.

• You feel harder as there are some resistances.

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 Basics about electricity
The (electrical) Resistance

• Resistance is the opposition to current flow in the circuit.

• Basically: This is because as the electrons move through a material they will
collide with the atoms of the conductor.
• A resistor is a material that provides a specified resistance in an electric circuit.

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 Basics about electricity
How to Measure the Resistance

• Multimeter
– Resistance is measured in ohm ().

• The electronic color code has been

used since the early 1920s.

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 Basics about electricity

Resistor color codes

• Black,
• Brown,
• Red,
• Orange,
• Yellow,
• Green,
• Blue,
• Violet,
• Gray,
• and White

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 PIA-3

What is the resistance value of

the resistor?
violet
54.9 kΩ ± 0.10%

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 Basics about electricity
The Power
• Power is the amount of work that is done in the circuit per unit time.
– It is measured in Watts (W) = joule per second.
– Depends on the volts and amps
• Watts = Volts x Amps=V*I

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 Water System Analogy
Electrical
Water System Function
System
The prime mover. Supplies energy to the system.
Pump Generator
Converts motion to electrical energy
Object on which the electrical current flows. The
Pipe Conductor larger the pipe or conductor the more water or
current will flow.
The pressure or the push that moves the water or
Water Pressure Voltage
electrical impulse in the system.
Water Flow Current The amount of water or electricity that is flowing.
Restriction of the The characteristic that restricts water and
Resistance current flow.
water pipe
This is the rate at which electrical energy is changed
Amount of water
Power into useful work. The quantity of water delivered per
delivered unit time.

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 Ohm’s law
• When a voltage V (volt V) is applied across a resistor R (ohm Ω),
the current I (ampere A) through the resistor is given by

Georg Simon Ohm

Germany
16 March 1789 – 6 July 1854

https://en.wikipedia.org/wiki/Georg_Ohm

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 Ohm’s law
• The resistance R of a material is directly proportional to its length L and inversely
proportional to its cross-sectional area S,
R = ρ L /S （Ω）

where ρ is the resistivity （電阻率）, which is small for a conductor but large for
an insulator.
• Power P dissipated when a current I passes through an object with resistance R is
given by P = V I = I 2R, (W = J/s)

• A large amount of energy delivered by a large current will raise

the temperature of the conductor rapidly, emitting light and heat,
and will finally set the object on fire.
http://www.youtube.com/watch?v=MUfMPjMAwx8 0:23
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Electricity Generation

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 Generation - Fuel Types
Thermal Power

Coal

Nuclear

Natural Gas
Oil
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 Generation – Renewable types

Hydro Electric Geothermal

Solar Wind

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Coal-fired electric power plant layout

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Coal-fired electric power plant layout

https://www.youtube.com/watch?v=GI7AhajfhWE

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 Coal-fired electric power plant layout
1. The coal is brought and crushed to powder. This is feed to Boiler for
producing heat.
2. In boiler the water is converted to steam, then in super heater the
moisture is removed from the steam and the steam becomes super heated
steam.
3. The super heated steam rotates the shaft of the high pressure turbine.
4. The exhausted steam is sent to preheater and the steam then rotates the
intermediate pressure turbine.
5. The steam from the turbine is then feed to low pressure turbine.
6. The turbine shaft is connected to the generator, which produces electric
power.
7. The power generated is then transmitted for end-use.
8. Coal ash has to be removed from the boiler.

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Energy transfer process

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 Energy transfer process
➢ Typically, of the fossil energy in coal, ⅓ is turned into electricity, ⅔
is turned into low grade heat which is dumped to the sea or river or
the atmosphere via a cooling tower.
➢ The 2nd Law of Thermodynamics dictates that it is not possible to
convert all the low-grade heat energy into high grade electricity.

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 Steam turbine
• In commercial electric power generation, the magnetic rotor is rotated by a
steam turbine.

https://www.youtube.com/watch?v=A
yAd-gLO9CE 3:10 Basics

http://www.youtube.com/watch?v=
MulWTBx3szc 7:07 Detailed

Cross section view

• Steam turbines, powered first by coal, then later by oil, natural gas, and eventually
nuclear reactors, now generate about 80% of all electricity in the world. The rest is
contributed by water turbine, wind turbine…….
• Turbine power outputs of 1,000MW (1 GW) or more are typical for electricity
generating plants.
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 What is the steam turbine?
➢ Turbine is an engine that converts energy of fluid into mechanical energy. The steam turbine
is steam driven rotary engine.
➢ The steam turbine is a prime-mover in which pressure energy of steam is transformed into
kinetic energy, and later in its turn is transformed into the mechanical energy of rotation of
turbine shaft.
➢ A simple design of a turbine contains a rotor assembly, which is the moving part, having
shaft or drums with blades attached to them. The movement of the blades, which is caused by
the flow of steam, creates rotational energy which is imparted to the rotor.
➢ To maximize the efficiency of steam turbine the steam is expanded, generating work in
several stages.
➢ Multiple stages turbines are highly efficient.

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 PIA-4
In the fossil fuel power plant, the energy efficiency of generating
electricity as a percent of the heating value of the fuel consumed is
determined by the efficiency of:

A. Combustion chamber

B. Boiler

C. Steam turbine

D. Generator

E. All the above

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 Answer: 5) All of the above
• There is a theoretical limit to the percentage of energy that can be converted
from heat to mechanical energy in any heat engine, which is the steam turbine
does. This limit depends on the difference in temperature between the heat
source (burning coal) and the heat sink (the steam coming out the end of the
turbine). The higher the difference in temperature, the more efficient. Most coal
fired plants are well below the theoretical limit for their temperature delta, and
typical efficiencies are in the 30-40% range.
• The energy conversion efficiency of the high capacity generators can be as high
as 98% or 99% for a very large machine. (Note: This means that a 1000MW
generator must dissipate 20 MW of waste heat and such generators require
special cooling techniques.)
• Coal quality also has an impact on efficiency. For example, coal with a high
moisture content will be less efficient, because some of the heat energy in the
coal will be used up converting the water in the coal into steam, rather than into
heat.
http://www.green-energy-efficient-homes.com/energy-saving-facts.html
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