f3 chapter 8 - generation of electricity

7/28/2019 F3 Chapter 8 - Generation of Electricity

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SCIENCE INTENSIVE PROGRAMME FOR FROM 3

CHAPTER 8 : GENERATION OF ELECTRICITY

SMK SUNGAI PASIR , O8OOO SUNGAI PETANI , KEDAH DARULAMAN.

TEL : 04-421 1764 FAX : 422 0203 LAMAN WEB : WWW.SMKSP.COM

1 Generator is a divice used to change mechanical

energy into electrical energy.

Structure og a transformer

Principle of a generator 5 When an alternating current is passed through the

primary coil, a changing magnetic field is produce in

the coil. This magnetic field will produce electric

current in the secondary coil.

(Note : A direct current cannot be used to shows how

a transformer works)

6 There are two types of transformer :[1] Step-up Transformer

Dynamo as a simple model of generator

2 There are various types of generators used in the

power stations :

Hydroelectric generator

Nuclear generator

Thermal generator

Gas turbine generator Function Increase the input voltage.

Diesel generator Characteristics

1. Secondary coil has more turns than

(The electric current produced in a power station is primary coil. alternating current .) 2. Out voltage higher than input voltage.

3 Alternative sources of energy : [2] Step-down Transformer

Biomass energy

Solar energy

Wind energy

4 Transformer is a divice used to increase(step up) or

decrease(step down)the voltage of alternating current.

Function Decrease the input voltage.

Characteristics1. Primary coil has more turns than

secondary coil.

2. Out voltage lower than input voltage.

Transformer at a substation

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input

voltage

input

voltage

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7 A transformer is never 100% efficient because : 11 The wiring system at home :

Resistance in the coil.

Energy lost in the coil (in the form of heat energy)

8 The efficiency of a transformer can be increase by

using :

Low resistance wire for the coil.

( e.g. copper wires)

Laminated soft iron plates to form the core.

(to reduce amount of heat produced in the core)

9 The relationship between the voltage and the number

of turns of the core is given by the following equation : 1. The voltage supplied to the house is 220 V - 240 V.

2. The current supplied to the house is an alternating current

Primary input voltage=

Number of turns in primary coin with a frequency of 50 Hertz (Hz).

Secondary output voltage Number of turns in secondary coin 3. Current is brought to the house by live wire and returned

to the substation by the neutral wire, which is earthed

10 The components in the electricity transmission and 4. The live wire and the neutral wire are connected to :

distribution system : Main fuse box : It controls the electrical supply to the

whole house.

Meter : It measure the electrical energy (not current)

used in kilowatt-hours (kWh)

Main switch : It controls the electrical supply to all the

circuits in the house.

Circuit breaker : It trips and cuts off the current to the

whole house if there is excessive current leakage

to the earth.

Distribution fuses(MCB) : A distribution fuse controls

only one circuit in one part of the house. If the fuse

blows, only the circuit it controls will have no current.

5. All the lighting and the power circuits are connected in

parallel so that each bulb or appliance can be controlled by its own switch.

6. There are two types of electrical wiring :

1. The power station generates alternating current. Single Phase Wiring :

2. A set-up transformer than increase the input voltage to a very Usually used in houses for a voltage supply of 220v-

high output voltage. 240V.

3. The electricity than channelled into switch zone which can cut Three Phase Wiring :

off the electric supply automatically if a short circuit occurs. Usually used in houses, multi-storey office buildings

4. National Grid Network will channelled the electricity from & industrial buildings for a voltage supply which more

switch zone to all the main power station in the country. than 415 V. Houses that use certain air conditioner that

5. At the main substation, the voltage is stepped down and need high voltage need to use three-phase wiring.

channelled the electricity to branch substation in various areas.6. At the branch substation, the voltage is stepped down further

depending on the requirements of the areas.

(e.g. Industrial area : 415 V , Residential are : 220-240 V)

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18 Cost of electrical energy usage at home is calculate in a unit called kilowatt-hour (kWh)

Kilowatt-hours = Kilowatts x hours

19 In residential areas, cost of electrical energy usage based on the following rates :

Usage of electrical energy (unit) Payment rate(RM)

First 200 units 0 . 218

Next 800 units 0 . 258

Subsequent additional units 0 . 278

An air conditioner unit of 2 kW is used for 5 hour.

Calculate the cost of electricl energy usage.

Kilowatt-hours = Kilowatts x hours

= 2 kW x 5 hours

= 10 kW

Cost = 10 units x RM 0 . 218

= RM 2 . 18

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12 A 3-pin plug is used to connect an electrical appliance It has an earth wire to carry any leaked current

to the power circuit because : from the appliance to the Earth.

It has a fuse to safeguard the appliance from

excess current. 13 The colour code of the wire in the 3-pin plug follow

the international colour code :

Wiring in a 3-pin plug

14 The earth wire is a safety divice which connected to the metallic body of an electrical appliance. Any current

leaks from the body of the electrical appliance will be channelled safety to Earth (Earthed).

Socket 3-pin plug Cable for 3-pin plug Appliance (e.g. Kettle)

15 Fuse also a safety device to prevent excessive current from flowing through a circuit/electrical appliance when

a short-circuit occurs.

16 There are two types of fuse :

Wire Fuse Cartridge Fuse

17 A fuse is rated in amperes and can determined by using the following formula :

Current =Power

Voltage

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Causes of electrical accidents at home

20 The most common hazards of electrical accidents are electric shock and fire.

21 Steps to be taken when get electric shock :

(1) Switch off the electrical supply at once.

(2) Use a suitable insulator (e.g. long wooden stick) to push the victim away from the power source.

(3) If victim not breathing, apply artificial respiration (mouth-to-mouth resuscitation)

(4) Call ambulance or send the victim to a doctor immediately.

22 Importance of conserving electricity :

Saving money

Saving energy resources

Saving the environment

Reducing risk of power loss.

23 Ways to conserve electricity :

Always turn off electrical appliance when they are not in use.

Always consider the energy efficiency when buying electrical appliance.

Use the electrical appliance efficiently :

- Wash and iron if only full loads of clothing.

- Do not open refrigerator and freezer doors too often.

24 Problem of electricity shortage :

Price of electricity increase

Affect the investor's confidence.Slow down the economic growth.

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f3 chapter 8 - generation of electricity

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