SC 6.3

• 1. The generators at a power station produce alternating current with a voltage of 11 kV or 25 kV
  2. This current enters a transformer station. Here, this voltage is raise to 132 kV or 275 kV using a step-up transformer
  3. This alternating current then flows through a network of transmission cables called the National Grid Network
• 1. Then, from National Grid Network, it enters into a regional control and switching zone. Here, the electrical power is controlled before it is sent where and when it is needed. It is also allowing some stations and lines to be shut down without cutting off power supply
  2. From this zone, the alternating current flows through a series of step-down transformer and switching zones at the main substation and its branches before distributing to consumers
• The components involved in the electrical power transmission and distribution system are

  • Power station
  • Step-up transformer station
  • National Grid Network
  • Step-down transformer station
  • Substation

  
• National Grid Network

  1. A network of cables connecting all the power stations in the country
  2. The cable are made up of copper or aluminium
  3. Electrical energy from the power stations can be sent out to any are requiring without interruption
• The advantage of the National Grid Network

  1. Any area requiring additional electrical energy can be supplied by an additional power
  2. The function of a power station which is interrupted for maintenance can be taken over by another power station in the network
  3. Very large power stations are not necessary. Any are requiring a large quantity of electrical energy can be supply by two or more power station in the network
• Impact on residences located near the National Grid Network pylons

  • Strong magnetic field is produced by the high voltage alternating current and can be detected in the surrounding areas close to the pylons
  • Increases in the risk of getting cancer, headache, anxiety, fatigue and insomnia
• Electricity supply and wiring system in homes

  • Alternating current with a voltage of 240 V is supplied to our homes by the live wire
  • Current is returned to the substation by the neutral wire
  • Types of electrical wiring system
  • Single-phase wiring
  • Three-phase wiring
• Single-phase wiring

  • This type of wiring is only suitable and stable enough for electrical energy usage not exceeding 10 kW or 50 A
  • Requiring low and medium electricity
  • Two cables namely live wire and neutral wire
  • Supplies 240 V of electricity
  • Example: the residential areas in the country side (rural residential area)
• Three-phase wiring

  • For electrical energy usage exceeding 10 kW or 50 A, three-phase wiring that is more stable and more reliable is often used
  • Installed in industrial and commercial areas and residential homes using high-voltage motor and air conditioners
  • Three cables namely red cables, yellow wires and blue cables
  • Supplies 415V of electricity or higher
  • Example: the commercial and industrial areas
• Electrical supply and wiring system in homes

  • Fuse box
  • Protects a house circuit from damage caused by a large current or overloading
  • Main switch
  • Controls the amount of current which flows through the circuit into the house
  • Circuit breaker
  • Breaks the circuit by springing out or tripping
  • Earth Leakage Circuit breaker (ELCB)
  • Disconnect all internal circuits if the supplied current is greater than the specified one
  • Miniature Circuit breakers (MCB)
  • Segregate electrical circuits to other electrical appliances
  • Live wire
  • Carries current at a voltage of 240 V from the local substation to home

  
• • Neutral wire
  • Returns the current from homes to substation
  • Earth wire
  • Connects an appliance directly to earth as a safety measure
  • Electric meter
  • Records the amount of electrical energy that has been used
  • Main fuse
  • Controls the amount of electricity supplied to the home. Breaks the circuit automatically if excessive flow passes through it
• 3-pin plug

  • Used for high power appliances that use and electric current of up to 15 A such as electric kettles, electric rice cooker and air conditioners
  • Three types of wire
  • Live wire (L) Brown colour
  • Neutral wire (N) Blue colour
  • Earth wire (E) Yellow and green stripes
  • Has a cartridge fuse with a rating of 13 A
  • Widely used in Malaysia, Singapore, United Kingdom and Ireland
• 2-pin plug

  • Used for low-power appliances such as radios, electric shaver and electirc clocks
  • Two types of wire
  • Live wire (L) Brown colour
  • Neutral wire (N) Blue colour
  • No earth wire and fuse
  • China, Belgium and Germany use this type of plugs
• Plug

  • Used to connect electrical equipment to power circuits through socket
• Safety components in-home wiring systems:

  1. Fuse
  2. Earth wire
  3. Circuit breaker
  4. Lightning conductor
  5. Switch
• Fuse

  Function

  • Control an electric current in the circuit
  • Protects electrical appliances in electrical circuits from being damaged due to overflow of electric current
  • Avoid fire and accidents caused by short circuit
• How fuse work

  • If the stream is 'big' or excessive flowing in the circuit that is the current exceeds the value of the fuse, the fuse wire heat up, melt and break
• Fuse

  • Fuse consists of a short wire with a low melting point
  • Fuse wire are made of tin alloy and high resistance lead
  • The fuse are connected in the series in the circuit and mounted on the live wire (L)
  • Fuse are determined according to rating such as 1 A, 2 A, 3 A, 5 A, 10 A and 13 A
  • The value or rating of the fuse indicates the maximum current allowed through the circuit
  • Different electrical equipment require fuses of different value
  • The appropriate fuse is the fuse with rating that is slightly higher than the amount of current required by the equipment to operate
• Appropriate fuse rating for electrical equipment

  Formula

  • Current (I) = Power (W) / Voltage (V)
• Earth wire

  • A tool that connects the metal parts of electrical equipment to the earth
  • Any leaked current in the metal body of an electrical appliance will be safely passed to earth through the earth wire. The leaking current is said to have been grounded
  • If there is no earth wire, a person touching the metal body of an electric device with a current leakage is exposed to electrical shock causing injury or death.
  • Equipment that has been grounded is safe. A person will not be exposed to electric shock because a large current will flow through the earth wire and will not flow through the body
• Replaceable wire fuse

  • Wire-shaped
  • The rate is fixed
  • Broken fuse wires can be replaced
  • The body of the fuse is made of heat resistance materials like ceramic and bakelite

  Cartridge fuse

  • The rate is fixed
  • Broken fuse wire cannot be replaced
• Circuit breaker

  • An electric switch that automatically breaks all electrical circuits when there is a short circuit or 'electric load'
  • The difference between the circuit breaker and the fuse is that the fuse can be used only once but the circuit breaker can be reused after it is reset manually or automatically
  • Example
  • Moulded case circuit breakers (MCCBs)
  • Miniature circuit breakers (MCB)
  • Controls the value of current flowing to various parts of the circuit in the house
  • Earth leakage circuit breakers (ELCB)
  • Disconnect the electrical circuit when a large current is flowing
• Lightning Conductor

  • Lightning may cause death, fire and damage to building structures as well as electrical or electronic equipment
  • Installation of lightning conductors on high rise building is important to prevent unwanted occurrences
  • A lightning conductor is a long and thick iron rod where one sharp and branched tip is on the roof. The other tip is planted directly in the ground
  • Lightning conductor are installed at the highest part of the building
  • Lightning will snap on the terminal part of the conductor lightning and electric current will continue to flow to ground.
• Switch

  • A tool that can control an electric circuit and stop the flow of electric current
  • The switch is mounted on a live wire in the house wiring system
  • Types of switch
  • Toggle switch
  • Push switch
  • Two way switch
• Cause of electrical accidents

  • Most dangerous - electric shock and fire
  • The causes of electrical accidents
  • excessive flow
  • broken wire insulation
  • Wire insulation is installed to protect us when touching the wires, but the damaged insulation of live wire and Earth wire can cause electric shock and short circuit
  • Short circuit events cause excessive flows in the circuit and trigger fire
  • damp condition
• Safety in the use of electrical appliances

  • Electrical wiring at home must be installed in accordance with the regulations set by Tenaga Nasional Malaysia to ensure safety
  • Electricity can harms if we do not use it properly and cautiously
• Safety measures to prevent electrical accidents:

  • All cables and plugs are checked regularly and replaced if damaged
  • Do not charge the power plug
  • The 3-pin plug wiring should always be checked and made sure to be fitted with the correct fuse
  • Make sure the cable is away from water and heaters
  • Use the correct fuse rating for fuse installed in electrical appliances
  • Switch the electric appliance off after using it
  • Avoid self-repair of any electrical damage
  • Avoid pulling the wires when removing them from the socket
• Measures to be taken during electric shock

  • Switch off the main switch
  • Remove victims from sources of electricity using insulation material such as wood, rubber or plastic. Never touch the person with bare hand
  • Lay the victim in a comfortable state to breath
  • Open the victim's mouth and remove any food or barrier
  • If the victim is breathing with difficulty, immediately do Cardiopulmonary Resuscitation (CPR)
  • Contact the hospital emergency unit to send the victim for immediate medical attention
• In case of electrical fire

  • Switch off the main switch
  • use a powder fire extinguisher to put out the fire
  • call the fire brigade
• Sources of electrical accidents

  • The installation of too much electrical equipment on the same source cause the 'electric load' to be 'overloaded'
  • Damaged wire insulation can cause short circuit / fire
  • Touching the switch with moist hand can cause electric shock
• Safety measures to prevent electrical accidents:

  • Do not overload electrical sockets
  • Do not poke anything into an electric socket
  • Do not touch electrical appliances or switch with wet hand