6.1 Generation of Electricity
Electricity is generated through various energy sources, which are broadly classified into renewable and non-renewable energy sources.
Energy Sources
- Renewable Energy Sources: Energy sources that can be replenished continuously and will not run out. Examples: Hydro, Solar, Wind, Biomass, Geothermal, Wave.
- Non-Renewable Energy Sources: Energy sources that are limited and cannot be replenished once depleted. Examples: Fossil fuels (Coal, Petroleum, Natural Gas), Nuclear energy.
Process of Generating Electricity
Most power stations use a generator to convert kinetic energy into electrical energy. A generator works on the principle of electromagnetic induction: when a conductor (copper wire coil) cuts across magnetic flux lines (or a magnet rotates inside a wire coil), an induced electric current is produced.
| Power Station Type | Energy Changes |
|---|---|
|
Thermal (Fossil Fuel) | Chemical energy → Heat energy → Kinetic energy (steam turns turbine) → Electrical energy |
|
Hydroelectric | Gravitational potential energy (water in dam) → Kinetic energy (flowing water turns turbine) → Electrical energy |
|
Nuclear | Nuclear energy → Heat energy → Kinetic energy (steam turns turbine) → Electrical energy |
|
Solar (Photovoltaic) | Solar energy (light) → Electrical energy (directly via solar cells, no turbine) |
|
Wind | Kinetic energy (moving air turns wind turbine) → Electrical energy |
Direct Current (d.c.) and Alternating Current (a.c.)
- Direct Current (d.c.): Electric current that flows in one fixed direction only. Produced by batteries, dry cells, solar cells, and d.c. dynamos.
- Alternating Current (a.c.): Electric current whose direction of flow reverses periodically. Produced by power station generators and a.c. dynamos. Standard household supply in Malaysia is 240 V, 50 Hz a.c.
- Cathode Ray Oscilloscope (C.R.O.): An electronic device used to display electric voltage waveforms, measure potential differences, and determine current types (d.c. appears as a straight horizontal line; a.c. appears as a sinusoidal wave).
6.2 Transformer
A transformer is an electrical device that increases or decreases the voltage of an alternating current (a.c.) based on the principle of electromagnetic induction.
Structure of a Simple Transformer
Consists of a laminated soft iron core wrapped with two insulated wire coils:
- Primary Coil ($N_p$): Connected to an alternating current (a.c.) input supply ($V_p$).
- Secondary Coil ($N_s$): Connected to an output load ($V_s$).
Types of Transformers
| Feature | Step-Up Transformer | Step-Down Transformer |
|---|---|---|
|
Primary vs Secondary Voltage | $V_s > V_p$ | $V_s < V_p$ |
|
Number of Turns | $N_s > N_p$ | $N_s < N_p$ |
|
Primary vs Secondary Current | $I_s < I_p$ | $I_s > I_p$ |
|
Application | Power stations (raises voltage for transmission) | Sub-stations and electrical appliances (lowers voltage to safe levels) |
Transformer Formula
For an ideal transformer (100% efficiency, where Input Power = Output Power):
$$\frac{V_p}{V_s} = \frac{N_p}{N_s}$$
where $V_p$ = Primary voltage, $V_s$ = Secondary voltage, $N_p$ = Primary turn count, $N_s$ = Secondary turn count.
6.3 Transmission and Distribution of Electricity
Electricity generated at power stations must be transmitted over long distances to consumers via the National Grid Network.
National Grid Network Components
- Power Station: Generates electricity at 11 kV or 25 kV a.c.
- Step-Up Transformer Station: Step-up transformer boosts voltage to 132 kV, 275 kV, or 500 kV to reduce energy loss during long-distance transmission.
- National Grid Network: High-voltage transmission lines on pylons that connect power stations nationwide. High voltage keeps transmission current extremely low, minimizing power loss as heat ($P = I^2 R$).
- Switch Zone / Main Sub-station: Directs electricity to regional networks and allows isolated shutdowns for maintenance.
- Step-Down Transformer Stations: Gradually step down voltage (e.g., 33 kV for heavy industry, 11 kV for light industry, down to 240 V for residential homes).
Electrical Supply and Wiring System in Homes
- Single-Phase Wiring: Suitable for residential homes with low to moderate electricity demand ($240\text{ V}$).
- Three-Phase Wiring: Suitable for commercial and industrial buildings or homes with high power consumption ($415\text{ V}$).
Main Components in Household Wiring
- Live Wire (Brown): Carries electric current at $240\text{ V}$ from the main supply to appliances.
- Neutral Wire (Blue): Completes the circuit by returning current back to the supply at $0\text{ V}$.
- Earth Wire (Green/Yellow striped): Safety wire connected to a metal rod in the ground ($0\text{ V}$); conducts leaked current away from metallic appliance casings to prevent electric shocks.
- Fuses & Miniature Circuit Breakers (MCB): Safety devices designed to melt or trip and break the circuit when excessive current flows due to short circuits or overloads.
- Electric Meter: Measures total electrical energy consumed in kilowatt-hours (kWh).
6.4 Energy Efficiency and Cost of Electricity
Energy efficiency is the percentage of total energy input that is converted into useful energy output:
$$\text{Energy Efficiency} = \left( \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \right) \times 100\%$$
Power, Voltage, and Current
Electrical Power ($P$) is the rate of electrical energy consumption, measured in Watts (W) or Kilowatts (kW):
$$P = V \times I \quad \text{or} \quad E = P \times t$$
where $P$ = Power (W), $V$ = Voltage (V), $I$ = Current (A), $E$ = Energy (J or kWh), $t$ = Time (s or hours).
Calculating Cost of Electricity Consumption
1 unit of electricity = 1 kilowatt-hour (1 kWh), which is the energy consumed by a 1 kW appliance operating for 1 hour.
$$\text{Energy consumed (kWh)} = \text{Power (kW)} \times \text{Time (hours)}$$
$$\text{Cost of Electricity} = \text{Energy consumed (kWh)} \times \text{Tariff rate per unit}$$
Energy Conservation and Green Technology
- Use energy-efficient appliances labeled with 5-Star Energy Rating.
- Replace incandescent bulbs with LED lamps (which convert more electrical energy into light rather than waste heat).
- Practice habitual energy conservation (turning off unused appliances, setting air conditioners to $24^\circ\text{C}-26^\circ\text{C}$).