Lesson Notes By Weeks and Term v4 - SHS 1
ELECTRICAL SYSTEMS DESIGN
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
ELECTRICAL SYSTEMS DESIGN
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Applied Technology
Class: SHS 1
Term: 1st Term
Week: 19
Grade code: 1.3.1.LI.2
Strand code: 3
Sub-strand code: 1
Content standard code: 1.3.1.CS.1
Indicator code: 1.3.1.LI.2
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRICAL SYSTEMS DESIGN
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
This lesson explores the incredible journey electricity takes from its generation point, like the Akosombo or Bui Dam, all the way to the sockets in our homes, schools, and local businesses. We often take electricity for granted, but understanding how it is transmitted and distributed across Ghana helps us appreciate this essential resource, use it safely, and understand the roles of companies like GRIDCo, ECG, and NEDCo. This knowledge is crucial for anyone aspiring to be an engineer, an electrician, or simply a well-informed and responsible citizen who understands why we sometimes experience "dumsor" and the dangers of illegal connections.
The Journey of Electricity: From Dam to Dumsor Switch
The electricity we use follows a three-stage journey. Think of it like a water delivery system. Stage 1: Generation (The Source) This is where electricity is produced. In Ghana, our main sources are: Hydroelectric: Using the force of water (e.g., Akosombo Dam, Bui Dam). Thermal: Burning gas or oil to create steam that turns turbines (e.g., Aboadze Thermal Plant, Karpower ships). Solar: Using sunlight (e.g., Navrongo Solar Power Station). The company mainly responsible for generation is the Volta River Authority (VRA) and other Independent Power Producers (IPPs). At the power station, electricity is generated at a moderately high voltage, typically around 11kV to 25kV (11,000 to 25,000 Volts). Stage 2: Transmission (The Highway) What is Transmission? This is the process of transporting large amounts of electricity over long distances, from the power plants to major substations near towns and cities. The Key Player: In Ghana, the Ghana Grid Company (GRIDCo) is solely responsible for this "electricity highway." You see their work in the huge metal towers (pylons) that carry thick cables across the country. Why High Voltage? Before transmission, a step-up transformer at the power plant increases the voltage to extremely high levels. Analogy: Imagine trying to send a lot of water through a very long, thin pipe. You need very high pressure to push it through efficiently. Similarly, high voltage "pushes" electricity through wires with less energy loss. The Science: Electrical power loss in a wire is calculated by the formula P = I²R (where P is power loss, I is current, and R is resistance). By increasing the voltage (V), we can decrease the current (I) for the same amount of power (since P = VI). A lower current means significantly lower power loss (I²). Advantages of High Voltage Transmission: Minimizes Power Loss: Less electricity is wasted as heat in the wires over long distances. Allows for Thinner Cables: Since the current is lower, the conductor cables can be smaller and lighter, which saves money. Disadvantages of High Voltage Transmission: Increased Danger: Extremely dangerous, requiring large pylons and significant clearance from buildings and trees. Higher Insulation Cost: Requires expensive and large insulators to prevent electricity from escaping. Typical Transmission Voltages in Ghana: 400 kV (400,000 V): Used for major international connections (e.g., West African Power Pool). 275 kV (275,000 V): Major national grid backbone. 161 kV (161,000 V): The most common transmission voltage across Ghana, connecting major regions. 132 kV (132,000 V): An older standard, still in use in some areas. Stage 3: Distribution (The Local Roads) What is Distribution? This is the final stage of delivering electricity from the major substations to our homes, schools, factories, and shops. The Key Players: In Ghana, this is handled by two main companies based on location: Electricity Company of Ghana (ECG): Operates in the southern parts of Ghana (Greater Accra, Ashanti, Western, Eastern, Central, Volta Regions). Northern Electricity Distribution Company (NEDCo): Operates in the northern parts of Ghana (Northern, Savannah, North East, Upper East, Upper West, and parts of Bono, Bono East, and Oti Regions). The Role of Substations: At a substation, a step-down transformer does the opposite of a step-up transformer. It reduces the very high transmission voltage to safer, lower levels for distribution. A typical distribution substation is a fenced-off area with large transformers, circuit breakers, switches, and insulators. It takes in high voltage (e.g., 161kV or 33kV) and sends out lower voltage. Distribution Voltage Levels in Ghana: Primary Distribution (33 kV, 11 kV): This voltage is sent from the main substation to smaller distribution substations on poles or concrete pads in our neighbourhoods. It also supplies power directly to large industrial customers like factories, mines, and universities. Secondary Distribution (415V / 240V): The pole-mounted or ground-mounted transformer near your house steps the voltage down from 11kV to the voltage we use. Single-Phase vs. Three-Phase Power
Once the electricity reaches our neighbourhood transformer, it is distributed in two main ways: Three-Phase Power (415 Volts): This system uses three live wires and one neutral wire. It provides a more constant and powerful supply of electricity. Application: Ideal for heavy-duty equipment with powerful motors like industrial machines, large air conditioners, corn mills, and welding machines. This is what factories and large workshops use. Single-Phase Power (240 Volts): This is a subset of the three-phase system. It uses one of the three live wires and the neutral wire. Application: This is the standard supply for our homes and small businesses. It is sufficient for lighting, televisions, refrigerators, computers, and other household appliances. The socket in your wall provides single-phase power.
| Voltage Level | Stage | Responsible Company | Typical Application | | --------------------- | ------------- | ------------------- | ---------------------------------------------------------- | | 161 kV, 275 kV, 400 kV | Transmission | GRIDCo | Long-distance bulk power transfer between regions. | | 33 kV, 11 kV | Distribution | ECG / NEDCo | Supplying power to large industries and neighbourhood substations. | | 415 V (3-Phase) | Distribution | ECG / NEDCo | Factories, workshops, large buildings with heavy machinery. | | 240 V (Single-Phase) | Distribution | ECG / NEDCo | Homes, schools, small shops, offices. | The Problem of Illegal Power Connections