Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 2nd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Technology
Previous Lesson: Transmission: Meaning, Types and Accessories.
Topic: DISTRIBUTION
Subject Matter: meaning of distribution of electrical power, diagram of generation transmission and distribution, single phase supply, three phase supply, identifying voltage points on the chain.

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define electrical power distribution.
Describe the stages of electrical power delivery.
Differentiate between single-phase and three-phase supply.
Identify various voltage levels in the power distribution chain.

Affective Domain:

Appreciate the importance of electrical power distribution in daily life.
Show interest in understanding different electrical supply systems.

Psychomotor Domain:

Sketch the diagram of generation, transmission, and distribution of electrical power.
Accurately draw the power distribution diagram.

Participate actively in class discussions about electrical distribution.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Electrical Installation and Maintenance Work.
Lagos State Unified Scheme of Work for Electrical Installation and Maintenance Work SSS 1.
Baddoo, F.P.L. (2007). Electrical Installation Technology. Spectrum Books Limited.

Instructional Materials

The teacher will teach this lesson with the aid of:

Board diagrams showing power generation, transmission, and distribution.
Power system charts.
Pictures of distribution transformers.

Rationale for the Lesson

This lesson helps pupils understand how electricity is delivered from power stations to their homes and communities. It enables them to recognize the different stages and types of electrical supply, which is important for appreciating the infrastructure that powers daily activities.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of electricity, its sources, and simple electrical circuits.

Lesson Content/Board Summary

Electrical Power Distribution

Meaning of Electrical Power Distribution

Electrical power distribution is the final stage in the delivery of electricity. It involves carrying electricity from the transmission system to individual consumers through a network of substations and power lines.

Diagram of Generation, Transmission, and Distribution

The entire process of delivering electrical power involves three main stages:

Generation: Electricity is produced at power stations (e.g., hydropower, thermal, solar) at relatively low voltages (e.g., 11kV, 25kV).
Transmission: The generated voltage is stepped up by transformers to very high voltages (e.g., 132kV, 330kV) for efficient long-distance transport through transmission lines.
Distribution: At various substations, the high transmission voltage is stepped down to lower voltages (e.g., 33kV, 11kV, 415V/240V) suitable for supply to homes, businesses, and industries. This network includes primary and secondary distribution lines.

The teacher will sketch or display a diagram illustrating these stages, showing power stations, step-up transformers, transmission lines, step-down transformers (substations), distribution lines, and consumers.

Single-Phase Supply

Single-phase supply is an alternating current (AC) power system that uses two conductors: one phase (live) and one neutral. The voltage between the live and neutral conductors varies in unison.

The following are characteristics and uses of single-phase supply:

It is suitable for small loads and domestic appliances.
Commonly used in residential homes, small offices, and shops.
Provides a voltage of approximately 220V to 240V (line-to-neutral) in Nigeria.

Three-Phase Supply

Three-phase supply is an alternating current (AC) power system that uses three alternating currents, each having a phase difference of 120 degrees from the other two. It typically consists of three phase conductors and often a neutral conductor.

The following are characteristics and uses of three-phase supply:

It is suitable for large loads and industrial applications.
Commonly used in factories, large commercial buildings, and for heavy machinery (e.g., large motors).
Provides a voltage of approximately 400V to 415V (line-to-line) and 220V to 240V (line-to-neutral) in Nigeria.

Voltage Points in the Power Distribution Chain

Electrical power is transformed to different voltage levels at various points:

Generation Voltage: 11kV, 25kV (at power plants)
Transmission Voltage: 132kV, 330kV (for long-distance transport)
Sub-Transmission/Primary Distribution Voltage: 33kV, 11kV (to substations and industrial consumers)
Secondary Distribution/Consumer Voltage: 415V (three-phase), 240V (single-phase) (for homes and small businesses)

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them how electricity gets to their homes from the power stations. The teacher briefly reviews the concept of electricity generation.
Pupils’ Activity: Pupils respond to the questions and recall previous knowledge.
Learning Point: Pupils are prepared for the new lesson and connect it to prior knowledge.

Step 2: Explanation of Electrical Power Distribution

Time: 8 minutes
Teaching Skill: Explanation/Lecture
Teacher’s Activity: The teacher defines electrical power distribution and explains its role as the final stage of electricity delivery. The teacher highlights why it is important to step down voltages for safe use.
Pupils’ Activity: Pupils listen attentively and take notes.
Learning Point: Pupils understand the meaning and significance of electrical power distribution.

Step 3: Presentation of Generation, Transmission, and Distribution Diagram

Time: 10 minutes
Teaching Skill: Demonstration/Visualisation
Teacher’s Activity: The teacher sketches the diagram of generation, transmission, and distribution on the board or displays a chart. The teacher explains each stage, its purpose, and the components involved (e.g., power plant, transformers, transmission lines, substations).
Pupils’ Activity: Pupils observe the diagram, copy it into their notebooks, and ask questions for clarification.
Learning Point: Pupils visualize and understand the complete process of electrical power delivery.

Step 4: Introduction to Single-Phase Supply

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher introduces single-phase supply, explaining its characteristics (two conductors, uniform voltage variation) and typical uses in residential and small commercial settings. The teacher mentions the common voltage level (240V).
Pupils’ Activity: Pupils listen and note the key features and applications of single-phase supply.
Learning Point: Pupils understand what single-phase supply is and where it is used.

Step 5: Introduction to Three-Phase Supply

Time: 5 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher introduces three-phase supply, explaining its characteristics (three phase conductors, 120-degree phase difference) and typical uses in industrial and large commercial settings. The teacher mentions common voltage levels (415V/240V) and highlights the advantages for heavy loads.
Pupils’ Activity: Pupils listen, compare with single-phase supply, and note down the information.
Learning Point: Pupils understand what three-phase supply is and its applications, and can differentiate it from single-phase.

Step 6: Identifying Voltage Points

Time: 4 minutes
Teaching Skill: Identification/Reinforcement
Teacher’s Activity: Using the previously drawn diagram, the teacher points out and labels the different voltage levels at each stage: generation, transmission, sub-transmission, and distribution. The teacher emphasizes the purpose of stepping voltages up and down.
Pupils’ Activity: Pupils identify the voltage points on their copied diagrams and ask questions.
Learning Point: Pupils can identify and recall typical voltage levels at different stages of power delivery.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define electrical power distribution.
List three main stages in the delivery of electrical power.
State two differences between single-phase and three-phase supply.
Mention two typical voltage levels found in the transmission stage of power delivery.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the main points of the lesson, reiterating the importance of electrical distribution and the different types of supply. The teacher assigns homework: “Draw and label a complete diagram showing the generation, transmission, and distribution of electrical power, indicating typical voltage levels at each stage.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Distribution – The final stage of delivering electricity to consumers.
Generation – The production of electrical power.
Transmission – The long-distance transport of high-voltage electricity.
Single-phase – An AC power system with one phase and one neutral conductor, suitable for small loads.
Three-phase – An AC power system with three phase conductors, suitable for large industrial loads.
Voltage – The electrical potential difference between two points.

Differentiation

For pupils who grasp concepts quickly, the teacher can ask them to research the advantages and disadvantages of AC versus DC transmission. For pupils needing more support, the teacher will provide simplified diagrams and allow peer tutoring to reinforce understanding.

Note for teachers using this lesson plan

Ensure that the diagrams drawn on the board are clear and large enough for all pupils to see. Encourage pupils to ask questions to clarify any doubts, especially regarding the voltage levels and the difference between single-phase and three-phase systems. Real-life examples of appliances using single-phase versus industrial machinery using three-phase can help pupils relate to the concepts.