Electric Motor Rewinding, Conductors and Insulation for SS 3

Class: SS 3
Term: First Term
Week: 9
Age: 16-17 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Electrical Machines and Power Systems
Previous Lesson: Winding Drawings, Wave and Lap Windings
Topic: REWINDING OF ELECTRIC MOTOR
Subject Matter: MOTOR; Size of conductors and types of insulating methods; Construction of winding formers; Connection f winding coil; Continuity and earthing test

Specific Objectives

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

Cognitive Domain

• Explain the purpose of electric motor rewinding.
• Identify different sizes of conductors used in motor rewinding.
• Describe various types of insulating methods for motor windings.
• Explain the process of constructing winding formers.
• Describe the steps involved in connecting winding coils.
• Explain the importance of continuity and earthing tests.

Psychomotor Domain

• Construct a simple winding former.
• Demonstrate the connection of a winding coil.
• Perform a continuity test on a winding coil.
• Perform an earthing test on a motor winding.

Affective Domain

• Appreciate the importance of safety precautions during motor rewinding.
• Demonstrate precision and care in handling winding materials.
• Value the need for accurate testing of rewound motors.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Electrical Installation and Maintenance Work for Senior Secondary Schools, Book 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Winding formers
• Copper coils
• Copper wire (various sizes)
• Varnish insulator
• Insulating paper/material
• Multimeter/Ohmmeter
• Sample electric motor (for demonstration)
• Tools for former construction (e.g., wood, saw, hammer)

Rationale for the Lesson

This lesson is important as it provides students with practical skills in electric motor maintenance, a critical aspect of electrical installation. Understanding motor rewinding enables students to diagnose and repair faulty motors, extending their lifespan and reducing replacement costs. This knowledge is essential for future electricians and technicians in various industries.

Prerequisite/Previous Knowledge

Students should have prior knowledge of basic electrical circuits, types of electric motors, and the function of conductors and insulators in electrical systems.

Lesson Content/Board Summary

REWINDING OF ELECTRIC MOTOR

Electric Motor Rewinding

Electric motor rewinding is the process of replacing the worn-out or damaged copper windings inside an electric motor with new ones. This process restores the motor’s functionality and efficiency, often after insulation breakdown or overheating.

Size of Conductors and Types of Insulating Methods

The size of conductors (copper wire) used in motor rewinding depends on the motor’s power rating, voltage, and current requirements. Larger motors require thicker gauge wires to carry higher currents without overheating.

Types of insulating methods are crucial to prevent short circuits between windings and between windings and the motor frame. Common methods include:

1. Varnish Insulation: Applying insulating varnish to the completed winding to seal and protect the coils from moisture, dust, and vibration.
2. Insulating Paper/Mylar: Placing insulating paper or Mylar sheets between coil layers and between coils and the motor core slots.
3. Sleeving: Using insulating sleeves (e.g., fiberglass or PVC) over lead wires and coil connections.
4. Epoxy Resins: Encapsulating windings in epoxy for severe environmental conditions.

Construction of Winding Formers

Winding formers are templates used to shape the new coils to the correct size and shape before they are inserted into the motor’s stator slots. They are typically made from wood, plastic, or metal and are designed to match the specific dimensions of the motor’s stator slots and coil pitch.

Steps for constructing a winding former:

1. Measure the internal dimensions of the stator slots and the required coil span.
2. Cut and shape material (e.g., wood blocks) to create the desired coil shape.
3. Assemble the shaped pieces securely to form a rigid former.
4. Ensure smooth surfaces to prevent damage to the winding wire during coiling.

Connection of Winding Coils

After winding the coils on the former and inserting them into the stator slots, they must be correctly connected. The connection method depends on the motor type (e.g., single-phase, three-phase) and desired winding configuration (e.g., series, parallel, star, delta).

General steps for coil connection:

1. Identify the start and end leads of each coil.
2. Connect coils in series or parallel according to the winding diagram.
3. Ensure correct phase sequence for three-phase motors.
4. Solder or crimp connections securely and insulate them properly with sleeving and varnish.

Continuity and Earthing Test

After rewinding and connecting the coils, it is essential to perform tests to ensure the motor operates safely and correctly.

1. Continuity Test

   A continuity test checks for an unbroken path in the winding circuit. It ensures there are no open circuits in the coils. A multimeter set to resistance (ohms) is used. A low resistance reading indicates continuity, while an infinite reading indicates an open circuit.

2. Earthing Test (Insulation Resistance Test)

   An earthing test, also known as an insulation resistance test, checks for insulation breakdown between the windings and the motor frame (earth). It ensures that the current does not leak to the motor casing, which could cause electric shock. A multimeter (on a high resistance range) or a megohmmeter is used. A very high resistance reading (ideally infinite) between the winding and the motor frame indicates good insulation. A low reading indicates a fault to earth.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Engaging/Recalling

Teacher’s Activity: The teacher greets the students and asks them to recall the basic components of an electric motor and the function of its windings. The teacher then introduces the topic of electric motor rewinding and its importance.

Pupils’ Activity: Students respond to questions about motor components and listen attentively to the introduction.

Learning Point: Motor winding importance

Step 2: Motor Rewinding Overview and Conductor Sizes

Time: 8 minutes

Teaching Skill: Explaining/Illustrating

Teacher’s Activity: The teacher explains what motor rewinding entails and why it is necessary. The teacher then describes different sizes of conductors (copper wire) used for motor windings, explaining that the size depends on motor specifications. The teacher shows samples of different wire gauges.

Pupils’ Activity: Students observe the wire samples, ask questions, and take notes on conductor sizes.

Learning Point: Conductor size selection

Step 3: Types of Insulating Methods

Time: 7 minutes

Teaching Skill: Describing/Demonstrating

Teacher’s Activity: The teacher describes and shows samples of various insulating materials and methods used in motor rewinding, such as varnish, insulating paper, and sleeving. The teacher explains the purpose of each method.

Pupils’ Activity: Students examine the insulating materials and ask questions about their application.

Learning Point: Insulation methods explained

Step 4: Construction of Winding Formers

Time: 7 minutes

Teaching Skill: Demonstrating/Guiding

Teacher’s Activity: The teacher explains the purpose of winding formers and demonstrates how a simple former can be constructed or shows a pre-made former, explaining its features. The teacher encourages students to sketch a winding former.

Pupils’ Activity: Students observe the demonstration, sketch a winding former, and ask questions about its construction.

Learning Point: Winding former construction

Step 5: Connection of Winding Coils

Time: 6 minutes

Teaching Skill: Demonstrating/Explaining

Teacher’s Activity: The teacher demonstrates the basic steps involved in connecting winding coils, using a simplified model or diagram. The teacher emphasizes the importance of following a winding diagram and ensuring secure, insulated connections.

Pupils’ Activity: Students observe the demonstration and discuss the connection process.

Learning Point: Coil connection techniques

Step 6: Continuity and Earthing Test

Time: 5 minutes

Teaching Skill: Demonstrating/Explaining

Teacher’s Activity: The teacher explains the importance of continuity and earthing tests. The teacher then demonstrates how to perform both tests using a multimeter on a sample winding or a rewound motor, explaining the expected readings.

Pupils’ Activity: Students observe the testing procedures and note the expected readings for continuity and earthing.

Learning Point: Winding testing procedures

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

1. What is the primary purpose of motor rewinding?
2. Mention two types of insulating methods used in motor windings.
3. Why is it important to construct a winding former accurately?
4. Briefly explain how to perform a continuity test on a winding coil.
5. What does a low resistance reading during an earthing test indicate?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Motor rewinding assessment

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on motor rewinding, conductor sizes, insulation methods, former construction, coil connection, and testing into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Rewinding concepts recorded

Step 9: Conclusion

Time: 3 minutes

Teaching Skill: Summarising/Reinforcing

Teacher’s Activity: The teacher briefly summarises the key aspects of electric motor rewinding, emphasizing the practical skills acquired and the importance of safety and accuracy in the process. The teacher encourages students to practice these skills.

Pupils’ Activity: Students listen and ask any final clarifying questions.

Learning Point: Motor rewinding reinforced

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Answer the following questions and attempt the practical task:

1. List three factors that determine the size of conductor used for motor rewinding.
2. Describe the steps you would take to construct a winding former for a small single-phase motor, assuming you have the necessary measurements.
3. Explain the difference between a continuity test and an earthing test in the context of motor rewinding.
4. Using available scrap materials (e.g., wood, cardboard), attempt to construct a simple winding former based on a hypothetical motor dimension (e.g., 5cm x 3cm coil size).
5. Research and identify two common faults that necessitate electric motor rewinding.

Lesson Keywords

• Rewinding – Replacing old or damaged motor windings with new ones.
• Conductor – Material, usually copper wire, that allows electric current to flow easily.
• Insulation – Material used to prevent electric current from escaping its intended path.
• Winding Former – A template used to shape coils to specific dimensions.
• Coil Connection – The process of joining individual winding coils to form a complete circuit.
• Continuity Test – An electrical test to check for an unbroken path in a circuit.
• Earthing Test – An electrical test to check for insulation breakdown between windings and the motor frame.
• Varnish – An insulating liquid applied to windings for protection.

Differentiation

For learners who grasp the concepts quickly, provide additional motor diagrams with different winding configurations (e.g., star/delta) for them to interpret and discuss connection strategies. For students needing more support, provide pre-drawn diagrams of winding formers and step-by-step pictorial guides for the testing procedures. Encourage peer-to-peer teaching during practical demonstrations.

Suggested Lesson Videos

For further understanding, students can search on YouTube for:
electric motor rewinding ss3 nigeria

Teacher Guide for Using This Lesson Plan

Teachers should ensure all practical materials, including different gauges of copper wire, various insulating materials, and a multimeter, are ready before the lesson. Begin by engaging students with questions about motor functions to activate prior knowledge. During the lesson, emphasize the practical aspects by demonstrating the construction of a winding former, the connection of coils, and the continuity/earthing tests. Allow students to observe closely and ask questions. When conducting the tests, clearly explain what each reading signifies. Ensure students understand the safety precautions associated with handling electrical components and testing. The Board Summary should be copied by students after the main teaching points have been covered and understood. Provide individualized support during practical activities and encourage faster learners to assist their peers. Regularly check for understanding through questions and practical observations.