Transformer Classification and Efficiency for SS 3

Class: SS 3
Term: First Term
Week: 2
Age: 14 years
Duration: 45 minutes
Subject: Basic Electricity
Previous Lesson: Trans
Topic: TRANSFORMER EFFICIENCY -Calculation of transformer efficiency.
Subject Matter: Classification of transformer by phase and by core: Definition of transformer efficiency

Specific Objectives

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

Cognitive Domain

• Classify transformers by phase (single-phase and three-phase).
• Classify transformers by core construction (core-type and shell-type).
• Define transformer efficiency.
• State the formula for calculating transformer efficiency.

Affective Domain

• Appreciate the importance of transformer efficiency in power transmission.
• Show interest in identifying different types of transformers.

Psychomotor Domain

• Calculate the efficiency of a transformer using given input and output power values.
• Illustrate the different types of transformer core constructions.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Basic Electricity for Senior Secondary Schools textbook
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Various types of transformers (e.g., small single-phase, three-phase, core-type, shell-type if available)
• Charts or diagrams illustrating transformer classification by phase and core.
• Whiteboard and markers
• Calculator

Rationale for the Lesson

This lesson is important as it provides students with a fundamental understanding of transformer types, which are essential components in electrical power systems. Understanding transformer efficiency helps in appreciating energy conservation and the economic aspects of power transmission. This knowledge forms a basis for further studies in electrical engineering.

Prerequisite/Previous Knowledge

Students should have a basic understanding of what a transformer is, its main components, and its working principle from previous lessons.

Lesson Content/Board Summary

TRANSFORMER EFFICIENCY

Classification of Transformers

Transformers can be classified based on different criteria, primarily by the number of phases and by their core construction.

By Phase

Transformers are classified by phase as follows:

1. Single-phase Transformers: These transformers are used in single-phase power systems. They have one primary winding and one secondary winding. They are commonly used for domestic power supply and in small electrical appliances.
2. Three-phase Transformers: These transformers are used in three-phase power systems, which are common for industrial applications and long-distance power transmission. A three-phase transformer consists of three sets of primary and secondary windings, either built as a single unit or as three separate single-phase transformers connected together.

By Core Construction

Transformers are classified by their core construction as follows:

1. Core-type Transformers: In a core-type transformer, the windings surround a significant portion of the core. The core is typically rectangular, and the windings (both high-voltage and low-voltage) are placed around the two limbs of the core. This construction provides good insulation and cooling.
2. Shell-type Transformers: In a shell-type transformer, the core surrounds a significant portion of the windings. The windings are usually wound on the central limb of a three-limbed core, and the core material forms a shell around the windings. This construction offers better mechanical protection for the windings and improved cooling due to a larger surface area for heat dissipation.

Definition of Transformer Efficiency

Transformer efficiency is a measure of how effectively a transformer transfers electrical power from its primary winding to its secondary winding. It is defined as the ratio of the output power (power delivered to the load) to the input power (power drawn from the source), usually expressed as a percentage. An ideal transformer would have 100% efficiency, meaning no power is lost during the transformation process, but in reality, all transformers have some losses.

Calculation of Transformer Efficiency

The efficiency of a transformer ((eta)) is calculated using the following formula:

Formula

(eta = frac{text{Output Power (P_{out})}}{text{Input Power (P_{in})}} times 100%)

Alternatively, considering the power losses within the transformer:

(eta = frac{text{Output Power (P_{out})}}{text{Output Power (P_{out}) + Total Losses (P_{losses})}} times 100%)

Where:

1. (P_{out}) = Output power (power delivered to the load) in Watts (W).
2. (P_{in}) = Input power (power drawn from the source) in Watts (W).
3. (P_{losses}) = Total power losses within the transformer (sum of copper losses and core losses) in Watts (W).

It is important to note that (P_{in} = P_{out} + P_{losses}).

Example 1

Question: A transformer has an input power of 1200 W and an output power of 1140 W. Calculate its efficiency.

Solution:

Step 1: Write the formula for efficiency.

(eta = frac{P_{out}}{P_{in}} times 100%)

Step 2: Substitute the given values.

(eta = frac{1140 text{ W}}{1200 text{ W}} times 100%)

Step 3: Simplify and write the answer.

(eta = 0.95 times 100%)

Answer: (eta = 95%)

Example 2

Question: A transformer delivers 9.5 kW to a load. If the total losses in the transformer are 500 W, calculate its efficiency.

Solution:

Step 1: Convert all power values to the same unit (Watts).

(P_{out} = 9.5 text{ kW} = 9.5 times 1000 text{ W} = 9500 text{ W})

(P_{losses} = 500 text{ W})

Step 2: Write the formula for efficiency using output power and losses.

(eta = frac{P_{out}}{P_{out} + P_{losses}} times 100%)

Step 3: Substitute the values.

(eta = frac{9500 text{ W}}{9500 text{ W} + 500 text{ W}} times 100%)

(eta = frac{9500 text{ W}}{10000 text{ W}} times 100%)

Step 4: Simplify and write the answer.

(eta = 0.95 times 100%)

Answer: (eta = 95%)

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Problem Solving

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling previous knowledge

Teacher’s Activity: The teacher greets the students and asks questions about the previous lesson on transformers, such as “What is a transformer?” and “What are its main parts?”.

Pupils’ Activity: Students respond to the questions, recalling their knowledge of transformers.

Learning Point: Transformer basic concepts

Step 2: Classification of Transformers by Phase

Time: 8 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the classification of transformers by phase (single-phase and three-phase), displaying relevant diagrams or samples if available. The teacher highlights their uses.

Pupils’ Activity: Students observe the diagrams/samples, listen attentively, and ask questions for clarification.

Learning Point: Transformer phase classification

Step 3: Classification of Transformers by Core

Time: 8 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the classification of transformers by core construction (core-type and shell-type), using diagrams or physical models to illustrate the differences.

Pupils’ Activity: Students observe the illustrations, listen to the explanation, and identify the differences in core construction.

Learning Point: Transformer core classification

Step 4: Definition of Transformer Efficiency

Time: 5 minutes

Teaching Skill: Defining/Explaining

Teacher’s Activity: The teacher defines transformer efficiency as the ratio of output power to input power, explaining why efficiency is important in electrical systems.

Pupils’ Activity: Students listen and write down the definition of transformer efficiency.

Learning Point: Meaning of efficiency

Step 5: Formula for Transformer Efficiency

Time: 5 minutes

Teaching Skill: Formula introduction

Teacher’s Activity: The teacher writes the formula for transformer efficiency on the board and explains each term ((P_{out}), (P_{in}), (P_{losses})) and their units.

Pupils’ Activity: Students copy the formula and the explanation of terms into their notebooks.

Learning Point: Efficiency formula components

Step 6: Calculation of Transformer Efficiency

Time: 5 minutes

Teaching Skill: Problem Solving/Guided Practice

Teacher’s Activity: The teacher works through Example 1 and Example 2 from the Board Summary on the board, explaining each step clearly. The teacher encourages students to follow along and use their calculators.

Pupils’ Activity: Students follow the teacher’s steps, perform calculations on their own, and ask questions if they encounter difficulties.

Learning Point: Calculating transformer efficiency

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. Mention two ways transformers are classified.
2. Define transformer efficiency.
3. State the formula for calculating transformer efficiency.
4. A transformer has an input power of 500 W and an output power of 475 W. Calculate its efficiency.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Transformer classification and efficiency

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 transformer classification, definition, and efficiency calculation into their notebooks.

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

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 0 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher briefly recaps the main points of the lesson, reiterating the importance of understanding transformer types and efficiency. The teacher then dismisses the class.

Pupils’ Activity: Students listen to the recap and prepare for dismissal.

Learning Point: Lesson summary

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook:

1. Differentiate between core-type and shell-type transformers, illustrating with simple sketches.
2. A transformer has an output power of 2.8 kW and experiences total losses of 200 W. Calculate the efficiency of the transformer.
3. Explain why transformer efficiency is never 100%.

Lesson Keywords

• Transformer – An electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.
• Efficiency – The ratio of useful output power to total input power, expressed as a percentage.
• Single-phase – An electrical system with one alternating current (AC) voltage.
• Three-phase – An electrical system with three alternating current (AC) voltages, typically 120 degrees out of phase with each other.
• Core-type – A transformer construction where windings surround the core.
• Shell-type – A transformer construction where the core surrounds the windings.
• Output power – The power delivered by the transformer to the load.
• Input power – The power supplied to the transformer from the source.
• Losses – Power dissipated as heat within the transformer (e.g., copper losses, core losses).

Differentiation

For weaker learners, the teacher will provide simplified diagrams of transformers and offer additional guided practice on efficiency calculations with simpler numbers. Faster learners will be challenged to research the different types of losses in a transformer and their impact on efficiency.

Suggested Lesson Videos

For further understanding, students can search for “Transformer Classification and Efficiency” on YouTube.

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have clear diagrams or actual samples of single-phase, three-phase, core-type, and shell-type transformers available for display. Prepare the whiteboard with the key definitions and formulas for efficiency. Begin by reviewing previous knowledge to ensure students recall transformer basics. Proceed with classifying transformers by phase and then by core, using visual aids to make the concepts concrete. Clearly define transformer efficiency and introduce the formula, explaining each term. Work through the provided examples step-by-step, encouraging student participation and calculator use. During the note-taking stage (Step 8), ensure students accurately copy the Board Summary. Pay attention to common errors in calculation and reinforce the importance of unit consistency. Support weaker learners by simplifying explanations and providing extra practice, while challenging faster learners with deeper inquiries into transformer losses. Ensure a safe classroom environment, especially if handling actual transformer samples.