Basic Electricity - Senior Secondary 3

TERM: 1^ST TERM

WEEK NINE

Class: Senior Secondary School 3

Age: 17 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC ELECTRICITY

Topic: PROTECTIVE DEVICES II

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Discuss the working principle of a fuse

II.) Discuss the working principle of a circuit breaker

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION	TEACHER’S ACTIVITY	STUDENT’S ACTIVITY
STEP 1 INTRODUCTION	The teacher explains that working principle of fuses and discuss the functions of fuses	Students listens attentively to the teacher
STEP 2 EXPLANATION	Teacher discusses the working principles of circuit breaker and state the functions of circuit breaker	Students exhibit attentiveness and active engagement
STEP 3 NOTE TAKING	The teacher writes a summarized note on the board	The students copy the note in their books

NOTE

PROTECTIVE DEVICES II

Principle of operation of electrical devices

The principles of operation of electrical devices depend on their specific type and function. However, many electrical devices operate based on fundamental principles of electromagnetism, electrical resistance, and thermal effects. Below is a general overview of how some common electrical devices work:

Working of a fuse: Fuses operate on the principle of electrical resistance and thermal effects. When current flows through a fuse, it encounters resistance in the fuse element, which causes it to heat up. If the current exceeds the rated value for the fuse, the heat generated by the excessive current melts the fuse element, interrupting the circuit and disconnecting the power supply.

Fuses are designed to protect electrical circuits from overcurrents and short circuits by sacrificing themselves to prevent damage to downstream equipment.

Functions of fuses

I.) Protection against overcurrents: Fuses interrupt the flow of current when it exceeds the rated value, protecting electrical circuits and equipment from damage due to overloads and short circuits.

II.) Safety: Fuses reduce the risk of electrical fires and hazards by disconnecting power in the event of excessive current flow.

Working of a crcuit Breaker: Circuit breakers operate based on the principles of electromagnetism, electrical resistance, and thermal effects. Unlike fuses, circuit breakers can be reset manually or automatically after tripping.

When a fault occurs in the circuit, such as an overload or short circuit, the current exceeds the rated value for the circuit breaker. The increased current generates a magnetic field that actuates a trip mechanism within the circuit breaker, causing it to open and disconnect the circuit.

Functions of Circuit Breakers

I.) Overcurrent protection: Circuit breakers trip and disconnect circuits when they detect overcurrents, preventing damage to equipment and wiring.

II.) Short circuit protection: Circuit breakers quickly interrupt the flow of current in the event of a short circuit, minimizing the risk of electrical faults and hazards.

III.) Manual and automatic operation: Circuit breakers can be manually reset after tripping or automatically reset depending on their design and application.

IV.) Remote operation: Some circuit breakers feature remote tripping capabilities, allowing for centralized control and monitoring of electrical systems.

EVALUATION: 1. Describe briefly the working principle of a circuit breaker

State 4 functions of circuit breakers
Discuss the working principle of a fuse
Mention 3 functions of a fuse

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively

Basic Electricity - Senior Secondary 3 - Protective devices II