Basic Electricity - Senior Secondary 3 - Transformers efficiency

TERM: 1^ST TERM

WEEK TWO

Class: Senior Secondary School 3

Age: 17 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC ELECTRICITY

Topic: TRANSFORMERS EFFICIENCY

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

I.) Discuss the construction of a single phase and a three-phase transformer

II.) Describe the working principles of a transformer

III.) State the uses a transformer.

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

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

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

TRANSFORMERS EFFICIENCY

Construction of transformers

1. Single Phase Transformer Construction:

   - It consists of a magnetic core made of laminated steel sheets.

   - There are two windings: primary and secondary, wound around the core.

   - The windings are insulated from each other and from the core to prevent short circuits.

   - The transformer may have a casing or enclosure for protection and insulation.

2. Three Phase Transformer Construction:

   - Similar to single-phase transformers, but with three sets of windings: primary and secondary for each phase (A, B, C).

   - The windings are arranged in either a core type or shell type configuration.

   - In core type, the three pairs of windings are placed around the limbs of a common core.

   - In shell type, each winding is placed around the core like layers of a shell.

   - Both types are typically housed in enclosures for insulation and protection.

Working principles of a transformer

The working principle of a transformer relies on electromagnetic induction. When an alternating current flows through the primary winding, it creates a changing magnetic field in the transformer's core. This changing magnetic field induces a voltage in the secondary winding through electromagnetic induction. The induced voltage in the secondary winding depends on the turns ratio between the primary and secondary windings.

Transformation ratio

The transformation ratio of a transformer is defined as the ratio of the number of turns in the secondary winding (N2) to the number of turns in the primary winding (N1). Mathematically, it is represented as:

Transformation Ratio (K) = N2 / N1

The transformation ratio determines the ratio between the primary and secondary voltages. For an ideal transformer (one with no losses), the ratio of primary voltage (V1) to secondary voltage (V2) is equal to the turns ratio:

V2 / V1 = N2 / N1

Uses of transformers

Transformers are extensively used in electrical power distribution systems to step up or step down voltages.

1. Step-up Transformer: Increases the voltage from the primary winding to the secondary winding. It is used in power transmission from generating stations to substations to reduce transmission losses.
2. Step-down Transformer: Decreases the voltage from the primary winding to the secondary winding. It is used in distribution networks to provide lower voltages suitable for residential and commercial use.

EVALUATION: 1. Discuss briefly the construction of a three-phase transformer

2. Describe the working principle of a transformer
3. State the use a step-down transformer

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively