Transformer - Electrical Engineering and Instrumentation

TRANSFORMER

Introduction

A transformer is a device that changes ac electric power at one voltage level to ac electric power at another voltage level through the action of a magnetic field.

There are two or more stationary electric circuits that are coupled magnetically.

It involves interchange of electric energy between two or more electric systems.

Transformers provide much needed capability of changing the voltage and current levels easily.

They are used to step-up generator voltage to an appropriate voltage level for power transfer.

Stepping down the transmission voltage at various levels for distribution and power utilization.

1. Transformer Classification

In terms of number of windings

Conventional transformer: two windings

Autotransformer: one winding

Others: more than two windings

In terms of number of phases

Single-phase transformer

Three-phase transformer

Depending on the voltage level at which the winding is operated

Step-up transformer: primary winding is a low voltage (LV) winding

Step-down transformer : primary winding is a high voltage (HV) winding

2. Primary and Secondary Windings

A two-winding transformer is shown below. It consists of two windings interlinked by a mutual magnetic field.

Primary winding –energized by connecting it to an input source.

Secondary winding –winding to which an electrical load is connected and from which outputenergy is drawn.

3. Functions of Transformer Parts

4. Principle of Operation

          When current in the primary coil changes being alternating in nature, a changing magnetic field is produced

This changing magnetic field gets associated with the secondary through the soft iron core

Hence magnetic flux linked  with the secondary coil  changes.

Which induces e.m.f. in the secondary.

5. Ideal Transformer

          An ideal transformer is a transformer which has no loses, i.e. it’s winding has no ohmic

          resistance, no magnetic leakage, and therefore no I2 R and core loses.

However, it is impossible to realize such a transformer in practice.

Yet, the approximate characteristic of ideal transformer will be used in characterized the practical transformer.

For ideal transformer E1=V1 and E2= V2