Transformer: Construction and Classification

Transformer: Construction and Classification

There are two main parts of the transformer;

  1. Magnetic core
  2. Winding or Coil

1) Magnetic Core

The magnetic core provides a path for magnetic flux. Maximum flux is passing through the core. Hence, there are two types of losses occurs in the core that is hysteresis loss and eddy current loss. The summation of these two losses is known as magnetic loss or iron loss.

We need to design a transformers, in such a way that these two losses remains as minimum as possible. Generally, the core made up of high-grade silicon steel. Earlier, the core is made up of the iron. But, the silicon steel has high permeability compared to the iron. So, hysteresis loss is less in silicon steel core.

The core is made up of thin laminations to reduce the eddy current loss. The eddy current loss is due to the high width of the magnetic material. So, by providing lamination, we can divide width into small parts which help to reduce the eddy current loss. These laminations separated by insulating material like varnish.

2) Winding

Windings are wound on the limb of the core. There are two windings primary winding and secondary winding. The current passes through the winding and produce I2R loss. We choose material for winding which has low resistivity to reduce I2R loss. Generally, the copper wire used for the windings. The windings are insulated with each other.

Classification of Transformers

(A) Based on the arrangement of core and winding

there are two types of the transformers;

  1. Core type Transformer
  2. Shell type Transformer

1) Core type Transformer

Here, it has one magnetic circuit. The winding encircles the core. In other words, the core is surrounded by winding.

Core type and shell type transformer

2) Shell type Transformer

Here, it has two magnetic circuits. The core encircles the winding. In other words, the winding surrounded by the core. This type of transformer uses in high voltage application.

(B) Based on the change in Voltage level

This type of transformer categories according to a number of turns in the primary and secondary windings and the induced EMF.

  1. Step-up Transformer
  2. Step-down Transformer

1) Step-up Transformer

It uses to transforms a low voltage high current AC power into a high voltage low current AC power. In a transmission system, the power transmitted at high voltage to reduce transmission losses. So, step-up transformer uses to increase voltage level. The secondary winding has a greater number of turns compared to the primary winding.

Step-up and Step-down Instrument Transformer

2) Step-down Transformer

It uses to transforms a high voltage low current AC power into low voltage high current AC power. In a distributed system, the step-down transformers uses to decrease voltage level before supplies to the load. The primary winding has a greater number of turns compared to the secondary winding.

(C) Instrument Transformer

This type of transformers are also known as an isolation transformers and measuring transformers. The instrument transformers uses to isolate the secondary winding when primary winding has a high voltage high current supply. So, the measuring instruments like relay and energy meter connected to the secondary winding.

There are two types of instrument transformers

  1. Current Transformer (CT)
  2. Potential Transformer (PT)

1) Current Transformer (CT)

The current transformers uses to decrease the current level. CT is a step-up transformer. The secondary current of CT is 1A or 5A.

2) Potential Transformer (PT)

The potential transformers uses to measure the voltage of HV components. The primary winding of PT connects to the HV component and all measuring instruments connected to the secondary winding. PT is a step-down transformer. Generally, the secondary voltage of PT is 110V.

(D) According to the number of phases

  1. Single-phase Transformer
  2. Three-phase Transformer

1) Single-phase Transformer

Generally, single-phase transformers uses for the low voltage applications. This type of transformers are not used in the power system.

2) Three-phase Transformer

Three-phase transformers are nothing but a combination of three single-phase transformers. These type of transformers widely uses in the power system for transmission and distribution of AC power.

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