Types of Transformer

Types of Transformer

The transformer is a device that is used to convert the electrical power at one voltage level to the other voltage level. If the transformer is used to convert a low voltage level to a higher voltage level, it is known as the step-up transformer. And if the transformer is used to convert a higher voltage level into a lower voltage level, it is known as the step-down transformer. In this article, we will explain different types of transformer.

Hence, according to the use of the transformer, it classified into two types;

  • Step-up transformer
  • Step-down transformer

The transformer core is the most important part of the transformer. According to the construction of the transformer (core), is classified as;

  • Core type transformer
  • Shell type transformer

Core Type Transformer

The transformer core is made of laminated magnetic material with low reluctance. It shaped rectangular with two L-shape strips. In this type of transformer, high voltage and low voltage winding are wound on both the limbs.

To minimize the leakage flux, the low voltage winding wound first and over that high voltage windings wound. Due to this type of connection, less insulation is required in the transformer.

Shell Type Transformer

In this type of transformer, the windings are sandwiched on the central limb. The low voltage winding is placed near to the yoke. And the flux produced in the limb will pass through the yoke.

There are many differences in the core type and shell-type transformer.

Difference Between Core type and Shell Type Transformer

Sr no Characteristic Core type transformer Shell type transformer
1 Number of limbs Two Three
2 Requirement of copper Less More
3 Transformer Winding Winding surrounding the core Core surrounding the winding
4 Winding type Cylindrical Sandwiched or multi-layer
5 An iron requirement in Core Less More
6 Core loss and other Transformer loss More Less
7 Overall efficiency Less More
8 Magnetic circuit One magnetic circuit Two magnetic circuit
9 Maintenance Easy Difficult
10 Design Easy Difficult
11 Heat dissipation Better Inferior
12 Application It is used in power transformer and auto-transformer, where high voltage is required. It is used in the electronics circuit with a low voltage application.

According to Type of Power

The transformer is classified into two types according to the type of electrical power is converted;

  • Single-phase transformer
  • Three-phase transformer

If the transformer is used for the single-phase supply, the transformer is known as a single-phase transformer.

If the transformer is used for the three-phase supply, the transformer is known as a three-phase transformer.

According to Application

There are many types of transformer for a particular application. Hence, according to the use of a transformer, it is classified as many types as listed below.

  • Power transformer
  • Distribution transformer
  • Instrument transformer
  • Autotransformer
  • Isolation transformer

Power Transformer

In the transmission system, the power transformer is used to step-up the voltage at the generating station. This types of transformer is designed to operate near the knee-point of the BH curve.

The maximum efficiency is getting when the iron loss and copper loss are equal. And naturally, at peak load, this transformer matched iron loss and copper loss.

Distribution Transformer

While designing the distribution transformer, the all-day-efficiency keeps in mind. Hence, the design of the core has to consider the peak load as well as all-day-efficiency.

The main difference between the power transformer and distribution transformer is that the power transformer is designed to operate on full load. And the distribution transformer is designed to operate continuously with less than the full load. Therefore, it is designed with the core loss is minimum.

The flux density in the power transformer is higher compared to the distribution transformer.

Difference between Power Transformer and Distribution Transformer

  Power Transformer Distribution Transformer
1 The power transformer is used in the transmission network The distribution transformer is used in the distribution network
2 Voltage level > 33 kV Voltage level < 33kV
3 Fewer Load fluctuations More Load fluctuations
4 The consumer is not directly connected Consumers are directly connected
5 While designing copper losses are kept the minimum. While designing copper iron is kept the minimum.
6 CRGO steel is used in the core of this transformer. Amorphous steel is used in the core of this transformer.
7 Copper losses and iron losses take place steadily throughout 24 hours. The copper loss takes place based on the load cycle of the consumer and iron loss takes place steadily throughout 24 hours.
8 Full load copper loss is almost the same as an iron loss. Full load copper loss is twice of the iron loss
9 Efficiency maximum occurs at nearer to the full load Maximum efficiency occurs at 70-75% of full load.
10 Specific weight is less Specific weight is more
11 The average load on the power transformer is almost nearer to the full load. The average load on the distribution transformer is 70-75% of the full load.

Instrument Transformer

In a power system network, the instrument transformers are used to measure the quantities like current and voltage. For the protection of the power system, it is also used along with the protective relays.

The function of the instrument transformer is to convert the voltage or current level down. There are two types of instrument transformers;

  • Current transformer
  • Voltage transformer or potential transformer

Current Transformer

The current transformer is connected in series with the part or element of the system to measure the current flowing through it. The typical ratio of the current transformer is 1000:5 A. It means that when the system current is 1000A, it will show the result of 5A. Therefore, the current transformer is a measuring device and converts system current into a lower level.

Potential Transformer

It is connected in shunt with the system to measure the voltage. The typical ratio of PT is 600:120. It means when the system voltage is 600V, it will give a result of 120V.


The autotransformer is a special kind of which has a common winding for the primary and secondary winding.

The operating principle of the autotransformer is the same as the normal transformer. But, the construction of autotransformer is different compared to the normal transformer.

It consists of only one winding wound on a laminated magnetic core. It has a rotary movable contact. Therefore, from the autotransformer three terminals are brought out for connection. Out of these three contacts, two contacts are fixed (A and B) and one contact is moving (C).

Click here: Difference between Conventional Transformer and Autotransformer

Isolation Transformer

An isolation transformer is used for safety purposes to isolate the power source with the device. It provides galvanic isolation and a non-conducting path between the source and load.

It is a 1:1 ratio transformer. That means, the number of turns in the primary winding is the same as the number of turns in the secondary winding.

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