Types of Transformer

There are mainly two types of transformer from core construction point of view: Core Type Transformer and Shell Type Transformer. A transformer can be classified into various types based on core construction, winding design, application, cooling medium and power supply to which it is connected. .

In core type, transformer HV and LV windings are wound on both the limbs of transformer whereas in shell type, it is only wound on the central limb.

Types of Transformer on the Basis of Application:

On the basis of application, it can be divided into five types:

• Power Transformer
• Distribution Transformer
• Instrument Transformer
• Single Phase Transformer
• Three Phase Transformer

Power Transformer: This type of transformer is used for transmission of electric power in high voltage circuit. It is designed for handling higher power. It can either be step-up or step-down type.

Distribution Transformer: It is used for stepping down the voltage level for the distribution of electric power in the locality. This is generally step-down transformer of voltage rating 11 kV / 415 V. It is pole mounted and often seen in the residential societies.

Single Phase Transformer: A transformer which receives electrical power from a single phase source and delivers power to single phase load is called single phase transformer.

Three Phase Transformer: It is supplied with three phase power source and delivers power to either single phase or three phase load. The three primary and secondary phases are either connected in STAR or DELTA. Therefore, a three phase transformer may either be STAR-STAR, STAR-DELTA, DELTA-STAR or DELTA-DELTA type. In case of STAR-STAR three phase transformer, an additional winding connected in DELTA is provided. This is called tertiary winding. The purpose of this tertiary winding in STAR-STAR transformer is to eliminate the harmonics.

Instrument Transformer: These transformers are used for the measurement and instrumentation purposes. It is of two types, viz. Current Transformer and Potential transformer. Current transformer is used for the measurement of electric current flowing through a circuit. It steps down the current to a measureable value. Potential Transformer or PT is used for the measurement of voltage of a line. It steps down the line voltage to a practically measurable value.

Types of Transformer on the Basis of Winding:

On the basis of winding design, there are four types of transformer:

• Step-up Transformer
• Step-down transformer
• Isolation Transformer
• Auto Transformer

A transformer comprises of two types of winding: Primary Winding and Secondary Winding. Theses windings are electrically isolated but magnetically coupled. Primary winding is one connected to the supply main whereas secondary winding is connected to the load.  The number of turns in primary and secondary may be different. If the number of turns in the primary winding is more than that of secondary winding, the voltage of primary winding will be more than secondary. Therefore this type of transformer is called Step-down Transformer. Similarly, if the secondary winding has more number of turns than the primary, secondary voltage will be more and hence this type of transformer is called the Step-up Transformer.

An isolation transformer is one in which the number of turns in primary winding and secondary windings are same. The main purpose of this transformer is to electrically isolate the two circuits.

There is one more type of transformer, called the Auto Transformer, in which primary and secondary winding are electrically connected. In fact, secondary winding of Auto transformer is a portion of primary winding. For detail of Auto Transformer, please read “Basic Principle of Auto Transformer”.

Types of Transformer on the Basis of Cooling Medium:

On the basis of cooling medium, there are two types of Transformer: Oil cooled transformer and Air Cooled Transformer. In oil cooled type, mineral oil is used for the cooling of winding and core of transformer. Whereas in air cooled transformer, core & winding cooling is provided by natural air. This type of transformer is also called Dry Type Transformer. Dry type transformer is used for indoor application to minimize fire hazard.