Types of Transformers

There are many types of transformers. These can be classified on a different basis. The following are the main types of transformers.

Types of Transformers based on Voltage Level

1. Step-Down Transformer: The transformers having K > 1 i.e. N2 > N1 are known as the step-up transformer. Here, we get high output voltage as compared to the applied voltage, hence the name step-up. They are usually used in the power system to increase the voltage level.

2. Step-Up Transformer: The transformers having K < 1 i.e. N2 < N1 are known as the step-down transformer. In such types of transformers, we get low output voltage as compared to the applied voltage, hence the name step-down.

3. Isolation Transformer: The transformers having K = 1 i.e. N2 = N1 are known as the one-to-one transformer. Here, the output voltage is equal to the input voltage. The main function of such transformers is to provide isolation between the input and output circuit, hence this transformer is also known as the isolation transformer.

Types of Transformers Based on Core Arrangement

Based on core and winding arrangement, following are the main types of transformers:

1. Core type transformer: In the core type transformer magnetic core is made from ‘L’ shape strips. The core-type transformer consists of an iron core surrounded by windings. The core of this transformer has two limbs. Each limb carries the same flux. Therefore, the area of both limbs is equal.

 The low-voltage winding is placed next to the core and high-voltage winding is placed over it. Proper insulation is provided in between the core, low voltage winding and high voltage windings.

2. Shell-type transformer: In the core-type transformer, the iron core is surrounded by the windings whereas, in the shell-type transformer, the windings are surrounded by the iron core. The core of shell type transformer is made from ‘E’ and ‘I’ strips. 

The laminations of this transformer have three limbs. The side limbs carry half of the flux whereas the central limb carries the whole of the flux. Therefore, the width of the central limb is more than that of the outer limbs.

Both the windings are placed on the central limb concentrically or side by side. The low-voltage winding is placed next to the core and high voltage winding is placed over it. Proper insulation is provided in between the core, low voltage winding and high voltage windings.

3. Berry-type transformer

Types of Transformers based on Usage

1. Power Domain

Power Transformer: These transformers are used in the power system to step up the voltage for transmission purposes and to step down the voltage at the receiving substations. These are large-sized transformers.

These transformers are usually operated near the full load which would cause high copper loss. Thus, to have minimum losses, such transformers are designed with low copper losses and to give maximum efficiency at near the full load.

 Distribution Transformer: These transformers are used to step down the voltage at the distribution substations. The load on such transformers varies for all 24 hours from no load to full load. Such transformers are designed with low iron loss and to give maximum efficiency at about 75% of the full load to obtain high efficiency.

Instrument Transformer: These transformers are used to measure high voltage, high current and to operate protective devices. To measure high voltage, it is stepped down with an instrument transformer which is known as the potential transformer (PT), and then applied to a voltmeter. Similarly, to measure high current, it is stepped down with an instrument transformer which is known as the current transformer (CT), and then applied to an ammeter.

2. Electronics Domain

Pulse Transformer: Pulse transformer is used in Switch Mode Power Supply circuits to change the voltage level. They operate at very high frequencies. So the ferrite is used as the core material.

Pulse Transformer

Audio Output Transformers: They are iron-cored transformers. They have two, three, or more copper windings according to requirement. They are used in the output stage of the audio amplifier for impedance matching with the speaker.

Types of Transformers based on Core material

1. Iron core transformer: In these transformers, iron is used as the core material.

2. Ferrite core transformer: In these transformers, ferrite is used as the core material. They are generally used in electronic circuits for RF frequency applications. At RF frequencies, we can not use iron as a core material. If we do so, iron losses in the core would be very high due to very high frequency. Therefore, in such applications, iron as a core material becomes useless.

Ferrite core has very high resistivity as compared to the iron core which keeps the core losses very low at high frequencies.

3. Toroidal core transformer: Toroidal core transformers have a toroid-shaped core. Due to such shape, the leakage inductance is very low and the transformer offers very high mutual inductance and Q factors. The windings and the weight is very low compared to traditional transformers. They are used where high electrical performance is required.

Toroidal core transformer

4. Air core transformer: In air core transformers, the air is used as core material i.e. no core is used. They are used in radio frequency applications.

Transformer Types based on Winding Arrangement

1. Two Winding Transformers: They have two separate windings (primary and secondary) and both the windings are electrically insulated from each other. Electrical energy is transferred from one circuit to the other circuit magnetically. They provide very high electrical isolation between the input and output circuits.

2. Auto Transformer: In this case, both the windings are connected electrically and magnetically. Therefore they don’t provide isolation between input and output circuits. They are used in voltage stabilizers to increase or decrease the supply voltage. They are usually used in applications where the transformation ratio is nearly equal to 1.

Transformer Types based on Insulation Used

  • Dry Type Transformer
  • Oil Immersed Transformer

Transformer Types based on Number of Phases

  • Single Phase Transformer
  • Three Phase Transformer

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