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Difference Between Single Phase and Three Phase Transformer: Must Know

Difference between single phase and three phase trasformer

Before understanding the difference between a three-phase transformer and a single-phase transformer let us understand Transformers are used for power transmission, they are used throughout alternating current systems from generating plants to our home. Transformers can increase or decrease the voltage, for transmitting power for long-distance power lines, the voltage must be increased, then reduced by other transformers before the power enters our house.

The transfer of electricity is done indirectly, electricity is converted into magnetic energy, and then it’s reconverted back to electricity at a special voltage. Transformers convert power voltage to the required levels for various applications. Household applications, for example, require low voltage. In this case, transformers convert high voltage to low voltage suitable for powering a television or running a washer. Industries and manufacturing plants demand voltages several times above that of domestic applications. Transformers cater to the heavy voltage needs of such commercial applications also.

A major difference between the single-phase and the three-phase is that for completing a circuit the single-phase uses one conductor and one neutral wire whereas the three-phase supply uses three conductors and one neutral wire.

Difference Between Single Phase and Three Phase Transformer

Single Phase Transformer

When a single pair of a coil, one primary and one secondary is used to produce the desired voltage is referred to as a single-phase transformer. It consists of two highly inductive coils wound on an iron or steel core, the winding which is connected to the AC supply is named the first winding and the other one is secondary. Single-phase transformers are typically used for residential requirements, as they convert the high voltage into low voltage like a step-down transformer, which is most suited for residential and office requirements. 

It has four terminals, two on the input (phase & neutral), and two on the output (phase & neutral), no delta or star connections are available here,

In most cases, no cooling system is required for a single-phase transformer

The magnetic core of Single-phase differs from that of the 3Phase

Single-phase transformers are preferred for domestic and lighter commercial purposes for 2 key reasons – low cost and lower electricity input requirement.

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  • Single Phase systems have a less complex design.
  • Design cost is less in SP systems cost less in designing
  • SP has enhanced efficiency that Delivers AC power supply of about 1000 watts efficiently
  • SP systems are employed in multiple kinds of industries and applications.

3 Phase Transformer

A 3phase transformer is made by winding three single-phase transformer on one core, 3phase transformer contains six coils, three for the primary side, and another three coils for the secondary side and all 3 coils are each separated from the opposite by an angular difference of 1200, to achieve the specified voltage, transformers are then placed in an enclosure and crammed with dielectric oil. 

3 phase transformers are well-known for their efficiency to cater to the needs of heavy-duty applications that are most suitable and highly reliable for heavy industrial applications. 

With only a little conductor these transformers can transmit the required level of voltage over long distances, helping in the smooth functioning of industrial equipment. 

A three-phase transformer has star and delta connections & twelve terminals with different connections to connect with them.

Three-phase transformers are most often deployed as influence or distribution transformers, with high rated KVA.

Three-phase transformers require a hefty cooling system depending on the transformer’s power rating, cooling is achieved by (oil\forced oil), (air\forced air), or (forced water).

Three-phase transformers can only perform efficiently if the Coils or windings are arranged and connected in a proper fashion corresponding to the incoming voltage.

The transformer converts the incoming voltage to the required voltage level while also retaining proper phasing and polarity.


  • Less copper is needed for power supply in 3 phase transformers.
  • Employs operating on 3P systems bear minimal risk.
  • Greater conductor efficiency is seen in the 3P system.
  • 3P systems have the capability to function with an extended range of power loads.

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