What is three phase transformer? Its construction, working, advantages, disadvantages & Applications

Three-phase transformer consists of three primary coils and three secondary coils and is represented as 3-phase or 3ɸ. The transformer system can be constructed using three individual identical single-phase transformers, and such a 3-phase transformer is known as the bank of three transformers. On the other hand, the transformer can be built on a single core. The windings of a transformer can be connected in either delta or wye configurations. The working of the system is similar to a single-phase transformer, and they are normally employed in power generation plants

Construction of three-Phase Transformer:

Three Phase Transformer Diagram

A transformer of a single unit is used widely because it is lighter, cheaper, and occupies less space than the bank of three single-phase transformers. The transformer construction is of two types: core type and shell type.

Working of Three-Phase Transformers:

This figure is simplified to show only primary windings and their connection to the three-phase power supply. As soon as the three-phase supply is excited, the currents IR, IY, and IB are carried by the primary windings and thus induce the fluxes ɸR, ɸY, and ɸB individually in each core. The centre leg will carry the sum of all the fluxes, and the centre leg combined all the legs of a core.

For instance, if the sum of the currents IR+IY+IB is zero in a three-phase system, then the sum of all the three fluxes also becomes zero, resulting in the center leg carrying no flux. Therefore, removing the center leg makes no difference for other transformer conditions.

Working of Three Phase Transformer

Advantages of a Three-Phase Transformer:

  • Needs less space to install and it is easier to install
  • Less weight and reduced size
  • Higher efficiency
  • Low cost
  • Transportation cost is low


  • The entire unit shuts down in case of fault or loss occurs in any one unit of a transformer as a common core is shared by all three units.
  • Repair costs are higher
  • The cost of spare units is high


These transformers are used in electrical grids, power transformers, and distribution transformers

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