Difference between Single-Phase and Three-Phase Transformer


In electrical engineering, a transformer is a static electrical machine which is employed for transforming the level of alternating voltage, i.e. for stepping-up and stepping down the voltage, for transmitting the electric power from generating station to utility points.

The transformer changes the level of alternating voltage without changing its frequency. The transformer works on the principle mutual inductance. A typical transformer consists of two windings one is primary winding and the other is secondary winding. The input supply is connected to the primary winding of the transformer, while the transformed output is taken from the secondary winding, also the load is attached to it.

Depending upon the type of supply system in which the transformer is being used, the transformers are of two types viz. −

  • Single Phase Transformer
  • Three Phase Transformer

This article is meant for explaining the differences between single-phase transformer and three-phase transformer. But, before discussing the differences, it is advantageous to know the basic details of the single-phase and three-phase transformers.

What is a Single-Phase Transformer?

A type of transformer which consists of only one pair of the transformer coils or windings, i.e., one primary winding and one secondary winding, and is used for transforming the single-phase alternating voltage to the desired value, is known as single-phase transformer.

The core and winding arrangement of a typical single-phase transformer is shown in Figure-1. The winding of the single-phase transformer which is connected to the 1-phase AC supply is called the primary winding and the winding to which the load is connected is called the secondary winding.

The single phase transformers are commonly used in different applications such as for supplying electric power to domestic loads in rural areas where the demand and cost is less, in home inverters, in welding machines, in television sets and other electronic devices for regulating the voltage.

What is a Three-Phase Transformer?

A transformer which consists of three-pairs of transformer windings placed in a three-section iron core, where each section contains a pair of a primary winding and a secondary winding, and is used to step-up or step-down the three-phase alternating voltage is known as a three-phase transformer.

The schematic of a typical core type three-phase transformer is shown in Figure-2. However, a three-phase transformer can also be designed by using three identical single phase transformers and this type of three-phase transformer is known as bank of three transformers.

The three-phase transformers are widely used in electric power system for transmission and distribution of electric power. As a single 3-phase transformer can supply three single-phase circuits, hence it is economical than a single phase transformer. In practice, most of the distribution transformers used in urban areas are the three-phase transformers. Also, there are several three-phase loads such as 3-phase induction motors, synchronous motors, etc. which are supplied by using 3-phase transformers.

Difference between Single-Phase Transformer and Three-Phase Transformer

The key differences between single phase and three phase transformers are highlighted in the following table

ParameterSingle-Phase TransformerThree-Phase Transformer
DefinitionA type of transformer which consists only one pair of transformer windings (one primary winding and one secondary winding) and is used to step-up or step-down the single phase alternating voltage is known as 'single-phase transformer'.A transformer which has three pairs of transformer windings arranged in a three-section iron core, where each section containing a pair of primary and secondary windings, and is used for transforming the 3-phase alternating voltage to the desired value is known as 'three-phase transformer'.
Number of primary and secondarySingle-phase transformer has only one primary winding and one secondary winding.Three-phase transformer has three-primary windings and three secondary windings.
Input and output terminalsSingle-phase transformer has two input terminals and two output terminals viz. phase (P) and neutral (N).In case of three-phase transformer, there are three input terminals for line wires and one terminal is for neutral (depending upon the type of primary winding connection), and similarly, at the output, three line terminals and one neutral terminal be provided, again the presence of neutral terminal depends upon the type of secondary winding connection.
SizeThe size of a single-phase transformer is small.A three-phase transformer is relatively larger in size.
SubstitutionA single-phase transformer cannot be used for supplying a three-phase load.A three-phase transformer can be used to supply both 1-phase and 3-phase loads.
Power handling capacityThe power handling capacity of a single-phase transformer is less due to use of only one set of windings.A three-phase transformer can handle more power than a 1-phase transformer.
Winding configurationThere is only one primary winding and one secondary winding, thus no specific winding configuration exists in case of a single-phase transformer.Based on the connection of three primary windings and three secondary windings, the following winding configurations are defined for the three-phase transformerrs:
  • Star-Start (Y-Y) Connection
  • Delta-Delta (Δ-Δ) Connection
  • Star-Delta (Y-Δ) Connection
  • Delta-Star (Δ-Y) Connection
DesignSingle-phase transformers are simple in design.The design of three-phase transformer is relatively complex due to presence of three windings.
EfficiencyFor same ratings, the efficiency of a single-phase transformer is less.A three-phase transformer has high efficiency compared to 1-phase transformer.
Capital costThe initial cost of a single-phase transformer is less.The initial cost of a three-phase transformer is relatively higher than that of 1-phase transformer.
EconomicalThe single-phase transformers are less economical in long term.The powerful and fast performance of the three-phase transformers make them more economical over the long term.
Parallel operationParallel operation of single-phase transformers is difficult.The parallel operation of three-phase transformers is easier than that of the 1-phase transformers.
ApplicationsSingle-phase transformers are used for small loads such as to supply single-domestic loads like pumps and lightings, etc., used in various electronic devices like in TVs, mobile chargers, etc. for voltage regulation, in home inverters for stepping up voltage, etc.Three-phase transformers are used for supplying high power single-phase as well as three-phase loads as induction motors, etc. Also used in power systems for power transmission and distribution

Conclusion

In this article, we have discussed all the noticeable differences between a single-phase transformer and a three-phase transformer. Both are used for stepping-up or stepping-down the alternating voltage to the desired value. One major difference between single-phase and three-phase transformers is that a single-phase transformer consists only one pair of windings, while a three-phase transformer consists of three-pairs of transformer windings.

Updated on: 04-Jul-2022

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