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The Advantages of Three-Phase Transformer

Mar. 22, 2021


Three-phase (also known as 3φ) power supplies are used for power generation, transmission and distribution and for all industrial purposes. Three-phase power supplies have many electrical advantages over single-phase power supplies. When considering the use of a three-phase transformer, we must deal with three AC voltages and currents that differ by 120 degrees in phase.

Transformers cannot be used as phase change devices and cannot convert single phase to three-phase or three-phase to single phase. In order to make transformer connections compatible with three-phase supplies, we need to connect them together in a specific way to form a three-phase transformer configuration.

Three-Phase Oil Immersed Transformer

Three Phase Transformers

Three-phase oil-immersed transformers are the backbone of electrical power distribution whether Delta or Star connected windings.

Thus far we have looked at the construction and operation of the single-phase, two winding voltage transformer which can be used to increase or decrease its secondary voltage with respect to the primary supply voltage. But voltage transformers can also be constructed for connection to not only one single phase, but for two-phases, three-phases, six-phases and even elaborate combinations up to 24-phases for some DC rectification transformers.

If we take three single-phase transformers and connect their primary windings to each other and their secondary windings to each other in a fixed configuration, we can use the transformers on a three-phase supply.

Three-phase, also written as 3-phase or 3φ supplies are used for electrical power generation, transmission, and distribution, as well as for all industrial uses. Three-phase supplies have many electrical advantages over single-phase power and when considering three-phase transformers we have to deal with three alternating voltages and currents differing in phase-time by 120 degrees as shown below. 

Three Phase Voltages and Currents

A transformer can not act as a phase changing device and change single-phase into three-phase or three-phase into a single phase. To make the transformer connections compatible with three-phase supplies we need to connect them together in a particular way to form a Three-Phase Transformer Configuration.

A three-phase transformer or 3φ transformer can be constructed either by connecting together three single-phase transformers, thereby forming a so-called three-phase transformer bank, or by using one pre-assembled and balanced three-phase transformer which consists of three pairs of single-phase windings mounted onto one single laminated core.


The advantages of building a single three-phase transformer are that for the same kVA rating it will be smaller, cheaper and lighter than three individual single-phase transformers connected together because the copper and iron core are used more effectively. The methods of connecting the primary and secondary windings are the same, whether using just one Three Phase Transformer or three separate Single Phase Transformers. 

Baoding Zhongyi Electrical material Manufacturing Co., Ltd mainly produces oil-immersed power transformers, dry-type transformers, box-type substation, high and low voltage switchgear assembly and a variety of special-type transformers. The hoisting, tooling and testing equipment are complete. Our company has passed the ISO9001-2015 international standard quality management system certification. All performance indicators of the products have reached the relevant national standards and international standards.


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