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What Is a Delta-Wye Transformer?

K. Hamilton
K. Hamilton

A delta-wye transformer is a piece of electronic equipment that is able to convert — without a neutral wire — three-phase electric power into power that has a neutral wire. Electrical transformers such as the delta-wye transformer are popular and commonly used in industrial and commercial areas as well as residential communities that are highly dense. There are two types of delta-wye transformers: those that are made as single three-phase units and that that are created from three separate, single units.

The term "delta-wye transofmer" is used only in some parts of the world, including the United States. In other parts of the world, such as Europe, the term "delta-star" is used. Three-phase electric power, however, is the same no matter which term is used. A delta-wye transformer is also related to the high-leg delta, which is more commonly found in older installations of the three-phase electric system.


A good example of a delta-wye transformer is a distribution transformer that has a delta primary, which runs on three separate 11-kilovolt wires without a neutral wire, and a wye secondary for providing a 400-volt, three-phase source. Another common use for the delta-wye is in machinery such as a motor soft starter. It is commonly found in alternating current (AC) motors and works to reduce the torque and load during start-up. This reduces the stress on the motors as well as the power cables that are attached to it.

The use of these transformers will increase the lifespan of any system that has an electronic distribution network. Using the three-phase electric power ensures that infrastructures run smoothly and have a steady supply of power. Besides the uses for industrial and residential purposes, delta-wye transformers are widely used by manufacturing corporations. They apply to industries such as pharmaceutical firms and those in the food and beverage sectors.

It is quite easy to spot delta-wye transformers from the right vantage point. At a hydroelectric dam or a large manufacturing plant, transformers that are grouped in threes probably are three-phase transformers with delta-wye connections. Seeing the actual connections, however, is not possible from a distance.

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