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Three Phase Transformers

Three phase transformers are very commonly used throughout commercial and inudstrial projects in North America to change voltgae and current. Three phase power is produced, transmitted and distributed on a regular basis by the utility companies so its essential to understand how to utilize it with three phase transformers.

Three phase transformers differ from single phase transformers by the way the connections are made. Single phase transformers have two phases on the primary and two phases on the secondary. But three phase transformers have a variety of connections, most notably the Delta-to-Wye connection.

A delta-wye transformer has its primary winding connected in delta and its secondary winding connected in wye.

A very common usage of this application is in 480v 3ø to 208v 3ø systems:

The diagram above demonstrates that the incoming voltage is 480v 3ø and the outgoing voltage is 208v 3ø. This very common type of transformer is typically used in commercial buildings over 30,000 s.f. and in most industrial applications. The reason is that by utilizing a higher voltage electrical service, the amperage of the electrical service will be much less than if it were 208v 3ø. The lower the amperage, the mofe economical the service will be. In the typical scenario of this system, the lighting and hvac equipment is supplied on the 480v panelboards and the power receptacles and other 120v power is served by the 208v 3ø panelboard. The diagram below illustrates the exact details of this system.

Download this riser diagram in PDF format

For more examples of transformers in riser diagrams, click here.

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