Transformer Terms & Frequently Asked Questions
What is WYE / Delta?
The terms "Y" and delta are used to describe the connections on transformers when used on 3 phase. A "Y" connection is made by connecting the finishes of the primaries or secondaries of three single phase transformers into a common bank. The starts or other end of the windings will then connect to the 3 line leads of the 3 phase supply. Should the fourth wire be available on the 3 phase system, this would be connected to the common junction or their center of the "Y". When the connections drawn out schematically, it resembles the capital Y. Transformers connected in "Y" will operate at a higher 3 phase voltage than their single phase rating. For example, transformers with 120 volts, single phase windings may be connected in "Y" for 208 volts, 3 phase. The delta connection is used for connecting 3 single phase transformers for 3 phase operation. Each side of the delta would represent one winding of each transformer. The 3 corners of the delta are then connected to the 3 phase supply or load. A delta connection does not offer a way to make a fourth wire connection. Also, the single phase voltages and 3 phase voltages of a transformer are alike when the are used on the delta connection. These delta and "Y" connections are not necessarily limited to single phase transformers, but apply equally well on connections of coils on a 3 phase transformer.