Substation1
Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

T-connection
term often used to describe, with some ambiguity, two distinct transformer connections - one to simply convert voltage levels in a 3-phase power system, and the other to convert between 3-phase and a 2-phase voltages. Both connections use only two single-phase transformers, one called the main and the other the teaser, arranged in a T
configuration. Details of each configuration are described below. These connections are also often referred to as Scott connections, since they were first proposed by Charles F. Scott.

Conversion of 3-phase voltage levels: In this configuration, the main transformer in the T-connection is a center-tapped unit that is connected between two lines of the three-phase system. The teaser transformer is connected between the center-tap of the main transformer and the third line of the 3-phase power system. Additionally, the coils of the
teaser transformer have 86.6% of the turns in the corresponding coils in the main transformer. The result is a balanced three-phase voltage on the secondary. In most applications, the main and teaser transformers are actually identical, full voltage units with center taps and two 86.6% taps, one with respect to each terminal. This allows main and teaser units to be interchanged, plus it provides for true, 3-phase, 4-wire system with a neutral connection.
See teaser transformer