The Scott connection of the transformer is a standard method of connecting two single-phase transformers to perform the three-phase to two-phase conversion and vice versa. Scott connection of transformer is also known as T – T connection.

In Scott-T connection two single-phase transformers are connected electrically not magnetically.

One transformer is called the main transformer and the other is known as an auxiliary transformer as shown in the below Scott connection circuit diagram.

The main transformer is center tapped at point D and connected across lines B & C of the three-phase side.

The main transformer has a primary side BC and The secondary of this transformer is a1a2. The auxiliary transformer's primary is connected between line A and the center tapping D on the main transformer primary.

The teaser transformer (Auxillary transformer) has primary AD and the secondary is b1b2.

In the Scott connection of the transformer generally, the same interchangeable transformers are used in which each transformer has a primary winding having Tp turns and is provided with tapping at 0.289Tp, 0.5Tp, and 0.866Tp.

### Phaser diagram of Scotts connection

_{AB ,}V

_{BC ,}V

_{CA }are balanced as shown in the below phaser diagram.

_{AB }|=|V

_{BC}|=|V

_{CA }|=|V

_{L}|

_{}

_{BC}be taken as a reference

_{BC}= V

_{L}∠0º

_{CA}=V

_{L}∠-120º

_{AB}=V

_{L}∠+120º

_{P/2}

_{}

_{BD}and V

_{DC}are equal and they are in phase with V

_{BC}

_{BD}=V

_{DC}=1/2V

_{BC}

_{L}∠0º

_{AD}=V

_{AB}+V

_{BD}

_{L}∠120º+1/2V

_{L}∠0º

_{}

_{L}∠90º

_{AD}is the voltage across the primary auxiliary transformer is 0.866 of the main transformer and 90º from it in time.

_{AD}is applied across the auxiliary transformer therefore the secondary voltage V

_{2t}of the Auxiliary transformer will lead the secondary terminal voltage V

_{2m}of the main transformer by 90º.

For the same
flux in each transformer, the voltage per turn should be the same. To keep the voltage per
turn in same in the primary of the main and auxiliary transformers the number of turns
in the primary of the auxiliary transformer that is T_{AD} should be equal
to √3/2 T_{p}

V_{2t}=V_{2m}

The secondary of
both transformers have equal ratings since V_{2t} and V_{2m} are
equal in magnitude and displace by 90 degrees from each other and they result
in a balanced 2-phase system.

### Applications of Scott connection

- Used in the electric furnace, where required to operate two single-phase furnaces together and received supply from the balanced three-phase balanced source.
- To link a three-phase system with a two-phase system with a flow of power in both directions.
- Scott connection of the transformer allows conversation o a three-phase system to a two-phase system and vice versa.