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What is a Scott T transformer

This connection was initially developed and is a practical solution for the conversion of three phase primary to a two phase secondary. On the three phase side a neutral point is available for grounding or for loading. On the two phase side the windings may be connected to give three or four wire supply.


(1) Third harmonic voltages are eliminated by the circulation of the harmonic current trapped in the primary Delta winding.
(2) The secondary neutral can be grounded and it can be utilized for giving four-wire supply which can accommodate both single and three phase loads.
(3) An unbalanced four wire supply may be given and the resulting unbalanced voltages are relatively small, being proportional only to the internal impedance of the windings. Balanced and unbalanced loads may therefore be supplied simultaneously.
(4) Phase angles between the phases are symmetrical allowing 3 phase balanced loads (motor, drives) to be supplied with no regard to imbalance occurring.


1. No primary neutral point is available for grounding. This is not necessarily a disadvantage, as the system on the primary side of a transformer is generally grounded at the generator or at the step-up transformer secondary
2. A fault of one phase renders a three-phase unit inoperative until that phase is repaired. This also can be an advantage for safety reasons.


The primary application for the Delta Wye connection is used for stepping down to supply a four wire load which may be balanced or unbalanced. This connection allows for a combination of loads such as motors and lighting to be combined and supplied by one circuit. This connection is equally suited for stepping-up to supply high voltage distribution or transmission lines. As the third harmonic voltages are eliminated in the high voltage, the neutral is available for grounding.

For selection of Eaton's transformers please see our Catalog Volume 2 Tab 2.