Scott-T transformer
The Scott connection is an electrical circuit that allows, using two different transformers, three-phase power converting systems in two phase systems. The circuit was developed in the late 1890s by Charles F. Scott, an engineer at Westinghouse Electric.
General
The effect of the circuit can be explained with illustrations alongside. Tensions L12, L13 and L23 form a three-phase voltage system. With the voltages V12 and V12 to obtain a two-phase voltage system, which can be expanded to the four-phase using, U12 and V12.
The construction of the circuit, two different single-phase transformers T1 and T2 are needed. A winding, it comprises N turns, be designed on the primary side of T1 must for the delta voltage and have a center tap. It is connected between the two first phases L1 and L2. The primary winding of the second transformer T2 must be connected and be designed for a voltage of ≈ 0.866 times the values of V12 corresponding to the voltage V12 between the center tap of the first transformer T1 and the third remaining outer conductor L3. The primary winding of T2 thus has a low number of turns by the same factor as the primary winding of T1. This fact is indicated by the open end of the primary winding of T2 right of the circuit diagram.
If the two secondary voltages are phase-shifted by 90 ° in theory, be of equal size, and the secondary windings of the two transformers to which the primary side windings and N correspond to be equal.
Basically, the energy flow can be reversed, that is, that even two 90 ° phase-shifted sinusoidal voltages (generated eg by power converters ) can generate a three-phase voltage system. This possibility has been discussed intensively in the sixties of the twentieth century, as the power semiconductors were still very expensive. Because of falling semiconductor prices and the still the same prices for copper and iron, such solutions were rejected.
In practice there under load asymmetries in the magnitudes of the voltages and their angles to each other.