Scott-T Transformer - Unbalanced Loads

Unbalanced Loads

Two-phase motors draw constant power the same as three-phase motors, so a balanced two-phase load is converted to a balanced three-phase load. However if the two-phase load is not balanced (more power on one phase than the other), the Scott-T transformer cannot fix this. Unbalanced current on the two-phase side causes unbalanced current on the three-phase side. As the typical 2 phase load was a motor, equality of the current in the 2 phases was inherently presumed during the Scott development. In modern times people have tried to revive the Scott connection as a way to power single phase electric railways from 3 phase Utility supplies. This will not result in balanced current on the 3 phase side as it is unlikely that 2 different railway sections connected as the 2 phases will at all times conform to the Scott presumption of being equal. The instantaneous difference in loading on the 2 sections will be seen as an imbalance in the 3 phase supply, there is no ability to smooth it out.

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