EHV Application of Autotransformers

The universal method of voltage transformation from EHV levels to lower voltage systems is through the use of the autotransformer. The characteristic of the autotransformer is profoundly influenced by the tertiary winding or the lack of it. This paper discusses the influence of the tertiary winding and its placement, fault magnitude and short circuit duty, autotransformer loading, overexcitation, protection of unloaded tertiaries, loading of paralleled autotransformers, and the use of single-phase units while presenting a circuit for studying unequal impedances in paralleled banks.