Effect of Transient Voltages on Power Transformer Design-III Non-Resonating Auto-Transformer

Transient voltage phenomena within auto-transformers differ from those in transformers, because in the former there are two points of the winding connected to independent transmission lines. This allows independent variation of the potential of these points. When a surge comes to an auto-transformer from one line only, the other line acts practically as a ``solid ground´´ for internal oscillations of the windings, provided it is long enough. Transient voltage stresses between turns and between coils, therefore, are higher in auto-transformers than in transformers of the same voltage rating. The non-resonating auto-transformer has been developed for commercial use. In mechanical construction it is essentially the same as the non-resonating transformer. The presence of two independent lines connected to an autotransformer permits several conditions of surge excitation. This allows corresponding variations in the design of shields.