- An electrical connection between the primary and secondary is not always desirable, particularly when the voltages levels on both the sides of transformer are quite different. If the neutral point is not solidly earthed, the lower voltage side can be subjected to high potential in the event of earth fault on high voltage side. In general practice, auto transformers are only used on distribution systems where the neutral is connected to the earth
- Auto-transformers are particularly sensitive to the atmospheric over-voltages. Therefore the auto-transformer requires much highs standard of insulation compared to normal transformer. Surge Arrester protection is required
- As the short circuit impendace values of the auto-transformer are low, short circuit currents can reach higher critical values.