The autotransformer has the advantages described below:
– decrease in weight and size of equipment;
– Reduction of losses;
– Lower series impedance and better voltage regulation. Rubber A69
And it has disadvantages:
– Loss of insulation between the primary and secondary circuits;
– It does not allow some three-phase connections, like -Y and Y-;
– The opening of the common winding will repress the secondary the same voltage imposed on the primary, which can be catastrophic when operated at high voltage levels.
– Larger fault currents, because of reduced series impedance.
Ideal transformers can be eliminated when PU units are used, however, it may be convenient to leave them simulated in the circuit as 1: 1 transformers. Thus, the multiple winding transformer admits:
– Connection of several systems operating at different voltage levels;
– When three-phase, the use of an interconnected winding for harmonic filtering, which can also be applied as power source for different loads;
– Better control of voltage regulation;
– Probability of redundancy in the supply of a critical load: two windings isolated from each other, at the same voltage level, supplying the same load;
– Power supply for auxiliary services in substations.