Are transformer stabilizing windings necessary?

FOR MANY YEARS it has been common practice to include a Δ-connected stabilizing winding in Y-Y-connected transformers and Y-connected autotrans-formers. This applies to 3-phase units of all types of core construction as well as 3-phase banks of single-phase units. The practice has been followed so closely for such a long time that it is generally taken for granted that the stabilizing winding is a necessary part of all Y-connected transformers. In many cases it is; but it is not necessary or even desirable to include a stabilizing winding in all cases regardless of type of core construction and system characteristics.