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The equivalent series impedance Z(%) of the double stack (four-winding) transformer:
The contents of Articles 1 and 2 can be summarized that the equivalent series impedance Z(%) of
the double stack (four-winding) transformer can be expressed as follows: ZL refers to the equivalent
series impedance of the low-voltage winding, and ZL refers to the equivalent series impedance of
the high-voltage winding.
A neutral point is not needed in the low-voltage side. Nonetheless, if a neutral point appears in
the low-voltage side, this neutral point shall not be connected or grounded.
The double stack (four-winding) transformer that has various windings at each of the high-
voltage and low-voltage sides can be used. For example, YNd11d11, YNd5d5, YNd1d1 or
Dy11y11, Dy5y5, Dy1y1 has a neutral point that is not grounded at the low-voltage side.
