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Power Transformers Theory Testing and Commissioning Chapter | 5 55
FIGURE 5.10 On-load tap changer using a resistor.
FIGURE 5.11 Three-phase power transformer connection vector group (Group 4 with 30
degrees lead).
of all possible three-phase transformer connections are categorized as
follows:
Group 1: 0 degree phase displacement (Yy0, Dd0, Dz0).
Group 2: 180 degrees phase displacement (Yy6, Dd6, Dz6).
Group 3: 30 degrees lag phase displacement (Dy1, Yd1, Yz1).
Group 4: 30 degrees lead phase displacement (Dy11, Yd11, Yz11).
See also Figs. 5.11 5.13.
