GE G30 Instruction Manual page 308

SYSTEM SETUP CHAPTER 5: SETTINGS
The reason the source phase sequence must be stated when describing the winding phase relationships is that these
relationships change when the phase sequence changes. The following example shows why this happens, using a
transformer described in IEC nomenclature as a type "Yd1" or in GE Multilin nomenclature as a "Y/d30."
The example shows the physical connections within the transformer that produce a phase angle in the delta winding that
lag the respective wye winding by 30°. The currents in the windings are also identified. Note that the total current out of the
delta winding is described by an equation.
Figure 5-60: Example of transformer
Now assume that a source, with a sequence of ABC, is connected to transformer terminals ABC respectively. The currents
then present for a balanced load are shown in the following figure.
Figure 5-61: Phasors for ABC sequence
5
Note that the delta winding currents lag the wye winding currents by 30° (in agreement with the transformer nameplate).
Now assume that a source, with a sequence of ACB is connected to transformer terminals ACB respectively. The currents
present for a balanced load are shown in the following figure.
5-134 G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL