5-152 T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
SYSTEM SETUP CHAPTER 5: SETTINGS
5
Figure 5-70: Phasors for ABC sequence
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.
Figure 5-71: Phasors for ACB sequence
Note that the delta winding currents leads the wye winding currents by 30°, (which is a type Yd11 in IEC nomenclature and
a type Y/d330 in GE Multilin nomenclature) and which is in disagreement with the transformer nameplate. This is because
the physical connections and hence the equations used to calculate current for the delta winding have not changed. The
transformer nameplate phase relationship information is only correct for a stated phase sequence.
Phase relationship for the ACB sequence can be returned the transformer nameplate values by connecting source phases
A, B, and C to transformer terminals A, C, and B respectively. Although this restores the nameplate phase shifts, it causes
incorrect identification of phases B and C within the relay and is therefore not recommended.
All information presented in this manual is based on connecting the relay phase A, B, and C terminals to the power system
phases A, B, and C respectively. The transformer types and phase relationships presented are for a system phase
sequence of ABC, in accordance with the standards for power transformers. Users with a system phase sequence of ACB
must determine the transformer type for this sequence.
If a power system with ACB rotation is connected to the Wye winding terminals 1, 2, and 3, respectively, from a Y/d30
transformer, select a Power Rotation setting of ACB in the relay and enter data for the Y/d330 transformer type.
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