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5 SETPOINTS
Note that the Delta winding currents lag the Wye winding currents by 30°, which is in agreement with the trans-
former nameplate.
Now assume that a source, with a sequence of ACB is connected to transformer terminals A, C, B respectively.
The currents that would be present for a balanced load are shown below:
I
B
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 Power Management nomenclature) 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.
It may be suggested that for the ACB sequence the phase relationship can be returned to that shown on the
transformer nameplate by connecting source phases A, B and C to transformer terminals A, C, and B respec-
tively. This will restore the nameplate phase shifts but will cause 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.
GE Power Management
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A
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C
Figure 5–4: PHASORS FOR ACB SEQUENCE
745 Transformer Management Relay
5.2 AUTO-CONFIGURATION
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5
5-7
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