GE Multilin 745

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Transformer Management Relay
Setpoints
http://www.GEindustrial.com/multilin
5–8
GE Multilin
FIGURE 5–3: Phasors for ABC Sequence
Note that the Delta winding currents lag the Wye winding currents by 30°, which is
in agreement with the transformer 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:
FIGURE 5–4: 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)
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 respectively. 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.
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