GE 745 Instruction Manual page 106

AUTO-CONFIGURATION
5.2.4 Phase Angle Correction
5–10
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.
The following diagram shows the internal connections of the Y/d30° transformer of our
example:
FIGURE 5–5: Wye/delta (30° lag) transformer
FIGURE 5–4: Phasors for ACB sequence
WINDING 1 (WYE)
A B C
a b c
WINDING 2 (DELTA)
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
N