6–52
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
S2 SYSTEM SETUP
CHAPTER 6: SETPOINTS
Winding 2 CT: measured
Eq. 4
- winding 2 nominal current
Based on 100% transformer loading, the compensated currents expressed in times CT (w1)
as a reference and used by the percent differential protection will be as shown:
Eq. 5
Eq. 6
PHASE SHIFT COMPENSATION
The source phase sequence must be stated when describing the winding phase
relationships since these relationships change when the phase sequence changes. The
example below shows why this happens, using a transformer described in IEC
nomenclature as “Yd1” or in GE Multilin nomenclature as “Y/d30.”
Figure 12: Example transformer
The above figure shows the physical connections within the transformer that produce a
phase angle in the delta winding lagging the respective wye winding by 30°. The winding
currents are also identified. Note that the total current out of the delta winding is described
by an equation. Now assume that a source, with a sequence of ABC, is connected to
transformer terminals ABC, respectively. The currents that would be present for a balanced
load are shown below.
897716A1.CDR
A
I
A
I '
a
B
C
N
a
b
c
I
B
I
C
I '
b
I '
c
I =
a
I ' – I '
a
c
I =
b
I ' – I '
b
a
I =
c
I ' – I '
c
b
