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9.4 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
Table 9–10: PHASE DISTANCE INPUT SIGNALS FOR WYE-DELTA TRANSFORMERS
TRANSFORMER
LOOP
CONNECTION
Yd9
AB
BC
CA
Yd11
AB
BC
CA
Equations from the "Current Transformation" and "Voltage Transformation" columns are used to derive inputs to the three
(AB, BC, and CA) phase distance elements. For example, if the CTs are located at the delta side of the Delta-Wye 11 trans-
former, and a given zone is set to look through the transformer into the system connected to the Wye winding, the CT loca-
tion setting for that zone shall be set to Dy11 and the relay would use
phase distance element.
The current supervision pickup setting applies to the currents specified in the "Current Transformation" columns.
A distance zone originates at the location of the VTs (regardless of the location of the CTs). For more information on set-
tings please refer to Chapter 9: Application of Settings.
Consider the system shown below:
9
Normally, in order to respond to the fault shown in the figure, a distance relay shall be applied at the relaying point X. The
relay input signals at this location are shown in the following table.
9-32
CURRENT
TRANSFORMATION
1
------ - 2I
I
I
I
AB_21P
C
A
B
3
1
------ - 2I
I
I
I
BC_21P
A
B
C
3
1
------ - 2I
I
I
I
CA_21P
B
A
C
3
1
------ - I
I
I
2I
AB_21P
A
C
B
3
1
------ - I
I
I
2I
BC_21P
A
B
C
3
1
------ - I
I
I
2I
CA_21P
B
C
A
3
150 MVA, 10%
13.8kV/315kV
delta
wye, 330 lag
H
X
VT = 13.8kV/120V
CT = 8000:5
2.57Ω∠88.4°
Figure 9–12: SAMPLE SYSTEM CONFIGURATION
L90 Line Current Differential System
9 THEORY OF OPERATION
VOLTAGE
TRANSFORMATION
V
3V
AB_21P
C
V
3V
BC_21P
A
V
3V
CA_21P
B
V
3V
AB_21P
B
V
3V
BC_21P
C
V
3V
CA_21P
A
3I
instead of a traditional
B
°
AB
Ω∠
Z = 30.11
85°
L
VT = 315kV/120V
CT = 300:5
Ω∠
0.688
85°
837727A2.CDR
I
I
for the AB
A
B
9.4.2 EXAMPLE
GE Multilin
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