GE UR Series L90, Instruction Manual, Page: 578 / 846

9-32 L90 Line Current Differential System GE Multilin
9.4 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS 9 THEORY OF OPERATION
9
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
instead of a traditional for the AB
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.
9.4.2 EXAMPLE
Consider the system shown below:
Figure 9–12: SAMPLE SYSTEM CONFIGURATION
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.
Yd9 AB
BC
CA
Yd11 AB
BC
CA
Table 9–10: PHASE DISTANCE INPUT SIGNALS FOR WYE-DELTA TRANSFORMERS
TRANSFORMER
CONNECTION
LOOP CURRENT
TRANSFORMATION
VOLTAGE
TRANSFORMATION
I
AB _21 P
1
3
-------
2 I
C
I
A
I
B
 
V
AB _21 P
3 V
C
I
BC _21 P
1
3
-------
2 I
A
I
B
I
C
 
V
BC _21 P
3 V
A
I
CA _21 P
1
3
-------
2 I
B
I
A
I
C
 
V
CA _21 P
3 V
B
I
AB _21 P
1
3
-------
I
A
I
C
2 I
B
 
V
AB _21 P
3 V
B
I
BC _21 P
1
3
-------
I
A
I
B
2 I
C
 
V
BC _21 P
3 V
C
I
CA _21 P
1
3
------- I
B
I
C
2 I
A
 
V
CA _21 P
3 V
A
3 I
B
I
A
I
B
837727A2.CDR
AB
wye, 330 lag
°
0.688 85°
Ω∠
2.57
Ω∠
88.4°
150 MVA, 10%
13.8kV/315kV
Z = 30.11 85°
L
Ω∠
VT = 315kV/120V
CT = 300:5 VT = 13.8kV/120V
CT = 8000:5
delta
H X