GE UR Series L90, Instruction Manual, Page: 599 / 846

GE Multilin L90 Line Current Differential System 9-53
9 THEORY OF OPERATION 9.6 FAULT LOCATOR
9
• Relay 1: 0.38781 pu  0.26811°
• Relay 2: 0.30072 pu 
–
12.468°
• Relay 3: 0.37827 pu  8.9388°
Since they have a common per-unit base, the composite voltages are used at all locations. The currents are ratio matched
using the tap settings.
For example, the composite current at relay 1 is 1.3839 pu of its local CT; that is, 1.3839 × 1200 A = 1.6607 kA. When cal-
culated at relay 2 from the data sent from relay 1 to relay 2, this value is 1.6607 kA / 1000 A = 1.6607 pu of the relay 2 CT.
This is due to the procedure of applying tap settings to the received phase currents before calculating the composite signal.
As a result, the three relays work with the following signals.
The line impedances entered in secondary ohms are recalculated as follows (refer to the previous sub-section for equa-
tions).
Using the data in the previous two tables, the tap voltages are calculated as follows (refer to the previous sub-section for
equations).
From the above table, it is already visible that:
• Looking from relay 1 there is no fault between the tap and the local terminal and between the tap and remote 2 termi-
nal. Therefore, the fault must be between the remote 1 terminal = relay 2 and the tap.
• Looking from relay 2 there is no fault between the tap and the remote 1 terminal, and between the tap and remote 2
terminal. Therefore, the fault must be between the local terminal = relay 2 and the tap.
• Looking from relay 3 there is no fault between the tap and the remote 1 terminal, and between the tap and the local ter-
minal. Therefore, the fault must be between the remote 2 terminal = relay 2 and the tap.
Note that the correct value of the tap voltage is equal for all three relays. This is expected since the per-unit base for the
composite voltages is equal for all three relays.
The three relays calculate the differences as follows (refer to the previous sub-section for equations).
Table 9–37: COMPOSITE SIGNALS AT ALL THREE RELAYS
VALUE RELAY 1 RELAY 2 RELAY 3
V
LOC ( X )
0.38781 pu

0.26811° 0.30072 pu

–12.468° 0.37827 pu

8.9388°
V
REM 1( X )
0.30072 pu

–12.468° 0.38781 pu

0.26811° 0.38781 pu

0.26811°
V
REM 2( X )
0.37827 pu

8.9388° 0.37827 pu

8.9388° 0.30072 pu

–12.468°
I
LOC ( X )
1.3839 pu

–84.504° 5.4844 pu

–85.236° 1.2775 pu

–56.917°
I
REM 1( X )
4.5704 pu

–85.236° 1.6607 pu

–84.504° 1.0379 pu

–84.504°
I
REM 2( X )
1.7033 pu

–56.917° 2.0439 pu

–56.917° 3.4278 pu

–85.236°
Table 9–38: PER-UNIT LINE IMPEDANCE
VALUE RELAY 1 RELAY 2 RELAY 3
Local to tap 0.088509 pu

80.5° 0.12644 pu

80.5° 0.092735 pu

80.5°
Remote 1 to tap 0.15174 pu

80.5° 0.073754 pu

80.5° 0.11801 pu

80.5°
Remote 2 to tap 0.069551 pu

80.5° 0.057957 pu

80.5° 0.20232 pu

80.5°
Table 9–39: CALCULATED TAP VOLTAGES USING TERMINAL DATA
VALUE RELAY 1 RELAY 2 RELAY 3
V
T ( LOC )
0.26581 pu

2.2352° 0.39755 pu

–178.9° 0.26535 pu

2.4583°
V
T ( REM 1)
0.39758 pu

–178.9° 0.26582 pu

2.2351° 0.26581 pu

2.2352°
V
T ( REM 2)
0.26535 pu

2.4583° 0.26535 pu

2.4587° 0.39758 pu

–178.9°