GE L90 Instruction Manual page 524

9.4 FAULT LOCATOR
Consequently, the positive-sequence line secondary impedance entered under in the fault locator menu yields following
signals used for calculation. For two-terminal applications, we have:
For three-terminal applications, we have:
Z
1LINE
Z
REM1 TAP
Z
REM2 TAP
L
LOC T
For two-terminal applications, fault calculations can be executed directly using the signals above. For three-terminal appli-
cations, it is first necessary to define the faulted line segment. This is done by estimating the tap voltage as seen from all
three line terminals.
The fault current is calculated as follows.
The faulted segment can be found by recognizing that the sum of the voltage drops around a loop through the unfaulted
segments is zero. The residual voltage phasors are computed for each loop. The loop with the lowest residual voltage con-
tains the two unfaulted segments. Therefore, the differences between each pair of estimates is calculated as follows.
The faulted segment is selected as follows.
Where:
9
A similar set of equations is applied to determine whether the fault is between the tap and the local terminal or between the
tap and remote terminal 1.
Next, having all the data prepared, the following universal equation is used to calculate the fault location.
9-26
CT
sec
-------------- - for wye-connected VTs
Z Z
pu sec
VT
sec
CT
-------------- - for delta-connected VTs
Z 3 Z
pu sec
VT
Z Z
1LINE
L corresponding line length
Z
LOC T
Z
REM1 T
Z
REM2 T
L L corresponding lengths of the three line segments
REM1 T REM2 T
V V
T LOC LOC X
V V
T REM1 REM1 X
V V
T REM2 REM2 X
I I
FLT X LOC X
V
LOC REM1
V
LOC REM2
V
REM1 REM2
If V min V
LOC REM1 LOC REM1
and V max 0.025
LOC REM1
then the fault is between the tap and remote terminal 2
L L
REM2 T
Z Z
REM2 T
1
-- - V
V
TAP X
2
I I
TAP X LOC X
V V
1 X REM2 X
L90 Line Current Differential System
sec
sec
Z I
LOC T LOC X
Z I
REM1 T REM1 X
Z I
REM2 T REM2 X
I I
REM1 X REM2 X
V V
T LOC T REM1
V V
T LOC T REM2
V V
T REM1 T REM2
V V
LOC REM2 REM1 REM2
V V 0.01 pu
T LOC T REM1
V
T LOC T REM1
I
REM1 X
9 THEORY OF OPERATION
(EQ 9.41)
(EQ 9.42)
(EQ 9.43)
(EQ 9.44)
(EQ 9.45)
(EQ 9.46)
(EQ 9.47)
(EQ 9.48)
GE Multilin