10-52
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
FAULT LOCATOR
CHAPTER 10: THEORY OF OPERATION
10
The following composite signals in (in per-unit values) are obtained from the base equation (first equation shown), taking
into account system phase rotation, CT nominal values, and VT nominal values and connections as set under the phase VT
bank of the first 87L source.
Eq. 10-47
where
I
LOC(A, B, C)
is the phasor of the local current, for phases A, B, and C
I
LOC(X)
is the phasor of the local composite (mixed) current
I
REM1(A, B, C)
is the phasor of the first remote current, for phases A, B, and C
V
LOC(A, B, C)
is the phasor of local A, B, and C voltages
V
LOC(X)
is the phasor of the local composite voltage
Composite currents are calculated locally at each terminal locally. Composite voltage is continuously transmitted to
remote terminals, where upon receipt it is labeled as V
REM1(X)
for channel 1 and V
REM2(X)
for channel 2. The transmitted
composite voltage signal is supervised by a VT fuse fail condition of the first source of 87L function. During VT fuse fail
conditions, transmitted voltage is substituted with zero, signaling to remote peers that multi-ended fault location should
be inhibited.
The impedance for fault location calculation (in per-unit values) is calculated as follows:
Eq. 10-48
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:
Eq. 10-49
For three-terminal applications, we have:
Eq. 10-50
For two-terminal applications, fault calculations can be executed directly using the signals above. For three-terminal
applications, 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.
Eq. 10-51
The fault current is calculated as follows:
Eq. 10-52
