2 Functions
152
7ST6 Manual
E50417-G1176-C251-A3
2.14
Fault Locator
This function is optional, i.e. not included in all device variants.
The measurement of the distance to a fault is an supplement to the protection func-
tions. Availability of the line for power transmission within the system can be in-
creased when the fault is located and cleared faster.
2.14.1 Functional Description
Initiation Condi-
tions
The fault locator in the overhead contact line protection 7ST6 is a function which is in-
dependent of the distance measurement. It has a separate measured signal memory
and dedicated algorithms for determination of the loop reactance and the fault loca-
tion.
The short-circuit protection merely has to provide a start command to allow the selec-
tion of the best suited time interval for the storage of the measured signals.
The fault locator can be triggered either by the trip command of the short-circuit pro-
tection, or by each fault detection. In the latter case, a fault location calculation is also
possible if a different protection device clears the fault.
For a fault outside the protected overhead contact line, the fault location information is
not always correct, as the measured values can be distorted by, e.g. intermediate
infeeds or by loads along the line.
Determination of
the Fault Location
The measured value pairs of fault currents and fault voltages are the basis for calcu-
lating the impedance.
Filtering of the measured values and the number of impedance calculations are auto-
matically adapted to the number of measured value pairs provided in the available
data window. If a sufficient data window with appropriate measured value pairs could
not be determined, the alarm
„Flt.Loc.invalid“
(FNo.1132) is issued.
The evaluation of the measured quantities takes place after the fault has been cleared.
At least three result pairs of R and X are calculated from the stored and filtered mea-
sured quantities in accordance with the line equations. The calculated average for X
is the fault reactance which is proportional to the distance to fault.
For the fault locator up to 5 line sections (respectively for forward and reverse direc-
tion) with different reactance per unit length characteristics can be defined. Calculation
of the fault location is thus possible even with inhomogeneous line sections. The figure
below illustrates how the distance to fault is computed from the fault reactance deter-
mined by the fault location calculation.
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