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Functions
2.21 Fault Locator
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
387
2.21 Fault Locator
The measurement of the distance to a fault is an important supplement to the protection functions. Availability
of the line for power transmission within the system can be increased when the fault is located.
2.21.1 Functional Description
General
The fault locator is an autonomous and independent function which uses the line and power system parameters
set in other functions. In the event of a fault, it is triggered by the functions provided in the 7SD5 device. For
lines with two ends, the 7SD5 provides the option of a double-ended fault locating, which significantly improves
accuracy of fault locating especially in the case of double-ended infeed, faults involving earth currents, and high
resistance faults. In the event of a fault, both line ends exchange their local measured values (phase currents
and phase-to-earth voltages) via the protection data interface. For this function, the 7SD5 of both line ends
must be equipped with the „double-ended fault locator“ option. If there are more than two line ends, single-
ended fault locating will be used.
When double-ended fault locating is used, the single-ended (conventional) fault locator may be initiated simul-
taneously, depending on the information from the remote end, if
• double-ended fault locating is switched off or blocked,
• no values from the opposite end are available, or
• no fault locating is possible because of heavily distorted measuring signals or faults outside the protected
object.
The protected object can be an inhomogeneous line. For calculation purposes, the line can be divided into dif-
ferent sections such as a short cable followed by an overhead line. In such protected objects, you can configure
each section individually. Without this information, the fault locator uses the general line data (see Section
2.1.4).
For the internal decision whether the single-ended or the double-ended fault locating method will be used, the
device calculates, on the basis of the line's known voltage profile, a distance difference from measurement
errors, line asymmetry and line geometry. If this distance difference is too large in proportion to the length of
the respective line section, the result of the double-ended fault locating is discarded, and the distance is calcu-
lated on a single-end basis.
Double earth faults with different base points, reverse faults and faults that extend beyond the opposite line end
are calculated and output with single-ended fault location only.
Fault locating can be triggered by the trip command of the short circuit protection or by each pickup. In the latter
case, a fault location calculation is also possible if a different protection device clears the fault.
Fault locating using the single-ended fault locator
The measuring principle of the single-ended fault locator is very similar to that of the distance protection func-
tion. Here, too, the device calculates the impedances.
The value pairs of fault currents and fault voltages (at intervals of 1/20 period) are stored in a cyclic buffer and
frozen shortly after the trip command is issued before any distortion of the measured values occurs due to the
opening of (even very fast) circuit breakers. The filtering of the measured values and the number of impedance
calculations are automatically adapted to the number of stabilized measured value pairs in the determined data
window. If no sufficient data windows with stabilized values could be determined for fault location, the
„Flt.Loc.invalid“
indication is issued.