Fault Locator; Functional Description - Siemens siprotec 7SD5 User Manual

2 Functions
2.19

Fault Locator

The measurement of the distance to a fault is an important supplement to the protec-
tion functions. Availability of the line for power transmission within the system can be
increased when the fault is located and cleared faster.

2.19.1 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 addressed
by the protection functions provided in the 7SD5 device. For lines with two ends, the
7SD5 provides as an option a double-ended fault locator functionality, which allows
better fault locating especially in the case of double-ended infeed, faults involving
earth currents, and high fault resistances. In the event of a fault, both line ends ex-
change their local measured values (phase current and phase-to-earth voltages) via
the protection data interface. For this function, the 7SD5 of both line ends must be
equipped with the option „double-ended fault locator". If there are more than two line
ends, single-ended fault locator will be used.
When double-ended fault locating is used, the single-ended (conventional) fault
locator may be invoked simultaneously, 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
When double-ended fault locating is used, the results of single-ended fault locating are
output in any case in additional indications.
The protected object can be an inhomogenous line. For calculation purposes, the line
can be divided into different 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 (refer to Section 2.1.4).
For the internal decision of whether the single-ended or the double-ended fault locat-
ing 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 ge-
ometry. If this distance difference is too great in proportion to the length of the line
section considered, the result of the double-ended fault locating is discarded, and the
distance output is calculated on a single-end basis. With increasing accuracy, this cal-
culated quality index is output as an indication with a value ranging from 0 to 10.
Double earth faults with different base points, reverse faults and faults that extend
beyond the opposite device are calculated and output with single-ended fault locator
only.
The fault locating function can be triggered by the trip command of the short-circuit
protection, or also by each fault detection. In the latter case, a fault locating calculation
is also possible if a different protection device clears the fault.
348
outside the protected object.
7SD5 Manual
C53000-G1176-C169-1