Fault Locator; Description - Siemens siprotec SJ62 User Manual

2.15

Fault Locator

Applications

2.15.1 Description

Initiation
Measurement
Process
Loop Selection
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
The measurement of the distance to a fault is a supplement to the protection functions.
• Power transmission within the system can be increased when the fault is located
and cleared faster.
Fault location is initiated if the directional or non-directional overcurrent relay elements
have initiated a trip signal. Once initiated, the fault locator determines the valid mea-
surement loop and measurement window. Sampled value pairs of short-circuit current
and short-circuit voltage, are stored in a buffer, and made available for the impedance
calculations R (Resistance) and X (Reactance). Measured quantity filtering and the
number of impedance calculations are adjusted automatically to the number of stable
measured value pairs.
Fault location can also be initiated using a binary input. However, it is a prerequisite
that pickup of the time overcurrent protection is performed at the same time (direction-
al or non-directional). This feature allows fault location calculations to proceed even if
another protective relay cleared the fault.
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. If fewer than three pairs of R
and X are calculated, then the fault location feature will generate no information.
Average and standard deviations are calculated from the result pairs. After eliminating
"questionable results", which are recognized via a large variance from the standard
deviation, average values are calculated once again for X. This average is the fault
reactance, and is proportional to the fault distance.
Note
No calculation of the fault locations is carried out if the voltages are connected phase-
phase!
Using the pickup of the overcurrent time elements (directional or non-directional), the
valid measurement loops for the calculation of fault reactances are selected. The fault
reactances can, of course, only be calculated for phase-to-ground loops if the device
is connected to three current transformers connected in a grounded-wye configuration
and three voltage transformers connected in a grounded-wye configuration.
Table 2-16 shows the assignment of the evaluated loops to the possible pickup sce-
narios of the protective elements given that the device is supplied from three voltage
transformers connected in a grounded-wye configuration. If the voltage transformers
are connected in an open delta configuration, then Table 2-17 applies. Of course, no
phase-to-ground loops can be measured in this case.
In addition, loops are not available for further calculation if one of the two currents in
a loop is less than 10% of the other current in that loop, or if any currents in the loop
are less than 10% of the nominal device current.
2.15 Fault Locator
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