Siemens SIPROTEC 7SJ62 Instruction Manual

Functions
6-1437SJ62 Manual
C53000-G1140-C121-1
6.15 Fault Location
Measurement of the distance to a short-circuit fault is an important feature of the
7SJ62 relay allowing faster determination of the fault location. Fault location is only
possible if the device is connected to both current and voltage transformers.
6.15.1 Description of Fault Location
Initiation 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 pairs of values of short circuit cur-
rent and short circuit voltage, are stored in a buffer, and made available for the imped-
ance calculations R (Resistance) and X (Reactance). Measurement quantity filtering
and the number of impedance calculations automatically adjust to the number of rele-
vant measurement value pairs stored in the buffer.
Fault location can also be initiated using a binary input as long as a directional or non-
directional overcurrent relay element has picked up. This feature allows fault location
calculations to proceed even if another protective relay (load side relay, etc.) cleared
the fault,( e.g. the internal time-overcurrent elements did not trip).
Measurement
Process
The evaluation of the measured quantities takes place after the fault has been has
been isolated and cleared. At least three result pairs of R and X are calculated from
the stored and filtered measured 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 re-
sult 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.
Path Selection Using the pickup of the overcurrent time elements (directional or non-directional), the
valid measurement paths for the calculation of fault reactance’s are selected. The fault
reactance’s can, of course, only be calculated for phase-to-ground paths 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 6-3 shows the assignment of the evaluated paths to the possible pickup scenar-
ios 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 6-4 applies. Of course, no
phase-to-ground paths can be measured in this case.
In addition, paths are not available for further calculation if one of the two currents in
a path are less than 10% of the other current in that path, or if any currents in the path
are less than 10% of the nominal device current.
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Siemens SIPROTEC 7SJ62 Specifications

General

Brand	Siemens
Model	SIPROTEC 7SJ62
Category	Relays
Language	English