Siemens siprotec 7SA6, Manual

Page: 433 / 876

Functions
6-243
7SA6 Manual
C53000-G1176-C156-2
•
the distance to fault d in % of the line length, calculated based on the set reactance
per unit length and the set line length.
The fault location indicated in per cent can, at the same time, be output as BCD-code
(Binary Coded Decimal). This, however, must have been preset in address
138
during
the configuration of the protection functions (Section 5.1, “Special Cases”, page 3. A
further prerequisite is that the required number of binary outputs is allocated for this
purpose (see Section 5.2). 10 output relays are needed. They are classified in the fol-
lowing:
•
4 outputs for the units (1·2
0
+ 1·2
1
+ 1·2
2
+ 1·2
3
),
•
4 outputs for the tens (10·2
0
+ 10·2
1
+ 10·2
2
+ 10·2
3
),
•
1 output for the hundreds (100·2
0
),
•
1 output for the ready-state annunciation “
BCD dist. VALID
”.
Once a fault was located, the corresponding binary outputs pick up. Then the output
“
BCD dist. VALID
” signalizes that the data are then valid. The duration can be se-
lected. In the event of a new fault the data of the former fault are terminated automat-
ically.
The output range extends from 0 % to 195 %. Output “197” means that a negative fault
was detected. Output “199" describes an overflow, i. e. the calculated value is higher
than the maximum possible value of 195 %.
The fault location indicated in per cent can also be output as analog value (0 mA to 20
mA). It is a prerequisite that the device is provided with (an) analog output(s) (accord-
ing to the ordering code) and that an analog output was allocated to the fault location
in address
152
or
153
during the configuration of the protection functions (Section 5.1,
in “Special Cases”, page 3. For more information about the analog output settings
please refer to Subsection 6.20.
Note: The distance can only be applicable in the form of kilometres, miles or percent
if the relevant line section is homogeneous. If the line is composed of line sections with
different reactance per unit length characteristic, e.g. overhead line–cable sections,
the reactance calculated by the fault location function can be subjected to a separate
computation to derive the distance to fault.
Correction of
Measured Values
on Parallel Lines
(optional) In the case of earth faults on double circuit lines, the measured values obtained for
calculation of the impedance are influenced by the mutual coupling of the earth imped-
ance of the two parallel lines. This causes measuring errors in the result of the imped-
ance computation unless special measures are taken. The device is therefore provid-
ed with a parallel line compensation function. This function takes the earth current of
the parallel line into consideration when solving the line equation, thereby compensat-
ing for the coupling influence as was the case with the derivation of the distance by
the distance protection (refer to Sub-section 6.2.3 under “Measured Value Correction
for Parallel Lines (optional)” and Figure 6-27). The earth current of the parallel line
must, of course, be connected to the device and the current input I
4
must be config-
ured accordingly during the setting of the Power System Data (Sub-section 6.1.1 un-
der “Current Transformer Connection”).
The parallel line compensation only applies to faults on the protected feeder. For ex-
ternal faults, including those on the parallel line, compensation is impossible.