Siemens siprotec 7SA6 User Manual page 404

Functions
Correction of
Measured Values
on Parallel Lines
6-222
• 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 
during the configuration of the protection functions (Section 5.1, "Special Cases", page
5-3. 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
following:
• 4 outputs for the units (1·2
• 4 outputs for the tens (10·2
• 1 output for the hundreds (100·2
• 1 output for the ready-state annunciation "%&' GLVW 9$/,'".
Once a fault was located, the corresponding binary outputs pick up. Then the output
"%&' GLVW 9$/,'" signalizes that the data are then valid. The duration can be
selected. In the event of a new fault the data of the former fault are terminated
automatically.
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)
(according to the ordering code) and that an analog output was allocated to the fault
location in address  or  during the configuration of the protection functions
(Section 5.1, in "Special Cases", page 5-3. For more information about the analog
output settings please refer to Subsection 6.18.
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.
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
impedance of the two parallel lines. This causes measuring errors in the result of the
impedance computation unless special measures are taken. The device is therefore
provided with a parallel line compensation function. This function takes the earth
current of the parallel line into consideration when solving the line equation, thereby
compensating 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" and Figure 6-27). The earth current of the parallel line
must, of course, be connected to the device and the current input I
configured accordingly during the setting of the Power System Data (Sub-section
6.1.1 under "Current Transformer Connection").
The parallel line compensation only applies to faults on the protected feeder. For
external faults, including those on the parallel line, compensation is impossible.
0 1 2 3
+ 1·2 + 1·2 + 1·2 ),
0 1 2
+ 10·2 + 10·2 + 10·2
0
),
3
),
must be
4
7SA6 Manual
C53000-G1176-C133-1