Siemens siprotec 7SA6 User Manual page 294

Functions
Inverse Time
Overcurrent Stage
with Logarithmic–
Inverse
Characteristic
6-112
For the inverse time overcurrent stage 3I
curves depending on the version of the relay and the configuration (Section 5.1,
address ) that was selected. If an inverse overcurrent stage is not required, the
address  is set to (DUWK )DXOW 2& = 'HILQLWH 7LPH. The 3I
then be used as a fourth definite time stage (refer to "Definite Time Stages" above) or
deactivated. In the case of the ANSI–curves (address  (DUWK )DXOW 2& =
72& $16,) the following alternatives are available in the address  $16, &XUYH:
,QYHUVH,
6KRUW LQYHUVH,
/RQJ LQYHUVH,
0RGHUDWHO\ LQY,
9HU\ LQYHUVH,
([WUHPHO\ LQY and
'HILQLWH LQY
The curves and equations the curves are based on are illustrated in the technical data
(Section 10.5, Figure 10-1 and 10-3).
The setting of the pick-up threshold ,S 3,&.83 (address ) is similar to the
setting of definite time stages (see above). In this case it must be considered that a
safety margin has already been included between the pick-up threshold and the
setting value. The stage only picks up when the measured signal is approximately
10 % above the setting value.
The time multiplier setting ,S 7LPH 'LDO (address ) is derived from the
grading coordination chart which was set up for earth faults in the system.
In addition to the inverse current dependant time delay, a constant (fixed length) time
delay can also be set if this is required. The setting $GG7'(/$< (address ) is
added to the time of the set curve.
For the inverse time overcurrent stage with logarithmic inverse characteristic the
operating mode is initially set: 2S PRGH ,S (address ). This stage can be
set to operate )RUZDUG (usually towards line) or 5HYHUVH direction (usually towards
busbar) or 1RQ'LUHFWLRQDO (in both directions). If this stage is not required, set its
mode to ,QDFWLYH.
For the inverse logarithmic curves (address  (DUWK )DXOW 2& = 72&
/RJDULWKP) the following can be set: address  /2* &XUYH = /RJ
LQYHUVH
The curves and equations the curves are based on are illustrated in the technical data
(Section 10.5, Figure 10-4). Figure 6-68 illustrates the influence of the most important
setting parameters on the curve. ,S 3,&.83 (address ) is the reference value
for all current values, while ,S 6WDUWSRLQW (address ) determines the
beginning of the curve, i.e. the lowest operating range on the current axis (referred to
,S 3,&.83). The timer setting ,S 0D[7'(/$< (address ) determines
the starting point of the curve (for 3I
'LDO (address ) changes the slope of the curve. For large currents, ,S
0LQ7'(/$< (address ) determines the lower limit on the time axis. For currents
larger than 30·,S 3,&.83 the operating time no longer decreases.
Finally in address  $GG7'(/$< a fixed time delay can be set as was done for
other curves. This, however, has almost the same effect on the characteristic as an
increase of ,S 0D[7'(/$< (address ), but no effect on ,S 0LQ7'(/$<
(address ).
it is possible to select from a variety of
0P
= ,S 3,&.83). The time factor ,S 7LPH
0
–stage can
0P
7SA6 Manual
C53000-G1176-C133-1