Siemens siprotec 7SA522 User Manual page 253

Inverse Time Over-
current Stage with
Logarithmic–
Inverse Character-
istic
7SA522 Manual
C53000-G1176-C119-2
For the inverse time overcurrent stage 3I
curves depending on the version of the relay and the configuration (Section 5.1, ad-
dress ) that was selected. If an inverse overcurrent stage is not required, the ad-
dress  LV VHW WR (DUWK )DXOW 2& = 'HILQLWH 7LPH. The 3I
can then be used as a fourth definite time stage (refer to "Definite Time Stages"
above). 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 10.9).
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 set-
ting 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 grad-
ing 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 op-
erating mode is initially set: 2S PRGH ,S (address ). This stage can be set
to operate forward (usually towards line) or reverse direction (usually towards bus-
bar) or non-directional (in both directions). If an individual stage is not required, set
its mode to inactive .
For the inverse logarithmic curves (address  (DUWK )DXOW 2& = 72& /RJD
ULWKP) 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 6-63 illustrates the influence of the most important setting pa-
rameters 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'(/$< (address ) determines the start-
ing point of the curve (for 3I
(address ) changes the slope of the curve. For large currents, ,S 0LQ7'(
/$< (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 as an increase of ,S
0D[7'(/$< (address ).
it is possible to select from a variety of
0P
= ,S 3,&.83). The time factor ,S 7LPH 'LDO
0
Functions
–stage
0P
6-105