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Functions
2.16 Backup Time Overcurrent Protection
If the IP stage, when switching the line onto a fault, is to retrip without delay or with a short delay SOTF Time
DELAY (address 2602, see above under side title „General"), set parameter I(3I0)p SOTF (address 2671)
to YES. We recommend, however, not to choose the sensitive setting for the fast tripping as switching onto a
fault typically causes a solid short circuit. It is important to avoid that the selected stage picks up due to tran-
sients during line energization.
Additional Stage I
>>>
ph
The I>>> stage can be used as an additional definite-time overcurrent stage since it operates independently of
the other stages In this case, the enable input „>I-STUB ENABLE" (no. 7131) must be activated permanently
(via a binary input or CFC).
Since the I>>> stage has an additional enable input, it is also suitable e.g. as an emergency stage if the re-
maining stages are used as backup stages. The enable input „>I-STUB ENABLE" (no. 7131) is then assigned
the output signal „Emer. mode" (no. 2054) - either via binary outputs and inputs or via the user-definable CFC
logic functions.
When using the I>>> stage as an emergency function, similar considerations apply as for the I> stages. The
setting value Iph> STUB (address 2630) must here too be higher than the maximum operational current to
be expected, in order to avoid pickup without fault. The delay T Iph STUB (address 2631) however, can be
shorter than defined in the time grading schedule since this stage works only in emergency operation, i.e. in
case of a communication failure of the differential protection or a local measurement voltage failure of the dis-
tance protection. One grading time above the base time of the differential protection is usually sufficient
Accordingly, the earth current stage 3I0> STUB (address 2632) should pick up on the smallest earth current
to be expected during an earth fault and the delay T 3I0 STUB (address 2633) should exceed the base time
of the differential protection by one grading time. If only the phase currents are to be monitored, set the pickup
value of the earth current stage to ∞.
The I>>> stage can also be accelerated by the release signal „>O/C InstTRIP" (no. 7110) e.g. before au-
tomatic reclosing. This is defined using parameter I-STUB Telep/BI (address 2634). Set this parameter to
YES if you want the I>>> stage to trip instantaneously while the binary input „>O/C InstTRIP" is active or
the internal automatic reclosing function is ready to operate.
Instantaneous tripping by the ready automatic reclosing function should only be chosen if the I>>> stage is
used as an emergency function. If the main protection - differential and/or distance protection - is out of oper-
ation, this emergency stage ensures instantaneous tripping before automatic reclosure.
Instantaneous tripping when the line is switched onto a fault is also possible with the I>>> stage. Set parameter
I-STUB SOTF (address 2635) to YES if instantaneous tripping is desired.
314
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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