Siemens SIPROTEC 7SD610 Manual page 119

The above example shows that the maximum expected operating current may directly be applied as setting
here.
Primary: Set value IP = 630 A,
Secondary: Setting value IP = 5.25 A, i.e. (630 A/600 A) X 5 A.
The set time multiplier Time Dial TD Ip (address 2643) or D Ip Dir. (address 2691) results from the
grading coordination chart defined for the network. For the use as emergency overcurrent protection, shorter
delay times make sense (one grading time step above instantaneous tripping), since this function is to work
only in case of an interruption of the data communication for the differential protection.
The time multiplier TimeDial TD3I0p (address 2653) orD 3I0p Dir. (address 2696), can normally be set
shorter, according to a separate time grading schedule for ground currents. If only the phase currents are to be
monitored, set the pickup value of the residual current stage to ∞.
In addition to the current-dependent delays, a time fixed delay can be set, if necessary. The setting T Ip Add
(address 2646 ) or T Ip Add Dir. (address 2692) for phase currents and T 3I0p Add (address 2656 )
or T 3I0p Add Dir. (address 2697) for earth currents add to the times of the set characteristics.
The parameter I(3I0)p Tele/BI (address 2670) or IPDir.Telep/BI (address 2698) determines wheth-
er, via the binary input „>O/C InstTRIP" (No 7110), the delay T Ip Time Dial (address 2642) or T Ip
Dir. (address 2690) including additional delayT Ip Add (address 2646) or T Ip Add Dir. (address 2692)
and T 3I0p TimeDial (address 2652) or T 3I0p Dir. (address 2695) including additional delay T 3I0p
Add (address 2656) or T 3I0p Add Dir. (address 2697) can be bypassed. The binary input (if allocated)
is applied to all stages of the time-overcurrent protection. With I(3I0)p Tele/BI = YES or
IPDir.Telep/BI = YES you define that the IP>stages trip without delay after pickup if the binary input was
activated. For I(3I0)p Tele/BI = NO or IPDir.Telep/BI = NO, the set delays are always active.
Instantaneous tripping by the operational auto-reclosure function should only be chosen if the overcurrent pro-
tection is set to emergency function. Since the differential protection guarantees a fast and selective tripping
with or without auto-reclosure, the overcurrent protection as a backup protection may not perform a non-selec-
tive trip, even before auto-reclosure.
If the IP stage, when switching the line onto a fault, is to re-trip without delay or with a short delay SOTF Time
DELAY (address 2602, see above under margin heading „General"), the parameter I(3I0)p SOTF (address
2671) or IP Dir. SOTF (address 2699) is set to YES. We recommend, however, not to choose the sensitive
setting for the fast tripping as switching onto a fault could cause a solid short circuit. It is important to avoid that
the selected stage picks up due to transients 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.
The considerations for the use of the I>>> stage as an emergency function are the same 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 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. Normally, one grading time above the base time
of the differential protection is sufficient.
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
2.9 Backup Time Overcurrent Protection
Functions
119