Siemens SIPROTEC 7SD610 Manual page 118

Functions
2.9 Backup Time Overcurrent Protection
The set time multiplier T Ip Time Dial (address 2642) or T Ip Dir. (address 2690), 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 T 3I0p TimeDial (address 2652) or T 3I0p Dir. (address 2695), 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
whether 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.
Time Overcurrent Stages I
In the case of the inverse time overcurrent stages, various characteristics can be selected, depending on the
ordering version of the device and the configuration (address 126). With ANSI characteristics (address 126
Back-Up O/C = TOC ANSI) the following options are available in address 2661 ANSI Curve:
Inverse,
Short Inverse,
Long Inverse,
Moderately Inv.,
Very Inverse,
Extremely Inv. and
Definite Inv..
The characteristics and equations they are based on are listed in the „Technical Data". They apply for direc-
tional and non-directional stages alike.
For the setting of the current thresholds Ip> (address 2640) or Ip> Dir. (address 2689) and 3I0p PICKUP
(address 2650) or. 3I0p Dir. (address 2694), the same considerations as for the overcurrent stages of the
definite time protection (see above) apply. In this case, it must be noted that a safety margin between the pickup
threshold and the set value has already been incorporated. Pickup only occurs at a current which is approxi-
mately 10°% above the set value.
118
, I
, 3I Dir, 3I Dir for inverse-time O/C protection with ANSI characteristic
P 0P P 0P
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011