Siemens SIPROTEC 7SD610 Manual page 117

The settable delay time T Iph> (address 2621) or T Iph> Dir. (address 2682), results from the grading
coordination chart defined for the network. If implemented as emergency overcurrent protection, shorter delay
times are advisable (one grading time step above instantaneous tripping)..
The time T 3I0> (address 2623) or T 3I0> Dir. (address 2685) can normally be set shorter, according to
a separate time grading schedule for ground currents.
The set times are mere additional delays for the independent stages, which do not include the inherent oper-
ating time of the protection. If only the phase currents are to be monitored, set the pickup value of the earth
fault stage to ∞.
The parameter I> Telep/BI (address 2624) or I>Dir.Telep/BI (address 2686), determines whether the
delay times T Iph> (address 2621) or T Iph> Dir. (address 2682) and T 3I0> (address 2623) or T 3I0>
Dir. (address 2685), can be bypassed via the binary input „>O/C InstTRIP". The binary input (if allocated)
is applied to all stages of the time-overcurrent protection. With I> Telep/BI = YES or I>Dir.Telep/BI =
YES, you define that the I>stages trip without delay after pickup if the binary input was activated. For I>
Telep/BI = NO or I>Dir.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 principally guarantees a fast and selective
tripping with or without auto-reclosure, the overcurrent protection as a backup protection may not perform a
non-selective trip, even before auto-reclosure.
If the I> 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> SOTF (address 2625)
or I> Dir. SOTF (address 2687) 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 IEC characteristics (address 126
Back-Up O/C = TOC IEC) the following options are available in address 2660 IEC Curve:
Normal Inverse (inverse, type A according to IEC 60255-3),
Very Inverse (very inverse, type B according to IEC 60255-3),
Extremely Inv. (extremely inverse, type C according to IEC 60255-3), and
LongTimeInverse (longtime, type B according to IEC 60255-3).
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.
The above example shows that the maximum expected operating current may directly be applied as setting
here.
Primary: Set value IP = 630 A,
Secondary: Set value IP = 5.25 A, i.e. (630 A/600 A) X 5 A.
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
, I
, 3I Dir, 3I Dir for inverse-time O/C protection with IEC characteristic
P 0P P 0P
2.9 Backup Time Overcurrent Protection
Functions
117