Siemens siprotec 7SD5 User Manual page 278

2 Functions
time-overcurrent protection. With I> 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 the set delays are always active.
Instantaneous tripping by the operational auto-reclosure function should only be
chosen if the overcurrent protection is set to emergency function. Since the fast main
protection function - differential protection and/or distance protection - guarantees a
fast and selective tripping with or without auto-reclosure, the overcurrent protection as
a back-up protection may not perform a non-selective trip, even before auto-reclosure.
If the I> stage, when switching the line on to a fault, is to trip without delay or with a
short delay, SOTF Time DELAY (address 2680, see above under margin heading
„General"), the parameter I> SOTF (address 2625) is set to YES. We recommend,
however, not to choose the sensitive setting for the switch on to a fault function as en-
ergizing of the line on to a fault should cause a large fault current. It is important to
avoid that the selected stage picks up due to transients during line energization.
Overcurrent Stages In the case of time inverse overcurren stages, various characteristics can be selected,
, 3I in Inverse- depending on the ordering version of the device and the configuration (address 126),
I
P 0P
with IEC characteristics (address 126 Back-Up O/C = TOC IEC) the following
Time O/C Protec-
options are available in address 2660 IEC Curve:
tion with IEC Char-
acteristics
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".
For the setting of the current thresholds Ip> (address 2640) and 3I0p PICKUP (ad-
dress 2650) 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 approximately 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, d.h. (630 A/600 A) X 5 A.
The time multiplier T Ip Time Dial (address 2642) derives from the time grading
schedule set 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 a failure of the main protection functions, i.e.
differential and/or distance protection.
The time multiplier setting T 3I0p TimeDial (address 2652) can usually be set
smaller according to a separate earth fault grading plan. If only the phase currents are
to be monitored, set the pickup value of the earth fault stage to ∞.
In addition to the current-dependent delays, a time fixed delay can be set, if necessary.
The settings T Ip Add (address 2646 for phase currents) and T 3I0p Add (address
2656 for earth currents) are in addition to the time delays resulting from the set curves.
The parameter I(3I0)p Tele/BI (address 2670) defines whether the time delays
T Ip Time Dial (address 2642), including the additional delay T Ip Add (address
2646), and T 3I0p TimeDial (address 2652), including the additional delay T
3I0p Add (address 2656), can be bypassed by the binary input „>O/C InstTRIP"
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7SD5 Manual
C53000-G1176-C169-1