7SR11 & 7SR12 Applications Guide
Page 36 of 48 ©2017 Siemens Protection Devices Limited
It is important that all the relays in an ARC scheme shadow this process – advancing through their own ARC
sequences when a fault is detected by an element pickup even though they are not actually causing a trip or
reclose. This is termed Sequence Co-ordination and prevents an excessive number of recloses as each
successive relay attempts to clear the fault in isolation. For this reason each relay in an ARC scheme must be set
with identical Instantaneous and Delayed sequence of trips.
Figure 4.1-1 Sequence Co-ordination
The relay closest to the fault (D) would step through its Instantaneous Trips in an attempt to clear the fault. If
unsuccessful, the relay would move to a Delayed Trip sequence.
The other relays in the network (A, B and C) would recognise the sequence of Pick-up followed by current switch-
off as ARC sequences. They would therefore also step to their Delayed Trip to retain co-ordination with the
respective downstream devices.
The next Trip would be subject to current grading and Lockout the ARC sequence such that the fault is cleared by
the correct CB.
4.1.1 Auto-Reclose Example 1, typical advanced distribution network sequence
Requirement: Settings shall provide four phase fault recloses – two instantaneous and two delayed - and only two
delayed recloses for faults detected by the SEF protection.
Proposed settings include:
CONTROL & LOGIC > AUTORECLOSE PROT’N:
79 P/F Inst Trips: 50-1
79 P/F Delayed Trips: 51-1
79 SEF Delayed Trips: 51SEF-1
CONTROL & LOGIC > AUTORECLOSE CONFIG
79 Num Shots: 4
CONTROL & LOGIC > AUTORECLOSE CONFIG > P/F SHOTS
79 P/F Prot’n Trip 1 : Inst
79 P/F Prot’n Trip 2 : Inst
79 P/F Prot’n Trip 3 : Delayed
79 P/F Prot’n Trip 4 : Delayed
79 P/F Delayed Trips to Lockout : 3
CONTROL & LOGIC > AUTORECLOSE CONFIG > SEF SHOTS
79 SEF Prot’n Trip 1 : Delayed
79 SEF Prot’n Trip 2 : Delayed
79 SEF Delayed Trips to Lockout : 3
Note that Instantaneous’ trips are inhibited if the shot is defined as ‘Delayed’
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