7SR11 & 7SR12 Applications Guide
©2017 Siemens Protection Devices Limited
Chapter 7 Page 35 of 48
Section 4: Control Functions
4.1 Auto-reclose Applications
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Automatic circuit reclosing is extensively applied to overhead line circuits where a high percentage of faults
that occur are of a transient nature. By automatically reclosing the circuit-breaker the feature attempts to
minimise the loss of supply to the customer and reduce the need for manual intervention.
The function supports up to 4 autoreclose (ARC) sequences. That is, 4 x Trip / Recloses followed by a Trip &
Lockout. A lockout condition prevents any further automatic attempts to close the circuit-breaker. The number of
sequences selected depends upon the type of faults expected. If there are a sufficient percentage of semi-
permanent faults which could be burnt away, e.g. fallen branches, a multi shot scheme would be appropriate.
Alternatively, if there is a high likelihood of permanent faults, a single shot scheme would minimise the chances of
causing damage by reclosing onto a fault. In general, 80% of faults will be cleared by a single Trip and Reclose
sequence. A further 10% will be cleared by a second Trip and Reclose. Different sequences can be selected for
different fault types (Phase/Earth/Sensitive Earth faults).
The Deadtime is the interval between the trip and the CB close pulse being issued. This is to allow for the line to
go ‘dead’ after the fault is cleared. The delay chosen is a compromise between the need to return the line to
service as soon as possible and prevented unnecessary trips through re-closing too soon. The Reclaim Time is
the delay following a re-closure before the line can be considered back in service. This should be set long enough
to allow for protection operation for the same fault, but not so long that two separate faults could occur in the
same Autoreclose (ARC) sequence and cause unnecessary lockouts.
The Sequence Fail Timer provides an overall maximum time limit on the ARC operation. It should therefore be
longer than all the set delays in a complete cycle of ARC sequences; trip delays, Deadtimes, Reclaim Time etc.
Generally this will only be exceeded if the circuit-breaker has either failed to open or close.
Since large fault currents could potentially damage the system during a prolonged ARC sequence, there are also
settings to identify which protection elements are High-sets and these can cause an early termination of the
sequence.
Where a relay is to operate as part of an ARC scheme involving a number of other relays, which may or may not
provide the ARC function, the 7SR device can be configured to clear any transient faults quickly without regard to
normal fault current grading because ARC will quickly restore the network back into service. This is achieved by
defining each protection element to be one of two types, Delayed or Instantaneous (Inst). The ARC shots of the
sequence are then each defined to be either Delayed or Inst. During a type Inst shot the Inst protection elements
will clear the fault quickly without grading and then initiate reclose of the circuit breaker but during type Delayed
shots the Inst protection elements will be automatically inhibited so that type Delayed elements will clear the fault
with grading applied. Instantaneous Trips are typically set to operate at just above maximum load current with
small delays while Delayed Trips are set to suit current grading based on actual fault levels with suitable delays.
This should not be confused with the 50 and 51 element DTL and IDMTL functionality which use similar
instantaneous and delayed terminology.
If this complex autoreclose sequence is not required, all protection elements that are required to initiate
autoreclose should be set to type Delayed, not to type Inst so that no element is ever inhibited by this available
flexibility because setting configuration could result in the desired protection elements being inhibited and even a
situation where there are no protection elements in service at all.
Any element which is not mapped as either an Inst or Delayed element can still trip but will not initiate ARC. Such
an element can also be mapped to drive Lockout if it is desirable to prevent ARC initiation from an element which
may operate simultaneously or to provide the Lockout alarm..
A typical sequence would be 2 Inst Trips followed by a Delayed Trip & Lockout:
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When any fault occurs, the relay will trip using the Inst protection elements and then reclose and
increment to Shot 2.
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If the fault was transient and no longer present the relay will time out the Reclaim timer then return
to shot 1. If the fault is still present, the relay will operate Inst protection and then reclose again and
move to shot 3.
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If the fault is cleared this time the relay will time out Reclaim then return to shot 1. If the system fault
is still present as it is a permanent fault the protection Trip will be by a Delayed element as Inst
protections are inhibited and so suitable for grading with the rest of the network will be applied. This
will allow downstream protection time to operate first.
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If the fault is not cleared by a downstream circuit breaker, the local trip will Lockout the ARC
sequence and prevent further recloses.
Summary of Contents for Argus 7SR11
Page 1: ...Energy Management 7SR11 7SR12 Argus Overcurrent Relay Reyrolle Protection Devices ...
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Page 4: ...7SR11 7SR12 Argus Contents 2015 Siemens Protection Devices Limited Page 2 of 2 ...
Page 170: ...7SR120 Technical Manual Chapter 4 Page 2 of 84 2017 Siemens Protection Devices Limited ...
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Page 254: ...7SR11 7SR12 Installation Guide Chapter 5 Page 2 of 32 2017 Siemens Protection Devices Limited ...
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