Section 4: Control & Logic Functions; Autoreclose (79); Overview - Siemens 7SR224 Technical Manual

Section 4: Control & Logic Functions
4.1

Autoreclose (79)

4.1.1 Overview

A high proportion of faults on an Overhead Line (OHL) network are transient. These faults can be cleared and the
network restored quickly by using Instantaneous (Fast) Protection trips followed by an automated sequence of CB
reclosures after the line has been dead for a short time, this 'deadtime' allows the fault current arc to fully
extinguish. Typically, this autoreclose (AR) sequence of Instantaneous Trip(s) and Reclose Delays (Dead times)
followed by Delayed Trip(s) provides the automatic optimum method of clearing all types of fault i.e. both
Transient and Permanent, as quickly as possible and achieving the desired outcome of keeping as much of the
Network in-service as possible.
The AR function, therefore, has to: -
Control the type of Protection trip applied at each stage of a sequence
Control the Autoreclose of the Circuit Breaker to provide the necessary network Dead times, to allow
time for Arc extinction
Co-ordinate its Protection and Autoreclose sequence with other fault clearing devices.
A typical sequence would be – 2 Instantaneous+1Delayed+HighSet Trips with 1 sec & 10 sec dead times.
The Autoreclose feature can be switched off if it is not required by the setting:
79 Autoreclose ENABLE/DISABLE (AUTORECLOSE CONFIG menu)
When the Autoreclose feature is enabled by the above setting, it may be switched in and out of service by a
number of methods, these are:
A keypad change from the CONTROL MODE
Customer programmed function key (using Quick Logic)
Via the data communications channel(s),
From a 79 OUT binary input. Note the 79 OUT binary input has priority over the 79 IN binary input - if
both are raised the autoreclose will be Out of Service.
Knowledge of the CB position status is integral to the autoreclose functionality. CB auxiliary switches must be
connected to CB Closed and CB Open binary inputs. A circuit breaker's service status is determined by its
position i.e. from the binary inputs programmed CB Open and CB Closed. The circuit breaker is defined as being
in service when it is closed. The in service status has a drop-off delay of 2 sec, this delay is known as the circuit
memory time. This functionality prevents autoreclosing when the line is normally de-energised, or normally open.
Autoreclose (AR) is started by a valid trip relay operation while the associated circuit breaker is in service.
The transition from AR started to deadtime initiation takes place when the CB has opened and the protection
pickups have reset and the trip relay has reset. If check synchronising feature is included, the line or bus voltage
must be detected as dead, unless the Live Line Check setting in the Autoreclose Config menu is set to disabled. If
any of these do not occur within the 79 Sequence Fail Timer setting the relay will Lockout. This prevents the AR
being primed indefinitely. 79 Sequence Fail Timer can be switched to 0 (= OFF).
Once an AR sequence has been initiated, up to 4 reclose operations can be attempted before the AR feature is
locked-out. Number of recloses is determined by 79 Num Shots. Each reclosure (shot) is preceded by a time
delay - 79 Elem Deadtime n - giving transient faults time to clear. Separate dead-time settings are provided for
each of the 4 recloses and for each of the four fault types – P/F, E/F, SEF and External.
Once a CB has reclosed and remained closed for a specified time period (the Reclaim time), the AR sequence is
re-initialised and a Successful Close output issued. A single, common Reclaim time is used (Reclaim Timer).
When an autoreclose sequence does not result in a successful reclosure the relay goes to the lockout state.
©2010 Siemens Protection Devices Limited
7SR224 Argus Description of Operation
Chapter 1 Page 39 of 70