The protection element also provides a non-sensitive area to avoid instability due to small asymmetries and unbalances that can generally be present in the network system. This condition is represented by the characteristic reproduced below, where the hatched area is the tripping zone.
Autoreclose logic description
The autoreclose function provides the ability to automatically control the autorecloser (two,
three or four shot cycle, settable using “Phase Cycles” and “E/Gnd Cycles” menu). Dead
times for all the shots (reclose attempts) can be independently adjusted.
The number of shots is directly related to the type of faults likely to occur on the system and
the voltage level of the system (for instance medium voltage networks).
The Dead Time (tD1, tD2, tD3 and tD4) starts when the CB has tripped (when the 52a input
has disappeared). Dead Time is adjusted to start autoreclose when circuit breaker is closed.
NOTE: If an electromagnetic relay is used (working on the principle of disc in
the electromagnetic field due to eddy current generated in the disc),
an additional dead time, depending of the tripping cause, is settable,
At the end of the relevant dead time, “CB FLT” input is sent (see § 5.2.2.1).
The reclaim time (tR) starts when the CB has closed. If the circuit breaker does not trip
again, the autoreclose function resets at the end of the reclaim time.
If the protection operates during the reclaim time, the relay either advances to the next shot
that is programmed in the autoreclose cycle, or it locks out (see § 5.2.6).
The total number of reclosures is displayed under the “MEASUREMENTS/Reclose Stats”
menu.
5.2.5 Autoreclose Inhibit Following Manual Close
The “Inhib Time tI” timer can be used to block the autoreclose being initiated after the CB is
manually closed onto a fault. The Autoreclose is blocked during the “Inhib Time tI“ following
manual CB Closure.
5.2.6 Recloser lockout
If the protection element operates during the reclaim time, following the final reclose attempt,
the relay will lockout and the autoreclose function is disabled until the lockout condition
resets.
The lockout condition can reset by a manual closing after the "Inhib Time tI".
The Autoreclose can also be locked out using a “CB FLT” input. This information can be
issued from the "not charged" or "Low gas pressure" indications of CB springs.
Note that Autoreclose can also be locked by:
− The fact that the CB doesn’t open after tBf delay (CB Fail)
− An operating time that is above programmed thresholds.
5.2.7 Setting group change lockout
The change of setting groups is only possible if there are no protection or automation
functions running (except the thermal overload function). During the autorecloser cycle, if the
relay receives an order to change setting groups, this order is kept in memory, and will only
be executed after the timer has elapsed.
5.2.8 Rolling demand
This specific counter avoids a frequent operation of a CB in case of frequent intermittent
fault. The numbers of shoot can be adjusted from 1 to 100 in the cell “Max cycles nb”,
settable in a time period from 10min to 24 hours.
The rolling demand is used when a definite number of successfully recloses are made on a
definite time.
