Areva MiCom P120, Техническое руководство

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P12x/EN AP/A96 Application Guide
Page 54/80
MiCOM P120/P121/P122/P123
22.2.6 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. The external information can
be generated by the spring of the CB is not charged or suffers a low gas.This CB FLT
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.
22.2.7 Setting group change lockout
The change of setting groups on MiCOM P122 and P123 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.
22.3 Setting Guidelines
22.3.1 Number Of Shots
There is no perfect rule to define the number of shots for a particular application. For
medium voltage systems it is common to use two or three autoreclose shots. However, in
some countries, for specific applications, the use of four shots is not uncommon. The
advantage of using four shots is that the final dead time can be set for a time long enough to
allow thunderstorms to stop before definitive final reclose. This scheme prevents
unnecessary lockout caused by consecutive transient faults.
Typically, the first trip, and sometimes the second, are caused by the instantaneous
protection. Since 80% of faults are transient, the following trips will be time delayed, and all
will have increasing dead times to clear non-permanent faults.
In order to determine the number of shots required, it is important to take into account the
following factors.
The first factor is the ability for the circuit breaker to perform several trip-close operations in a
short time and, the effect of these operations on the maintenance period.
If the statistics made on a particular system reveal a moderate percentage of non-permanent
faults which could be burned out, two or more shots are justified. In addition to this, if fused
‘tees’ are used and the fault level is low, the timer of the fuses may not discriminate with the
main IDMT relay and it would then be useful to have several shots. The use of several shots
would then be useful, as this would warm up the fuse to a such extent that it would
eventually blow before the main protection operated.
22.3.2 Dead Timer Setting
It is important to take the following factors into consideration when setting the dead timer.