MC2-30MW
Doc. N°
MO-0495-ING
Copyright 2018
Date
17.03.2022
Rev.
2
Pag. 38
of
66
17.7.2 – Blocking Logic (BO-BI)
For each Protection Function it is possible to activate a Blocking Logic allowing for inhibiting their operation
by external signals supplied to the Digital Input.
17.7.2.1 – Output Blocking signal “BO”
All the protection functions that can be programmed to operate in the blocking logic mode, element, have
an instantaneous element (beside the time delayed) which is operated as soon as the controlled quantity
exceeds the set trip level (I > [Is] for current, etc..) and is instantaneously reset when the input quantity
drops below the reset level (normally 0.95Is).
The instantaneous element can control one of the user programmable output relays that, by its contacts,
makes the signal available for blocking an external element (BO = Blocking Output).
In case, “tBO” sec after the set trip time “ts” has expired, the Protection function is still in operation
(current above trip level), the Blocking Output relay (instantaneous element) is anyhow reset to
eventually remove the Blocking signal from a back-up protection.
17.7.2.2 – Blocking Input “BI”
For all the functions controllable by the Blocking Logic, it is possible to inhibit the time delayed tripping
by an external signal that activates a Digital Input programmed for this functionality.
The programmed Digital Input gets activated by an external cold contact closing across its terminals.
With the variable “tBI” set to “OFF” (tBI=OFF), the tripping of the delayed function is blocked as long as
the Blocking Input signal is present at the terminals of the Digital Input.
With the variable “tBI” set to “2xtBI” (tBI=2xtBI), 2xtBI seconds after the set trip time delay of the
function has expired the blocking input is anyhow ignored and the function enabled to trip.
17.7.3 - Automatic doubling of Overcurrent thresholds on current inrush
For some of the phase Overcurrent functions it is possible to have the set trip level [Is] automatically
doubled when strong inrush current is detected.
If at circuit Breaker switch-on (i.e. when the input current rises from zero to a minimum measurable value)
the current increases from 0 to 1.5 times the rated value [In] in less than 60ms, the set minimum pick-up
level [Is] is dynamically doubled ([Is]
→
[2Is]) and keeps this value until the input current drops below
1.25xIn or the set time [t2xI] has elapsed.
This functionality is very useful to avoid spurious tripping of the instantaneous, or short-time delayed
Overcurrent elements, that could be experienced at switch-on when energizing the feeder.
