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• By input at the digital I/O module IOM040 or IOM300, which was triggered by an external
signal
• By input at the digital I/O module IOM040 or IOM300, which was triggered by an internal
signal, for example, the pre-alarm response thresholds (PAL)
• Automatically after a defined delay time, after the circuit breaker has been closed.
MCR - making current release
Statistically, most short-circuits and faults occur when the power distribution is connected or
reconnected after commissioning or maintenance (connection to existing short-circuit).
The making current release (MCR) for early detection of short-circuits increases short-circuit
protection at the moment the circuit breaker is closed by enabling definition of individual
operating currents and faster break times. For this, the ETU requires an external power
supply.
The MCR protection function is based on the behavior of the instantaneous short-circuit
protection (INST) and can be used as an alternative to it. This means that, when this function
is activated, the INST is disabled, which is indicated by a message on the display of the ETU.
A time is also defined within which the MCR protection will remain active after closure.
After this time, the function, and therefore also instantaneous short-circuit protection, is
automatically deactivated. Unless it is activated in another way, only ST protection is then still
active after the switch-on phase in normal operation of the installation to achieve optimum
selectivity.
Current unbalance I-NBA
The current unbalance protection function provides protection from undesired unbalance of
the current between the phases and load unbalances in the distribution and at the load. It
can open the circuit breaker with a constant, definable delay time t
(L1, L2, L3) deviates by more than the set operating value I
the phase currents. The deviation of the operating value from the mean value is stated as a
percentage [%].
Additional functions
Pre-alarms response thresholds - PAL (function trigger)
This function permits definition of four independent current setting thresholds that can
be configured and switched when freely definable outputs are crossed (e.g. via the IOM040/
IOM300 input and output modules). In this way, the logic functions can be defined and
corrective action taken that, for example, triggers cooling systems in the plant, or sheds
loads to prevent the overload release from tripping the circuit breaker.
Two thresholds are defined as a selectable multiple of the overload current I
thresholds as a selectable multiple of the circuit breaker current rating I
It is also possible to choose the direction in which the threshold is crossed. For example, a
signal can be set if a current falls and the threshold is crossed in the downward direction.
2nd parameter set (set A/B)
The ETUs of the 6-series can store and manage a complete second set of alternative
parameters for the protection functions. It is possible to switch to this second set of
3VA27 molded case circuit breakers & 3WL10 air circuit breakers
Equipment Manual, 10/2023, L1V30499596002-03
2.9 Electronic trip unit ETU
if a phase current
nba(I)
from the arithmetic mean of
nba
and two
r
.
n
Description
57
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