Siemens SENTRON 3WL10 Series Manual page 46

Description
2.4 Electronic trip unit ETU
DAS - Arc fault mitigation
The DAS function provides a way of defining a reduced, alternative operating value of the
instantaneous short-circuit protection (INST), but otherwise it behaves in the same way.
This function is advantageous if you want to reduce the operating value of the instantaneous
short-circuit protection automatically and immediately with an external command or input to
provide a certain level of protection for persons and/or equipment, for example, during
maintenance work and on unauthorized access to the switchroom or opening of the control
cabinet door. This can reduce the arc energy released in the event of a fault.
As soon as the command is changed and the input signal is canceled, the parameters for
instantaneous short circuit protection are reset back to their default protection settings
defined for normal operation.
There are different ways of activating the DAS function:
● Locally, on the display of the ETU of the 6-series
● Via communication
● 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 [%].
44
if a phase current
nba(I)
from the arithmetic mean of
nba
Air circuit breaker 3WL10
Manual, 11/2017, L1V30499596002-01