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Description
2.9 Electronic trip unit ETU
Ground fault residual current protection (Rc)
Residual currents from 3 A to 30 A can be measured directly with an external summation
current transformer and evaluated by the ETU660 (LSIG), which is additionally equipped with
a rating plug Rc for residual current protection and the metering function MF Advanced.
Direct measurement of ground faults with a summation current transformer is an alternative
to the calculated ground-fault protection method of the GF protection function.
Ground fault return (G
Currents in the grounding conductor of the transformer star point can be directly measured
with high accuracy using an external toroidal-core transformer and evaluated with the
ETU660 (LSIG). Direct measurement of ground faults with a toroidal-core transformer is an
alternative to the vector sum calculation of the GF protection function. The ETU requires
an external power supply for the function (e.g. Breaker Connect module or MF Advanced
metering module)
Monitoring of the switch-on phase (start-up inrush adaptation)
Using this function it is possible to individually adapt the operating value of the protection
functions ST, INST, and GF toward higher thresholds over a certain time and thus to make
them less sensitive. During the switch-on and starting phase, for example, of motors with
high inrush currents or during heavy starting, and also for transformers or lamps, this can
prevent undesired false tripping of the circuit breaker.
The duration in which this monitoring and the alternative, individually set values for ST, INST,
and GF are active can vary between 100 ms and 30 s. After this, the parameters are reset to
their default protection settings defined for normal operation.
In a self-powered ETU, monitoring of the switch-on phase and activation of the alternative
protection parameters are started every time the circuit breaker closes.
In an externally powered ETU, you define an activation threshold between 0.1 and 10 x I
Startup is possible again whenever the peak value of the phase with the largest current falls
below this threshold. If this threshold is then crossed as the current rises, the new monitoring
is automatically started again.
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
panel 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
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3VA27 molded case circuit breakers & 3WL10 air circuit breakers
Equipment Manual, 10/2023, L1V30499596002-03
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