Description
2.5 Protection functions
3VA molded case circuit breakers with UL and IEC certification
68
Manual, 01/2019, L1V30435333-01
Setting the parameters for electronic trip units ETU 5-series and 8-series
Trip units of the ETU 5-series and 8-series are equipped with an LCD display and operator
buttons. These can be used to change the parameters.
The powerconfig software can also be used to input parameter settings. The TD500 test
device and the COM800/COM100 breaker data server combined with the COM060
communication module can be used as the software interface.
2.5.4
Overload protection (L)
The ID letter for overload protection is L (stands for "Long-time (protection)").
The trip unit is inverse-time delayed and exhibits the following characteristics depending on
the trip unit type:
●
Bimetal characteristic with thermal-magnetic trip units
●
I
2
t characteristic with electronic trip units
The setting value of the current (and the breaker rating) is designated with I
r
, and the
associated time delay with t
r
.
The time delay with the device-specific reference point defines the current-dependent curve
shape of the setpoint characteristic. With 3VA UL molded case circuit breakers, this
reference point of the overcurrent trip is 6 times the current setting value I
r
. The following
mathematical equation determines the remaining curve of the setpoint characteristic:
I
2
t = constant
Thermal memory
The electronic trip units have a so-called thermal memory via which temperature rises in the
past are taken into account for tripping.
Thermal memory activated (ON)
If the thermal memory is activated, the previous thermal history is taken into account. After
tripping, the thermal memories of the phases are set to a value corresponding to 85 % of the
thermal equivalent of the warmest phase. This setting allows reclosure of the contacts of the
molded case circuit breaker. This is followed by a cool-down period according to an
exponential function with a time constant T
au
(τ).
