Configuration
6.2 Overload relays in motor feeders
SIRIUS 3RU thermal overload relays / SIRIUS 3RB electronic overload relays
64 Manual, 09/2016, A5E03656507420A/RS-AB/003
Operation with frequency converters
3RU21 thermal overload relays
3RU21 thermal overload relays are suitable for operation with frequency converters.
Depending on the frequency of the converter, eddy current and skin effects that occur mean
that in some cases, a current higher than the rated motor current has to be set.
3RB20 / 3RB21 and 3RB30 / 3RB31 electronic overload relays
3RB20 / 3RB21 and 3RB30 / 3RB31 electronic overload relays are suitable for frequencies
of 50 / 60 Hz and their associated harmonics. This makes it possible to use a 3RB20 /
3RB21 and 3RB30 / 3RB31 on the input side of the frequency converter. If motor protection
is required on the secondary side of the frequency converter, we recommend 3RN thermistor
motor protection devices or 3RU21 thermal overload relays.
can be found on the Internet at
about setting corrections and
other factors when using circuit
breakers and overload relays on
the secondary side of frequency
Circuit breakers and overload relays on the secondary side of
frequency converters - influences and criteria
(http://support.automation.siemens.com/WW/view/en/24232798)
about the influence of frequency
converters on thermal motor
protection devices in the case of
about the influence of frequency converters/inverters on thermal
motor protection devices in the case of pulsed voltage
(http://support.automation.siemens.com/WW/view/de/24153083)
Is available in the appendix ...
About the currents to be set "References" under "Manuals - SIRIUS Modular System
(Page 168)" in the "SIRIUS Innovations - SIRIUS 3RV motor
starter protectors" manual.
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