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Configuration
6.2 Overload relays in motor feeders
6.2.5
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.
3RB30/3RB31 solid-state overload relays
3RB30/3RB31 solid-state overload relays are suitable for frequencies of 50 / 60 Hz and their
associated harmonics. This makes it possible to use a 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.
Reference
More information ...
about setting corrections and
other factors when using circuit
breakers and overload relays on
the secondary side of frequency
converters
about the influence of frequency
converters on thermal motor
protection devices in the case of
pulsed voltage
Reference
More information ...
About the currents to be set
54
can be found on the Internet at
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/inverters on thermal
motor protection devices in the case of pulsed voltage
(http://support.automation.siemens.com/WW/view/de/24153083)
SIRIUS Innovations - SIRIUS 3RU2 thermal overload relays / SIRIUS 3RB3 solid-state overload relays
Is available in the appendix ...
"References" under SIRIUS Innovations manuals
(Page 148) in the "SIRIUS Innovations -
SIRIUS 3RV2 motor starter protectors" manual
Manual, 09/2014, A5E03656507420A/RS-AA/002
- Quick Links:
- 3Ru21 Thermal Overload Relays
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