SIRIUS 3RU2/3RB3 overload relays
5.5 Configuration
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
505
5.5.1.3 Contactor assembly for star-delta (wye-delta) start
Overload relays in contactor assemblies for star-delta (wye-delta) start
When using overload relays in conjunction with contactor assemblies for star-delta (wye-
delta) start, you need to bear in mind that only 1/√3 times the motor current flows through the
line contactor. An overload relay mounted onto a line contactor has to be set to this 0.58-
times motor current.
NOTICE
Internal ground-fault detection on the 3RB31
If you are using the 3RB31 solid-state overload relay in conjunction with contactor
assemblies for star-delta (wye-delta) start, internal ground-fault detection must not be
activated due to the occurrence of transient current peaks when switching over from star
(wye) to delta operation. These can cause ground-fault monitoring to respond.
5.5.1.4 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 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 outgoing side of the frequency
converter, we recommend the 3RN thermistor motor protection devices or 3RU21 thermal
overload relays.
Reference
More information ... Can be found in the chapter titled ...
About the currents to be set Project guidelines for use downstream of
frequency converters/inverters with pulsed
voltage (Page 398)
To Next Page
Loading...
