Technical Background Information - Siemens SIRIUS 3RT Series System Manual

SIRIUS 3RT2 contactors/contactor assemblies
2.4 Configuration
The SIRIUS modular system offers 3RA27 function modules for connection to the
automation level; they are fitted with terminals for connection to AS-Interface or IO-Link.
Note
If the 3RA24 contactor assembly for star-delta (wye-delta) start is to be connected to a
control, the delivery will include a contactor with a communication interface.
The function module replaces all the wiring in the control circuit and can be used in the
voltage range from 24 to 240 V AC/DC. The changeover delay of 50 ms (timing relay
functionality) is already integrated in the star-delta (wye-delta) function module.
The illustration below shows the 3RA24 contactor assemblies for star-delta (wye-delta) start
without a communication connection in size S0 with a screw-type connection system:
Figure 2-10
Rated powers
The performance range of the 3RA24 contactor assemblies for star-delta (wye-delta) start in
size S00 extends up to 11 kW at a voltage of 400 V. In size S0, the maximum power value
is 22 kW at a voltage of 400 V.
Note
With the 3RA24 contactor assembly for star-delta (wye-delta) start the auxiliary switches
integrated in the contactor can still be used. Additional auxiliary switch blocks cannot be
fitted with the function modules attached.
2.4.10.1

Technical background information

Starting current ratio
Star-delta (wye-delta) startup can only be used if the motor normally operates in a delta
connection or starts softly, or if the load torque is low and does not rise sharply during star
startup. In the star (wye) stage motors can be subjected to around 50% (class CL16) or
30% (CL10) of their rated torque. The starting torque falls to about 1/3 of the relevant value
during direct switch-on.
The starting current is approximately 2 to 2.7 times the rated motor current.
136
Contactor assembly for star-delta (wye-delta) start with screw-type connection system
without a communication connection (size S0)
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03