SIRIUS 3RT2 contactors/contactor assemblies
2.4 Configuration
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
137
Switching over
The switchover from star (wye) to delta cannot be carried out until the motor has been fully
accelerated to the rated speed. The necessary changeover delay and interlock are
integrated in the contactor assembly; drives which require this switchover to be performed
earlier are not suitable for star-delta (wye-delta) start.
Reducing the switchover current peak by means of preferred wiring
During star-delta (wye-delta) switching of three-phase motors, the motor may be subjected to
compensation processes, which would result in higher current peaks than would be the case
if the stationary motor were connected directly in the delta circuit.
The worst-case scenario would lead to the following problems, which can be minimized by
using preferred wiring:
● Tripping of short-circuit protection devices
● Welding or substantial contact erosion of the delta contactor
● High dynamic load on the motor
Using a favorable method of connection for the main circuit will reduce the equalizing
currents and current peaks which occur when switching over from a star to a delta circuit.
Preferred wiring used
The phasor diagram below shows the voltages which occur in a motor running in the
clockwise direction when switching over from star to delta. According to the preferred wiring,
the motor terminals are connected correctly, i.e. phase L1 is connected to motor
terminals U1 and V2, L2 to V1 and W2, and L3 to W1 and U2.
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9
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9
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Figure 2-11 Correct connection of motor phases for clockwise rotation
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