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6.13 Starting three-phase motors with reduced starting current peaks (contactor assembly for star-delta (wye-
delta) start)
6.13
Starting three-phase motors with reduced starting current peaks
(contactor assembly for star-delta (wye-delta) start)
Applications
A contactor assembly for star-delta (wye-delta) start is used for starting three-phase motors
requiring a reduction in system load and prevention of false tripping of protection equipment
as a result of excessively high current peaks. With this circuit type, the motor's starting
current is reduced by 1/3 (proportional load torque) compared with direct startup.
Note
Increased current peaks
When switching over from star operation to delta operation, the motor may be subjected to
compensation processes (fueled by an unfavorable line frequency/rotor field constellation),
which would result in higher current peaks than would be the case if the stationary motor
were connected directly in the delta circuit. This must be taken into account when configuring
a contactor assembly for star-delta (wye-delta) start.
For detailed information, please refer to section "Technical background information
(Page 153)"
Note
The preferred wiring for the 3RA24 contactor assembly minimizes this effect.
The 3RA24 contactor assemblies for star-delta (wye-delta) start described below have been
dimensioned for standard applications.
Note
Contactor assemblies for star-delta (wye-delta) start for special applications, such as very
heavy starting or star-delta (wye-delta) startup of special motors, must be customized. When
dimensioning contactor assemblies for special applications such as these you can obtain
support from Technical Assistance (http://www.siemens.com/sirius/technical-assistance).
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
Configuration
147
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