
3RT1/3RH1 contactors
SIRIUS System Manual
GWA 4NEB 430 0999-02b
3-43
Frame size S2
Figure 3-24: Star-delta combination (frame size S2)
Field of application
The star-delta combination is used to start three-phase induction motors
which require a low load torque during startup.
Starting current ratio
Star-delta starting can only be used when the motor is switched to delta
mode, starts with no load, or if the load torque during the star startup is
small and does not increase rapidly.
In the star stage, the motors can be loaded with approximately 50 %
(torque class KL16) and 30 % (KL10) of its rated torque.
The tightening torque is reduced to approximately 1/3 of the value at direct
power-up.
The starting current is approximately 2 to 2.7 times the rated current for the
motor.
Switchover
Switching from the star to the delta stage can only be carried out once the
motor has completed startup to the rated speed.
The required switchover pause and interlock is included in the contactor
combination.
Important
Drives that require an early switchover are not suitable for star-delta star-
ting.
Overload protection
The fully assembled combinations are not equipped with overload protec-
tion. Overload relay (3RU11) and tripping devices for thermistor motor pro-
tection must be ordered separately.
The overload relays can be attached to the contactor directly or set up sepa-
rately. The overload relay is set to 0.58 times the set current I
e
. See
Chapter 4 on overload relays for further information.
Time-delay auxiliary
switch block, at side