Siemens 3RW51 Series, Руководство пользователя

Страница: 9 / 192

Description
1.3 Operating principle
3RW51 Soft Starter
Manual, 06/2019, A5E37108631002A/RS-AB/002
9
1.3 Operating principle
Soft starters are used to start three-phase induction motors with reduced torque and reduced
starting current.
The 3RW51 soft starter starts the motor as soon as the switch-on command is issued (t
1
).
During the ramp-up time (t
1
to t
3
), the current is conducted via power semiconductors which
starts up the motor smoothly.
The 3RW51 soft starter features internal run-up recognition. The following operation occurs
when the motor reaches its rated operating speed before the ramp-up time expires:
● The motor voltage is immediately increased to 100 % of the line voltage (t
2
)
● The external bypass contactor close
● The power semiconductors are bypassed and the soft starter is in bypass operation.
Coast-down to zero speed is activated when the switch-on command is cancelled (t
4
) and
the motor is shut down. The power semiconductors also ensure that the motor coasts down
smoothly to a stop. The power supply to the motor is maintained (t
5
) until the end of the
ramp-down time is reached (t
4
to t
5
). It may take longer for the motor to actually coast down
to a standstill (t
6
).
①
Speed t
5
End of the set ramp-down time (t
5
-t
4
)
②
Voltage t
6
Motor at standstill
t
1
Motor start-up with set starting voltage U
S
U
S
Set starting voltage
t
2
Rated speed n
e
achieved U
e
Rated operational voltage
t
3
End of the set ramp-up time (t
3
-t
1
) n
e
Rated motor speed
t
4
Switch-on command is cancelled, motor is
switched off