3RW55 Failsafe soft starter
① Main circuit connection (line power supply)
② 3RW5 HMI High Feature
③ Diagnostics LEDs
④ Eye for lead seal
⑤ Slot for 3RW5 communication module (accessory)
⑥ Connectable conductor cross sections
You will also nd the conductor cross-sections that can be connected in the Technical specica‐
tions (Page 285).
⑦ Main circuit connection (motor)
⑧ Control terminals (inputs/outputs)
⑨ Control cable duct with cover
3.3 Operating principle
Soft starters are used to start three-phase induction motors with reduced torque and reduced
starting current.
The 3RW55 and 3RW55 Failsafe soft starters start 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 (switching elements), which start the motor smoothly.
The 3RW55 and 3RW55 Failsafe soft starters feature internal start-up recognition. If the 3RW55
or 3RW55 Failsafe soft starter detects a motor start-up before the ramp-up time elapses, the
motor voltage is immediately increased to 100% of the line voltage (t
2
). The internal bypass
contacts close and the power semiconductors are bypassed. The 3RW55 or 3RW55 Failsafe soft
starter is in bypass mode.
Description
3.3 Operating principle
SIRIUS 3RW55 and 3RW55 Failsafe Soft Starters
Equipment Manual, 02/2022, A5E35630887002A/RS-AF/006 25
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