Dc Braking With External Braking Contactor - Siemens SIRIUS 3RW55 Manual

Functions
7.3 Run-down
7.3.5

DC braking with external braking contactor

Operating principle
In the case of DC braking, the coasting down or the natural stopping of the load is shortened
by electrical braking using a braking contactor. The soft starter imposes a (pulsating) direct
current in phases L1 and L2 on the motor stator. This current generates a permanent
magnetic field in the stator. Since the rotor is still rotating due to its mass inertia, currents are
induced in the short-circuited rotor winding that generate a DC braking torque. If the braking
process is not completed on expiry of the stopping time, the motor coasts down.
In order to guarantee a secure premature cancelation of the braking process, an external
motor standstill detection can be used to detect the motor standstill before the stopping time
has elapsed. To do this, activate the input action "Motor standstill" or the associated bit in the
process image output "Motor standstill".
For more information about the operating principle, see Chapters 3RW55 soft starters in
inline circuit and stopping function, DC braking with a braking contactor (Page 212) and
3RW55 soft starters in inline circuit and stopping function, DC braking with 2 braking
contactors (Page 214).
Application
● Use the "DC braking" function if applications with small mass inertias (centrifugal masses)
are to be stopped (J
● Lathes (e.g. when replacing tools)
● Circular saws
● Punches
● Conveyor belts
102
≤ 5 x J ).
load motor
SIRIUS 3RW55 soft starter
Manual, 08/2018, A5E35630887002A/RS-AB/002