Failsafe; Operating Principle - Siemens SIRIUS 3RW55 Equipment Manual

Functions

8.15 Failsafe

Restriction of the possible parameters:
Parameters
Starting mode
Motor heating
1)
Stopping mode / Alternative stopping mode
DC braking 1)
Dynamic DC braking
1)
Reversing DC braking
1)
Parameter not available for the 3RW55 Failsafe soft starter.
1)
8.15 Failsafe
8.15.1

Operating principle

Observe the safety instructions in chapter Failsafe (Page 20).
Behavior of the failsafe digital input F‑DI
The 3RW55 Failsafe soft starter is only switched on by a control command if an ON command is
present at the failsafe digital input F‑DI. As long as the ON state is present at the failsafe digital
input F‑DI, the 3RW55 Failsafe soft starter first executes the parameterized starting function and
then moves on to the parameterized operating state. The 3RW55 Failsafe soft starter remains in
the parameterized operating state until the control command is canceled. The 3RW55 Failsafe
soft starter then performs the parameterized shutdown operation. Canceling the ON command
at the failsafe digital input F‑DI executes the safety function "Safe Torque Off" (STO).
Activation of the "Safe Torque Off" (STO) safety function
The safety function "Safe Torque Off" (STO) is activated by applying an OFF command at the
failsafe digital input F‑DI. If the 3RW55 Failsafe soft starter receives the request for safe
shutdown "Safe Torque Off" (STO) via the failsafe digital input F‑DI (change from ON command
to OFF command), the current operating state is interrupted immediately and the stopping
mode "Coasting down" is used. Note that, in this case, the 3RW55 Failsafe soft starter does not
consider any differently parameterized shutdown operation. The 3RW55 Failsafe soft starter
signals activation of the safety function "Safe Torque Off" (STO) by an error with the message text
"Safety-related shutoff". One exception is the SIL 3 (STO) application with coupling of the control
signal at the digital input DI to the enable signal at the failsafe digital input F‑DI. In this case, the
3RW55 Failsafe soft starter does not produce an error with message text because the coupling
causes the control command at control input DI to be set to OFF automatically.
212
Relevant for parameter "Ex application: Yes, with ..."
Complete motor protection
selectable
selectable
selectable
selectable
Electronic motor overload
protection
not selectable
not selectable
not selectable
not selectable
SIRIUS 3RW55 and 3RW55 Failsafe Soft Starters
Equipment Manual, 02/2022, A5E35630887002A/RS-AF/006
Thermistor motor protec‐
tion with temperature sen‐
sor
selectable
selectable
selectable
selectable