ABB ACS355 series User Manual page 424

424 Appendix: Safe torque off (STO)
Use
1. Open the activation switch, or activate the safety functionality that is wired to the
STO connection.
2. STO inputs on the drive control unit de-energize, and the drive control unit cuts off
the control voltage from the drive IGBTs.
3. The control program generates an indication as defined by parameter 3025 STO
OPERATION.
4. The motor coasts to a stop (if running). The drive will not restart while the
activation switch or safety relay contacts are open.
5. Deactivate the STO by closing the activation switch, or resetting the safety
functionality that is wired to the STO connection.
6. Reset any faults before restarting.
WARNING! The Safe torque off function does not disconnect the voltage of
the main and auxiliary circuits from the drive. Therefore maintenance work
on electrical parts of the drive or the motor can only be carried out after
isolating the drive from the main supply.
WARNING! (With permanent magnet motors only) In case of a multiple
IGBT power semiconductor failure, the drive system can produce an
alignment torque which maximally rotates the motor shaft by 180/p
degrees regardless of the activation of the Safe torque off function. p
denotes the number of pole pairs.
Notes:
• If a running drive is stopped by using the Safe torque off function, the drive will cut
off the motor supply voltage and the motor will coast to a stop. If this causes
danger or is not otherwise acceptable, stop the drive and machinery using the
appropriate stop mode before activating the Safe torque off function.
• The Safe torque off function overrides all other functions of the drive unit.
• The Safe torque off function is ineffective against deliberate sabotage or misuse.
• The Safe torque off function has been designed to reduce the recognized
hazardous conditions. In spite of this, it is not always possible to eliminate all
potential hazards. The assembler of the machine must inform the final user about
the residual risks.