Appendix: Safe Torque Off (Sto); What This Appendix Contains; Basics - ABB ACS355 User Manual

Appendix: Safe torque off (STO) 399

Appendix: Safe torque off
(STO)

What this appendix contains

The appendix describes the basics of the Safe torque off function (STO) for the
ACS355. In addition, application features and technical data for the safety system
calculation are presented.

Basics

The drive supports the Safe torque off (STO) function according to standards
EN 61800-5-2; EN/ISO 13849-1:2006, IEC/EN 60204-1:1997; EN 61508:2002,
EN 1037:1996, and IEC 62061:2005 (SILCL 3). The function also corresponds to an
uncontrolled stop in accordance with category 0 of IEC 60204-1.
The STO may be used where power removal is required to prevent an unexpected
start. The function disables the control voltage of the power semiconductors of the
drive output stage, thus preventing the inverter from generating the voltage required
to rotate the motor (see the diagram below). With this function, short-time operations
(like cleaning) and/or maintenance work on non-electrical parts of the machinery can
be performed without switching off the power supply to the drive.