Safe Torque Off (Sto) - ABB ACS800-U7 Hardware Manual

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Safe torque off (STO)

The drive supports the Safe torque off (STO) function according to standards
EN 61800-5-2:2007; EN/ISO 13849-1:2008, IEC 61508, and EN 62061:2005. The
function also corresponds to an uncontrolled stop in accordance with category 0 of
EN 60204-1 and Prevention of unexpected start-up of EN 1037.
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 power feed to the connected motor (see the
diagram below). By using 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.
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 system from
the main supply.
Note: The Safe torque off function can be used for stopping the drive in emergency
stop situations. In the normal operating mode, use the Stop command instead. If a
running drive is stopped by using the function, the drive will trip and stop by coasting.
If this is not acceptable, eg, causes danger, the drive and machinery must be
stopped using the appropriate stopping mode before using this function.
Note concerning permanent magnet motor drives in case of a multiple IGBT
power semiconductor failure: In spite of the activation of the Safe torque off
function (option +Q968) or the Prevention of unexpected start-up (option +Q950)
function, the drive system can produce an alignment torque which maximally rotates
the motor shaft by 180/p degrees. p denotes the pole pair number.
For more information on the Safe torque off function, see Safety options for ACS800
cabinet-installed drives (+Q950, +Q951, +Q952, +Q963, +Q964, +Q967 and +Q968)
Wiring, start-up and operation instructions (3AUA0000026238 [English]).
Planning the electrical installation