48 Planning the electrical installation
Safe torque off (option +Q967)
The drive supports the Safe torque off (STO) function according to these standards:
• EN 61800-5-2:2007
• EN ISO 13849-1:2008
• IEC 61508
• IEC 61511:2004
• 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 can 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 drive from generating the voltage required
to rotate the motor (see diagram below). By using this function, short-time
operations (such as cleaning) 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.
The Safe torque off function can be used to stop the drive in emergency stop
situations. In the normal operating mode, use the Stop command instead. If the Safe
torque off function is activated when the drive is running, the control voltage of the
power semiconductors is cut off and the motor coasts to a stop. If this is not
acceptable, for example, if it 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, 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 installation of the Safe torque off function, see chapter
Installation of the ASTO board (Safe torque off, +Q967)
(page 81).
For more information on the Safe torque off function and the relevant safety data,
see
ACS800-01/04/11/31/104/104LC Safe torque off function (+Q967), Application
guide
(3AUA0000063373 [English]).
An example circuit diagram is shown below.
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