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58 Planning the electrical installation
Safe torque off (option +Q967)
The drive supports the Safe torque off (STO) function according to standards:
•
EN 61800-5-2:2007
•
EN ISO 13849-1:2008
•
IEC 61508
•
IEC 61511:2004
•
EN 62061:2005
The function also corresponds to Prevention of unexpected start-up of EN 1037.
The STO may be used where power removal is required to prevent an unexpected
start-up. 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 (like cleaning) and/or maintenance work on non-electrical parts of the
machinery can be done 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 trips and coasts to a stop. If
this is not acceptable, for example, because 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
p
shaft by 180/
degrees.
For more information on the installation of the Safe torque off function, see
Installation of the ASTO board (Safe torque off, +Q967)
For more information on the Safe torque off function and the relevant safety data,
ACS800-01/04/11/31/104/104LC Safe torque off function (+Q967), Application
see
guide
(3AUA0000063373 [English]).
An example circuit diagram is shown below.
p
denotes the pole pair number.
(page 87).
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