Hardware Manual

Table Of Contents
Safe Torque off function 237
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 inverter IGBTs.
3. The control program generates an indication as defined by parameter 31.22 (refer
to the firmware manual of the drive).
4. Motor coasts to 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 reseting 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 system from the main supply.
WARNING! (With permanent magnet or synchronous reluctance [SynRM]
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 (with permanent magnet motors) or 180/2p (with synchronous reluctance
[SynRM] motors) 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.
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.