Safe torque off function 225
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 output 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 resetting 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 from the main supply.
WARNING! (With permanent magnet motors 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 degrees (with permanent magnet motors) or 180/2p degrees (with synchronous
reluctance [SynRM] motors) regardless of the activation of the Safe torque off function. p
denotes the number of pole pairs.
Notes:
• 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 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.
Maintenance
After the operation of the circuit is validated at start-up, the STO function shall be
maintained by periodic proof testing. In high demand mode of operation, the maximum
proof test interval is 20 years. In low demand mode of operation, the maximum proof test
interval is 5 or 2 years, see section Safety data (SIL, PL) (page 226). It is assumed that all
dangerous failures of the STO circuit are detected by the proof test. To perform the proof
test, do the Acceptance test procedure (page 223).
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