ABB ACS880-04F, Hardware Manual, Page: 161 / 172

Safe torque off function 161
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 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.
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 (page 162 ). 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 159 ).
Note: See also the Recommendation of Use CNB/M/11.050 published by the European
co-ordination of Notified Bodies concerning dual-channel safety-related systems with
electromechanical outputs:
•
When the safety integrity requirement for the safety function is SIL 3 or PL e (cat. 3 or
4), the proof test for the function must be performed at least every month.
•
When the safety integrity requirement for the safety function is SIL 2 (HFT = 1) or PL d
(cat. 3), the proof test for the function must be performed at least every 12 months.
The STO function of the drive does not contain any electromechanical components.
In addition to proof testing, it is a good practice to check the operation of the function when
other maintenance procedures are carried out on the machinery.
Include the Safe torque off operation test described above in the routine maintenance
program of the machinery that the drive runs.
If any wiring or component change is needed after start-up, or the parameters are
restored, follow the test given in section
Acceptance test procedure on page 159 .
Use only ABB approved spare parts.
Record all maintenance and proof test activities in the machine logbook.