A860-0309 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 drive IGBTs. 3. The control program generates an indication as defined by parameter 31.22 STO indication run/stop. 4. The motor coasts to a 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 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 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 unit. • 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. Safe torque off function 129 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 2 years. The test procedure is given in section Acceptance test procedure (page 127). 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 (page 127). Use only ABB approved spare parts. Fault tracing The indications given during the normal operation of the Safe torque off function are selected by parameter 31.22 STO indication run/stop. The diagnostics of the Safe torque off function cross-compare the status of the two STO channels. In case the channels are not in the same state, a fault reaction function is performed and the drive trips on an “STO hardware failure” fault. An attempt to use the STO in a non-redundant manner, for example activating only one channel, will trigger the same reaction. See the drive firmware manual for the indications generated by the drive, and for details on directing fault and warning indications to an output on the control unit for external diagnostics. Any failures of the Safe torque off function must be reported to ABB |
