190 Appendix: Safe Torque Off (STO)
Special considerations for using the STO function
Drive location
The MicroFlex e190 and all associated STO wiring must be installed in an indoor
location. The MicroFlex e190 must be installed in a cabinet. The suitability of the
cabinet for the intended environment must be determined by the installer. See
Ambient conditions on page 157 for further details.
Hazard analysis
A hazard analysis of the application should be performed before using the STO
function in the application.
Additional stopping methods
It is not recommended to stop the drive by using the STO function. If a running drive
is stopped by using the function, the drive trips and stops by coasting. If this is not
acceptable e.g. causes danger, the drive and machinery must be stopped using the
appropriate stopping mode before using this function. For example, suspended or
tensioned loads (e.g. cranes, hoists) will require additional brakes or mechanical
interlocks.
IGBT failure
If a permanent magnet motor drive experiences multiple power semiconductor failure,
the drive system can produce an alignment torque which maximally rotates the motor
shaft by 180/p degrees (p = pole pair number), even if the STO function has been
correctly activated.
Failure of one or more IGBTs can cause the drive output to fail due to:
• IGBT desaturation protection causing all IGBTs to be stopped.
• Rupture of the AC input fuse.
Terminology
‘Active’ or ‘activated’ means that the STO function has been triggered. This removes
power from the motor and disables the drive. The drive cannot be restarted without
further operator intervention.
‘Standby’ means that the STO function has not been triggered. The drive can power
the motor, provided all other criteria are satisfied to allow motor operation.
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