Program Features, Settings And Diagnostics; Operation Of The Sto Function And Its Diagnostics Function - ABB ACS355 User Manual

400 Appendix: Safe torque off (STO)
Control
circuit
WARNING! The STO 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.
Note: It is not recommended to stop the drive using the STO. If a running drive is
stopped with this function, the drive will trip and stop by coasting. If this is not
acceptable eg, it causes danger, the drive and machinery must be stopped using the
appropriate stopping mode before using this function.
Note: Permanent magnet motor drives in case of a multiple IGBT power
semiconductor failure: In spite of the activation of the STO function, the drive system
can produce an alignment torque which maximally rotates the motor shaft by 180/p
degrees, where p denotes the pole pair number.

Program features, settings and diagnostics

Operation of the STO function and its diagnostics function

When both STO inputs are energized, the STO function is in the standby state and
the drive operates normally. If either of the STO inputs is de-energized, the STO
function awakes, stops the drive and disables start. Start is possible only after the
X1C:1 OUT1
+24 V
X1C:2 OUT2
Output stage
(1 phase
shown)
ACS355
X1C:3 IN1
X1C:4 IN2
UDC+
U2/V2/W2
Notes:
• The contacts of the safety circuit
UDC-
must open/close within 200 ms of
each other.
• The maximum cable length
between the drive and the safety
switch is 25 m (82 ft).
Safety circuit
(switch,
relays, etc.)