Operation Principle - ABB ACS800 Series Application Manual

12 Option description
The STO function corresponds to Prevention of unexpected start-up as specified by
EN ISO 14118:2018 (ISO 14118:2017), and Uncontrolled stop (stop category 0) as
specified in EN/IEC 60204-1.

Operation principle

1. The user opens the Safe torque off circuit with an STO activation switch (or it is
opened by a device such as safety relay).
2. The STO inputs on the drive/inverter de-energize.
3. The STO cuts off the control voltage from the inverter IGBTs.
4. The control program generates an indication as defined in the table below.
5. Motor coasts to a stop (if running). The drive/inverter cannot restart while the
activation switch or safety relay contacts are open. After the contacts close, a new
start command may be required to start the drive (depends on parameter settings).
Example diagram of STO in R8i module
with safety relay
INVERTER MODULE R8i