In circumstances where external influences (with vertical loads for example) are present, additional
measures (mechanical brakes for example) might be necessary to prevent any hazards.
Procedures to check the safety function periodically according to the result of risk assessment and
prescriptions in §6.2 must be set-up.
STO integrated safety function is single fault safe system (within the drive unit). No single fault or
component failure can cause a loss of safety state, inducing drive to produce motor torque.
Wiring and connections of the system must appropriately implemented and tested in order to
support same fault tolerance (1) at system level.
In the event of the failure of two output IGBTs in the drive, when Safe Torque Off has been
activated, the drive may provide energy for up to 180° of rotation in a 2-pole motor before torque
production in the motor ceases.
In case of induction motor, no movement is possible even when several faults occur (in the IGBT
power stage). That is, no failure on IGBT drivers, in absence of controlled pulses coming from
regulation, can generate current able to establish rotating field.
It must be checked if this condition can cause a dangerous machine movement.
When the safety function is activated (motor unable to produce torque), the DC-link (high voltage
dc bus) of the drive is still connected to mains supply.
In this case drive control is deactivated and after motor coasting to standstill or already stopped,
high voltage are present on motor and drive terminals.
For authorised personnel to work on live parts, drive shall be electrical isolated from mains supply
(mains switch) and appropriate time shall be elapsed (more than 5minutes) to allow high-voltage
DC-link to discharge.
This is called "Mains supply disconnection (isolating )and switch-off ", isolation from power supply
system, requested by EN 60204-1.
The mains supply switch-off function may performed only with the use of appropriate isolating