Safe Torque Off; General Description; Warnings - Vacon 20 X Installation, Technical And Maintenance Manual

Safe Torque Off

9. S T
AFE ORQUE
This chapter describes the Safe Torque Off (STO) function which is a functional safety feature pres-
®
ent into VACON 20 X drive products as standard.
9.1

General description

The STO function brings the motor in no-torque-state as defined by 4.2.2.2 of the IEC 61800-5-2:
"Power that can cause rotation (or motion in the case of a linear motor) is not applied to the
motor. The Power Drive System (Safety Related) will not provide energy to the motor which can
generate torque (or force in the case of a linear motor)."
Therefore, the STO function is suitable for applications that rely on the immediate removal of power
to the actuator, resulting in an uncontrolled coast to stop (activated by an STO demand). Additional
protective measures need to be applied when an application requires a different stop method.
9.2

Warnings

Designing of safety-related systems requires specialist knowledge and skills. Only
qualified people are permitted to install and set up the STO function. The use of STO
does not itself ensure safety. An overall risk evaluation is required for ensuring that
the commissioned system is safe. Safety devices must be correctly incorporated into
the entire system which must be designed in compliance with all relevant standards
within the field of industry.
The information in this manual provides guidance on the use of the STO function. This
information is in compliance with accepted practice and regulations at the time of
writing. However, the end product/system designer is responsible for ensuring that
the end-system is safe and in compliance with relevant regulations.
When a permanent magnet motor is used and in case of a multiple IGBT power semi-
conductor failure, when the STO option energizes the drive outputs to the off state,
the drive system may still provide an alignment torque which maximally rotates the
motor shaft by 180°/p (where p is the number of poles of the motor) before the torque
production ceases.
Electronic means and contactors are not adequate for protection against electric
shock. The Safe Torque Off function does not disconnect the voltage or the mains
from the drive. Therefore hazardous voltages may still be present on the motor. If
electrical or maintenance work has to be carried out on electrical parts of the drive
or the motor, the drive has to be completely isolated from the main supply, e.g. using
an external supply disconnecting switch (see EN60204-1 section 5.3).
This safety function corresponds to an uncontrolled stop in accordance with stop cat-
egory 0 of IEC 60204-1. The STO function does not comply with Emergency Switching
Off according to IEC 60204-1 (no galvanic insulation from the Mains in case the motor
is stopped).
The STO function is not a prevention of unexpected start-up. To fulfil those require-
ments, additional external components are required according to appropriate stan-
dards and application requirements.
In circumstances where external influences (e.g. falling of suspended loads) are
present additional measures (e.g. mechanical brakes) may be necessary to prevent
any hazard.
STO shall not be used as a control for starting or stopping the drive.
Service support: find your nearest Vacon service center at www.vacon.com
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