Invertek Drives elevator CORE Quick Start-Up Manual page 49

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19. Safe Torque Off
19.1. Safe Torque Off
Safe Torque OFF will be referred to as "STO" through the remainder of this section.
19.1.1. Responsibilities
The overall system designer is responsible for defining the requirements of the overall "Safety Control System" within which the drive will be
incorporated; furthermore, the system designer is responsible for ensuring that the complete system is risk assessed and that the "Safety
control System" requirements have been entirely met and that the function is fully verified, this must include confirmation testing of the "STO"
function before drive commissioning.
The system designer shall determine the possible risks and hazards within the system by carrying out a thorough risk and hazard analysis, the
outcome of the analysis should provide an estimate of the possible hazards, furthermore, determine the risk levels and identify any needs for
risk reduction. The "STO" function should be evaluated to ensure it can sufficiently meet the risk level required.
19.1.2. What STO Provides
The purpose of the "STO "function is to provide a method of preventing the drive from creating torque in the motor in the absence of the
"STO" input signals (STO1 & STO2), this allows the drive to be incorporated into a complete safety control system where "STO" requirements
1
need to be fulfilled.
The "STO" function can typically eliminate the need for electro-mechanical contactors with cross-checking auxiliary contacts as per normally
required to provide safety functions.
The drive has the "STO "Function built-in as standard and complies with the definition of "Safe torque off"as defined by IEC 61800-5-2:2007.
The "STO "Function also corresponds to an uncontrolled stop in accordance with category 0 (Emergency Off), of IEC 60204-1. This means that
the motor will coast to a stop when the "STO" function is activated, this method of stopping should be confirmed as being acceptable to the
system the motor is driving.
The "STO" function is recognised as a fail-safe method even in the case where the "STO" signal is absent and a single fault within the drive has
occurred, the drive has been proven in respect of this by meeting the following safety standards :
Safe Torque Off (STO)
Note : The values achieved above maybe jeopardised if the drive is installed outside of the Environmental limits detailed in section 4.2 and
7.2.
19.1.3. What STO does not provide
Disconnect and ISOLATE the drive before attempting any work on it. The "STO"function does not prevent high voltages from being
present at the drive power terminals.
1 Note: The "STO"function does not prevent the drive from an unexpected re-start. As soon as the "STO" inputs receive the
relevant signal it is possible (subject to parameter settings) to restart automatically, Based on this, the function should not be used
for carrying out short-term non-electrical machinery operations (such as cleaning or maintenance work).
2
Note: In some applications additional measures may be required to fulfil the systems safety function needs: the "STO" function
does not provide motor braking. In the case where motor braking is required a time delay safety relay and/or a mechanical brake
arrangement or similar method should be adopted, consideration should be made over the required safety function when braking
as the drive braking circuit alone cannot be relied upon as a fail-safe method.
When using Gearless (Permanent Magnet) motors and in the unlikely event of a multiple output power devices failing then the
motor could effectively rotate the motor shaft by 180/p degrees (Where p denotes number of motor pole pairs).
2
IEC 61800-5-2:2016
EN ISO 13849-1:2015
EN 61508 (Part 1 to 7): 2010
EN 60204-1: 2006 & A1: 2009
EN 62061: 2005 & A2: 2015
Independent Approval
www.InvertekDrives.com
SIL 3
PL "e"
SIL 3
Cat 0
SIL CL 3
Pending