• • • SAFETY IN ENGINEERING • • •
When it comes to safety, communication is key
Variable speed drives (VSDs) employ a wide range of functional safety features, and now with new advances in drive technology, these features can be integrated with wider process control architecture through PROFIsafe, as Liam Blackshaw, UK product manager for LV drives at ABB, explains
n any industrial process it is vital that when something goes wrong a machine is brought quickly and safely to a safe state, which typically means a no torque (i.e. stop) state, in which it must remain until the safety risk is removed. Modern variable speed drives (VSDs) include many safety features. Some are relatively basic, such as safe torque off (STO), which carries out the job of a mechanical safety contactor, and brings a machine to a complete stop when activated. It not only reacts faster than a contactor, but also takes up less cabinet space. As time has gone by, and applications grow more complex, VSD-based functional safety is becoming a fundamental aspect of machine design, permitting a variety of types of stop or slowdown of the motor depending on the circumstances.
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The introduction of a new module, FSPS-21, for certain ABB drives, now allows these safety functions to be integrated and performed at a much lower cost by involving the PLC. By using PROFIsafe and PROFINET communication capabilities, this unlocks the ability to combine different types and sizes of drives with any safety PLC supporting these protocols, requiring fewer
components and less installation time, with no compromise on safety function.
This is ideal for situations where only a small amount of I/O is required, as the communication protocols can carry out many of the most essential safety functions required. The VSD’s safety functionality is thus governed by the PLC, which can activate STO and SS1 (Safe Stop 1) when called upon via an emergency stop, manual shutdown, or other parameters such as detected overspeed. For applications which already use a safety PLC, this saves duplication of efforts in programming safety functions, as the PROFIsafe and PROFINET communication capability within the drive means that functions can be programmed largely within the PLC. This means that drive-based safety functions can be activated by the PLC when required anywhere across the whole system, and not just when detected by an individual drive. The module complies with SIL 3 and PL e safety levels.
Using the module eliminates the hassle of hooking up and wiring the VSD logic with safety relays and contactors, as the safety functions are always predesigned within the module for ease
of commissioning. It also means that safety functions for several VSDs and machines can be governed from a single source (i.e. the safety PLC).
The module also allows for the grouping of VSDs according to the applicable safety zones in the application – for example overspeed of a drive on a conveyor line may require all associated VSDs to stop, which is achieved by activating the integrated STO.
Where safety in automation systems previously required many external add-on devices, a modern VSD and safety PLC can now carry out essential safety functions without the need for additional installation and programming. As systems grow more complex, this can help to ensure ease of maintenance, and simplify the provision of safety functions within a system.
An industrial environment can be a dangerous place. Integrated functional safety in VSDs is not a new concept, but by combining this functionality with a PLC system, it can help to better ensure that safety features are triggered precisely where and when they’re needed to prevent workplace injuries, without compromising on productivity and longevity of machines.
26 ELECTRICAL ENGINEERING • MARCH 2023
electricalengineeringmagazine.co.uk
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