LATEST DRIVE TECHNOLOGIES BRING KEY ADVANCES TO DIGITAL PLANT ARCHITECTURE

Phil Black - PII Editor 20/06/2011

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By using intelligent variable speed drives (VSD) in the plant network, process control engineers can employ a complete digital control strategy enabling functionality such as real-time control, predictive diagnostics, fast drive commissioning and easy trouble-shooting – and save energy too!

Processes often utilise automation equipment containing fans and blowers, pumps, compressors, centrifuges, mixers, agitators, fluidised bed dryers, mills and conveyors powered by induction motors. In the early days, these applications were controlled by motor starters (start or stop), but as technology evolved, process control engineers began to use smart switches to provide a digital link to the control room. Now, however, things have moved on so that the digital control interface is within the drive itself, providing real-time information on drive performance and much more.

When it comes to setting up drives, the number of configuration options and parameters can be daunting to commissioning technicians. To help with set-up and to diagnose problems, many drives manufacturers now use Electronic Device Description Language (EDDL) to define how the drives are displayed in the system.

EDDL, an open standard, describes the information that is accessible in many digital devices used in the process industry and supports device diagnostics and calibration. It is a text file, not software, and is independent of the operating system, therefore is not only easy to set-up, but also easy to manage and maintain in the long term. This makes EDDL secure, robust and avoids device version conflicts, making integration easier.

Drives typically have multiple control systems from the DCS as well as discrete and analogue status feedback signals to process. Hardwiring all of these can be very expensive, increase the vulnerability to faults and make future changes complex. Compromises often result, meaning that drive capability is not fully utilised or managed to give optimum performance. Bus technology offers a better solution, using a standard bus connection for many drives, eliminating a huge amount of cabling – and significantly reducing project costs. Each bus cable can support all of the control and feedback signals for multiple drives, as well as providing access to remote configuration and diagnostics – and these latter functions can be carried out without going near the electrical panel.

Many process plants use different bus technologies for different applications – for example, Foundation fieldbus for process systems and alarms, hard-wired Hart for instruments on safety systems, WirelessHart for indication and Profibus-DP for motor controls. This is a further complication for process plant managers, with technicians having to master different programs and requiring additional training – and costs.

The EDDL standard (IEC 61804-3) provides a solution to these problems, being the only device integration technology that spans all of these different standards, enabling devices using these various protocols to be managed from the same intelligent device management software throughout their life-cycle. So, for example, variable-speed drives can now be commissioned, configured and diagnosed from the same intelligent device management software as the plant’s field instrumentation – software that also provides around-the-clock device alert monitoring.

Drives manufacturers have started to use EDDL to define how their drives are displayed by the control system. Drives digitally integrate with the DCS and the intelligent device management software, making use of their visualisation software, alarm and event logging, audit trail and history log. A separate system is not required – all device alerts can be seen in one place. When a drive fault is detected, the drive can be interrogated from the device management software.

Energy Savings
In the process industry, as with thousands of other environments, variable speed drives can save a significant amount of energy, which translates into a cleaner environment and reduced operating costs. Running induction motors at the optimum speed for the fan or pump application, is a major cost saver. At 80% of full speed, electricity consumption is cut to 50% and at 50% speed, only 12.5% is used! So by varying the speed to match plant need, second by second, huge savings can be made over the whole manufacturing process.
This is equally true in the heating and ventilating system and in refrigeration plant, where close control using variable speed drives invariably gives fast returns on investment.

Control Techniques Ltd
Newtown
Powys
Can be contacted on:

Tel: 01686 612000
Fax: 01686 612999
E-mail: controltechniques@emerson.com
Web: www.controltechniques.com