Automation Technology Learn about an Innovative Approach to a New Motor Control Center

Author / Editor: Oliver Vogel / Dr. Jörg Kempf

Water treatment is not the environment in which one expects to find state of the art automation technology — And yet, sewage treatment plants could benefit greatly from the latest developments in drives and process control systems. All that is needed is an open mind for innovative thinking and new technologies, as a major English water distributor experienced.

Related Companies

Investigating the possibilities of new technology: Severn Trent Water, the bigest water company in the UK, have been assesing the feasibility of advanced, integrated motor control centers (MCCs) from Rockwell Automation with their design and build contractors, NMC Nomenca.
Investigating the possibilities of new technology: Severn Trent Water, the bigest water company in the UK, have been assesing the feasibility of advanced, integrated motor control centers (MCCs) from Rockwell Automation with their design and build contractors, NMC Nomenca.
(Picture: Rockwell Automation)

Severn Trent Water is the UK’s second-biggest water company, serving more than 3.7 million homes and businesses in England and Wales. The company delivers almost 2 billion litres of water every day through 46,000 km of pipes. A further 91,000 km of sewer pipes take wastewater to more than 1,000 sewage treatment works. The company has a positive attitude towards innovation: It has a formal advisory group, whose members come from both within and outside the company, to assess new approaches and technologies for the benefit of both company and customers.

It was this desire to explore new technology that led Severn Trent Water and one of its Tier 1 contractors, NMC Nomenca, to investigate the feasibility of advanced, integrated motor control centers (MCCs) from Rockwell Automation. The approach also included Form 2 construction: a proven, space-saving approach from other indus-tries.

Severn Trent Water gave engineers from NMC Nomenca the green light to investigate new technologies for a new inlet at Melton Mowbray sewage treatment works. The complete job involved replacing the current screenings, screens handling, and grit removal installation at the Lake Terrace terminal pumping station, which transfers raw sewage to Melton Mowbray.

Tight Space, New Thinking

The existing pumps at Lake Terrace will be retained, but the screening infrastructure will be relocated to Melton Mowbray. Given the space limitations and inherent hazards at Lake Terrace, the project gave the engineers the opportunity to consider new ideas for the site. Following an investigation by the ICA Community of Practice group and a competitive tender, MCC and associated technology from Rockwell Automation were chosen.

“We wanted to do something a little different with the MCCs,” explains Chris Webb, Contracts Engineer at NMC Nomenca and the company’s representative on the ICA COP group. “Severn Trent Water was looking for innovation in the new equipment and was also looking to save money (15 % compared to other solutions). I had a few ideas based around the MCC, especially relating to the use of Form 2 construction, which is not very common in the UK water industry even though it is in the current standards. As well as using Form 2 to reduce the overall size of the MCC, I also wanted to try out some different, contemporary technologies, such as those offered by Rockwell Automation.”

Innovation in Motor Control

The Form number defines the way the metalwork of the MCC is constructed: Form 4, a mature design based on older standards and less-reliable equipment, is currently the “normal” method in the water industry. Using Form 4, the motor starters would be isolated from each other and installed in separate compartments. A Form 2 MCC, however, requires just one compartment. Recent advances in equipment reliability make Form 2 not only possible, but also more desirable for installations with restricted space. Chris Webb presented his ideas for a Form 2 MCC to the Severn Trent Water ICA COP and in due course received approval to go ahead.

Other significant design features include Allen-Bradley 141a busbars and MCS isolation modules. These components allow the motor starters to be configured in a modular fashion, so that they can be installed side by side (starters normally clip on to a “top-hat” rail). The MCS modules, in contrast, are plastic bases that clip on to a busbar, providing a direct connection and eliminating the need for wires. This design is not only simpler but also allows for an unclipping of the starters while the busbar is live (hot swap).

Rockwell Automation's solution included and in intelligent Motor Control Center (MCC) in Form 2 construction with Allen-Bradley CompactLogix PAC.
Rockwell Automation's solution included and in intelligent Motor Control Center (MCC) in Form 2 construction with Allen-Bradley CompactLogix PAC.
(Bild: Rockwell Automation)
The complete installation comprises a range of Allen-Bradley products including a Compact Logix programmable automation controller, PanelView 15 touchscreen HMI, three-component starters (MCB/contactor/E3+ overload relay), the 141a busbar, MCS ISO (isolating) modules with control plugs, PowerFlex 70 variable-speed drives and an open Device Net network connected to the PAC via Ethernet/Device Net bridges. The fixed-speed drives will be connected via twin Device Net networks (to allow duty/standby separation), with connection to the PAC via Ethernet/DeviceNet bridge modules — negating the need to install scanner cards.

Lower Costs, Improved Operability

The new design could bring numerous benefits for Severn Trent Water, NMC believes: The MCC Form 2 setup has a smaller footprint than a Form 4 construction, reducing both cost and size of the MCC itself, the building housing it and the base slab. The total saving in capital cost is 23 % compared to standard Form 4 construction. The use of Ethernet communications via Ethernet/DeviceNet bridge modules saves costs in connecting to the PLC. “The use of Form 2, busbars, MCS and ISO was seriously considered following a visit from Peter Plows from Rockwell Automation,” Chris Webb explains. “I went to Rockwell Automation’s UK HQ for a presentation and I left with a head full of ideas. I decided that the next time I attended an ICA COP meeting, I would present the technology. As a result, the group bought into it and it all moved forwards.”

Chris Webb adds: “The Ethernet connectivity deployed within the MCC is very useful and flexible and is almost certainly the way forward regarding control networks. Why put in a closed network when such a powerful open network is out there?”

“Rockwell Automation’s products are probably the easiest to use on the market,” he concludes. And more: “They are extremely versatile and well supported. Personal interaction is also open, friendly approachable and supportive.”

* The author is Solution Architect Process & Information Software at Rockwell Automation.

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