Digital drives take control of critical tasks

Digital drives control all the critical operations at the head of the line on the latest continuous slab caster at the Corus steelworks in Port Talbot, South Wales.

Drives from Control Techniques again feature on the latest continuous slab caster at the Corus steelworks in Port Talbot, South Wales, controlling all of the critical operations at the head of the line.

This means that the total output of the plant, expected to be 4.7 million tonnes in 2006, is dependent on drives from Control Techniques.

The new Continuous Caster 3 (CC3) was installed to supply additional production capacity in line with the new blast furnace No5 that was installed last year.

As CC3 was a completely new operation, aimed to increase the output of the plant by 25%, the project team had the flexibility to choose either the AC or DC route.

The previous major contracts for Control Techniques had been upgrades, re-using existing DC drives, so the drive of choice was the digital DC drive, Mentor II.

Now, looking to the potential benefits of reduced motor maintenance from a switch to AC, and the reduced downtime that this implies, the project team grasped the opportunity for increased efficiency.

Again stating a preference for Control Techniques on the CC3 project, Corus elected for the advanced Unidrive SP AC drive for the key drives on the twin strand caster - the turret drives and the twin tundish car lateral movements, as well as tundish raise and lower control, the withdrawal drives and roller tables - a total of around 60 drives in all.

"This is the first vertical mould caster for Corus", says Corus Concast Engineer, Roger Morgan, "and our first real experience with Control Techniques' Unidrive SP AC drives".

"We've found them to be very reliable, easy to use and easy to configure".

"The whole approach to this project has been a move forward in technology, with no analogue to digital interfaces - it's all digital - with greatly reduced wiring; in most instances just two wires instead of hundreds".

A proposition was based on the latest AC drive and motor technology from Emerson Industrial Automation companies Control Techniques and Leroy Somer.

All the motors ensured totally enclosed protection for improved reliability and less downtime.

The scope incorporated two new AC drive motor control centres (Form 4 MCCs), employing some 60 off AC Unidrive SP variable speed drives and Leroy Somer AC motors, controlling the caster strand withdrawal sections, the auxiliary caster machines and equipment including the run-out tables.

The drives provided a much improved load sharing, a more consistent casting speed, shorter rethread times, and a big boost in reliability.

All these features (essential for reliability and superior speed control), were a prerequisite for greater productivity and finished steel quality.

Corus' markets include the very demanding tinplate and automotive markets, producing steel with a high surface finish and clean internally.

The project successfully integrated new plant over one year phase, and concluded in the successful commissioning, in 2005, of new strand drives, as well as PLC and Scada hardware and software for the control monitoring of both the casting plant and water treatment plant.

The new line is key to Corus' target of 4.7 million tonnes output in 2006.

Many of the key new benefits have arisen by implanting digital control and high-speed data fieldbus communications, as well as a high level of redundancy built into the system design configuration, as a means of future-proofing the plant for many years of high reliability, accurate control and low-maintenance.

The implications of a total system failure on a continuous caster are extremely serious, so that back-up redundancy in all areas was a key part of the design.

In conjunction with Corus, a dual redundant control and communications system was implemented.

The plant interface is direct to two PLCs, one operating in full time production, the other acting as hot standby.

Furthermore, two communications links are provided between the PLCs and the Control Techniques drive system, and a failure to communicate via one of the routes automatically initiates a communications link via the second route.

Key to the successful operation of the plant was the PID-based load sharing system, preprogrammed into each of the Unidrive SP drives, using the onboard facility of the plug-in application modules.

The success of this software, with its benefits of reduced wear and tear and more consistent casting speed, is very evident in the motor current trends.

Rethread times are also much faster, with any limitations being factors other than the drives/electrics on the strands, the end result being a much more stable drive control system, which is reflected in improved product quality.

New AC motors were also supplied by Control Techniques, each fitted with digital encoders and brakes on the vertical part of the caster.

The drive control included on board intelligence/specific application software, part of which included closed loop to open loop changeover in the event of a feedback device failure, thus ensuring the caster continues to run.

The drives suites were manufactured and tested at Control Techniques UK Drive Centre in Telford, and additional in-house trials were conducted using Corus' system PLCs and the new motors to replicate plant operation and fault modes.

These verification trials proved invaluable, as the time spent in in-depth testing at Telford significantly reduced the on-site commissioning period.

"The whole system is now more modular", explains Corus Port Talbot's Concast Engineer Roger Morgan.

"The intelligence in the system is now distributed rather than central, and this means that just one Unidrive SP Inverter is designated as the master and communicates with the plant PLC".

"This master then communicates in turn via CT-Net with all the other strand drives, keeping them digitally synchronised".

"For reasons of dual redundancy, automatic seamless master transfer passes master control to the next drive in line, in the event of failure".

"This means that, if necessary, the line could be run manually".

"It's now much more flexible and reflects many of the lessons we have learnt over many years of steel-making".

"The evidence of its success is reflected in the 30% increase in strand speed and the reduced turn-around times".

"We are very pleased with the results of this major project", comments Morgan.

"In many ways the approach has been simplified thanks to new technology of course, and we anticipate much greater plant utilisation because of the inherent reliability of modern electronics".

"The after sales support we receive from Control Techniques has been excellent and indeed our long standing experience of good support over several major schemes was a factor in Control Techniques being chosen for this project".

The principal contractor responsible for the overall project was VAI UK (Stockton office), with Control Techniques acting subcontract to VAI, undertaking the electrical project management and control system design and engineering.

Control Techniques has successfully automated many continuous casters throughout the years and has developed an excellent strength in application knowledge and understanding of the metals industry.

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