Mechanical Technology July 2015

⎪ Power transmission, bearings, bushes and seals ⎪

Left: Two of Europe’s largest synchronous motors ever used in a reversing roughing mill have been commissioned by ABB at Tata Steel’s Port Talbot hot strip mill in South Wales. Right: The upgrade aims to increase steel production significantly while improving final product quality.

Europe’s largest motors and drives power steel roughing mill ABB has commissioned two of Europe’s largest synchronous motors and medium voltage drives at the roughing mill at Tata Steel’s hot strip mill in Port Talbot, South Wales.

was a potentially catastrophic situation with the overloaded dc motors into an unprecedented success, breaking a series of ‘all time’ production records.” For reversing roughing mills, reliability is paramount. ABB’s extensive experi- ence of mill applications together with proven design technology and manufac- turing know-how combined with thor- ough quality control and comprehensive testing throughout the production cycle, combined to make Tata Steel’s decision to use the company easier. Tata Steel meticulously structured the shutdown of the existing facility; a process of design, planning and risk management that began back in 2011. This risk mitigation strategy lead to some 90% of the installation being completed, commissioned and tested before the plant shutdown. Over a four-week period, starting in August 2014, the plant completely closed for what was to be the most intense upgrade in 25 years. The old motors and spindles were removed and the foundation for the new equipment prepared. The pre-assembled new mo- tors were then lifted into position at the same time that the new spindle system was being installed. The two motors were connected with the spindle system and all the pre-installed and commissioned services and control equipment was connected ready to run the new motors. “It’s fantastic to see the installation progress to schedule and really justifies the approach we took on this project with 90% of equipment pre-installed before shut down,” says Winkley. “We are really happy with ABB, in terms of the equipment and the compa- ny; both performed absolutely brilliantly,” he concludes. q

T wo of Europe’s largest synchro- nous motors, along with the highest power-rated medium voltage (MV) drives ever used in a reversing roughing mill, have been commissioned by ABB at Tata Steel’s Port Talbot hot strip mill in South Wales. The replacement motors and drives were the focus of a major £25-million reversing roughing upgrade – a key part of the rolling process which transforms a 23 cm thick slab of red-hot steel into sheet, less than 3.5 cm thick, before further reducing it to produce hot rolled strip. The upgrade aims to significantly increase steel production while improving final product quality. The reversing rougher is a heavy torque application and as such demands two ABB 12.5 MW salient pole synchro- nous motors, together with two ABB MV drives rated at 36 MVA at 3.1 kV, to power the slab between a set of rolls. Previously, two 6.0 MW direct current (dc) motors, installed in 1985, were operated some 30% over their intended capacity. The overload regularly stressed the windings, making the motors difficult to maintain and subject to potential catastrophic failure. Although operating in overload the roughing mill was still the bottleneck process for 50% of the time, putting a hard limit on plant output. The new synchronous motors give

the response demanded while the ACS6000 MV drives with their motor control platform that uses direct torque control (DTC), provide unrivalled speed and torque control. As the slab enters the reversing rougher there is no perceived speed drop, as happened with the dc mo- tors. The new motors and drives control the slab precisely, with no over shoot in speed. This results in the slab being pro- cessed much faster and reduces unneces- sary torque reversals in the mechanical drive train. The slow control of the dc motors caused severe torque swings in the drive train, resulting in fatigue cycling to the mechanical equipment. This no longer occurs, resulting in a much quieter and safer operating environment, with improved production capacity together with increased reliability. “With the old system, the average cycle time was 95 seconds. Today, it is 80 seconds,” says Steve Winkley, Tata Steel’s project manager for the roughing mill project. “When we change direction of the bar, it’s much faster than ever before. When we take advantage of the motors maximum top speed, this will result in an average production speed increase of 30 t per hour – that is a staggering 200 000 t per year. This sig- nificant increase in production is almost a side effect of having to replace the dc machine. We successfully turned what

Mechanical Technology — July 2015

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