Breaker Boosts Steel-Making Capabilities
EP Editorial Staff | April 25, 2019
Innovative switching technology for electric-arc furnaces is increasing output while improving safety, efficiency, and reliability.
Steel is one of the world’s most innovative and essential materials. As demand has grown, so has the need for innovative techniques and technologies to boost output and increase safety, efficiency, and reliability within the steel industry.
According to data from the World Steel Association, Brussels (worldsteel.org), NUCOR Steel, Charlotte, NC (nucor.com), produces more than 27 million tons of steel each year. The corporation has become North America’s largest recycler and the world’s most sustainable steelmaker, offering a full range of steel and steel products.
Through customer-driven development, NUCOR and ABB, Cary, NC (abb.com), have modernized power distribution for the steel industry, enabling NUCOR to improve efficiency and reliability, and, in turn, increase production output.
Steel is produced through two primary methods: the blast-furnace-basic-oxygen-furnace method and the electric-arc-furnace (EAF) method. Historically, the steel industry has used the blast-furnace method with coal-fired plants to process iron ore. This method is costly, inefficient, and generates significant pollution. As more producers have turned to recycled-steel metals, arc-furnace technology has become more prevalent, with the promise of lower costs, longer operations and uptime, and less pollution. EAFs are unique in that they can be charged with 100% steel scrap.
EAFs use electricity to melt scrap and turn the pieces over to a ladle metallurgy furnace (LMF) to reheat and form the metal. This further refines the chemistry and temperature of the molten steel while it is still in the ladle, before it’s sent to be cast.
Today, in the U. S., 25% of steel is produced using the blast-furnace method and 75% using EAFs. Globally, that ratio is reversed. NUCOR only has a handful of blast furnaces remaining in the U. S.; most have been converted to EAF.
While EAF methods have demonstrated efficiency, the steel industry has continued to search for innovative means to improve processes. Producers such as NUCOR are, thus, embracing the Industry 4.0 push to digitize manufacturing and increase uptime, decrease cost, and streamline procedures.
The technology used to operate an arc furnace wasn’t originally designed for this application. It was, instead, derived from medium-voltage components such as transformers and switches designed for the utility market. In those types of applications, an electrical arc would be something to avoid. For the furnace application, the intent is to generate a specialized, controllable arc that, essentially, creates a short circuit. Accordingly, a circuit breaker is needed to switch the EAF.
Because arc-furnace operations use equipment in a way not intended in the design, limitations are quickly revealed, especially in demanding production environments. Most EAFs use mechanical-spring-charged circuit breakers as the primary switching means. Such breakers are usually in series with an upstream SF6 breaker for fault clearing.
Spring-actuated technology has mechanical limitations that make it unsuitable for highly demanding, continuous EAF operation. The main reason these medium-voltage vacuum circuit breakers are employed on an EAF is their ability to meet the high-voltage, current, and fault-breaking requirements in a single compact semi-cost-effective device. Only with the advent of vacuum technology did a suitable device for arc furnaces emerge. Unfortunately, it couldn’t last very long in extreme high-switching or fault-breaking situations. The stresses of hellacious environments marked by high contamination, high heat, and high operations were simply too much for those devices.
To solve this problem, ABB developed the VD4-AF breaker, a specialized EAF device that delivers 150,000 maintenance-free operations and easily clears furnace-fault currents as high as 31.5 kA. The customized breaker provides transformer-inductive-load switching and is quickly replaced through a floor-rolling design. It also provides health-status monitoring, allowing NUCOR personnel to predict when maintenance is needed.
“We hoped to revolutionize our operations, boost output, and lead the steel market into Industry 4.0 digitalization initiatives. With their high degree of knowledge on the latest technology, including those for digital solutions, we knew we had a partner in ABB to help us drive standardization and increase asset utilization levels across our facilities,” said Bill Brewer of NUCOR Steel.
ABB built the desired solution from other innovations it had introduced. It collected lessons learned from its medium- and high-voltage motor drives, and utility projects involving the DS1 design and combined them with the best solutions from its robotics and motor divisions. By combining servomotor technology and robotically controlled feedback, the VD4-AF breaker is able to reduce mechanical vibrations, ensure fast and precise operational response, and deliver consistent speed and timing checks with every operation.
NUCOR selected a facility for beta testing in Seattle, WA. That successful test was followed by implementation at a next site in San Zeno, Italy. After the satisfactory performance of those pilot installations, the company extended the EAF solution-implementation to include a retrofit of its plant in Indiana.
According to Brewer, the VD4-AF has exceeded NUCOR’s expectations for relentless arc-furnace operations. Supported by ABB with a dedicated team to ensure customer satisfaction and 24-hr. emergency response, the product, he noted, “has reduced downtime and provided worry-free EAF operations so that maintenance personnel can attend to other critical site activities.” Specifically, since installation of the new breakers, NUCOR has experienced a 50% reduction in total cost of ownership and reduced maintenance costs by as much as 50% on the furnaces. Moreover, circuitbreaker performance has been taken to a level that is 5 to 10 times higher than that of other solutions.
“ABB succeeded in guaranteeing continuous and reliable operation of our critical processes,” Brewer stated. “With such exceptional results, we are pursuing the VD4-AF with PowerBloc enclosure for all EAF and LMF applications in other facilities to further our drive toward steel Industry 4.0.” EP