Protecting Tomago’s rectifiers
ABB took on a critical project to improve the safety and reliability of the high-power rectifier local control panels operating at the aluminium smelter in NSW.
The business of smelting aluminium requires nerves of steel – pardon the mixed-metal metaphor. Constant supply of high-voltage power to the all-important Potline operation is essential, and the rectifiers that draw that energy from the grid are mission critical-assets for the aluminium industry.
“In the Potline, the aluminium oxide is liquefied and cast into ingots, which requires high-current power,” explains Ivar Smits, Sales Manager for High Power Rectifiers at ABB Australia. The aluminium pots operate at low voltage and high current, with multiple pots connected in a series, with high current flowing through each pot and a small voltage drop across each pot. Precise and continuous power supply is critical. “Disruption of power to the Potline is the biggest risk,” says Smits. “It takes only a couple of hours without power for the Aluminium to solidify in the Potline. These Potlines can stretch up to 1000m long and if they solidify, it’s a crisis that in the worst event can require the demolition and rebuilding of the entire Potline.”
That makes it crystal clear why “maintaining availability of this high-current power to the Potline is critical”.
Rectifiers convert power from the grid and supply it into the smelter infrastructure and Tomago Aluminium Company Pty Limited contracted ABB to upgrade the local control panel (LCP) system for two of them, which had originally been installed by a competitor.
“The existing control system was at an obsolete stage,” explains Paul Emblow, ABB’s bids and proposals manager for High Power Rectifiers, who was sales manager when ABB won the project. “They couldn’t get any parts for repairs and it was clear they needed to replace the LCP to ensure reliability of the system so it wouldn’t fail.”
There are 15 rectifiers at Tomago Aluminium, five for each of the three potlines. Tomago Aluminium is Australasia’s largest aluminium smelter and has been operating 24 hours a day since 1983. The company contributes $1.5 billion annually to the Australian economy and the smelter produces 590,000 tonnes of aluminium every year, which is 25% of Australia’s primary aluminium.
As well as being unable to find replacement parts for the old system, there was no local service team available for it. “ABB has a team of field service technicians available locally, whereas the previous system required a crew from overseas, and that became another big aspect of the project, that we could provide local support,” says Emblow.
For obvious reasons, this is very specialised technology. “Every rectifier is built exactly for the process that it’s controlling,” explains Smits. “They’re specifically designed to work with the characteristics of that potline. The LCPs were also bespoke for the rectifier.”
The Tomago upgrade used ABB’s high-speed electronics controller (ABB AC 800 PEC controller) and the pre-magnetisation unit (DCS800 Premag) and Fibre Optic Current Sensor DC current measurement system, all key components for rectifiers in aluminium smelting.
“The high-speed PEC controller is a piece of technology that’s ABB intellectual property,” says Smits. “It’s a high-speed controller specifically designed for use in high-speed power electronic applications. ABB uses it across a portfolio of applications, and it’s usually modified by business units to work with specific assets. For example, a locomotive, a charging station or a grinding mill. In this case, we integrated the ABB PEC and the DCS800 Premag to replace the existing control system, to maintain closed-loop current control of the rectifier. This control upgrade offers superior control stability over the existing system.”
The first upgrade for Tomago was installed before the pandemic, so ABB were able to fly in support staff from Switzerland for the commissioning. “ABB’s Centre of Excellence in high power rectifiers is in Switzerland,” explains Emblow.
ABB Australia is an accredited local execution centre, “which means we are licensed to deliver projects in country,” says Smits. “The Centre of Excellence supports us from Switzerland, so it’s a teamwork effort and our engineering team works closely with theirs.”
The Tomago Aluminium upgrade saw the introduction of the latest technology from Switzerland, and the Australian service engineers were fully trained up on it, before the pandemic hit. “We invested in that training so we can support the rectifiers in the future, and it was also invaluable for the commissioning of the second LCP,” says Emblow. COVID arrived before the commissioning of the second LCP, which meant the Switzerland-based team provided remote support, if required, via video during its commissioning.
Both rectifier LCPs were replaced without stoppage to the potline operation, another key requirement from the 24/7 smelter.
In upgrading the LCP panels, Tomago also took the opportunity to further improve safety on the site, which is paramount for the company. The control panels were relocated further from the rectifier, housed in purpose-built fiberglass rooms. “The LCPs are operated remotely from a central control room, but if they have to be accessed for maintenance, it’s a walk-in room and it’s now further away from the rectifier, which is safer” says Emblow. The fiberglass solution also overcame issues with rust, which is an issue on the site which is inland from Newcastle, NSW, and subject to salt air.
The engineering for the upgrade project was a combination of the ingenuity of both the Swiss and Australian teams. “The DCS800 Premag and the fuse monitoring systems were designed out of Switzerland, then all the design and assembly of everything else for the LCPs was done here in Australia,” says Emblow. “The installation period was five days, and the shutdown was 48 hours, during which time the potlines ran off the other rectifiers.”
At the end of the project, it was thumbs up from Tomago. “Tomago Aluminium are extremely happy with the upgrade to protection and control systems provided by ABB HPR on our G11 and G31 rectifier groups,” says Tony Camps, sourcing advisor for capital and major maintenance at Tomago. “The contract was delivered on schedule, within cost constraints and to the required high quality. Special thanks to Greg Calthorpe, Christo Malherbe, Tomas Figueroa and Paul Emblow for their efforts, and willingness to work closely with us to deliver this work.”
Visit ABB’s website to learn more about the high power rectifiers and its applications.
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