Billions of litres of diesel are consumed annually by the global mining industry, which is under severe pressure from weak commodity prices. Up to 80% of this costly fuel consumption comes from haulage trucks moving uphill on ramps.
A Namibian uranium mine is overcoming this challenge with six 11 MW Siemens substations that provide electric power to the overhead DC (Direct Current) power lines, which in turn provide the DC (Direct Current) power to the adapted diesel-electric haulage trucks.
Siemens SA launched one of three completed units at its North Riding facilities today (2 September 2016). They will be used to power a fleet of Komatsu 960E trucks, which are among the industry’s biggest and highest capacity mine haulage vehicles, with a load capacity of 214 m3 or 327 tonnes.
Another breakthrough for this new order is that 90% of components in the containerised substations are entirely manufactured by Siemens, compared to past units that contained approximately 30% Siemens components. “Consistent innovation has kept us at the forefront of mining technology, and sourcing nearly all of our components internally means greater quality control, improved functionality, and greater capacity,” says Siemens SA project manager Phiwa Thindwa.
Each 11 MW containerised substation boasts 1.8 kV of DC voltage and up to 10 000 A (amps) to ensure that it can run two trucks continuously, three trucks for ten minutes or four trucks for one minute along the overhead power lines. This combination of substation and overhead line is known as trolley assist technology used in the mining industry.
A trolley assist solution is installed on any uphill stretch between the mineral ore loading (pit) and offloading points (dump or process plant), as the speed on the gradient is limited by the diesel engine’s horsepower, Thindwa explains.
With the inclusion of the electric drives, the electric power supplied to the wheel motors of the haulage trucks enables the vehicles to move faster uphill, which results in quicker turnaround times and higher productivity for the mining operation.
Engine operating and maintenance costs are directly linked to hours of operation of the haulage trucks and using trolley assist on gradients reduces the cycle time of the haulage trucks, thus increasing the intervals for maintenance.
It leads to longer intervals between engine overhauls, which are proportional to the hours that the haulage truck is in operation. The engine is maintained after every 2500 hours of operation. The end result is reduced downtime and improved productivity on an around-the-clock basis.
Pushing for more localisation
Siemens’ DC containerised substations are manufactured in Pretoria with components currently imported from Germany. “The company aims to manufacture components such as switchgears and control panels locally in future,” says Siemens SA Country Business Unit Lead: Rail Electrification, Joey Govindasamy.
“Siemens South Africa – Rail Electrification has established itself as a world leader in manufacturing DC containerised substations, and we have the skill sets locally to manufacture components at our North Riding factory. This is not only just good for job creation, but also reduces manufacturing costs which in turn contributes to lower prices and improved turnaround times.”
Siemens’ trolley assist solutions for the mining sector were first developed in South Africa in 1981, and the local operation has since remained a global leader in installed capacity. Currently Siemens SA is the only provider of the trolley solution in the Siemens group.
The technology has been supplied to open cast mines in South Africa, Namibia, the DRC, Zambia and as far afield as North America. Siemens has new business interest from mining companies in Botswana, DRC and Sweden. Given the success of the solutions in the mining sector, Govindasamy notes that Siemens will be targeting rail customers in the near future.
About the Siemens containerised substations
Each substation is housed in a 6m x 3.3m x 3m container that weighs approximately 8.5 tonnes when fully commissioned. Siemens SA offers full assembly, installation, testing and commissioning of these fully automated facilities.
The container includes the 1.8kV DC switchgear, rectifiers, 33 kV ring main unit, Siprotec AC protection device and Sitras Pro DC Feeder protection device. The control and protection of the entire substation is automated with a Siemens PLC and distributed Input / Output units connected via Profibus, significantly reducing the number of interface cables between equipment and allowing for the effective control and monitoring of the substation and equipment via a touch panel.
Cooling of this unit is provided by two inverter air conditioners, keeping the inside temperatures between 18 to 22 oC under normal load conditions.
Karl van Rensburg, Siemens’ lead engineer who designed the substation, comments: “Our experience gained over the past 20 years of providing DC mobile substations for trolley assist projects at various mines has greatly contributed to the success of this project.”