Electric motors and drives are expected to play an increasingly larger role in mining and other heavy industries. OEMs are upgrading design, fabrication and support capabilities to ensure their product lines are up to the challenge.

The latest standard electric-motor product lines offer increased modularity and flexibility to meet the requirements of a wide range of applications. However, unique site conditions or performance demands often call for custom designs such as these cylindrical-cased 6,600-v, 1,700-kW squirrel cage motors engineered by Menzel Motors to power an underground mine’s ventilation system.

By Russell A. Carter, Contributing Editor

In the roughly 125 or so years since the first truly useful electric motors for industrial purposes were introduced, their role has steadily expanded to include almost any application that requires rotary power. One recent estimate from a major motor supplier has electric motor-driven systems accounting for about 45% of the world’s energy usage. 

For the mining industry, all indications are that motor usage will continue to grow as companies study, structure and execute plans to electrify operations from pit to plant. 

A motor has to be properly engineered for its intended application. A list of the main reasons why motors fail, as shown in the accompanying chart, indicates that many failures can be traced back to incorrect initial selection. As OEMs develop new concepts for motor design, aimed at offering products that have higher torque density, better cooling performance and smaller physical footprints, they’re also implementing features and services that enable customers to more accurately choose the correct product and monitor its performance throughout the duty cycle.

OEMs are also aware of the need to conserve materials, both during original fabrication and for end-of-life recycling, and are pursuing strategies aimed at optimized or reduced use of copper wire and magnet material. For example, late last year ABB announced plans to use Boliden’s certified recycled and low-carbon copper in its high-efficiency electric motors and other equipment. As of 2023, ABB said it will purchase that copper to cover the demand for certain IE5 Ultra-Premium Efficiency and other motor types produced in Europe. The two companies have also signed a memorandum of understanding that will see ABB supporting Boliden in identifying inefficient low-voltage motors across its operating units. These motors can then be replaced with high efficiency motors within ABB’s take back upcycling framework, with the old motors recycled to provide raw material for Boliden’s recycled copper.

According to ABB, Boliden’s low-carbon copper is produced by using secondary raw material from recycled products. A typical 75-kW motor weighing 650 kg might include 80 kg of copper. Using Boliden’s copper saves approximately 200 kg of CO2 emissions for every one of these motors manufactured, said the company.

In another copper-related development researchers at Pacific Northwest National Laboratory (PNNL), a national laboratory managed and operated by Battelle for the U.S. Department of Energy, found a way to increase the conductivity of copper wire by about 5% — enough to make a significant improvement in motor efficiency. For example, the actual number of large motors installed every year is relatively low, but their power ratings are so high that even a small increase in efficiency can cut losses by tens of kilowatts per machine. Given that they typically run for more than 8,000 hours per year, a small increase in efficiency can mean huge energy savings. Higher conductivity also means that less copper is needed for the same efficiency. 

Using a new manufacturing platform developed at PNNL, researchers added graphene — a highly conductive, nano-thin sheet of carbon atoms — to copper and produced wire. The increase in conductivity compared to pure copper, according to PNNL, was made possible by a first-of-its-kind machine that combines and extrudes metal and composite materials, including copper.

In cooperation with General Motors, the lab tested the improved copper for use in vehicle motor components. As part of a cost-shared research project, the team validated the increased conductivity and found that it also has higher ductility. In other physical properties, it behaved just like regular copper; it can be welded and subjected to other mechanical stresses with no degradation of performance. This means that no specialized manufacturing methods would be necessary to assemble motors — just the new advanced PNNL copper composite. 

Finding the Best Fit Gets Easier

There’s an old mining maxim that says, “If you’ve seen one mine, you’ve seen…one mine,” alluding to the fact that almost no two mineral deposits, mines, process plants or related facilities are identical due to differences in the specific conditions or available company resources at any given mine project. That doesn’t mean that every electric motor on-site has to be a special-purpose model. The latest generation of motors from leading suppliers offer greatly expanded modularity and customization features to fit a wide range of applications. 

ABB recently introduced its AMI 5800 NEMA modular induction motor, designed to provide better energy efficiency and reliability in demanding applications such as pumps, compressors, fans, conveyors and crushers. Rated for a power output of up to 1,750 hp, the AMI 5800 line brings a high degree of modularity and customization to suit both new build and upgrade projects, according to the company.

ABB describes the AMI 5800 motor as a true NEMA design with one of its key features being a high-strength welded steel frame typically found only in motors with larger frame sizes. This lowers stress on the motor while mitigating vibrations and resonance to ensure reliable operation in harsh conditions with a design life of 25 years or 20,000 starts. Another claimed advantage is a shorter bearing-to-bearing span compared with previous models. This improves performance at high speeds and enables the motor to be used as a simple drop-in replacement to upgrade existing equipment. 

According to ABB, the majority of regular AMI 5800 designs not only meet but exceed North American standards for energy efficiency. Further customization will allow some models to operate above the IE4 equivalent level of energy efficiency while meeting NEMA electrical performance standards.

The new motor is configured for optimal airflow, meaning that it will run as cool as possible in an open-air installation or enclosed with a cooler. ABB said its MICADUR insulation system makes the motor suitable for starting high-inertia loads direct online but also for use with variable speed drives.

In April, Regal Rexnord’s Commercial Systems group launched a new line of general-purpose motors, any one of which could potentially replace up to any one of 18 different traditional general-purpose motors, according to the company. Features of the Flex-in-1 line include the ability for the motor to operate at 60 to 50 hertz, capability for inverter duty and a removable repositionable base that enables the conduit box to be rotated into the desired NEMA F-2 and F-3 mounting positions. The motor ships with the conduit box in the F-1 mounting position.

The Flex-in-1 motor, said the supplier, is the only NEMA motor with a patent-pending repositionable base plus C-Face design with rolled-steel construction. The combination C-Face rolled steel and base design gives the motor added strength and durability. Repositioning the base can be done in 5-10 minutes or less vs. the approximate 60 minutes in time that it would take to configure a standard general-purpose motor reducing downtime required for installations, repairs, and retrofits.

Motor suppliers do, however, encounter specific site conditions or customer requirements that call for specialized designs or features. Here are few recent examples:

WEG, the Brazil-based motor suppler, knows that motors for use in desalination plants must operate in severe climates around the clock, be extremely durable and protected against corrosion. The company recently supplied motors fit for this type of duty to a crucial mine-water Infrastructure project in northern Chile, where WEG’s W22 IE3-class efficiency motors are used in the feed and recirculation circuits of the desalination plant. Vertical application motors were also supplied for the plant’s capture system. All were treated with a special epoxy paint finish for performance in severe marine environments with a high salt index.

Berlin-based Menzel Motors designed and built three unusual 6,600-v squirrel cage motors for an underground mine’s ventilation system. The customer specified cylindrical motor casings — a challenge, according to Menzel, to implement the required rated power of 1,700 kW in the most compact cylindrical casings possible. Menzel said it met design requirements by fabricating fin-cooled squirrel cage motors in frame size 630, an extremely unusual design for motors this large. Because the driven fans are mounted directly on the motor shafts, the motors’ bearings had to able to handle radial loads up to 20,700 N and axial loads up to 27,000 N, which required a special bearing setup in order to meet the targeted bearing service life of 100,000 hours.

FLSmidth selected these WEG water-cooled motors with automatic brush lifting system for a plant expansion project in Brazil.

AI has Arrived

As the demand for special-purpose and customized motors grows, manufacturers are looking towards artificial intelligence technology to assist in expediting both motor design and production.

Last year, Toshiba Mitsubishi-
Electric Industrial Systems Corp. (TMEIC) announced that together with Mitsubishi Electric they’ve developed an electrical motor-design support system incorporating Mitsubishi Electric’s Maisart AI technology that is claimed to dramatically shorten the time required to produce electrical motor designs that achieve the same performance as conventional design methods deployed manually by skilled engineers. TMEIC said it planned to adopt the system for internal operations in 2023.

The new system, it was reported, can be used to design electrical motors for pumps, compressors and fans. Formerly, engineers had to iteratively adjust design specifications to balance performance versus design, such as power efficiency versus motor size. 

Using the new system experimentally to perform design tasks normally completed in the past by engineers, Mitsubishi Electric found that design time can be reduced to three hours compared with one day for experienced engineers and up to three days for less experienced engineers. The system, according to the company, also helps to simplify and standardize design processes, since performance targets can be simply adjusted to have the AI generate appropriate new specifications. In addition, the system is expected to support the transfer of design skills to less experienced engineers to help them become more proficient.

According to TMEIC, the new electrical motor-design support system achieves results equal to manually produced designs. Engineers input performance requirements and then the AI proposes the best specifications by referring to historical design data. Engineers then check the AI-proposed specifications for performance, adjust targets if necessary to obtain finely tuned new AI-proposed specifications. The interactive process can be repeated until specifications that best satisfy the final performance targets are achieved. The results are equivalent to conventional manually produced designs.

In addition, the company said performance-prediction and specification-optimization technologies dramatically cut design time. AI technology predicts electrical motor performance using design specifications accumulated in the past by TMEIC. Engineers can interact with the AI by fine-tuning performance targets to obtain precise specifications based on past designs that the AI searches and then optimizes. Design time is dramatically reduced from one to three days to just three hours.

Some key details about the system, as described by TMEIC:

Interactive multi-objective electrical motor-design technology produces high-quality designs quickly. Using conventional multi-objective optimization techniques, it has been difficult to quickly produce ideal design specifications that satisfy all performance targets covering every category, such as motor size, power efficiency and heat generation, some of which are inversely related.

New technology, however, enables performance specifications to be designed within a remarkably short time by using both meta-heuristics, a method for efficiently searching combinations of parameters, and a back-and-forth process in which engineers interact with the AI. 

This interactive procedure can be repeated until the engineers are satisfied with a design that best satisfies the final performance targets.

High-speed performance prediction technology and efficient presentation technology. The AI technology creates specifications by referring to past designs, searching for the best specifications and then presenting multiple combinations of possible specifications optimized to performance targets. Engineers can choose the specifications that best suit overall needs and quickly determine a final design that matches their final performance targets.

The TMEIC AI initiative certainly isn’t the only large-scale program under way to apply AI tools to motor design and production. For instance, last year Bosch announced a major expansion of its North American facilities for manufacturing electric motors; the company said it would begin production at its Charleston, South Carolina site — ironically, at a facility previously devoted to production of components for diesel engines — and planned to spend more than $260 million in the future to expand capacity there even further. The new facility reportedly will use AI to design production lines that will be highly configurable for various customer requirements.

It’s part of a larger corporate effort, according to recent remarks from Bosch executives. “In recent years, Bosch has made good progress in the development of AI in its divisions and at its locations worldwide,” said Tanja Rückert, member of the board of management and chief digital officer of Bosch GmbH. “We are bringing AI into our applications quickly and successfully.” 

The company stated that before the end of this year, all of its products and solutions will either contain AI or have been developed or manufactured with its help.

Switching to AC

Another aspect of expanding electric motor usage — in this case, one that goes hand-in-hand with the mining industry’s pursuit of higher equipment efficiency, sustainability and circularity — is the option to upgrade older equipment, such as DC-powered mining shovels, to AC power for better performance, safety and lower maintenance requirements. 

This trend has been gaining industry interest, with the benefits offered by AC power strongly influencing OEM product line strategy, particularly in their largest-capacity machines. In 2021, Komatsu said it would be offering all of its P&H electric rope shovels as AC-powered machines going forward, citing production improvement gains that were measured by comparing machine performance data and input from customers reporting that they could regularly achieve higher productivity with the company’s AC models. Liebherr has offered AC power throughout its range of mining excavators for many years and has adopted a modular design approach for excavators that is intended to facilitate upgrades or retrofits as new drive technology becomes available.

Caterpillar, which was an early adopter in introducing AC technology to mining equipment — starting with analog GTO control technology then introducing IGBT digital control — has had a long-term partnership arrangement with Siemens to develop custom-designed AC drive systems for rope shovels. The latest motor-related improvements are featured on the company’s new-production 7495 and 7495 HF shovels, which offer a drive system design that uses common motors in multiple applications. These motors, according to Cat, have higher power densities, smaller frame sizes and optimized footprints. 

For older DC shovels that may be mothballed, under-utilized or still in production — but with high maintenance costs and risks — repowering with AC components offers a range of benefits. Mike Onsager, director of technology at power and control systems specialist Flanders, outlined those advantages for an audience at the recent Haulage & Loading Conference, held April 2-5 in Tucson, Arizona and sponsored by Mining Media International.

Flanders offers custom electric motor design and manufacturing, along with engineering and manufacturing expertise gained through upgrading dozens of P&H shovels and converting draglines and other equipment from DC to AC drives and components. The “numbers” — the machine-specific benefits of shovel conversion to AC — are clear-cut, said Onsager, and can be summarized in a few bullet points:

Safer – Less motor maintenance, inspection and testing; eliminates DC commutators. 

More reliable – Eliminates carbon brushes and dust. Addresses obsolescence and digitalization. 

Energy efficiency – 10+% more efficient than DC. Active Front End (AFE) drive precisely controls power factor and reduces harmonics. Reduced power system losses. 

Productivity – Faster, smoother operation with custom control system. Increased tons per hour. 

The advantages of switching to AC power extend beyond the machine, said Onsager, starting with additional power capacity becoming available to a mine while using the same distribution system. “You can operate more equipment on the same system, have more flexibility with substation location, length of trail cables, along with how many other machines are in the pit and how they’re affected,” he explained. “Plus, the (AC) motors for the shovels and draglines are custom manufactured by Flanders to be drop-in fit replacements.”

A typical conversion takes about a month and is handled by six technicians and three engineers. “We have a long-term perspective when it comes to these conversions,” he explained. “Given that industrial drives and other electronic components typically have a five to seven years lifespan, we address obsolescence concerns by producing our own inverters and digital control cards. We have implemented a unified control platform for shovels and draglines, allowing us to support this platform in the future without depending on OEM or industrial-supply sources.”

Reutilization of existing machines is gaining interest as mine operators seek to reduce their overall carbon footprint and engage in sustainable, circular equipment ownership and operational strategies. Onsager pointed out that some draglines were approaching 70 years of service, and with ongoing maintenance, refurbishment and upgrades where appropriate, could reach the century mark. Although that might not be the case with a typical mining rope shovel or AC motor, AC motor and control upgrades can keep these machines operating at highly productive levels for many years — and avoid “making new steel to replace old iron.”

This article was adapted from an article that was originally published in the July 2023 edition of Engineering & Mining Journal (E&MJ).