By Steve Fiscor, Editor-in-Chief
Electric motors are an integral part of mining and mineral processing and, more recently, several trends have been taking place above and below ground. Historically, the mining business used a lot of DC motors. Steadily those motors are being replaced with AC motors, especially in underground coal mining applications. Likewise drive systems are evolving from fixed to variable speed. Similar to AC motors taking over DC motors, the mining business is seeing a move from induction motors to synchronous motors on the surface.
The mining industry is usually a little slower to adopt new technologies than other industries. Miners are not any less tech-savvy; it’s a safety concern. In many cases, especially in the underground environment, the equipment has to be approved by the Mine Safety and Health Administration, which means motors and drive systems have to meet more stringent specifications. On the surface, the sheer size of the equipment leaves less room for error.
“The safety aspects and the approval and modification process to get a new system into a mine can be costly and time-consuming,” said Rich Schaefer, marketing manger for Baldor Electric’s variable speed and specialty products. “If there is justifiable demand, then a motor and drive system can be designed for specific applications. We do that in a lot of cases with our motors where an OEM has a proprietary product.”
In addition to better control, AC motors are also easier to maintain than DC motors. Many of the OEMs for underground coal mining equipment are converting DC systems to AC systems with variable frequency drives (VFDs). DC motors require a lot of maintenance, especially with brushes, commutators, etc. A lot of those issues will disappear when an AC motor is placed in the same application.
“Underground, technology has reached the point where we can monitor the machines and better understand the data we receive from them,” said John Kowaleski, global support-underground mining, Baldor Electric. “The controls that the OEMs are placing on new machines are becoming more sophisticated. We routinely add devices that monitor the temperature of bearings and windings, vibration, etc.”
As drive technology progresses, motors adapt. “We work jointly with the drive manufacturers to develop power-matched systems,” Kowaleski said. “The OEM gives us a set of performance criteria. They will specify a drive and a motor to perform a function. Then we complete extensive compatibility testing under load to verify that it will work before we place it in the field.” The object is to develop the most efficient system, Kowaleski explained. Baldor provides drive manufacturers the information they need so that they can generate the algorithms to control the motors in the most precise way.
For underground coal applications, space is critical. “Underground equipment manufacturers want the most power they can get in the smallest package,” Kowaleski said. “We’re working on a more power dense motor specifically for underground mining. It’s still in the R&D stage. We are adjusting the motor to make it super efficient. Heat is always the problem. If the motor gets too hot, things start to deteriorate and fail. We are doing what can to remove as much heat as possible in the most efficient way possible. Then we can put more power into it and get a higher rating in a smaller package.” Kowaleski said that Baldor is targeting specific applications with the technology and the more power dense motor should be available some time next year.
Synchronous Technology is the Future
Any discussion of electric motor technology, such as variable- and high-speed opportunities, will eventually lead to power density—getting more power into a smaller package. Baldor recently introduced a line of cooling tower motors, which use a very compact, power-dense, pancake style motor directly under the fan eliminating the gear and jack shafts in favor of direct drive. The technology that made this possible is the permanent magnet (PM) rotor, or the synchronous motor. “We believe that synchronous motor technology is the future because it eliminates virtually all of the secondary losses in the rotor,” Schaefer said.
Synchronous motors have a permanently magnetized rotor that uses high performance neodymium iron-boron magnets. “We’re using interior salient pole designs and we believe that synchronous motors will replace induction motors,” Schaefer said. “Not in all cases and certainly not overnight but, just as AC has taken over DC, we see the next evolution being the synchronous motor taking over the induction motor.”
This new technology is similar to what’s being employed with hybrid automobiles, such as the Honda Accord or Toyota Prius. “In those vehicles, a pancake-style electric motor is sandwiched between the engine and the transmission and it uses the neodymium iron-boron magnets embedded in the rotor,” Schaefer said. “That technology can be adapted to industrial motors to develop a more power dense motor.”
Induction motors by their very nature are already pretty darn efficient, Schaefer explained. “The question is: How do you get the next 1% or 2% efficiency gain?,” Schaefer said. “Eliminating rotor losses would allow incremental steps in efficiency improvement.” Baldor introduced a line of synchronous motors in January of this year.
Some of the attributes that make PM motors attractive for surface mining applications might hinder its use underground. Because the rotor is always magnetized, it makes an excellent generator. In a traction situation where the application is driving the motor, it becomes a generator. There are a lot of cases underground where mine operators would not want that motor reversing its role.
In certain situations, this attribute could be viewed as a positive. Harnessing the power generated from synchronous motors could be used to recharge batteries. But what would happen if a lead was cut? “We will have to consider XP applications carefully,” Kowaleski said. “We would need to find a way to let the power dissipate.” Some of the OEMs are looking at this technology and how it’s applied.
Motors and drive systems always seem to be in a constant state of development. “It’s an evolutionary process,” Schaefer said. “Once a product is designed and developed; it’s on to the next one.” Motor and system efficiency will always be a driving force in the mining business and power density will remain fundamental.