When Things Get Hot

When Things Get Hot

Looking at recent inquiries, there appears to be a growing demand for motors that can operate in high-temperature environments.

Although they were previously a “space age” or military domain, we are now seeing a need for higher temperature systems in the commercial world. This trend is primarily driven by the oil and gas industry, where motors that operate in holes deep below the surface must be able to withstand extremely high heat, and yes — it is hot down there. But we also see other high-temperature applications emerging, such as in the automotive markets and factory automation.

What do high-temperature motors offer for the industry? A common reason is simply due to necessity. The main applications of these motors are in harsh temperature environments, such as the previous example of deep-hole drilling or cleaning robots for the insides of boilers.

When looking at these applications, it appears that high temperature motors are a niche requirement. However, there are possible advantages that exist with the technology.  Some of these advantages include lack of cooling systems, mounting locations, and smaller, lighter builds.

First, let us take a look at the volume considerations. The size of a motor is primarily determined by the torque that it must produce. Many users classify a motor by its power rating, which is a carryover from the AC induction (ACI) motors where motors operated at only a few standard rpm settings as defined by the number of poles. Thus, for a given rpm, torque and power are directly related. These days ACIs are routinely driven by inverters and they operate at a wide variety of unconstrained speeds. Therefore we really should focus on the torque, which is a more objective rating that directly conveys important information about the motor torque and size.

However, the motor design is bound by limitations such as internal operating temperatures and surface cooling. This results in the motor being larger than it is required from a pure magnetic design standpoint, due to cooling and temperature considerations.

If we were not bound by these constraints, motors could in many cases be smaller and lighter. Weight and size are important considerations for customers, but even more so the cost, which is directly related to the material content. Other considerations, such as operator safety, obviously must also be considered. Yet in many instances these motors are installed in protected locations and safe from accidental contact.

What if we could strictly focus on the magnetic design without regard to thermal considerations? The skeptic would respond that the magnets will demagnetize and the wire resistance will increase and kill the motor efficiency; but that that is not necessarily true. We now have new magnetic materials that can operate at 500° C (930° F), along with new conductors that have virtually the same resistance at room temperature as they do at 500° C (930° F).  In addition, we also have bearing technology and lubricants that can operate at similar temperatures. Thus, it is technically feasible to build these high-temperature motors today.

What about cost? I will readily admit that these new materials are more expensive and our initial cost proposition may, in fact, not yet be feasible today. But that is the old chicken and egg question: we do not use these materials in sufficient quantities, so prices are high; and because prices are high, we do not yet use these materials commercially.

As specialty applications proliferate and we build more and more high-temperature motors, we should see prices fall, which in turn opens up new applications. For now, we will wait and see, but it is interesting to know that we have the technical ability to enter a new realm of motor design and applications.

 

About Author

George Holling

With over 70 publications and 9 U.S. patents on sensorless and efficient motor controls and low-cost power circuits to his credit, George Holling (PI) is an in-demand consultant to many major U.S. and International corporations for motors and drives. At present he holds significant influence in two companies — as technical director of Electric Drivetrain Technologies (2011– present) Moab, UT and as CTO of Rocky Mountain Technologies (2001– present), Basin, MT. Holling is a graduate of the University of Aachen, earning his B.S. (1974), M.S. (1978) and Ph.D. degrees there, while picking up his MBA here at the University of Wisconsin. His career has spanned both the commercial and academic arenas, the latter including stops at (Dean, Computer Science & Engineering) Utah Valley University, 2001 – 2003; and (Adjunct Professor), Western Michigan University, 1997 – 2002. From the commercial side, apart from his current positions, Holling has served as Project Engineer and Product Line Manager, UNICO; Franksville, WI (1978-1981); Project Engineer, General Electric, Medical Products Division, Milwaukee, WI (1981-1983; Manager R&D, Pacific Scientific/Honeywell Motor Products, Rockford, IL (1983-1985); Vice President of Engineering, Regdon Solenoid, Brookfield, IL (1988-1990); President, Advanced Motor Controls, Sun Prairie, WI (1990 – 1999); and Vice President of Engineering, Cordin Company, Salt Lake City, UT (1999 – 2000). Holling has also spearheaded projects for the development of high-efficiency motors and drives up to 400 kW, and has successfully negotiated licensing agreements with U.S., Chinese, Japanese and Indian customers for the licensing of motor and drive technology.

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