Electric motors are an essential part of our everyday lives. Although usually hidden from view, they perform countless tasks that make our lives easier, enhance our comfort, and make us more productive. At home, washing machines, vacuum cleaners, microwaves, hairdryers, and many other appliances rely on motors. Motors are just as prevalent in the commercial world and industry, where they are key components in pumps, fans, elevators, and air compressors. They allow us to complete many jobs, from brute force tasks such as pushing huge volumes of liquid through pipes to delicately ensuring the tiniest electronic component is precisely placed on a circuit board. In the ongoing transition to a more sustainable economy, motors are again at the heart of that change, powering electric vehicles with high-efficiency heat pumps and enabling renewable power generators to operate at the highest efficiency possible. Almost every electrical machine or device with mechanical movement uses a motor to accomplish its task.
Motors are available in a wide variety of sizes; for example, one of the world’s largest and most powerful motors is the 105MW two-pole electric motor that Siemens has developed for a Chinese energy storage project. At the opposite end of the spectrum, one of the smallest motors in the world is a 1nm device that scientists manufactured from a single molecule of butyl methyl sulfide.
Being an integral part of many applications means an enormous market for electric motors. According to MarketsandMarkets Research, it was worth US$134 billion in 2022, and that figure is expected to rise to US$186 billion in 2027, providing a compound annual growth rate (CAGR) of 6.8 percent.1 There are billions of motors in operation worldwide. Finding an overall figure for the current number of electric motors is difficult. Still, the EU estimates that there are eight billion motors installed in its economic area alone.2 These motors use a staggering amount of electricity. They are estimated to consume up to 46 percent of the total electricity generated globally and almost 70 percent of the electricity used in industrial applications.3 As such, there is a strong desire to reduce the amount of electricity motors use by making their operation more efficient.
Increased efficiency can be achieved in the fabrication of the motor itself through more precise manufacturing techniques and advanced materials; supporting components can also be designed to drive the motor more efficiently. For example, variable-speed drives (VSD) and variable-frequency drives (VFD) match the motor’s rotation to the load’s requirements, ensuring that the system is always performing at optimal efficiency. VSDs and VFDs are not new technologies, but they are becoming more widely deployed to save energy and offer additional benefits, such as soft start, longer operational lifetimes, and performance analytics.
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Advanced materials that have been brought to the market relatively recently, such as gallium nitride (GaN) and silicon carbide (SiC), can deliver power to the motor more efficiently. Those power devices are often supported by complex digital computing technologies to control the power flow to the motor accurately. Using these technologies can make electric motors considerably more energy efficient, reducing running costs while improving the performance of the systems.
Additionally, governments and trade organizations around the world use legislation to promote the use of more efficient drives. The United States began regulating electric motors in 1992 as part of its Energy Policy Act. Five years later, the country introduced minimum efficiency performance standards (MEPS) for motors manufactured or sold in the US market for industrial, commercial, and residential applications. On a global level, the International Electrotechnical Commission (IEC) developed the IEC 60034-30:2008 standard, which harmonized efficiency classifications for motors manufactured and sold worldwide. The regulation was updated in 2014, and the IEC 60034-2-1:2014 standard was introduced to specify how to determine motor efficiencies and losses using established testing methodology. The classifications in the standard range from IE1 up to IE5, with IE1 being the least efficient and IE5 the most efficient.
Governing bodies have used these IE classifications to mandate a minimum level of efficiency for motors. For example, (EU) 2019/1781, the EU regulation on electric motors and variable speed drives, came into force on July 1, 2021. It expanded on previous legislation and provided classifications for VSDs and minimum performance levels for the first time. Motors that are not exempt from the regulation will have to meet IE2, IE3, or IE4 efficiency levels, depending on their rated power and other characteristics. The legislation means that the EU is the first body to mandate IE4 as a minimum level of efficiency for motors in the scope of the regulation.
Motor Operation and Types
At its most basic level, the electric motor is a simple machine that converts electrical energy into mechanical motion. This process is possible because of the interaction of magnetic fields, where opposite poles attract and similar poles repel. In most motors, the magnetic fields are created by permanent magnets and/or electromagnets. When constructing a basic electric motor, the electromagnet is wound around a core on an axle at the center of the construction. The permanent magnet is on the outside of the structure with poles on directly opposite sides.
As shown in Figure 1, when power is supplied to the rotor, an electric field is created, and the north pole of the electromagnet is repelled by the north pole of the permanent magnet while being attracted to its south pole. It rotates to match the opposing pole of the permanent magnet. When it gets to that position, its power supply is reversed, which also reverses the magnetic field, and the rotor is repelled from the magnet that it is near and attracted by the magnet on the opposite side of the device; when it gets there, the polarity is again reversed to keep the rotation going. This type of device is known as a DC motor, as the current supplied to the electromagnet is DC.
Figure 2 shows the main constituent parts of a DC motor. The electromagnet windings, also known as the armature, are part of the rotor construction, which usually also contains a core, bearings, and an axle to allow it to rotate freely. The permanent magnet’s north and south poles, respectively, on the left and right of the rotor, make up the stator.
In a motor, poles always come in pairs, and the pole count of a motor is the number of permanent magnetic poles. Therefore, a single permanent magnet would be used in a two-pole motor, such as the one shown in Figure 2. Depending on the number of poles in the motor, there is a trade-off between speed and torque. A two-pole motor will be capable of rotating roughly twice as fast as a four-pole motor of the same size, but the four-pole motor will have more torque. A split-ring commutator switches the polarity of the current every time the rotor reaches its opposite pole. The brushes are electrical contacts that conduct current from the power supply to the rotor. More sophisticated motor designs may use an electromagnet on both the rotor and stator or have the permanent magnet on the rotor and the electromagnet on the stator.
The other main category of electric motors is the AC motor, which, as the name suggests, works off an AC power supply. AC motors are like DC motors in that they use a rotor and a stator. However, the stator has multiple coils that energize in pairs in a set sequence to produce a magnetic field that rotates around the outside of the motor. Because the stator powers the rotor, the rotor does not require power like in a DC motor. The magnetic field generated by the stator induces a current in the rotor, which, in turn, produces its own magnetic field that interacts with the stator’s magnetic field, causing the rotor to rotate. The AC motor does not require a commutator to switch the current direction as AC switches polarity naturally.
AC motors can be single or three-phase, with three-phase motors using three AC currents, which are out of phase with each other in a triangle of coils. At any time during operation, one coil attracts the rotor, one repels, and one is neutral. As the rotor does not require external power, AC motors don’t require brushes, which makes them more robust while running cooler and quieter.
Both AC and DC motors have further subdivisions, as shown in Figure 3. Later articles will give more details on these type of motors, how they operate, and the applications where they can be best employed.
Comparison of Benefits
Every application is different; choosing between an AC motor or a DC motor requires many complex decisions, which this guide will address later. Generally, AC motors are more robust and, because of the way they operate, have higher torque levels than DC motors. They are flexible with controllable startup current levels, and their acceleration and speed can be matched to loads more easily. DC motors are more straightforward to install and maintain. They offer high power and torque straight from power up and respond more quickly to starting, stopping, and acceleration.
The Future of Electric Motors
Electric motors have been around almost as long as electricity has been reliably harnessed. Only 34 years separated Alessandro Volta’s invention of the battery in 1800 and Moritz Jacobi’s development of an electric motor with usable mechanical power. Since then, motors have continued to evolve to meet the demands of users. The need for more efficient motors drives the current market and will continue to do so in the near- to medium-term future. Even though there has been a lot of progress made recently toward making both motors and the circuits that drive them more efficient, there is still a massive demand for further innovation. For example, electric vehicle manufacturers are demanding more powerful and lighter motors to increase energy density and mileage. In other applications, designers want motors that do not use rare-earth minerals in their construction to make them cheaper and negate any supply chain issues that may arise. Those demands will ensure that motor technology is as relevant as ever and will continue to be extended into the future.
Sources
1 “Electric Motors Market Size, Share,
Industry Analysis [2022-2030],”
MarketsandMarkets, November 2024,
https://www.marketsandmarkets.com/
Market-Reports/electric-motor-marketalternative-fuel-vehicles-717.html.
2 “Electric Motors and Variable Speed
Drives,” European Commission, accessed
January 26, 2024, https://commission.
europa.eu/energy-climate-changeenvironment/standards-tools-and-labels/
products-labelling-rules-and-requirements/
energy-label-and-ecodesign/energyefficient-products/electric-motorsand-variable-speed-drives_en.
3 Fluke, “New Testing Approach Matches
Real World Conditions,” Blog, May 9,
2021, https://www.fluke.com/en-us/
learn/blog/power-quality/testingmatches-real-world-conditions.
About the author: Alistair Winning
