introduction
In recent years, with the development of power electronics, computer technology, and control theory, the global industrial motor market has experienced significant growth. The emergence of rare-earth permanent magnet materials and magnetic composite materials has led to the development of various new, high-efficiency, and special-purpose motors. As the international community increasingly emphasizes energy conservation, environmental protection, and sustainable development, the production of high-efficiency motors has become the global trend in industrial motor development. Against the backdrop of global efforts to reduce energy consumption, various energy-efficient policies have been introduced, further accelerating the development of the global industrial motor manufacturing industry.
1. The motor industry is transforming towards intelligent and energy-saving technologies.
Currently, while general low-voltage motor technology is relatively mature, significant technological hurdles remain in areas such as high-power high-voltage motors, motors for special environments, and ultra-high-efficiency motors. Looking at the global electric motor market development trends, the main characteristics are as follows: the industry is moving towards intelligent and integrated development. Traditional motor manufacturing has already achieved the cross-integration of advanced electronic technology and intelligent control technology. In the future, the development trend of the electric motor industry will be to continuously develop and optimize intelligent control technology for small and medium-sized motor systems used in industrial fields, achieving integrated design and manufacturing of motor system control, sensing, and drive functions.
2. Motor manufacturing is developing towards differentiation, specialization, high efficiency, and energy saving.
Electric motors are widely used in various fields such as energy, transportation, petroleum, chemical industry, metallurgy, mining, and construction. With the continuous deepening of the global economy and the continuous improvement of technology, the past situation where the same type of electric motor was used for different purposes and occasions is being broken. Electric motor products are gradually developing towards specialization, differentiation, and specialization.
In recent years, global environmental policies have provided clear guidance for improving the efficiency of motors and their control systems. Therefore, the motor industry needs to accelerate the energy-saving transformation of existing production equipment, promote efficient and green production processes, develop next-generation energy-saving motors, motor systems and control products, testing equipment, improve the technical standards system for motors and systems, and strive to enhance the core competitiveness of motor and system products.
3. Optimized design and material selection for high-efficiency and energy-saving motors
High-efficiency, energy-saving motors utilize premium materials and optimized design to achieve higher efficiency. For example, a higher aluminum content in the rotor and a higher slot fill factor in the stator result in lower resistance losses. Optimized rotor structure and rotor-stator air gap reduce stray load losses. Improved cooling fan design minimizes air resistance losses during motor cooling, and the use of higher quality and thinner steel laminations in the rotor and stator cores significantly reduces magnetization losses.
3.1 Optimize the dimensions of the stator and rotor laminations and the quality of the steel used.
Hysteresis loss and eddy current loss are collectively referred to as core loss, accounting for approximately 20% of total losses due to eddy currents and core saturation. Eddy currents generated in the laminations move relative to a constantly changing magnetic field, leading to significant power loss. Laminated stator cores can reduce eddy current losses, and based on the iron's mass, resistivity, density, thickness, frequency, and magnetic flux density, eddy current losses can be minimized by using more laminations.
Hysteresis loss arises when the magnetic flux in the magnetic circuit changes continuously. Most load materials used in motors are steel for the stator and rotor cores. Minimizing flux density and core losses is achieved by reducing lamination thickness. Hysteresis loss can be reduced by annealing to select a better grade of lamination steel to alter the grain structure for easier magnetization. Eddy current losses can be reduced by increasing the resistivity of silicon-containing steel, but the silicon content increases die wear during stamping because it increases the steel's hardness. Damaged steel crystals during stamping severely degrade the magnetic quality of the affected volume. Annealing flattens the laminations and recrystallizes the damaged crystals from stamping, thus extending a thinner sheet thickness into the lamination.
3.2 Stator lamination using immersion process
Impregnating the stator strengthens the electrical insulation of the stator windings, protects against chemicals or harsh environments, and enhances heat dissipation. Thermosetting plastics, including epoxy resins, phenolic resins, and polyesters, are used for stator impregnation. Immersion involves immersing the stator in the resin for an extended period to ensure optimal penetration and protection. Another impregnation method is called vacuum pressure, which uses a vented and then pressurized tank to achieve stator penetration. This removes cavitation from the windings, improving their thermal conductivity.
3.3 Optimize the design of the stator slots to maximize the volume of copper that can be inserted.
Slot fill factor significantly impacts stator winding quality; a low fill factor can lead to up to 60% of total losses. Therefore, to reduce total losses, the stator winding mass must be greater to lower resistance. Compared to standard efficiency motors, high-efficiency motors contain over 20% more copper, and the stator's insulated windings are placed within slots in steel sheets. The cross-sectional area must be large enough to meet the motor's rated power. Generally, induction motors use open or semi-closed stator slots. In semi-closed slots, the slot opening is much smaller than the slot width, making winding more difficult and manufacturing more time-consuming compared to open slots. The number of stator slots must be selected during the design phase, as this affects weight, cost, and operating characteristics. The advantages of more slots include reduced leakage reactance, reduced tooth pulsation losses, and improved overload capacity. The disadvantages of more stator slots include increased cost, increased weight, increased magnetizing current, increased iron losses, poor cooling, increased temperature rise, and reduced efficiency.
3.4 The rotor die-casting uses high-quality pure aluminum.
Custom-designed rotors can maximize starting torque, reduce conductor resistance, and improve efficiency. Most induction motor rotors use a squirrel-cage design. They are robust, simple in structure, and inexpensive, but their starting torque is relatively low. Copper rotors improve efficiency, but are both difficult and expensive to manufacture.
3.5 The air gap between the rotor and stator reaches its optimal value.
The air gap is the radial distance between the rotor and stator of a standard radial motor. To improve design efficiency, an optimal air gap needs to be maintained. The air gap dimension is involved in the design of the stator, rotor, motor housing, and bearings. All of these affect the precise alignment of the stator and rotor shafts.
3.6 High-performance electromagnetic enameled wire is used.
Magnets or enameled wires are electrolytically refined copper or aluminum wires that have been fully annealed and coated with one or more layers of insulation. For example, wires with a total of 12 layers of insulation are used. Typical insulation films include polyethylene, polyurethane, polyester, and polyimide, with temperatures reaching up to 250°C. Thicker rectangular or square magnet wires are wrapped with high-temperature polyimide or fiberglass tape, using more copper. Larger conductor bars and conductors increase the cross-sectional area of the stator and rotor windings, reducing winding resistance and current losses. High-efficiency motors typically have 20% more copper in their stator windings.
An electric motor consists of many components, each with different structural and functional attributes, resulting in varying functions within the motor system. The quality of each component's function ultimately affects the motor's input performance. By optimizing the performance of each component, the motor's overall performance can be optimized.
4. Conclusion
Currently, in order to cope with global market competition, the motor manufacturing industry is gradually shifting from a "large and comprehensive" model to a "specialized and intensive" one. With the development and improvement of intelligent control systems for motors, the industry is further promoting the development of specialized production models. In the future, driven by low-carbon and environmental protection policies, industrial motors will comprehensively develop towards green and energy-saving technologies.
References:
[1] Chen Jingang, Huang Liming, Energy-saving system design for low-voltage high-efficiency variable frequency motor [J], Marine Electric Technology, 2019(2):34-36.
[2] Chen Weihua, Development and Policy Opportunities of the Motor Industry [J], Motor and Control Applications, 2017(7):1-6+25.
[3] Sun Hongchao, Liu Wenhui, Wang Fuchun, Research on design method of high efficiency motor [J], Explosion-proof motor, 2014(2):1-4.
About the author:
Chen Jingang, male, born in October 1974, graduated from Beijing University of Aeronautics and Astronautics in 1996 with a major in electromechanical engineering. He has been engaged in the design, selection, testing and fault analysis of low-voltage electrical equipment at Dezhou Hengli Motor Co., Ltd., and was promoted to senior engineer in 2020.
