Current Status and Development Trends of Main Insulation Materials for Motors
Release time:
2024-12-29
Main insulation is crucial for the safe operation of motors, including electromagnetic wire insulation, slot insulation, inter-phase insulation, slot wedge insulation, and impregnating varnish. Secondary insulation mainly serves as auxiliary insulation while providing mechanical support and protection for the coils, including insulating sleeves, binding ropes, busbar insulation, and solder joint coatings.
Main insulation is crucial for the safe operation of motors, including electromagnetic wire insulation, slot insulation, inter-phase insulation, slot wedge insulation, and impregnating varnish.
Secondary insulation mainly provides auxiliary insulation effects while offering mechanical support and protection for the coils, including insulating sleeves, binding ropes, busbar insulation, and solder point coatings.
02 Corona-resistant enameled wire
As the drive motor spins faster and the power density of electric drive systems increases, the performance and quality requirements for enameled wire are bound to become stricter.
Currently, the main type used in electric vehicle drive motors is corona-resistant enameled wire modified with nanoparticles, rated H-class (or above).
The enamel film of this enameled wire has evolved from the early three-coat system to the later two-coat system. Due to the short lifespan and relatively poor adhesion of the three-coat system, it gradually fails to meet requirements.
In 2000, DuPont developed a two-coat corona-resistant enameled wire, with the bottom coat being a nanoparticle-modified polyester imide corona-resistant coating and the top coat being a PAI coating.
Since the introduction of the two-coat system, it has been widely applied in the field of drive motors. In recent years, with the rise of oil-cooled motors, PAI single-coat corona-resistant enameled wire has seen increasing application due to its resistance to ATF oil and high temperatures.
Corona-resistant enameled flat copper wire
As we all know, the choice of materials and technologies is constantly changing based on the evolving technology of the application subject; there is no one-size-fits-all material.
With the rapid development of flat wire technology, higher slot fill rates and power densities have led more OEMs to choose flat wire motors.
Traditional round conductor stator slot diagram
Rectangular conductor stator slot shape
However, the coating process for the four "R" corners of corona-resistant enameled flat wire is poor, and current applications often face issues such as decreased corona resistance and unstable performance.
In addition, some recent commercial applications are using PEEK materials extruded onto enameled wire as a replacement for solvent-based impregnation.
03 Insulation impregnating resin
The insulation treatment of motor stators mainly uses vacuum impregnating resin (VI) and vacuum pressure impregnating resin (VPI). Generally, the base resin is a high-strength, high-heat-resistant modified polyester or polyester imide.
It is worth mentioning the nanoparticle modification technology, which can improve paint hanging efficiency, heat resistance, and corona resistance by adding nano inorganic particles.
Speaking of the current situation, in recent years, resins that adapt to new processes such as energized heating curing, UV curing, and rotary dipping have also come into people's view.
Among them, the energized heating process is a more efficient new method, requiring only a few minutes from impregnation to resin gel, and the entire treatment process can be completed in about an hour. Moreover, it allows for precise control of paint hanging amount, has good filling performance, and does not produce resin curing waste.
However, the main equipment for the energized heating process is currently controlled by foreign companies from Germany and Italy, and the import prices are relatively high, so it has not yet been widely expanded domestically.
04 Soft composite materials
Currently, the mainstream non-oil-cooled drive motor slot insulation, slot wedges, and inter-phase insulation mainly use two layers of polyamide fiber paper (such as Nomex) and one layer of PI film composite, forming a soft composite material.
This insulation material has an H-class heat resistance rating and is lower in cost, so it has been widely applied. However, its corona resistance and resistance to ATF oil are slightly inferior.
With the popularity of oil-cooled motors, such non-oil-resistant soft materials are beginning to struggle, easily leading to delamination and thus reducing insulation performance.
This creates a "vicious cycle": to enhance oil resistance, motor development designs will use single-layer thick polyamide fiber paper with better oil resistance.
However, this material has relatively poor electrical performance, and to improve insulation performance, the material design thickness must be increased, which inevitably affects power density and thus increases the overall manufacturing cost of the motor.
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