Current Applications of Mainstream Insulation Materials in Electric Motors
The primary properties of insulation materials used in electric motors include dielectric performance, insulation resistance, dielectric strength, heat resistance, moisture resistance, and lightning protection. These materials are also expected to be easy to process. Commonly used insulation materials include impregnating varnishes, coating varnishes, impregnated fiber products, non-impregnated fiber products, electrical-grade films, and composite materials. Improper selection of insulation materials can negatively impact both the repair quality and service life of electric motors.
Current Applications of Major Insulation Materials in New Energy Vehicle Drive Motors
Secondary insulation mainly serves a supplementary role, enhancing insulation while also providing mechanical support and protection for the coils. This includes insulating sleeves, binding threads, busbar insulation, and coating of welding joints.01. Insulation System
The insulation system in new energy vehicle (NEV) drive motors primarily includes:
- magnet wire insulation
- inter-turn insulation
- slot insulation
- phase-to-phase insulation
- ground insulation
- impregnation insulation
Currently, typical insulation solutions for drive motors are generally divided into primary insulation and secondary insulation.
Primary insulation is critical to the safe operation of the motor. It includes magnet wire insulation, slot insulation, phase-to-phase insulation, slot wedge insulation, and impregnating varnish.
Since its introduction, the dual-layer design has been widely adopted in the field of drive motors due to its superior performance.
In recent years, with the rise of oil-cooled motors, single-layer PAI corona-resistant magnet wire has seen increasing use. Its strong resistance to automatic transmission fluid (ATF) and high temperatures makes it particularly suitable for this application.
02. Corona-Resistant Magnet Wire
As drive motors continue to spin faster and the power density of electric drive systems increases, the performance and quality requirements for magnet wire have become increasingly demanding.
Currently, H-class (or higher) corona-resistant magnet wire, enhanced with nano-particle modifications, is widely used in electric vehicle drive motors. The insulation film of this type of wire has evolved from an early three-layer coating to a more advanced dual-layer coating.
The three-layer coating, while once common, has gradually fallen out of favor due to its relatively short service life and weaker adhesion. In 2000, DuPont developed a dual-layer corona-resistant magnet wire that quickly gained traction in the industry. This design features:
- A base layer made of nano-particle-modified polyesterimide with corona-resistant properties
- A top layer of polyamide-imide (PAI) coating
Corona-resistant enameled flat copper wire
As we all know, the choice of materials and technologies constantly evolves with the core application's technical requirements; no single material is a universal solution.
With the rapid advancement of flat wire technology, higher slot fill rates and power densities have led more and more OEMs to choose flat wire motors.
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| Traditional circular conductor stator slot design diagram | Traditional round conductor stator slot profile diagram |
However, the four "R" corners of corona-resistant enameled flat wire have poor coating processability, often resulting in decreased corona resistance and unstable performance in current applications.
Additionally, some recent commercial applications have started using PEEK material extruded onto enameled wire as a replacement for solvent-based dipping coatings.
03.Insulating impregnation resin
Motor stator insulation treatment primarily uses vacuum impregnation resin (VI) and vacuum pressure impregnation resin (VPI). Generally, the base resin is a high-strength, high-heat-resistant modified polyester or polyimide.
Notably, nanoparticle modification technology has emerged, where adding nano inorganic particles improves coating adhesion, heat resistance, and corona resistance.
In recent years, resins compatible with new curing processes-such as energized winding heat curing, UV curing, and rotary drip impregnation-have also gained attention.
Among these, the energized heating process is a highly efficient new method. It takes only a few minutes for the resin to gel after impregnation, and the entire treatment can be completed in about an hour.
This process allows precise control of the coating amount, ensures excellent filling performance, and produces no resin curing waste.
However, the main equipment for energized heating is currently controlled by foreign companies from Germany and Italy, making imported machines expensive. As a result, large-scale domestic adoption has not yet occurred.
04.Flexible composite materials
Currently, mainstream slot insulation, wedge insulation, and phase insulation for non-oil-cooled drive motors mainly use a flexible composite material composed of two layers of polyaramid fiber paper (such as Nomex) combined with a layer of polyimide (PI) film.
This insulation material has an H-class heat resistance rating and is more cost-effective, which has led to its widespread use. However, its corona resistance and resistance to ATF oil are somewhat limited.
With the growing adoption of oil-cooled motors, this oil-sensitive flexible material struggles to keep up, often experiencing delamination that reduces insulation performance.
This creates a vicious cycle: to improve oil resistance, motor designers opt for single-layer, thicker polyaramid fiber paper with better oil resistance;
but this material has poorer electrical properties, so to enhance insulation, the material thickness must be increased. Increasing thickness inevitably reduces power density, which in turn raises the overall manufacturing cost of the motor.
And this issue isn't limited to just oil-cooled motors-if you factor in the increasingly popular 800V electrical systems, these problems become even more severe.
