Magnet Wire Compatibility Test for Electric Drivetrain Fluid Development 2023-32-0145

New global regulations are being implemented, with the intent of reducing pollutants, greenhouse emissions, and continuing improvements in fuel economy. This has caused OEMs to accelerate vehicle electrification in recent years. One of the key components of the electric drive unit is an electric motor (eMotor) constructed with a significant amount of magnet wire (MW). The MW is composed of a copper wire coated with a polymeric insulation material. Other insulation materials found in the eMotor are slot liner, wedge, phase separator, heat shrinkable materials, varnish, etc. However, MW compatibility with electric transmission fluids (ETFs) is the most important performance criteria as poor compatibility can lead to a decrease in performance, electrical short, and even cause catastrophic eMotor failure.

This paper discusses new insights gained around MW compatibility with various ETFs. The testing procedures described are MW sample preparation, sample aging method, test equipment, and evaluation methods. Adhesion, breakdown voltage, and partial discharge behavior of insulation coating are the main performance criteria. MWs with round and rectangular shapes and various types of coating materials such as polyester, polyamide, polyimide, are investigated. The effect of water concentration in ETF on MW performance upon aging is also investigated. Lubricant’s additive package or formulation chemistry leads to significant MW performance differences. The authors discuss the mechanism of MWs’ deterioration and how to work around lubricant formulation for better MW compatibility.