Down to the wire
Supporting e-motor reliability and efficiency through predictive testing for ETF compatibility with magnet wire
In the name of e-motor efficiency, OEMs are focused on increasing power output while reducing size. One of the elements influencing e-motor size is magnet wire, the insulated copper wire used in stator windings. If the magnet wire can be made thinner, the windings take up less space.
Electrified transmission fluid (ETF) used in direct-cooled e-motors must be compatible with every material it contacts. Despite no obvious current issues, increasingly harsh e-motor operating conditions and a widening range of insulating materials – varying in thickness, composition, and thermal stability – mean that future compatibility cannot be assumed.
Afton Chemical understands how ETF additive componentry like detergents, dispersants, and anti-wear agents can affect magnet wire compatibility. Formulating a well-balanced and compatible ETF is a complex, lengthy process that benefits greatly from predictive bench testing.
Without an industry standard magnet wire compatibility test, Afton has developed a robust, in-house screening test for OEM partners, tier suppliers, and oil marketers. This incorporates ETF field performance data gained by analyzing fluid from multiple HEVs and EVs at increasing mileage. Dissolved copper was minimal, even over 330,000km, thanks to good insulation and compatibility. Iron content was low but rose gradually with wear, while water remained below expected levels throughout.
Using these insights, Afton derived a test protocol that ages magnet wire in ETF at 150°C, with specified amounts of water, for 48-120 hours. At each stage, after
visual inspection, the wire undergoes a partial discharge inception voltage (PDIV) and a breakdown voltage (BDV) test. Using bespoke rigs, these tests subject either twisted round magnet wires or rectangular wires clamped side-by-side to increasing voltage steps.
For BDV testing, the lower the voltage at which current passes between two magnet wires, the more the insulation has deteriorated. This is a challenging test to perform on an actual e-motor, as it can cause catastrophic hardware failure. A robust screening test is invaluable.
PDIV is a more sensitive test.
Partial discharge events give an earlier indication of potential insulation problems before actual breakdown occurs; the higher the PDIV, the greater the magnet wire durability. As the smallest insulation defect can trigger a partial discharge, PDIV makes a useful test of insulation quality in fresh magnet wire. A repetitive PDIV test, showing the minimum voltage at which five or more partial discharge events occur in 10 applied voltage impulses, offers the best representation of magnet wire condition.
Any shape or thickness of magnet wire and any type of
insulation can be aged and screened using this in-house test. While each magnet wire performs differently, longer aging – especially with water levels above 2,000ppm – compromises insulation more markedly.
Given the growing range of magnet wires and fluid additive components in use, Afton’s predictive screening test can significantly improve the speed and success of ETF development. Fluid compatibility can have too great an impact on e-motor cost, reliability, and longevity to allow things to literally go down to the wire. aftonchemical.com