Electrified Mechanical Contact Arcing Surface Damage and Reduction by Silver Nanoparticle Enhanced Greases

Mechanical components most operate reliably for a variety of electrical applications, including automotive, manufacturing, and renewable energy technologies. Stray or leakage currents have been found to reduce the reliability of electric vehicle mechanical components such as motor bearings, wheel bearings and gears (electrically induced bearing damage). For the current to escape the vehicle it may need to cross the oil films generated due to elastohydrodynamic lubrication in these components. To cross the relatively non-conductive oil film a micro-scale plasma arc can form and damage the surfaces. The damage is in the form of ablated round pits. This work finds that silver nanoparticles provide an effective lubricating grease additive for reducing the arc pitting. This is confirmed via SEM and profilometry measurements of the sample surfaces. The reciprocating experiments also find that the damage concentrates near the ends of the wear track, where the velocity changes direction and film thickness may decrease. Additionally, a theoretical analysis based on elastohydrodynamic lubrication theory confirms the likelihood of arcing in greases without nanoparticles. The analysis also suggests that the inclusion of nanoparticles increases the dielectric breakdown strength of the greases by at least an order of magnitude.