Effect of current discharges across MTM and MPR tribological contacts with negatively charged MTM ball and MPR roller

Stray currents in wind turbines have been associated with the premature failure of bearings through lubricant degradation and wear mechanisms. Tribological contacts under electrical current flow can be described as electrolytic cells, where the interacting bodies act as cathode and anode. This study investigated how cathodic polarity and current densities in tribological contacts impact tribofilm formation and wear mechanisms. Applied voltages higher than the dielectric strength of the oil enabled current flow across the tribological contact. The tribofilm predominately formed on the anode which attracted dissociated anions from additives and increased with current density, while the cathode remained unprotected. The damage on the cathode took the form of micro-pitting, wavelets and at low current densities, sub-surface WECs surrounded by WEAs. • Tribofilms are generated predominantly on the positively charged body (anode). • The wear track of the cathode is affected by micro-pitting and wavelet wear. • The coefficient of friction increased with the current density. • WECs formed only with cathodic polarity and at low current density.