Comparative Effects of Conductive Ring and Common Mode Choke on Bearing Voltage Characteristics and Electrical Damage in an Actual EV Drive Bearing

Abstract

Motor bearings in electric vehicles (EVs) are prone to electrical discharge damage from self‑generated shaft voltage. Two common mitigation methods—the conductive ring and the common mode choke—are widely used, but their comparative performance under real‑EV's conditions remains unclear. This study investigated bearing voltage and electrical damage across varying speeds under these two methods as well as the unprotected original state. Results showed that both methods reduced the bearing voltage by more than 50% compared with the original state. However, the conductive ring lost effectiveness at high speeds, allowing capacitive voltage buildup and causing coupled mechanical‑electrical damage on bearing surfaces. In contrast, the common mode choke consistently maintained bearing voltage below 1 V across the entire speed range, eliminating electrical discharge damage. This was attributed to their different voltage‑reduction principles: the conductive ring provided an additional discharge path but could not prevent capacitive voltage generation across the lubricant film, whereas the common mode choke suppresses common‑mode voltage at its source, fully preventing capacitive buildup. These findings provided a theoretical basis for selecting an electrical‑damage elimination method for EV drive bearings.