Application of Static Charge Dissipation to Mitigate Electric Discharge Bearing Currents

Today, the physical cause-and-effect chains of inverter-induced high-frequency bearing currents have been well understood, but little has been known on not only theoretically possible, but also cost-effective mitigation techniques for a certain drive configuration. This paper focuses on the mitigation of discharge bearing currents, which occur predominantly with smaller motors of up to several kilowatts. We present a new mitigation technique where any voltage build-up across the bearing is discharged via static charge dissipation through a parallel path before an electric breakdown inside the bearing occurs. The technique is based on the field emission effect, has ultralow friction and negligible wear, and is very robust toward contamination, when compared with conventional carbon-based brushes.