Understanding Shaft Currents in VFD-Driven Motors

This ABB technical guide explains how variable frequency drives (VFDs) can induce harmful shaft currents in electric motors, the risks they pose to bearings, and the protective measures available to prevent costly downtime.

Key Points

  • VFDs generate common-mode voltages that can create shaft currents in motors.
  • ABB explains measurement techniques and key warning signs of bearing current issues.
  • Selection of the right protection method depends on motor size, application, and coupling type.
  • Shaft currents damage bearings, reducing motor reliability and lifespan.
  • The guide outlines multiple mitigation methods, including insulated bearings and shaft grounding solutions.
  • Proper design and preventive measures can significantly reduce maintenance costs.