AEGIS® Bearing Protection - Why Shaft Grounding?


Bearing Currents


Electric Motors Operating on Line Voltage

Balanced Voltage Condition
Balanced Voltage Condition Diagram
  • Electric induction motors are designed for operation on 3 phase sine wave power - either 50 or 60 Hz.
  • The input power is balanced in frequency, phase (120 degree phase shift) and in amplitude.
  • Common mode voltage - the sum of the 3 phases always equals zero volts when properly balanced

NOTE: Bearing protection generally not needed except for large frame motors.

Electric Motors Operated by Variable Frequency Drives (VFD)

Unbalanced Voltage Condition
Unbalanced Voltage Condition Diagram
  • When operated by VFD, the power to the motor is a series of positive and negative pulses instead of a smooth sine wave.
  • The input voltage is never blanced because the voltage is either 0 volts, positive, or negative with rapid switching between pulses in all three phases.
  • The common mode voltage is usually a "square wave" or "6 step" voltage wave form

InfoBearing protection needed to mitigate electrical discharge machining (EDM) damage in bearings.