Phenomena appearing in oil film of bearings in induction motors supplied from PWM inverters

The paper discusses the electrical properties of ball bearings in induction motors. The investigations showed that the electrical properties of bearings depend on the lubricant temperature, speed, load and value of bearings voltage. Experiments have been performed on specially modified motors (insulated bearings), so that rotors were electrically separated from stators. The tests of electrical properties of bearings were carried out at three kinds of bearing voltage: DC voltage; AC sinusoidal voltage; and AC voltage resulting from additional side-effects created in structural components of a PWM inverter fed motor. The paper presents the results of experiments.