Investigations on bearing currents in converter-fed electrical motors

Abstract

As shown in [6], the issue of current flowing through a motor bearing is a system-related topic. Different aspects have to be taken into account to identify countermeasures to avoid or dampen the current flow. Up until now, it is not possible to define clear limits where the changes in the bearing raceways lead to the so called corrugation and with this to a possible bearing failure. This paper shows the latest results that were obtained with the investigation schematic presented in [6]. New results in the area of field experience with the so called "Bearing Current Sensor" (BCS) will be discussed. Additional results in the area of parameter tests, which take into account the dependency of temperature, speed, voltage as well as the type of lubricant grease, are shown.

Response of electrical drives to gear and bearing faults — Diagnosis under transient and steady state conditions

“…This last part is the main focus of this work, although analysis and techniques developed based on he use of vibrations signals are addressed, since they can possibly be used for other signals. For the case of bearing faults especially, when bearing currents may be the cause of the fault, alternatives also include measuring the bearing voltage and/or current as has been proposed in [2], [3] and by others.…”

“…For bearing faults caused by bearing current, the work of Busse et al [24] in 1997 provided an early overview of the effects of a PWM drive on the bearings; effects that result in fluting, where metal is displaced (EDM Electric Discharge Machining) and where lubricant breaks down due to high du/dt. This work was followed and expanded in [25], [8] [3].…”

“…They used Finite Elements to determine the ladder circuit parameters to determine the common mode shaft currents and voltage, predict discharges and bearing damage. Tischmacher et al [3] recently presented work where they combined electrical measurements of bearing currents with measurements of mechanical vibrations.…”

Advances in Electrical Machine, Power Electronic, and Drive Condition Monitoring and Fault Detection: State of the Art

“…Indeed, this latter issue has been the motivation of a number of recent works that have focused on the influence of converters on the bearing damage. For instance, [46] studies the effects of bearing currents on different quantities of converter-driven IMs. In [47], the same group of authors develops a complete study that demonstrates that it is possible to calculate in advance the bearing currents in inverted-fed IM to estimate the lifetime of the bearings.…”

On inverter induced bearing currents, bearing maintenance scheduling, and prognosis

“…The impact of the vibrational excitation on the number of bearing voltage breakdowns has been explicitly reported on in [28] and the breakdown to occur in groups of the vibrational excitation frequency at low vibration frequencies.…”