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Motor Bearing
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Motor bearing failures due to induced bearing currents and shaft voltages have been recognized for almost a century [6.46]. A shaft voltage arises from various sources in electric motor, such as winding faults, unbalanced supplies, electrostatic effects, magnetized shaft or other machine members, and asymmetries of the magnetic field [6.47]. The shaft voltage can cause the bearing current that flows through the bearings. Several surveys have indicated that 30% of all motor failures operated with 60 Hz sine wave voltage are due to bearing current damage [6.48]. In recent years, there is an increase in motor failures due to bearing current.
Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
A second and more common source of shaft voltage results from an alternating flux linking the motor shaft. This radial flux and associated bearing current as depicted in Fig. 13.15 a may be caused by asymmetries in the magnetic field as depicted in Fig. 13.15b. A net alternating flux links the circuit formed by the rotor shaft, bearings, and frame producing an end-to-end shaft voltage. The shaft voltage can be sufficient to raise the voltage across the bearing lubricant film beyond its withstand voltage-producing arcing and bearing damage [22].
Converter-Based Advanced Diagnostic and Monitoring Technologies for Offshore Wind Turbines
Published in Md. Rabiul Islam, Md. Rakibuzzaman Shah, Mohd Hasan Ali, Emerging Power Converters for Renewable Energy and Electric Vehicles, 2021
Yi Liu, Xi Chen, Md. Rabiul Islam
Since the capacitive voltage of the DFIG bearing is greater than that of the traditional stator-side inverter-fed machines, the bearing of the DFIG will be more likely to suffer the effects of common mode current. One common way in which to ensure a minimal shaft voltage is to use the shaft grounding by means of one or more grounding brushes, which may avoid the damaging current circulating through the bearing to its pedestal [29].
Enhanced predictive torque control of multi-level inverter fed open-end winding induction motor drive based on predictive angle control
Published in EPE Journal, 2020
Kunisetti V. Praveen Kumar, Thippiripati Vinay Kumar
In (1–6), Vao, Vbo and Vco represents pole voltages of VSI-1, Va'o', Vb'o' and Vc'o' represents pole voltages of VSI-2, ΔVaa', ΔVbb' and ΔVcc' represents difference of pole voltages, Vcmv is the common-mode voltage, Vaa', Vbb' and Vcc' are the resultant phase voltages of OEWIM drive. In the proposed OEWIM drive configuration, common-mode currents are absent but there exist CMV between the points OO'. The presence of CMV causes shaft voltage through electrostatic effects. In OEWIM drive, there exist electrostatic coupling between stator and rotor winding, rotor and frame. The developed shaft voltage creates flow of shaft currents and causes premature failure of motor bearings. To abate these limitations and also to increase the life span of OEWIM drive it is necessary to reduce CMV, therefore the third term of objective function in the developed PTC strategy comprises CMV term.