Bearing Current and Shaft Voltage in Electrical Machines: A Comprehensive Research Review

Abstract

The reliability assessment of electric machines plays a very critical role in today’s engineering world. The reliability assessment requires a good understanding of electric motors and their root causes. Electric machines mostly fail due to mechanical problems and bearing damage is the main source of this. The bearings can be damaged by mechanical, electrical, and thermal stresses. Among all stresses, the researcher should give special attention to the electrical one, which is bearing current and shaft voltage. This review paper introduces a comprehensive study of bearing current and shaft voltage for inverter-fed electric machines. This study aims to discuss several motor failure processes, as well as the sources and definitions of bearing current and shaft voltage. The different kinds of bearing currents are addressed and the parasitic capacitances, which are the key component to describe bearing current, are determined. Several measurement approaches of bearing current will be discussed. Furthermore, modeling of bearing current will be covered together with the machine’s parasitic capacitances. Moreover, the different bearing current mitigation techniques, as described in many papers, will be thoroughly addressed. The use of rewound multiphase machines for mitigation of bearing current will be proposed and compared to a three-phase machine. Finally, various pulse width modulation techniques of multiphase systems that reduce bearing current and shaft voltage will be investigated, and the findings described in the literature will be summarized for all techniques.

Analysis of capacitive discharges in motor bearings under different operation conditions

“…Based on the description of EDM currents presented in Refs [28,29], the capacitive discharge consists of the following phases:…”

“…It is worth mentioning that the variation of DA throughout the test duration was not considered in this test; therefore, the discharge occurrence frequency expressed in Figure 8 is the average frequency. The chosen test intervals and limit values for each parameter were set based on the literature [19,20,[28][29][30], as well as the test bench limitations. For example, the voltage test values were initially set to (5…30) V. Then, the results showed rare occurrence of discharge for voltage levels above 20 V; this justifies not taking these values into consideration in the following results.…”

Comparison of 2L + 2M and 6L SVPWM for Five-Phase Inverter to Reduce Common Mode Voltage

“…Some of these methods increase the time calculation of switching. A modified SVPWM approach that reduces the CMV compared with conventional SVPWM was developed in [42]. However, the modified method increased the THD of both the phase voltage and current.…”