Bearings plays an important role in mechanical systems which enables smooth rotational or linear motion by reducing friction between moving components and helping in evenly distribution of loads. They are integral part in wide range of applications such as automotive engines, industrial machinery, aerospace systems, and household appliances. A thorough understanding of bearing behavior and performance is essential for optimizing system efficiency, minimizing wear, and extending the operational lifespan of mechanical assemblies. One significant challenge in modern systems are within the electric motor-driven applications due to electrically induced bearing damage. This phenomenon occurs when stray electrical currents pass through motor bearings causing thermal decomposition of lubricants and physical damage to bearing surfaces. This degradation could affect the performance and lead to premature failure. Therefore, mitigating electrically induced bearing damage is critical for ensuring the durability and reliable operation of electric motors across various industries, including electric vehicles, wind turbines, and aviation systems.
Figure-1 The different types of bearing morphology damage [1]
Electrically induced bearing damages in electric motors arises from various factors such as electromagnetic, electrostatic, and operational factors. One of the major cause is magnetic flux asymmetry, which results in low-frequency shaft voltages and circulating currents capable of damaging bearing surfaces. Electrostatic charge buildup from frictional contact between moving components can also lead to sudden discharges across the bearing and causes localized wear. Further, the use of inverter-driven motors, especially those with high-frequency PWM switching, introduces high-frequency common mode voltages that promote EDM within the bearings. Additionally, breakdown of the lubricant film particularly in elastohydrodynamic regimes creates conductive paths that enable damaging current spikes. Finally, larger and more powerful motors tend to experience greater capacitance and circulating current effects, making them more susceptible to bearing-related failures, especially in high-load, high-speed applications. These factors are listed in the Table-1
Table-1 The factors affecting the electrically induced bearing damage
| Factor |
Description | Impact on Bearings |
| 1. Magnetic Flux Asymmetry |
Caused by uneven magnetic pole distribution or shaft misalignment, generating low-frequency shaft voltages. 
|
Leads to circulating currents that pass through bearings, causing electrical erosion over time. |
| 2. Electrostatic Effects |
Electrostatic charge buildup from tribocontact between dissimilar materials in motion. |
Sudden discharges damage bearing surfaces and degrade lubricant properties. |
| 3. Inverter-Induced Voltages |
High-frequency PWM switching in VFDs induces common mode voltages (CMV) on the shaft. |
Causes capacitive EDM discharges, leading to micro-pitting, lubricant breakdown, and surface damage. |
| 4. Lubricant Film Breakdown |
Thin EHD films act as capacitors; when breakdown voltage is exceeded, high-current discharges (~3A) occur. | Results in micro-cratering, local heating, and rolling contact fatigue. |
| 5. Increased Motor Power/Size | Larger motors have higher capacitance between stator and windings, increasing circulating currents. | Higher stray currents increase EDM activity and bearing wear, especially in heavy-duty applications. |
There are various methods that helps in varying the effectiveness of mitigation of electrically induced bearing damages depending on the type of current. High-frequency shaft grounding brushes are among the most effective which offers a complete suppression of both EDM and rotor-to-ground currents, especially when paired with insulated bearings. Further, ceramic hybrid bearings also stand out for their ability to fully eliminate both EDM and circulating currents. On the other hand, passive filters mainly help to reduce circulating currents by limiting impact on EDM currents and potential drawbacks if not paired with proper grounding methods. Insulated couplings are effective in blocking rotor-to-ground currents but can unintentionally increase EDM currents unless combined with additional mitigation techniques. Meanwhile, using one or two insulated bearings can reduce EDM and rotor-to-ground currents to some extent, though not completely. Overall, a combination of methods is often necessary to address all current paths effectively.
