Bearing Currents
From destructive transients to system-level reliability
Variable Frequency Drives (VFDs) increase operational flexibility and efficiency, but they inevitably introduce high-frequency voltage transients. These invisible forces seek a path to ground through the weakest points of your machine: the winding insulation and the bearing grease. At ORBITS, we translate complex high-frequency measurements into concrete solutions to stop premature bearing failure and insulation degradation.
Why Analyze Bearing Currents?
Simply replacing a failed bearing does not solve the underlying problem if the driving forceācommon mode voltageāremains present4. Our approach treats the drive-train as a complete system:
Protect your bearings: High-frequency transients charge the parasitic capacitance of the bearing until a destructive discharge occurs through the dielectric grease.
Prevent winding failure: Rapid voltage rise rates (dv/dt) stress motor insulation, leading to accelerated aging and unexpected short circuits.
Eliminate EMC Noise: Stray currents often cause interference in encoders and sensors, leading to unexplained process interruptions.
Our methodology: From problem to solution
Not every leaking current is mitigated in the same way. Through a dedicated measurement campaign, we analyze the statistical distribution of high-frequency transients at the motor terminals to select the proper remedy.
1. Grounding Optimization
Reliability starts with a perfect high-frequency connection. We optimize grounding using specialized materials like EMC brass brushed glands and flat braided litzes to create a low-impedance path for stray currents.
2. High Frequency Chokes
If the data indicates the need, we implement chokes as effective high-frequency attenuators.
Common Mode Chokes: Filter the leaking currents that cause bearing damage.
Differential Mode Chokes: Reduce motor winding stresses by mitigating cable reflections.
3. Advanced Filtering
For critical applications, we advise specific filter topologies:
dv/dt Filters: Limit the voltage rise rate to safe levels, usually around 1 kV/Āµs.
Sine wave filters: Eliminate transients almost entirely by generating a sinusoidal output voltage.
Common mode topology: Essential when bearings are at stake, as only this topology can disable the driving force behind common mode currents.
Tangible results for your operation
A system-level approach to stray currents delivers direct value:
Maximum bearing life: Prevent "fluting" and the premature degradation of lubricating grease.
Operational certainty: Eliminate unexplained trips in encoders and sensors caused by EMI.
Validated investments: We balance implementation costs and space requirements with effectiveness based on hard data.
Stop Destructive Currents Today
Understand the electrical forces within your drive-train before they cause permanent damage.