Bearing Currents – Understanding and solving high-frequency stray currents in electric motors

Modern electric motors are increasingly controlled by variable frequency drives, introducing new electrical phenomena that are often not visible with classical measurements. High-frequency stray currents can travel through a motor’s shaft and bearings, potentially causing severe damage in a short time. In this course you will learn how these currents originate, how they behave, and why they are often misinterpreted as purely mechanical issues. The focus is on understanding the interaction between the motor, drive, cabling, and grounding. You will be provided with a practical framework to detect these issues purposefully and solve them sustainably.

1. Interaction Between Motor and Drive

You will gain insight into how modern variable frequency drives influence the electrical behavior of electric motors. The course explains how common-mode voltages and fast switching frequencies arise — phenomena that often form the basis for the occurrence of high-frequency stray currents.

2. What Are Stray Currents and How Do They Originate?

This section covers the formation and behavior of bearing currents in electric motors. You will learn how these currents travel through the shaft and bearings and what damage patterns they cause. It also explains why such damage is often hard to detect at an early stage.

3. Detection and Measurement of Stray Currents

Recognizing stray currents requires a different perspective than classical maintenance measurements. You will learn which measurement principles and techniques are used to identify their presence. Emphasis is placed on correct interpretation of measurement results and avoiding incorrect conclusions.

4. Effective Measures and Solutions

Not every solution works in every situation. In this part you will learn which technical interventions are possible — such as grounding, filters, modified cabling, or special bearings. You will gain insight into how these measures work, along with useful tips to optimize EMC topology and extend machine service life.

Learning objectives

This training is suitable for maintenance specialists who want to understand and solve high-frequency machine problems when classical mechanical explanations fall short.

The course is particularly relevant for those working with / on:

• Electric motors driven by variable frequency drives
• Pumps, fans, and compressors
• Conveyor systems and production lines
• Drive lines with long motor cables
• Installations where bearing damage occurs prematurely or repeatedly

Approach

BEMAS and Orbits organize four individual training courses that can be followed on their own, or together as a coherent, practice-oriented learning package focused on machine diagnosis and reliable maintenance. The learning path combines early detection, deep analysis, structural understanding, and targeted mitigation. By following the courses step by step, you build an integrated understanding of machine behavior — from cause to solution — leading to better maintenance decisions, higher reliability, and less unplanned downtime. For those seeking maximum practical impact, it is recommended to follow all four courses.

Further information about these courses can be found on the respective dedicated pages.

• Machine Health Scan: Early detection of machine degradation
   
• Machine Fault Analysis – uncovering the root cause of machine failure
   
• Machine Motion Analysis – Controlling unexpected machine vibrations