Background

Modern electric drives, including inverter-fed motors, electric vehicles, and wind turbines, operate with high-frequency voltages that can generate harmful currents within rolling elements. This electrical stress can lead to a distinct failure mechanism known as fluting. Therefore, understanding how electrical conditions influence their lifespan is essential for developing effective diagnostic and mitigation strategies. This study takes a purely experimental approach to investigating electro-erosive fluting in inverter-driven rolling bearings exposed to controlled DC bias. The research systematically examines the effect of different voltage levels on bearing fatigue life, aiming to establish a voltage-life (V-N) curve like the stress-life (S-N) curve commonly used in mechanical fatigue analysis. By precisely applying predefined DC voltage offsets and tracking the number of operating hours until measurable damage occurs, this study builds upon the principles of the classical Wöhler S-N curve. The resulting V-N characteristic enables the classification of voltage regimes into distinct failure progression stages – early, medium, and late – offering a structured, data-driven basis for predictive maintenance protocols and the design of more electrically resilient bearing systems.

Target and task description

The main objective is to establish the voltage-life (V-N) relationship by testing bearings under different electrical conditions while meticulously monitoring key parameters including voltage, current, rotational speed, temperature, and vibration. The successful candidate will be responsible for the following tasks:

• Experimental Setup and Execution: Design, set up, and execute experiments to apply controlled DC voltage offsets to inverter-driven rolling bearings.
• Data Acquisition: Implement and manage a data acquisition system to continuously monitor voltage, current, speed, temperature, and vibration signals during the experiments.
• Damage Monitoring: Define and implement a methodology to detect and quantify bearing damage (fluting) over time, correlating it with the applied electrical conditions and operating hours.
• Data Analysis: Analyse the collected data to identify wear trends, determine voltage thresholds associated with early, moderate, and late (or no) failure, and apply appropriate statistical methods to assess the reliability of the findings.
• Correlation Establishment: Establish meaningful correlations between the applied electrical conditions and the observed mechanical damage (fluting).

Requirements

Basic knowledge of electromagnetic field, high frequency modelling. Knowledge of numerical simulation methods and first experience with JMAG simulation software is helpful. Having passed the lecture “Motor development” would be beneficial.