Capacitance calculation of cylindrical roller bearings – Modeling of cylinder-raceway- and cylinder-flange-contact

Jan Manteufel

Summary

In order to circumvent the emission of climate-damaging greenhouse gas, the combustion of fossil fuels is being replaced in many areas by electric alternatives. In most applications, electric motors are used for this purpose. The frequency inverter of electric motors induces electrical currents that place additional strain on all components and especially damage bearings. To model the electric behavior of these bearings and predict damage patterns, it is necessary to develop calculation models. Previous research into the capacitive properties of rolling bearings has been limited to ball bearings and point contact.

In applications where large radial loads are applied cylindrical roller bearings are predominantly used. Therefore, we develop calculation methods for the electrical capacitance of cylindrical roller bearings consisting of raceway-contact and flange-contact. The calculation method for raceway-contacts and flange-contacts considers geometric conditions, operating conditions of the bearing and assumes hydrodynamic lubrication.

To evaluate the calculation model radial and axial load, rotation speed and temperature were varied on a test bench. Initially, measurements were taken of cylindrical roller bearings, with steel flanges substituted for plastic flanges on the outer and inner ring. This was done to calculate the capacitance of the running surface contact in isolation. Conversely, the capacitance of NU-208 and NJ-208 cylindrical roller bearings is measured to evaluate the flange-contact model under various conditions and the influence of axial load.

The simulated capacitance value of the isolated raceway-contact and those of the NU bearings fit well to the measured values. The agreement for the NJ bearing results is marginally lower.