Calculation of the influence of insulated bearings and insulated inner bearing seats on circulating bearing currents in machines of inverter-based drive systems

The high frequency circulating bearing current that may occur in machines of inverter-based drive systems can be reduced or even completely suppressed by use of insulated bearings or insulated inner bearing seats. The influence of the thickness of the insulating coat can be calculated as a function of several machine design parameters. The parameters of the equivalent circuit are derived from an eddy-current model. The calculation considers the transient nature of the current flow. For motors up to 500 kW rated power, a minimum thickness of the insulating coat of 250 mum is required to reduce the circulating bearing currents down to less than 30%