Patent ID: 7446989

Claim:
Device for protecting a bearing of an electrical machine against damaging passage of current, wherein the electrical machine comprises a stator and a rotor pivotally mounted relative to the stator by the bearing, the device comprising: a compensation circuit for producing a compensation current which compensates for a parasitic current arising during operation of the electrical machine and passing through the bearing, the compensation current has a corresponding magnitude as the parasitic current but opposite in phase to the parasitic current; a coupling element for direct or indirect coupling of the compensation current into the bearing; the compensation circuit comprising an artificial star point which prepares a star point voltage at which chase voltages for operation of the electrical machine are found, the artificial star point is formed by three identical impedances; and the compensation circuit also comprising a polarity reversal transformer having a primary side to which the star point voltage is supplied at least in part and a secondary side which produces a voltage opposite in phase to the star point voltage.