INSOCOAT® – The SKF solution to prolong bearing life in electric machinery.
What are INSOCOAT bearings? SKF provides electrically insulated bearings, called INSOCOAT, to protect against damages caused by electric currents. These bearings have an electrically insulating coating on the outer ring (VL0241 execution), or on the inner ring (VL2071 execution). The inner ring coating can be made from bore diameters above and including 70 mm. The coating consists of a nominal 100-µm thick aluminium oxide layer and is applied by a unique coating process using plasma-spraying technology.
Electric behavior of INSOCOAT bearings One has to distinguish between DC current and AC current applications. In DC applications the insulating coating acts as a pure resistor where the ohmic resistance R of the aluminum oxide layer is the important quantity. The breakdown voltage of the standard layer is larger than 1000 V DC and the resistance is larger than 50 MΩ, which provides efficient insulation of the bearing. In AC applications, especially in variable speed drives (VSDs) one has to consider the impedance of the ceramic coating. The impedance describes the voltage-current relationship in AC circuits. The value of the impedance depends mainly on two electrical characteristics of the coating: the ohmic resistance and the capacitance. The capacitance should be as small as possible to counteract the effects of high frequency electric currents. The impedance of the aluminium oxide coating can be modelled as a parallel connection of a resistor and a capacitor.