Electrically Insulated Bearings Protect Machines

NKE Austria offers electrically insulated rolling bearings in standard sizes with outer ring diameters between 80 and 400mm. Special sizes are available upon request. The electrically insulated bearings are available in different design variations. Bearings with an oxide ceramic insulating layer have a minimum breakdown voltage of 1kV AC or DC. The insulation coating is applied to the outer rings by a plasma spraying method. For smaller bearings, rolling elements made of oxide ceramic (silicon nitride) can be used. The load ratings, boundary dimensions and tolerances of the electrically insulated bearings are identical to those of standard bearings, and therefore completely interchangeable with conventional bearings. Electrically insulated bearings protect against bearing damage caused by electro-corrosion, and therefore improve reliability of electrical machines compared with conventional bearings. For modern electrical machines with high degrees of performance, and demanding reliability and service life, equipment failures by electro-corrosion could cause significant problems. Under unfavourable operating conditions, bearings in electrical machines could be damaged by the passage of electrical currents. Such a passage of current can be caused by faulty or damaged insulation of the bearing shields or an ineffective earth connection of the machine. The appearance and the degree of electrical damage of bearings depend on the individual operating conditions, for example the actual effective voltage. The machinery user may notice this process only by symptoms such as increased running noise or vibrations, until the bearing fails prematurely. The appearance of the damage may vary from visually detectable single craters and to fluting with discolorations around the affected areas. In most cases, the effective electrical insulation of the end shields entails extra costs and efforts. For existing designs, the improvement of electrical insulation could be technically complicated. One answer is to use electrically insulated rolling bearings, which are integrated with an efficient electrical insulation that prevents the passage of electric currents through the bearings. Consequently, the additional electrical insulation of the end covers can be omitted. Besides saving costs, the means for the user an increase in reliability and service life of the machines.