Finally, electromagnetic bearings involve complex design problems to ensure that the heavy spindle, with its high inertia, does not fall and damage the magnetic bearing when power is shut off or momentarily discontinued. Therefore, a noninterrupted power supply is required to operate the magnetic bearing, even at no load or at shutdown conditions of the system. In order to secure safe operation in case of accidental power failure or support of the rotor during shutdown of the machine, an auxiliary bearing is required. Rolling-element bearings with large clearance are commonly used. During the use of such auxiliary bearings, severe. | load capacity of the bearing is limited by the available electrical power supply from the amplifier. e. Finally electromagnetic bearings involve complex design problems to ensure that the heavy spindle with its high inertia does not fall and damage the magnetic bearing when power is shut off or momentarily discontinued. Therefore a noninterrupted power supply is required to operate the magnetic bearing even at no load or at shutdown conditions of the system. In order to secure safe operation in case of accidental power failure or support of the rotor during shutdown of the machine an auxiliary bearing is required. Rolling-element bearings with large clearance are commonly used. During the use of such auxiliary bearings severe impact can result in premature rollingelement failure. ROLLING-ELEMENT BEARINGS Rolling-element bearings such as ball cylindrical or conical rolling bearings are the bearings most widely used in machinery. Rolling bearings are often referred to as antifriction bearings. The most important advantage of rolling-element bearings is the low friction and wear of rolling relative to that of sliding. Rolling bearings are used in a wide range of applications. When selected and applied properly they can operate successfully over a long period of time. Rolling friction is lower than sliding friction therefore rolling bearings have lower friction energy losses as well as reduced wear in comparison to sliding bearings. Nevertheless the designer must keep in mind that the life of a rollingelement bearing can be limited due to fatigue. Ball bearings involve a point contact between the balls and the races resulting in high stresses at the contact often named hertz stresses after Hertz 1881 who analyzed for the first time the stress distribution in a point contact. When a rolling-element bearing is in operation the rolling contacts are subjected to alternating stresses at high frequency that result in metal fatigue. At high speed the centrifugal forces of
