Experimental Analysis of Dropdown Control with Active Magnetic Bearing in a Suspended Rotor Test Rig

The rotor suspended by active magnetic bearing (AMB) requires protection from touchdown bearings (TDB) when it drops down due to failure or high transient loads. In horizonal and vertical rotors, the dropdown behaviors are different. In order to change the rotor dropdown orbit to reduce friction loss, a dropdown control method is proposed where a bias electromagnetic force (EMF) brought by AMB control is applied during dropdown process. A universal suspended rotor test rig has been built that enables both horizonal and vertical dropdown experiment. The experimental analyses are developed and the dropdown behaviors in different situations are presented, where the main conclusion is as follow: when bias EMF that has reasonable value is opposite to gravity direction of the rotor, the friction and wear loss of TDB can be obviously reduced, which can effectively improve the safety and service life of TDB. If bias EMF is applied in any other direction, it is either detrimental to TDB or not as effective as the opposite direction of gravity.