Page 97 - Steam Turbines Design, Applications, and Rerating

78 Chapter Three

Figure 3.29 Basic active magnetic bearing configura-
tion. (MTI, Inc., Latham, N.Y.)

Both the stator and the journal are constructed of stacked, ferro-
magnetic laminations. Laminated materials reduce eddy currents that
would cause power loss and degrade bearing performance.
The basic operation in an active magnetic bearing is:
2
current
Magnetic force ∝
air gap
While this is a nonlinear relationship, linearization of bearing dynam-
ics is achievable if the air gap is large, relative to the journal excursion,
and the steady-state current supplied through each sector is large,
compared to the dynamic control current. This steady-state or bias cur-
2
rent produces the I R loss, the primary power loss in an active mag-