Radial magnetic bearing

Rotor diameters, or quasi journals, include dimensions ranging from 14 mm (0.55 in.) to 600 mm (24 in.). Similarly, the load range accommodated by radial magnetic bearings is 0.3 N (0.007 lb) to 200 kN (45,000 lb). Rotational speeds range from a virtual standstill to as high as 800,000 rpm. 

Figure 5-42. Radial magnetic bearing with a view of the circumferential electromagnets. (Courtesy of MafhTrem Corp.)...

Figure 5-43. Radial magnetic bearing rotor sleeve. (Courtesy ofMafi-Trench Corp.)...

Magnetic Bearing, Fig.1 Radial magnetic-bearing configuration... 

FIG. B-7B Radial magnetic bearing rotor and stator. (Source Revolve.)... 

This chapter discusses the most popular features and controls that are critical to turboexpander operations. Among those discussed are magnetic bearings, squeeze film dampers, radial fit bolts, valve arrangements for FCC expanders, FCC expander load shedding technology, and surge detection and avoidance. 

In a radial active magnetic bearing, the rotor is held in position by electromagnets located on the stator (Figure 6-3). The rotor-to-stator position is constantly monitored by sensors that communicate with the electronic control system. If the rotor deviates from its position, the control system adjusts the current flow to the electromagnets to return the rotor back to its proper position. 

The magnetic bearing is made up of a series of electromagnets located circumferentially around the shaft to form the radial bearing. The electromagnets (Figure 5-42) are laminated to limit the eddy current losses. The shaft must be fitted with a laminated sleeve (see Figure 5-43) for the... 

Actuators and sensors. This represents closed-loop control of one axis on a radial bearing. To provide support in more than one direction, magnetic poles are oriented about the periphery of a radial hearing. This is shown in Fig. B-7A, along with a photograph of a radial magnetic hearing rotor and stator (Fig. B-7B). 

An active magnetic axial bearing consists of two stators and a rotor disk (Figure 6-4). A sensor located at the end of the shaft monitors and maintains the rotor position between the two stators. The principle of operation is the same for both axial and radial bearings any deviation from the normal position of the rotor is communicated to the electronic control system, which adjusts the electric current going to the electromagnets to correct the rotor position. 

Contactless bearing, in which the shaft is held in position by magnetic forces in the axial and radial directions (CIRP Dictionary of Production Engineering 2004). 

Turbo-machine Design Parameters Net Shaft Power Rotational Speed LP Compressor Stages HP Compressor Stages Turbme Tip Speed Bearings 298 MW 3600 RPM 14 19 322 m/sec Active magnetic, 3 radial, 1 thrust... 

Single shaft radial flow turbine scalability to 200 kWe is possible based on existing turbomachinery. While past NASA closed loop Brayton hardware was low power (up to 15 kWe), Capstone Turbines has developed a prototype for a 200 kWe unit (Reference 2) and Hamilton Sundstrand built and tested the 200 kWe Integrated Power unit (IPU) for the Air Force (Reference 3). The Capstone unit has gas foil bearings and a permanent magnet alternator, similar to that envisioned for Prometheus. 

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