Electromagnetic motors

The most common macroscopic actuators are motors. Electromagnetic motors do not operate efficiently at the microscale, but alternative actuation mechanisms become favorable. In conventional MEMS, other types of actuators have been used to generate movement, such as electrostatic actuators, thermal actuators, piezoelectric crystals, SMAs, and magnetic actuators. 

Each train is driven by an electric motor called a linear induction motor. Electromagnetic windings, or coils, on the train generate a magnetic field in which the magnetic poles shift along the train. 

Magnetizing losses, however, as the name implies, are a phenomenon in electromagnetic circuits only. They are absent in a non-magnetic circuit. A motor is made of steel laminates and the housing is also of steel, hence these losses. Some manufacturers, however, use aluminium die-cast stator frames in smaller sizes, where such losses will be less (the bulk of the losses being in the laminations). 

For a lower range of motors, say up to a frame size of 355, the silicon steel normally used for stator and rotor core laminations is universally 0.5-0.65 mm thick and possesses a high content of silicon for achieving better electromagnetic properties. The average content of silicon in such sheets is of the order of 1.3-0.8% and a core loss of roughly 2.3-3.6 W/kg, determined al a flux density of I W[ym and a frequency of 50 Hz. For medium-sized motors, in frames 400-710, silicon steel with a still better content of silicon, of the order of 1.3-1.8% having lower losses of the order of 2.3-1.8 W/kg is prefeired, with a thickness of lamination of 0.5-0.35 mm. 

Protection against overloading This can be achieved by an overcurrent relay. The basic requirement of this relay is its selectivity and ability to discriminate between normal and abnormal operating conditions. Three types of such relays are in use thermal, electromagnetic and static. Thermal relays are employed for motors of up to medium size and electromagnetic and static relays for large LT and all HT motors, as discussed in Section 12.5. 

The attraction and repulsion between the poles on the rotor and stator cause the electromagnet to rotate. Direct-current motors usually need commutators to achieve continuous motion. 

Alternating-current motors are classified as induction motors or synchronous motors. Faraday found that a stationaiy wire in a magnetic field produced no current. However, when the wire continues to move across magnetic lines of force, it produces a continual current. When the motion stops, so does the current. Thus Faraday proved that electric current is only produced from relative motion between the wire and magnetic field. It is called an induced current—an electromagnetic induction effect. 

There are four competing maglev technologies electromagnetic suspension, electrodynamic suspension, linear synchronous motor, and linear induction motor. 

An elementary motor consists of a rotating electromagnet and a fixed permanent magnet. 

Both rotary and mud motor systems use an electromagnetic wireline telemetry to relay the data from the near-bit sub to the mud telemetry sub. 

The new geosteering system offers measurements at the bit (below the mud motor) of inclination, rpm, azimuthal gamma ray, azimuthal resistivity, and bit resistivity as seen in Figure 4-298. The signals are transmitted electromagnetically to the MWD sub located above the mud motor, then relayed to surface with the standard mud pressure transmission system. To summarize, the following is recorded Just above the drill bit ... 

Angular displacement sensed by differential transformers speed indication from electromagnetic sensor on output shaft of drive motor G M G M... 

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