Special Electrical Machines

Topics: Electric motor, Electric motors, Magnetic field Pages: 6 (850 words) Published: December 28, 2012


Electrical machine that converts mechanical energy to electrical energy, converts electrical energy to mechanical energy, or changes alternating current from one voltage level to a different voltage.There are several non traditional machines such as stepper motors, switched reluctance motors, permanent magnet dc machines, resolvers, linear induction machines etc. These machines are finding ever increasing applications, typically in position control systems, robotics, mecatronics, electric vehicles, high speed transportation etc.

* A reluctance motor is a type of synchronous electric motor which induces non-permanent magnetic poles on the ferromagnetic rotor.

* Torque is generated through the phenomenon of magnetic reluctance. Operating principle
* Whenever a piece of ferromagnetic material is located in a magnetic field a force is exerted upon the material tending to bring it into the position of densest portion of the field. * The force tends to align the specimen of the material so that the reluctance of magnetic path passing through the material will be at a minimum. Applications

* Used where regulated speed control is required in applications such as metering pumps and industrial process equipment. * Synthetic fiber manufacturing equipment
* Wrapping and folding machine
* Auxiliary time mechanism
* Synchronized conveyors
* Metering pumps
Advantages of syrm:
* Freedom from permanent magnets,
* Ability to maintain full load torque at zero speed.
A stepper motor is a digital actuator whose input is in the form of programmedenergization of the stator windings and whose output is in the form of discrete angular rotation.

Applications of stepper motor :

* Floppy disc drives
* Quartz watch
* Camera shutter operation
* Small tool application
* Robotics

* It can be driven in open loop without feedback.
* It requires little or no maintenance.
* It is mechanically simple.
* Low efficiency
* Fixed step angle
* Limited power output.
Switched reluctance motors

* It is a doubly salient, single excited motor.
* This means that it has salient poles on
both rotor and the stator.
* But only one member carries winding.
* The rotor has no windings, magnets or
case windings.

* No brushes and requires less maintenance
* Construction is very simple
* Rotor carries no winding
* It requires a position sensor
* Stator phase winding should be capable of carrying magnetizing currents Applications
* Fans
* Washing machines
* Robotic control applications
* Vacuum cleaner
* Future auto mobile applications
Permanent magnet brushless dc motors

The PMBL DC motor is also called electronically commutated motor because the phase windings of PMBL DC motor is energized by using power semiconductor switching circuits.

* Regenerative braking is possible
* Speed can be easily controllable
* It requires a rotor position sensor
* It requires a power semiconductor
switching circuits.

* Power alternators
* Automotive applications
* Computer and Robotics applications
* Textile and Glass industries

permanent magnet synchronous
* Permanent magnet synchronous motor have a cage rotor having rare-earth permanent magnet instead of wound field. * Such motors start like an induction motor when fed from a fixed frequency supply. *

* It runs at constant speed,
* No field winding,
* No field loss,
* Better efficiency.
* Power...
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