The rotor is a moving component of an

electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...

system in the

electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...

electric generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...

, or

alternator An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.Go ...

. Its

rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...

is due to the interaction between the

windings An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in de ...

and

magnetic fields A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

which produces a

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

around the rotor's axis.Staff. "Understanding

Alternators An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.Gord ...

. What Is an Alternator and How Does It Work." N.p., n.d. Web. 24 November 2014 .

Early development

An early example of

rotation was the first rotary

machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...

built by

Ányos Jedlik Ányos István Jedlik ( hu, Jedlik Ányos István; sk, Štefan Anián Jedlík; in older texts and publications: la, Stephanus Anianus Jedlik; 11 January 1800 – 13 December 1895) was a Hungarian inventor, engineer, physicist, and Bened ...

with

electromagnets An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in t ...

and a

commutator In mathematics, the commutator gives an indication of the extent to which a certain binary operation fails to be commutative. There are different definitions used in group theory and ring theory. Group theory The commutator of two elements, a ...

, in 1826-27. Other pioneers in the field of

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...

include

Hippolyte Pixii Hippolyte Pixii (1808–1835) was an instrument maker from Paris, France. In 1832 he built an early form of alternating current electrical generator, based on the principle of electromagnetic induction discovered by Michael Faraday. Mohamed A. El- ...

who built an

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

generator in 1832, and William Ritchie's construction of an electromagnetic generator with four rotor coils, a

and

brushes A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped durin ...

, also in 1832. Development quickly included more useful applications such as

Moritz Hermann Jacobi Moritz Hermann or Boris Semyonovich (von) Jacobi (russian: Борис Семёнович Якоби; 21 September 1801, Potsdam – 10 March 1874, Saint Petersburg) was a Prussian and Russian Imperial engineer and physicist of Jewish descent. Jac ...

's motor that could lift 10 to 12 pounds with a speed of one foot per second, about 15

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...

s of mechanical power in 1834. In 1835, Francis Watkins describes an electrical "toy" he created; he is generally regarded as one of the first to understand the interchangeability of motor and

generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...

Type and construction of rotors

Induction (asynchronous) motors, generators and

alternators An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.Gord ...

(

synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...

) have an electromagnetic system consisting of a

stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...

and rotor. There are two designs for the rotor in an induction motor: squirrel cage and wound. In generators and alternators, the rotor designs are

salient pole A field coil is an electromagnet used to generate a magnetic field in an electro-magnetic machine, typically a rotating electrical machine such as a motor or generator. It consists of a coil of wire through which a current flows. In a rotating ...

cylindrical A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...

Squirrel-cage rotor

The

squirrel-cage rotor A squirrel-cage rotor is the rotating part of the common squirrel-cage induction motor. It consists of a cylinder of steel laminations, with aluminum or copper conductors embedded in its surface. In operation, the non-rotating stator winding i ...

consists of laminated

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

in the core with evenly spaced bars of copper or

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

placed axially around the periphery, permanently shorted at the ends by the end rings.Parekh, Rakesh. 2003. AC Induction Fundamentals 30 November 2014 Web. 29 November 2014.http://ww1.microchip.com/downloads/en/AppNotes/00887a.pdf This simple and rugged construction makes it the favorite for most applications. The assembly has a twist: the bars are slanted, or skewed, to reduce magnetic hum and slot harmonics and to reduce the tendency of locking. Housed in the stator, the rotor and stator teeth can lock when they are in equal number and the magnets position themselves equally apart, opposing rotation in both directions. Bearings at each end mount the rotor in its housing, with one end of the shaft protruding to allow the attachment of the load. In some motors, there is an extension at the non-driving end for

speed sensors This is a list of sensors sorted by sensor type. Acoustic, sound, vibration *Geophone *Hydrophone *Microphone * Pickup *Seismometer *Sound locator Automotive *Air flow meter *AFR sensor *Air–fuel ratio meter *Blind spot monitor *Crankshaf ...

or other electronic controls. The generated torque forces motion through the rotor to the load.

Wound rotor

The wound rotor is a cylindrical core made of steel lamination with slots to hold the wires for its 3-phase windings which are evenly spaced at 120 electrical degrees apart and connected in a 'Y' configuration. The rotor winding terminals are brought out and attached to the three slips rings with brushes, on the shaft of the rotor.University of Taxila. Three Induction Motor. 2012. Web. 28 November 2014 http://web.uettaxila.edu.pk/CMS/SP2012/etEMbs/notes%5CThree%20Phase%20Induction%20Motors.pdf Brushes on the slip rings allow for external three-phase resistors to be connected in series to the rotor windings for providing speed control. The external resistances become a part of the rotor circuit to produce a large

when starting the motor. As the motor speeds up, the resistances can be reduced to zero. Innenpolmaschine

Salient pole rotor

A Salient Pole Rotor is built upon a stack of "star shaped" steel laminations, typically with 2 or 3 or 4 or 6, maybe even 18 or more "radial prongs" sticking out from the middle, each of which is wound with copper wire to form a discrete outward facing electromagnet pole. The inward facing ends of each prong are magnetically grounded into the common central body of the rotor. The poles are supplied by direct current or magnetized by

permanent magnets A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

.Cardell, J. PRINCIPLES OF OPERATION OF SYNCHRONOUS MACHINE (n.d.). Web.http://www.science.smith.edu/~jcardell/Courses/EGR325/Readings/SynchGenWiley.pdf The armature with a three-phase winding is on the stator where voltage is induced.

Direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...

(DC), from an external exciter or from a

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

bridge mounted on the rotor shaft, produces a magnetic field and energizes the rotating field windings an