Afunction generatoris usually a piece of electronic test equipment or software used to generate different types of electrical wave forms over a wide range of frequencies.U.S.NRCimage of a modern steam turbine generator (STG).Inelectricity generation, agenerator[1]is a device that convertsmotive power(mechanical energy) intoelectrical powerfor use in an externalcircuit. Sources of mechanical energy includesteam turbines,gas turbines,water turbines,internal combustion enginesand even handcranks. The first electromagnetic generator, the Faraday disk, was invented in 1831 by British scientistMichael Faraday. Generators provide nearly all of the power forelectric power grids.

The reverse conversion of electrical energy into mechanical energy is done by anelectric motor, and motors and generators have many similarities. Many motors can be mechanically driven to generate electricity and frequently make acceptable manual generators.

Electromagnetic generators fall into one of two broad categories, dynamos and alternators.

Dynamosgenerate pulsingdirect currentthrough the use of acommutatorAlternatorsgeneratealternating currentMechanically a generator consists of a rotating part and a stationary part

Rotor: The rotating part of anelectrical machineStator: The stationary part of an electrical machine, which surrounds the rotorOne of these parts generates a magnetic field, the other has a wire winding in which the changing field induces an electric current

Field windingor field magnets (PMs): Themagnetic fieldproducing component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either wire windings calledfield coilsorpermanent magnets. Electrically excited generators includes anexcitation systemto control the field winding flux. A generator usingpermanent magnets(PMs) is sometimes called amagneto, orpermanent magnet synchronous generators(PMSMs).Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current, which provides power to an external circuit.The armature can be on either the rotor or the stator, depending on the design, with the field coil or magnet on the other part.

Before the connection betweenmagnetismandelectricitywas discovered,electrostatic generatorswere invented. They operated onelectrostaticprinciples, by using movingelectrically chargedbelts, plates, and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms:electrostatic inductionor thetriboelectric effect. Such generators generated very highvoltageand lowcurrent. Because of their inefficiency and the difficulty ofinsulatingmachines that produced very high voltages, electrostatic generators had low power ratings, and were never used for generation of commercially significant quantities of electric power. Their only practical applications were to power earlyX-ray tubes, and later in some atomicparticle accelerators.

A coil of wire rotating in a magnetic field produces a current which changes direction with each 180° rotation, analternating current(AC). However many early uses of electricity requireddirect current(DC). In the first practical electric generators, calleddynamos, the AC was converted into DC with acommutator, a set of rotating switch contacts on the armature shaft. The commutator reversed the connection of the armature winding to the circuit every 180° rotation of the shaft, creating a pulsing DC current. One of the first dynamos was built byHippolyte Pixiiin 1832.

Thedynamowas the first electrical generator capable of delivering power for industry. TheWoolrich Electrical Generatorof 1844, now inThinktank, Birmingham Science Museum, is the earliest electrical generator used in an industrial process. It was used by the firm ofElkingtonsfor commercialelectroplating.