UW-11-EE-BSc-069,081Experiment No. 04Title:- To investigate basic concepts of alternator, exciter, brushless exciter & pilot exciter.Objective:- Following are some objectives of this experiment To study basics of alternator What is exciter and purpose of exciter Types of exciter like brushless exciter & pilot exciterTheory:-Alternator Analternatoris an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, mostalternatorsuse a rotating magnetic field with a stationary armature. In principle, anyACelectrical generatorcan be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses apermanent magnetfor itsmagnetic fieldis called amagneto. Alternators inpower stationsdriven bysteam turbinesare called turbo-alternators.Principle of Operation A conductor moving relative to a magnetic field develops anelectromotive force (EMF) in it, (Faraday's Law). This emf reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a rotating magnet, called therotor turns within a stationary set of conductors wound in coils on an iron core, called the stator. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn. Therotating magnetic fieldinduces anAC voltagein the stator windings.

Exciter Anelectric generatororelectric motorconsists of a rotorspinning in amagnetic field. The magnetic field may be produced bypermanent magnetsor byfield coils. In the case of a machine with field coils, a current must flow in the coils to generate the field; otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is calledexcitation and device or circuit used is called exciter.

Brushless Exciter Brushless Exciters Rectifiers mount directly on the exciters shaft and rotate at the machine speed. The field exciter for a brushless synchronous motor typically consists of an AC generator with the field windings on its stator, armature windings on its rotor, and with its rotor mounted on the motor shaft. The output of the generator is rectified by solid-state rectifier elements also mounted on the rotor shaft and fed directly to the motor field windings without the need for brushes or slip rings. Because of the proliferation of solid-state power electronic technology, and because the brushless-type motors require less maintenance almost all new synchronous motors are brushless-type. It is possible to adjust the field current on the main machine by controlling the small DC field current of the exciter generator (located on the stator).

Pilot Exciter Apilot exciter is a small ac generator with permanent magnets mounted on the rotor shaft and a 3-phase winding on the stator. It produces the power for the field circuit of the exciter, which in turn controls the field circuit of the main machine. If a pilot exciter is included on the generator shaft, then no external electric power is required.The pilot exciter is an 8 pole, 8,000 rpm, ac generator. The pilot exciter field is mounted on the main generator rotor shaft and is connected in series with the main generator field. The pilot exciter armature is mounted on the main generator stator. The ac output of the pilot exciter is supplied to the voltage regulator, where it is rectified and controlled, and is then impressed on the exciter field winding to furnish excitation for the generatorConclusion:- In this lab we study basic concepts of alternator, exciter, brushless exciter & pilot exciter and concluded that exciters are necessary for alternators and exciters can be internal and external.