AC Generators AC GENERATOR THEORYAC GENERATOR THEORYAC generators are widely used to produce AC voltage. To understand how thesegenerators operate, the basic theory of operation must first be understood.EO 1.2 Given the speed of rotation and number of poles,CALCULATE the frequency output of an AC generator.EO 1.3 LIST the three losses found in an AC generator.EO 1.4 Given the prime mover input and generator output,DETERMINE the efficiency of an AC generator.TheoryofOperationA simple AC generator consists of:Figure 3 Simple AC Generator(a) a strong magnetic field, (b)conductors that rotate through thatmagnetic field, and (c) a means bywhich a continuous connection isprovided to the conductors as theyare rotating (Figure 3). The strongmagnetic field is produced by acurrent flow through the field coilof the rotor. The field coil in therotor receives excitation throughthe use of slip rings and brushes.Two brushes are spring-held incontact with the slip rings toprovide the continuous connectionbetween the field coil and theexternal excitation circuit. The armature is contained within the windings of the stator and isconnected to the output. Each time the rotor makes one complete revolution, one complete cycleof AC is developed. A generator has many turns of wire wound into the slots of the rotor.The magnitude of AC voltage generated by an AC generator is dependent on the field strengthand speed of the rotor. Most generators are operated at a constant speed; therefore, the generatedvoltage depends on field excitation, or strength.Rev. 0 Page 5 ES-10
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