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INTERNATIONAL UNIVERSITY - HO CHI MINH CITY VIETNAM NATIONAL UNIVERSITY

PHYSICS 3 REPORT

ALTERNATING CURRENT GENERATORS

Student name: Hà Tiến Đạt Student ID: ITITIU19095 Lecturer: Assoc. Prof. Phan Bảo Ngọc Ho Chi Minh City, June 2020

I. INTRODUCTION An alternating current generator or AC generator is a device that is used to converts mechanical energy into electrical energy in the form of alternating current. The generated electrical energy is in the form of an alternating current sinusoidal output waveform. The mechanical energy is usually supplied by steam turbines, gas turbines, hydroelectric power engine and combustion engines. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. There are various types of alternating current generators are utilized today; however, they all perform the same basic function. This report focuses on the fundamentals of an AC generator in terms of components, mechanism, practical advantages and limitations.

Figure 1: The horizontal turbines spin on Lignum Vitae water-lubricated bearings.

II. COMPONENTS The main components of an AC generator often are field , armature, prime mover, rotor, stator and slip rings. To understand how a generator operates, the function of each component of the generator must first be understood. 1. Field The field consists of coils of conductors that receive a voltage from the source and produce magnetic flux. The magnetic flux in the field cuts the armature to produce magnetic flux. This voltage is the output voltage of the AC generator.

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Figure 2: Basic AC generator components

2. Armature The part of an AC generator in which the voltage is produced is known as an armature. This component primarily consists of coils of wire that are large enough to carry the full-load current of the generator. 3. Prime Mover The component used to drive the AC generator is known as a prime mover. The prime mover could either be a diesel engine, a steam turbine, or a motor. 4. Rotor The rotating component of the generator is known as a rotor. The generator’s prime mover drives the rotor. Based on the type of generator, this component may either be the armature or the field. The rotor will be the armature if the voltage output is generated there; the rotor will be the field if the field excitation is applied there. 5. Stator The stator of an AC generator is the stationary part. As the rotor, this component may be the armature or the field, depending on the type of generator. The stator will be the armature if the voltage output is generated there; the stator will be the field if the field excitation is applied there. 6. Slip Rings Slip rings are electrical connections that are used to transfer power to and from the rotor of an AC generator. They are typically designed to conduct the flow of current from a stationary device to a rotating one. III. MECHANISM AC generators work on the principle of Faraday’s law of electromagnetic induction which states that electromotive force -EMF or voltage – is generated in a current-carrying conductor 2

that cuts a uniform magnetic field. This can either be achieved by rotating a conducting coil in a static magnetic field, or by rotating the magnetic field that contains the stationary conductor. The preferred arrangement is to keep the coil stationary because it is easier to draw induced alternating current from a stationary armature coil than a rotating coil. Consider a coil of N turns and area A being rotated at a constant angular velocity θ in a magnetic field of flux density B, its axis being perpendicular to the field (Figure 3). The e.m.f ℰ generated between the ends of the coil is:

ℰ = B A N ω sin θ (V)

Figure 3: A rotating coil in an uniform

Figure 4: Fleming’s Right Hand Rule

magnetic field

When the armature rotates between the poles of the magnet upon an axis perpendicular to the magnetic field, the flux linkage of the armature changes continuously. Due to this, an emf is induced in the armature. This produces an electric current that flows through the galvanometer and the slip rings and brushes. The galvanometer swings between positive and negative values. This indicates that there is an alternating current flowing through the galvanometer. The direction of the induced current can be identified using Fleming’s Right Hand Rule (Figure 4).

IV. ADVANTAGES AND LIMITATIONS OF AC GENERATORS 1. Advantages Following are a few advantages of AC generators over DC generators: 

For the most part, an AC generator comes with a simple design since it only contains a single moving part, the rotor. As a result, AC generators are easier to maintain, cheaper to own, quieter with how it operates and lasts longer compared to DC ones.

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For optimal use, it is important for a DC generator to produce a voltage at a certain level. The AC generator allows you to convert the current to another voltage using a transformer. In fact, transformers are compatible with AC, but not with DC.

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AC generators do not require commutators and brushes, because they can use a rotating magnet inside a fixed armature. This is not possible in DC generators. This reduces the wear and tear of the AC generator’s parts. 2. Limitations Despite their benefits, AC generators do have some limitations to consider.

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There is a higher level of insulation due to the massive voltages required to supply a fixed amount of power. As a result, there is the challenge in the safe handling of AC generators. Working with AC may pose some difficulties and risks, as compared to those of DC generators.

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It is worth noting that AC power may be susceptible to sparks and overheating due to its production of high currents. Such phenomenon results in electric shock and fires. These fires are detrimental to the properties and lives of electrical engineers.

V. REFERENCE 

http://webdirectory.hcmiu.edu.vn/Portals/25/userfiles/4627/Ngoc/Lecture15.pdf

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https://en.wikipedia.org/wiki/Alternator#Principle_of_operation

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https://auto.howstuffworks.com/alternator4.htm

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http://www.cmm.gov.mo/eng/exhibition/secondfloor/MoreInfo/2_4_1_ACGenerator.html

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