generators

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Electrical Engineering

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Feb 20, 2024

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1 Alternating Current Generators Chanse S. Bartram College of Aeronautics, Embry-Riddle Aeronautical University- Worldwide AMNT 260: Aircraft Electrical System Theory Dr. James Stockton September 08, 2021

2 Alternating Current Generators In 1831 Michael Faraday discovered the power of electromagnetic induction. He discovered that changes in the magnetic environment of a coil of wire will produce a voltage (“Basic AC”, N.D). Prior to that discovery scientists speculated whether a magnetic field could create current flow in conductors. This discovery led to the development of modern-day generators ( Aviation maintenance, 2018 ). Basics of Alternating Current Generators Alternating current generators produce power by the interaction between conductors, and a magnetic field. When that conductor moves through the magnetic field an electromagnetic force occurs. A basic alternator goes through five phases ( Aviation maintenance, 2018 ). In this cycle the voltage progresses to a peak positive potential, peak negative potential, and returns to zero. The cycle is comprised of two portions including the positive alteration, and the negative alteration. That voltage depending on the type of generator exits via sliprings, also known as brushes ( Aviation maintenance, 2018 ). Generally, there are two ways generation of power can occur. The rotating armature generator produces power by the armature rotating in between the stator cutting through magnetic fields and producing voltage. That voltage exits via sliprings to the external circuit (“Basic AC,” N.D). The rotating field generator performs via power from an external source supplying the windings on the rotor. As the rotor turns it produces a rotating magnetic field that acts upon the windings in the stator producing voltage. The voltage travels out via fixed terminals (“Basic AC,” N.D). Types of A/C Generators There are a variety of alternators used in aviation. The classification of these alternators differs by the number of phases, the type of stator and rotor used, and method of excitation. A

3 single-phase generator has a single circuit where output voltage generates, and a single-phase winding on the stator ( Aviation maintenance, 2018 ). Two phase generators differ from the single phase in that there are two or more single phase winding on the stator. Those winding are electrically separate from each other and placed in such a way that the voltage is 90 degrees out of phase from the other winding ( Aviation maintenance, 2018 ). The three-phase generator is the most common in aviation. There are three single phase windings positioned in a way on the stator, that 120 degrees of difference in phase exists between the other two windings (“Basic AC”, N.D). Generator Control Units The generator control unit performs several functions within an electrical system. All of which are related to regulation, protection, and sensing of the system. The unit in all its functions provides voltage protection, and system control ( Aviation maintenance, 2018 ). The unit samples output voltage and compares it to the system in which it is pushing power. If there is a variance in the output voltage & the system, the unit sends power back to the excitation control and adjusts ( Aviation maintenance, 2018 ). When that difference in voltage occurs, the system will prevent the connection to the bus, preventing damage. The GCU works in conjunction with excitation system, supplying more or less current to modulate the magnetic fields, regulating the voltage output. Permanent Magnetic Generators Permanent magnetic generators differ from electromagnets in that they do not require current to generate an electromagnetic field. Generally, AC generators have field windings on the inner rotor receiving current through brushes. As this rotor turns, the field windings induce an electromagnetic force on the stator windings producing power (Rucker, 2005). The permanent

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4 magnetic generator differs by replacing the field windings on the rotor with permanent magnets. This makes possible through just rotation of the rotor to produce an electromagnetic force (Rucker, 2005). The magnets rotating inside the stator produce a current in the stator windings. Generators can contain both electromagnets, and permanent magnets that work in conjunction with each other. Conclusion Alternating current generators have many variations. The number of phases, different types of excitation, and varying level of power output. Whether they use Permanent magnetic generators, or excitation through brushes, this class of generators has shown continuing promise in the industry of aviation. These generators have replaced a large majority of direct current generators in the industry due to efficiency, weight, and overall compatibility with aircraft systems. This technology far improves the capabilities of aircraft.

5 References Aviation Maintenance Technician Handbook - General FAA-H-8083-30A Aviation Supplies & Academics Inc – 2018 “BASIC AC ELECTRICAL GENERATORS.” Www.brown.edu , www.brown.edu/Departments/Engineering/Courses/ENGN1931F/AC_Electrical_Generat ors_ASOPE.pdf . Rucker, J. E. (2005). Design and Analysis of a Permanent Magnet Generator for Naval Applications . https://core.ac.uk/. Retrieved from https://core.ac.uk/download/pdf/36704409.pdf .