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Polyphase power systems This worksheet and all related files are licensed under the Creative Commons Attribution License, version 1.0. To view a copy of this license, visit http://creativecommons.org/licenses/by/1.0/, or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. The terms and conditions of this license allow for free copying, distribution, and/or modification of all licensed works by the general public. Resources and methods for learning about these
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  Polyphase power systems This worksheet and all related files are licensed under the Creative Commons Attribution License,version 1.0. To view a copy of this license, visit http://creativecommons.org/licenses/by/1.0/, or send aletter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. The terms andconditions of this license allow for free copying, distribution, and/or modification of all licensed works bythe general public.Resources and methods for learning about these subjects (list a few here, in preparation for yourresearch):1  Questions Question 1What is polyphase electric power, and how does it differ from single-phase power?file 02197Question 2All large electric power generating systems in the world today produce three phase power, rather thansingle phase power. Explain why this is so, in terms of advantages of distribution and use.file 01888Question 3How is polyphase (especially three-phase) electric power generated? Single-phase power is easy tounderstand, but how do we create three-phase AC voltage?file 004162  Question 4Suppose a set of three neon light bulbs were connected to an alternator with three sets of windingslabeled A , B , and C : AABBCC NS ABCABC The schematic diagram for this alternator/lamp system is as follows: Alternator A B CB AC If the alternator spins fast enough (clockwise, as shown), the AC voltage induced in its windings willbe enough to cause the neon lamps to ”blink” (neon bulbs have very fast reaction times and thus cannotmaintain a glow for very long without current, unlike incandescent lamps which operate on the principle of a glowing-hot metal filament). Most likely this blinking will be too fast to discern with the naked eye.However, if we were to videorecord the blinking and play back the recording at a slow speed, we shouldbe able to see the sequence of light flashes. Determine the apparent ”direction” of the lamps’ blinking (fromright-to-left or from left-to-right), and relate that sequence to the voltage peaks of each alternator coil pair.file 02198Question 5What is meant by the term phase rotation sequence , in a polyphase electrical system?file 004173  Question 6This is a schematic diagram of a Y-connected  three-phase generator (with the rotor winding shown): Rotor windingABC Three-phase Y alternator  . . . to a three-phase load How much AC voltage will appear between any two of the lines ( V   AB , V   BC  , or V   AC  ) if each stator coilinside the alternator outputs 277 volts? Draw a phasor diagram showing how the phase (winding) and linevoltages relate.file 02199Question 7This is a schematic diagram of a Delta-connected  three-phase generator (with the rotor winding shown): Rotor windingABC. . . to a three-phase load Three-phase Delta alternator  How much AC current will each of the lines ( I  A , I  B , or I  C  ) conduct to a load (not shown) if each statorcoil inside the alternator outputs 17 amps of current?file 02200Question 8Suppose the electrical power supplied to a commercial building is labeled as ”208/120 volt”. What doesthis label mean, exactly? Relate this description to a schematic diagram.file 004204
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