MOTOR AND GENERATORS TEXTBOOK

Transcription

1 ALAN NGUYEN S MOTOR AND GENERATORS TEXTBOOK (SAMPLE)

2 1. Edisn vs Westinghuse Students: Analyse secndary infrmatin n the cmpetitin between Westinghuse and Edisn t supply electricity t cities. Actin Verbs: Analyse BOSTES Glssary f Key Wrds: Analyse: Identify cmpnents and the relatinship between them; draw ut and relate implicatins. Identify: Recgnise and name. Describe: Prvide characteristics and features. Steps used t answering an analyse questin: Identify the key ideas and hw they relate t ne anther. In this case identify the difference between the technlgy used by Edisn and Westinghuse. Describe the effect f these key ideas and advantages and disadvantages. Thmas Edisn Thmas Edisn in 1878 was the first persn t set up a business t supply electricity. His system was based n the DC SYSTEM OF ELECTRICITY. His system was successful and began develping DC mtrs and ther appliances which used DC electricity. Gerge Westinghuse Nikla Tesla wrked fr Edisn and was the inventr f the AC system f electricity in Edisn did nt develp this idea.

3 Gerge Westinghuse bught the patent fr the AC system f electricity and created his wn cmpany which cmpeted against Edisn s DC system. The Smear Campaign Edisn claimed that AC technlgy was UNSAFE t use. Edisn had a public demnstratin where he executed a dzen farm animals in West Orange, New Jersey. Edisn als prmted the use f AC vltage in the electric chair when the New Yrk Legislature passed a bill establishing electrcutin as the state s methd f executin. Shrtly after, electrcutin is being referred t as being Westinghused. Edisn als legally prevented Westinghuse frm implementing AC technlgy int his inventins. Even with Edisn s limitless resurces used t publicly defame the Westinghuse in the end AC technlgy was fund t be superir. The Niagra Falls Cmpetitin Edisn and Westinghuse cmpeted t build a pwer plant using the pwer f Niagra Falls t supply electricity t distant cities. WESTINGHOUSE WAS THE WINNER BECAUSE THE AC SYSTEM WAS MORE EFFICIENT. 1. AC vltage can be readily transfrmed by transfrmers which made electricity transmissin ver lng distances mre efficient. AC electricity has much less energy lsses cmpared t DC electricity. 2. Maintaining DC generatrs were extremely expensive. At high rtatin split-ring cmmutatrs sparked and needed frequent maintenance and replacement.

4 Exercise Examples 1. Westinghuse and Edisn were bth in cmpetitin t supply electricity t cities. Which f the fllwing reasns described why Westinghuse s electricity generatin prevailed? (a) Westinghuse s AC pwer supply culd efficiently travel ver lng distances as AC transfrmatin was easy and cheap, hence pwer statins culd be placed utside the city. (b) Westinghuse s DC pwer supply culd be transfrmed, and DC was seen t be much safer than AC. (c) Westinghuse s AC pwer supply allwed fr a faster transmissin and was nt seen t be dangerus. (d) Westinghuse s DC pwer supply mdel succeeded in supply pwer 35 km away frm the hydrelectric pwer plant at Niagra Falls and hence was a superir frm f pwer generatin. 2. Bth DC and AC systems were used in early electricity generatin and distributin systems in the United States. Cmpetitin between the supprters f AC and DC systems raged fr ver twenty years. Wh champined AC systems during this perid f intense cmpetitin? (a) Edisn. (b) Westinghuse. (c) Faraday. (d) Oersted.

5 3. [2004 HSC Q24] In the late nineteenth century Westinghuse and Edisn were in cmpetitin t supply electricity t cities. This cmpetitin led Edisn hlding public demnstratins t prmte his system f DC generatin ver Westinghuse s system f AC generatin. Prpse arguments that Westinghuse culd have used t cnvince authrities f the advantages f his AC system f generatin and distributin f electrical energy ver Edisn s DC supply. [6 marks]

6 Ntes frm the marking centre Mst candidates demnstrated a familiarity with the cmpetitin between Westinghuse and Edisn and were able t shw an understanding f the differences between AC and DC generatin and distributin. A majrity f respnses prpsed arguments that Westinghuse culd have used t prmte AC ver DC with the better respnses fcused n bth generatin and distributin. A significant number f respnses prpsed arguments fr distributin f AC but did nt deal with generatin at all. Mst candidates displayed a sund understanding f the functin f the transfrmer in the prcess f distributin f AC but few candidates culd explain the advantages f the AC generatr ver the DC generatr. Weaker respnses gave a list f features and/r advantages f AC but were unable t link the advantages t the features t frm arguments. MARKING GUIDELINES Criteria Well presented arguments discussing the advantages f Westinghuse s AC system f generatin and distributin Refers t bth generatin and distributin ver lnger distances Marks 5 6 Outlines advantages f AC ver DC Makes references t generatin and distributin 4 Prvides sme reasns t supprt argument Outlines advantages f AC and DC Makes well presented arguments fr generatin r distributin 3 Prvides sme reasns t supprt argument Answer gives attributes f AC but n reference t advantages ver DC Supprting statements are lists nly OR 1 2 Features f AC discussed with brief utline but n clear evidence f understanding why an advantage

7 Transfrmers in Sciety Students learn t: Explain the rle f transfrmers in electricity sub-statins. Gather and analyse secndary infrmatin t discuss the need fr transfrmers in the transfer f electrical energy frm a pwer statin t its pint f use. The Electrical Pwer Distributin System Belw is a diagram f the electrical distributin system. Label the relevant parts. (Surce: Students Guide t HSC Physics) (i) Electrical Pwer Statins This is the beginning f the electrical transmissin prcess where AC generatrs prduce AC electricity. These electrical pwer statins are lcated hundreds f kilmetres frm the final cnsumer. Because transmissin lines have a finite resistance (R) what must happen t minimise energy lss?

8 Therefre, the rle f transfrmers in electrical pwer statins is t step up vltage in rder t minimise energy lss. The vltages are apprximately 300 kv t 500 kv. (ii) Electricity Sub-statins As seen in the diagram abve these transmissin lines will carry this high vltage AC electricity t an electricity sub-statin. It is nt feasible and safe t carry this vltage directly t the final cnsumer. Therefre, we must slwly reduce the AC vltage when it cmes clser t the final user. What is the rle f transfrmers at electricity sub-statins? (iii) Distributin Transfrmer A distributin transfrmer prvides the final vltage transfrmatin in the electrical pwer distributin system, stepping dwn the vltage t the level used by the cnsumer. This is typically the 240 V AC in Australia. They are typically lcated n street pylns as seen in the diagram belw. (Surce: _ jpg)

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