Download alan nguyen`s motor and generators textbook (sample)

Alan Nguyen [email protected] 0478 009 301 ALAN NGUYEN’S
MOTOR AND GENERATORS TEXTBOOK
(SAMPLE)
Alan Nguyen [email protected] 0478 009 301 1. Edison vs Westinghouse
Students:
•
Analyse secondary information on the competition between Westinghouse and Edison to supply
electricity to cities.
§ Action Verbs: Analyse
BOSTES Glossary of Key Words:
Analyse: Identify components and the relationship between them; draw out and relate implications.
Identify: Recognise and name.
Describe: Provide characteristics and features.
Steps used to answering an “analyse” question:
§
Identify the key ideas and how they relate to one another.
§
In this case identify the difference between the technology used by Edison and
Westinghouse.
Describe the effect of these key ideas and advantages and disadvantages.
§
§ Thomas Edison
o
Thomas Edison in 1878 was the first person to set up a business to supply electricity. His
system was based on the DC SYSTEM OF ELECTRICITY.
o
His system was successful and began developing DC motors and other appliances which
used DC electricity.
§ George Westinghouse
o
Nikola Tesla worked for Edison and was the inventor of the AC system of electricity in 1883.
Edison did not develop this idea.
Alan Nguyen o
[email protected] 0478 009 301 George Westinghouse bought the patent for the AC system of electricity and created his
own company which competed against Edison’s DC system.
§ The Smear Campaign
o
Edison claimed that AC technology was UNSAFE to use.
o
Edison had a public demonstration where he executed a dozen farm animals in West
Orange, New Jersey.
o
Edison also promoted the use of AC voltage in the electric chair when the New York
Legislature passed a bill establishing electrocution as the state’s method of execution. Shortly
after, electrocution is being referred to as being “Westinghoused”.
o
Edison also legally prevented Westinghouse from implementing AC technology into his
inventions.
o
Even with Edison’s limitless resources used to publicly defame the Westinghouse in the end
AC technology was found to be superior.
§ The Niagra Falls Competition
o
Edison and Westinghouse competed to build a power plant using the power of Niagra Falls
to supply electricity to distant cities. WESTINGHOUSE WAS THE WINNER BECAUSE THE
AC SYSTEM WAS MORE EFFICIENT.
1. AC voltage can be readily transformed by transformers which made electricity
transmission over long distances more efficient. AC electricity has much less energy
losses compared to DC electricity.
2. Maintaining DC generators were extremely expensive. At high rotation split-ring
commutators sparked and needed frequent maintenance and replacement.
Alan Nguyen [email protected] 0478 009 301 § Exercise Examples
1. Westinghouse and Edison were both in competition to supply electricity to cities. Which of the
following reasons described why Westinghouse’s electricity generation prevailed?
(a) Westinghouse’s AC power supply could efficiently travel over long distances as AC
transformation was easy and cheap, hence power stations could be placed outside the city.
(b) Westinghouse’s DC power supply could be transformed, and DC was seen to be much safer
than AC.
(c) Westinghouse’s AC power supply allowed for a faster transmission and was not seen to be
dangerous.
(d) Westinghouse’s DC power supply model succeeded in supply power 35 km away from the
hydroelectric power plant at Niagra Falls and hence was a superior form of power
generation.
2. Both DC and AC systems were used in early electricity generation and distribution systems in the
United States. Competition between the supporters of AC and DC systems raged for over twenty
years.
Who championed AC systems during this period of intense competition?
(a) Edison.
(b) Westinghouse.
(c) Faraday.
(d) Oersted.
Alan Nguyen [email protected] 0478 009 301 3. [2004 HSC Q24] In the late nineteenth century Westinghouse and Edison were in competition to
supply electricity to cities. This competition led Edison holding public demonstrations to promote
his system of DC generation over Westinghouse’s system of AC generation.
Propose arguments that Westinghouse could have used to convince authorities of the
advantages of his AC system of generation and distribution of electrical energy over Edison’s DC
supply. [6 marks]
Alan Nguyen [email protected] 0478 009 301 Notes from the marking centre
Most candidates demonstrated a familiarity with the competition between Westinghouse and Edison
and were able to show an understanding of the differences between AC and DC generation and
distribution.
A majority of responses proposed arguments that Westinghouse could have used to promote AC
over DC with the better responses focused on both generation and distribution. A significant number
of responses proposed arguments for distribution of AC but did not deal with generation at all.
Most candidates displayed a sound understanding of the function of the transformer in the process of
distribution of AC but few candidates could explain the advantages of the AC generator over the DC
generator.
Weaker responses gave a list of features and/or advantages of AC but were unable to link the
advantages to the features to form arguments.
MARKING GUIDELINES
Criteria
•
Marks
Well presented arguments discussing the advantages of Westinghouse’s AC
system of generation and distribution
•
Refers to both generation and distribution over longer distances
•
Outlines advantages of AC over DC
•
Makes references to generation and distribution
•
Provides some reasons to support argument
•
Outlines advantages of AC and DC
•
Makes well presented arguments for generation or distribution
•
Provides some reasons to support argument
•
Answer gives attributes of AC but no reference to advantages over DC
•
Supporting statements are lists only OR
•
Features of AC discussed with brief outline but no clear evidence of
understanding why an advantage
5–6
4
3
1–2
Alan Nguyen [email protected] 0478 009 301 § Transformers in Society
Students learn to:
•
Explain the role of transformers in electricity sub-stations.
•
Gather and analyse secondary information to discuss the need for transformers in the transfer of
electrical energy from a power station to its point of use.
§ The Electrical Power Distribution System
o
Below is a diagram of the electrical distribution system. Label the relevant parts.
(Source: Students Guide to HSC Physics)
(i) Electrical Power Stations
o
This is the beginning of the electrical transmission process where AC generators produce AC
electricity. These electrical power stations are located hundreds of kilometres from the final
consumer.
o
Because transmission lines have a finite resistance (R) what must happen to minimise energy
loss?
Alan Nguyen o
[email protected] 0478 009 301 Therefore, the role of transformers in electrical power stations is to step up voltage in
order to minimise energy loss. The voltages are approximately 300 kV to 500 kV.
(ii) Electricity Sub-stations
o
As seen in the diagram above these transmission lines will carry this high voltage AC
electricity to an electricity sub-station. It is not feasible and safe to carry this voltage directly
to the final consumer.
o
Therefore, we must slowly reduce the AC voltage when it comes closer to the final user.
o
What is the role of transformers at electricity sub-stations?
(iii) Distribution Transformer
o
A distribution transformer provides the final voltage transformation in the electrical power
distribution system, stepping down the voltage to the level used by the consumer. This is
typically the 240 V AC in Australia.
o
They are typically located on street pylons as seen in the diagram below.
(Source: http://upload.wikimedia.org/wikipedia/commons/3/33/240v_transformer_-_geograph.org.uk__1062014.jpg)
Alan Nguyen [email protected] 0478 009 301