Transcript H9 H11 H12 H13 H14 1. Motors use the effect of forces

Analyse secondary information on the competition between
Westinghouse and Edison to supply electricity to cities
ANALYSE -Identify components and the relationship between them; draw out and relate implications
In November
and December
1887, Teslanamed
filed for
seven Westinghouse,
U.S. patents in the field
An adventurous
Pittsburghofindustrialist
George
of polyphase
motors
power
transmission.
These
comprised
complete
inventor ofAC
railroad
airand
brakes,
heard
about Tesla's
invention
and athought
it
system
generators,
transformers,
transmission
lines,
motors and
So
couldofbe
the missing
link in long-distance
power
transmission.
Helighting.
came to
original
were
issued without
a successful
challenge,
Tesla's
labthe
andideas
madethat
an they
offer,were
purchasing
the patents
for $60,000,
which and
With
the out
breakthrough
provided
byshares
Tesla's
patents,
athe
full-scale
industrial
would
turn
to beinthe
most
valuable
patents
sinceinthe
telephone.
included
$5,000
cash
and
150
of
stock
Westinghouse
It war
was erupted.
at this time
that Edison
launched
a propaganda
war against
alternating
At
stake,
in effect,
was
the
futureofof$2.50
industrial
development
Corporation.
He
also
agreed
to
pay
royalties
per
horsepower
of
current.
Westinghouse
recalled:
inelectrical
the United
States,sold.
andWith
whether
alternating
currentspent
or
capacity
moreWestinghouse's
inventions in mind,
Tesla quickly
Edison's
direct
current
wouldtelling
beathe
chosen
I remember
Tom
[Edison]
them
thattechnology.
direct current was like a river
half
of his
newfound
wealth
on
laboratory.
Meanwhile,
a murderer
was
about
to new
be executed
in the first electric chair at
flowing peacefully to the sea, while alternating current was like a torrent
New
York's
Auburn
State good
Prison.
Professor
Brown had for
succeeded in illegally
In
spite
of the
bad press,
things
were
happening
rushing
violently
over a precipice.
Imagine
that! WhyWestinghouse
they even hadand
a
purchasing
a
used
Westinghouse
generator
in
order
to
demonstrate
once
and
Tesla.professor
The Westinghouse
Corporation
wonwent
the bid
for illuminating
The Chicago
named Harold
Brown
who
around
talking
to audiences...
The
Columbian
Exposition
opened
on
May
1,
1893.
That
evening,
President
Grover
for
all
the
extreme
danger
of
alternating
current.
The
guinea
pig
was
William
World's
Fair,
the first all-electric
fair
history.right
Theon
fairstage,
was also
called
the
and
electrocuting
dogs
and
oldinhorses
to show
how
Cleveland
pushed
a button
and
a hundred
thousand
incandescent
lamps
illuminated
Kemmler,
a
convicted
ax-murderer,
who
died
horribly
on
August
6,
1890,
in
Columbian
Exposition
—
in
celebration
of
the
400th
Anniversary
of
Columbus
dangerous
alternating
current
was.
the
neoclassical
buildings.
This "City
of technique
Light" waswas
the later
work dubbed
of Tesla,
"anfairground's
awful spectacle,
than
The
discovering
America.far
Upworse
against
thehanging."
newly formed
General Electric
Company
Westinghouse
and twelve new thousand-horsepower AC generation units located in the
"Westinghousing."
(the
company that had taken over the Edison Company), Westinghouse
Hall of Machinery. In the Great Hall of Electricity, the Tesla polyphase system of
undercut GE's million-dollar bid by half. Much of GE's proposed expenses were
alternating current power generation and transmission was proudly displayed. For the
tied to the amount copper wire necessary to utilize DC power. Westinghouse's
twenty-seven million people who attended the fair, it was dramatically clear that the
winning bid proposed a more efficient, cost-effective AC system.
power of the future was AC. From that point forward more than 80 percent of all the
electrical devices ordered in the United States were for alternating current.
source: http://www.pbs.org/tesla/ll/ll_warcur.html
Assess the effects of the development of AC
generators on society and the environment
It was thought that electricity would allow people more leisure time by reducing the amount of
physical labour. Physical tasks have been made easier, through the use of washing machines,
vacuum cleaners etc. Refrigeration and cooking are easier and more efficient. There are advantages
in information processing and leisure due to computing and multimedia entertainment. However,
instead of more leisure time we have less unskilled jobs and more unemployment.
AC generators also brought the prospect of decentralisation, as power supplies were no longer
restricted to large cities. This brought power benefits to country areas. However, the main
decentralisation has not been to country areas but to the outer suburbs where the middle class can
afford larger houses on larger blocks.
AC generators have affected the environment in a number of ways. Fossil fuel power
stations cause air pollution (due to particles, nitrogen oxides and sulfur oxides),
thermal (heat) pollution and acid rain. Carbon dioxide contributes to the greenhouse effect
The continued development of ‘clean’ power stations will prove to have an increasingly
positive affect on the environment, reducing some of the problems mentioned above.
Wind power, tidal power, geothermal and wave power all use AC generators without
the emission problems of fossil fuels. There are, however, problems with effects on local
ecosystems including biotic and abiotic factors. Nuclear power uses AC generators but
has obvious problems with mining and operational safety and waste disposal. Fusion power
is still in the development stage and has problems with containment of the fusion.
Question 3
List two detrimental impacts of fossil fuel
generators on the environment.
3
2 marks
Fossil fuel generators produce greenhouse gases such as
carbon
dioxide which hinder the Earth radiating heat out of the atmosphere.
This causes the ‘greenhouse effect’, in which the Earth slowly heats
up which can ruin ecosystems.
Fossil fuel generators produce carbon dioxide which can combine
with water to produce carbonic acid (acid rain). Sulfur dioxides can
also cause acid rain. This acid rain can kill organisms on the Earth
such as fish in rivers where acid concentrations reach higher than
acceptable levels.
Discuss the energy losses that occur as
energy is fed through transmission lines
from the generator to the consumer
There is usually a substantial distance from power stations to the cities where the
power is used. There are energy losses (mainly as heat) across these distances.
Transmission lines have resistance
R=r l/A
where
r = resistivity of wire
l = length of wire
A = cross-sectional area
SO THE LONGER A CERTAIN TYPE OF WIRE IS, THE GREATER THE RESISTANCE
Using Ohm’s Law, if they carry current then
there is a voltage drop across them.
V= IR
SO FOR A GIVEN VALUE OF CURRENT FLOWING, MORE RESISTANCE MEANS MORE VOLTAGE DROP
WHICH MEANS LESS VOLTAGE AVAILABLE AT THE END OF THE LINE
and power lost,
P= VI=I2R
where
V = voltage drop across lines
I = current in lines
R = total resistance of lines
Discuss the energy losses that occur as
energy is fed through transmission lines
from the generator to the consumer
To reduce this lost energy and ensure that there is adequate voltage
still available after transmission across large distances, voltage is ‘stepped up’
to a higher voltage (using a transformer) prior to transmission.
If a power station generates 200 kW of power at 400 V,
If the transmission lines have R = 0.5 W,
I = P/V = 200000/400= 500 A
Power loss = P = I2R = 5002 x 0.5 = 125000 W
What if the voltage is stepped up to 2000 V before transmission?
If a power station generates 200 kW of power at 2000 V,
I = P/V = 200000/2000= 100 A
Less current!
If the transmission lines have R = 0.5 W,
Power loss = P = I2R = 1002 x 0.5 = 5000 W
A lot less power loss!
The above examples indicate the importance of transformers. They enable electricity to be distributed across
large distances without wasting as much energy. This means that locations of cities are not restricted to
locations of coal mines, hydroelectricity etc. and that power station pollution is not dumped on nearby cities.
Voltages are then stepped down at substations and pole transformers for domestic use
Gather and analyse information to identify how transmission lines are:
–
insulated from supporting structures
–
protected from lightning strikes
Read Jacaranda text p.163-164
Because the voltage of each phase is different from each other, and different from ground
(defined as zero voltage) all phase wires should be insulated from each other and from ground.
The insulation is accomplished by keeping enough distance (air) between the phases and ground.
The higher the voltage, the more distance is needed. The phase wires are connected to the tower
by an insulator or insulator string which is often made of glass, ceramics or synthetic rubber.
Electrical energy is normally transmitted through AC (Alternating Current) systems having a
frequency of 50 or 60 Hertz. An electrical circuit consists of three phases, mostly called A, B and
C. Phase B follows phase A on a distance of one third of a cycle, phase C follows phase B on a
distance of one third of a cycle, and the same distance is again between phase C and phase A.
In the top, the tower has on both sides so called shield or ground wires. These wires protect the
line from lightning strikes and are usually grounded in every tower.
Below the ground wires on both sides of the tower the bundled phase wires (a bundle of two for
each phase) are suspended from the tower by insulator strings. The phases of each circuit are
attached on different sides of the tower.
Question 2
Transmission towers carry lines with a potential difference of 330 kV.
(a) Explain how these transmission lines are insulated from the towers.
(b) Explain how these transmission lines are protected from lightning strikes.
2
(a) 1 mark
Porcelain attachments separate the tower from the line.
These are largely unaffected by weather and are good insulators
(b) 1 mark
A lightning wire is strung above the transmission line.
This lightning wire intercepts any strikes and safely earths them.