Analyse secondary information on the competition between Westinghouse and Edison to supply electricity to cities

In November and December of 1887, Tesla filed for seven U.S. patents in the field of polyphase AC motors and power transmission. These comprised a complete system of generators, transformers, transmission lines, motors and lighting. So original were the ideas that they were issued without a successful challenge, and would turn out to be the most valuable patents since the telephone.

The Columbian Exposition opened on May 1, 1893. That evening, President Grover Cleveland pushed a button and a hundred thousand incandescent lamps illuminated the fairground's neoclassical buildings. This "City of Light" was the work of Tesla, Westinghouse and twelve new thousand-horsepower AC generation units located in the Hall of Machinery. In the Great Hall of Electricity, the Tesla polyphase system of alternating current power generation and transmission was proudly displayed. For the twenty-seven million people who attended the fair, it was dramatically clear that the 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.

In spite of the bad press, good things were happening for Westinghouse and Tesla. The Westinghouse Corporation won the bid for illuminating The Chicago World's Fair, the first all-electric fair in history. The fair was also called the Columbian Exposition — in celebration of the 400th Anniversary of Columbus discovering America. Up against the newly formed General Electric Company (the company that had taken over the Edison Company), Westinghouse undercut GE's million-dollar bid by half. Much of GE's proposed expenses were tied to the amount copper wire necessary to utilize DC power. Westinghouse's winning bid proposed a more efficient, cost-effective AC system.

Meanwhile, a murderer was about to be executed in the first electric chair at New York's Auburn State Prison. Professor Brown had succeeded in illegally purchasing a used Westinghouse generator in order to demonstrate once and for all the extreme danger of alternating current. The guinea pig was William Kemmler, a convicted ax-murderer, who died horribly on August 6, 1890, in "an awful spectacle, far worse than hanging." The technique was later dubbed "Westinghousing."

It was at this time that Edison launched a propaganda war against alternating current. Westinghouse recalled:

I remember Tom [Edison] telling them that direct current was like a river flowing peacefully to the sea, while alternating current was like a torrent rushing violently over a precipice. Imagine that! Why they even had a professor named Harold Brown who went around talking to audiences... and electrocuting dogs and old horses right on stage, to show how dangerous alternating current was.

With the breakthrough provided by Tesla's patents, a full-scale industrial war erupted. At stake, in effect, was the future of industrial development in the United States, and whether Westinghouse's alternating current or Edison's direct current would be the chosen technology.

An adventurous Pittsburgh industrialist named George Westinghouse, inventor of railroad air brakes, heard about Tesla's invention and thought it could be the missing link in long-distance power transmission. He came to Tesla's lab and made an offer, purchasing the patents for $60,000, which included $5,000 in cash and 150 shares of stock in the Westinghouse Corporation. He also agreed to pay royalties of $2.50 per horsepower of electrical capacity sold. With more inventions in mind, Tesla quickly spent half of his newfound wealth on a new laboratory.

ANALYSE -Identify components and the relationship between them; draw out and relate implications

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 powerstations 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 increasinglypositive affect on the environment, reducing some of the problems mentioned above.Wind power, tidal power, geothermal and wave power all use AC generators withoutthe emission problems of fossil fuels. There are, however, problems with effects on localecosystems 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 3List 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 thepower is used. There are energy losses (mainly as heat) across these distances.

Transmission lines have resistance R=l/A

Using Ohm’s Law, if they carry current thenthere is a voltage drop across them.

V=IR

P=VI=I2Rand power lost,

where = resistivity of wire l = length of wire A = cross-sectional area

SO THE LONGER A CERTAIN TYPE OF WIRE IS, THE GREATER THE RESISTANCE

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

where V= voltage drop across lines = 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 voltagestill 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, I = P/V = 200000/400= 500 A

If the transmission lines have R = 0.5 , 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

If the transmission lines have R = 0.5 , Power loss = P = I2R = 1002 x 0.5 = 5000 W

Less current!

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

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.

Read Jacaranda text p.163-164

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.