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Exercise 39 Pre-text discussion.
What kind of energy sources do you know? What are the most dangerous of them and the most environmentally friendly? What do you think is the best way for any country to break the addiction to foreign oil? What alternative energy sources are the cleanest, cheapest and most reliable? What alternative energy sources can be used for powering homes, businesses, and automobiles? What energy source provides more than half of the Ukraine’s electricity supply? What do you know about the development of semiconductor materials that convert sunlight directly to electricity?
POWER SUPPLY SYSTEM
(1)Nowadays technical progress including the progress in railway engineering is unthinkable without the proper power supply system. In fact, one can hardly find a sphere where power is not required. Most of the power required is obtained mainly from two sources. The first way is burning fossil fuels (coal, natural gas, oil) to produce heat for internal and external combustion engines. Many of these engines will actuate generators producing electricity. The second way is converting power of steam and water into electricity.
One of the biggest consumers of energy is railway network system. And most of the energy is consumed by locomotives. There are four major types of locomotives used: Steam locomotive, Electric locomotive, Diesel locomotive, and Magnetic levitation locomotive1.
(2) Steam locomotivesburn coal, wood, or other materials, converting water into steam. Before the middle of the 20th century electric and diesel locomotives began replacing steam locomotives. Some advantages that electric and diesel locomotives offered were much more fuel efficiency and less pollution. Because of heat losses and incomplete combustion of fuel, thermal efficiency of steam locomotives was rarely more than 6 percent.
(3) Electric locomotives are externally supplied with electric power, either through an overhead pickup2 or through a third rail. Though the cost of electrifying a track is rather high, electric trains and locomotives are significantly cheaper to run. Almost all high-speed train systems use electric locomotives. These locomotives can use either direct or alternating current. While recently designed electrified railway systems operate on alternating current, many existing direct current systems are still in use. Electric locomotives are usually very powerful, fast and long-lived machines.
(4) Diesel locomotives may be divided into four groups: Diesel-electric, Diesel-mechanical, Diesel-hydraulic3 and Gas turbine-electric locomotives.
Diesel-electric locomotives were introduced in the United States in 1924, and have become the most widely used type of locomotives. The modern diesel-electric locomotive is a self-contained4, electrically propelled5 unit. In the 1970s British Rail (BR) developed a high-speed diesel electric locomotive called the High Speed Train, which was capable of reaching speeds of up to 284km/h, although in service it only reached a speed of 200km/h.
Diesel-mechanical locomotives are less powerful than electric and diesel-electric systems, they are only used with the smallest trains.
Diesel-hydraulic locomotives use fluids under pressure to transmit and regulate power to the wheels.
Gas turbine-electric locomotives are of the rarest type. They are similar to the diesel-electric ones but use a gas turbine to drive the generator. The technology is used primarily on turbotrains, high-speed passenger trains that do not have locomotives but instead are powered by units built into one or more of their cars.
(5) Magnetic levitation locomotives (Maglev) present the newest technology in locomotives. These electrically powered trains have a special open motor, which floats the train above the rail without the need for wheels. Very few systems are in service and the cost is very high. The experimental Japanese magnetic levitation train has reached 581km/h.
(6) There is a growing interest around the world in alternative fuels because railways are demanding increased haulage capability to improve productivity, which means pulling more cargo with the same number of locomotives.
In 2007 GE Transportation (USA) developed its first hybrid diesel-electric/battery locomotive capable of recycling energy as stored power in onboard batteries6. It will feature a series of innovative batteries that will capture and store energy dissipated during dynamic braking. The energy stored in the batteries will reduce fuel consumption and smog-causing emissions by as much as 10% compared with most of the freight locomotives in use today.
(7) Railway Technical Research Institute (RTRI) has studies underway to get a fuel cell powered train into service by about 2010. Hydrogen7-fuelled cells are being used for motorcars, buses, and lorries, but the rail project is the most ambitious application so far. Fuel cells are solid-state devices that directly convert energy of the fuel into electric power and can be easily replaced. They are based on electric-chemical reactions between hydrogen and oxygen leaving water as the only by-product, and are said to be efficient, quiet, and have zero emissions.
(8)The environmental consequences of today’s energy policies are potentially catastrophic. Burning fossil fuels causes the global warming which may lead to the green house effect and acid rains, contributing to the death of large areas of forests in Europe. Air, water, soil are all harmed by pollution. Toxic heavy metals are also found in high concentrations in soils and vegetation in many places in Europe. The risks associated with nuclear energy are also great, as illustrated by the Chernobyl accident.
The issue of energy has two main aspects: type of energy used and amount of energy used. The answer lies partly in the development of renewable energy sources such as biomass, methane, sun, wind, waterfall and wave power. The other part of the solution lies in using less energy, getting more out of each unit of energy and applying improved environmentally friendly technologies.
1 Maglev – потяг на магнітній підвісці, «маглев»
2 an overhead pickup – струмоприймач
3 diesel-hydraulic locomotive – локомотив з гідравлічною передачею
4 self-contained – автономний
5 propelled – що приводиться до дії
6 onboard batteries – батареї, що розташовані у локомотиві (бортові)
7 hydrogen – водень
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