A. Before reading the article about electricity, discuss with your partner the following questions.

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1 READING A_ part 1 A. Before reading the article about electricity, discuss with your partner the following questions. 1. Brainstorm as many different kinds of energy as you can. 2. What do we need electric energy for? 3. Make a list of activities you cannot do when there is a black out. 4. Brainstorm as many different reasons for a black out as you can. 5. What type of power plants are there in the Slovak Republic? B. Read the first passage about the history of electric power system and put the paragraphs in the correct order. The first and last paragraph has been given to you. _1_Electricity supply involves the conversion of the basic fuel (oil, coal, nuclear, water, sun,...) into electricity, and the transmission and distribution of this energy by a system of transmission lines, distribution lines - feeders, transformers, etc. - with appropriate protective devices at all stages [1]. The commercial use of electricity began in the late 1870s when arc lamps were used for lighthouse illumination and street lighting [2]. With the development of polyphase systems by Nikola Tesla, the AC system becomes even more attractive. By 1888, Tesla held several patents on AC motors, generators, transformers and transmission systems. Westinghouse bought the patents to these early inventions, and they formed the basis of the present-day AC systems [2]. The development of the transformer and AC transmission by L. Gualard ad J.D. Gibbs of Paris, France, led to AC electric power systems. George Westinghouse secured rights to these developments in the United States. In 1886, William Stanley, an associate of Westinghouse, developed and tested a commercially practical transformer and a AC distribution system for 150 lamps at Great Barrington, Massachusetts. In 1889, the first AC transmission line in North America was put into operation in Oregon between Willamette Falls and Portland. It was a single-phase line transmitting power at V over a distance of 21 km [2]. In spite of the initial widespread use of DC system, they were almost completely superseded by AC (Alternating Current) systems. By 1886, the limitations of DC systems were becoming increasingly apparent. They could deliver power only a short distance from the generators. To keep transmission power losses and voltage drops to acceptable levels, voltage levels had to be high for long-distance power transmission. Such high voltages were not acceptable for generation and consumption of power; therefore, a convenient means for voltage transformation became a necessity [2]. The first complete electric power system (comparison a generator, cable, fuse, meter and loads) was built by Thomas Edison - the historic Pearl Street Station in New York City which began operation in September This was a DC (Direct Current) system consisting of a steam-enginedriven DC generator supplying power to 59 customers within an area roughly 1.5 km in radius. The load, which consisted entirely of incandescent lamps, was supplied at 110 V through an underground cable system. Within a few years similar systems were in operation in most large cities throughout the world [2]. E.g. a DC scheme existed in France from 1905 to This was the Tury system, which transmitted 4 MW at 57 kv over a distance of 112 miles and was based on a constant-current scheme [1]. With the development of motors by Frank Sprague in 1884, motor loads were added to such systems. This was the beginning of what would develop into one of the largest industries in the world [2]. _6_In the 1890s, there was considerable controversy over whether the electric utility industry should be standardized on DC or AC. There were passionate arguments between Edison, who advocated DC,

2 and Westinghouse, who favoured AC. By the turn of the century, the AC system had won out over the DC system for the following reasons [2]: voltage levels can be easily transformed in AC systems, thus providing the flexibility for use of different voltages for generation, transmission and consumption, AC generators are much simpler than DC generators, AC motors are much simpler and cheaper than DC motors. C. Read the text again and decide whether the following six statements are true (T) or false (F) and state in which paragraph you found the evidence. Correct the false statements. 1. Resources for producing electric energy are limited. 2. The main limitation of AC systems was that they could deliver power only a short distance from the generators. 3. Tesla`s patents formed the basis of the present-day AC systems. 4. Arc lamps used for street lighting were supplied at 110 V through an underground cable system. 5. DC system has proved superior only due to increased price of motors. 6. The first AC transmission line was a two-phase line. D. Look at the words in bold in the text above and match them with definitions below. There are two more definitions that you do not need to use. 1. the electrical charge occasionally reverses flow of direction 2. the electrical charge flows only in one direction 3. it takes the AC and converts it to higher/voltage current 4. it flows through a resistor when an electric charge moves around a circuit 5. the process of getting electric power from other sources of primary energy 6. a network of electrical components used to supply, transfer and use electric power 7. an electrical component or portion of a circuit that consumes 8. the actual energy demand 9. the difference between input power and output power 10. the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation 11. the transformation of a circuit with a voltage source to the equivalent circuit with a current source 12. the set of physical phenomena associated with the presence and flow of electric charge E. Confusing words: Electric vs Electrical. These two words are pretty much interchangeable; however, many students misuse them. Study the following table below and fill in the sentences. Then create your own examples. Word Explanation Example electric used with special nouns My uncle used to play an electric guitar. electrical used with general nouns We must save electrical energy. electronic adjective Young people like electronic music. electronically adverb The application has to be handed in electronically. 1. The night lights pose a risk of fire from a potential short circuit in the light. 2. New research in China shows that cars have an overall impact on pollution that could be more harmful to health than conventional vehicles. 3. The case gave the court an occasion to examine just how far police can go when it comes to searching gadgets. 4. There is the alternative of paying your bill.

3 5. On April 4, a short in an fan resulted in a flash fire in the home of Dr. Foot. 6. The saws, which can grow more than a meter long in some species, have previously been identified as able to sense prey by their fields. 7. The newest vehicle charging station in central Massachusetts is being installed in Auburn. 8. Medical research findings can be distributed for peer review, and feedback can be instant F. Consider these cases and match the words with explanations. 1. An electric chair An electronic chair 2. An electric toaster An electronic toaster a) a toaster that lets you program in an image to burn into the toast, and which sends you an when the toast is done. b) a chair which predominantly features electricity c) a chair which has some feature made of a complex circuit (for example, the seats in cars which are automatically-adjusting) d) a toaster that is a run of the mill toaster G. Quiz 1. In what sort of electricity does current flow in one direction only? a) AC b) DC 2. You will see AC written on electrical appliances. What does it mean? a) alternative current b) alternating current 3. Which current was used to construct the first electric chair? a) direct current b) alternating current 4. Who was the winner of the War of Current in the late 1880 (AC vs. DC)? a) Nikola Tesla b) Tomas Edison c) Jára Cimerman 5. What is the unit of energy consumption? a) Watt (Wt) b) Watt (We) c) kilowatt per hour 6. Which country produces some of its electricity from geothermal sources? a) New Zealand b) Norway c) Iceland 7. What is a pathway for the flow of electricity? a) circuit b) wire c) tunnel

4 READING A_ part 2 H. Read the second passage about the victory of the AC system. The words in bold have been scrambled, try to put the letters into correct order. The first three-phase line in North America went into operation in a V, 12 km line in southern California. Around this time, AC was chosen at Niagara Falls because DC was not practical for transmitting power to Buffalo, about 30 km away. This decision ended the AC versus DC controversy and established victory of the AC system [2]. In the early period of CA eprow tsroinssimna, ncuyeqrfe was not standardized. Many different frequencies were in use: 25, 50, 60, 125 and 133 Hz. This posed a problem for interconnection. Eventually 60 Hz was adopted as standard in North America, while 50 Hz was adopted in Europe. The increasing need for transmitting larger amount of power over longer distances created an incentive to use progressively higher voltage levels, because the power transmittability increases and transmission losses decrease with increasing ogleatv levle. The larger the blocks of power to be transmitted and the greater the distance over which they must be wheeled, the higher must be the operating voltage chosen [3]. The first transmission of three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. A 25 kv transmission line connected Lauffen on the Neckar and Frankfurt am Main, on a 175 km long distance [Hughes-history]. The early AC systems used different voltage levels. To avoid the proliferation of an unlimited number of voltages, the industry has standardized voltage levels. The standards IEC (mainly Europe) and ANSI C84.1 (North America) define following AC voltage levels (RMS values): owl Voltage (LV) nominal voltage V or less, diuemm Voltage (MV) greater than V but less than 35 kv (100 kv in ANSI C84.1), hihg Voltage (HV) class of nominal system voltages from 35 kv (100 kv in ANSI C84.1) to 230 kv, axehirg-ht Voltage (EHV) greater than 230 kv but less than 800 kv (1 000 kv in ANSI C84.1), trhaluh-ig Voltage (UHV) system voltages that are equal to or greater than 800 kv (1 000 kv in ANSI C84.1). With the development of mercury arc valves in the early 1950s, hhig voagelt CD (DCHV) aossmsnsritin tymssse become economical in special situations. The HVDC transmission is attractive for transmission of large blocks of power over long distances. The cross-over point beyond which DC transmission may become a competitive alternative to AC transmission is around 500 km for overhead lines and 50 km for underground or submarine cables. HVDC transmission also provides an asynchronous link between systems where AC interconnection would be impractical because of system stability considerations or because nominal frequencies of the systems are different. The first modern commercial application of HVDC transmission occurred in 1954 when Swedish mainland and the island of Gotland were interconnected by a 96 km submarine cable [2]. Interconnection of neighbouring utilities usually leads to improved system security and economy of operation. Improved security results from the mutual emergency assistance that the utilities can provide. Improved economy results from the need for less generating reserve capacity on each system. In addition, the interconnection permits the utilities to make economy transfers and thus take advantage of the most economical sources of power. These benefits have been recognized from the beginning and interconnections continue to grow. Almost all the utilities in the United States and Canada are now part of one interconnected system. The same situation is also in Europe. The result is very large system of enormous complexity. The design of such a system and its secure operation are indeed challenging problems [2].

5 I. You could read about five different voltage levels in the second passage of the text. Fill in the following sentences with the most suitable word, which stem is volt. 1. is the measurement of how much energy is transferred by electricity. 2. It is measured in (V) with a device. 3. This device is called a, looks like an ammeter but it measures voltage and is always connected in a circuit in parallel to a component J. Based on the knowledge gained from the second passage, fill the gaps with the words from the box. There are two extra words that you do not need to use. acceptance various Low Ultra began Extra (2x) LED traffic voltages volts solar High gardens Medium electric HV two finished electronic AC voltages have been classified in 1 manners. In earlier times, there were just 2 categories LV and HV. As the level of 3 increases, there was a need for more levels. However, there was ambiguity as to where each band ended and the other 4. For instance, 11kV can be MV in some systems and 5 in another. The International Electrotechnical Commission has classified the voltages into the following levels (IEC 60038). This classification system is fast gaining 6. 7 Voltage 8 Voltage 9 Voltage 10 High Voltage - up to 1000V V to 35kV - 35kV to 230 kv - above 230 kv. In some situations, the term 11 High Voltage is used to denote voltages above 800 kv. In addition, the IEC defines a voltage band known as the 12 Low Voltage with a AC voltage less than 70 V. Extra low voltage refers to reduced voltages which are used in houses, parks, 13, swimming pools to eliminate the risk of 14 shock. AC voltages below 50 volts and DC voltages below are considered to be Extra low Voltage. In many countries, Extra Low Voltage supplies are used to power 16 signals. This has been facilitated with the advent of 17 lighting technology. Extra Low voltage systems can also be easily integrated with 18 panels as the generating voltage is lower. K. In this circuit, three resistors receive the same amount of voltage (24 volts) from a single source. Calculate the amount of current drawn by each resistor, as well as the amount of power dissipated by each resistor: