Electric Power

Electric power is generated by converting heat, light, chemical en­ergy, or mechanical energy to electrical energy. Most electrical energy is produced in large power stations by the conversion of mechanical en­ergy or heat. The mechanical energy of falling water is used to drive turbine generators in hydroelectric stations, and the heat derived by burning coal, oil, or other fossil fuels is used to operate steam turbines or internal-combustion engines that drive electric generators. Also, the heat from the fissioning of uranium or plutonium is used to generate steam for the turbine generator in a nuclear power plant.

Electricity generated by the conversion of light or chemical energy is used mainly for portable power sources. For example, a photoelectric cell converts the energy from light to electrical energy for operating the exposure meter in a camera, and a lead-acid battery converts chemical energy to electrical energy for starting an automobile engine.

Electric power produced in large power stations generally is trans­mitted by using an alternating current that reverses direction 25, 50, or 60 times per second. The basic unit for measuring electric power is the watt - the rate at which work is being done in an electric circuit in which the current is one ampere and the electromotive force is one volt.

Ratings for power plants are expressed in kilowatts (1,000 watts) or megawatts (1 million watts). Electric energy consumption normally is given in kilowatt-hours - that is, the number of kilowatts used times the number of hours of use. Electricity is clean, inexpensive, and easily transmitted over long distances. Since the 1880's, electricity has had an ever-increasing role in improving the standard of living. It now is used to operate lights, pumps, elevators, power tools, furnaces, refrigerators, air-conditioners, radios, television sets, industrial machinery, and many other kinds of equipment. It has been counted that in developed coun­tries about 43% of the electric power is generally used for industrial purposes, 32% in homes, and 21% in commercial enterprises.

27. Read the text and find in it the answer to the question that follows it. Electric Power Interruptions

On November 9, 1965, at 5:16 p.m., a back-up relay failed at one of the five main transmission lines at No. 2 station near Toronto, Canada. As the load had shifted to the other four lines, they became overloaded, and as a result the relays failed in all four lines. The failure resulted in the load being shifted to the other plants in the system. The plants got overloaded, which caused them to shut down. Within minutes, power plants in Canada, New York, and the New England states got out of service. The blackout affected 30 million people and covered an area of 306,000 sq m. In some areas, such as New York City, power was not restored for about 13 hours.

This massive power blackout resulted in the construction of the na­tional Electric Reliability Council in June 1958. This council sets stan­dards for the design, operation, and maintenance of generating and transmission systems. These standards serve to prevent a failure in one power system from spreading to other systems. Yet local system fail­ures cannot be avoided.

Nowadays in some European countries and in the US there are from 60 to 80 power interruptions per year, in which there is a loss of service for customers for more than 15 minutes. Mostly these interruptions are caused by weather conditions - ice, freezing snow, lightning or storms. There can be also failures of equipment - transformers, relays, insulators and so on. However, the reliability of electric service is extremely high.

Have you been a witness to an electric service failure? Describe it, please.

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28. Read and translate the text. What do you think is meant by "Member countries"? Give the new units for the following: rontgen, rad, rem, curie.

Quantities and Units

For many years, special measurement units for quantities of interest in radiation protection were used, which were not coherent with the In­ternational System of Units (SI). These old units (rontgen, rad, rem and curie) have been superseded in the last few years by a new set of units which are coherent with the SI system.

These new units, the gray for absorbed dose, the sievert for dose equivalent, and the becquerel for activity of radioactive materials, have been progressively adopted in Member countries, although some resid­ual cases of use of the old units are still being observed. The relation­ships between the new SI units and those previously used are shown in the following table:

Fig.24. Cross-section through the main structures and units of hydroelectric power plant

Quantity	SI Unit	New Name and Symbol	Old Unit and Symbol	Conversion Factors
Exposure	kg'	—	rontgen (R)	1 С kg^1 = 3876 R 1 R = 2.5 x 10"^4 С kg"^1
Absorbed dose	J kg'	gray (Gy)	rad (rad)	1 Gy=100rad lrad=10^2Gy
Dose equivalent	J kg'	sievert (Sv)	rem (rem)	1 Sv = 100 rem 1 rem=10'^2Sv
Activity	s-'	becquerel (Bq)	curie (Ci)	1 Bq = 2.7xlO-"Ci lCi = 3.7xl0^,0Bq

29. Read the text and find in it the answers to the questions that follow it. Electric Power Plants

The two main types of power plants traditionally have been the fos­sil-fuel steam-electric plant and the hydroelectric plant. Other types, in­cluding internal-combustion-engine plants and nuclear plants also have been built. The selection of a particular type of generating plant and its location involves consideration of a number of factors such as plant, fuel, and transmission line costs; availability of cooling water; and en­vironmental considerations.

For several reasons, the relative importance of the various types of power plants has been shifting. Good sites for new hydroelectric plants have become scarce in many countries. Distribution networks have been extended so that less expensive power from large steam-electric stations has been replacing power from smaller diesel-generator units. Nuclear-electric power plants have been built instead of fossil-fuel steam-electric plants because the cost of coal and oil has been increasing.

In the United States in 1970, fossil-fuel steam-electric plants ac­counted for 76% of the power generated, hydroelectric plants for 16%, and nuclear plants for 2%.

In 2000 45% of the electric power in the United States is generated from fossil-fuel steam-electric plants, 45% from nuclear plants, and 10% from hydroelectric plants.

1. What kinds of power plants are in use nowadays?

2. What does the selection of a type of generating plant depend on?

3. For what reason are nuclear-electric power plants being built instead of fossil-fuel steam-electric plants?

30. Study Fig. 25 and read the text. Describe a nuclear power plant.

Nuclear Power Plants

The energy for operating a nuclear power plant comes from the heat released during the fissioning of uranium or plutonium atoms in a nu-

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clear reactor. This fission heat is used to generate steam, which drives a turbine generator. Thus, there are two main differences between a nu­clear power plant and a steam-electric power plant: the nuclear plant uses a nuclear fuel instead of a fossil fuel, and it uses a nuclear reactor instead of a boiler.

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