Елохова.Профессиональный английский язык. Учебно-методическое

coal-fired power plant uses steam to turn the turbine blades; whereas a hydroelectric plant uses falling water to turn the turbine. The results are the same (see Fig. 1).

Fig. 1. Hydroelectric power: How it woks

The theory is to build a dam on a large river that has a large drop in elevation. The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carries electricity to jour home. The water continues past the propeller through the tailrace into the river past the dam.

As to how this generator works, the Corps of Engineers explains it this way: «A hydraulic turbine converts the energy of flowing water to mechanical energy. A Hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it caused the field poles (electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals» (see Fig. 2).

Demand for electricity is not «flat» and constant. Demand goes up and down during the day, and overnight there is less need for electricity in homes, business and other facilities. Hydroelectric plants are more efficient at providing for peak power demands during short periods than are fossil-fuel and nuclear plants, and one way of doing that is by using «pumped storage», which reuses the same water more than once.

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Fig. 2. Generator

Pumped storage is a method of keeping water in reserve for peak period power demands by pumping water that has already flowed through the turbines back up a storage pool above the power plant at a time when customer demand for energy is low, such as during the middle of the night. The water is then allowed to flow back through the turbine-generators at times when demand is high and a heavy load is placed on the system.

The reservoir acts much like a battery, storing power in the form of water when demands are low and producing maximum power during daily and seasonal peak periods. An advantage of pumped storage is that hydroelectric generating units are able to start up quickly and make rapid adjustments in output. They operate efficiently when used for one hour or several hours. Because pumped storage reservoirs are relatively small, construction costs are generally low compared with conventional hydropower facilities.

Exercise 1. Combine the word combinations:

Exercise 2. Complete the sentences:

1.Hydroelectric and coal-fired power plants produce electricity in … .

2.The theory is to build a dam on a large river that has … .

3.… causes water to fall through the penstock inside the dam.

4.There is less need for electricity in homes, businesses and other facilities … .

5.Hydroelectric plants are more efficient at providing for peak power demands during short periods than are … .

6.An advantage of pumped storage is … .

Exercise 3. Answer the questions and give examples:

1.What does a coal-fired power plant use to turn the turbine blades?

2.What does a hydroelectric plant use to turn the turbine?

3.Where is the water intake?

4.What is a turbine propeller turned by?

5.Does the generator produce the power?

6.Is demand for electricity «flat» and constant? Why? Why not?

7.What is «pumped storage»?

8.Does the reservoir act much like a battery? Why? Why not?

9.Why are construction costs generally low compared with conventional hydropower facilities?

Text 5

Exercise 1. Read and translate the text:

Hydropower Facilities

Hydropower or water power is power derived from the energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, domestic lifts and paint making. Since the early 20th century, the term is used almost exclusively in conjunction with the modern development of hydroelectric power, which allowed use of distant energy sources.

Hydro comes from the Greek word for water. Hydroelectricity, or hydropower, is usually generated by turbines in a dam in a river. The dam means that a great body of water builds up in the river valley behind the dam. This is released through the turbines when electricity is needed. Smaller than dams are barrages across the mouths of rivers which capture water from high tides and release it to generate electricity. Smaller still are turbines in river and tidal streams which do the same thing.

Hydropower is one of the largest sources of energy accounting for roughly 20 % of the worldwide demand of electricity and for well resourced countries it accounts for majority of the energy. Compared to other sources of energy, hydroelectric power is one of the cheapest, non-carbon emitting, non polluting

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sources. Hydropower plants have been developed to almost full potential in developed countries because of their superior characteristics and many more are being constructed by developing countries like China and India. However hydro power like all other things in life suffers from disadvantages as well. The failure of a hydro dam can result in massive losses of human life and cause widespread devastation. Large dams have always been controversial leading to displacement of people and ecology. They have also been cited as the reason for earthquakes due to large land changes.

There are three types of hydropower facilities: impoundment, diversion, and pumped storage. The most common type of hydroelectric power plant is an impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level. A diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock. It may not require the use of a dam. When the demand for electricity is low, pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

Exercise 2. Find key words and phrases which best express the general meaning of each paragraph.

Exercise 3. Write a summary of the text.

Unit V. How is Electricity Produced

Text 1

Electrical Energy

(1)The electrical energy supplied by a current to an appliance enables it to do work or provide some other form of energy such as light or heat. Electric power is usually measured in Watts, kilowatts (1,000 watts), and megawatts (1,000,000 watts). The amount of electrical energy used by an appliance is found by multiplying its consumed power by the length of time of operation. The units of electrical energy are usually watt-seconds (joules), watt-hours, or kilowatt-hours. For commercial purposes the kilowatt-hour is the unit of choice.

(2)Electrical energy occurs naturally, but seldom in the forms that can be used. Generally, practical electric-power-generating systems convert the mechanical energy of moving parts into electrical energy. The electric generator is a machine that is used to change mechanical energy into electrical energy. It operates on the principle of electromagnetic induction, discovered (1831) by

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Michael Faraday. When a conductor passes through a magnetic field, a voltage is induced across the ends of the conductor. The generator is simply a mechanical arrangement for moving the conductor and transmitting the current produced by the voltage to an external circuit, where it actuates devices that require electricity.

(3)While systems that operate without a mechanical step do exist, they are at present either excessively inefficient or expensive because of a dependence on elaborate technology. While some electric plants derive mechanical energy from moving water (hydroelectric power), the vast majority derive it from heat engines in which steam is the working substance. The steam is generated with heat from combustion of fossil fuels or from nuclear fission.

(4)The conversion of mechanical energy to electrical energy can be accomplished with an efficiency of about 80%. In a hydroelectric plant, the losses occur in the turbines, bearings, penstocks, and generators. The basic limitations of thermodynamics fix the maximum efficiency obtain able through converting heat to electrical energy. The necessity of limiting the temperature to safe levels also helps to keep the efficiency down to about 41% for a fossil-fuel plant. Most nuclear plants use low-pressure, low-temperature steam operation, and have an even lower efficiency of about 30 %. Nuclear plants have been able to achieve efficiency up to 40 % with liquid-metal cooling. It is thought that by using magneto hydrodynamic «topping» generators in conjunction with normal steam turbines the efficiency of conventional plants can be raised to close to 50 %. These devices remove the restrictions imposed by the blade structure of turbines by using the steam or gasses produced by combustion as the working fluid.

Exercise 1. Read the text and decide which paragraph:

a explains what the electric generator is.

B gives reasons why the efficiency of power plants is lower than could be expected. C indicates the principle the electric generator operates on.

D mentions how hydroelectric plants derive mechanical energy from the energy of moving water.

E names the person who discovered the principle of electromagnetic induction. F informs about the units used to measure electrical energy.

G shows the way to increase the efficiency of conventional plants.

H indicates that electrical energy exists in nature, but in the forms that can hardly be used by a human.

Exercise 2. Decide if the statements are True or False:

1.Electrical energy can be converted into some other form of energy such as light or heat.

2.Electric power is measured in Amperes.

3.1 joule is equivalent to 1 watt-second.

4.As electrical energy occurs naturally, it is almost always in the forms that can be used.

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5.The generator changes mechanical energy into heat energy.

6.The generator operates on the principle of electromagnetic induction.

7.The vast majority of electric plants derive mechanical energy from heat engines in which water is the working substance.

8.The conversion of mechanical energy into electrical energy is accomplished almost without losses.

Exercise 3. Answer the questions:

1.How does an electrical appliance work?

2.What does the amount of energy used (or supplied) depend on?

3.What is the unit of electrical power used for commercial purposes?

4.What energy is converted into electrical energy by electric-power-generating systems?

5.Why do most nuclear plants have less efficiency than fossil-fuel or hydroelectric plants?

6.What are the possible ways to increase the efficiency of nuclear plants?

Text 2

Exercise 1. Decide if these sentences are True or False. Read the text:

1.There are several different transformation processes, among which are chemical, photo-voltaic, and electromechanical.

2.The turbine-generator conversion process is the most economical and most common in the industry today.

Generating Electricity

Generation of electrical power is a process whereby energy is transformed into an electrical form. There are several different transformation processes, among which are chemical, photo-voltaic, and electromechanical. Electromechanical energy conversion is used in converting energy from coal, petroleum, natural gas, uranium into electrical energy. Of these, all except the wind energy conversion process take advantage of the synchronous a. c. generator coupled to a steam, gas or hydro turbine such that the turbine converts steam, gas, or water flow into rotational energy and the synchronous generator then converts the rotational energy of the turbine into electrical energy. It is the turbine-generator conversion process that is by far most economical and consequently most common in the industry today.

The a. c. synchronous machine is the most common technology for generating electrical energy. It is called synchronous because the composite magnetic field produced by the three stator windings rotate at the same speed as the magnetic field produced by the field winding on the rotor. A simplified circuit model is used to analyze steady-state operating conditions for a synchronous machine. The phasor diagram is an effective tool for visualizing the relationships between internal

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voltage, armature current, and terminal voltage. The excitation control system is used on synchronous machines to regulate terminal voltage, and the turbinegovernor system is used to regulate the speed of the machine.

The operating costs of generating electrical energy is determined by the fuel cost and the efficiency of the power station. The efficiency depends on generation level and can be obtained from the heat rate curve. We may also obtain the incremental cost curve from the heat rate curve.

Exercise 2. Answer the questions:

1.What is the generation of electrical power?

2.What are the forms of transformation process?

3.How does the a. c. synchronous machine work?

Exercise 3. Fill in the blanks with the necessary forms of the words from the right

Exersice 4. Translate the text in written form:

Three-phase induction motor

The three-phase induction motor is the most commonly used type. It has been widely used in recent years. Normally an induction motor consists of a cylindrical core (the stator) which carries the primary coils in slots on its inner periphery. The primary coils are arranged for a three-phase supply and serve to produce a revolving magnetic field. The stator encircles a cylindrical rotor carrying the secondary winding in slots on its outer periphery.

The rotor winding may be one of two types: squirrel-cage and slip-ring for wound-rotor. In a squirrel-cage machine the rotor winding forms a complete closed circuit in itself. The rotor winding of a slip-ring machine is completed when the slip rings are connected either directly together or through some resistance external to the machine. The rotor shaft is coupled to the shaft of the driven mechanism.

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The rotor is stationary at some instant of time. The revolving magnetic field of the stator winding cuts across the stationary rotor winding at synchronous speed and induces an e.m.f. in it. The e.m.f. will give rise to a current which sets up a magnetic field. The rotor starts rotating.

It is the interaction between the rotor current and the revolving magnetic field that has created torque and has caused the rotor to rotate in the same direction as the revolving magnetic field. Tine speed of the rotor is 98–95 per cent of the synchronous speed of the revolving magnetic field of the stator. Hence another name for this type of motor is the asynchronous motor. As a matter of fact, the speed of the rotor cannot be equal to synchronous speed. If it were equal to the latter, the revolving magnetic field would not be able to cut the secondary conductors and there would not be any current induced in the secondary winding and no interaction between the revolving field and the rotor current, and the motor would not run.

Text 3

Generators

The dynamo invented by Faraday in 1831 is certainly a primitive apparatus compared with the powerful, highly efficient generators and alternators that are in use today. Nevertheless, these machines operate on the same principle as the one invented by the great English scientist. When asked what use his new invention had, Faraday asked in his turn: «What is the use of anew-born child?» As a matter of fact, «the new-born child» soon became an irreplaceable device we cannot do without.

Although used to operate certain devices requiring small currents for their operation, batteries and cells are unlikely to supply light, heat and power on a large scale. Indeed, we need electricity to light up millions of lamps, to run trains, to lift things, and to drive the machines. Batteries could not supply electricity enough to do all this work.

That dynamo-electric machines are used for this purpose is a well-known fact. These are the machines by means of which mechanical energy is turned directly into electrical energy with a loss of only a few per cent. It is calculated that they produce more than 99.99 per cent of all the world’s electric power.

There are two types of dynamos, namely, the generator and the alternator. The former supplies d. c. which is similar to the current from a battery and the latter, as its name implies provides a. c.

To generate electricity both of them must be continuously provided with energy from some outside source of mechanical energy such as steam engines, steam turbines or water turbines, for example.

Both generators and alternators consist of the following principal parts: an armature and an electromagnet. The electromagnet of a d. c. generator is usually called a stator for it is in a static condition while the armature (the rotor) is rotating.

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двигатель; при неподвижном состоянии; якорь вращается; неподвижный якорь; вращающийся электромагнит; вращается со скоростью

Exercise 3. Find the wrong statements and correct them:

1.An armature and an electromagnet are the main parts of both generators and alternators.

2.The electromagnet of a d. c. generator is rotating.

3.Alternators are equipped with a stator in a static condition and a stationary armature.

4.The amount of the output voltage depends on the rotor revolutions per minute.

Exercise 4. Combine suitable parts of the sentences:

Exercise 5. Translate into English:

1.Динамо-машины, изобретенные Фарадеем, - примитивные устройства по сравнению с генераторами постоянного и переменного тока.

2.Они стали незаменимыми устройствами, которые мы используем сегодня.

3.Элементы и батарейки не обеспечивают электрической энергией в большом объеме.

4.При помощи генераторов механическая энергия превращается в электрическую.

5.Источники механической энергии – паровые двигатели, паровые турбины.

6.Генератор для производства электричества использует энергию из внешних источников.

7.Составляющие части генератора – якорь и электромагнит.

8.При неподвижном состоянии генератора якорь вращается.

9.В конструкции генератора можно увидеть якорь, электромагнит, параллельную обмотку и коммутатор.

Exercise 6. Discuss the following questions:

1.if batteries can supply light, heat and power on a large scale.

2.if the electromagnet is temporary magnet provided by electricity.

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