Учебные задания по английскому языку для студентов 2 курса направления бакалавриата «Электроэнергетика и электротехника» 4 семестр

5. Complete each sentence (a-g) with one of the endings (1-7).

a.Nuclear energy is…

b.The energy of any system is…

c.The total energy in a system is…

d.When a fossil fuel such as coal is…

e.Water and carbon dioxide are produced and heat is…

f.This amount of energy is typical of chemical reactions…

g.A part of the energy released as heat…

1.…always conserved, but it can be transferred to another system or changed in form.

2.…released, equivalent to about 1.6 kilowatt-hours per kilogram or about 10 electron volts per atom of carbon.

3.…manifested by the system’s ability to do work or release heat or radiation.

4.…keeps the adjacent fuel hot enough to keep the reaction going.

5.…resulting from changes in the electronic structure of the atoms.

6.…energy released during the splitting or fusing of atomic nuclei.

7.…burned, atoms of hydrogen and carbon in the coal combine with oxygen atoms in air.

6.Complete the text with a suitable preposition in each space.

WORLD ELECTRIC POWER PRODUCTION

___ the period ___ 1950 ___ 1999, the most recent year ___ which data are available, annual world electric power production and consumption rose ___ slightly less than 1,000 billion kilowatt hours (kwh) ___ 14,028 billion kwh. A change also took place ___ the type of power generation. ___ 1950 about two-thirds of the electricity came ___ thermal (steam-generating) sources and about one-third ___

hydroelectric sources. ___ 1998 thermal sources produced 63 percent of the power, but hydropower had declined ___ 19 percent, and nuclear power accounted ___ 17 percent of the total. The growth ___ nuclear power slowed ___ some countries, notably the United States, ___ response ___ concerns about safety. Nuclear plants generated 20 percent ___ U.S. electricity ___ 1999; ___ France, the world leader, the figure was 76 percent.

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SPEAKING

Make a presentation on a type of transformer for a particular voltage.

WRITING

Write an advertisement introducing new devices for voltage regulation. MODULE I

ASSESSMENT

Translate from English into Russian.

CIRCUIT BREAKERS

To protect all elements of a power system from short circuits and overloads, and for normal switching operations, circuit breakers are employed. These breakers are large switches that are activated automatically in the event of a short circuit or other condition that produces a sudden rise of current. Because a current forms across the terminals of the circuit breaker at the moment when the current is interrupted, some large breakers (such as those used to protect a generator or a section of primary transmission line) are immersed in a liquid that is a poor conductor of electricity, such as oil, to quench the current. In large air-type circuit breakers, as well as in oil breakers, magnetic fields are used to break up the current. Small air-circuit breakers are used for protection in shops, factories, and in modern home installations. In residential electric wiring, fuses were once commonly employed for the same purpose. A fuse consists of a piece of alloy with a low melting point, inserted in the circuit, which melts, breaking the circuit if the current rises above a certain value.

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MODULE II

UNIT ONE

ELECTRIC MOTORS AND GENERATORS

READING

1. Read the following text. Some phrases have been left out of the text. Choose from phrases A-H below to complete the gaps. There is one phrase you will not need.

Electric motors and generators are devices used to convert mechanical energy into electrical energy, or electrical energy into mechanical energy, by electromagnetic means. A machine that converts mechanical energy into electrical energy is called a generator, (1)___________, or dynamo, and a machine that converts electrical energy into mechanical energy is called a motor.

Two related physical principles (2)____________the operation of generators and motors. The first is the principle of electromagnetic induction discovered by the British scientist Michael Faraday in 1831. If a conductor is moved through a magnetic field, or if the strength of a (3)____________is made to vary, a current is set up or induced in the conductor. The converse of this principle is that of electromagnetic reaction, first observed by the French physicist Andre Marie Ampere in 1820. If a current is passed through a conductor located in a magnetic field, the field exerts a mechanical force on it.

The simplest of all dynamoelectric machines is the disk dynamo

(4)____________by Faraday. It consists of a copper disk mounted so that part of the disk, from the center to the edge, is between the poles of a horseshoe magnet. When the disk is rotated, a current is induced between the center of the disk and its edge by the action of the field of the magnet. The disk can be made (5)____________as a motor by applying a voltage between the edge of the disk and its center, causing the disk to rotate because of the force produced by magnetic reaction.

The magnetic field of a permanent magnet is strong enough to operate only a small practical dynamo or motor. As a result, (6)_____________, electromagnets are employed. Both motors and generators consist of two basic units, the field, which is the electromagnet with its coils, and the armature, the structure that supports the

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conductors (7)_____________and carry the induced current in a generator or the exciting current in a motor. The armature is usually a laminated soft-iron core around which conducting wires are wound in coils.

A. stationary conducting loop, B. convert,

C. underlie, D. developed,

E. which cut the magnetic field,

F. alternator,

G. to operate,

H. for large machines.

VOCABULARY PRACTICE

1.Explain the words and word combinations in bold in the text.

2.Find English equivalents to the following words and word combinations.

a.прилагать напряжение;

b.генератор постоянного тока;

c.приводить в действие механическую силу;

d.применяться, использоваться;

e.край (диска);

f.якорь;

g.подковообразный магнит;

h.пластинчатый сердечник из мягкой стали.

3. Complete the text with words formed from the words in capitals.

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4. Write out the passage using the correct verb form in brackets.

Electric generator is any machine that (1)__________(convert) mechanical energy to electricity for transmission and distribution over power lines to domestic, commercial, and industrial customers. Generators also (2)___________(produce) the electrical power (3)___________(require) for automobiles, aircraft, ships, and trains.

The mechanical power for an electric generator is usually

(4)___________(obtain) from a (5)___________(rotate) shaft and is equal to the shaft torque (6)__________(multiply) by the rotational, or angular, velocity. The mechanical power may (7)________(come) from a number of sources: hydraulic turbines at dams or waterfalls; wind turbines; steam turbines (8)________(use) steam

(9)__________(produce) with heat from the combustion of fossil fuels or from the fission of heavy atomic nuclei; gas turbines (10)__________(burn) gas directly in the turbine; or gasoline and diesel engines. The construction and the speed of the generator may (11)_________(vary) considerably (12)___________(depend) on the characteristics of the mechanical prime mover.

UNIT TWO

DIRECT-CURRENT (DC) GENERATORS

READING

1. Read the text and complete statements 1-6 with the best ending A, B

or C.

1) Direct current in the armature can be obtained by…

A. removing one of the field poles.

B. halving the number of revolutions.

C. changing the current flow in the opposite direction during each revolution.

2) A commutator…

A. reverses the current flow.

B. slows down the armature revolving.

C. is an insulator.

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3) If a DC generator worked at high voltage, there would be a danger of…

A. sparking.

B. reversal.

C. ignition.

4) Drum armatures…

A. constitute a multiple commutator.

B. contain a multitude of windings.

C. are set in the core.

5) A multiple commutator…

A. helps to keep the current flow steady.

B. connects many segments.

C. delivers the current through the armature.

6) Large additional electromagnetic poles…

A. cause magnetic distortions.

B. compensate for the magnetic effects.

C. reinforce the magnetic field.

If an armature revolves between two stationary field poles, the current in the armature moves in one direction during half of each revolution and in the other direction during the other half. To produce a steady flow of unidirectional, or direct, current from such a device, it is necessary to provide a means of reversing the current flow outside the generator once during each revolution. In older machines this reversal is accomplished by means of a commutator, a split metal ring mounted on the shaft of the armature. The two halves of the ring are insulated from each other and serve as the terminals of the armature coil. Fixed brushes of metal or carbon are held against the commutator as it revolves, connecting the coil electrically to external wires. As the armature turns, each brush is in contact alternately with the halves of the commutator, changing position at the moment when the current in the armature coil reverses its direction. Thus there is a flow of unidirectional current in the outside circuit to which the generator is connected. DC generators are usually operated at fairly low voltages to avoid the sparking between brushes and commutator that

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occurs at high voltage. The highest potential commonly developed by such generators is 1500 V. In some newer machines this reversal is accomplished using power electronic devices, for example, diode rectifiers.

Modern DC generators use drum armatures that usually consist of a large number of windings set in longitudinal slits in the armature core and connected to appropriate segments of a multiple commutator. In an armature having only one loop of wire, the current produced will rise and fall depending on the part of the magnetic field through which the loop is moving. A commutator of many segments used with a drum armature always connects the external circuit to one loop of wire moving through the high-intensity area of the field, and as a result the current delivered by the armature windings is virtually constant. Fields of modern generators are usually equipped with four or more electromagnetic poles to increase the size and strength of the magnetic field. Sometimes smaller interpoles are added to compensate for distortions in the magnetic flux of the field caused by the magnetic effect of the armature.

VOCABULARY PRACTICE

1.Explain the words and word combinations in bold in the text.

2.Find English equivalents to the following words and word combinations.

a.выпрямитель (преобразователь);

b.установленный на валу якоря;

c.менять направление на противоположное;

d.дополнительный полюс;

e.коллектор (переключатель);

f.продольные отверстия (щели);

g.служить клеммами;

h.искрение;

i.однонаправленный ток.

3. Combine the verbs from list A with the most suitable prepositions from list B. Use the most appropriate form of the verbs to complete the sentences.

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a.Proper machine operation greatly__________ proper maintenance.

b.The cells of the battery are____________ one another.

c.Modern power plants are always___________ new powerful generators.

d.Home owners should __________their homes _____ energy loss.

e.Nothing can_____________ the loss of one’s health.

f.The dynamo disk is made___________ two poles.

g.An electric power system___________ a power station, generators and transmission lines.

4. Write out the passage using the words from the list.

Direct-current generators were widely used (1)________to the availability of economical rectifier systems (2)__________by alternators. For example, they were

(3)___________ employed for charging batteries and for (4)__________purposes. In some (5)_________, the direct-current generator retains an (6)__________over the alternator-rectifier in that it can (7)________as a motor as well, reversing the direction of power flow. An alternator, by contrast, must be (8)__________with a more complex rectifier-inverter system to (9)____________power reversal.

5. Complete the text with a suitable preposition in each space.

TYPES OF DC GENERATORS

DC generators are commonly classified according ___ the method used to provide field current ___ energizing the field magnets. A series-wound generator has its field ___ series ___ the armature, and a shunt-wound generator has the field connected ___ parallel ___ the armature. Compound-wound generators have part ___

their fields ___ series and part ___ parallel. Both shunt-wound and compound-wound

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generators have the advantage ___ delivering comparatively constant voltage ___

varying electrical loads. The series-wound generator is used principally to supply a constant current ___ variable voltage. A magneto is a small DC generator ___ a permanent-magnet field.

UNIT THREE

DC MOTORS

READING

1.Scan the first paragraph of the text and say why DC motors can be called “backward running generators”.

2.Read the rest of the article and answer the questions.

a.Why is it necessary to use special devices for starting DC motors?

b.What are possible reasons for damaging the commutator?

c.What should be done to avoid such damage?

d.How are the magnetic field and the speed of a DC motor related?

e.How can the rate of rotation be controlled?

In general, DC motors are similar to DC generators in construction. They may, in fact, be described as generators “run backwards.” When current is passed through the armature of a DC motor, a torque is generated by magnetic reaction, and the armature revolves. The action of the commutator and the connections of the field coils of motors are precisely the same as those used for generators. The revolution of the armature induces a voltage in the armature windings. This induced voltage is opposite in direction to the outside voltage applied to the armature, and hence is called back voltage or counter electromotive force (emf). As the motor rotates more rapidly, the back voltage rises until it is almost equal to the applied voltage. The current is then small, and the speed of the motor will remain constant as long as the motor is not under load and is performing no mechanical work except that required to turn the armature. Under load the armature turns more slowly, reducing the back voltage and permitting a larger current to flow in the armature. The motor is thus able to receive more electric power from the source supplying it and to do more mechanical work.

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Because the speed of rotation controls the flow of current in the armature, special devices must be used for starting DC motors. When the armature is at rest, it has virtually no resistance, and if the normal working voltage is applied, a large current will flow, which may damage the commutator or the armature windings. The usual means of preventing such damage is the use of a starting resistance in series with the armature to lower the current until the motor begins to develop an adequate back voltage. As the motor picks up speed, the resistance is gradually reduced, either manually or automatically.

The speed at which a DC motor operates depends on the strength of the magnetic field acting on the armature, as well as on the armature current. The stronger the field, the slower is the rate of rotation needed to generate a back voltage large enough to counteract the applied voltage. For this reason the speed of DC motors can be controlled by varying the field current.

VOCABULARY PRACTICE

1.Find Russian equivalents to the words and word combinations in bold.

2.Find English equivalents to the following words and word combinations.

a.ускорять ход;

b.давать возможность;

c.катушки возбуждения (электромагнита);

d.скорость вращения;

e.следовательно;

f.вручную;

g.противодействовать;

h.соответствующий.

3. Put each verb in brackets into a suitable verb form.

In an elementary form of a DC motor, a stationary magnetic field

(1)_______(produce) across the rotor by poles on the stator. These poles may

(2)________(encircle) by field coils (3)_______(carry) direct current, or they may

(4)_______(contain) permanent magnets. The rotor or armature (5)_______(consist)

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