Lesson 4. Power transmission

TEXT 4 A. Power Transmission;

Grammar Exercises (The Gerund. The Gerundial Complex. The Functions of the Gerund);

TEXT 4 B. Electric Power Consumers and Power Systems;

TEXT 4 C. Electric Power Interruptions.

Pre-Text Exercises

Active Vocabulary

I. Practise reading the words written below. You’ll come across them in text 4 a.

to expand …………………… to convert …………………... interconnection …………….. owing to ………….………… wire ………………………… branch …………….………… to subdivide ………………… distribution ……….………… to deliver …………………… overhead ……………………. conductor …………………… insulator ……………………. support ……………………… to exceed …………………… load ………………………… loss …………………………. to protect …………………… fuse ………………………… relay ………………………… overcurrent …………………. short-circuit ………………… cord ………………………… bus …………………………. consumer …………………… feeder ………………………. isolator ……………………… switchgear ………………….. circuit breaker ……………… step up (step down) substation to supply ……………………. storage battery ……………… auxiliary structure ………….. flexible ……………………... fault …………………………

расширять, увеличивать превращать объединение (энергосистем) благодаря провод ветвь, ответвление подразделять распределение доставлять воздушный, надземный проводник изолятор опора, опорная стойка превышать нагрузка потеря защищать плавкий предохранитель, пробка переключатель, реле перенапряжение короткое замыкание шнур электрическая шина потребитель питатель, подающий механизм изолятор переключатель автоматический переключатель подстанция с растущим (падающим) напряжением доставлять аккумуляторная батарея вспомогательное устройство, вспомо-гательный механизм гибкий авария, повреждение, неисправность

II. Put the words from the box into the correct columns. Translate them into Russian.

overhead, flexible, normally, to subdivide, intercon-nection, conductor, consumer, overcurrent, exceedingly, undesirable, feeder, greatly, inefficient, insulator, distri-bution, reliable, combination, comparatively, resistance.

Noun (what/who?)	Adjective (what kind of?)	Verb (what to do?)	Adverb (in what manner?)
…	…

III. Read text 4 a. Try to understand its content. Text 4 a. Power Transmission

They say that more than a hundred years ago, power was never carried far away from its source. Later on, the range of transmission was expanded to a few miles. Nowadays in a comparatively short period of time it has become possible converting mechanical energy into electrical and transmitting of the electricity over long distances and the length of transmitting power lines varies from area to area. So, a power system is an interconnection of electric power stations by high voltage power transmission lines. It isn’t difficult to understand that the above process has been made possible owing to generators, transformers, and motors as well as to other necessary electrical equipment.

A wire system is termed a power line in case it has no parallel branches and a power network in case it has parallel branches.

According to their functions, power lines and networks are subdivided into transmission and distribution lines. Transmission lines serve to deliver power from a station to distribution centers. Distribution lines deliver power from distribution centers to the loads. Lines are also classed into: 1) overhead; 2) indoor; 3) cable (underground).Overhead lines include line conductors, insulators, and supports. The conductors are connected to the insulators, and these are connected to the supports. Conductors used for electric wiring are commonly produced of copper and aluminium. Wires connecting the components of various installations may be insulated. They may also be used without insulating. Since in short lengths of wire power loss is exceedingly low one can ignore it. However, the longer the wire, the greater is its resistance to current flow. On the other hand, the higher the offered resistance, the greater are the heating losses in electric wires. Reducing these undesirable losses is possible in two ways, namely, one can reduce either the resistance or the current. It’s easy for us to see how we can decrease resistance: making use of a better conducting material is necessary and as thick wires as possible. However, such wires are calculated to require too much material and hence, they will be too expensive. Is the decreasing of the current permissible? Yes, it’s quite permissible to reduce the current in the transmission line by employing transformers. In effect, the waste of useful energy has been greatly decreased due to high-voltage lines. It’s well-known that high voltage means low current in its turn results in reduced heating losses in electrical wires. However, using of power at very high voltages for anything’s dangerous but transmission and distribution. For that reason, the voltage is always reduced again before making use of power. Power loss in a line should not exceed a definite value. If this value is exceeded the line becomes inefficient.

One should know that the efficiency of a line isn’t constant - it may reverse. The value of the line efficiency depends on the load: the greater the load, the lower is the line efficiency. Protecting devices, fuses and relays are employed to protect the circuit against overcurrents and short-circuits.

The next line type is indoor line which includes conductors, cords and buses. The conductor may consist of one wire or a combination of wires not insulated from one another. They deliver electric current to the consumers.

As to underground lines, they are used in city areas and in the areas of industrial enterprises.

Also substations play an important role in transmitting the electric power. They are designed to receive energy from a power system, convert it and distribute it to the feeders. Thus a substation serves as a distribution centre. Substation feed various consumers provided that their basic load characteristics are similar. Therefore the energy is distributed without transforming of the voltage supplied.

Common substations comprise isolators, switchgear buses, oil circuit breakers, fuses, power and instrument transformers and reactors.

Substations are classed into step up and step down ones. The step up substation includes transformers that increase the voltage. Connected to the busbars of the substation are the power transmission lines of power plants of the system. As to step down substations, they reduce the voltage to 10 or 6 kV. At this voltage the power is supplied to the distribution centers and to the transformer substations of power consumers. A transformer substation serves for transmitting and distributing electric power. It comprises a storage battery, control devices and auxiliary structures. These substations are applied for feeding industrial enterprises. They possess certain advantages: they have flexible construction and easy and reliable operation. In case of a fault in the left-hand section, the main circuit breaker opens while the normally open section circuit breaker closes and puts the voltage of the section to normal.