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UNIT 7 (PART 2). CONDUCTORS AND INSULATORS
1. Words to remember.
suspension insulator –подвесной изолятор
spool insulator –катушечный изолятор
strain insulator –натяжной изолятор
string –подвесной провод
a sharp curve– кривая малого радиуса
guy cable/wire –оттяжка (антенны)
to pierce –протыкать,пробивать отверстие
secondary main –вторичная электрическая цепь
tapered hole –заостренное, конусообразное отверстие
secondary rack –вторичная стойка
to loop – соединить в петлю
2. Read the text.
The higher the voltage, the more insulation is needed. Transmission lines use extremely high voltages, 69,000 to 375,000 volts, for example. At these voltages the pin or post-type insulator becomes too bulky and cumbersome to be practical, and the pin which must hold it would have to be inordinately long and large. To meet the problem of insulators for these high voltages, the suspension insulator was developed. The suspension insulator hangs from the cross arm, as opposed to the pin insulator which sits on top of it. The line conductor is attached to its lower end. Because there is no pin problem, any distance can be put between the suspension insulator and the conductor can be provided just by adding more insulators to the “string”. The entire unit of suspension insulators is called a string. How many insulators this string consists of depends on the voltage, the weather conditions, the type of transmission construction, and the size of insulator used. It is important to note that in a string of suspension insulators one or more insulators can be replaced without replacing the whole string.
Strain Insulators. Sometimes a line must withstand great strain for instance at a corner, at a sharp curve, or at a dead-end. In such a circumstance the pull is sustained and insulation is provided by a strain insulator. On a transmission line, this strain insulator often consists of an assembly of suspension insulators. Because of its peculiarly important job, a strain insulator must have considerable strength as well as the necessary electrical properties. Although strain insulators come in many different sizes, they all share the same principle; that is, they are constructed so that the cable will compress the porcelain. Strain insulators are sometimes used in guy cables, where it is necessary to insulate the lower part of the guy cable from the pole for the safety of people on the ground. This type usually consists of a porcelain piece pierced with two holes at right angles to each other through which the two ends of the guy wires are looped, in such a manner that the porcelain between them is in compression.
Spool Insulators. The spool-type insulator, which is easily identified by its shape, is usually used for secondary mains. The spool insulator may be mounted on a secondary rack or in a service clamp. Both the secondary low-voltage conductors and the house service wires are attached to the spool insulator. The use of such insulators has decreased greatly since the introduction of cabled secondary and service wires. The tapered hole of the spool insulator distributes the load more evenly and minimizes the possibility of breakage when heavily loaded. The “clevis” which is usually inserted in this hole is a piece of steel metal with a pin or bolt passing through the bottom.
3. Give the Russian equivalents of the following expressions.
Transmission lines; post – type insulator; inordinately large; to hang from the cross arm; a dead – end; assembly of suspension insulator; electrical properties; a guy cable; pierced with two holes; a right angle; to minimize the possibilities of breakage; a looped wire; to withstand a strain; “string”; too bulky and cumbersome; spool insulator; a secondary rack; “clevis”.
4. Match items in column A with items in column B.
Column A Column B
1. consists of a. the porcelain
2. hang from b. the cross arm
3. sit on c. the pin insulator
4. insulate d. many different sizes
5. attach to e. guy cable
6. compress f. a great strain
7. opposed to g. porcelain piece
8. come in h. secondary main
9. use in i. for the safety of people
10. withstand j. top of insulator
11. mount k. two end of the guy wires
12. minimize l. the possibilities of breakage
13. use for m. on a secondary rack
5. Complete the table using information from the texts.
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