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Electric power is generated at power plants and it must be transmitted to other parts of the country. Thick wires carry electric power over long distances. The wires are not always made of copper, often they are made of other metals.
A number of wires put together form one thick cable. A cable consists of a number of wires put together and a pair consists of two insulated conductors forming a metallic circuit. Thus the basic transmission element of communications is a long transmission line. A cable is the main part of this long transmission line. Nowadays the electricity is transmitted over long distances and the length of transmitting power lines varies from area to area.
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Answer the following questions
1. Where is electric power generated?
2. What carries electric power over long distances?
3. What is the main part of the transmission line?
4. What elements form one thick cable?
15.2 Choose the correct variant:
1. The transmission line may consist of …
a) thick wires
b) long and thick copper wires
c) thick copper cables
d) metallic conductors
2. Thick cables …
a) carry electric power
b) form the main part of the line
c) carry electric current
15.3 Translate the following word combinations: copper wire; power plants; electric cable; metallic cable; metallic circuit; metallic conductor; insulated conductor; insulated circuit of transmission line; a number of cables; thick wire; main parts; a number of pairs; this part; thick cables.
Electric lines and their efficiency
Wires are used to deliver electric power and to interconnect different
components of electrical installations. Conductors used for electric wiring are commonly produced of copper and aluminium. Aluminium is widely used nowadays due to its low cost. Copper is also widely used in electrical engineering but its cost is much higher.
Wires connecting the components of various installations may be insulated. They may also be used without insulation. In long wires (longer than 10m), power loss cannot be ignored since it is rather high. 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 is not constant – it may change. The value of the line efficiency depends on the load: the greater the load the lower is the line efficiency. At voltage losses of 2 to 5 per cent the efficiency of a line is 98 – 95 per cent. Protecting devices, fuses and relays are used to protect the circuit against overcurrents and short – circuits.
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