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. Since in short lengths of wire power loss is exceedingly low one can ignore it. In long wires (longer than 10 m), 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.

3. Complete the sentences using the correct variant:

1. Aluminium is used due to its

a) high cost.

b) low cost and high efficiency.

 

2. Cross-section of different conductors

 a) varies.

b) is the same.

 

3. Power loss can be ignored

a) in short wires.

b) in long wires.

 

4. A definite value of loss

a) can be exceeded.

b) should not be exceeded.

 

5. Electric lines nowadays are

a) efficient.

b) inefficient.

 

6. Installations are protected

a) by switches.

b) by fuses.

4. Complete these sentences using while.

 

1. The cost of aluminium is comparatively low while....

2. In a short length of wire power loss is extremely low while....

3. The greater the load the lower is the efficiency of the line....

 

5. Answer these questions:

 

1. Why is aluminium widely used nowadays?

2. Is its cost very low or comparatively low?

3. What is the cross-section of copper conductors?

4. May one ignore power loss in short wire? Why?

5. What does the efficiency of a line depend on?

6. What are fuses used for?

7. When does a line become inefficient?

 

Think of three questions about this extract and put them to your

Groupmates.

consumer - потребитель; relation – отношение

 

When electric energy is produced at the power station, it is to be transmitted over electric wires to the consumer. Wire conductors offer resistance to the current flow; the longer the wire, the greater is its resistance to the current flow.  Accordingly, the higher the offered resistance, the greater are the heating losses in the wire.

 

Практическое занятие 22. Линии электропередач

Lesson 22. Transmission Lines

1. Read and learn the words:

area - площадь, область

distance - расстояние

network - сеть электролиний

support - опора, мачта

cord - провод

bus - шина

enterprise - предприятие

to term - называть, именовать

to divide - делить, разделять

to support - поддерживать

to distribute - распределять

accordingly - соответственно

as to -... что касается;... что до

long distance - большое расстояние

length of transmission lines - длина линий передачи

power consumption - потребление энергии

distribution centre - распределительный центр

city area - район городской застройки

 

Read and translate the text.

Transmission Lines

A power system is an interconnection of electric power stations by high voltage power transmission lines. Nowadays the electricity is transmitted over long distances and the length of transmitting power lines varies from area to area.

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 centres. Distribution lines deliver power from distribution centres 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. The greater the resistance, the higher are the heating losses in the conducting wires. In order to reduce the losses, a step-down transformer can be used.

Indoor lines include conductors, cords, and buses. The conductor may include 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. Accordingly, they are used in cities and towns, and in the areas of industrial enterprises.