 |
Transmission Lines. 3. Complete these sentences using the correct variant. 4. Complete the sentences using while or as to. Follow the model on page 13.
|
|
|
|
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.
3. Complete these sentences using the correct variant.
| 1. Electric power is transmitted | a) by electric lines. b) by power networks. |
| 2. Lines are divided into | a) overhead and underground. b) overhead, indoor and underground. |
| 3. An overhead line includes | a) conductors and supports. b) conductors, insulators and supports. |
| 4. The insulators are connected | a) to the buses. b) to the supports. |
| 5. Conductors consist of | a) bare wire. b) insulated wire. |
| 6. Underground lines are used | a) in cities. b) in areas of enterprises. c) in agricultural areas. |
4. Complete the sentences using while or as to. Follow the model on page 13.
1. The system is termed a power line in case it has no parallel branches ….
2. Transmission lines deliver power from a station to distribution centres ….
3. Low current results in decreased heating losses ….
4. Overhead lines are used in open areas ….
5. Answer these questions:
1. By what means is electric power system transmitted?
2. Which system has no parallel branches?
3. Into what groups are all the transmitting lines classed?
4. What components does an overhead line have?
5. What elements do conductors consist of?
6. In what areas are overhead (underground) lines used?
Unit Twenty-Seven [27]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
|
|
|
b) Cover the left column and translate the Russian words back into English.
| safe | безопасный | |
| safety | безопасность; предохранительный | |
| danger | [ˈ deɪ ndʒ ə ] | опасность |
| strength | [streŋ θ ] | сила |
| earth | [ə ː θ ] | заземление, земля |
| ground | земля, почва | |
| dead | [ded] | выключенный |
| dangerous | [ˈ deɪ ndʒ rə s] | опасный |
| strong | сильный, яркий (о свете) | |
| to save | спасать | |
| to disappear | исчезать | |
| to appear | появляться | |
| live | [laɪ v] | под напряжением |
| dry | сухой | |
| wet | сырой, мокрый |
2. Read the words and put down their Russian equivalents. Then translate them back into English (orally).
| [ˈ æ tmə sfɪ ə ] | atmosphere | ___________________________ |
| [ˌ pə ː sə ˈ nel] | personnel | ___________________________ |
| [ˈ kɔ ntæ kt] | contact | ___________________________ |
| [ˈ reɡ julə ] | regular | ___________________________ |
| [kə nˈ troul] | control | ___________________________ |
| [dɪ ˈ tekt] | detect | ___________________________ |
3. Put down the corresponding nouns. Form nouns from these adjectives and translate them into Russian.
Model: wide - wid th
| strong - | ________________ | broad - | ________________ |
| long - | ________________ | high - | ________________ |
4. Put down the Russian for:
| under voltage | _______________________________________________ |
| under 20 V | _______________________________________________ |
| over 30 V | _______________________________________________ |
| the power is on | _______________________________________________ |
| the power is off | _______________________________________________ |
| great strength | _______________________________________________ |
| dry air | _______________________________________________ |
| dead conductor | _______________________________________________ |
| live conductors | _______________________________________________ |
5. Choose the suitable words and translate the sentences:
1. The danger of electric shock (appears, disappears) when the conductor becomes (live, dead).
2. Current passes through faulty (earthed, unearthed) part of installations when the power is on.
3. Low accuracy of measurement is (an advantage, a disadvantage) of the measuring device.
4. The danger of electric shock (increases, decreases) in the wet and hot atmosphere.
5. No current flows through a (dead, live) conductor.
6. Fill in using the verbs to detect, to appear, to disappear, to decrease:
1. When resistance increases, the risk of electric shock ….
2. Faults in electric installations are … by means of special devices.
|
|
|
3. Electric power … only on live conductors with power on.
4. When the device is switched off electric power ….
Safety Earthing System. Electric Shock
The strength of current depends on both the voltage and the resistance in a circuit. A current of 50 mA is dangerous for a man and a current of 100 mA and higher is lethal.
| a) Contact with an ungrounded motor frame | b) Contact with a grounded motor frame |
Fig. 19
Earthing system serves to protect attending personnel from electric shocks when voltage appears on parts that are normally dead. The risk of an electric shock decreases with decreasing voltage. In wet and hot atmosphere the risk of electric shock increases. Safe voltage for circuits used in dry atmosphere is under 36 V. When the power is on, contacts with live conductors are dangerous for life. Thus, measures are taken to protect attending personnel from contacts with live parts of installations under voltage.
The danger of an electric shock disappears provided the metal parts of installations under voltage are connected with ground by means of safety earthing.
Connecting to ground is made by means of earthing electrodes which are connected directly with ground.
The insulation resistance of any installation should be regularly controlled by means of measuring devices. The faulty parts should be detected, eliminated, and replaced by new ones.
7. Complete the sentences using the correct variant:
| 1. Earthing system serves | a) as protection from an electric shock. b) as connection with ground. |
| 2. Voltage appears on | a) dead parts. b) live parts. |
| 3. Contact with live conductors is | a) dangerous. b) safe. |
| 4. Connection to ground is made | a) by means of wire conductors. b) by means of earthing electrodes. |
| 5. Danger of an electric shock disappears if the frame | a) is earthed. b) is unearthed. |
|
|
|
