UNIT 8

CABLES

Active Vocabulary

to assume – принимать, приобретать conductor – проводник, провод, жила screening – экранирование, защита от излучения armouring – защитная оболочка, броня кабеля purity – чистота, беспримесность impurity - примесь, загрязняющее вещество superconductor – сверхпроводник resistivity – удельное сопротивление cross-sectional area – площадь поперечного сечения solid conductor – одножильный провод stranded conductor – многожильный (скрученный) провод solid – твердый, сплошной liquid – жидкий gaseous- газообразный varnish – лак film – пленка

fiberglass – стекловолокно to impregnate – пропитывать to induce – вызывать, побуждать polyvinyl chloride – поливинилхлорид polyethylene – полиэтилен cross-linked polyethylene – сшитый полиэтилен, полиэтилен с межмолекулярными связями ethylene propylene rubber – этиленпропиленовый каучук “live” wire – провод под напряжением legislation – законодательство to sheathe – заключать в оболочку, защищать to anneal – отжигать, прокаливать short-circuit - короткое замыкание to mount – устанавливать, монтировать, собирать, закреплять to embed – вмонтировать, вставлять, встраивать conduit – кабелепровод, трубопровод

1. Complete the sentences with the correct form of the verbs from the box.

impregnate sheathe induce mount assume embed anneal

1. This cloth __________ with a special chemical which protects it against rain.

2. Global warming might __________ dramatic changes in our climate.

3. One of the most important technical innovations implemented by the naval antagonists

during the American Revolution was the __________ of ship's hulls with copper.

4. When you __________ metal or glass, you heat it and then cool it in order to make it less

brittle and more malleable.

5. The controls of Deborah’s machinery were wall _________, it was Geoffrey himself who

had designed this.

6. The idea of __________ solar cells in roofing materials isn’t new.

7. Financial management __________ greater importance nowadays.

Reading 1

2. Read the text and answer the following questions:

1. How is power transmission carried out?

2. What are the reasons for choosing this or that type of cables?

3. Why has the matter of reliability of cables become more important nowadays?

4. What materials are commonly used for making conductors?

5. What materials can be used for insulation?

6. What are the reasons for the choice of different insulation materials?

Cables

Cables have been used in transmission and distribution networks since the early days of the electrical power industry. Generally, long distance power transmission is carried out through overhead lines. However, transmission and distribution in densely populated urban areas mostly uses underground cables. Although significantly more expensive than the overhead lines, the cables are preferred in urban areas due to safety, reliability and aesthetical considerations. As a result of developments in insulating materials and manufacturing techniques, high voltage cable technology has improved significantly over the years. With a continuous increase in the overall length of cable networks, questions regarding reliability, failure modes and diagnostics of such cables have assumed greater significance.

CABLE MATERIALS

Conductors

Cables are constructed using a variety of materials for conductors, insulation, screening and armoring. The most common conductor materials are copper or aluminum of high purity (99,5% purity), since the resistivity of such materials significantly increases with impurity content. Sometimes, sodium is also used as the conductor material. In recent years, the possibility of using high temperature superconducting materials for power applications is also being examined. The choice between aluminum and copper is normally based on resistivity (ρ), cost as well as mechanical and manufacturing considerations. Table 1 compares resistivity values for a few materials used in cables. For a given current rating, aluminum requires a larger conductor cross-sectional area than copper. Both solid and stranded conductors are used; the choice depends upon total cross-sectional area, flexibility and manufacturing considerations. For larger cross sections, stranded construction with alternate layers spiraled in opposite directions is generally preferred.

Table 1 Resistivity of Some Conductors at 20°C

Material	ρ(μΩ-cm)
Copper Aluminum Sodium Lead Steel	1.73 2.83 4.68 21.5 10.20