Insulation

The most important insulation material is air. A variety of solid, liquid, and gaseous insulators are also used in electrical apparatus. In smaller transformers, generators, and electric motors, insulation on the wire coils consists of up to four thin layers of polymer varnish film. Film insulated magnet wire permits a manufacturer to obtain the maximum number of turns within the available space. Windings that use thicker conductors are often wrapped with supplemental fiberglass insulating tape. Windings may also be impregnated with insulating varnishes to prevent electrical corona and reduce magnetically induced wire vibration. Large power transformer windings are still mostly insulated with paper, wood, varnish, and mineral oil; although these materials have been used for more than 100 years, they still provide a good balance of economy and adequate performance.

The cable insulation usually consists of impregnated paper, synthetic polymers and compressed gases. Early cables mostly used impregnated paper insulation. Next stage was the introduction of oil-filled paper insulation. At present, polymers are widely used. The polymers most often used are polyvinyl chloride (PVC) for low-voltage cables, polyethylene (PE), cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) for medium-voltage cables; and XLPE and EPR for high-voltage cables. Flexible insulating materials such as PVC are used to insulate the circuit and prevent human contact with a 'live' wire – one having voltage of 600 volts or less. Alternative materials are likely to become increasingly used due to EU safety and environmental legislation making PVC less economic.

Use of English 1: vocabulary

3. Match each word with the correct preposition or prepositions from the box. Check your answers in the text.

of with for on upon in

1 variety 2 consist 3 impregnate 4 insulate 5 use

6 wrap 7 result 8 possibility 9 depend 10 base

4. Choose the correct preposition.

1. Air in most urban areas is made up of an array of contaminants, some gases, some

microscopic particles, all containing a variety (for/of) chemical ingredients.

2. The Ringhals power station consists (of/on) four reactors in southern Sweden, near

Gothenburg.

3. The paper is impregnated (in/with) mineral oil to provide more insulation.

4. No, you won't get shocked - the carbon fiber carrying the charge will be sandwiched

and insulated (with/on) other composite materials.

5. For years, engineers have studied the possibility (of/upon) all those car batteries being used

to store energy.

6. Because it depends (upon/in) radio signals moving through the air, there's a lot that can

interfere.

7. Enfucell’s batteries are made of low-cost, environmentally friendly materials based (in/on)

zinc and manganese dioxide with zinc chloride as an electrolyte.

8. Apple has an exclusive agreement to use liquid-metal technology (in/of) consumer

electronics.

9. The group's Web site was knocked out of service for extended periods Sunday as

a result (with/of) the attacks.

10. Some media and entertainment companies use optical discs (of/for) video archiving. 

11. To seal off reactor buildings, engineers are planning to wrap them (with/on) polyester

sheets stretched over steel frames.

12. As for reading your e-mail, it depends (upon/for) what e-mail program he's running and

whether it can open mail in the format you are sending.

Use of English 1: grammar Conditionals

5. Complete conditional sentences by putting the verbs in brackets in the correct forms.

1. If we ______ (have) enough funds to buy hand-held computers for the college, we would be able to attract more students to come here.

2. If it is inappropriate to have state-of-the-art equipment installed in this building, we ______ (take) it back to the suppliers.

3. If he wasn’t such a technophobe, he ______ (get on) much better with his kids as they are mad about all types of technology.

4. If the computer software ______ (be) more user-friendly, we wouldn’t have had as many problems as we did.

5. Provided that the new equipment is efficient, we ______ (be able to) increase productivity

within a few weeks.

Reading 2