4. Make up the plan to the text and retell it. Unit 17 (part 4). Transformers

1. Words to remember.

prevent – предотвращать, не допускать

injury – повреждение

agent – вещество

cooling – охлаждение

submerge – погружать

substitute – заменитель

varnish – лак

sealed dry type – запечатанный сухой тип

2. Read the text. Methods of Transformer Cooling

The wasted energy in the form of heat generated in transformers due to unpreventable iron and copper losses must be carried away to prevent excessive rise of temperature and injury to the insulation about the conductors. The cooling method used must be capable of maintaining a sufficiently low average temperature. It must also be capable of preventing an excessive temperature rise in any portion of the transformer, and the formation of ‘hot spots.’ This is accomplished, for example, by submerging the core and coils of the transformer in oil, and allowing free circulation for the oil. Sometimes, for reasons of safety, the use of oil as a cooling agent is prohibited. (Oil can be a fire hazard.) In these situations, special fluids, known as ‘askarels’ can be used in place of oil. However, when using these substitutes, the varnishes which are generally applied to the insulation of the coils must be chosen carefully. For indoor use, in clean, dry locations, open dry-type air cooling can be used. For outdoor or indoor, use, a sealed dry type can be obtained.

Some transformers are cooled by other means: (a) by forced air or air blast, (b) by a combination of forced oil and forced air, and (c) in some special applications, by water cooling.

3. Put questions to the text.

4. Speak about.

1. The reason of carrying away the wasted energy in the form of heat generated in transformers.

2. Types of cooling and substances (agents) used for cooling.

Unit 17 (part 5). Transformers

1. Words to remember.

distribution transformer – распределительный трансформатор

to step up/down – повышать/понижать

mains – сети

closed-loop – закрытая петля

to be wound – быть намотанным

to be immersed – быть погруженным

bushing – проходной изолятор, переходной фитинг

lead – свинец

tank – корпус

lug – опора, кронштейн

2. Read the text.

Distribution Transformers

Besides conductors and insulators, many other pieces of equipment are necessary to get electric power from the generator to a consumer. The distribution transformer is certainly the most important of these pieces of equipment. Without the distribution transformer, it would be impossible to distribute power over such long distances. The purpose of a transformer is to step up or step down voltage. In the case of the distribution transformer, the voltage is stepped down from that of the primary mains of a distribution circuit to that of the secondary mains. In most cases, this is from 2400, 4160, or 13,800 volts to 120 or 240 volts.

Most distribution transformers consist of (1) a closed-loop magnetic core on which are wound two or more separate copper coils, (2) a tank in which the corecoil assembly is immersed in cooling and insulating oil, (3) bushings for bringing the incoming and outgoing leads through the tank or cover.

Bushings

A bushing is an insulating lining for the hole in the transformer tank through which the conductor must pass. Primary bushings are always much larger because the voltage is higher at that point. Sometimes the primary and secondary bushings are called high-voltage and low voltage bushings.

Distribution transformers are almost always located outdoors where they are hung from crossarms, mounted on poles directly.

How a transformer is mounted is a matter of considerable importance. The distribution transformer must stay put and continue functioning even in the midst of violent winds, pouring rain, freezing cold, sleet, and snow. Besides weather, there is danger of the pole itself being hit by a carelessly driven vehicle.

Modern pole-mounted transformers have two lugs welded directly on the case. These lugs engage two bolts on the pole from which the whole apparatus hangs securely. This method, which is known as direct mounting eliminates the need for crossarms and hanger irons thus saving a considerable amount of material and labor.

A transformer should not be mounted on a junction pole (a pole supporting lines from three or more directions) as this makes working on such a pole more hazardous for the worker.

Manufacturers produce two types of distribution transformers: the conventional and the completely self-protected. (CSP)

A conventional distribution transformer consists only of a case containing the transformer unit with protective devices, usually a primary fuse cutout and a lightning arrester, mounted separately on the pole or crossarm.