Unit 11 (part 1). The distribution system

1. Words to remember.

feeder – питающая линия

underground conduit – подземный кабельный канал

tap – снабжать, подавать

primary distribution – первичная распределительная линия

distribution transformer – распределительный трансформатор

step down – понижать

secondary distribution main – вторичная распределительная линия

2. Read the text. The distribution system

At the substations, the incoming power is lowered in voltage for distribution over the local area. Each substation feeds its local load area by means of primary distribution feeders, some operating at 2400 volts and others at 4160 volts and 13,800 volts or higher.

Ordinarily, primary feeders are one to five miles in length; in rural sections where demands for electricity are relatively light and scattered, they are sometimes as long as 10 or 12 miles. These circuits are usually carried on poles; but in the more densely built-up sections, underground conduits convey the cables, or the cable may be buried directly in the ground.

Distribution transformers are connected to the primary distribution lines. These transformers step down the primary voltage from 2400 volts, 4160 volts, or 13,800 volts, as the case may be, to approximately 120 volts or 240 volts for distribution over secondary mains to the consumer’s service.

The lines which carry the energy at utilization voltage from the transformer to consumer’s services are called secondary distribution mains and may be found overhead or underground. In the case of transformers supplying large amounts of electrical energy to individual consumers, no secondary mains are required. Such consumers are railroads, large stores, and factories. The service wires or cables are connected directly to these transformers. Transformers may also serve a number of consumers and secondary mains; they are located in practically every street in the area served by utility companies.

Services and meters link the distribution system and the consumer’s wiring. Energy is tapped from the secondary mains at the nearest location and carried by the service wires to the consumer’s building. As it passes on to operate the lights, motors, and various appliances supplied by the house wiring, it is measured by a highly accurate device known as the watt-hour meter. The watt-hour meter represents the cash register of the utility company.

3. Answer the questions.

1. How does each sustain feed its local load area?

2. What is the length of a primary feeder?

3. What transformers step down the primary voltage?

4. What lines are called secondary distribution mains?

5. How are the service wires or cobles connected?

6. Where may transformers serve?

4. Give the Russian equivalents of the following expressions.

Primary distribution feeder, rural sections, local road area, underground conduit, primary distribution line, utility company, for the consumer’s service, service wires, to tap.

5. Discuss the distribution system.

Unit 11 (part 2). Determining distribution voltages

1. Read the text.

Determining distribution voltages

There are two general ways of transmitting electric current-overhead and underground. In both cases, the conductor may be copper or aluminum, but the insulation in the first instance is usually air, except at the supports (poles or towers) where it may be porcelain or glass. In underground transmission, the conductor is usually insulated with rubber, paper, oil, plastic, or other material.

In overhead construction, the cost of the copper or aluminum as compared to the insulation is relatively high. Therefore, it is desirable when transmitting large amounts of electric power, to resort to the higher electrical pressures-or voltages, thereby necessitating slimmer, less expensive conductors. Low voltages necessitate heavy conductors which are bulky and expensive to install, as well as intrinsically expensive.

However, there is a limit to how high the voltage may be made and how thin the conductors. In overhead construction there is the problem of support-poles or towers. If a conductor is made too thin, it will not be able to support itself mechanically. Then the cost of additional supports and pole insulators becomes inordinately high. Underground construction faces the same economic limitation. In this case, the expense is insulation. Underground a cable must be thoroughly insulated and sheathed from corrosion. The higher the voltage, the more insulation is necessary, and the bigger the conductor, the more sheathing is necessary.