Unit 3 Railway Electrification

Railway must operate at variable speeds using different electrification systems such as AC (alternating current) and DC (direct current).

DC is a constant flow of electricity which travels around a circuit in one direction.

Unlike a DC supply, an AC supply flows backwards and forwards: its direction continually alternates. The rate at which the current alternates, called the frequency, is measured in hertz (Hz). For example, in the UK, AC supply is 50 Hz: it alternates 50 times per second.

Electricity supply is generated at power stations, which use large generators. A generator converts mechanical energy into electrical energy. Current from the generators leaves the power station and enters the power grid – the network of power lines (cables) which transmits it around the country.

DC voltages between 600V and 800V are used by most tramways (streetcars), trolleybus networks and underground (subway) systems. The DC system is quiet simple but it requires thick cables and short distances between feeder stations.

3kV DC is used in Belgium, Italy, Spain, Poland, Czech Republic, Slovakia, Slovenia, Croatia, South Africa and former Soviet Union countries.

DC is also used in third-rail systems. Third rail is applied in small-diameter tunnels and subway systems. There is also a four-rail system, which is used in the London underground.

AC is only used on overhead wires, as it implies very high voltages. Inside the locomotive, the transformer steps the voltage down for use by traction motors.

Ex.1. Match the words (1-6) with the definitions (A-F).

1. voltage 4. ohm

2. AC 5. current

3. DC 6. volt

1. a measurement of the force of electricity;

2. a current that flows in two directions;

3. a measurement showing resistance;

4. the quantity of electricity in a wire;

5. the strength of moving electricity;

6. a current that flows in one direction.

Ex.2. Fill in the gaps with the words from the box.

electron, resistance, watt, amperes

1. A(n) ……. is too small to see without a powerful microscope.

2. Many wires are made out of copper because of its low …. .

3. A(n) …….. measures how much electrical power is being used.

4. A common way to measure electric current is …. .

Ex.3. Listen to the dialogue and mark the statements as true (T) or false (F).

1. The student doesn’t understand the difference between two types of currents.

2. Remembering what the letters stand for helps the student.

3. The student is learning about AC and DC for the first time.

Ex.4. Listen again and complete the conversation.

Instructor: Yesterday, we discussed AC and DC. Now, let’s move on to…

Student: Excuse me, Mr. Green. I still don’t understand ……………………..

Can you explain that again?

Instructor: Sure, do you remember…………………………………………….?

Student: Yes, AC is……………… DC is ………………….

Instructor: Good! Now, simply remember this:……………………………….

Student: What do you mean?

Instructor: Alternating current ………………….. It goes back and forth. ……

………. does not.

Student: Oh, ………………… Thanks.

Ex.5. Read and translate the following attributive groups.

One direction electricity flow, negative charge particles, electric current increase, electrical supply electromotive force, high resistance materials, power station generator, power cables network, third-rail subway system, high voltage overhead wires.

Ex.6. Give three forms of the adjectives. Use the adjectives in your own sentences.

Positive Comparative Superlative

low lower the lowest

high …………… …………..

small ……………. …………..

large ……………. …………..

powerful more powerful the most powerful

efficient ……………. ………….

useful …………… …………..

little less the least

far farther/further the farthest/furthest

good …………… …………..

bad …………… …………..

Ex.7. Complete the article about electric and diesel-electric locomotives using the words in the box.

An electric locomotive is one that is (1)... by an external energy (2)…, most often via overhead electric lines. This differs from a diesel-electric locomotive, which has an onboard fuel tank and a diesel-powered generator to provide electricity for its motors. Purely electric power has numerous advantages over diesel-electric power, explaining the choice of electric locomotives for use in high-speed trains.

Firstly, an electric locomotive needs to carry neither a generator nor fuel. Its mass is, therefore, lower than a diesel-electric equivalent. This results in a significant efficiency (3)…, as the electric locomotive’s smaller mass means less (4)… is done – measured as a total number of (5)… - on a given journey. For a comparable rate of acceleration, its motors are also required to provide less (6) ….

As they use a lower (7)…., this means less (8)… motors can be used, making them smaller, thus further reducing weight and improving (9)… In addition, electric locomotives use only (10)… energy. This means there is no need to (11)… energy from one (12)… to another on board the train (electricity can be generated more efficiently in power stations).

In a diesel-electric unit, the energy conversion process starts with (13)… energy, which is (14)… within the hydro-carbon compounds of diesel. This fuel is burned to produce (15)… energy, and the heat is then converted by the engine into (16)… energy, which provides the movement to drive the train. This process is a very long way from being 100% (17)… - only a small percentage of the initial chemical energy is converted to the (18)… energy that is actually used to drive the train, with a significant percentage being (19)… into the air in the form of heat, constituting (20)… energy.

Ex.8. Read and translate the following words and fill in the table. Make up your own sentences with these words.

Verb	Noun	Adjective	Adverb	Attribute

Electric, electrical, electricity, electrify, electrified, electrification; effect, efficient, efficiently, efficiency; require, requirements, required, requiring; reduce, reducing, reduction, reduced; improve, improvement, improving, improved, power (n,v), powerful, powered, movement, move, moving, moved; use (n,v), user, useful, useless, usefully, uselessly, used; generate, generated, generation, generating.

Ex.9. Translate the following sentences using the Passive Voice.

1. Электроэнергия вырабатывается на электростанциях.

2. На железной дороге используется и переменный, и постоянный ток.

3. Механическая энергия преобразуется в электрическую посредством генератора.

4. Скорость изменения тока называется частотой и измеряется в Гц.

5. Электроток передается от генератора в электросеть.

6. Постоянный ток используется в системе городского транспорта.

7. Третий рельс применяют в тоннелях и метро.

8. Переменный ток используют на высоковольтных линиях.

9. Напряжение понижается при помощи трансформатора.

10. Электроток измеряется в амперах.

Ex.10. Tell the class about:

1. the difference between AC and DC;

2. third rail system;

3. the difference between three types of locomotives: electric, diesel-electric and diesel one;

4. types of railway electrification used in different countries.