II. Read the statements and define if they are true or false (according to the text content). If the statement is false, correct it.

1. In a single-phase alternator all the armature conductors are connected in series as one winding. 2. In a two-pole, single-phase alternator the rotor consists of two poles of the same polarity. 3. The windings are electrically separated from each other. 4. Each winding is made up of several parts which are not connected. 5. The voltage induced in any of three single-phase windings is phase-displaced by 180 degrees from the other two. 6. Two-phase and single-phase alternators are more efficient than three-phase alternators.

Text 2

Ø Translate the following text in writing, using the given vocabulary.

Induction Motors

The induction motor is the most commonly used a.c. motor because of its simplicity, its robust construction and low manufacturing cost. These characteristics of the induction motor are due to the fact the rotor is a self-contained unit which is not connected to the external source of voltage. The induction motor derives its name from the fact that a.c. currents are induced in the rotor circuit by the rotating magnetic field in the stator.

The stator construction of the induction motor and of the synchronous motor is almost identical, but their rotors are completely different. The induction motor rotor is a laminated cylinder with slots in its surface. The windings in these slots are one of the two types. The most common is called a 'squirrel-cage winding', which is made up of heavy copper bars connected together at either end by a metal ring made of copper or brass. No insulation is required between the core and the bars because of very low voltage generated in the rotor bars. The air gap between the rotor and stator is kept very small so as to obtain maximum field strength.

The other type of winding contains coils placed in the rotor slots. The rotor is then called a 'wound rotor'.

Regardless of the type of rotor used, the basic principle of operation is the same. The rotating magnetic field generated in the stator induces an e.m.f. in the rotor. The current in the rotor circuit caused by this induced e.m.f. sets up the magnetic field. The two fields interact and cause the rotor to turn.

TEST YOURSELF

I. Check if you remember the following words and word combinations. Consult a dictionary if necessary.

a) temporary magnet, equal, toward, magnetic flux, rectifier, the latter, capacitance, both, ammeter, watthourmeter, ensure, brush gear, drive motor, output, amplifier, compound generator, cumulatively compounded, alternator, relative, slip ring, however;

b) катушка, заряд, вращаться, магнитное поле, электродвижущая сила, источник питания, напряжение, измерительный прибор, мощность, монтировать, коллектор, обмотка возбуждения, совпадать, генератор независимого возбуждения, генератор параллельного возбуждения, противодействовать, статор, подходить, асинхронный двигатель, отличаться.

II. Give the words to the following definitions.

What do you call:

1) the properties of the molecules of iron to store energy in a field?

2) the study of electricity in motion?

3) a piece of iron or steel which being magnetized retains its magnetism?

4) the method of producing electricity based on operation of rotating generators in which electricity is produced by conductors moving through a magnetic field?

5) a driving force making electrons move through a metal conductor?

6) an electric current that doesn't change its direction and magnitude?

7) an electric unit intended for measuring the strength of electric current in a surface?

8) an external force applied to a circuit to overcome the opposition to the flow of current?

9) a device used for measuring voltage?

10) the rotating part of a d.c. machine?

11) the element of a d.c. machine which is intended to convert alternating e.m.f. induced in the armature into direct one?

12) the element which brings into rotation the armature?

13) the type of a d.c. generator the field winding of which obtains its supply from a separate current source?

14) the stationary part of a d.c. machine?

15) the element of a d.c. machine that is designed for collecting the current from the armature winding and leading it to the latter?

16) the type of a d.c. generator the field winding of which is connected in parallel with the armature winding?

17) a combined series and shunt generator?

18) a generator if the series field opposes the shunt field?

19) the type of alternator with a stationary armature winding and a rotating field winding?

20) an alternator operated as a motor, in which a.c. is applied to the stator and d.c. is applied to the rotor?

Grammar Reference

The Infinitive (Инфинитив)

Инфинитив является неличной формой глагола. Он выражает действие, и его признаком является частица to: to speak.

Формы инфинитива

Употребление

Инфинитив в функции подлежащего

To explain this law is not very easy. – Объяснить этот закон не очень просто.

Инфинитив в функции обстоятельства

Newton came to Cambridge to continue his education. – Ньютон приехал в Кембридж, чтобы продолжить своё образование.

Инфинитив в составном именном сказуемом

The task of our engineers is to use solar energy for peaceful purposes. – Задача наших инженеров заключается в том, чтобы использовать солнечную энергию в мирных целях.

Инфинитив в составном модальном сказуемом

The scientist was to read a paper at the conference. – Учёный должен был выступить с докладом на конференции.

Инфинитив в функции определения

1. The instruments to be used. – Приборы, которые следует использовать (можно использовать, будут использоваться).

2. The problem to consider – Вопрос, который следует рассмотреть... (будет рассматриваться...)

3. Не was the first to discover... – Он первый открыл...

4. The first scientist to discover... – Первым ученым, который открыл... Первым ученым, открывшим...

Инфинитив в функции дополнения

1. Не forgot to insulate a conductor with insulating material. – Он забыл изолировать проводник изоляционным мате­риалом.

2. Не is going to change the applied voltage. – Он собирается изменить приложенное напряжение.