Unit 11

Task 1. Study new words and word combinations.

1	mutual induction	['mjuːʧuəl ], ['mjuːtjuəl]	взаимоиндукция
2	turn		виток
3	step up		повышать
4	step down		понижать
5	transfer	[træns'fɜː]	передавать
6	primary winding	['praɪmərɪ]	первичная обмотка
7	secondary winding	['sekəndərɪ]	вторичная обмотка
8	supply	[sə'plaɪ]	поставлять, запас
9	operate	['ɔpəreɪt]	работать, функционировать
10	magnetic field	[mæg'netɪk fiːld]	магнитное поле
11	induced voltage	['vəultɪʤ ], ['vɔltɪʤ]	индуцируемое напряжение
12	power transmission		передача энергии
13	ferromagnetic core		ферромагнитный сердечник
14	power grids		энергетические сети
15	magnetic flux		магнитный поток

TASK 2. Read the text and translate it from English into Russian.

TRANSFORMERS

A transformer is a device which is used to transfer electrical energy from one circuit to another. Besides, a transformer is used to change the voltage and current in a circuit. A transformer is based on the fundamental principle of mutual induction. A simple transformer consists of two coils and a core. The coils are called the primary and the secondary. These coils are wound over a common core. Transformers can have either air or magnetic cores. It depends on the frequency at which they are to be operated. The primary winding is connected to the voltage source. It receives energy. The secondary winding is connected to the load resistance and supplies energy to the load. There are two types of transformers: a step-up transformer and a step-down transformer. In a step-down transformer the number of turns in the primary is greater than the number of turns in the secondary. This transformer steps down the voltage. In a step-up transformer the number of turns in the secondary is greater than in the primary. The important thing in transformer design is the insulation of windings. There are 3 main classifications of transformers: for power-frequency circuits, for audio-frequency and for radio frequency.

TASK 3. Complete the sentences.

1. A transformer is a device which is used to . . .

2. A transformer is based on . . .

3. The coils of the transformer are called . . .

4. The primary winding of the transformer is connected . . .

5. The important thing in transformer design is . . .

TASK 4. Answer the following questions and retell the text.

1. What is a transformer used for? 2. What principle is a transformer based on? 3. What cores can transformers have? 4. What is the function of a primary winding? 5. What two types of transformers does the text discuss? 6. What is the important thing in transformer design? 7. What three main classifications of transformers do you know?

TASK 5. Make up the sentences using the following words and word combinations.

A transformer, a device, to transfer electrical energy, to change voltage and current in a circuit, mutual induction, two coils, a core, the primary winding, the secondary winding, to receive energy, to supply energy, a step-up transformer, a step-down transformer, the number of turns, the insulation of windings.

TASK 6. Translate the sentences, pay attention to the degrees of comparison.

The simplest condenser consists of two plates separated by an insulator. 2. In practice the most common types of dielectrics are: air, mica, paper. 3. We think that he is the best inventor of our plant. 4. I work worse than he does. 5. This new device works better that the old one. 6. Scientists try to get better knowledge of the mineral resources of this region. 7. The proton was found to be 1,840 times heavier than the electron. 8. Radio is one of the greatest achievements of modern engineering.

TASK 7. Read the text about transformers and complete it with the following words and phrases.

magnetic field, winding, mutual induction, conductors

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled 1) … – the transformer’s coils. A varying current in the first or primary 2) … creates a varying magnetic flux in the transformer’s core, and thus a varying 3) … through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or “voltage” in the secondary winding. This effect is called 4) … .

number of turns, primary voltage, ferromagnetic core, induced voltage

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the 5) … in the secondary winding(VS) is in proportion to the 6) … (VP), and is given by the ratio of the 7) … in the secondary (NS) to the number of turns in the primary (NP) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be “stepped up” by making NS greater than NP, or “stepped down” by making NS less than NP.

In the vast majority of transformers, the windings are coils wound around a 8) … , air-core transformers being a notable exception.

power transmission, power grids, electronic circuits

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of 9) … . All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some 10) … , transformers are still found in nearly all electronic devices designed for household (“mains”) voltage. Transformers are essential for high voltage 11) … , which makes long distance transmission economically practical.

TASK 8. a) Match the names with the descriptions.

Power transformers

Auto transformer