Unit 15 Topic: Transformers

1. Pre-reading tasks.

a) you will read a text about transformers. What kinds of transformers do you know?

b) Read and memorise the following words and word-combinations in their specialized meanings.

1. alternating voltage – перемінна напруга

2. flux – течія, поток

3. core – серцевина

4. neutral wire – нейтральний кабель, провід

5. copper – мідь

Transformers

A transformer is a static electric device (that is, one free from rota­ting or moving parts) most, often used to convert one alternating voltage to another alternating voltage (or other alternating voltages) at the same frequency by mutual induction.

A transformer has at least two windings linked by a common magnetic flux but electrically insulated from each other (except in an autotransformer).

The purpose of the core is to enhance the inductive coupling between the windings, and the objective of using a laminated core is to reduce eddy currents (Fig. 8.1). No cores are used in air-cored transformers operating at frequencies above around 20 kHz, since the core is not magnetized all the same because of a marked increase in eddy currents.

The transformer winding connected across a supply source (which may be power line, a generator, etc.) is called primary. All the quantities associated with this winding are also called primary (the primary turns, the primary voltage, the primary current, etc.)

Transformers may be shigle-phase and three-phase. In a three-phase transformer, the primary or secondary winding refers to the three phase windings carrying the respective (primary or secondary) voltage.

According to the manner in which transformers are cooled, they are classed into dry and oil – immersed.

Each transformer has a nameplate which bears all of its ratings. These include the volt­age on the high-voltage side, the voltage on the low-­voltage side; its appa­rent power; its current at the rated apparent power; the 'frequency; tne number of phases; the phase interconnecton and the method of cooling.

A three-phase system of currents or voltages might be handled by three single-phase transformers operating as a coordinated unit. The actual practice, however, is to combine the three single-phase transformers into a single three-phase unit. In doing so, a good deal of materials is saved, and we will show how this is achiev­ed.

To begin with, we build the core of a three-phase transformer by joining together the cores of the single-phase units and leaving un­changed their parts carrying the windings. This ar­rangement may be likened to a star connection of three electric cir­cuits. As will be recalled, no neutral wire is needed for a three-phase system operating into a balanced load, because no current would flow in it. By doing well without a neutral wire, we save a fairly good quantity of copper.

An assemblage of three single-phase transformers is more expen­sive than one three-phase transformer of the same power rating; it takes up a larger floor area.

3. Find the answers to the questions.

1. What is a transformer?

2. What are the main elements of the transformer?

3. What kinds of transformers do you know?

4. Why are they classed into dry and oil-immersed?

5. An assemblage of three single-phase transformers is more expensive, isn’t it?

4. Complete the sentences:

1. A transformer is a static electric device often used to ... .

2. ... is called primary.

3. Transformers may be ... .

4. ... they are classed into dry and oil-immersed.

5. Each transformer has ... .

6. A three-phase system of currents or voltages might be ... .

5. Match the following English words and word-combinations.

1. induction a) навантаження

2. winding b) взаємний

3. reduce c) відправляти

4. mutual d) індукція

5. refer e) обмотка, перемотка

6. nameplate f) марка

7. combine g) об’єднувати, сполучати

8. eddy h) зменшувати

9. load i) вихідний, початковий

10. primary j) вихор

6. True or false statements:

1. A transformer is a machine that converts electrical energy into mechanical energy.

2. A transformer has an armature, a commutator, brushes.

3. Transformers are classed into dry and oil-immersed.

4. Each transformer has electric drives.

II Retell the text “Transformers” ... .

III Rendering

1. Read the text and translate it into Ukrainian using new words in their specialized meanings below.

1. permeable –

2. limb –

3. yoke –