II. Read and translate the text.

A transformer is used to transfer energy. Due to the transformer electric power may be transferred at a high voltage and reduced at the point where it must be used to any value. Besides, a transformer is used to change the voltage and current value in a circuit.

 

 A two-winding transformer consists of a closed core and two coils (windings). 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.

The value of voltage across the secondary terminal depends on the number of turns in it. In case it is equal to the number of turns in the primary winding the voltage in the secondary winding is the same as in the primary.

In case the secondary has more turns than the primary the output voltage is greater than the input voltage. The voltage in the secondary i_s greater than the voltage in the primary by as many times as the number of turns in the secondary is greater than the number of turns in the pri­mary. A transformer of this type increases or steps up the voltage and is called a step-up transformer. In case the secondary has fewer turns than the primary the output voltage is lower than the input. Such a trans­former decreases or steps down the voltage, it is called a step-down transformer.

Compare Г and T₂ in the diagram. Г, has an iron core. For this rea­son it is used for low-frequency currents. T₂ has an air core and is used for high frequencies.

Common troubles in transformers are an open in the winding, a short between the primary and the secondary, and a short between turns. In case a transformer has a trouble it stops operating or operates badly. A transformer with a trouble should be substituted.

 

III. Find English equivalents.

      

   Сердечник, виток, обмотка, повышать, понижать, частота, из-за.

 

IV. Finish the sentences.

1. A transformer is used………

2. A two-winding transformer………

3. The value of voltage…….

4. In case the secondary has……………

5. The voltage in the secondary i_{s……………..}

6. Common troubles in transformers are…………

7. Current transformers are used……………….

8. Current transformers also insulate…………..

V. Complete these sentences using while. Follow the model on page 13.

  

    1.The secondary winding of a transformer is connected to the load re­sistance....

2.The primary winding receives energy....

3.A step-down transformer decreases the primary voltage....

4.An air core transformer is used for high-frequency currents 

5.In a step-up transformer the number of turns of the secondary winding

is greater than the number of the primary winding……..

 

 

VI. Read about current transformers. Answer the questions that follow.

Current Transformers

Current transformers are used for operating ammeters, wattcmeters, ant other measuring devices. They produce in the meters a current lower that the measured current but proportional to it.

Current transformers also insulate the instrument from the circuit which is being measured. This is necessary for high voltage circuits.

1.What is a current transformer used for?

2.What type of current does it produce?

 

 

VII. Answer the questions.

What is a transformer used for?

What does a transformer consist of?

What is the function of the primary winding?

What is the function of the secondary winding?

What type of transformer is called a step-up transformer?

What type of transformer is used for high-frequency currents?

What type of transformer is called a step-down transformer?

What type of transformer is used for low-frequency currents?

What is the relation between the numbers of turns in the windings is the value of current?

What are common troubles in a transformer?

What should be done in case a transformer has a trouble?

 

        

 

ПРАКТИЧЕСКАЯ РАБОТА № 11

TYPES OF CURRENT

Цели: Введение и активизация в речи лексики по теме «Виды электрического тока».

Оборудование: комплект тестов, раздаточный материал.

                                                 Vocabulary

I. Learn the words and expressions.

Alternating                                    переменный

Direct                                       прямой

Direction                                   направление

Flow                                    течение

Necessary                                  необходимый

To consider                               рассматривать

Use                                           использование