 |
4. Complete these sentences using while. Follow the model on page 13.
|
|
|
|
4. 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 turns of the primary winding ….
5. Pair work. Put these questions to your groupmate and ask him/her to answer them.
1. What is a transformer used for?
2. What does a transformer consist of?
3. What is the function of the primary winding?
4. What is the function of the secondary winding?
5. What type of transformer is called a step-up transformer?
6. What type of transformer is used for high-frequency currents?
7. What type of transformer is called a step-down transformer?
8. What type of transformer is used for low-frequency currents?
9. What is the relation between the number of turns in the windings and the value of current?
10. What are common troubles in a transformer?
11. What should be done in case a transformer has a trouble?
6. Read about current transformers. Answer the questions that follow.
Current Transformers
Current transformers are used for operating ammeters, wattmeters, and other measuring devices. They produce in the meters a current lower than 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?
Unit Thirteen [13]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
b) Cover the left column and translate the Russian words back into English.
| alternating | [ˌ ɔ ː ltə ˈ neɪ tɪ ŋ ] | переменный |
| diˈ rect | прямой | |
| diˈ rection | направление | |
| flow | [flou] | течение |
| necessary | [ˈ nesɪ sə rɪ ] | необходимый |
| to con'sider | рассматривать | |
| use | [juː s] | использование |
2. Read the words and write down their Russian equivalents:
| [ˈ saɪ kl] | cycle | ___________________________ |
| [taɪ p] | type | ___________________________ |
| [pə ˈ sekə nd] | per second | ___________________________ |
3. Put down the Russian for:
| one time | ____________ | direct voltage source | ____________ |
| five times | ____________ | alternating voltage source | ____________ |
| sixty times | ____________ | direction of flow | ____________ |
|
|
|
Types of Current
Current is a flow of electricity through a circuit. Let us consider two main types of current: direct and alternating. A direct current (d. c. ) flows through a conducting circuit in one direction only. It flows provided a direct voltage source is applied to the circuit.
An alternating current (a. c. ) is a current that changes its direction of flow through a circuit. It flows provided an alternating voltage source is applied to the circuit. Alternating current flows in cycles. The number of cycles per second is called the frequency of the current. In a 60-cycle alternating current circuit the current flows in one direction 60 times and in the other direction 60 times per second.
It is easy to transform a. c. power from one voltage to another by a transformer. Transformers are also used to step down the voltage at the receiving point of the line to the low values that are necessary for use.
When necessary a. c. can be changed into d. c. but this is seldom necessary.
4. Complete the sentences using the correct variant:
| 1. D. c. is a current that | a) changes its direction of flow. b) flows in one direction. |
| 2. A. c. flows provided | a) a direct voltage source is applied. b) an alternating voltage source is applied. |
| 3. In an alternating current circuit | a) current flows in one direction 60 times per second. b) current flows in one direction 60 times and in the other direction 60 times per second. |
| 4. A. c. | a) can be changed into d. c. b) cannot be changed into d. c. |
5. Complete these sentences using while. Follow the model on page 13.
1. An alternating current changes its direction of flow ….
2. A direct current flows provided a direct voltage source is applied ….
6. Answer the following questions:
1. What is current?
2. What types of current do you know?
3. When does a direct current flow?
4. What type of current is called an alternating current?
5. What type of current is called a direct current?
6. What is called the frequency of current?
7. What device is used to transform a. c. power from one voltage to another?
8. Is it often necessary to change a. c. into d. c.?
7. Read about frequency, answer the question that follows.
Frequency
The number of cycles per second is the frequency of an alternating current. There are two frequencies: the standard for Europe is 50 cycles per second while the standard for the USA is 60 cycles per second. A standard frequency has a great advantage since different systems can be interconnected.
What is the advantage of a standard frequency?
Unit Fourteen [14]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
b) Cover the left column and translate the Russian words back into English.
| inˈ ductance | индуктивность | |
| coil | [kɔ ɪ l] | катушка |
| size | [saɪ z] | размер |
| unit | [ˈ juː nɪ t] | единица |
| fast | [fɑ ː st] | быстрый |
| mutual | [ˈ mjuː tʃ uə l] | взаимный |
| to induce | [ɪ nˈ djuː s] | индуктировать |
| to provide | [prə ˈ vaɪ d] | обеспечить |
| to touch | [tʌ tʃ ] | касаться |
| to bring | приносить, подносить | |
| that is | то есть | |
| definite | [ˈ defɪ nɪ t] | определенный |
|
|
|
|
|
|
