Практическое занятие 18. Электромагнитное реле

Lesson 18. Electromagnetic Relay

Read and learn the words:

 

Spring - пружина

cross-section - поперечное сечение

to close - замыкать, закрывать

close to - близко к (от)

to move - двигаться, приводить в движение

to switch on - включать

to switch off - выключать

various - различный, разнообразный

 

Read and translate the text.

Electromagnetic Relay

Electromagnetic devices called relays are widely used in various branches of industry.

The main parts of a relay are an electromagnet, a spring and an armature. When a current starts flowing in the electromagnet winding, the armature moves and the spring closes the contacts. The primary circuit o f a relay is its electromagnet circuit and the secondary circuit is the one closed by the contacts.

When there is no current in the relay’s primary circuit, the spring pulls the  armature and the contacts open.

Fig. shows how a relay is used to control the work of an electric motor. The relay is placed close to the motor which is connected to its secondary circuit. The armature closes the contacts of the secondary circuit, and the motor starts operating; it will stop when the relay opens.

Without a relay, conductors with a large cross-section would have to be brought to the motor. This would be very uneconomical. The current in a relay is tens and even thousands of times smaller than that used to power the motor. Therefore, the connecting wires can have small crosssections. In many systems the relay primary circuit operates automatically. Every evening and morning street lights are switched on and off from the main control panel by means of a great number of relays.

3. Complete the sentences using the correct variant:

 

1. The main parts of a relay are

a) an electromagnet, a capacitor, and a spring,

b) an electromagnet, an armature, and a spring.

 

2. When current starts flowing

a) the spring opens the contacts,

b) the spring closes the contacts.

 

3. The spring pulls the armature

a) when there is current in the primary circuit,

b) when there is no current in the primary circit

 

4. The wires connecting the panel with the relay

a) have a large cross-section,

b) have a small cross-section.

5. Street lights are switched on and off

a) by means of relays.

b) by means of electric motors.

 

4. Complete these sentences using while.

 

1. The primary circuit of a relay is its electromagnetic circuit..........

2. When there is no current in the relay’s primary circuit the contacts open...........

3. Without a relay conductors with a large cross-section should be used

4. Every evening street lights are switched on..........

 

5. Answer the following questions:

 

1. What are the main parts of a relay?

2. How is a relay put into operation?

3. When does the spring pull the armature?

4. What wires connect the panel with the relay?

5. By what means are street lights switched on and off?

Pair work

a) Match the questions and the answers, b) Ask the questions and let your groupmate answer them.

1. In what position does the switch have high (low) resistance?

2. What are the functions of the switch?

3. In what position is the switch open? closed?

4. In what way is the switch connected to the circuit?

a) Switches are used to open and close the circuits.

 

b) Closed is the on-position; open is the off-position.

c) The switch is connected in series with the load.

d) In the on-position the closed switch has a very low resistance, which results in maximum current in the load with zero voltage loss across the switch. When the switch is off it has a very high resistance and no current flows through the circuit.

 

Практическое занятие 19. Плавкие предохранители

Lesson 19. Fuses

1. Read and learn the words:

fuse - плавкий предохранитель

link - звено, связь

fault - дефект, неисправность

faulty неисправный

equipment - оборудование

installation - установка; pi. сооружения

to protect - защищать, предохранять

to utilize - использовать

to equip - оборудовать, снаряжать

to serve - служить

to melt - плавить

up to - вплоть до