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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 °f a relay is its electromagnet circuit and the secondary circuit is the °ne 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. 18 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

-51-


 

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?

in a relay is tens and even thousands of times smaller than that used [ power the motor. Therefore, the connecting wires can have small crosj sections.

Secondary rirciiit

Control switch

■ Primary circuit

Fig. 18

In many systems the relay primary circuit operates automatical!) Every evening and morning street lights are switched on and off froi the main control panel by means of a great number of relays.

5. Complete the sentences using the correct variant:


 

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.

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.


 


 

quartz [kwo:ts] base [beis]
1. The main parts of a re­lay are 2. When current starts flowing 3. The spring pulls the armature

 

a) an electromagnet, a capacitor, and a spring

b) an electromagnet, an armature, and a spriij

 

a) the spring opens the contacts.

b) the spring closes the contacts.

 

a) when there is current in the primary circuit

b) when there is no current in the primary cip cuit.

  4. The wires connecting the panel with the relay 5. Street lights are switched on and off

 

a) have a large cross-section.

b) have a small cross-section.

 

a) by means of relays.

b) by means of electric motors.

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

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

2. When there is no current in the relay's primary circuit the contal open

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

4. Every evening street lights are switched on

7. 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?

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a) Cover the right column and read the English words. Translate them into Russian and check your translation.

translate the Russian words back into

b) Cover the left column and English.

 

fuse [fju:z] плавкий предохранитель
link [lmk] звено,связь
fault [foiit] дефект, неисправность
faulty   неисправный
equipment [fkwipmant] оборудование
installation [.msta'leijn] установка; pi. сооружения
to protect [pra'tekt] защищать, предохранять
to utilize ['jurtilaiz] использовать
to equip [I'kwip] оборудовать, снаряжать
to serve   служить
to melt   плавить
up to   вплоть до

Read the words and put down their Russian equivalents. Then trans­late them back into English (orally).

quartz-sand fuse fusible link

-59-


principle __________ faulty protection device

stress faulty fusible link "!"

-«I

3. Form the words according to the model and translate them.

Model: charge - overcharge - перегрузка connect - disconnect - разъединять

pressure -__________________ -___________________________ _^

heat -__________________ - j

stress -__________________ - 1

current -_____________ ___ -__________________________

load -__________________ -___________________________

organize -__________________ -____________________________

place -__________________ -____________________________

stress -__________________ -____________________________ I

use -__________________ - I

4. Form the nouns from the given verbs according to the model. Translate

them.

Model: to protect - protection - защита

to utilize -______________________ -______________________

to install -______________________ -___________________ J

to reduce -______________________ -______________________

to connect -

5. Distribute the words below into the three columns:

actionprocessdoer

utilizer, utilize, installation, displace, overheater, displacement, overpr» duction, starter, equip, protection, disorganize

6. Translate into Russian. Mind both ... and, in case, up to:

1. Both solid and gaseous insulators are highly in use.

2. In case a fuse gets faulty it should be replaced by a new one.

3. Capacitors of very high capacity - up to 1000 and more mF - are util ized in modern installations.

Fuses

Fuses are widely used nowadays as protection devices. They ai* utilized in various circuits, electrical equipment and installations. Fusd| serve to protect them against overcurrents and short-circuits.

-6G-


There are different types of fuses in use nowadays. Of them, quartz-sand fuses serve for voltages up to 500 volts; fuses of this kind are pro­duced with current ratings of 15 to 60 amp and of 100 to 350 amp.

Fuses are commonly used in low-voltage industrial installations rated up to 1,000 V.

Fuse protection is based on a very simple principle: in case of a short-circuit or overcurrent, when the maximum value of current has been exceeded, the fusible link of a fuse is heated to its melting point. This opens the circuit and disconnects the circuit from the power source. In case of a fault, one should replace the faulty fusible element by a new one.

Fuses are used both in direct current (d.c.) and alternating current (a.c.) circuits.

7. Complete the sentences using the correct variant:

1. A fuse serves a) as a load.

b) as a protection.

2. Fuses are used a) for d.c. only.

b) for both a.c. and d.c.

3. In case of a fault a) the whole fuse should be replaced.

b) the faulty link should be replaced.

4. Fuse protection is based on a) a simple principle.

b) a complex principle.

8. Memorize the questions. Use them in a talk with your groupmate:

1. What does a fuse serve for?

2. For what type of current are fuses used?

3. What should be done in case of a faulty fuse?

4. What principle is fuse protection based on?

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.

incandescence [.mkaen'desns] накал, накаливание

incandescent lamp [mkaen'desnt laemp] лампа накаливания

-61-

I


 

copper steel to convert to deliver according to etc. = et cetera
Besides, electric circuits use different types of switches, protection devices (relays and fuses), and meters (ammeters, voltmeters, wattme­ters, etc.). 4. Complete the sentences using the correct variant: 1. The main components of electric a) loads and wires.
1. What are the main components of an electric circuit? 2. What is the function of an electric source? 3. What is the function of a load? 4. What is the function of wire conductors? 5. What other devices are utilized in a circuit? 6. Say a few words about your electrical engineering laboratory. Say what power sources and what loads are utilized there. Have a talk with your groupmate about their types and their operation.

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.

медь

сталь

[kanVa:t] [di'liva] [a'ka:dig ta] Let 'setara]

преобразовывать

питать, подавать

согласно

и так далее

Read the words and put down their Russian equivalents:

[.aelju'mmiam] aluminium

['kemikal] chemical

['d3enareita] generator ______

[ma'tianal] material

[mi'kaemkal] mechanical ________

['Qaxnl] thermal ________

['mouta] motor

3. Translate into Russian:

a. convertible values, protected power source, various fuses, variable re
sistors, chemical cells

b. cells delivering electric power
generator converting mechanical energy
circuits utilizing common fuses

с Primary cells deliver electric power.

Different kinds of energy can be converted into electric energy. Protection devices are utilized in any circuit.

Componentsof Electric Circuits

The main components of any circuit are devices that produce and utilize electric energy. They are: 1. power sources, 2. utilizing loads, 3. connecting conductors.

The most common power sources are electric generators and primary cells. Electric generators convert chemical energy into electric energy, j

Loads include electric heaters, electric motors, incandescent lampd etc. Motors convert electric energy into mechanical, incandescent lamps and heaters convert electric energy into light and heat. Utilizing devices or loads convert electric energy into thermal, mechanical or chemical energy.

Electric power is delivered from power sources to loads by electric wires. According to their material, wires can be aluminium, coppelsteel, etc.


circuits are

2. Power sources are used

3. Electric conductors are used

4. Protection devices are utilized

5. A switch is utilized

[I'fijansi]

efficiency ignorance dependence cost

5. Answer these questions:


b) power sources, load and wires.

a) to produce electric energy.

b) to deliver it to the loads.

 

a) to connect the circuit elements.

b) to deliver electric power.

 

a) in some circuits.

b) in any circuit.

 

a) in some circuits.

b) in any circuit.

отдача, эффективность незнание, неведение зависимость стоимость


 


Б?-


 


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loss потеря

length длина

to ignore не принимать во внимание

to depend (on) зависеть (от)

to exceed [ik'siid] превышать

long длинный

exceedingly чрезвычайно, очень

per cent процент

2. Read the words and put down their Russian equivalents:

[lain] line

j'steijan] station

[,end3i'ni9] engineer

Lend3rni3ng] engineering


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