Read the text and write four questions about it. Ask your groupmates to answer them

 

A man can get an electric shock when he comes into contact with the

electric fish. One of this kind is found in the tropical waters of South America: it is the electric eel. Small electric eels, one inch long, give a small shock. When the fish is 6 inches long its internal battery gives as much as 200 volts. A very big fish can generate 600 volts! When it is shortcircuited, a current of one ampere can be obtained. A two-meter long eel can light a dozen 5O watt lamps. The eel’s head is positively charged and the opposite end is negatively charged.

Практическое занятие 24. Электромоторы

Lesson 24. Electric Motors

 

1. Read and learn the words:

 

condition - условие

plant - завод

pole - полюс

torque - вращение, момент вращения

poor - бедный, плохой

nameplate - (заводская) табличка

2.

 

Read and translate the text. 

Electric Motors

Motors are used for converting different forms of energy into mechanical energy.

The main part o f a motor is a coil or armature. The armature is placed between the poles o f a powerful magnet. When a motor is put into operation current starts  flowing through the coil (armature) and the armature starts rotating.

Electric  motors are used practically in every branch of industry, transport, and agriculture. Naturally, they are produced in many different designs. They are used in industrial plants, and operate under different conditions.

Each motor is supplied with a nameplate which bears machine ratings: output power, voltage, the rated current, the starting current, the power factor, the efficiency, and the rated torque.

These motor ratings should be taken into consideration since they are necessary for the users. On them depends the length of motors’ service life, which is normally equal to about 10 years, provided that the operating conditions are normal. Naturally, under abnormal conditions the service life becomes much shorter: motors operate poorly and may have different faults.

3. Complete the sentences using the correct variant:

 

1. Motors are used

a) for transmitting energy.

b) for converting energy.

 

2. Motor’s main part is

a) the frame.

b) the armature.

c) the stator.

 

3. The armature is placed

a) between the poles of the magnet.

b) about the poles of the magnet.

 

4. Motors’ service life becomes shorter

a) under normal conditions,

b) under abnormal conditions.

 

5. Faulty motors operate

a) normally.

b) poorly.

 

4. Answer these questions. Use them in a talk with your groupmate:

 

1. What are motors used for?

2. What is the motor’s main part?

3. Where is the armature placed?

4. What ratings does the nameplate of a motor bear?

5. Under what conditions does a motor operate normally (poorly)?

 

Read about energy resources of today. Write three questions about the text and ask your groupmate to answer them.

Energy Resources of Today

People are energy-rich today. Solar energy is considered to be a potentially

limitless source of clean energy. The waters of the world contain potential fuel - in the form of a special isotope of hydrogen - deuterium. It is sufficient to power fusion reactors for thousands of years.

 

Практическое занятие 25. Неисправности моторов и способы их ремонта

Lesson 25. Faults of Motors and Ways of Their Repair

 

1. Read and learn the words:

to repair - ремонтировать

brush - щетка

gap - зазор, люфт

spark - искра

speed - скорость

noise - шум

slow - медленный

excessive - избыточный

check - проверка

to adjust - регулировать, подгонять

 

Read and translate the text. 

Faults of Motors and Ways of Their Repair

Motors may have different faults. A faulty motor does not start, or, when it is started, it operates at an excessive speed. Its brushes may spark and its windings and the commutator may be overheated and burnt. Besides, a motor may produce an abnormal noise, etc. All these and other faults should be detected and repaired.

In case the motor does not start it may have different faults (see the table):

 

Possible causes offaults	Ways of repair
1. Fuses are faulty.	1. Replace the fuses.
2. Motor is overloaded.	2. Reduce motor load.
3. Circuit in armature winding has an open.	3. Repair the armature winding.
In case the motor, when started, stops:
1. Rheostat is shorted.	1. Check the rheostat and repair it.
2. Rheostat switches from one position to another.	2. Slow down operation of rheostat handle.
Brushes may spark in case:
1. Motor is overloaded.	1. Reduce the load and remove overload.
2. Brushes are in poor condition.	2. Replace the brushes.
3. Pressure is low.	3. Adjust the pressure.
4. Pressure is excessive.	4. Adjust the pressure.
In case the armature winding is overheated:
1. Motor is overloaded.	1. Remove the overload.
2. Ventilation fails to operate properly.	2. Check for slowing down the speed of the motor.
In case of abnormal motor speed:
1. Motor is overloaded.	1. Reduce the load.
2. Rotor circuit has poor contact.	2. Repair the shorting mechanism.
In case rotor brushes against stator:
Rotor brushes against stator.	Adjust air gap.

3. Complete the sentences using the correct variant:

 

1. A motor with a fault

a) operates normally.

b) operates poorly.

 

2. Motor brushes spark in case

a) they are in normal conditions.

b) they are in poor conditions.

 

3. Burnt commutator should be

a) replaced.

b) repaired.

 

4. Brushes may spark in case

a) pressure is low.

b) pressure is excessive.

 

5. Air gap is adjusted in case

a) the rotor brushes against the stator.

b) the stator brushes against the rotor.

 

4. Answer these questions:

 

1. When does a motor operate poorly?

2. What should be done in case the motor is overloaded?

3. What should be done in case the fuses are faulty?

4. What should be done in case the rheostat is shorted?

5. What should be d6ne in case the brushes spark?

6. What should be done in case the pressure is low?

7. What should be done in case the ventilation does not operate?

8. What should be done in case the rotor brushes against stator?

 

5. Say a few words about your electrical engineering laboratory.

 

Are there any faulty devices in it? Have a talk with your groupmate about the faults and the ways to repair them.

 

Практическое занятие 26. Потребители электроэнергии и энергетические системы