- •Electrical engineering unit 14 Direct-Current Generators
- •Exercises
- •VII. Supplementary reading.
- •Text 8
- •A.C. Generators principles
- •Of operation
- •Unit 15 Alternating-Current Generators
- •Exercises
- •Text 9 powerhouse auxiliary motors
- •Transformers
- •Exercises
- •VI. Answer the following questions:
- •VII. Describe the structure of a transformer.
- •VIII. Supplementary reading. Text 10
- •Voltage transformers
- •Unit 17 Single-Phase Motors
- •Exercises
- •VII. Be ready to answer the following questions:
- •VIII. Choose one of the topics below and prepare to talk on it:
- •IX. Write a summary of the text.
- •Text 11 direct-current motors
- •Unit 18 Polyphase Induction Motors
- •Exercises
- •Text 12 direct-current motors
- •Unit 19 Electrical Measuring Instruments
- •Exercises
- •VI. Retell the text. Unit 20 Electrical Measuring Instruments
- •Exercises
- •Text 13 electrical measurements
- •Instruments and meters
- •Unit 21 Ammeters and Voltmeters.
- •Types of Ammeters and Voltmeters
- •Unit 22 Wattmeters
- •Exercises
- •Text 15 ammeters and voltmeters Hot Wire
- •Unit 23 Resistance Measurement
- •Exercises
- •VII. Supplementary reading. Text 16 ammeters and voltmeters
- •Unit 24 Low and Medium Resistance Measurements
- •Medium Resistance Measurement.
- •Exercises
МІНІСТЕРСТВО ОСВІТИ І НАУКИ УКРАЇНИ
Запорізький національний технічний університет
МЕТОДИЧНІ ВКАЗІВКИ
для самостійноїо роботи студентів 2 курсу ЕА з дисципліни
“Англійська мова”
Ч.II
денна форма навчання
2009
Методичні вказівки для самостійної роботи студентів 2 курсу ЕА з дисципліни «Англійська мова» - Ч.IІ денна форма навчання./ Укл. Яковлева О.В., Войтенко С.В. – Запоріжжя: ЗНТУ, 2009. – 46с.
Укладачі: Яковлева О.В.,ст. викладач
Войтенко С.В.,ст. викладач
Рецензент: Соболь Ю.О.,доц., к.ф.н.
Експерт кафедри ЕА: Жорняк Л.Б., доц.. , к.т.н.
Відповідальний за випуск: Яковлева О.В.
Затверджено
на засіданні кафедри
Протокол №8 від 15.06.2009
Electrical engineering unit 14 Direct-Current Generators
The construction and operation of a d.с. generator are practically the same as those of alternators, the main differences being the commutator action, the method of field excitation and the necessity of always having the armature — the rotating member. This latter is required to permit the commutator to function.
The commutator consists of a number of wedge-shaped copper segments fitted together around one end of the armature. The segments are separated from each other by some insulating material. As a matter of fact thin sheets of mica are widely used, the two terminals of each armature coil are connected to adjacent commutator segments.
In practice the brushes make contact on the outer surface of the commutators. The commutator progressively switches the brushes from one end of an armature coil to the other end, just as the coil starts to enter the opposite pole area. Thus although the direction of electron movement in the coil has reversed, the opposite end of the coil has been connected to the external circuit, direct current flowing out through the brush.
Direct-current generators are usually self-excited, some of the energy generated by the armature being Used to energize the field windings. This is impossible in alternators, because
the direction of the field flux must be constant; therefore direct current is required as a field excitation source.
Sufficient residual magnetism remains in the field poles to generate a small voltage when the armature starts to revolve. This current, fed into the field windings, is found to strengthen the magnetic field, which in turn causes more voltage to be developed in the armature. This process continues until the generator has been brought up to operating speed.
Exercises
I. Read the following words and their derivatives; observe that adding suffix -or does not shift the stress:
a) to 'operate, 'operator, ope'ration; to generate, generator, generation; to alternate, alternator, alternation; to commute, commutator, commutation; to insulate, insulator, insulation; to separate, separation; to ne'cessitate, ne'cessity, 'necessary, nece'ssarily.
II. Find in the text synonyms for the following words:
principal, to revolve, to call for, to allow, to be made up of, in effect, to apply, extensively, both, to join, to indicate, multiple, inner, in this way, though, motion, since, consequently.
III. Find in the text antonyms for the following words:
different, the former, to connect, conducting, internal, to weaken.
IV. Describe an end view of an armature, with commutator and coil connection as shown in Fig. 22.
V. Tell about the direct-current generator. VI. Answer the following questions:
1. What is the difference between the construction and operation of a direct-current generator and those of alternators? 2. What segments does a commutator consist of? 3. How are the segments separated from each other? 4. What are the two terminals of each armature coil connected to? 5. How does the commutator operate? 6. How are direct-current generators usually excited? 7. Why is this impossible in alternators?
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What does sufficient residual magnetism in the field poles generate?
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In what way is more voltage developed in the armature? 10. How long does this process continue?