Файл: Методическое пособие для студентов iv курса очного и заочного обучения специальности 26. 05. 07 "Эксплуатация судового электрооборудования и средств автоматики".doc

UNIT IV. TYPES OF D.C. MOTORS

1. Read and remember the following words and word combinations.

diagram	схема
exhibit/ feature/manifest	характеризоваться, проявлять, иметь отличительное свойство
moderately	незначительно
predominantly	в основном
at the expense of	за счет
rigid	жесткий
slightly inclined	с малым наклоном
start the motor idle	запускать двигатель вхолостую
within wide limits	в широких пределах
while running idle	при холостом ходе
at load	при нагрузке
overspeed	идти вразнос
significant	большой, значительный
internal voltage drop	внутреннее падение напряжения
mild	мягкий
under load	под нагрузкой
considerably inclined	с большим наклоном
square value of the armature current	квадрат тока якоря
shunting	шунтирование
haulage mechanisms	тяговые механизмы
starter	стартер
turning gear	валоповоротное устройство
differential compound motor	двигатель смешанного возбуждения с рассогласованным включением обмоток
cumulative compound motor	двигатель смешанного возбуждения с согласованным включением обмоток
series-compound motor	двигатель смешанного возбуждения с последовательным соединением обмоток
shunt-compound motor	двигатель смешанного возбуждения с параллельным соединением обмоток
lathe	станок

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2. Read and translate the texts.

1. SHUNT-WOUND MOTORS

This term is referred to a particular type of D.C. motor having the field winding connected in parallel with the armature winding.

This type of motor exhibits the following properties:

1. With the load increase from zero to its rated value the speed of rotation is altered moderately - by 1 - 5% of its rated value; predominantly at the expense of the voltage drop in the armature. Consequently, the speed characteristic curve is "rigid", i.e., slightly inclined.

With the change in the load the speed of rotation of a shunt-wound motor is kept constant. This can be explained by the fact that the field current and hence the flux remain unchangeable.

2. The motor may be started idle. Stepless speed regulation within wide limits is accomplished by putting both a regulating rheostat in the field current and an additional resistor in the armature circuit.

3. The starting torque of the motor is rather small, directly proportional to the armature current; this being so, the current consumed from the mains is proportional to the load on the shaft. The motor torque characteristic makes a straight line.

By virtue of the fact that a shunt-wound motor features a small starting torque, a "rigid" speed characteristic curve and a stepless speed regulation, it finds application in electric drives of fans, pumps, compressors and other mechanisms.

2. SERIES-WOUND MOTORS

A series-wound motor possesses a field winding connected in series with the armature circuit.

A series-wound motor manifests the following properties:

1. While running idle or at load which is 20 - 25% less than the filed one, the motor tends to overspeed. The reason is that at light loads the current value both in the armature circuit and in the field winding is small and, therefore, the flux and the voltage drop in the field winding are both moderate and, as a consequence, the speed of rotation is significant.

With the load increase the current value in the field winding and thus the flux rise. Moreover, the internal voltage drop grows and consequently the speed of rotation abruptly drops off. The motor speed characteristic makes up a "mild" curve, i.e., considerably inclined. The motor is only started under load.

2. The starting torque of a series motor is large, proportional to the square value of the armature current.

3. The regulation of the speed of rotation is accomplished by several methods, but the one which is economically attractive is performed by shunting the field winding, i.e., placing an adjusting rheostat in its parallel. As a result, the speed of rotation shows an increase when compared to the rated one.

A series-wound motor is used where a large starting torque is required. They drive haulage mechanisms (starters, turning gears etc.)

3. COMPOUND-WOUND MOTORS

This term relates to a specific type of D.C. motor which has two field windings: the shunt one and the series one. According to the method of the field winding connection the above mentioned motors may be either differential compound or cumulatively compound. A differential compound motor has the fluxes directed in opposition. It features a small starting torque and, therefore, hasn't found application on shipboard. A cumulative compound motor has the fluxes that add up. This type of D.C. motor is subclassified into series-compound and shunt-compound.

Series-compound motors are those provided with a predominant series field winding and an auxiliary shunt field winding. In properties, they are quite similar to series-wound motors which manifest a considerable starting torque. Nevertheless, series-compound motors while running idle don't tend to overspeed because of their shunt field winding. They are used for driving windlasses, capstans, cranes etc.

Shunt-compound motors are those which have the shunt field winding as predominant and the series field winding as auxiliary. In properties, they are similar to shunt-wound motors, but exhibit a considerable starting torque. Shunt-compound motors are in use in electric drives of lathes, pumps etc.
3. Match the following English and Russian word combinations.

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a) speed of rotation, rated value, to start the motor idle, to exhibit the property, to tend to overspeed

b) запускать двигатель вхолостую, скорость вращения, стремиться уйти в разнос, проявлять свойство, номинальное значение
4. Answer the questions.

1. What is the term of "shunt-wound motor" referred to?

2. How is the speed of rotation of a shunt-wound motor altered with the load increase?

3. Is it possible to start a shunt-wound motor idle?

4. How is stepless speed regulation of a shunt-wound motor accomplished?

5. What can you say about the starting torque of a shunt-wound motor?

6. Where exactly on board ship do shunt motors find application?

7. What do you call "series-wound motor"?

8. Why does a series-wound motor tend to overspeed?

9. What can you say about the starting torque of a series-wound motor?

10. What is shunting? Is shunting economically attractive?

11. What mechanisms do series-motors drive?

12. What do you call "compound-wound motor"?

13. What is the difference between a cumulative compound motor and a differential compound motor?

14. What type of compound motor is called "series-compound motor"? Where is it used?

15. What type of compound motor is called "shunt-compound motor"? Where is it used?
5. Put the verbs in brackets in the correct form - Present Simple Active or Present Simple Passive.

1. Fig 1 ... (illustrate) the diagram of a shunt-wound motor.

2. This type of D.C. motor . . . (exhibit) the following properties.

3. The speed of rotation of a shunt-wound motor . . . (keep) constant.

4. The field current and hence the flux . . . (remain) unchangeable.

5. Stepless speed regulation within wide limits . . . (accomplish) by putting a regulating rheostat in the field circuit and an addition resistor in the armature circuit.

6. The motor torque characteristic . . . (make) a straight line.

7. While running idle a series motor . . . (tend) to overspeed.

8. The motor . . . only . . . (start) under load.

9. The speed regulation of a series motor . . . (perform) by shunting the field winding.

10. A series motor . . . (use) where a large starting torque . . . (require).

11. A differential compound motor . . . (feature) a small starting torque.

12. This type of D.C. motor . . . (subclassify) into series- compounded and shunt-compounded.

13. Series-compound motors . . . (provide) with a predominant series field winding and an auxiliary shunt field winding.

14. Series-compound motors . . . (not tend) to overspeed while running idle.

15. Shunt motors . . . (find) application in the electric drives of fans, pumps, compressors etc.
6. Speak about types of D.C. motors.

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UNIT V. TRANSFORMERS

1. Read and remember the following words and word combinations.

emf of mutual induction	эдc взаимоиндукции
emf of self-induction	эдc самоиндукции
turn	виток
transformer ratio	коэффициент трансформации
bar-type transformer	стержневой трансформатор
ironclad transformer	бронированный трансформатор
cooling	охлаждение
airy	воздушный
oily	масляный
work safety rules	правила техники безопасности
air-cooled transformer	трансформатор с воздушным охлаждением
multiphased transformer	многофазный трансформатор
multicircuit transformer	многообмоточный трансформатор
tapping	ответвление, отвод
power transformer	силовой трансформатор
special purpose transformer	трансформатор спец. назначения
autotransformer	автотрансформатор
current measuring transformer	измерительный трансформатор тока
voltage measuring transformer	измерительный трансформатор напряжения
welding transformer	сварочный трансформатор
measurement limits	пределы измерений
operational safety	безопасность в эксплуатации
rated secondary voltage	номинальное вторичное напряжение
rated secondary current	номинальный вторичный ток
fuse	предохранитель
secondary open winding	вторичная разомкнутая обмотка
winding insulation breakdown	пробой изоляции обмотки
high voltage network	цепь высокого напряжения
body	корпус
ground	заземлять
product	произведение
arc welding	дуговая сварка
steeply drooping	круто падающая
magnetic conductor	магнитопровод
one- phase dry waterproof	однофазный сухой водонепроницаемый
one- phase dry splashproof	однофазный сухой брызгозащищенный
one- phase dry ironclad	однофазный сухой бронированный
waterproof transformer	водозащищенный трансформатор
electromagnetically	электромагнитным путем
closed magnetic conductor	замкнутый магнитопровод
conventional	условный
electrically	электрическим путем
wire of smaller section	провод меньшего сечения
mass	масса
volume	объем
magnetic losses	магнитные потери
efficiency level	к.п.д.
low voltage portable lighting	низковольтное переносное освещение
penetration	проникновение
step-down transformer	понижающий трансформатор
step-up transformer	повышающий трансформатор
mains voltage	напряжение сети
attending personnel	обслуживающий персонал

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2. Read and translate the text.

PURPOSE, CONSTRUCTION, TYPES

A transformer is an electromagnetic device converting an alternating current of one voltage into an alternating current of another voltage but of the same frequency. Although there are many types of transformers and a great variety of different applications, the operation principle is the same in each case.

A transformer is composed of a laminated iron core and two separate windings. The core is made of electrical sheet steel. The winding, to which the voltage U1 is led, is called the primary winding W1. The one from which the voltage U2 is collected, is called the secondary winding W2.

The operating principle of a transformer is based upon the phenomenon of mutual induction.

The currents in the transformer windings are inversely proportional to their voltages.

In construction, transformers are divided into two types - a bar- type transformer and an ironclad transformer. Their cooling may be either airy or oily.

On board ships, in accordance with the work safety rules, only air- cooled transformers are used.

In the number of phases, transformers are one-phased, two-phased, or multiphased; in the number of windings they are either two-circuit or multicircuit, there are also transformers which have windings with special tappings.

In application, transformers are classified as power transformers, special purpose transformers and autotransformers.
3. Match the following English and Russian word combinations.

a) bar-type transformer, ironclad transformer, air-cooled transformer multiphased transformer, mutual induction, power transformer, special purpose transformer, work safety rules

b) стержневой трансформатор, трансформатор спец. назначения, силовой трансформатор, многофазный трансформатор, трансформатор с воздушным охлаждением, взаимоиндукция
4. Answer the questions.

1. What kind of electromagnetic device is a transformer?

2. What elements is a transformer composed of?

3. What is the transformer core made of?

4. What sort of windings does a transformer have?

5. What is the operating principle of a transformer based upon?

6. In what proportion are the transformer currents to the transformer voltages?

7. What types of transformers do you know according to their 1)construction, 2)number of phases, 3)number of windings, 4)application?

8. What kind of cooling is used in shipboard transformers?
5. Read and translate the text.

SPECIAL TRANSFORMERS

Special transformers are available in three types: 1) current measuring transformers, 2) voltage measuring transformers, 3) welding transformers.

Transformers measuring current and voltage are designed to widen measurement limits of ammetres, voltmetres, wattmetres etc. in a.c. circuits. Above all, they provide operational safety of measuring instruments in a high voltage network.

The rated secondary voltage of voltage transformers is equal to 100V, the one of shipboard voltage transformers is 127V, therefore measuring instruments should be rated in accordance with this voltage.

The rated secondary current value of current transformers is equal to 5 A, the one of shipboard transformers should be 1A. Fuses are not mounted in current transformers' secondary circuits since in case they burn off, the transformer magnetic flux and the emf of the secondary open winding will go up to dangerous values: winding insulation breakdown, overheating of the core and electric shock hazard of an operating personnel become possible.

If measuring transformers are connected to a high voltage network their secondary windings and their bodies are grounded.

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