II. Найдите в тексте эквиваленты следующих слов и словосочетаний:
часть выходной мощности генератора, весь ток якоря, относительно мало витков, возбуждать, остаточный магнетизм, сила, нарастать, дальнейшее увеличение, точка насыщения, делает его полезным, требовать, независимо от изменений нагрузки, резко.
III. Образуйте от данных глаголов имена существительные и переведите их на русский язык.
Образец. To determine – determination (определять – определение).
To excite, to saturate, to observe, to operate, to generate, to connect.
IV. Заполните пропуски, выбрав нужный вариант.
1. Self-excited generators use part of ... to supply excitation current to the field (current of an external source, generator’s output). 2. The series field contains relatively ... turns of wire (many, few). 3. The amount of the e.m.f. ... the strength of the residual magnetism (produces, depends on). 4. With no load, no current can flow and therefore very ... e.m.f. is induced (much, little). 5. When the load draws more current from the generator, this additional current ... the field strength (increases, uses). 6. The shunt winding have a ... number of turns (small, large).
V. Вставьте нужный предлог: through, for, from, with, in, at, of, to.
1. ... a series generator the whole armature current flows ... both the field and load. 2. As the load draws more current ... the generator, this additional current increases the field strength. 3. A shunt d.c. generator has its field winding connected ... series ... the armature. 4. When a shunt generator is started, the build-up time ... rated terminal voltage ... the brushes is very rapid. 5. These generators are classified according … the type ... field connection used.
VI. Задайте вопросы к подлежащему, дополнению и определению, употребив вопросительное слово what.
Образец. As the load draws more current from the generator this additional current increases the field strength.
1. What draws more current from the generator? (the load) – подлежащее.
2. What current increases the field strength? (additional) – определение.
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3. What does this additional current increase? (the field strength) – дополнение.
4. What strength does this additional current increase? (field) – определение.
1. Self-excited generators use part of the generator’s output to supply excitation current to the field. 2. The series field winding contains relatively few turns of wire. 3. If a load is connected, current will flow, the field strength will build up, and the terminal voltage will increase. 4. The shunt field windings have a large number of turns. 5. The drop in the terminal voltage as the load current increases is relatively small. 6. If the load current drawn from the generator increases beyond point B, the terminal voltage starts dropping off sharply.
VII. Выразите согласие или несогласие с данными утверждениями, употребив выражения : I agree with you; You are quite right; I am afraid you are wrong (парная работа).
1. The drop in the voltage as the load current increases is very small. 2. The shunt field windings require a relatively small currents to produce the necessary field flux. 3. If the generator is not connected across a load, the circuit is incomplete and no current will flow to excite the field. 4. The fact that the output voltage of the series generator is proportional to its armature current makes it useless for some special applications. 5. The shunt generator is not used where a practically constant voltage is desired regardless of load changes. 6. If the load current drawn from the generator increases beyond point B, the terminal voltage starts dropping off sharply.
VIII. Расскажите о применении генератора с последовательным и параллельным возбуждением, употребив следующие слова и словосочетания:
series (shunt) generator, ordinary generator, useful for, special applications, where, practically constant voltage, regardless of load changes, is not used as, is, is used, is desired.
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Text 9
The Compound Generator
A compound generator is a combined series and shunt generator. There are two sets of field coils – one in series with the armature, and one in parallel with the armature. One shunt coil and one series coil are always mounted on a common pole piece.
If the series field is connected so that its field aids the shunt field, the generator is called "cumulatively" compound. If the series field opposes the shunt field, the generator is called "differentially" compound.
Compound generators were designed to overcome the drop in terminal voltage which occurs in a shunt generator, when the load is increased. This voltage drop is undesirable where constant voltage loads such as lighting systems, are used. By adding the series field, which increases the strength of the total magnetic field when the load current is increased, the voltage drop due to the added current flowing through the armature resistance is overcome, and constant voltage output is practically attained.
The voltage characteristics of the cumulative compound generator depend on the ratio of the turns in the shunt and series field windings.
If the series windings are so proportioned that the terminal voltage is practically constant at all loads, it is "flat-compounded". Usually in these machines the full-load voltage is the same as the no-load voltage, and the voltage at intermediate points is somewhat higher. Flat-compounded generators are used to provide a constant voltage to loads a short distance away from the generator.
An "overcompounded" generator has its series turns so selected that the full load voltage is greater than no-load voltage. These generators are used where the load is some distance away. The increase in terminal voltage compensates for the drop in the long feeder lines thus maintaining a constant voltage at the load.
When the rated voltage is less than no-load voltage, the machine is said to be "under-compounded". These generators are seldom used. Most cumulative compound generators are overcompounded.
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The terminal voltage can always be controlled by varying a field rheostat in series with the shunt field. In a differentially compounded generator, the shunt and series fields are in opposition. Therefore the difference, or resultant field becomes weaker, and the terminal voltage drops very rapidly with an increase in load current.
The characteristic curves for the four types of compound generators are illustrated below.
Words and Word Combinations
| compound generator | генератор смешанного возбуждения |
| combined p.p. | комбинированный |
| set n | комплект, набор, группа |
| mount v | устанавливать |
| common a | общий |
| aid v | помогать |
| cummulative(ly) compound(ed) | согласно компаундированный |
| oppose v | противодействовать |
| differentially compound(ed) | с дифференциальным компаундированием |
| overcome v | преодолеть |
| occur v | встречаться; случаться |
| undesirable a | нежелательный |
| lighting system | система освещения |
| add v | добавлять |
| due to prp | благодаря |
| attain v | достигать |
| ratio n | соотношение |
| proportion v | распределять |
| flat compound(ed) | равномерно компаундированный |
| full-load voltage | напряжение полной нагрузки |
| no-load voltage | напряжение без нагрузки |
| intermediate a | промежуточный |
| somewhat | несколько; отчасти; до некоторой степени |
| a short distance away from | на небольшом расстоянии от |
| overcompounded p.p. | перекомпаундированный |
| select v | выбирать |
| feed(er) line | питающая линия |
| maintain v | поддерживать; сохранять |
| undercompounded p.p. | недокомпаундированный |
| field rheostat | реостат возбуждения |
| become weaker | ослабевать; становиться слабее |
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E x e r c i s e s
I. Прочитайте и переведите на русский язык слова и словосочетания:
always, cumulatively, differentially, compound, desing, occur, undesirable, by adding, added, current, practically, attain, characteristic, ratio, proportion, within, maintain, rated, difference, resultant, load current.
II. Найдите в тексте эквиваленты следующих слов и словосочетаний:
комбинированный, всегда устанавливаются (монтируются), напряжение, на зажимах, падение напряжения, сила всего магнитного поля, соотношение витков в обмотках, постоянное напряжение при всех нагрузках, напряжение при полной нагрузке (без нагрузки), в промежуточных точках, несколько выше, с увеличением, редко, быстро.
III. Переведите данные ниже имена прилагательные и имена существительные, обратите внимание на их суффиксы:
1. parallel, terminal, undesirable, total, magnetic, constant, intermediate, resultant.
2. generator, voltage, strength, resistance, distance, difference.
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