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insulated system of electrical conductors external to it. The amount of electric-
ity obtainable from such a generator is dependent upon the mechanical energy
supplied. In the circuit external to a generator the e. m. f. causes the electricity
to flow from a higher or positive potential to a lower or negative potential. In
the internal circuit of a generator the e. m. f. causes the current to flow from a
lower potential to a higher potential. The action of a generator is based upon
the principles of electromagnetic induction.
The dynamo consists essentially of two parts: a magnetic field, produced
by electromagnets, and a number of loops or coils of wire wound upon an iron
core, forming the armature. These parts are arranged so that the number of the
magnetic lines of force of the field threading through the armature, coils will
be constantly varied, thereby producing a steady e. m. f. in the generator or a
constant torque in the motor.
II. Fill in the gaps with the words given below:
to convert, generator, reversible, obtainable, induction, loops
1. The term “dynamo” is applied to machines which.....either mechanical
energy into electrical or on the contrary electrical energy into mechanical energy.
2. A dynamo is a ..... machine capable of operation as a generator or mo-
tor as desired.
3. The amount of electricity ..... from such a generator is dependent upon
the mechanical energy supplied .
4. The action of a generator is based upon the principles of electromag-
netic ...... .
5. The dynamo consists of two parts: a magnetic field, produced by elec-
tromagnets, and a number of .....or coils of wire.
III. Find the Russian equivalents for the following English words and
word combinations:
1) to be applied to smth.; 2) to convert smth. into smth.; 3) rotation;
4) to utilize; 5) a properly insulated system; 6) internal (external) circuit;
7) capable of operation; 8) positive (negative) potential; 9) reverse order;
10) energy conversion.
IV. Answer the questions
1. What term can be applied to machines converting mechanical energy
into electrical and vice versa?
2. What kind of machine is a dynamo ?
3. What is the function of a generator ?
4. What is the action of a generator based upon ?
5. What parts does the dynamo consist of ?
V. Talk on the dynamo action
UNIT 10
I. Read the text
GENERATORS
The powerful, highly efficient generators and alternators that are in use
today operate on the same principle as the dynamo invented by the great Eng-
lish scientist Faraday in 1831.
Dynamo-electric machines are used to supply light, heat and power on a
large scale. These are the machines that produce more than 99.99 per cent of
all the world's electric power.
There are two types of dynamos – the generator and the alternator. The
former supplies d. c. which is similar to the current from a battery and the lat-
ter provides a. c. To generate electricity both of them must be continuously
provided with energy from some outside source of mechanical energy such as
steam engines, steam turbines or water turbines.
A generator is an electric machine, which converts mechanical energy
into electric energy. There are direct-current (d. c.) generators and alternating-
current (a. c.) generators. Their construction is much alike. A d. c. generator
consists of stationary and rotating elements. The stationary elements are: the
yoke or the frame and the field structure. The yoke forms the closed circuit for
the magnetic flux. The function of the magnetic structure is to produce the
magnetic field.
The rotating elements are: true armature and the commutator. They are on
the same shaft. The armature consists of the core and the winding. The wind-
ing is connected to the commutator. With the help of the brushes on the com-
mutator that conduct the electric current to the line the winding is connected to
the external circuit. The stationary element of an a. c. generator is called a sta-
tor. The rotating element is called a rotor.
The essential difference between a d. c. generator and a. c. generator is
that the former has a commutator by means of which the generated e. m. f. is
made continuous, i. e. the commutator mechanically rectifies the alternating e.
m. f. so that it is always of the same polarity.
D. c. generators are used for electrolytic processes such as electroplating.
Large d. c. generators are employed in such manufacturing processes as steel
making. The d. c. generator of small capacities is used for various special pur-
poses such as arc welding, automobile generators, train lighting systems, etc. It
also finds rather extensive use in connection with communication systems.
II. Give the Russian equivalents for the following English words and word
combinations:
1) generator; 2) alternator; 3) steam turbine; 4) water turbine; 5) armature;
6) rotor; 7) stationary; 8) commutator; 9) stator; 10) yoke; 11) brushes;
12) core; 13) frame; 14) winding.
III. Fill in the blanks
1. A generator is an electric machine, which a) ----- mechanical energy
into electrical energy.
2. A direct-current generator consists of b) ----- .
3. The dynamo was invented by c) ----- in 1831.
4. The d.c. generator is used for various purposes such as d) ----- .
IV. Work out the plan of the text
V. Speak on the following points:
1. The construction of a generator.
2. The direct current generators and their industrial application.
UNIT 11
I. Read the text
MAIN STRUCTURAL ELEMENTS OF A D. C. MACHINE
A direct-current machine consists of two main parts, a stationary part,
usually called the stator, designed mainly for producing a magnetic flux, and
a rotating part, called the armature or the rotor. The stationary and rotating
parts should be separated from each other by an air-gap. The stationary part of
a d.c. machine consists of main poles, designed to create the main magnetic
flux; commutating poles interposed between the main poles; and a frame. It
should be noted here that sparkless operation of the machine would be impos-
sible without the commutating poles. Thus, they should ensure sparkless op-
eration of the brushes at the commutator.
The main pole consists of a laminated core the end of which facing the
armature carries a pole shoe and a field coil through which direct current
passes. The armature is a cylindrical body rotating in the space between the
poles and comprising a slotted armature core, a winding inserted in the arma-
ture slots, a commutator, and a brush gear.
The frame is the stationary part of the machine to which are fixed the
main and commutating poles and by means of which the machine is bolted to
its bedplate. The ringshaped portion which serves as the path for the main and
commutating pole fluxes is called the yoke. End-shields or frame-heads which
carry the bearings are also attached to the frame.
Of these main structural elements of the machine the yoke, the pole cores,
the armature core and the air-gap between the armature core and the pole core
are known to form the magnetic circuit while the pole coils, the armature wind-
ings, the commutator and brushes should form the electric circuit of the machine.
II. Translate the following phrases, using the given variants of translation:
to consist – состоять : to consist of a stationary part and a rotating part;
separated – отдельный изолированный: the stationary and rotating parts
should be separated from each other by an air gap;
to serve – служить в качестве чего-либо: the ringshaped portion or yoke
serves as a path for the main and commutating pole fluxes.
III. Join the beginnings and the ends
Beginnings Ends
The stationary parts of a d. c. a laminated core the end of which
machine are .... carries a pole shoe and a field coil.
The two main parts of a direct main poles , commutating poles and
current machine are .... a frame
The main pole consists of .... A stationary part or stator and a rotating
part, called the armature or the rotor.
IV. Arrange synonyms in pairs and memorize them:
a) to consist of; to be separated from; to create; to be interposed between;
to pass; to rotate;
в) to be divided with; to produce; to introduce into; to permeate; to roll; to
revolve; to comprise.
V. Write out the names of the machine parts and describe their opera-
tional characteristics
UNIT 12
I. Read the text
THE ALTERNATOR
The alternator is an electric machine for generating an alternating current
by a relative motion of conductors and a magnetic field. The machine usually
has a rotating field and a stationary armature. In a synchronous alternator the
magnetic field is excited with a direct current. The direction of an induced
e.m.f. is reversed each time when a conductor passes from a pole of one polar-
ity to a pole at another polarity. Most machines of this type are used for light-
ing and power, but there are alternators with a revoking armature and a sta-
tionary field. They are used in small sizes mostly for special purposes.
Any electrical machine is reversible. When a machine is driven by a source
of mechanical power, it works as a generator and delivers electrical power. If it
is connected to a source of electrical power, it produces mechanical energy, and
operates as a motor. The alternator may also be operated as a motor.
The a-c .generator, or alternator, does not differ in principle from the d. c.
generator. The alternator consists of a field structure and an armature. The
field structure is magnetized by a field winding carrying a .direct current. An
electromotive force is generated in tine winding of the armature. In alternators
the field is usually the rotating element and the armature is stationary. This
construction has a number of advantages. Only two rings are needed with a ro-
tating field. These rings carry only a relatively light field current, at a voltage
generally of 125, and seldom exceeding 250. The insulation of such rings is
not difficult. A stationary armature requires no slip rings. The leads from the
armature can be continuously insulated from the armature winding to the
switchboard, leaving no bare conductor. The alternator with a rotating field
may be further divided into the vertical and the horizontal types.
The vertical type is usually applied for large water-wheel generators
where it is desirable to mount the water turbine below the generator. The more
common horizontal type is used with diesel and steam engine drive. A low-
speed alternator of this type is suitable for a diesel engine drive, a high speed
alternator is suitable for a steam turbine drive.
II. Form nouns, denoting devices with the help of the suffix – or. Translate them
To alternate, to commute, to conduct, to generate
III. Read the text and write out the key words, characterizing the alternator
IV. Translate the following word combinations paying attention to the
Participle 2
The leads from the armature can be continuously insulated from….., the
vertical type of alternator applied for large water-wheel generator; alternators
with a revoking armature and a stationary field used in small sizes mostly for
special purposes; a machine driven by a source of mechanical power; the di-
rection of an induced e. m. f. …
V. State 5 questions to the text
VI. Points for discussion:
1. The structure of the alternator;
2. The application of the alternator.
UNIT 13
I. Read the text
THE INDUCTION MOTOR
An induction motor like any other motor consists of a stationary part, the
stator, and a rotating part, the rotor. The rotor of an induction motor is not
connected electrically to the source of power supply. The currents which circu-
late in the rotor conductors are the result of voltage induced in the rotor in the
magnetic field set up by the stator. The rotor is fitted with a set of conductors
in which currants flow. As these conductors lie in the magnetic field produced
by the stator, a force is exerted on the conductors and the rotor begins to re-
volve .The operation of the motor depends upon the production of a rotating
magnetic field. The speed at which the field of an induction motor turns is
called the synchronous speed of the field or of the motor.
The induction motor is the simplest of the various types of electric motors
and it has found more extensive application in industry than any other type. It
is made in two forms – the squirrel cage and the wound rotor, the difference
being in the construction of the rotor.
The stator of the induction motor has practically the same slot and wind-
ing arrangement as the alternator and has the coils arranged to form a definite
number of poles, the number of poles being a determining factor in connection
with the speed at which the motor will operate. The rotor construction, how-
ever, is entirely different.
The squirrel-cage rotor is a simpler form and has been used in many ma-
chines.
Instead of coils the winding consists of heavy copper bars.
The wound-rotor type has a winding made up of well-insulated coils,
mounted in groups whose end connections are brought out to fill in rings. The
purpose of this winding is to provide for variation in the amount of resistance
included in the rotor circuit.
Provision for ventilation is made by leaving passageways through the core
and frame, through which air is forced by fan vanes mounted on the rotor. In main
cases the motors now built in as an integral part of the machine it is to drive.
There being no electrical connection between the rotor circuits of the in-
duction motor and the stator circuits, or supply line, the currents which flow in
the rotor bars or windings correspond to the induced voltages, the action being
similar to that of a transformer with a movable secondary. With but a single-
phase winding on the stator, however, the torques produced in the two halves
of the rotor would be in apposition, and the motor would not start. With more
than one set of windings two for a two-phase motor, three for a three-phase
motor a resultant field is produced which has the effect of cutting across the
rotor conductors and induces voltages in them. This field is considered to be
revolving at uniform speed.
The term “revolving field” should not be taken to mean actual revolution
of flux lines. The magnetic field from the coils of each phase varies in strength
with changes in current value but does not move around the stator. The revolu-
tions are those of the resultant of the three, or two, phases, as the case may be.
A motor with a single-phase winding is not self-starting but must be provided
with an auxiliary device of some kind to enable the motor to develop a starting
torque. The effect of the revolving field is the same as would result from actual
revolution of a stator having direct-current poles. As voltages have been in-
duced in the bars or windings of the rotor, currants start flowing as a result of
these voltages, and a torque is produced which brings the motor up to speed.
II. Find in the text the English equivalents for the word combinations
given below:
1) асинхронный двигатель; 2) неподвижная часть; 3) вращающаяся
часть; 4) проводник; 5) одновременная скорость; 6) широкое применение;
7) паз; 8) механизм обмотки; 9) трансформатор; 10) вращающий момент.
III. Complete the following sentences according to the contents of the text
1. The Induction Motor is …….. of electric motors and is more exten-
sively applied in industry than any other type.
2. The purpose of this winding is …….. for variation in the amount of re-
sistance included in the rotor circuit.
3. The effect of …. is the same as would result from actual revolution of
a stator having direct-current poles.
IV. Answer the following questions:
1. What parts does the induction motor consist of?
2. What are the names of its rotating and stationary parts?
3. What does the motor operation depend on?
4. How can the difference between stator and rotor construction be ex-
plained?
5. What does the term “revolving field” mean?
V. Translate the sentences from the text paying attention to the Nomina-
tive Absolute Participle Constructions:
1. The induction motor is made in two forms – the squirrel cage and the
wound rotor, the difference being in the construction of the rotor.
2. The stator of the induction motor has practically the same slot and
winding arrangement as the alternator and has the coils arranged to form a
definite number of poles, the number of poles being a determining factor in
connection with the speed at which the motor will operate.
3. There being no electrical connection between the rotor circuits of the
induction motor and the stator circuits, or supply line, the currents which flow
in the rotor bars or windings correspond to the induced voltages, the action be-
ing similar to that of a transformer with a movable secondary.
VI. Discuss the following points:
1) The construction of an induction motor;
2) Induction motor operation principle.
UNIT 14
I. Read the text
TYPES OF INDUCTION MOTORS
TEXT 1
SINGLE – PHASE MOTOR
The single-phase induction motor differs from poly-phase type principally
in the character of its magnetic field, as an ordinary single-phase winding will
not produce a rotating field, but a field that is oscillating, and the induced cur-
rents and poles produced in the rotor by this field will tend to produce equal
torque in opposite directions, therefore, the rotor cannot start to revolve. How-
ever, if the rotor can in some manner be made to rotate at a speed correspond-
ing to the frequency of the current in the stator windings then the reaction of
the stator and rotor flux is such as to produce a torque that will keep the rotor
revolving.
In practice the starting of single-phase induction motors is accomplished
by three general methods applicable to small-sized motors only.
First: the split-phase method, in which an auxiliary stator winding is pro-
vided for starting purposes only, this winding being displaced from the main sta-
tor winding by 90 electrical degrees. It has a higher inductance than the main sta-
tor winding, thus causing the currant in it to lag far enough behind the current in
the main winding to produce a shifting or rotating field during the starting pe-
riod, which exerts a starting torque on the rotor sufficient to cause rotation.
When nearly normal speed has been reached the auxiliary winding is out
of circuit by a switch and clutch in the motor, which operates automatically by
centrifugal force, and the rotor continues to run as a single-phase motor. The
starting torque of such motions being limited, they are frequently constructed