Method of and Apparatus for Converting the Electrical Energy of Alternating Currents into Mechanical Motion.
Year: 1891

page_text: Date of Application, 22nd Sept., 1891-Accepted, 14th Nov., 1891
COMPLETE SPECIFICATION.
Method of and Apparatus for Converting the Electrical Energy of
Alternating Currents into Mechanical Motion.
We, CHARLES SCHANCK BRADLEY, of Avon, in the County of Livingston,
and State of New York, Electrical Engineer, ROBERT S. TAYLOR, of Fort
Wayne, in the County of Allen, and State of Indiana, Attorney-at-Law, and
RANALD TREVOR MCDONALD, of Fort Wayne, in the County of Allen and
State of Indiana, Manufacturer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :—
This invention relates to the conversion of the electrical energy of alternating-
currents into mechanical motion, the object being to render such conversion more
efficient than is practicable with modes of operation or systems of conversion hereto-
fore proposed. In the present state of the art the conversion is made by means of
alternating-current motors, the operation of such motors depending for the most
part upon a progressive travel of a polar line created by two currents differing in
their time-periods, such difference of period being either created at the generating
station and transferred thence by two independent circuits to the motor, or some
local device being used to create a lag of one set of waves behind the other, so that
they may be carried through independent circuits in the motor. By our invention
no such provisions are necessary but a motor may be connected directly to a pair
of alternating-current terminals, the voltage of such currents being preferably
reduced to a convenient and safe tension in the circuit in which the motor is placed.
An ordinary electric motor provided with laminated, field-magnets and armature
will operate, under such conditions, but its efficiency very low by reason of the
high degree of self-induction and the low effective counter-electro-motive-force
developed. It is a well understood characteristic of electric motors that efficiency
varies directly as the counter-electro-motive-force developed by the operation of
the motor. The low efficiency of alternating-current motors as compared with
direct-current motors is due principally to the large amount of self-induction
developed in such motors by the alternating waves of current and the consequently
low effective counter-electro-motive-force. Self-induction opposes the passage of
current through the motor and such opposition is not accompanied by the develop-
Counter-electro-motive-
ment of useful work on the rotating element of the motor.
force also opposes the passage of current through the motor but such opposition is
all useful and proportionally as the counter-electro-motive-force rises the useful
work increases. Any method which will lower the self-induction per se will increase
the useful work by permitting more current to be utilized. Any method also which
raises the counter-electro-motive-force per se will correspondingly increase the
amount of useful work. It follows from this that a relative increase of the counter-
electro-motive-force compared with the self-induction will increase the amount of
useful work given off by the motor. It is the object of my invention to attain this
end. The result is accomplished by developing in each armature coil of a motor a
greater number of waves of counter-electro-motive-force during the travel of the
rotating member through any given angle than the number of waves of supply
current which traverses the line and acts to propel the motor in the time occupied
by such travel. The motor is so organized that when interposed in an alternating-
current circuit or forming part of an alternating-current system with a frequency of
reversal for which the motor is adapted each armature coil cuts the magnetic field
developed by any half wave of alternating-current more than once while such half
wave lasts. In carrying out the invention each half wave is sub-divided by a

page_text: commutator into several independent periods and the periods of current are led
through the armature circuit in such a way that the field of force developed by
the wave is cut as often as there are sub-divisions of the wave, thus creating a
high counter-electro-motive-force by reason of cutting an increased number of lines
of force.
Our invention therefore consists in the method of and apparatus for converting
the electrical energy of an alternating-current into mechanical motion by raising
the amount of effective counter-electro-motive-force developed by rotation
relatively to the self-induction; it also consists in the method of and apparatus for
making such conversion by developing a phase of counter-current during the passage
through the motor of less than a corresponding phase of the line current; it also
consists of an alternating-current system provided with a generator for delivering
currents of a determinate frequency of reversal and a motor so organized that
when operating at its working speed under the influence of such current the
armature coils will cut the fields of force developed by the field-magnets oftener in
a definite interval than the number of reversals of current developed on line by the
generator during such interval; it also involves other features which will be
specifically indicated in the claims appended to this Specification.
The invention will be more thoroughly understood by reference to the accom-
panying drawings, in which
Figure 1 illustrates diagrammatically an alternating-current-generator and one
form of motor involving the features of the invention; and
Figure 2 is a diagrammatic illustration of the manner in which the wave of
alternating-current is sub-divided by the commutator.
1 is an alternating-current-generator of the multipolar type, though other forms
of alternating-current-generator might be used, and 2, 3 are the mains by which the
current is led from the generator to any distant point. 3 and 4 are service
conductors connecting the mains with the motor. In these service conductors the
current is made of a suitable tension if the line current is of very high voltage by
means of transformers or other reducing devices. Upon the shaft of the motor are
mounted two continuous ring-contacts 5, 6 upon which the brushes 7, 8 bear. The
ring 5 is connected directly with one set of segments of the commutator and the
ring 6 is connected first with the field-magnet circuit, by which is meant that
circuit of the motor which is not commutated, and then with an alternating set of
segments of the commutator. As shown in the illustration there are 18 poles to the
field-magnet. There are as many connected commutator plates as there are field-
magnet poles. In the motor illustrated there are two sets of armature poles, each
set having as many as there are in the field-magnet. As the current preserves the
polarity of one set of armature poles only during the movement of the field-magnet
from one armature pole to the next there are 36 segments to the commutator.
Only 18 of these segments are, however, as stated before, connected, the other 18
being simply idle blocks which may therefore be either of metal or of insulating
material as may be desired. Upon the commutator bear two pairs of brushes 9, 10
and 11, 12, the former pair being connected with one armature circuit and the
latter pair with the other armature circuit, the two sets of armature poles being
alternately arranged, as shown, the letters a a representing one set and the
other. The brushes are so set that as one pair passes out of action the other pair
will be just coming into action. As shown in the drawing the brushes 9 and 10
have come into action and 11 and 12 have just passed out of action. The set of
armature coils marked a a are therefore now receiving current and the set of
armature coils marked bb have just been cut out of circuit. This condition
of affairs will last until the field-magnet has rotated through a radial angle equal
to that occupied by one commutator segment, when the coils of a a will be cut out
and those of bb will be cut into circuit. As the field-magnet revolves, therefore,
it will be understood that during the continuation of a single wave of the generator
current, the circuit is progressively shifted from one set of armature coils to the

page_text: other, while its connection remains continuous with the field-magnet circuit, and
the coils are so wound that the field-magnet poles will at any instant be of an
opposite polarity to the adjacent armature poles in advance of them in the direction
of rotation. Under these conditions a continuous rotary torque is exerted upon the
field-magnet. The number of poles to the field-magnet is made greater than the
number of poles to the supply generator in order to increase the extent of sub-
division of the waves, so that when operating at its normal speed but a fractional
portion of any wave will pass through one set of armature coils before the current
is shifted to the other set by the commutator. Let us analyze the condition of the
motor during the passage of any portion of an alternating wave, as from z to m in
Fig. 2, and suppose the direction of the flow at this instant to be from the supply
conductors to the brush 8. The path through the machine will then be from the
brush 8 to ring 5, thence to the commutator segment and brush 9, through the
armature-circuit a a, magnetizing alternate poles of the armature system, thence by
conductor 13 to the brush 10, to commutator segment, to field-magnet circuit by
conductor 14, through the field-magnet circuit to ring-contact 6, and thence out
by brush 7. During this time the alternate field-magnet poles will be magnetized
north and south, and the series of armature poles marked a correspondingly
magnetized S and N. Direction of rotation will then ensue as indicated by the
arrow, until the commutator has moved angularly the space occupied by one of its
segments, when the other set of brushes 11, 12 will come into operation and the
current will be switched through brush 11 by way of conductor 14 to the armature
circuit, polarizing successive poles of this circuit in the same sense as corre-
sponding poles of the circuit just cut out, thence by conductor 15 to brush 12, to
the commutator segment 16, to the field-magnet circuit by conductor 14, through
the field-magnet circuit to ring 6, to brush 7, and out. It will thus be seen that
although the current has been shifted to the series of armature coils in advance of the
field-magnet it still continues in the field-magnet circuit. This progressive transference
from one set of armature coils to the other continues during the operation and
preserves the rotation of the field-magnet. Each alternating-current wave is thus
sub-divided and the several sub-divisions parceled out to the two armature circuits
in succession. In passing through the field-magnet coils the first half wave of
current will produce a certain magnetic field; it also produces a certain amount of
self-induction. It therefore follows that we must cut the lines of force of the
magnetic field at a rate which will give us a counter-electro-motive-force the
magnitude of which bears a certain relation to the electro-motive-force of self-
induction in order that the motor shall be effective with a reasonable current over
the lines and through the motor and generator. We have found that this effect
is not reached until the fields of force developed by the applied current are cut
oftener in a given time than the number of current waves which occur in that
time. Having once attained a high counter-electro-motive-force relatively
to the self-induction, the counter assists in reducing the self-induction.
the counter-electro-motive-force corresponds in time to the waves of alternating
current (for the reason that the field-magnet is produced by the current) it follows
that the counter-electro-motive-force lags behind the applied electro-motive-force,
and while the first part of the counter-electro-motive-force due to any wave
opposes such wave the last part from the amount of lag assists the applied electro-
motive-force of the following wave of opposite kind, and this in turn by virtue of
hastening the reversal of magnetism in the motor reduces the lag, and these reach
practical value when the cutting of magnetic fields of force occurs with a rapidity
greater than the rate of alternation of supply current and best when about three
times the frequency; that is to say, the motor should in all cases be designed with
reference to the rate of alternation under which it is designed to operate or with
reference to the generator producing such rate of alternation. If the generator
delivers a current on line having a frequency of sixteen thousand per minute the
motor will be provided with such a number of pole-pieces that throughout its range
As

page_text: of working speed the fields of force will be cut by the armature coils a greater
number than sixteen thousand times per minute, and as the counter-electro-motive-
force delivered by the armature is determined by the number of lines of force it
cuts in a given time it is evident that the counter-electro-motive-force must be
greater than in a case where the armature coils cut the fields of force a less
number of times per minute than the number of reversals on line during the
minute. Such a result is evidently impossible with the two-pole laminated machine
hereinbefore referred to, since if a ten-pole generator were supplying current the
motor must revolve at least five times as fast as the generator in order to enable
the motor armature to cut the field of force with the same frequency as the
generator armature. Such a result is also evidently impossible with multipolar
synchronous machines, since at all stages below synchronisin the armature coils
must cut the fields of force less frequently than the generator coils and at
synchronism they can only cut them with the same frequency. When however we
provide the motor with a number of field-magnet poles in excess of the number of
field-magnet poles in the generator or with a number of field-magnet poles, such
that during one revolution of the armature more reversals of current will be
produced in the armature coils than there are reversals of supply current during
such revolution, and so arrange the commutator of the motor that the counter-
current shall be in the same direction so long as the field-magnetism due to any
half wave lasts, the motor will operate with increased efficiency and will exert a
strong torque.
In the diagram Fig. 2 the areas enclosed by any two vertical lines illustrate the
method in which the commutator divides the wave of current.
We desire to have it understood that while we have described a motor of a
specific design our invention is applicable to other forms of motor. The details as
to the mode of establishing the polar points, and arrangement of the commutator
and the winding of the several magnetic elements, may be variously arranged in
order to attain the desired result. We have found that good results may be
secured with continuous armature coils if a multipolar field be adopted for use
therewith. For example, the Müller winding for dynamo machines as described
in United States Patent No. 331,726 of 1885 when provided with a sufficient
number of poles relatively to the generator may be used to carry out our method.
In all cases our method of conversion of electrical energy into mechanical notion
requires for its development the production of a greater number of reversals of
magnetism in the motor armature per minute when operating at its working speed
than the frequency per minute of the current under which the motor is designed to
operate.
Having now particularly described and ascertained the nature of this said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. The method of converting the electrical energy of an alternating current into
mechanical motion which consists in leading such current through an electric
motor and raising the effective counter-electro-motive-force developed by the
rotation of the motor relatively to the self-induction by cutting the field of force
rapidly relatively to the period of the propelling current.
2. The method of converting the electrical energy of an alternating current into
mechanical motion which consists in leading such current through an electric
motor and developing in each armature coil a greater number of counter-electric
waves during the travel of the rotative member through any part of a cycle of
rotation than the number of alternating current waves utilized during such
travel.
3. The method of converting the electrical energy of an alternating current into
mechanical motion which consists in leading such current through an electric
motor and developing in each armature coil a phase of counter-electro-motive-

page_text: force during the passage through the motor of less than a corresponding phase of
the propelling alternating current.
4. The method of converting the electrical energy of an alternating current
into mechanical motion which consists in leading such current through an electric
motor and developing by its rotation during any interval a greater number of
magnetic reversals in the armature than the number of reversals of the propelling
current.
5. The method of converting the electrical energy of an alternating current into
mechanical motion which consists in leading the current through an electric motor
and developing throughout the range of working speed of the motor a number of
magnetic reversals in the armature produced by its rotation in the field exceeding
the number of reversals of the propelling current by passing the current around a
suitable number of field-magnet poles of alternating sign and through a suitable
combination of coils in the armature.
6. The method of converting the electrical energy of an alternating current into
mechanical motion which consists in leading such current continuously through the
exciting circuit of one member of the motor and leading fractional portions of each
impulse thereof progressively through changing circuits of the other member of
the motor, whereby the effective counter-electro-motive-force of the motor is
increased relatively to the self-induction.
7. The method of converting the electrical energy of an alternating current into.
mechanical motion which consists in leading such current unaltered through one
member of an electric motor while in the other member of the motor it passes
through groups of coils suitably connected and arranged and thereby cutting
progressively by more than one group of coils throughout the working speed of the
motor the lines of force induced in the field-magnet for each successive wave or
impulse of the propelling current.
8. In an alternating current motor designed to operate within given limits of
speed and in a circuit of predetermined rate of alternation a multipolar field-
magnet, an armature provided with groups of coils, and a commutator connected
with the groups, the number of field poles so adapted to the alternations of the
current, that throughout the range of working speed of the motor there shall take
place a progressive travel of the polar line through each group of coils on the
armature while a single impulse or less of the propelling current lasts.
9. An alternating current electric motor having such number of field poles of
alternating sign, in combination with such number and grouping of coils on the
armature that throughout its predetermined working range of speed the magnetic
reversals in the armature produced by its rotation in the field shall exceed the
reversals of the propelling current.
10. In an alternating current motor designed to operate within given limits of
speed and in a circuit of predetermined rate of alternation a multipolar field-
magnet and armature, the latter having its coils connected with each other and
with a commutator and brushes in groups, the field poles and armature groups
being of such number that throughout the range of the working speed of the motor
the armature coils shall cut the fields of force with a greater frequency than the
reversals of the propelling current.
11. In an alternating current motor designed to operate within given limits of
speed and in a circuit of predetermined rate of alternation a multipolar field-
magnet and an armature having such number of poles and number and grouping of
circuits respectively that throughout the range of its working speed while each
separate wave of the alternating current passes through the exciting circuit of one
member of the motor, fractional portions of the same wave shall pass progressively
through changing circuits of the other member of the motor.
12. The combination of an alternating current generator a distribution circuit
connected therewith and a multipolar electric motor having a number of field-
magnet poles sufficient to develop within the range of working speed of the motor

page_text: more reversals of magnetism in the armature than reversals of current delivered
by the generator, and a commutator for shifting the relation of the armature coils
to the brushes.
Dated this Fifth day of August 1891.
CHARLES SCHANCK BRADLEY.
ROBERT S. TAYLOR.
RANALD TREVOR MCDONALD.