Improvements in Alternating Current Electro-magnetic Motors.
Year: 1889

page_text: [Communicated' from abroad by NIKOLA TESLA, of the City and State of New York,
United States of America, Electrician.]
Improvements in Alternating Current Electro-magnetic Motors.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
Southampton Buildings, in the County of Middlesex, 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 that form of alternating current motor in which there are
two or more energizing circuits through which alternating currents differing in phase
are caused to pass.
Various forms or types of this motor are now known to the public. First, motors
having two or more energizing circuits of the same electrical character and in the
operation of which the currents used differ primarily in phase. Second, motors with
a plurality of energizing circuits of different electrical character, in or by means of
which the difference of phase produced artificially, and third, motors with a
plurality of energizing circuits, the currents in one being induced from currents in
another. The application of the present invention to these several types will be
shown.
Considering the structural and operative conditions of any one of them, as for
example that first named, the armature which is mounted to rotate in obedience to the
cooperative influence or action of the energizing circuits, has coils wound upon it
which are closed upon themselves, and in which currents are induced by the
energizing currents with the object and result of energizing the armature core.
But under any such conditions as must exist in these motors, it is obvious that a
certain time must elapse between the manifestations of an energizing current impulse
in the field coils, and the corresponding magnetic state or phase in the armature
established by the current induced thereby, consequently a given magnetic influence
or effect in the field which is the direct result of a primary current impulse, will
have become more or less weakened or lost before the corresponding effect in the
arinature, indirectly produced, has reached its maximum. This is a condition
unfavorable to efficient working in certain cases, as, for instance, when the progress of
the resultant poles or points of maximum, attraction is very great, or when a very
high number of alternations is employed, for it is apparent that a stronger tendency
to rotation will be maintained if the maximum magnetic attractions or conditions in
both armature and field coincide, the energy developed by a motor being measured by
the product of the magnetic quantities of the armature and field.
The object, therefore, in this invention is to so construct or organize these motors
that the maxima of the magnetic effects of the two elements, the armature and field,
shall more nearly coincide.
This is accomplished in various ways, which, may be best explained by reference
to the drawings, in which various plans for accomplishing the desired results are
illustrated.
Figure 1. This is a diagrammatic illustration of a motor system in which the
alternating currents proceed from independent sources and differ primarily in
phase.
A designates the field, or magnetic frame of the motor, B, B, oppositely located
pole pieces adapted to receive the coils of one energizing circuit and C, C, similar
pole pieces for the coils of the other energizing circuit. These circuits are
designated respectively by D, E, the conductor D₁ forming a common return, to the
generator G.

page_text: .
Between these poles is mounted an armature, for example a ring or annular
The
armature wound with a series of coils F forming a closed circuit or circuits.
action or operation of a motor thus constructed is now well understood. It will be
observed, however, that the magnetism of poles B, for example, established by
current impulse in the coils thereon precedes the magnetic effect set up in the
armature by the induced current in coils F, consequently the mutual attraction
between the armature and field poles is considerably reduced. The same conditions
will, be found to exist, if, instead of assuming the poles B or C as acting inde-
pendently, we regard the ideal resultant of both acting together, which is the real
condition.
To remedy this the motor field is constructed with secondary poles B¹ C¹ which are
situated between the others. These pole pieces are wound with coils D' E¹, the
former in derivation to the coils D, the latter to coils E. The main or primary
coils D and E are wound for a different self-induction from that of the coils D¹
and E¹, the relations being so fixed that if the currents in D and E differ, for
example, by a quarter phase, the currents in each secondary coil, as B C will differ
from those in its appropriate primary B or C by say 45 degrees, or one eighth of a
period.
The explanation of the action of this motor is as follows: Assuming that an
impulse or alternation in circuit or branch E is just beginning while in the branch D
it is just falling from maximum,-the conditions of a quarter phase difference; the
ideal resultant of the attractive forces of the two sets of poles B, C, therefore may be
considered as progressing from poles C to poles B while the impulse in E is rising to
maximum and that in D is falling to zero or minimum. The polarity set up in the
arinature, however, lags behind the manifestations of field magnetism and hence the
maximum points of attraction in armature and field instead of coinciding are
angularly displaced. This effect is counteracted by the supplemental poles B¹ C¹.
The magnetic phases of these poles succeed those of poles B C by the same, or nearly
the same, period of time as elapses between the effect of the poles B C and the
corresponding induced effect in the armature, hence the magnetic conditions of
poles B C and of the armature more nearly coincide and a better result obtained.
As poles B¹ C¹ act in conjunction with the poles in the armature established by
poles B C, so in turn poles C B act similarly with the poles set up by B¹ C¹
respectively.
Under such conditions the retardation of the magnetic effect of the armature
and that of the secondary poles will bring the maximum of the two more nearly
into coincidence and a correspondingly stronger torque or magnetic attraction
secured.
In such a disposition as is shown in Figure 1 it will be observed that as the
adjacent pole pieces of either circuit are of like polarity they will have a certain
weakening effect upon one another. It is therefore desirable to remove the secondary
poles from the direct influence of the others. This may be done by constructing a
motor with two independent sets of fields, and with either one or two armatures
electrically connected, or by using two armatures and one field. These modifications
will be illustrated hereinafter.
Figure 2 is a diagrammatic illustration of a motor and system in which the difference
of phase is artificially produced.
There are two coils D D in one branch and two coils E E in the other branch of
the main circuit from the generator G. These two circuits or branches are of
different self induction, one, as D being higher than the other. For convenience this
is indicated by making coils D much larger than coils E.
By reason of this difference in the electrical character of the two circuits the phases
of current in one are retarded to a greater extent than the other. Let this difference
be thirty degrees.
A motor thus constructed will rotate under the action of an alternating current,
bit as happens in the case previously described the corresponding magnetic effects of

page_text: The
the armature and field do not coincide owing to the time that elapses between a given
magnetic effect in the armature and the condition of the field that produces it.
secondary or supplemental poles B: C₁ are therefore employed.
There being a thirty degrees difference in phase between the currents in
coils D E the magnetic effects of poles B₁ C¹ should correspond to that produced
by a current differing from the current in coils D or E by 15 degrees. This
may be accomplished by winding each supplemental pole B¹ C with two coils H, H¹.
The coils H are included in a derived circuit having the same self-induction as
circuit D and coils H¹ in a circuit having the same self-induction as circuit E,
so that if these circuits differ by 30 degrees the magnetism of poles B₁ C¹ will
correspond to that produced by a current differing from that in either D or E by
15 degrees.
This is true in all other cases, for example, if in Figure 1 the coils D¹ E¹ be
replaced by the coils H H¹ included in derived circuits, the magnetism of the
poles B C will correspond in effect or phase if it may be so termed, to that
produced by a current differing from that in either circuit D or E by 45 degrees
or one-eighth of a period.
This invention as applied to a derived circuit motor is illustrated in Figures 3 and 4.
The former is an end view of the motor with the armature in section, and a diagram
of connections, and Figure 4 a vertical section through the field.
These figures are also drawn to show one of the dispositions of two fields that may
be adopted in carrying out the invention.
The poles B B, C C, are in one field, the remaining poles in the other. The
former are wound with primary coils I J and secondary coils I'¹ J¹, the latter with
coils K L. The primary coils I J are in derived circuits between which, by reason
of their different self-induction, there is a difference of phase, say of 30 degrees.
The coils IK' are in circuit with one another, as also are coils J¹ and there
should be a difference of phase between the currents in coils K and L and their
corresponding primaries of, say, 15 degrees.
If the poles B C are at right angles the armature coils should be connected
directly across, or a single armature core wound from end to end may be used,
but if the poles B C be in line there should be an angular displacement of the
armature coils as will be well understood.
The operation will be understood from the foregoing. The maximum magnetic
condition of a pair of poles as B¹ B¹ coincides closely with the maximum effect in the
armature, which lags behind the corresponding condition in poles B B.
There are many other ways of carrying out this invention, but they all involve the
same broad principle of construction and operation..
In using expressions herein to indicate a coincidence of the magnetic phases or
effects in one set of field magnets with those set up in the armature by the other,
approximate results only are meant, but this of course will be understood.
In these and similar motors the total energy supplied to effect their operation is
equal to the sum of the energies expended in the armature and the field.
The power developed, however, is proportionate to the product of these quantities.
This product will be greatest when these quantities are equal, hence, in constructing
a motor it is desirable to determine the mass of the armature and field cores and the
windings of both and adapt the two so as to equalize as nearly as possible the magnetic
quantities of both.
In motors which have closed armature coils, this is only approximately possible as
the energy manifested in the armature is the result of inductive action from the other
element, but in motors in which the coils of both armature and field are connected
with the external circuit, the result can be much more perfectly obtained.
-
In further explanation of this object let it be assumed that the energy as
represented in the magnetism in the field of a given motor is 90 and that of the
armature 10. The sum of these quantities which represents the total energy
expended in driving the motor is 100. But assume that the motor be so con-
structed that the energy in the field is represented by 50, and that in the armature

page_text: by 50, the sum is still 100, but while in the first instance the product is 900, in
the second it is 2,500, and as the energy developed is in proportion to these
products, it is clear that those motors are the most efficient, other things being
equal, in which the magnetic energies developed in the armature and field are
equal.
These results may be obtained by using the same amount of copper or ampere
turns in both elements, when the cores of both are equal or approximately so, and
the same current energizes both. Or, in cases where the currents in one element
are induced by those of the other, by using in the induced coils an excess of copper
over that in the primary element or conductor.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as commmunicated
to me by my foreign correspondent I declare that what I claim is,-
1. In an alternating current motor the combination with an armature wound with
closed coils, of main and supplemental field magnets or poles, one set of which is
adapted to exhibit their maximum magnetic effect simultaneously with that set up in
the armature by the action of the other, as set forth.
2. In an electro-magnetic motor the combination with an armature of a plurality of
field or energizing coils included respectively in main circuits adapted to produce a
given difference of phase and supplementary or secondary circuits adapted to produce
an intermediate difference of phase, as set forth.
3. An electro-magnetic motor in which the field and armature magnets exhibit
equal strength or magnetic quantities under the influence of a given energizing
current, as set forth.
4. In an alternating current motor, the combination with field and armature cores
of equal mass of energizing coils containing equal amounts of copper as herein set
forth.
Dated this 3rd day of December 1889.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant. 3