Improvements in Means for Generating Alternating Electric Ourrents.
Year: 1899

page_text: Date of Application, 11th Nov., 1899-Accepted, 30th Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Means for Generating Alternating Electric
Ourrents.
We, THE BRITISH THOMSON-ПOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of
this invention (which has been communicated to us from abroad by Charles P.
Steinmetz, of Schenectady, in the County of Schenectady, State of New York,
United States of America, Electrical Engineer), and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement:-
Our present invention relates to the generation of alternating current and
involves in its mode of operation, the rotation of a closed conductor in syu-
chronism with and in inductive relation to a magnetic field of force produced by
a current or currents of alternating polarity. For a more precise statement as
to the scope of our invention, reference is to be had to the claims appended
hereto, the same to be taken in connection with the following description and
the accompanying drawings.
Before preceding to a detailed explanation of the apparatus which we employ
for carrying out our invention, it is desirable to refer first to certain principles
of operation, in order the better to make clear its mode of action.
When a closed conductor is placed within the influence of a field of force due
to an alternating current or currents, currents of electricity may be induced in
that conductor by either or both of two causes. First by the actual motion of
the conductor through the field of force or second, by the induction of the
field of force upon the conductor without any relative motion, such for example
as exists in the ordinary transformer.
So far as the nature of the induced currents is concerned, the same result
is produced whether the closed conductor be maintained stationary with respect
to the inducing circuits or be rotated in synchronism with the field due to such
circuits. If the conductor be rotated at synchronism, the only electro-motive
force in the apparatus will be the electro-motive force of self induction, or in
other words the electromotive force produced by the action of the alternating
current upon itself. If there are no internal losses of energy in the apparatus,
this electro-motive force will be displaced 90 degrees from the alternating current
Howing and will therefore be wattless, in other words it will neither produce nor
consume energy. If however this counter-electro-motive force be caused in some
manner to have an energy component the machine will act either as a generator
or as a motor, depending upon the phase relation between the counter-electro-
motive force and current. We have discovered that if mechanical power be
applied to a conductor rotating as described in a magnetic field, the equivalent
sine wave of current will be brought partially into phase with the counter-
electromotive force of self induction acting in the machine. This represents a
consumption of power and its conversion into electrical energy in the alternating
current circuit. The apparatus thus acts as a generator.

page_text: The reason why the counter-electro-motive force of self induction of the alter-
nating current inducing circuit is not wattless, may be explained by the fact that
the said circuit acts upon a moving closed conductor in inductive relation to it,
which closed conductor, by its relative motion, causes a cyclic change in the
mutual inductive relation existing between the two circuits. The better the
mutual induction the more closely the closed conductor approximates a short
circuited secondary, while the poorer the mutual induction the more the alter-
nating supply circuit resembles an inductance or kicking coil.
As is well known, an inductance coil has a comparatively high coefficient of
self induction and its admittance is therefore low, while on the other hund an
alternating circuit with a short circuited secondary possesses high admittance
due to the fact that the secondary acts to reduce the self induction of the primary,
and to add an energy component to the primary current.
The effect therefore of synchronously revolving a closed conductor in a magnetic
field produced by alternating currents, is to cause a pulsation in the admittance
of the exciting circuit or circuits. When the closed conductor passes from one
exciting pole to the next exciting pole, the admittance, which is evidently the
same for each of these positions, must pass through one cycle in its progressivo
variation. The admittance therefore varies with twice the frequency of the
alternating exciting current. By reason of this pulsation of admittance, the
wave of exciting current is distorted and its symmetry destroyed in such a manner
as to cause its equivalent sine wave, or wave of current equivalent in effect, to
be displaced in phase from the wave of magnetization, which wave is in quad-
rature with the counter-electro-motive force of self induction. The equivalent
sine wave of current therefore differs in phase from the counter electro-motive
force by an angle which may be either greater or less than 90 degrees. This angle
may be made less than 90 degrees and thus represent the consumption of
mechanical power and the production of electrical energy, by giving the rotating
closed conductor a positive forward thrust. In other words, the closed conductor,
although rotating in synchronism, is to be urged forward by mechanical means.
The result is the production, in the alternating current circuit, of a wave of
current, more or less distorted from the sinc form.
In the drawings, Figs. 1 and 2 represent modifications of apparatus embodying
our invention.
In Fig. 1, G represents any suitable source of alternating current, which as
shown, is a dynamo electric machine of the single phase type. The primary
member of the generating device O is suitably wound to correspond and may
resemble the inducing member of the ordinary single phase motor. Within
tho influence of the field produced by the member P is shown a relatively revolving
member or armature of practically uniform magnetic reluctance in all directions
at right angles to its axis, and having short circuited windings so related to
each other as to add their effects and produce a distinct polar line or lines.
other words the coils in their resultant action have a common axis or axes, so
that in one position their mutual inductive relation with the exciting winding I'
is a maximum, while in another direction it is a minimum, thus differing from
the armature of an ordinary induction motor in which the mutual inductive
relation between the two members of the motor is approximately constant in
all positions.
In
For the purpose of applying power to the armature A, we may employ a belt
as indicated in dotted lines at P, but it will be obvious that any other suitable
and convenient means may be used.
Fig. 2 shows the application of our invention to a multiphase current circuit.
At G, we have indicated a suitable source of current connected to translating
devices through lines 3, 4, 5. The machine indicated at O' has its primary
member supplied in any usual manner with a three phase winding connected
through suitable leads with the mains 3, 4, 5. The secondary member of the
machine consists of a shuttle armature A', provided with the closed circuited coil

page_text: or winding W, revolving within the influence of the primary member P. This
type of armature differs from that shown in Fig. 1 in that it has a variable
magnetic reluctance due to its lack of symmetry, although both armatures are
characterized by closed circuited windings acting upon the armature to produce a
resultant polar line or lines, thus varying the admittance of the primary exciting
circuit with varying relative positions of the two members of the machine. The
armatures shown may be used interchangeably, although for purposes of illus
tration we have shown one type as employed with a multiphase exciting current
and the other with a single phase circuit, but for most purposes we prefer to
employ the armature having uniform magnetic reluctance.
Whichever type of machine be utilized, it is to be understood that suitable
electrical connections are to be made between the primary member of the machine
and the alternating current circuit in connection with which it is to be employed
and that some appropriate means for supplying mechanical power to the machine
is to be provided, as for instance a belt or a direct mechanical connection with
a source of power.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same
is to be performed, we declare that what we claim is:-
An alternating current dynamo electric machine having a pulsating ad-
mittance and a magnetic circuit of substantially constant magnetic reluctance.
2-The method of generating electrical energy which consists in passing an
alternating current through an electric circuit, thereby producing a magnetic
field, rotating a closed conductor within the influence of said field, and causing
a pulsation of the primary circuit of such mature as to bring the primary current
partially into phose with respect to the electro-motive force in said primary
circuit.
A dynamo electric machine excited by alternating currents and operating
at synchronism to generate current.
4 The method which consists in supplying mechanical power to a synchronous
induction machine, excited by alternating currents and operating at synchronism,
thereby converting mechanical power into electrical energy.
5-The method of generating current which consists in positively rotating a
closed conductor in synchronism with and in inductive relation to a field of
force due to the agency of alternating currents.
Dated this 31st day of October 1899.
THE BRITISH THOMSON-HOUSTON CO. LTD.,
ALFRED CLEMENTS,
Assistant Secretary,
W. MARTINDALE, }
A. R. MONKS,
Directors.