Improvements in Alternating Current Induction Motors.
Year: 1898

page_text: Date of Application, 5th May, 1898-Accepted, 9th July, 1878
COMPLETE SPECIFICATION.
Improvements in Alternating Current Induction Motors.
We, THE BRITISH THOMSON-HOUSTON 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. Stein-
metz, of Schenectady, County of Schenectady, State of New York, United States
of America), and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:
-
In another application for Letters Patent of even date herewith, it is shown how
the operation of an alternating induction current motor can be improved by
providing an auxiliary induced circuit on the inducing member in inductive
relation to the inducing and induced circuits, or to the induced circuit alone, and
by advancing the phase of the currents in the auxiliary induced circuit it is there
pointed out that when the only object is to compensate for the self induction and
lagging or magnetizing current in the motor, it is preferable to arrange the
auxiliary induced circuit at such an angle with the inducing circuit that it receives
induction only through the induced member of the motor, a result which is
accomplished when the auxiliary induced circuit is arranged at an angular dis-
tance of one-fourth of the polar pitch from the inducing circuit. By the expression
"one-fourth of the polar pitch" is meant one-fourth of the angular distance from
one North pole to the next North pole in the same phase, for example, in a two
pole motor, or a motor having one resultant polar line, the polar pitch is 360°.
It is also pointed out in the above mentioned application, that when the auxiliary
induced circuit has to lend starting torque to a single phase motor, it should be
so disposed upon the machine as to receive induction directly from the inducing
member, as well as from the induced member. This arrangement is necessary
in order that the dephased current may be induced in the auxiliary induced
circuit as soon as the main switch of the motor is closed, to produce a rotary
field and to lend starting torque to the machine. In order to accomplish this
result, it is only necessary to arrange the inducing and auxiliary induced circuit
windings upon the core at an angular distance other than one-fourth of the polar
pitch. It is, however, obvious that these two windings should not be so super-
posed one upon the other that no rotary field will be produced.
In the other application of even date above mentioned, generic claims were
made covering both of the forms described, and also certain other claims more
specifically directed to that form in which the inducing and auxiliary induced
circuits are in inductive relation only through the induced member while in this
present application, it is proposed to claim that modification, or embodiment, of
the more generic invention, which comprises an auxiliary induced circuit in
which the alternating currents are maintained, and which is in inductive relation
both to the inducing and induced circuits of the motor, so as to secure starting
torque as well as to compensate for the self induction and lagging current of the
machine.
In the present application are also included certain claims directed to methods

page_text: of operating motors, related to the method claims in the above mentioned applica-
tion in accordance with the line of division above set forth, and various more
specific details to be hereinafter more particularly pointed out and claimed.
In the drawings annexed to this specification. Figs. 1, 2, and 3 are simple
diagrams showing various forms in which the invention may be embodied, and
Fig. 4 is a general view of a motor constructed in accordance with the diagram
shown in Fig. 1.
In Fig. 1, the mains of a single phase alternating circuit, or one branch of a
multi-phase circuit, or any other connection to a source of a single phase electro-
motive force, are shown. at A, B; while P is the inducing winding, or circuit,
of an alternating current induction motor, connected across the mains A, B, in
the ordinary way. P¹ is the auxiliary induced circuit, preferably wound upon
the same iron structure as that upon which the inducing member P is wound,
as will be illustrated in Fig. 4, and in such relation with the inducing circuit
that it may receive induction therefrom directly, as well as from the induced
member. The exact angular distance between these two windings may be one-
third of the polar pitch, as shown, but this is not absolutely necessary, as long as
the conditions above set forth are maintained. The auxiliary induced circuit is
closed on the phase advancing device C, preferably a condenser, and this condenser
is preferably so. arranged that its capacity can be varied by means of a switch S,
as will be understood from the diagram, since the amount of capacity required
for the production of a rotary field at starting is, in general, different from that
required for neutralizing the lagging current during the normal operation of the
machine..
The induced member S, is shown wound with a closed winding as is usual in
induction motors. This closed winding is shown as being of a multi-phase
squirrel-cage type, and it is greatly. preferred to use the multiphase winding,
for the reason that with such winding the main component of the current induced
by the inducing winding in the induced winding has a frequency proportional to
the slip, and therefore induces in the auxiliary induced circuit P an electromotive
force of a frequency constant and equal to the frequency of the electromotive force
impressed upon the mains A, B, which makes it possible to run the machine over
its normal range of speed, when once started, without adjusting the condenser.
Another advantage arising from the use of a multiphase induced winding is,
that it permits current to be, induced in the auxiliary induced circuit by the
inducing circuit through the induced member and vice-versa. It is preferred to
use a winding like that shown in the drawings, so that the coefficient of mutual
induction between the induced winding and either of the other windings will be
substantially constant at any position of the induced member.
The operation of the invention is as follows:-With the motor at rest the
current will be induced in the auxiliary induced circuit from the inducing circuit,
and this current will be dephased by the transformer action and by the condenser,
so that the inducing and auxiliary induced circuits together will produce a rotary
or shifting field in the induced member, which will create a good starting torque.
When the motor has attained a sufficient speed, the condenser may be cut out
of circuit though ordinarily it is preferred to so adjust the condenser, when a speed
approaching that of synchronism is attained, that the leading current created
thereby in the auxiliary induced circuit will be sufficient to reflect back an
advanced wave adapted to neutralize the self induction of all the windings of the
motor, thereby increasing the efficiency, output, and power factor.
Fig. 2 shows how the invention can be applied to existing types of motors
wound for polyphase circuits, but running on a single phase circuit. Here the
mains are represented at A, B, as before, connected to two points in the inducing
winding of a delta wound induction motor as will be understood from the diagram.
The inducing windings of the motor are lettered P1, P2, P3. The condenser C is
coupled to the winding P³, so that this winding, which is 60° displaced from the

page_text: winding P¹, acts as the auxiliary induced circuit, and the currents in that branch
of the circuit are maintained leading by the conductor.
Fig. 3 shows a construction very similar to Fig. 2, differing only in the addition
of a step-up transformer T, between the condenser C, and the winding P3, of the
motor, so as to give higher voltage across the terminals of the condenser than
would otherwise be practicable. The induced members of the motors in Fig. 2
and 3, are shown at S, and the winding is any ordinary closed circuit winding,
though it is preferred as above set forth, to use a multiphase induced member.
Fig. 4 shows a multipolar motor constructed in accordance with the diagram
of Fig. 1. A, B, are the mains as before, M is the ordinary main switch, P and P"
are the inducing and inducing windings, C is the condenser and S the condenser
switch, while D is the induced member, shown in this case as the motor, mounted
on the shaft E and wound with the multiphase induced windings S.
The inducing and auxiliary induced windings consist of coils wound in the
usual way on the inducing member but displaced by one-third of the polar pitch,
and connected together by the wires J and K. It will be seen that the construc-
tion of this machine is similar to that of an ordinary three-phase motor, with the
omission of one set of induction windings.
The construction of motors built in accordance with the diagram of Figs. 2 and 3
may be evidently similar to that of an ordinary three phase motor, and need not
be more fully described.
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 the claim is:-
1. The method of giving starting torque to an alternating current induction
motor upon a single phase circuit, which consists in producing and maintaining
leading currents in a closed electric circuit in inductive relation to the inducing
and induced circuits of the motor, as set forth.
2. The method herein described, which consists in maintaining leading currents
in a closed circuit in inductive relation to the inducing and induced circuits of an
alternating current motor running on a single phase circuits to lend starting
torque to the motor, and when the motor is at speed compensating for self induction
and magnetizing current by maintaining balancing leading currents in the motor
through a source of capacity, as set forth.
3. The method of starting and running an alternating current motor, which
consists in passing alternating current through an inducing winding, generating
thereby a current in an induced winding, inducing by the joint action of said
inducing and induced windings, an electromotive force in an auxiliary induced
winding, and causing the current in the auxiliary induced winding to lead the
electromotive force..
4. The method of starting and running an alternating current motor, which
consists in passing alternating current through an inducing winding, generating
thereby a current in an induced winding, generating by the joint of said inducing
and induced windings an electromotive force in an auxiliary induced winding,
and causing the current in the auxiliary induced winding to lead the said electro-
motive force, and reflecting back from the auxiliary induced winding an advanced
wave, to reduce the lagging currents in the machine.
5. The combination of an alternating current motor for single phase circuits,
having inducing and induced windings, an auxiliary induced circuit in inductive
relation to both the inducing and induced windings, and means for causing the
current in the auxiliary induced circuit to lead the electromotive force, as set
forth.
6. In an alternating current motor for single phase circuits, the combination
with an inducing winding, of an auxiliary induced winding displaced therefrom
by an angular distance of other than one-fourth of the polar pitch, an induced

page_text: winding capable of rotation relatively to said inducing winding, and means for
causing the current in the auxiliary induced winding to become leading.
7. In an alternating current motor for single phase circuits, the combination
with an inducing winding, of an induced winding capable of rotation relatively
to said inducing winding, and an auxiliary induced winding in inductive relation
with the inducing winding both directly and through the main induced winding,
and a phase advancing device so connected as to advance the phase of the current
in the auxiliary induced circuit.
S. In an alternating current motor for single phase circuits, the combination
with an inducing winding of an induced winding capable of rotation relatively to
said inducing winding, and an auxiliary induced winding in inductive relation
with the inducing winding both directly and through the main induced winding
and an adjustable phase advancing device so connected as to advance the phase
of the current in the auxiliary induced circuit.
9. The combination of an induction motor, having a deltawound inducing
member, one branch of which is connected across a single phase circuit, and a
condenser connected across a second branch of the inducing winding and in
inductive relation to the induced member, as set forth.
10. The combination in an alternating current induction motor for single
phase circuits of an inducing winding, an induced winding, an auxiliary induced
winding wound on the main induced member and displaced from the inducing
winding by an angular distance of other than one-fourth of the polar pitch, a
source of leading currents in the auxiliary induced winding, and means for
regulating the value of the leading current in the auxiliary induced circuit.
11. The combination of an alternating current motor for single phase circuits,
having inducing and multiphase induced windings, an auxiliary induced circuit
in inductive relation to both the inducing and induced windings, and means for
causing the current in the auxiliary induced circuit to lead the electromotive force,
as set forth.
12. The combination in an alternating current motor of the single phase type,
of an inducing winding, a relatively rotatable induced winding so designed that
the coefficient of mutual induction between the winding and either of the other
windings is substantially constant at any position of the induced winding, and
an auxiliary induced winding in inductive relation with the inducing winding
both directly and through the main induced winding.
13. The combination in an alternating current motor of the single phase type
of an inducing winding, a relatively rotatable main induced winding so designed
that the coefficient of mutual induction between the induced winding and either of
the other windings is substantially constant at any position of the induced wind-
ing, and an auxiliary induced winding in inductive relation with the inducing
winding both directly, and through the main induced winding, and a phase
advancing device arranged to act upon the auxiliary induced winding.
14. A single-phase-alternating-current motor having its inducing member
wound with windings displaced approximately one-third of the polar pitch, one
of said windings being connected to a pair of single-phase mains, and one being
shunted by a condenser.
Dated this 4th day of May 1898.
THE BRITISH THOMSON-HOUSTON Co. LIMITED.
ALFRED CLEMENTS,
Assistant Secretary.
A. R. MONKS,
Director.