Improvements in Alternating Current Induction Motors.
Year: 1898

page_text: Date of Application, 5th May, 1898-Accepted, 10th Sept., 1898
COMPLETE SPECIFICATION.
Improvements in Alternating Current Induction Motors.
We, THE BRITISHI 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:-
The object of the present invention is to improve the operation of alternating
current induction motors in various particulars, as will be hereinafter pointed
out. Owing to the self induction and magnetizing current in motors of this
description the current lags behind the electromotive force in the motors, and
unless compensated by a leading current of proper value this lag in the current
extends to the lines leading from the generator, and lessens the actual energy in
the circuit as compared with the apparent energy, thereby giving rise to a low
power factor.
Various arrangements have heretofore been proposed for compensating the
lagging currents in the lines, as for example, shunting the induction motor by
a condenser or other capacity. These expedients are effective only to correct the
current lag in that portion of the circuit external to the motor. They cannot
compensate for lagging currents within the motor itself. Furthermore, condensers
in shunt to alternating current motors require an impressed electromotive force
of sine wave shape in order to effectively compensate for lagging currents, and
are therefore, not well adapted for use with a large majority of alternators now
employed on single phase systems, which latter are so designed as to impress upon
the circuit electromotive forces having peaked or distorted wave shapes.
One feature of the present invention consists of an arrangement for compen-
sating for lagging currents within the motor itself as well as in the external
circuit, so as to increase the power factor, output and efficiency of the motor;
it has been found that this compensation can be secured in the manner herein
described, not only in sine wave circuits, but also in circuits with impressed
electromotive forces of irregular wave shape, such as are in use at the present
time. Generally this result is accomplished by producing leading currents in a
closed circuit in inductive relation to the induced member of the motor, or to
both inducing and induced members; these leading currents having the proper
values for compensating the self induction and magnetizing current of the
motor under a given load.
For example, the compensation may be made substantially perfect at three-
fourths load thus obtaining a power factor of 100 per cent. while above and below
this load, the compensation and hence the power factor may vary in value or
on the other hand the value of the leading currents may be regulated to improve
the power factor under various loads. The invention has another highly useful
application, which is in enabling induction motors on single phase circuits to
start with considerable torque. As is well known, single phase induction motors,

page_text: are not ordinarily self starting, but by arranging an auxiliary closed induced
circuit in which leading currents are maintained, as already suggested, in induc-
tive relation to both the inducing and induced circuits of the motor, then the
magnetism due to the inducing and to the auxiliary induced circuits will respec-
tively be out of phase and will secure the two phase effect desired for giving the
motor starting torque.
Furthermore, the same arrangement will also compensate for self induction and
magnetizing current of the motor, as heretofore explained, and in this way, the
efficiency, output and power factor of single phase motors, which are to-day less
than in polyphase motors, can be increased by a substantial amount, so that in
these respects the single phase motor becomes nearly equal and in some cases
perhaps quite equal to the multiphase motor.
It has been proposed to introduce capacity into the circuit of the induced
member of an induction motor by closing the induced circuit through a condenser,
but this is radically different from the present invention. When a condenser
is included in the induced circuit of an induction motor the frequency of the
currents in the condenser circuit varies with the speed of the motor, becoming
greater at low speed and less at high speed. It is, therefore, necessary to adjust
the capacity of the condenser for different speeds, and it is difficult to do this and
secure satisfactory results. By the present invention the frequency in the
auxiliary induced circuit is entirely independent of the speed of the motor, and
always corresponds with the frequency of the inducing circuit, irrespective of
changing the speed. A novel and valuable result secured by the present invention
is due to the fact that leading currents can be introduced into an induction motor
to compensate for the harmful effects of self induction in the induced' member,
without exposing the condenser or other phase advancing device to an electro-
motive force of varying frequency.
In this application it is proposed to set forth and claim the invention in its
more generic form and to make more specific claims to the arrangement of the
auxiliary induced circuit in a position 90° from the inducing motor circuit, so
that it receives induction only through the induced member of the motor, since
it is found that this arrangement is especially well adapted to compensate for self
induction and lagging currents in the motor, although it will not increase the
starting torque of a single phase motor of the usual type.
In another application of even date No. 10270 claims are made specifically
covering an arrangement of the auxiliary induced circuits, so that a starting torque
in a single phase motor may be obtained, and, when desired, compensation for
lagging currents in the motor.
In the accompanying drawings Figs. 1, 2, 3, 4, 5 and 6 are diagrams illustrating
various applications of the invention and various combinations in which it may
be embodied, as will be described hereinafter.
In Fig. 1, A, B, are the mains of a single phase alternating circuit supplied
either from a single phase generator or from one branch of a polyphase machine.
M represents an induction motor, having an. inducing coil connected across the
mains A, B, and an induced revolving member S containing closed circuits wound
any customary manner, though it is greatly preferred to use an induced
member having a multiphase winding, so that the coefficient of mutual induction
between the induced winding and either of the other windings will be substantially
constant for any given portion of the induced member; such an induced member
is shown in the drawings. T is an auxiliary induced coil wound on the inducing
member of the motor, but displaced 90° from the inducing circuit P. This
coil T is closed through a condenser C.
It will be seen that with this form of winding the coefficient of mutual induction
of the coils P and T, with the induced member at rest, is practically speaking,
As the induced member begins to revolve, current is induced in the coil T
of a frequency increasing directly with the speed of rotation of the induced member
zero.

page_text: and also with the frequency of the current in the induced member. But the
frequency of the current in the induced member varies inversely with the speed,
so that the frequency of the current induced in the coil T is substantially constant.
The condenser causes the current in the auxiliary induced circuit to lead,
and this, in turn, establishes a corresponding leading current in the induced
member of the motor, and also a corresponding leading current in the inducing
member, so that this arrangement compensates for lagging currents in the external
circuit, thereby securing an effect similar to that of a condenser in shunt to the
motor; it also fulfils the very useful and different function of compensation for
the self induction and lagging magnetizing current of the motor itself. The
capacity of the condenser will be adjusted to afford leading currents of the proper
value to perform the desired compensation under any given conditions. Instead
of the condenser other means for causing the current to lead in the auxiliary
induced circuit may be employed, as for example, an over-excited synchronous
motor, though a condenser will ordinarily be used in practice. In Fig. 1 is shown
such a synchronous motor M' connected by the dotted lines, to the auxiliary
induced circuit, and acting, instead of a condenser, as a source of capacity. The
arrangement of the inducing and induced circuits 90° apart, as shown in this
figure, will not give starting torque, for the reason that when the induced member
is at rest the current induced therein by the inducing member P flows in such
paths that it does not tend to induce current in the coil T. In other words, the
coefficient of mutual induction between P and T is, practically speaking, zero,
when the motor is at rest, whether we consider direct mutual induction, or indirect
mutual induction through the induced member. But this form of winding is
peculiarly well adapted to compensate for lagging currents, since the auxiliary
induced winding receives no induction except through the induced member, and
it also does not have to assist in starting the motor, so that the capacity of the
condenser C does not have to be adjusted for variation in motor load.
Next is shown in Fig. 2 a somewhat different embodiment of the invention
which will give starting torque as well as compensate for lagging currents. This
last arrangement will be included within the broader claims of the present inven-
tion, although it will be specifically claimed in the separate application, No. 10270
referred to as a modification of the invention differing from that shown in Fig. 1.
In Fig. 2 the same parts are shown as in Fig. 1 and are identified by corre-
sponding letters. The auxiliary induced circuit, however, is arranged at an angle
other than zero or 90° from the inducing circuit P so that the former circuit is
in inductive relation both to the inducing and induced circuits of the motor,
hence, currents will be induced in the auxiliary induced circuit even though the
motor be standing still and the currents therein induced will lead the currents
in the inducing circuit so that the induced member is within a two-phase rotating
field, and a starting torque secured.
Fig. 3 shows the same parts as in Fig. 1 and Fig. 2 but with the circuit T
placed 90° from the circuit P and connected to the condenser C through a step-up
transformer T, giving higher voltages at the condenser terminals than would
otherwise be practicable. In many cases it will be desirable to use such a step-up
transformer, both in this and in other combinations embodying the present
invention.
Fig. 4 shows how the invention can he applied to motors of existing types wound
for polyphase circuits but running on single-phase circuits. Here A, B, represent
the mains of a single-phase circuit, and P1, P2, P3, the inducing coils of a delta-
wound alternating motor. The induced member of the motor has any ordinary
closed circuit winding. The coil P¹ is connected across the mains A, B and the
coil P2 displaced 60° from Pl is closed through the condenser C. The operation
of this form of the invention will be easily understood.
Fig. 5 is a general view of a large motor constructed in accordance with the
diagram shown in Fig. 1. A, B, are the mains, connected through the switch M.
to the inducing windings P. These windings consist of a plurality of coils, con-
0

page_text: nected together by the wires K, as is well understood in the art. The auxiliary
induced windings T are arranged in the same manner, and connected together by
the wires J, and closed on the phase advancing device C. D is the revolving
induced member mounted on the shaft E, and wound with the closed windings S,
of any preferred character, though it is preferred to use a multiphase winding,
as above set forth.
Fig. 6 is a view of another large motor constructed in accordance with the
diagram shown in Fig. 2, and will be readily understood.
When an angle of 90° is mentioned in this specification, and in the claims hereto
attached, it will be evident to those skilled in the art that it refers to an angular
distance of one fourth of the distance from one north pole to-the next north pole
of the same phase.
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:-
1. The method of compensating for the self induction and magnetizing current
of an alternating current motor, which consists in inducing by the induced
members of the motor, leading currents in an auxiliary induced closed circuit in
inductive relation to the induced member.
2. The method of compensating for the self induction and magnetizing current
of an alternating current induction motor, which consists in balancing the lagging
currents in the inducing and secondary members by leading currents in a closed
circuit in inductive relation to the induced member, as described.
3. The combination of an alternating current induction motor, having inducing
and induced circuits, with an auxiliary induced circuit on the inducing member,
and means for causing the currents in the auxiliary induced circuit to lead the
electromotive force, as described.
4. The combination with the inducing and induced members of an induction
motor of an auxiliary induced circuit receiving induced currents through the
induced member of the motor, and a condenser in the auxiliary induced circuit,
as set forth.
5. The combination of an alternating current induction motor, having an induc-
ing winding connected or adapted to be connected across the mains of a single
phase circuit, a closed circuit induced member, an auxiliary induced coil in
inductive relation to the inducing coil through the induced member during the
normal operation of the motor, and a phase advancing device in the circuit of the
auxiliary induced coil, as set forth.
6. The combination with an induced winding of an alternating current induc-
tion motor, of a source of leading currents of a frequency independent of the
speed of the motor, so connected to said induced winding as to compensate for the
lagging throughout the various circuits of the motor, substantially as described.
7. The combination of an alternating current induction motor and an auxiliary
induced closed circuit in inductive relation to the inducing through the induced
member of the motor during the normal operation of the machine, with a source
of leading currents in the auxiliary induced circuit, whose frequency corresponds
to the frequency in the induced member of the motor, and is independent of the
speed of the induced member, as set forth.
8. The combination in an alternating current induction motor having inducing
and induced circuits, of an auxiliary induced closed circuit arranged on the
inducing member of the motor at an angle of 90° from the inducing winding,
a multiphase induced winding and a source of leading currents in the auxiliary
induced circuit.
9. In an alternating current induction motor, the combination of a source of
leading currents of a frequency independent of the speed of the motor, and an
inductive connection between the motor windings and the source of leading

page_text: currents, the value of the leading current being so proportioned as to compensate.
not only for lag in the external circuit, but also for lag in the motor itself.
10: The combination with the two members of an alternating current induction
motor and their circuits, of an auxiliary induced circuit receiving current by
induction from one member of the motor through the other member, and a source
of leading current in the auxiliary induced circuit.
11. The combination with the inducing and induced circuits of an alternating
current induction motor, of an auxiliary induced circuit on the inducing member
in inductive relation to the .induced member, and at an angle of 90° from the
inducing circuit, and a condenser in the auxiliary induced circuit, adjusted to
compensate not only for lag in the external circuit, but also for lag due to the
self induction and magnetizing current of the motor.
12. The combination of an induction motor having a winding connected across
a single phase circuit and supplied with current therefrom, a closed circuit induced
member, an auxiliary induced circuit closed upon a condenser, the capacity of
which is proportioned so as to balance or substantially balance the self induction
and magnetizing current in the motor.
13. The combination of an induction motor having inducing and induced wind-
ings, and an auxiliary induced circuit in inductive relation to the inducing circuit
through the induced circuit, with a source of leading currents, and a step-up
transformer inductively closing the auxiliary induced circuit through the said
source, substantially as described.
14. The method of reducing the self induction of an alternating current motor
which consists in- generating leading currents in an auxiliary induced winding,
and reflecting back an advanced wave through the induced member to the inducing
circuit.
15. In an alternating current motor, the combination of a pair of single phase
mains, an inducing field winding fed therefrom, an induced member, an additional
field winding receiving current by induction from said induced member, and a
condenser in shunt to said additional induced winding.
16. The combination in an alternating current motor, of an inducing winding,
an induced winding movable relative to the inducing winding and an auxiliary
winding in inductive relation with the inducing winding through the induced
member during the normal operation of the motor, and a phase advancing device
in circuit with the auxiliary induced winding.
17. The method of compensating for phase displacement in an induction motor,
which consists in generating, by the inductive action of the currents flowing in
the induced member of the motor, an electromotive force in an auxiliary induced
circuit, and causing the current in said circuit to lead the electromotive force, and
reflecting back an advanced wave through the induced to the inducing circuit of
the motor.
18. The method of compensating for phase displacement in an induction motor,
which consists in generating, by the inductive action of the currents flowing in
the induced member of the motor, an electromotive force in an auxiliary induced
circuit, fixed with relation to the inducing circuit of the motor, and causing the
current in said auxiliary induced circuit to lead the electromotive force, and
reflecting back an advanced wave through the induced to the inducing member
of the motor.
19. The combination, in an alternating current motor, of an inducing winding,
a relatively rotatable induced winding, and an auxiliary induced winding so
arranged that the mutual induction between the said auxiliary induced winding
and the inducing winding is small when the motor is at rest, and increases as
the motor begins to move, and a source of leading current in the circuit with the
auxiliary induced winding.
20. The combination in an alternating current motor, of an inducing member,
an auxiliary induced member, a phase advancing device arranged to act upon
the current in the auxiliary induced winding, and an induced member capable

page_text: of rotation with respect to the inducing and auxiliary induced members con-
structed in such a manner that the coefficient of mutual induction between the
induced and the inducing members or auxiliary circuit is substantially constant
at all positions of the induced member.
21. The combination, in an alternating current motor of an inducing circuit,
an auxiliary induced member so arranged that the coefficient of mutual induction
between the inducing and the auxiliary induced circuits is small when the motor
is at rest; a phase advancing device arranged to act upon the current in the
auxiliary induced member, and an induced member capable of rotation with respect
to the inducing and auxiliary induced members, constructed in such a manner
that the coefficient of mutual induction between the, induced and the inducing
or auxiliary induced circuit is substantially constant at all positions of the induced
circuit.
THE BRITISH THOMSON-HOUSTON CO. LTD.
ALFRED CLEMENTS,
Assistant Secretary.
A. R. MONKS,
Director.