Improvements in Devices for Starting Alternating Electric Current Motors.
Year: 1899

page_text: Date of Application, 14th Mar., 1899--Accepted, 6th May, 1899
COMPLETE SPECIFICATION.
Improvements in Devices for Starting Alternating Electric Current
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.
Steinmetz-and Ernst-J. Berg, residing-at Schenectady; in the County of Schenec-
tady, State of New York; United States of America, Electrical Engineers,) and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:―
This invention consists of new and useful improvements in devices for starting
alternating electric current motors.
We have illustrated in the accompanying drawings diagrammatic arrangements
which we consider within our invention; other arrangements may also be made,
but the principles herein exemplified will be sufficiently clear from the illus-
trations afforded.
Fig. 1 is a general view of a three-phase Y wound induction motor and
monocyclic starting device.
Fig. 2 is a diagram of a delta-wound motor constructed in accordance with
our present invention.
Figs. 3 and 4 show modifications.
Figs. 5 and 6 are illustrative diagrams.
The monocyclic starting device shown in Fig. 1 consists of two impedances of
different power factor, as, for example, the adjustable self induction, I, and
the adjustable resistance, R, connected in series through a switch, S, if preferred,
across the mains a, b, which are fed from the source of single phase current, A.
The. motor, M, may be of any of the modern types of induction or synchronous
motors having windings adapted for use in polyphase systems of distribution.
By preference, we may employ an ordinary three-phase motor of the induction
type, inasmuch as such a motor is particularly adapted for use with our inven-
Lion. We may, however, substitute a two-phase three-wire motor, or a monocyclic
motor. Such a motor, whether of the induction or synchronous type, will not
start when supplied with single-phase current. This has been one of the greatest
objections to the commercial use of such motors.
The particular type of motor illustrated in Fig. 1 is a three-phase Y wound'
induction motor having three inducing coils F, F, F, connected together at a
common point, leaving three free terminals. Two of these terminals are con-
nected to the mains a, b, while the other terminal is connected to a common
point between the two impedances I and R.
In using the monocyclic motor above referred to, the third or teaser coil would
obviously be connected between the phase modifying devices, in place of the
coil F. In any case we have little idle wire, and obtain high starting torque in
combination with good weight efficiency, and obviate the necessity of running
the motors to speed before the load is thrown on.

page_text: At starting, the switch S is closed, and the three terminals of the motor M
are thus all connected to line. Two of the coils are energized by the main
electro-motive force between the mains a, b, while the third coil is energized by
an electro-motive force of displaced phase, produced by the inductance I and
the resistance R. The motor will have impressed upon it, according to the pro-
portioning of the power factors of the various impedances, either three-puase
electromotive force or quarter-phase electromotive force or electromotive force
of other desired phase displacement. Thus energized, the motor will start under
load and will gradually acquire speed until it runs as an ordinary induction
motor of the single-phase type. At this time the switch S may be opened, and
the motor will derive, its entire energy from the mains a, b.
Having thus explained the nature and object of the monocyclic starting device,
we will proceed to describe those improvements within the scope of our present
invention.
Fig. 2 shows a motor, M, which differs from the motor shown in Fig. 1 in
that it is of the delta type. One of the energizing coils is connected directly
across the mains a, b, while the other two energizing coils are connected together
at one end, and the other ends are connected respectively to the terminals of the
first named coil. The common point of the two last named coils is connected,
as shown in dotted lines, to the common point of the two impedances I and C,
the condenser C being substituted, in this case, for the resistance R in Fig. 1.
Fig. 5 is an illustrative diagram showing the connections and also the electro-
motive force relations which exist in the form shown in Fig. 2. The main
.electro-motive force of the system is represented by the line b, the electro-
motive forces a-c and b-c, form, with the electromotive force a-b, a closed
triangle. Obviously if the phase modifying devices C and I are so arranged as
to dephase their respective currents by the theoretical angle of 90 degrees, there
would be produced an electromotive forcé triangle of infinite altitude, as indicated
by the lines -d and b-e, but inasmuch as the different reactances cannot be
made without resistance, there will be a point of convergence, shown at c.
particular position of this point of intersection, and therefore the particular
phase relation of the current in the various coils of the motor, depends on the
relation of the three factors, inductance, capacity, and reactance. If it is thus
easy to secure either three-phase or two-phase electromotive forces in the motor
as may be preferred.
The
In Fig. 3 we show a similar arrangement, but in this case, in order to reduce
the size of the condenser required, we insert a step-up transformer T, the primary
of which is in series with the inductance I, while its secondary, in which high
electromotive force and correspondingly small current is obviously developed, is
closed through the condenser C. With this arrangement a considerably smaller
condenser can be used with good results.
In Fig. 4 we show an arrangement embodying a condenser, an adjustable
resistance R provided with a switch S' by which different portions of the resistance
may be thrown upon either side of the circuit, and an inductance, the three being
in series between the lines, and the connection of the third coil of the motor
being to the switch S. It is thus possible to adjust the phase displacement in
the system with accuracy.
The diagram shown in Fig. 6 is similar to the form shown in Fig. 4, but we
have indicated at E an electrolytic cell substituted for the condenser C of Fig. 4.
It will be seen that an electrolytic cell, or a suitable number of electrolytic cells,
suitably connected, will form at one a true equivalent of the condenser and of
that portion of the ohmic resistance of Fig. 4 above the switch S. The upper
part of Fig. 6 shows the phase relations of the electromotive forces which might
be made to exist in such a system. a- represents, as in Fig. 5, the electro-
motive force impressed upon the system, while a-c, and bare the two
auxiliary electromotive forces forming in the particular case shown, a sym-

page_text: metrical system of three-phase electromotive forces. It will be obvious that
any of the various forms shown may be connected with the switch S etc., as
shown in Fig. 1.
C
In all of the diagrams illustrating the proper displacement of phase, the torque
is proportional to the perpendicular from the point to the base a, b, as shown
in dotted lines. It is therefore of advantage to have the displacement of the
phase as great as possible, limited only by the danger of having excessive electro-
motive forces at the terminals when the motor is not running. The different
reactances would therefore be so proportioned as to bring the point higher
at starting than was desired for normal running, the effect of connecting in the
motor being to bring this point down to the proper displacement of phase. The
proportions of the different devices may be arranged by following the principles
pointed out, so that any desired displacement of phase and starting torque may,
within reasonable limits, be obtained, either an exact sixty-degree relation, or
any other necessary, though in general the three-phase relation is a desirable
one. Ordinarily the switch S would be opened as soon as the motor was at speed,
but if the phase-modifying devices be of such a character as to be capable of
remaining in circuit without injury, the switch may be left closed and the motor
operated as a multiphase motor. The phase displacement being external to and
independent of the motor, any desired type of armature may be used, and the
resistance in its circuit to enable it to start may be dispensed with.
By our invention we are enabled to start motors provided with squirrel-cage
armatures even when of low resistance, whereas other devices, such as that of
the shaded pole, work best when the armature has a large resistance. We thus
dispense with sliding contacts leading to an external resistance, and obtain the
efficiency of a low resistance armature.
As already pointed out, since the phase displacement is independent of and
external to the motor, the particular type of the latter is unimportant, and we
may use a threephase, a monocyclic, a quarter-phase or other polyphase machine;
or we may employ any desired winding in the motor selected.
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-In a single phase alternating current system of distribution, an alternating
current motor having main and supplemental inducing windings, the main wind-
ings being directly connected to the supply lines of the system, phase-modifying
devices connected to the lines in parallel with the main inducing windings and
connecting the supplemental inducing windings to the supply lines, one of the
phase-modifying devices consisting of a phase advancing device in the secondary
circuit of a step-up transformer.
2-The combination of a single-phase supply circuit and a third conductor
between which and the mains a displaced electro-motive force is to be maintained,
with phase modifying devices connected in series across the main circuit, such
devices consisting of an inductive resistance, a capacity reactance, and an inter-
mediate resistance to a point in which the third conductor is connected.
3-The combination of a single-phase supply circuit and a third conductor
between which and the mains a displaced electromotive force is to be maintained,
with phase-modifying devices connected in series across the main circuit, such
devices consisting of an inductive resistance, a capacity reactance, and an inter-
mediate resistance to a point in which the conductor is connected, and means
for varying the point of connection between the intermediate resistance and the
third conductor.
In an alternating current electric motor the combination, with an induced
member, of an inducing coil connected across a pair of single-phase mains, two
impedances of different power factor also connected across the mains, and two
additional inducing coils, joined at one end to each other and to a point between

page_text: the two impedances, and at the other ends respectively to the ends of the first
named inducing coil.
5-The combination with a motor having two terminals connected to a source
of single phase current, of two dissimilar impedances connected across the said
source, with a connection from a third terminal of the motor to a point between
the said impedances, the two impedances being so adjusted and proportioned
as to cause the potential difference across their terminals to be large while the
motor is at rest, and to become less as the motor attains speed.
6-The method of starting and running an alternating current motor fed from
a single-phase system, which consists in supplying certain coils of said motor with
current from the single-phase system, through phase modifying devices adjusted
to cause a rise of potential, and reducing said rise of potential by the reactance
of the motor as the motor attains speed.
THE BRITISH THOMSON-HOUSTON Co., LTD.,
ALFRED CLEMENTS,
Assistant Secretary,
A. R. MONKS,
W. MARTINDALE,
}
Directors,