Improvements in Self-starting Alternating Electric Current Motors.
Year: 1899

page_text: Date of Application, 14th Mar., 1899-Accepted, 22nd Apr., 1899
COMPLETE SPECIFICATION.
Improvements in Self-starting Alternating Electric Current Motors.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 89, 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 ;-
-
Our invention relates to certain starting devices for alternating current motors,
being particularly applicable to induction motors, although it may be used with
synchronous machines. It has for its object to provide a simple and efficient
means for starting alternating current motors, and is particularly designed to
obviate the present difficulties attending their use upon single-phase circuits.
By the arrangements which we have described it is possible to start alternating
current motors under load and with sufficient torque to render them adaptable
to the ordinary uses of electric motors without other special arrangements-for
running them up to synchronism before throwing on the load.
To attain these ends we may employ any of the modern types of induction
or synchronous motors having windings adapting them for use in polyphase
systems. We preferably employ an ordinary three-phase motor of the induction
type, this being readily adapted to our device, but our invention may be limited
in this regard. In general a single-phase motor either of the synchronous or
induction type, will not start when current is first turned on, and this has been
the main objection to the use of such motors. Even when started, such motors
generally run until full speed is reached, with very little torque. By our in-
With it we take an ordinary
vention, however, these difficulties are obviated.
three terminal motor of any of the types above suggested, and connect one of
its terminals to one side and one to the other side of the single-phase circuit
hetween the lines of which any desired electro-motive force is maintained. The
other terminal of the motor we connect to both of the lines through phase-
modifying devices. For this purpose we prefer suitable combinations of resist-
ance, reactance and capacity, which are obtained, as in other cases. by the use
of common forms of rheostat, inductive coil and condenser. It is of course
possible to make a great many different arrangements of these devices without
effecting the essence of our invention. Some of the arrangements are illustrated
in the accompanying drawings in diagrami,
In the drawings annexed to this specification. Fig. 1 is a diagram illustrating
our invention applied to a three-phase motor in which an inductance, and
resistance are the phase-modifying devices used. In Fig. 2 we have shown sub-
stantially the same combination as in Fig. 1, except that the inductive coil and
condenser are employed. Figs. and 4 are certain diagrams illustrating the
electric actions as we at present understand them.
In Fig. 1. A is a generator of alternating electro-motive forces to be main-

page_text: tained between the positive and negative mains a, b. M is a motor connected
by two of its terminals across the mains b. The inducing member of this
motor is shown as composed of three coils F, F1, F2, and the armature Gis
arranged as is customary for rotation in the field of the coils. It is of the
ordinary closed circuited type. The field is shown in this diagram as Y-con-
nected. The terminal coil F is connected to the main b, the coil to the
main a, while the coil F (there being three coils in the motor shown), is con-
nected through phase modifying devices to both of the mains. The phase-modi-
fying devices of this figure consist of an inductance I and a resistance R; these
are connected in series across the mains of the circuit and are thrown into and
out of circuit by the switch S, of the ordinary double pole type.
At their
common junction they are connected as described to the coil F. In practical
operation at starting, the switch S is closed and the terminals of the field are
thus all connected to line. Two of the coils are energized by the main electro-
motive force across the circuit, while the third coil is energised by an electro-motive
force of displaced phase generated by the inductance I and resistance R.
The motor has impressed upon it, according to the proportion of the induct-
ance, resistance or capacity in the circuit of the third coil, either true three-
phase electro-motive forces or quarter phase or other desired phase displace.
ment, such for instance as that of the monocyclic system above referred to.
When it is energized, the motor starts under load and gradually speeds up
until it runs as an ordinary induction motor of the single phase type. By this.
time the switch S may be opened and the motor will take its entire energy
directly from the mains. If however the phase modifying devices be of such a
type and character as to remain uninjured by the current they may be left
permanently in circuit.
In Fig. 2 we show a phase displacing or modifying means consisting of a
condenser C and an inductance I connected like the arrangement shown in
Fig. 1. In this case we have illustrated a delta-wound motor, it being of course'
immaterial which type is used in our invention.
Referring to Figs. 3 and 4, we illustrated what we conceived to be the operation
of the phase modifying devices. In Fig. 3 we have shown diagrammatically an
arrangement like that shown in Fig. 1. The main electro-motive force across
the lines is shown in the triangle of electro-motive forces forming a part of the
figure, at a, b, while the auxiliary electro-motive force is measured by the dis-
placement of the point in the triangle. By employing suitable amounts of
inductance, and resistance, we may obtain an exact or approximate 90 degrees
displacement, as may be desired, suitable for operating a motor of the quarter
phase type; it being understood that the inductance tends to create a lag while'
the resistance tends to preserve the phase of the electro-motive force, and thus
by proner proportioning of the two factors we may obtain, within reasonable
limits, such displacement as is desired.
In Fig. 4, however, the phase-modifying means consists of the inductance I,
and condenser or equivalent capacity reactance arranged in series with the third con-
ductor leading from the common junction . The triangle of electro-motive forces is
in the upper part of the figure. As before, the main electro-motive is repre-
sented by the lines a, b. The effect of the inductance I is theoretically to produce
a lag of 90 degrees, while the condenser theoretically produces a lead of
90 degrees, so that if the devices could be made without resistance, there would.
be no meeting point to determine the extent of the displacement of phase. As
however it is impossible to make these devices without resistance, the common
junction at e, as indicated in dotted lines, will be obtained which however is
very far off.
:
The phase-modifying devices and motor windings may be so proportioned as
to give currents displaced by one-third of a period from one another, which is 5
the arrangement best suited to the well-known three-phase motor.
By following the principles which we have pointed out, this can easily be

page_text: done. The phase displacement being external to and independent of the motor,
any desired type of armature may be used, and external resistance in its circuit
may be dispensed with, as by our invention we may start motors having squirrel
cage armatures of very low or even practically no resistance, whereas other
devices for starting, such for instance as a shaded pole, work best when the arma-.
ture has a large resistance.
The starting device of our invention we have found to be useful both, with,
small and large motors.
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 electrical distribution, an.
alternating current motor having exciting windings connected directly to the
supply mains of the system, phase-modifying devices connected across the said
mains and in parallel with the above named exciting windings, and other exciting
windings connected through phase modifying devices to the supply main.
2. In a single-phase alternating current system of electrical distribution, an
alternating current motor having exciting windings connected directly to the
supply mains of the system, said exciting coils containing no phase-shifting
devices, phase-modifying devices connected across the said mains and in parallel
with the above named exciting windings and other exciting windings connected
at an intermediate point to the first-named exciting windings and also connected
to the single-phase mains through the phase modifying devices.
3. In a single-phase alternating-current system of electrical distribution, an
alternating-current motor having exciting windings connected directly to the
supply mains of the system: phase modifying devices consisting of a device
having capacity and a device having inductance connected across the said mains
in parallel to the first named exciting windings, and other exciting windings
connected to the first named exciting windings at an intermediate point and
connected at their free end to a point between the device having capacity and
the device having inductance.
4 In a single-phase alternating current system of electrical distribution, an
alternating current motor having exciting windings connected directly to the
supply mains of the system, said exciting coils containing no phase-shifting
devices, phase-modifying devices consisting of a device having capacity and a
device having inductance, connected in series across the mains in parallel to
the first named exciting windings, and other exciting windings connected to the
first named exciting windings at an intermediate point and connected at their
free ends to a point between the device having capacity and the device having
inductance.
5.-In a single phase alternating-current system of electrical distribution, an
alternating current motor having main and supplemental exciting windings,
the said main windings being connected directly to the supply mains of the
system, phase-modifying devices connected to said mains in parallel with, the
main exciting windings and in series with the supplemental exciting windings.
the said supplemental windings being connected to the supply mains of the
system through the phase-modifying devices.
6. In a single-phase alternating current system of distribution, an alternating
current motor having main and supplemental inducing windings, the main wind-
ings connected directly to the supply lines of the system, and the phase modifying
devices connected to the lines in parallel with the main inducing windings and
in series with the supplemental windings and connecting the latter to the mains,
the phase-modifying devices being adjustable to produce the desired displace-
ment of phase.
In a single-phase alternating current system of distribution, an alternating-
current motor having three sets of exciting windings, two of the sets being con-

page_text: nected directly to the supply mains of the system, and phase-modifying devices
iconnected to the mains in parallel with the direct-connected windings, and supply-
ing current to the third winding, the windings and phase-modifying devices
being so arranged that currents differing approximately by one-third of a period
from each other flow in the respective exciting windings.
8. The combination with a source of single-phase alternating current, of an
alternating current motor having a main winding supplied with single-phase
current directly from said source, two dissimilar phase-modifying devices, supplied
with current from said source in series, and an additional winding or windings
upon the said motor supplied with dephased current from said source through
the phase-modifying devices.
9. The combination with a source of single-phase alternating current, of an
alternating current motor receiving current from the said source, the inducing
member of said motor being wound with a winding supplied directly from said
source, and with an additional winding supplied from said source from a point
between two dissimilar phase-modifying devices connected in series across the
said source.
'.
10. The combination with a source of single-phase alternating current, of an
alternating-current motor receiving current from said source; the inducing mem-
ber of said motor being wound with a winding supplied directly from said
source, and with an additional winding supplied from said source from a point
between two dissimilar phase-modifying devices connected in-series across the
said source, and means for cutting out the additional winding.
11. The combination of the inducing member of an alternating current motor,
of a winding connected directly across a single-phase source, and an additional
winding supplied with energy from said source, joined to a point between a
source of leading currents and a self-induction coil connected in series across
the said source.
12 The combination in the inducing member of an alternating current
motor, of a winding connected directly across a single-phase source, and addi-
tional winding supplied with energy from said, source, joined to a point between
a condenser and a self-induction coil, connected in series across the said 'source,
and means for adjusting the relative. values of the condensance and reactance
of the said condenser and self-induction coil.
1300
THE BRITISH THOMSON-HOUSTON CO. LTD.
ALFRED CLEMENTS,
Assistant Secretary,
A. R. MONKS,
W. MARTINDALE,
Directors.