Improvements in Starting Devices for Single Phase Alternating Electric Current Motors.
Year: 1898

page_text: Date of Application, 10th May, 1898-Accepted, 17th Sept., 1898
Improvements in Starting Devices for Single Phase 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 Joseph P. Stone,
of Schenectady, County of Schenectady, State of New York, United States of
America, and Samuel E. Doane, of Marlboro; County of Middlesex, State of
Massachusetts, United States of America, Electrical Engineers), and in what
manner the same is to be perforined, to be particularly described and ascertained
in and by the following statement:-
The present invention relates to apparatus for starting single phase alternating
electric current motors; and has for its object to provide a device which shall be
more efficient than those in common use:
Various forms of starting devices have been devised, which depend upon supply-
ing the motor with electro-motive force of phase displaced from that across the
main lines; these devices being used to bring the motor up to speed, and being
in general cut out when their object has, been attained. One of the forms of this
apparatus with which we are familiar consists of a resistance and an inductance
in series across the lines of the main circuit, connection being taken from a point
between the resistance and inductance to a third terminal of the motor. This
device gives
an unsymmetrical three-phase relation. With it the switch leading
to the starting device should be opened before the motor has acquired full speed,
to avoid the possibility of the voltage induced in the motor rising above that sup-
plied to it by the phase-displacing devices, and thus tending to feed current back
into them. This invention obviates the necessity for thus opening the switch;
by it we provide a voltage at the third terminal of the motor which may be any-
thing desired, either a symmetrical three-phase relation or one which shall between
the third terminal and either main rise above the voltage across the lines. The
effect of coupling in the motor is to bring down the voltage at the third terminal;
by our device we may so proportion the voltage supplied to the motor that when
it is connected and starts up, the displaced electro-motive force will be reduced
so that a symmetrical three-phase relation is established.
To carry out the purpose of this invention, we employ a resistance as in the
device already mentioned, but instead of an ordinary inductance we employ a
transformer or compensator or auto-transformer, and we so proportion the wind-
ings and the connections of the motor that the voltages may be in any proportion
desired.
This invention is illustrated in the accompanying drawings, in which Figure 1
is a diagram of the connection, Figure 2 a diagram of the electro-motive forces,
and Figure 3 a modified form showing that the devices may be made adjustable.
In Figure 1, A is the alternator supplying the single phase mains a, b, from
which leads a, b go directly to the motor terminals. Between these two leads
the resistance D and the inductance, in the form of a compensator G, are con-

page_text: nected in series, suitable switches S, S₁ being provided to disconnect the start-
ing devices from the circuit. A lead U passes from the third terminal of the
motor to one end of the compensator, the other end of which is connected to the
lead ; while the connection from the resistance is to an intermediate point
of the compensator coil.
In Figure 3 the same arrangement of devices is shown, except that in this
instance the resistance D is made adjustable, the switch S being provided with
a number of contacts leading to different points in the resistance, and a similar
adjusting switch S¹ is adjusted to different points in the compensator coil. By
changing the proportions of the resistance and inductance, the exact displacement
of phase may be effected to suit the required conditions.
In Figure 2 we show a diagram illustrative of our present understanding of the
electro-motive forces in our invention. In the triangle abc, a represents
the electro-motive force across the mains, which, for the purpose of illustration,
may be taken as a hundred volts. With the former devices which we have named
in our statement of invention, the potential c¹ (as shown by the dotted lines), only
differs from that of each main by about seventy volts. By our invention, however,
the potential being stepped up by the compensator or transformer G, this displaced
voltage is raised to a degree illustrated by the point c, being the usual equilateral
arrangement illustrating three-phase electro-motive forces. This is however the
condition which is preferred after the motor has started; to obtain it, the com-
pensator is so wound as to raise the voltage a little more than would normally be
desired, or to the point 3, which gives an unsymmetrical three-phase relation
where the split phase electro-motive force is higher upon one side of the circuit
than the other, so that the difference between it and the outside mains would be,
for example, 120 volts on one side and approximately 100 volts on the other. When
the added inductance of the motor is brought into circuit, the relation of phase is
shown in the black line triangle a-b-c. The compensator is, for several reasons,
the preferred form of the device, but an ordinary transformer might be used
without departing from our invention, and such a variation or other ordinary
engineering variation we aim to include in our claims.
The inductive connection to the mains is also within our invention.; a diagram-
matic indication of such a connection is shown in Figure 3, the transformer T
having its primary in the .generator circuit, and the motor being connected to the
secondary.
In Figure 1 we show in dotted lines that the phase displacing devices may be
themselves included in the circuit of a step-up transformer T, the effect of which
would be to raise the potential difference between the middle terminal of the
motor and the mains; so that the point c of the triangle (in Figure 2) representing
the split phase electro-motive force would be, for instance, at 3, thus giving greater
starting torque.
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. A starting device for a single phase alternating electric current motor, com-
prising two phase-displacing devices in series across the mains, and in shunt to the
Dictor, one of the phase displacing devices consisting of a step-up transforming
device designed to deliver from a point between the phase-displacing devices to a
third terminal of the motor a higher than normal voltage.
2. In combination, an electric motor having three terminals, two of which are
connected to a source of single phase current directly or inductively, and the third
terminal of which is connected to the mains through phase-displacing devices
consisting of a resistance and step-up transformer in series across the mains, the
third terminal of the motor being connected between the phase-displacing devices.
3. As a means of starting a single phase alternating electric current motor, a
resistance and a compensator in series across the main circuit, the resistance being

page_text: connected at one end to one side of the main circuit and at the other end to
an intermediate point of the compensator, the latter being connected at one end
to the other side of the circuit and at the other end to the third terminal of the
motor,
Dated this 10th day of May 1898.
THE BRITISH THOMSON-HOUSTON CO., LTD.,
Applicants,
Per ALFRED CLEMENTS,
Assistant Secretary.
A. R. MONKS,
Director,