Improvements in Means for Controlling Electric Motors.
Year: 1899

page_text: Date of Application, 22nd Dec., 1899-Accepted, 3rd Feb., 1900
Improvements in Means for Controlling Electric 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 our
said invention (which has been communicated to us from abroad by Albert G.
Davis and William B. Potter, both of Schenectady, in the County of Schenectady,
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:―
In cases where resistance used for starting and controlling electric motors
a considerable amount of energy is dissipated in the resistance in the form of
heat. It is the aim of our present invention to prevent this waste of energy
thus occasioned, by substituting for the resistance or at least for the greater part
of it a device which in operation gives rise to a counter electromotive force.
This device may consist of an electric motor and, as employed by us, the same
is preferably connected to an air-compressor or other similar device in order to
store the mechanical energy produced by the motor. Whatever be the form of
counter electro-motive force device employed, we so arrange the same that the
counter-electro-motive force may be varied at will, thus securing by the use of
such a device the same advantages as are obtained by variation of resistance
where resistance alone is employed.
The nature of our invention will be better understood by reference to the
following description and accompanying drawings, while its scope will be indicated
in the appended claims.
Fig. 1 represents an electrically operated vehicle embodying our invention
and,
Fig. 2 is a diagram of circuits.
In Fig. 2, A and B represent motors which are to be regulated. As shown,
these motors are connected in series but it is to be understood that suitable means
may be provided for connecting them in parallel at will, or for making any
other desired connections between the same, the particular connections thus made
being unimportant so far as our present invention is concerned. A starting
resistance R. of comparatively small value, together with the regulating motor C
are arranged so as to be connected in series with the motors A and B. Connec-
tions are brought from one end of the resistance R. from intermediate points in
the field winding f of the motor C and from one terminal of the motor A to con-
tact fingers 1 to 7 inclusive on the controller K. These contact fingers operate
in conjunction with the contacts on the cylinder L of the controller K and, as
[Price 8d]

page_text: will readily be seen from the drawings, are so arranged that in the first position
of the controller, the three motors A, B and C, together with the resistance R,
are all in series across the mains, which in this case are indicated respectively
as the trolley T and a ground or track return G. At the next step of a con-
troller, the finger 2 makes contact with the cylinder L, thus short circuiting the
resistance R. As the controller is turned to its succeeding positions the sections
of the field winding f are cut out successively and at the last position shown
in Fig. 2, the armature of the motor C is cut out, thus leaving the motors A
and B in series across the mains. Any desired connections may then be made
between the motors A and B, but since such connections form no essential part
of our present invention, we have considered it unnecessary to illustrate the
same.
We have shown the regulating motor C as connected preferably to an air-com-
pressor D, shown in dotted lines in Fig. 1, and diagrammatically in Fig. 2. The
air compressor may be of any well known type and is connected by suitable pipes
to an air reservoir indicated at E. The pressure of air in this reservoir largely
governs the speed at which the motor Ooperates when carrying current. If this
pressure be allowed to continually increase during the operation of the motor
the resistance opposed to the rotation of the motor will correspondingly. increase,
and if the amount of current passing through the motor be limited, the speed
of the motor will decrease until its torque becomes equal to the torque opposed
thereto, when the motor will stop. Under these circumstances the function
of the motor C as a counter electro-motive force device disappears. For this
reason we prefer to provide the reservoir E with a blow off valve which is similar
in construction to an ordinary safety valve, and is conventionally indicated at E.
So long as the current supplied to the motor C is sufficient to set up torque of
a value great enough to cause the air compressor to force air into its reservoir,
the motor will continue to run and to oppose its counter-electro-motive force to
the current supplied thereto.
When the motors A and B are first connected in circuit through the motor C
and resistance R across the mains, there is an instantaneous rush of current which,
however, is limited in value by the resistance R and the combined resistance of
the motors A, B and C. This large flow of current causes the regulating motor C
to start up instantly and rapidly accelerate in speed, the quick acceleration being
due to a considerable extent of the low pressure upon the air compressor piston
at starting. The rapid rotation of the armature of the motor C sets up a counter-
electro-motive force which cuts down the current supplied from the mains. After
the motor C has however been in operation for a short time the pressure in the
reservoir E rises sufficiently to open the relief valve after which the 'motor C
works against a constant torque, thus eliminating the tendency to an indefinite
increase in load such as would bring the motor to a stop and deprive it of its
function as a 'regulator.
We preferably utilize the compressed air for operating the air brakes, and
since the air brakes are nearly always used in lowering the speed and in bringing
the motor to a stop it follows that the air compressor when next started up works
against the reduced pressure in the reservoir occasioned by the previous use of
the brakes.
•
The motors A and B work against a maximum torque during the time of start-
ing when they are overcoming the inertia of the car. As their speed rises how-
ever, the motors work against a constantly decreasing torque, but at the same
time their counter electro-motive force increases. The point is soon reached
therefore when the counter electro-motive force of the motors A and B and of the
regulating motor C taken together are enough to cut down the current flowing,
to an amount sufficient to just supply the frictional and other losses in propelling
the vehicle. The motors then run at a constant speed. If a further increase in
speed is desired it may be obtained, in the apparatus illustrated in the drawings,

page_text: by cutting out first the resistance R and then, step by step, the turns of the field
winding of the regulating motor C. The elimination of the resistance increases
the speed of the motors A and B in obvious manner, while the decrease in the
amount of effective field winding of the motor C decreases its counter-electro-
motive force and in a similar manner operates to supply additional energy to the
motors A and B. Simultaneously with cutting out the last section of the field
of the motor C, we find it desirable to cut out the armature as well, thus leaving
the motors A and B alone in circuit.
The feature of preventing an indefinite increase in the torque opposing the
rotation of the regulating motor, we consider of considerable value, since it allows
the motor to be kept in circuit indefinitely and to act as a regulator during the
whole time it is in circuit.
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 combination with a translating device to be regulated, an artificial
resistance and a counter electro-motive force device in series therewith, and means
for varying at will the counter electro-motive force of said device.
2 The combination of two independently rotatable electric motors, connected
in series, and means for varying the amount of effective field winding of one of
said motors.
The combination of a motor to be regulated, a regulating motor, an air
compressor driven by the regulating motor, and means for varying at will the
speed of said regulating motor.
4-The combination of a motor to be regulated, a regulating motor, an air
compressor driven by the regulating motor, and means for varying at will the
counter electro-motive force of said regulating motor.
5-The combination of a motor to be regulated, a regulating motor, an air
compressor driven by the regulating motor, and means for varying at will the
torque of said regulating motor.
6 The combination of a translating device to be regulated, a regulating motor
in series therewith, means for storing the energy of said motor in the form of
fluid pressure and means for varying at will the rate at which the energy is
stored.
7 The combination of a translating device to be regulated, a regulating motor
in series therewith, means for storing the energy of said motor in a form recover-
able at will, and means for varying at will the rate at which the energy is
stored.
8 The combination of a translating device to be regulated, a regulating motor
in series therewith, means for storing the energy of said motor in a form recover-
able at will and means for varying the amount of effective field winding of said
motor.
9 The combination of a translating device to be regulated, a regulating motor,
an air compressor driven by the motor, and means for varying the amount of
effective field winding of said motor.
10 The combination of a translating device to be regulated, a counter-electro-
motive device, an air compressor driven by energy derived from the counter
electro motive force device, and means for varying at will the counter electro-
motive force of said device.
11 The combination of a plurality of motors, loads for the different motors
such that the resistance to rotation of one of the motors is greatest when starting,
while the resistance to rotation of another motor is least when starting, and means
for varving the amount of effective field winding of the last mentioned motor.
12The combination of a plurality of motors connected in series, loads for
the different motors such that the resistance to rotation of one of the motors is

page_text: greatest when starting while the resistance to rotation of another motor is least
when starting, and means for decreasing the field strength of the motor last
mentioned.
Dated this 12th day of December 1899.
N-HOUSTON CO. LTD.,
ALFRED CLEMENTS,
Assistant Secretary,
J. J. MANHEIM,
T. R. THOMPSON,
Directors.
THE BRITISH THOMSON-HOUSTON CO. LTD.,
ALFRED CLEMENTS,
Assistant Secretary,
J. J. MANHEIM,
T. R. THOMPSON,
Directors.