Improvements in the Method of and Apparatus for Starting Electric Motors.
Year: 1892

page_text: Date of Application, 7th Oct., 1892
Complete Specification Left, 5th Aug., 1893-Accepted, 9th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Method of and Apparatus for Starting
Electric Motors.
We, THOMAS REGINALD ANDREWS and THOMAS PREECE, of the Firm of
Andrews and Preece, Limited, Borough Mills Bradford, in the County of York,
Electrical Engineers, do hereby declare the nature of this invention to be as
follows:-
The low resistance of an electric motor when at rest or after starting until it has
acquired considerable speed allows a comparatively large and in many cases a
dangerously powerful current to pass. It is thus generally not desirable to
suddenly switch on or apply the full force of the current at once and the object of
this invention is to enable a reduced current to be applied and the application to
be automatically increased to the full power after the field magnets have had time
to become sufficiently magnetized and the motor has acquired a fair speed.
"
"
"
For this purpose we introduce a resistance frame or rheostat or similar devices
in the circuit of a "series wound or "compound wound motor or in the
armature circuit of a "shunt wound or compound wound motor whereby the
resistance of the circuit is increased and we employ the core of a solenoid which
may be in series with the circuit in which the resistance is placed to automatically
switch the resistance out of circuit. A dash pot or its equivalent is arranged in
connection with the core of the solenoid so that it is only free to move at a com-
paratively slow speed when the current is applied. And the parts are so arranged
that when the current is cut off the core automatically returns to its original
position and again puts the resistance in circuit.
Any convenient method of arranging the said core to automatically cut out the
resistance may be employed but we prefer the following:
The several coils or their equivalent of the resistance device are connected to
thin metallic plates placed one above the other and tightly clamped together but
insulated from each other. These plates are mounted over a cup or cylinder of
mercury and have a central hole through them to admit a plunger to the mercury.
This plunger is connected to or operated by the core of the solenoid in such a
manner that when the current is applied the plunger is passed into the mercury and
the latter is forced up into the hole through the plates thus metallically connecting
such plates and cutting out the resistance.
The said core may be made hollow and be fitted with a piston to form a dash
pot and retard the motor of the core. Or the said cup of mercury may also be
utilized as a dash pot and the said plunger fitted therein for that purpose.
A spiral spring or its equivalent is provided to lift the core and plunger to its
original position when the current is cut off.
To prolong the time taken to remove the resistance a second solenoid may be
provided the core of which is also fitted with a dash pot and is so arranged
that it has to pass approximately to the end of its stroke before the first
solenoid is brought into circuit by means of a switch operated by the. second.
core.
Dated this 6th day of October 1892.
DRACUP & NOWELL,
Bradford, Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in the Method of and Apparatus for Starting
Electric Motors.
We, THOMAS REGINALD ANDREWS and THOMAS PREECE, of the Firm of
Andrews and Preece, Limited, Borough Mills Bradford, in the County of York,
Electrical Engineers, do hereby declare the nature of this invention and in what
mauner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
"
The low resistance of an electric motor when at rest or after starting until it has
acquired considerable speed allows a comparatively large and in many cases a
dangerously powerful current to pass. It is thus generally not desirable to
suddenly switch on or apply the full force of the current at once and the object of
this invention is to enable a reduced current to be applied and the application to
be automatically increased to the full power after the field magnets have had time
to become sufficiently magnetized and the motor has acquired a fair speed.
For this purpose we introduce a resistance frame or rheostat or similar devices
in the circuit of & ❝ series
wound motor or in the armature circuit of a
"shunt" wound motor or in the series circuit of a compound wound motor
whereby the resistance of the circuit is increased and we employ a solenoid which
may be in series with the circuit of the motor or as a shunt across the mains to
automatically switch the resistance out of circuit. A dash pot or its equivalent is
arranged in connection with the core of the solenoid so that it is only free to move
at a comparatively slow speed when the current is applied. And the parts are so
arranged that when the current is cut off the core automatically returns to its
original position and again puts the resistance in circuit.
66
"
Any convenient method of arranging the said core to automatically cut out the
resistance may be employed but we prefer the apparatus illustrated in the accom-
panying drawings forming a part of this Specification in which similar letters of
reference indicate corresponding parts in each of the figures.
Figure 1, represents a plan view of the apparatus.
Figure 2, is an elevation of the same.
Figure 3, is a vertical section.
Figure 4, is an elevation of an additional appliance employed in conjunction with
the above apparatus for starting large motors.
The resistance coils numbered 1 to 24 are mounted between the discs A and A¹
of non-conducting material connected together by the central pillar B. The
coils 1 to 24 are connected in series and preferably increase in conductivity
from the first to the last that is to say the wire forming the coil marked 24 is
a considerably better conductor or is of a larger gauge than the wire forming
the coil marked 1 and there may be a little difference in this respect between
each coil.
Besides being connected in series the resistance coils are each connected to one
of the 24 thin metallic plates C, by the connecting wire D, and the plates Care
thoroughly insulated from each other by a piece of non-conducting material E
introduced between each of the plates. The plates C and non-conducting
material E are clamped between the end plates F, F by the bolts G and are
mounted on the disc A over the cylindrical hole H. The hole H is formed in the
pillar Band is filled with mercury and a concentric hole J is formed through the
whole of the plates to admit the plunger K of non-conducting material to
the mercury.
The plunger K is connected to the core L of the solenoid M so that
when an electric current is passed through the solenoid the core L is drawn down-
wards into the solenoid thus driving the plunger into the mercury and the latter is

page_text: forced up into the hole through the plates thus metallically connecting such plates
one after the other and thereby cutting out the resistance one coil at a time until
when the mercury has connected the whole of the plates the resistance is entirely
cut out. When this has taken place there is full metallic connection between the
main conductors O, O' supplying the motor and connected to the couplings N
and N' by means of the wires D' and D' connected respectively to the top and
bottom plates C which plates are connected by the mercury forced up by the
plunger. In this case the ends P and Pi the wire forming the solenoid or
coil M are connected to the main conductors the solenoid is therefore a
across the main conductors and a hand switch is provided either in the main
circuit or the shunt circuit to enable the solenoid to be put in or out of circuit to
start or stop the motor.
66
shunt"
To retard the motion of the core of the solenoid when the hand switch is turned
to close the circuit and start the motor the core L is made with a cylindrical
recess Q and a piston R fitted therein. This piston is secured to the end of the
rod S fixed to the cap T mounted on the top of the tubular casing U. The
recess is partly filled with oil or other liquid and a number of holes V are made
through the piston which holes are covered by the disc or valve plate W. By this
mears the pressure of the atmosphere prevents the core moving downwards faster
than the oil can pass the piston to fill the space formed below the piston as the
core descends. The core however may be freely raised as pressure on the underside
of the piston readily raises the valve plate W sufficiently to open the holes V and
thus afford free passage to the oil.
An annular weight X surrounding the casing U is connected by the bands Y,
passing over the pulleys Z mounted in the cap T, to the top of the core and
raises the core to the position shown in the drawings as soon as the circuit of
the solenoid is broken by the above mentioned switch to stop the motor.
To prolong the time taken to cut out the resistance in the above mentioned
manner when the motor is started a second solenoid m as shown in Figure 4 may
be provided the core of which is fitted with a dash pot similar to the one above
described but in this case the core normally falls to the position shown and the dash
pot is arranged to prevent it rising too rapidly under the influence of the solenoid.
This is effected by placing the valve plate W on the underside of the piston, by
retarded
which means the core is at liberty to fall to the position shown but
when being raised by the solenoid. This second solenoid may be arranged as a
shunt across the main conductors and is provided with a hand switch to start the
motor. The core dips down into the cup of mercury a when the circuit is open
and the wire c from the core and the wire d from the cup of mercury are connected
to the wire of the first solenoid M and together with the core and cup a form a
short shunt" circuit off the wire of the solenoid so that as long as the core ! dips
down into the mercury in a the current passes in that direction instead of passing
through the solenoid M but it is so arranged that when the circuit is closed the
core gradually rises (being retarded by the dash pot) until when approximately.
at the top of its stroke the core is raised clear of the mercury and the current
being consequently prevented from passing that way passes through the
solenoid M.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed we declare that what we
claim is :
1. A motor starter consisting of a rheostat adapted to be cut out of circuit by
the core of a solenoid provided with a dash pot or its equivalent to retard its
motion, substantially as herein shown and described.
2. In a motor starter, the device for cutting out the resistance consisting of a
plunger operated by the core of a solenoid and adapted to raise mercury contained
in a cup beneath for the purpose of metallically connecting the several coils of the
rheostat, substantially as herein shown and described.

page_text: 3. The combination with the apparatus described in the first claim, of the
solenoid m, core and cup of mercury a, substantially as herein.shown and described
and for the purpose specified.'
Dated this 4th day of August 1893.
DRACUP & NOWELL,.
Bradford, Agents.