Improvements in and relating to Dynamo Electric Machines and Motors, and to Circuits for use in connection therewith.
Year: 1893

page_text: Date of Application, 27th Mar., 1893-Accepted, 29th Apr., 1893
COMPLETE SPECIFICATION.
Improvements in and relating to Dynamo Electric Machines and
Motors, and to Circuits for use in connection therewith.
I, ELIHU THOMSON of Swampscott County of Essex State of Massachusetts,
United States of America, Electrician, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
The present invention relates to high potential circuits and to the construction
of dynamo electric machines and motors, and is especially adapted to the construc-
tion and protection of alternating current machinery in which high potentials are
to be obtained and correspondingly high insulation is necessary. Some features of
my invention render it applicable also to the construction of a machine which is
divisible into moderate sized portions or parts of moderate weight, and which can
be assembled in the locality in which the machine is to be used. This is often an
important matter where the machines have to be carried into regions difficult of
access.
In the accompanying drawings
Fig. 1 is a plan of a dynamo electric machine as preferably used in my invention,
and designed to produce alternating currents by its being rotated or to utilize
alternating currents to produce power or to cause rotation. Fig. 2 is a sectional
view of the same.
Figs. 3 and 4 show an armature coil enclosed in a body of oil or other insulating
substance.
Figs. 5 and 6 are details of the core and coil portions.
Figs. 7 to 15 show the lightning arrester I prefer to use.
The dynamo machine is shown with its revolving field magnet mounted on a
vertical shaft, which may lead to a power transmitting device.
The connections for carrying out the currents are purposely left out as they may
be modified considerably. Neither are any commuting arrangements shown as
they would resemble, when used, similar devices employed in like machinery. The
shaft X, Figs. 1 and 2, has surrounding it a hub H, which carries perforated end
plates JJ, preferably of iron. These plates bind between them, suitable bolts
being provided as indicated in Fig. 5, the magnetic portion composed of projecting
field cores K of the desired number, whose inner ends are entered into recesses into
a laminated iron ring I held between the plates J J. The bolts which hold the
structure together pass through the end plates and engage half and half with the
laminated ring 12 and the field magnet cores, so as to operate as keys to retain
said cores in place. Each of said field magnet cores may be wound with a coil of
insulated wire for magnetizing it, the directions of the windings being such that
alternate north and south poles are formed exteriorly by the windings. To simplify
the construction, however, I dispense with one half of the coils and wind the coils C
on alternate cores, leaving the intervening cores K unwound. This makes fewer
parts and lessens the amount of insulation required. The coils C are wound upon
bobbins fitting into the spaces between the field cores, and the field poles are made
as shown with overhanging projections at their polar extremities holding the coil
bobbins in place during revolution and resisting centrifugal force. The bobbins
are introduced into the structure at the moment of putting it together, and the bolts
are then inserted to clamp the field projections and the central wheel or carrier
firmly together. The current passing through the coils C is such as will simply
magnetize the poles to the desired strength and may be a low or high potential
current as desired, being preferably taken in the usual manner from a separate or
exciting machine."

page_text: Outside of the revolving field poles is placed a divided structure of laminated
iron on which are supported the armature coil or coils in which the induced
currents are set up, such currents being conveyed away for work when the machine
is a dynamo, and said coils being utilized when the machine is used as a motor, to
receive alternating currents. These currents may be of very high potential and
the machine is constructed to allow such a condition while preserving the insulation.
The iron portion of the stationary armature, as it would be termed, is made up of
blocks of laminated iron N N N N N2 N2, the projections of which extend inward
close to the field poles. The armature coils A A' are set into deep notches between
the projections on the sections. Outside of these sections and bolted securely to
them is an enclosing frame F, made in sections bound together in any suitable way,
and formed with flanges or shoulders f embracing the armature sections N.
To enable the machine to run at very high voltages, I thoroughly insulate the
armature core sections from one another, from the enclosing frame and from the
coils. To enhance the insulation of the coils I prefer to provide a casing or
enclosing frame or shell S S, Fig. 3, in which the coil is fitted and in which a body
of oil may be placed surrounding the coil, permeating its convolutions and its
insulation and water-proofing it, and at the same time making it practically
incapable of leakage or destruction by static discharges. While said shell SS
might be made of non-conducting material, in which case could be made in one
piece and surround the coil without any special precautions, it is preferable to
make it of thin metal on account of toughness and permanence. For this purpose
highly resisting alloys would be selected, such as manganese alloys with copper
and nickel, or German silver, but in any case the shell or receptacle is to be cut at
some point, as at D, and the joint filled with insulating material so that no current
can flow around the shell parallel with the wire of the enclosed armature coil A. The
shell or frame with its enclosed coil is to be slipped over the projection of the
armature section N N, Fig. 6, and secured thereto in any desired way, as by an
ear e, and a screw entering the same, see Fig. 6. The shell S S is shown open at
the top and this would be the case whenever the position of the coil is such that
the receptacle can be placed upright, as when the machine is used as shown in the
drawings, but it is obvious that the casing may be closed so as to avoid spilling,
in case the coils are arranged in other ways or in case the coils themselves are
made rotatable instead of the field magnet. Furthermore it is obvious that any
number, or in fact all, of the coils may be included in a single casing, by properly
forming and arranging the same.
The coil carriers are preferably insulated from the iron armature section by
interposed insulation as indicated at R R, Fig. 4, so that an enhanced insulation is
obtained when high potentials are used. In the same way, interposed at all points
between the armature sections and the frame which supports them is a layer of
insulation n, which still further prevents grounding while the sections themselves
are insulated relatively to one another by interposed insulating material n¹. A
leak from the armature coil would first have to pass the insulation of the coil and
the oil surrounding it, then the insulation between the coil carrier or receptacle
and the iron segmental portion, such as N N. Further to reach the general frame-
work of the machine it would require to pass the insulation between the segmental
portions N N and the general framework F supporting the same. If the insulation
be of mica or other moisture-proof material, it will on account of these precautions
be almost impossible for grounds or short-circuits through the framework to occur.
The invention is equally applicable to other systems than the alternating.
The lightning arrester I employ avoids the continuance of arcs on an electric
circuit, and consequent injury to the discharge terminals across which the arc
exists, together with other known evils.
The invention will be found particularly useful on power circuits of such voltage
and character that an arc when once established is followed by a rush of current of
such volume that the ordinary arc rupturing devices with difficulty disrupt it. It
consists principally in supplementing or assisting this disruptive action by employing

page_text: means for limiting or checking the flow of after current to an amount less than
would otherwise be the case, so that the arc rupturing devices may quickly and
certainly extinguish the arc.
In a lightning arrester there is combined with the discharge plates and arc
rupturing devices commonly employed, a resistance in the ground connection, which
resistance is as non-conductive in character as possible, and limits the line current
tending to follow a discharge to ground to such an amount as will permit the arc
to be readily extinguished when once established over the spark gap or gaps of
the arrester.
On railway or similar power circuits it has been found by experience that a short
circuit at the arrester plates, even though powerful means for blowing out the arc
are provided, is often attended by destructive effects at the plates, and is further-
more almost invariably attended by opening of the circuit breakers of the circuit
from the dynamos, indicating that the current obtained from the constant potential
or over-compounded machines commonly present in the power station is of such
enormous amount that the ordinary means for rupturing the arc are often insufficient
for that purpose. To cut down this volume of current as already indicated, I insert
in the ground branch a resistance of such character as to give the least possible
opposition to lightning discharges, while at the same time offering such resistance
to the continued passage of the line current that the arc may be broken.
In Fig. 7, L represents a line circuit which is connected to ground at E. The
ordinary arrester plates separated by a spark gap are shown at G G₁ and an arc
rupturing magnet is provided at M. One of the plates G is connected to line, and
the other G to earth through a resistance B of a definite, determinate amount
sufficient to give the desired effect, and which for illustration on a 500 volt circuit
will be, say, from 5 to 10 ohms. This resistance will be as free from self-induction
as possible. I prefer for this purpose a wooden box or earthenware tube filled with
carbon sand and provided with end plates C in contact with the sand, the length
and section of the conducting path being adjusted to give the required resistance.
Fine perforations may be provided in the box for letting out any gases which may
form from time to time without letting the particles of sand escape.
In Fig. 8 a generally similar arrangement is shown, but with a modified form of
lightning arrester. A spark gap is provided between the plates G G¹ and the arc
rupturing device is supplied by the contacts at K which are separated by an electro-
magnet M when current passes to earth, the magnet M being in the earth branch,
and shunted by a small spark gap at O, which the discharge takes first so as to
prevent injury of the magnet. A. spring S holds the armature S' in such position
as to close the contacts until the discharge takes place. By using the limiting
resistance B the arc may be broken at K by a movement of the contacts through a
considerably shorter space than would otherwise answer, and danger is also to a
large extent avoided of melting the contacts K so as to stick and to refuse to open
at all.
In Fig. 9 the arc rupturing devices are shown as two magnets, one in each of the
line circuit wires L, L which are coiled respectively around the magnets at H H¹.
One of the plates of each arrester is connected to the resistance B which is grounded
at E so that a resistance of the required amount will be included in the path from
either of the arrester plates. A single tube filled with carbon sand is shown
provided with a central connection to earth.
Fig. 10 shows the spark gap at G between the resistance B and earth, and an
electro-magnet M, acting as already described in connection with Fig. 8, may be
inserted to widen the spark gap to any desired extent to extinguish the arc between
the plates.
Figs. 11 and 12 show an arrangement similar to Fig. 7, except that in Figure 11
an air jet J is used to disrupt the arc, and in Figure 12 the discharge terminals are
enclosed in a box J¹ such that the heat of the arc itself by expanding the air in the
box blows apart the terminals, one of which is pivoted at Y as shown.
In Fig. 13 a mode of constructing the resistance is shown having as before a

page_text: surrounding tube T of non-conducting material, such as indurated fibre or earthen-
ware, having at one end a terminal plate C in contact with the carbon sand P, and
at its other end a top plate C¹ pressed down against the carbon by a spring S¹ so
as to make good contact therewith.
While I have described carbon sand as the most suitable resistant material,
other materials like metallic oxides in fine grains may be used to provide a resist-
ance having the necessary non-inductive character, and which can be adjusted to
offer the desired amount of resistance without being too unwieldy or bulky.
In Figs. 14 and 15 another form of resistance is shown which may be used
though not so easily constructed as that already described. Here a resistance wire
is coiled into two flat spirals M, M' on the two sides of a sheet or plate N of glass
or porcelain, the spirals being wound reversely and connected at their centres so as
to give as high an insulation between the terminals as possible while maintaining a
demagnetizing effect upon each other, so that self-induction is nearly if not entirely
abolished. The length and section of the wires should be so proportioned to the
normal voltage of the line as to give such a degree of resistance as will limit the
'current to an amount such that the ordinary arc rupturing apparatus can be relied
upon to act with certainty and promptness."
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is -
1. A rotary portion in a dynamo electric machine, comprising a laminated ring
having notches in its periphery, laminated core sections inserted into said notches
and coils wound around or between said core sections.
2. A dynamo electric machine
ing a series of core sections, and coils wound
on the alternate sections and extending Cuso ng pers
3. In a dynamo electric machine the combination with a coil and its core, of an
oil containing casing around the coil.
4. The combination with the coil and its core, of an oil containing casing around
the coil and interposed between the coil and core.
5. The combination of a coil traversed by varying currents, of an oil containing
metal casing enclosing said coil, and having its electrical continuity interrupted by
an insulating joint, as described.
6. A dynamo electric machine having a series of laminated core sections, separate
coils wound thereon, a support surrounding said core sections and clamping the
same together, and insulation between the core sections and the support.
7. The combination of circuit terminals at which an arc is liable to form with an
arc rupturing device for extinguishing an are thereat, and a resistance or current
reducing means to limit the current flowing across said terminals incidental to
arcing thereat.
8. The combination with a lightning arrester having a spark gap or gaps and arc
rupturing devices, of a resistance in the ground connection, consisting of carbon
sand or like granular resistant material arranged to give the desired limiting effect
upon the current flowing from line to ground upon arcing at the spark gap, as
described.
Dal thin 14th d.. of Mounh 1002
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.