IMPROVEMENTS IN OR RELATING TO DYNAMO-ELECTRIC MACHINES FOR PRE- VENTING SPARKING IN SUCH MACHINES and in ised
Year: 1885

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I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex, Patent Agent do hereby declare the nature of this invention for
"IMPROVEMENTS IN OR RELATING TO DYNAMO-ELECTRIC MACHINES FOR PRE-
VENTING SPARKING IN SUCH MACHINES and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
"
i
This Invention relates to dynamo-electric machines in a broad sense including
not only all machines for converting energy in the form of dynamical power into
energy in the form of electric currents by the rotation of conductors in a magnetic
field, but also those electrical machines which, having a similar construction, but
operating in the reverse manner, are known as electric motors.
The object of the invention is to provide a simple, effective and inexpensive
means of preventing the occurrence, in such machines of the phenomenon known as
sparking; and the device for the accomplishment of this object consists of a
magnet, or a number of magnets, as the case may be, in addition to, or in extension
of the field magnet, of such a machine; which device may appropriately be termed
a neutralizing magnet from the circumstance that in the operation of the invention.
this magnet has an inductive effect upon the armature core the reverse of that of
the armature current. This magnet neither increases nor diminishes the useful
external current of the machine, but has for its sole purpose the production of a
current in those coils of the armature which are, for the time being, short-circuited
by the brush, or brushes, of the commutator.
And in order that the said Invention may be perfectly understood I shall now
proceed particularly to describe the best method with which I am acquainted of
carrying out the same and in so doing shall refer to the accompanying drawing
which is a diagrammatic representation of a dynamo-electric machine embodying
the invention. For the mere purpose of illustration and explanation, I have chosen
for the drawing a shunt dynamo, so called, having a drum armature.

page_text: In this drawing F is the field magnet the particular form of which is unimportant
in this connection. The north and south poles of the field magnet are lettered
respectively, N, and S. A is the revolving armature, provided with commutator C
and brushes b and b¹, as shewn, while n is the north pole of the armature, or
armature core, as magnetized by the armature current. P is the neutralizing
magnet, which is the principal feature of the invention, and consists of a core of
soft iron wound as an electromagnet having north and south poles lettered respec-
tively N¹ and S¹.
This core should preferably be in the form of a thin and narrow plate, (an edge
view of which is seen in the drawing) and may be suspended perpendicularly between
the arms of the field magnet. The same should be placed in a fixed position such
that its north pole N¹ shall be close to the armature at or near the middle point
between the poles N and S of the field magnet; or which is the same thing, should
be fixed opposite and near the theoretical neutral point of the armature A. The
best attachment of the neutralizing magnet, is by bolting the same to the field
magnet in the position mentioned, as shown in the drawing. The neutralizing
magnet P is of sufficient size, and is wound to a sufficient degree of electromagnetic
efficiency, to insure the control of the armature thereby, in the manner hereinafter
described; that is to say the neutralizing magnet is constructed to have a consider-
.ably higher magnetic efficiency than the armature A.
The coil of the neutralizing magnet is by preference to be placed in the armaturo
circuit, as distinguished from the field-magnet circuit, in order that the magnetiza-
tion of the neutralizing magnet may vary with the current in the former circuit,
and not with the current in the latter circuit, in the manner hereinafter explained.
As it is unnecessary in view of the mode of operation of this invention, to set the
brushes forward in generators, or backward in motors, in the manner which has
heretofore been practiced for the purpose of preventing sparking, the brushes, b
and b¹, are placed in such position as to make contacts with the commutator in
a perpendicular line through the neutral points of the armature.
The remaining features of construction and the appropriate connections of the
several parts of the dynamo embodying the invention, will sufficiently appear from
the drawings, and from the mode of operation as hereinafter explained.
It is a well known fact that in dynamo-electric generators heretofore constructed
and having the Pacinotti, or Siemens, system of armature-coil connections, it has
been necessary to set the brushes forward, and in dynamo-electric motors of like
construction to set the brushes backward, upon the commutator in order to prevent
sparking; which adjustment of the brushes, whether manual or automatic, has
nevertheless been not entirely efficacious to produce that result. Also it has been
necessary that the adjustment of the brushes should be variable, on account of the
variations in the absolute strength of the field magnet, or in the relative strength
of the field magnet as compared with the armature, due to variations in the electro-
motive force or current of the machine; for, by reason of such variations the
neutral point, or points, in the armature have been movable, and incapable of being
fixed by the brushes.
The mode of operation of the invention is as follows:-When the machine is in
operation, the electric current passes through the armature, and through the main
and shunt circuits in the courses and directions indicated in the drawings; whereby
the neutralizing magnet P is energized as an electromagnet in a degree dependent
upon, and varying with, the strength of the current through the armature:
which dependence and variation follow from the above-described location of the
neutralizing-magnet coil in the main circuit.
During the operation of the machine, therefore, the neutralizing magnet, whose
north pole is by the said construction near and opposite the theoretical neutral
point of the armature, causes, or tends to cause, a reversal in the direction of the
current traversing those coils of the armature which are for the time being passing
directly under that magnet. And this magnetic influence, or tendency to cause
reversal, automatically varies in strength according to the varying strength of the

page_text: current so to be reversed, for the reason before stated, namely, the inclusion of the
neutralizing-magnet coil in the armature circuit. A like result has hitherto been
accomplished by throwing the brushes over into such a position that those coils of
the armature which would otherwise produce sparking are brought under the direct
magnetic influence of the field magnet.
In the case of a dynamo having a ring armature, the neutralizing magnet will
affect in the manner described those armature coils only which are directly opposite
and adjacent thereto; hence it is necessary in dynamos of that class to place
a second neutralizing magnet upon the opposite side of the armature; and in
the case of dynamos having multiple poles, additional neutralizing magnets are
necessary.
Also I do not confine the invention to a dynamo-electric machine having a
neutralizing magnet in the main circuit with the armature; for the neutralizing
magnet may be placed in a shunt, or in an independent circuit; or may even be a
strong permanent magnet.
By means of the invention, any strength of current which the armature is
capable of carrying can be taken off from the commutator by the brushes without
sparking.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is
1st A dynamo-electric machine provided with a magnet whose north or south
pole is adjacent to the like pole of the armature, substantially as and for the
purpose hereinbefore described.
2nd In a dynamo-electric machine, a spark-preventing device, consisting of an
electromagnet whose helix is located in the main circuit of the machine, and one of
whose poles is adjacent to the like pole of the armature, substantially as herein-
before described.
3rd In a dynamo-electric machine, a spark-preventing device, consisting of an
electro magnet, which is attached to the field magnet, is located in its main circuit,
and has one of its poles adjacent to the like pole of the armature, substantially in
the manner and for the purpose herein before described.
4th In a dynamo-electric machine, a device to prevent sparking, consisting of
one or more magnets so placed that the neutral point or points of the armature
of such machine shall be within the magnetic field thereof substantially as and for
the purpose hereinbefore described.
5th In a dynamo-electric machine, a device to prevent sparking, consisting of
an electro magnet in circuit with the armature, and so placed relatively to the
armature, that one of the poles of such magnet and the like pole of the armature
shall be adjacent or next to each other, substantially as hereinbefore described.
Dated thin 15th day of T..1.. 10OK
TH J. HANDFORD,
42, Southampton Buildings, London, W.C.