Year: 1885

page_text: I THOMAS JOHN HANDFORD of 50 Bedford Row in the County of Middlesex
Patent Agent, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement :—
This invention relates to dynamo-electric generators of that class in which the
field magnet is excited by an electric current in a derived circuit about the work,
or, in other words, to shunt dynamos acting as generators. The object of this
invention is to render dynamo-electric generators, of the specified class, self-
regulating in such a sense that any such machine, on being driven with a constant
speed, shall produce a uniform and constant current in the working circuit,
regardless of variations of resistance in that circuit. The invention is designed to
render any dynamo which embodies the same, capable of operating with a constant
current any number of electric-arc lamps, or other resistances, arranged in series,
up to the full capacity of the machine. These results I accomplish by a compound
winding of the field magnet, whereby the latter becomes a differential electro
magnet. I proceed to point out the best method with which I am acquainted of
applying the invention.
The accompanying drawing is a diagrammatic representation of a shunt-wound
dynamo-electric generator, embodying this invention, and having electric-arc lamps
in the main circuit.
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. The arrows indicate the direction of the
current.
A is the armature, which is provided with commutator a and brushes a¹ a' in
the usual manner, as shown. The principal winding of the field magnet, and that
which determines the indicated polarity of the same, is by means of a fine
wire 1-2 in a shunt circuit about the work; and this fact has been permitted to
determine the above classification of the present generator as shunt-wound. An

page_text: additional helix 3-4 composed of wire which lies in the main circuit 5 with the
lamps b or other work, is also wound upon the field magnet, and is connected in
such a manner that this helix and the shunt helix referred to, shall operate
differentially, as respects each other. This wire should preferably be of the same
size as that which constitutes the rest of the main circuit.
It is necessary to point out more particularly the quantity of wire embraced in
the coarse and fine wire coils of the field magnet respectively. In the construction
of any particular dynamo, embodying the present invention, I determine these
particulars in the following manner. Having constructed and arranged as a
complete shunt-dynamo the several parts of the machine in hand, other than the
coarse wire coil of the field magnet, I introduce a small artificial resistance into
the shunt circuit, for a purpose which will hereinafter appear. The work which is
to be performed by the machine may be assumed to be the operating of electric-arc
lamps. I then introduce into the main circuit the maximum number of lamps
which the machine can operate in a proper manner, when run at the desired speed.
This determines the capacity to which the completed machine will be adjusted.
I next cut out of circuit all the lights but one, and then ascertain by trial what
quantity of coarse wire, of the size selected for the purpose, is sufficient, when
wound upon the field magnet and placed in circuit, to reduce the single remaining
light to normal brightness. The wire so determined having been wound upon the
field magnet and placed in circuit, in the manner shewn in the drawing and
already described, I turn on all the lights which the machine is intended to operate,
and restore the same to normal brightness by winding upon the field magnet, as a
part of the shunt coil shown in the drawing, so much additional fine wire as may
be necessary in order to produce that result. At this point I remove from the
shunt circuit so much of the artificial resistance before mentioned and introduced,
as is equal to the resistance introduced into that circuit by such addition to the
fine wire coil of the field magnet. Then again I turn out all the lights in circuit
but one, and if the single remaining light is too bright, I increase the main circuit
coil as before until the normal brilliancy is regained. These steps determine with
a fair degree of accuracy the quantity of wire which is necessary to be embraced
in the respective coils of the field magnet in order that the proposed regulation
may be secured. If a greater degree of accuracy is desired, the above process of
successive additions to said coils, may be continued until accurate self-regulation
is obtained both for a single lamp and for the maximum number of lamps which
the machine is designed to operate. The remaining features of construction,
involved in the present invention, as well as the appropriate electrical connections,
will sufficiently appear from the drawing, and from the mode of operation, as
hereinafter explained.
This construction results in the following mode of operation: The field magnet
operates as a differential electro-magnet, whose entire electromagnetic excitation
varies with the resistance in the main circuit in a manner which is the differential
effect of the joint operation of the field magnet coils. The intensity of the magnetic
field, in which the armature revolves, varies in the same manner. When the
magnetic field is strongest, the maximum number of lamps receives sufficient current
to bring those lamps to standard brightness, and no more; when the field is
weakest, a single lamp, when placed in circuit, receives sufficient current to bring
the same to standard brightness, and no more; and when the magnetic field is of
any intermediate intensity, the current is sufficient to bring to standard brightness
that intermediate number of lamps whose operation has, through the agency of the
said coils, affected the said field in such intermediate degree. It is well understood
that in the case of a shunt dynamo which has no regulator, the current in the
working circuit diminishes as the number of lamps increases, for the reason that
successive equal increments in the resistance in the working circuit and the corre-
sponding equal increments of current in the shunt circuit fail to produce successive
equal increments of magnetization in the field magnet. This is especially noticeable
when the latter approaches saturation, When the field magnet is near the point of

page_text: Baturation, the degree of its magnetization, and hence the intensity of its field,
increases less and lese for each successive lamp turned on, and diminishes more and
more for each successive lamp turned off; so that the light is too bright when a
single lamp is in operation; or is too dim when all the lamps are in operation; or,
as is frequently the case, both of these disadvantages co-exist in one and the same
system. The present invention obviates this difficulty by increasing the range of
variation in the intensity of magnetization of the field magnet, and by producing,
for every lamp turned on or off, an approximately uniform and equal variation in
that intensity, and consequently in the intensity of the magnetic field in which the
armature revolves.
In the operation of the differential field-magnet F, the fine-wire helix 1-2 tends
to produce in that magnet a degree of magnetization strictly proportionate to the
number of lamps in operation; but, without the coarse wire helix 3-4 would fall
short of producing that effect; exactly as in the typical shunt-dynamo, as just
explained. On the other hand the coarse wire helix 3-4 tends to produce in the
field magnet a degree of reverse magnetization which is uniform and constant,
whatever be the number of lamps in circuit. Hence the combined effect of the
operation of the field-magnet coils, with any number of lamps in circuit, within the
capacity of the machine, is equal to the algebraic sum of the separate effects which
would be produced under the same conditions by each of the said differential coils
without the other. The algebraic sum of these effects, when a single lamp is in
operation, is by construction such as to produce exactly the necessary current for
one lamp; and when the maximum number of lamps is in operation, the algebraio
sum of the said effects is such as to produce exactly that current which is necessary
for the maximum number of lamps. When any intermediate number of lamps is
in operation, the total magnetization produced in the field magnet, the same being,
as before, the algebraic sum of the unlike electro-magnetic effects of the said
differential coils, may be slightly in excess of that degree of magnetization which
is necessary in order to supply that intermediate number of lamps with their normal
current. The discrepancy, however, is insignificant and of no practical importance.
In the operation of the present invention, the variable electromagnetic effect of the
shunt coil is uniformly reduced by the constant electro-magnetic effect of the
coarse-wire coil. Hence the ratio in which the combined electro magnetic effect of
both coils, when all the lamps are on, exceeds the combined electromagnetic effect
of the same, when but a single lamp is on, is greater than the ratio in which the
effect of the shunt coil alone, when the maximum number of lamps is on, exceeds
the electro magnetic effect of the same when but a single lamp is on.
Hence, as already indicated, the difference between the greatest and least
excitation of the field magnet, constructed as above, is greater than the difference
between the corresponding states of a like field magnet, produced by the shunt
coil alone; indeed it is obvious that, by the mode of construction above described,
the first-mentioned difference can readily be made so great that the maximum
magnetization of the field magnet shall exceed the minimum magnetization of the
same exactly by any desired multiple of the latter. Accordingly in the improved
dynamo the range of variation in the intensity of the field-magnet, is such as to
allow for every lamp turned on or off a degree of variation which corresponds with
the degree of magnetization necessary for the operation of a single lamp. Yet
without departure from the principal of this invention, the mode of construction
may be varied by winding the said coils, in the manner above described, with
reference to the operation of several lamps; for instance, four or five lamps, instead
of a single lamp, regarded as a minimum resistance, and with reference to a number
of lamps which is less than the maximum number of lamps, for instance, four or
five less than the maximum number of lamps instead of the maximum number of
lamps, regarded as a maximum resistance. This modified construction results in
the described regulation between the limits so taken, and the regulation without
those limits needs no special attention.

page_text: 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 In a dynamo-electric generator, a field-magnet, consisting of a magnetic core
wound as a differential electromagnet, with two coils, or helices, which have a constant
'length, or resistance, and constantly closed circuit connections, one of the Baid
coils being placed in the main, or working, circuit of such generator, and the other
of the said coils being placed in a derived circuit about the work, substantially in
the manner and for the purpose herein before described.
'
2nd In a dynamo-electric generator, a field magnet consisting of a magnetic core,
wound as a differential electro-magnet with two coils, or helices, having constantly
closed circuit connections, one of the said coils being placed in the main, or working,
circuit of such generator, and the other of the said coils being wound to a constant
resistance, and placed in a shunt circuit about the work, substantially in the manner
and for the purpose hereinbefore described.
3rd In a dynamo-electric generator, a field magnet, consisting of a magnetic core
wound as a differential electro magnet with two coils, or helices, one of the said
coils being placed in the main circuit of such generator, and the other of the
said coils being wound to a constant resistance and placed in a constantly closed
circuit about the work, substantially in the manner and for the purpose hereinbefore
described.
4th In a dynamo-electric generator, a field magnet, consisting of a magnetic core
wound as a differential electro-magnet with two coils, or helices, of constant length,
one of the said coils being placed in the main circuit of such generator and the
other of the said coils being placed in a constantly closed circuit about the work,
substantially in the manner and for the purpose hereinbefore described.
Dated this 23rd day of September 1885.
THB J. HANDFORD,
50, Bedford Row, London, W.C.