Improvements in Dynamo Electric Machines and Motors.
Year: 1897

page_text: Improvements in Dynamo Electric Machines and Motors.
I, SIDNEY GEORGE BROWN, of 1, St. John's Road, Chelmsford, in the County of
Essex, Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to improvements in dynamo-electric machines and motors
having a short air space or clearance and slot or tunnel wound armatures, the
object being to overcome the tendency to sparking at the commutators which
nsually exists with machines of this class due to distortion of the magnetic field by
the armature reaction, and thereby to enable machines to be constructed of much
greater capacity relatively to their size, than ordinary machines of this kind.
Attempts have been made to overcome the difficulty above referred to by providing
auxiliary pole pieces projecting in advance of one of the main pole pieces, in
combination with a special winding of the coils on the armature the commutation
being effected as the coils are travelling between the main and the auxiliary pole
pieces.
Now according to my invention I obtain the non-sparking action wholly by a
modification in the construction of the field magnets, and am thus enabled to
dispense with any special winding of the armature, which latter may be provided
with the ordinary diametrical winding usual with drum or ring armature.
To this end I form the field magnet or each field magnet of two portions which
magnetically are entirely separate and distinct from one another but are arranged
one inside the other, being separated by a wide division space to prevent as far as
possible any magnetic flux or leakage from one portion to the other.
I am aware that in previous attempts in this direction, slots or division spaces
have been formed in the body of the field magnet, but these have only been for the
purpose of introducing a slight magnetic reluctance, to the cross turns whereas the
purpose of my wide division space is to allow the inner portion of the magnet to be
as much as possible magnetically isolated from the rest of the circuit, so that at the
maximum load on the armature there shall be a sufficient field for commutation.
The cross-section of this inner portion of the magnetic circnit need be no greater
than is sufficient to carry the field for commutation and the flux to compensate for
leakage.
The adjacent extremities of the two portions of my improved field magnet form
the pole pieces, one pair forming one pole and the other pair forming the opposite
pole, the two poles thus being symmetrical and each consisting of two portions
separated from each other by a relatively large space or gap. My improved field
magnet may be excited by coils wound around the adjacent limbs of each portion
thereof, and the exciting coils may be shunt, series, or compound wound, as
desired. By this means when the machine is at work the two portions of each
pole piece although energised by a common exciting coil, have different magnetic
potentials, which vary according to the load on the machine. Moreover in some
cases, in addition to the ordinary exciting coils, independent regulating coils may

page_text: be applied to one or other portion of the magnet, preferably the outer portion to
regulate or control its strength relatively to that of the other portion.
According to one construction applicable more particularly to machines of the
kind referred to having a double magnetic field, that is to say having two magnets
of the horse-shoe type one above and the other below the armature, I form each
of the magnets in the manner describod, their inner and outer portions being
each of horse shoe shape, the outer portion of the magnet being preferably larger
in sectional area than the inner portion. Care is to be taken that the number of
ampere-turns on the segment of the armature extending between the extremities
or poles of the inner portion of the magnet is less than the effective ampere-turns in
the exciting coils. Between the adjacent edges of the upper and lower field
magnets a suitable space or magnetic reluctance is left and the ends of the inner
and outer portions of the magnets which embrace the armature and form the poles,
are of aproximately quadrant shape.
The inner portions of the magnets may be retained in the outer portions by means
of blocks or fillets of brass or other suitable non-magnetic material, although in
some cases it might be practicable to cast the inner and outer portions of the
magnet in one, with connecting webs or pins so thin as not to materially effect the
magnetic flux between the said portions.
The construction above described is suitable for ordinary cases, and provides
against sparking up to a certain degree of load which varies with different
machines. In machines however intended to deal with loads subject to excessive
variation such as met with in tramway circuits for instance and where fixity of
brush is required I may provide an extra subsidiary pole piece fixed to the inner
field magnet and adapted to act upon the portion of the armature between the
poles of the field magnet. This subsidiary inagnet may be series wound so that
its strength varies according to the variations in the load.
According to another arrangement instead of both the inner and outer portions
of the field magnet being of horse shoe shape, the inner portion only may be of this
shape and the outer portion may consist really of two parts one parallel with each
of the limbs of the inner portion but separated therefrom by an air space.
Dated this 8th day of September 1897
Improvements in Dynamo Electric Machines and Motors.
SIDNEY GEORGE BROWN, Van Buren, Poole Road, Bournemouth (County of
Southampton) late of No. 1, St. John's Road, Chelmsford, Essex, Electrical
Engineer, 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 improvements in dynamo-electric machines and motors
having a short air space or clearance and slot or tunnel wound armatures, the
object being to overcome the tendency to sparking at the commutators which
usually exists with machines of this class due to distortion of the magnetic field by
the armature reaction, and thereby to enable machines to be constructed of much
greater capacity relatively to their size, tban ordinary machines of this kind.
Attempts have been made to overcome the difficulty above referred to by providing
auxiliary pole pieces projecting in advance of one of the main pole pieces, in

page_text: combination with a special winding of the coils on the armature the commutation
being effected as the coils are travelling between the main and the auxiliary pole
pieces.
Now according to my invention I obtain the non-sparking action wholly by a
modification in the construction of the field magnets, and am thus enabled to
dispense with any special winding of the armature which latter may be provided
with the ordinary diametrical winding usual with drum or ring armature.
To this end I form the field magnet or each field magnet of two or more portions
which magnetically are insulated from each other so as to be entirely seperate and
distinct from one another. If two portions be employed one may be arranged
inside the other, being seperated by a wide division space to prevent as far as
possible any magnetic flux or leakage from one portion to the other.
The cross-section of the inner portion a¹ of the magnet need be no greater than
is sufficient to carry the field for commutation and the flux to compensate for
leakage.
The adjacent extremities of the two portions of my improved field magnet form
the pole pieces, one pair forming one pole and the other pair forming the opposite
pole, the two poles thus being symmetrical and each consisting of two portions
seperated from each other by a relatively large space or gap.
My improved field magnet may be excited by coils wound around the adjacent
limbs of each portion thereof, and the exciting coils may be shunt, series, or
compound wound, as desired. By this means when the machine is at work the two
portions of each pole piece although energised by a common exciting coil, have
different magnetic potentials, which vary according to the load on the machine.
Moreover in some cases in addition to the ordinary exciting coils, independent
regulating coils may be applied to one or other portion of the magnet, preferably the
outer portion to regulate or control its strength relatively to that of the other
portion.
In order that my invention may be clearly understood and readily carried into
effect I will proceed to describe the same fully by aid of the accompanying
drawing, in which Figure 1 is a side view of so much of a dynamo as is necessary
to explain my invention.
Figure 2 is a corresponding view of a modification in which a small intermediate
pole piece is employed.
The construction shown in these figures are of the kind referred to as having
a double magnetic circuit that is to say having two magnets of the horse-shoe
type one above and the other below the armature. It will be understood,
however that the invention can also be applied to multipolar designs as well as the
bipolar.
A are the field magnets, B is the armature which preferably has its windings
in slots or tunnels, C are the exciting coils which may be arranged in any suitable
manner. Referring now more particularly to Figure 1, each of the magnets A is
formed in the manner described, of outer and inner portions a a' of horse shoe
shape, the outer portion of the magnet being preferably larger in sectional area
than the inner portion a', and its pole piece 2 being also larger than the
corresponding pole piece as of the inner portion of the magnet.
Care is to be taken that the number of ampere-turns on the segment b-b of the
armature extending between the extremities or poles as of the inner portion
of the magnet, is less than the effective ampere-turns in the exciting coils of the
corresponding field magnet.
a is the broad air space between the inner and outer parts of the magnet.
a a° are air gaps which are left between the tips of the adjacent pole pieces
of the upper and lower field magnets.
cc are blocks or fillets of brass or other suitable non-magnetic material whereby
the inner portions of the magnets may be retained in the outer portions although
in some cases it might be practicable to cast the inner and outer portions of the

page_text: magnet with connecting webs or pins of iron so thin as not to materially affect
the magnetic flux between the said portions.
The commutation is effected between the diametrically opposite poles a³ above
and below the armature.
For instance if the machine were running as a dynamo, the commutation would
take place under the left hand pole a³, whereas if it were running as a motor tho
commutation would take place under the right hand pole. It will be seen that the
magnetic circuit of the poles a³ is practically insulated from that of the poles a²,
and that the former poles have a much higher potential and have also much smaller
polar spans than the poles a³ distortion of the commutating field is thus practically
reduced to zero.
The construction above described is suitable for ordinary cases, and provides
against sparking up to a certain degree of load which varies with different
machines.
In machines however intended to deal with loads subject to excessive variation,
such as met with in tramway circuits for instance and where fixity of brush is
required I prefer as shown in Figure 2 to provide a subsidiary intermediate pole
piece a fixed to the inner field magnet and adapted to act upon the portion of the
armature between the poles of the field magnet.
This subsidiary pole piece may be series wound so that its strength varies
according to the variation in the load.
In Figure 2 I have shown this series winding as conveniently placed round both
sides of the main magnetic circuit and in such a manner that their sum will act on
the pole piece a while their difference only, effects the main magnetic circuit.
In other respects the arrangement shown in Figure 2 corresponds with that
shown in Figure 1. According to another arrangement instead of both the inner
and outer portions of the field magnet being of horse shoe shape, the inner portion
only may be of this shape and the outer portion may consist really of two parts one
parallel with each of the limbs of the inner portion but separated therefrom by an
air space.
I am aware that in previous attempts in this direction, slots or division spaces
have been formed in the body of the field magnet, but these have only been for the
purpose of introducing a slight magnetic reluctance, to the cross turns whereas the
purpose of my wide division space is to allow the inner portion of the magnet to bo
as much as possible magnetically isolated from the rest of the circuit, so that at
the maximum load on the amature there shall be a sufficient field for commutation.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. A field magnet for a dynamo or motor consisting of an inner and outer portion
separated and rendered magnetically distinct by a wide division space substantially
as described.
2. In a field maguet for a dynamo or motor the combination of an outer portion
and an inner portion magnetically distinct from one another, a wide division space
between said portions to prevent magnetic flux between them, and means for
exciting said portions substantially as described.
3. In a field magnet for a dynamo or motor, the combination of an outer magnetic
portion, an inner magnetic portion considerably smaller than said outer portion, and
a wide division space between said two portions substantially as described.
4. In a field magnet for a dynamo or motor, the combination of an outer magnetic
portion, an inner magnetic portion of only sufficient area to carry the field for
commutation, a wide division space extending all round between said two portions,
and means for exciting the magnet substantially as described.
5. In a field magnet for a dynamo or motor, the combination of an outer portion
having an extended pole face, an inner portion magnetically distinct from said onter

page_text: portion and having a contracted pole face, and means for exciting said two portions,
substantially as described.
6. In a field magnet for a dynamo or motor the combination of an inner portion
of horse shoe shape having contracted pole faces, and outer portions having
extended pole faces and magnetically independent.
7. In a field maguet for a dynamo or motor the combination of an inner and an
outer portion, a wide air gap or space dividing said portions and an intermediate
pole piece, between the poles of the inner portion, substantially as described.
8. In a field magnet for a dynamo or motor the employment of an inner portion
forming a distinct magnetic circuit from the rest of the magnetic circuit and having
a higher magnetic potential than the same, substantially as and for the purposes
described.
9. A dynamo or motor having a commutating field seperate from and at a
higher potential than the rest of the magnetic field, substantially as described.
10. In a dynamo or motor the combination of a field magnet having two distinct
and magnetically insulated portions seperated by a wide air gap, and an armature
having its coils wound in slots or tunnels, substantially as described.
11. In a field magnet for a dynamo or motor the combination of an inner and
an outer portion, an air gap or space dividing said portion and an intermediate
pole piece between the poles of the inner portion, and means for exciting the said
pole piece substantially as described.
12. In a dynamo or motor, the combination of a field magnet formed in two
magnetically insulated portions with a wide air space between them, and a
diametrically wound armature with its coils wound in slots or tunnels, and an
exciting coil surrounding both portions of said field magnet substantially as
described.
13. In a dynamo or motor the combination of a pair of field magnets each
formed in two magnetically insulated parts, one of said parts having a wider pole
piece than the other, an air space between said parts, another air space between
the adjacent parts of said magnet, and an armature having its coils wound in slots
or tunnels substantially as described.
14. In a dynamo or motor, the combination of a pair of field magnets formed in
two magnetically insulated parts an intermediate pole piece projecting from one of
said parts, and an armature having its coils wound in slots or tunnels substantially
as described.
15. In a field magnet for a dynamo or notor, the combination of an outer
magnetic portion and an inner magnetic portion both being cast together with thin
webs or iron rods or pins of small cross-section, substantially as described.
Dated this Second day of June 1898.