Improvements in Dynamo Electric Machines.
Year: 1894

page_text: Date of Application, 13th Feb., 1894
Complete Specification Left, 13th Nov., 1894-Accepted, 15th Dec., 1894
PROVISIONAL SPECIFICATION.
Improvements in Dynamo Electric Machines.
We, WILLIAM BROOKS SAYERS, of Glenwood, Bearsden, near Glasgow, in the
County of Dumbarton, Electrical Engineer, and HENRY ALEXANDER MAVOR,
WILLIAM ARTHUR COULSON, and SAMUEL MAVOR, all of 57 West Nile Street,
Glasgow, in the County of Lanark, Engineers and Electricians, do hereby declare
the nature of this invention to be as follows:-
This invention has reference to improvements in armatures for dynamo electric
machines of the type in which the armature winding is embedded in an iron core,
and it has for its object to lessen the self induction of the armature sections during
the period of commutation of the said sections whilst at the same time allowing of
the armature being run with a short interpolar space between it and the polar
surfaces of field magnets of solid construction without causing sensible heating of
the said field magnets by Foucault currents.
It has been experimentally found by one of us, viz. the said W. B. Sayers, that
in order to avoid such heating, it is necessary that the width of the outer ends
of the slots or passages of the armature core in which the 'armature sections are
placed, should not exceed the radial thickness of the said interpolar space by more
than one third, while on the other hand it is advantageous to make the said
outer ends of the slots or passages as broad as possible in order to make the
self induction of the said sections as small as possible and thus enable the minimum
reversing electromotive force to be used to effect the commutation of the sections
without sparking at the commutator.
Now in order to attain the object hereinbefore set forth under the apparently
contrary conditions mentioned, the notches in the iron discs of which the armature
core is composed, and which notches when the discs are put together form the slots
or channels in which the armature conductors are placed, are, according to. this
invention, each made with an angle or bend near the outer end, and the discs are
put together with the angles or bends in adjacent discs 'directed alternately in
opposite directions. Or instead of reversing the direction of the angles or bends
at each disc, several discs may be put together with the angles or bends directed
all one way,
and then a similar number be put together with the angles or bends all
directed in the opposite way, but the number of discs in each group should not
make up a total thickness of more than one and one third times the radial
thickness of the interpolar space, otherwise heating of the polar surface of the field
magnets will result.
In order to further reduce the self induction of the section of the armature
which is being reversed, a good conductor of electricity such as a plate or bar of
copper may be arranged opposite that portion of the armature where such com-
mutation takes place and at about the same distance from the armature as the
polar surfaces of the field magnets. The eddy or Foucault currents which will be
set up in this conductor by fluctuations or variations in the strength of the
magnetic field, will oppose and effectively reduce such variations or fluctuations
which are a measure of the self induction of the circuit carrying the varying
electric current from which they originate. In this way the self-induction of the
armature section that is being reversed, will be reduced. The copper plate may
be extended, or an additional plate or plates may be added, so as to cover the

page_text: commutator coils when these are used, and so reduce the self induction of these
coils also.
Dated this 13th day of February 1894.
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machines.
We, WILLIAM BROOKS SAYERS, of Glenwood, Bearsden, near Glasgow, in the
County of Dumbarton, Electrical Engineer, and HENRY ALEXANDER MAVOR,
WILLIAM ARTHUR COULSON, and SAMUEL MAVOR, all of 57 West Nile Street,
Glasgow, in the County of Lanark, Engineers and Electricians, 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 has reference to improvements in armatures for dynamo electric
machines of the type in which the armature winding is embedded in an iron core,
and it has for its object to lessen the self induction of the armature sections during
the period of commutation of the said sections whilst at the same time allowing of
the armature being run with a short interpolar space between it and the polar
surfaces of field magnets of solid construction without causing sensible heating of
the said field magnets, by Foucault currents.
It has been experimentally found by one of us, viz. the said W. B. Sayers, that
in order to avoid such heating, it is necessary that the width of the outer ends of
the slots or passages of the armature core in which the armature sections are
placed, should not exceed the radial thickness of the said interpolar space by more
than one third, while on the other hand it is advantageous to make the said onter
ends of the slots or passages as broad as possible in order to make the self induction
of the said sections as small as possible and thus enable the minimum reversing
electromotive force to be used to effect the commutation of the sections without
sparking at the commutator.
Now in order to attain the object hereinbefore set forth under the apparently
contrary conditions mentioned, the notches in the iron discs of which the armature
core is composed, and which notches when the discs are put together form the slots
or channels in which the armature conductors are placed, are, according to this
invention, each made with an angle or bend near the outer end, and the discs are
put together with the angles or bends in adjacent discs directed alternately in
opposite directions. Or instead of reversing the direction of the angles or bends
at each disc, several discs may be put together with the angles or bends directed
all one way, and then a similar number be put together with the angles or bends
all directed in the opposite way, but the number of discs in each group should not
make up a total thickness of more than one and one third times the radial thickness
of the interpolar space, otherwise heating of the polar surface of the field magnets
will result.
In the accompanying drawings
Figs. 1 and 2 show respectively in end elevation and plan, a part of an armature
core constructed according to this invention.
Figs. 3 and 4 show detached portions of two of the iron dises of which the portion
of the armature core shown in Figs. 1 and 2 is composed.
A, A, A, represent the notches in the iron discs Beach formed at its outer end
with an angle or bend A' the sides of which in this example are made inclined to
each other so that the said outer end is of flaring or divergent form. The
notches A may conveniently be punched in the discs with the angles or bends A³

page_text: all in the same direction the direction of the said angles or bends of the several.
discs being reversed in the armature core by arranging alternate groups of discs.
so that the angles or bends A' of the notches A therein point in an opposite
direction to those in the intermediate groups of discs. In this way the construction
of armature core represented in Figs. 1 and 2 is produced in which as will be seen
the width of the outer ends of the slots or channels formed in the core by the
notches A are contracted as seen in end view by the overhanging portions A² of
the discs, whilst the outer ends of the respective notches A in the discs are left
broad as and for the purposes hereinbefore mentioned.
:
Figs. 1, 2, 3 and 4 are similar views to Figs. 1, 2, 3 and 4 respectively but
in which the sides of the angle or bend A' at the outer end of each notch A are
arranged parallel with each other and in which, as shown in Fig. 24, a smaller
number of discs are arranged in each of the groups of discs in which the angles or
bends extend in the same direction.
In order to further reduce the self induction of the section of the armature which
is being reversed, a good conductor of electricity such as a plate or bar of copper
may be arranged opposite that portion of the armature where such commutation
takes place and at about the same distance from the armature as the polar surfaces.
of the field magnets. The eddy or Foucault currents which will be set up in this
conductor by fluctuations or variations in the strength of the magnetic field, will
oppose and effectively reduce such variations or fluctuations which are a measure
of the self induction of the circuit carrying the varying electric current from which
they originate. In this way the self-induction of the armature section that is
being reversed, will be reduced. The copper plate may be extended, or an
additional plate or plates may be added, so as to cover the commutator coils when
these are used, and so reduce the self induction of these coils also.
Figs. 5, 6, 7, & 8 each show in end view an armature and one half of a field.
magnet provided with a plate of copper or other good conductor for the purpose
just mentioned. In each of these figures C. D indicates the plane of commutation-
E, the field magnet, F the armature, and G the copper or other good conducting
plate. In Fig. 5, the plate G is represented as affecting that main armature coil
which is in process of being commutated. In Fig. 6 the plate G is represented as
extending over a sufficient area of the armature surface to cover both the main
armature coil and also the two commutator coils concerned at any time, when the
armature is constructed according to the Specification of Letters Patent
No. 10298/93 granted to one of us namely the said W. B. Sayers. In both
figures H represents a convenient form of support for holding the plate G in
position. In Figure 7 the plate G affecting a main armature coil only, is
represented as fixed to a bi-metallic bridge H₁ of the kind described in the said
prior Specification whilst in Fig. 8 a plate G adapted to affect both a main
armature coil and also the two commutator coils concerned at any time, is shown as
being carried by such a bridge. In Fig. 6 the commutator coils are affected by the
copper plate G only during that portion of the time in which a current is flowing
in them after they have passed out from under the pole tip, and in Fig. 8 the said
commutator coils are affected by the said plate G only during that portion of the
time in which a current is flowing in them after they have passed out from under the
pole tip and before they have passed under the magnetic portion of the bi-metallic
bridge H¹.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. A dynamo electric machine having an armature of the type herein referred
to in which the outer ends of the notches in the iron discs of which the armature
core is composed are each made with an angle or bend near the outer end, and the
discs are placed together so that the said angles or bends in adjacent discs or

page_text: adjacent groups of discs are directed in opposite directions substantially as herein-
before described for the purposes specified.
2. Providing a dynamo electric machine with one or more plates or bars of good
conducting material such as copper arranged opposite that portion of the armature
where commutation takes place and at about the same distance from the armature
as the polar surfaces of the field magnet, so as to reduce self induction in the
section of the armature winding that is being reversed and also if desired in
commutator coils in connection with such armature section, substantially as described
and shown.
Dated this 13th day of November 1894.
For the Applicants,
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.