Improvements in Dynamo Electric Machines.
Year: 1896

page_text: PROVISIONAL SPECIFICATION.
Improvements in Dynamo Electric Machines.
I, WILLIAM BROOKS SAYERS, of 189 St. Vincent Street, Glasgow, Engineer and
Electrician, do hereby declare the nature of this invention to be as follows:-
The current flowing in the armature winding of a continuous current dynamo has
the effect of distorting the field so that whereas when the machine is running "light"
the magnetic flux is of approximately the same density all over that portion of the
surface of the armature which is covered by the polar face, when a load is put upon
the machine the effect of the current in that portion of the armature conductors
which are under the polar face is to reduce the flux on one side of a line drawn
parallel to the axis of the armature and dividing the said portion of armature
conductors into two equal parts, and to increase the flux on the other side. If the
machine is run as a generator it is the part behind the said line relatively to the
direction of rotation, that is weakened and that in front which is strengthened. The
distribution of electro-motive force over the armature sections corresponds with that
of the magnetic flux-the E.M.F. generated in each section being proportional to the
density of the magnetic flux in which it is moving at any instant. If an additional
brush or brushes be arranged to bear upon the commutator at a point coinciding with
the central line above referred to, in other words at a point approximately inter-
mediate between the two ordinary brushes, and a voltmeter be connected between
each ordinary brush and the intermediate one, it will be found that when the machine
is running "light" the two voltmeters will give approximately equal readings but
when a load is put on, the voltmeter which is connected to the ordinary rearward
brush will show a lower reading, and that which is connected to the forward brush a
higher reading than when the machine is running light.
Now the object of this invention is to utilize this increase of E.M.F. with
increasing load for the purpose of making a machine self regulating. To this end
instead of winding the shunt coils of the field magnet for the full potential or E.M.F.
generated by the machine, I wind them to give the required number of ampere turns
for light load with about half this E.M.F. whilst making them capable of working
with a greater E.M.F. without overheating, one end of the shunt coils being adapted
to be connected to an additional brush located as hereinbefore described and the other
end to the ordinary forward brush so that the shunt winding will be excited by an
E.M.F. that will increase as the load increases and the machine be thereby rendered
self-regulating without the use of series winding. It is not essential that the inter-
mediate or additional brush be arranged to coincide with the centre line referred to,
as a larger or smaller fraction than one half the active armature sections may be used
to supply the exciting E.M.F. in the manner indicated, and the one end of the shunt
winding instead of being connected to the forward brush may be connected to the
rearward brush when it is desired to obtain a reduction of voltage with an increased
load. In general terms it may be stated that the greatest amount of increase of
E.M.F. with a given machine will he obtained when a sinall fraction of the active
coils near the ordinary forward brush is utilized, while obviously a decreasing E.M.F.
with increasing load will be obtained by using a portion of the active coils near
the rear brush, and any desired intermediate effect can be obtained by tapping a
suitable portion of the active coils.
By using two intermediate brushes, the ordinary brushes can be relieved of the
exciting current altogether.

page_text: In machines for high potentials, the use of this invention renders it possible to
use a larger size of wire for the 'shunt winding than heretofore, thus enabling a
saving in the cost of winding to be effected.
For electric motors, the field coils may be wound of conductor the diameter of
which is so proportioned that the coils can be used for a short period (at starting) in
series with a portion of the armature winding without undue heating, and when the
starting has been effected the remaining portion of the armature winding can be
coupled in parallel to it, whereupon the motor will become essentially a shunt motor.
For enabling the field coils to be thus coupled up, a special switch is provided so
constructed and arranged that upon moving the switch lever for starting, it will
connect one end of the field coils with the supply main in which the starting switch
is placed, the other end of the field coils being already connected to the intermediate
brush, then by a further movement of the switch lever the supply main and the first
mentioned end of the field coils are both connected with the remaining portion of the
armature winding for continued working.
The field coils when wound as described will have too great an electrical resistance
and an unnecessarily great magnetising force for continuous running as a series
motor, but both the resistance and the large magnetising force are advantageous
during starting. The E.M.F. of the section of the armature to which the field coils
are ultimately connected in parallel or as a shunt should be suitable for producing
the normal magnetising force required for the motor by means of the current flowing
through the said field coils. By the arrangement described I avoid the troublesome
switching arrangements heretofore necessary for starting shunt motors and also the
high inductive effect of the fine shunt winding of many turns required when high
potentials are used.
In all cases, a pair of intermediate brushes placed diametrically opposite to each
other and coupled together, may be used in place of a single brush using one side of
armature only. Also the pole pieces may have deep grooves formed in them in
positions corresponding with the position of the intermediate brush or brushes in
order to reduce or avoid sparking. The additional brush or brushes may be smaller
than the ordinary ones, and be of carbon; they may be fixed to but insulated from the
field magnet, or be carried by a frame mounted on insulated supports independently
of the rocker or other movable support carrying the ordinary brushes.
Dated this 2nd day of More 1806
I, WILLIAM BROOKS SAYERS, of 189 St. Vincent Street, Glasgow, Engineer and
Electrician, 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 :-
The current flowing in the armature winding of a continuous. current dynamo
has the effect of distorting the field so that whereas when the machine is running
"light" the magnetic flux is of approximately the same density all over that portion
of the surface of the armature which is covered. by each polar face, when a load
is put upon the machine the effect of the current in that portion of the armature
conductors which is under the polar face is to reduce the flux on one side of:a liue
drawn parallel to the axis of the armature and dividing the said portion of armature

page_text: conductors into two equal parts, and to increase the flux on the other side. If the
machine is run as a generator it is the part behind the said line relatively to the
direction of rotation, that is weakened and that in front which is strengthened. The
distribution of electro-motive force over the armature sections corresponds with
that of the magnetic flux-the E.M.F. generated in each section being proportional to
the density of the magnetic flux in which it is moving at any instant. If an
additional brush or brushes be arranged to bear upon the commutator at a point
coinciding with the central line above referred to, in other words at a point approxi-
mately intermediate between the two ordinary brushes, and a volt-meter be connected
between each ordinary brush and the intermediate one, it will be found that when the
machine is running "light" the two volt-meters will give approximately equal r.adings,
but when a load is put on, the volt-meter which is connected to the ordinary rearward
brush will show a lover reading, and that which is connected to the forward brush a
higher reading than when the machine is running light.
Now the object of this invention is to utilize the increase of E.M.F. with increasing.
load for the purpose of making the dynamo machine self regulating. To this end
instead of winding the shunt c ils of the field magnet for the full potential or E.M.F.
generated by the machine, I wind them to give the required number of ampère turns
for light load with about half this E.M.F. whilst making them capable of working with
a greater E.M.F. without overheating, one end of the shunt coils being connected to an
additional brush located as hereinbefore described and the other end to the ordinary
forward brush so that the shunt winding will be excited by an E.M.F. that will increase
as the load increases, and the machine be thereby rendered self-regulating without the
ure of series winding. It is not essential that the intermediate or additional brush be
arranged to coincide with the centre line referred to, as a larger or smaller fraction than
one half the active armature sections may be used to supply the exciting E.M.F. in the
manner indicated, and the one end of the shunt winding instead of being connected
to the forward brush may be connected to the rearward brush when it is desired to
obtain a reduction of voltage with an increased load. In general terms it may be
stated that the greatest amount of increase of E.M.F. with a given machine will be.
obtained when a small fraction of the active coils near the ordinary forward rush is
utilized, while obviously a decreasing E.M.F. with increasi g load will be obtain d
by using a portion of the active coils near the rear brush, and any desired intermediate
effect can be obtained by tapping a suitable portion of the active cuils.
Fig. 1 of the accompanying drawings is a diagram representing the distribution
of the magnetic field in a continuous current machine having an ordinary ring or
drum armature and such as will be obtained by measuring the E.M.F. between
the sections of the commutator by means of a suitable velt-meter and exploring
contacts in the well known manner. The dotted curve a represents the distribution
when the machine is running "light," and the full line 6 when a current is taken
from the armature. It will be clear that if the additional or intermediate brush bear
upon the commutator at a position corresponding with the central dotted line cand
the shunt cil which excites the field magnets is connected between this brush and
the main brush which would be situate somewhat in advance of the position
corresponding to the point d where the full curve reaches the zero line. then the
shunt oil will be subject to an increasing E.M.F. as the current in the external
circuit of the machine rises, and that an increasing excitation of the field, which
will tend to secure self regulation, will result. By placing the intermediate brush
at different positions on the commutator and properly proportioning the shunt
winding, varying degrees of regulati n can be secured.
It will be seen that in each case, the shunt coil will be excited by a E.M.F. that
is less than the total E.M.F. produced by the armature winding. The number of
turns used in the shunt coil will therefore be less and consequently the danger of
damage to the insulation of the machine on breaking the circuit of the said coil will
be reduced.
Fig. 2 represents diagrammatically a dynamo-electric machine constructed
according to this invention a is the armature, e the commutator, and b, 6 the

page_text: ordinary main brushes. B is the additional brush arranged about midway between the
ordinary brushes b, b', and S the shunt coil on the field magnet M, one end of this
coil. being shown connected to the additional brush B and the other end to the
forward brush b¹.
By using two intermediate or additional brushes such as B, B' B2 (Fig. 4) arranged
one behind the other, and connected to the ends of the shunt coil, the ordinary
brushes b b¹ can be relieved of the exciting current altogether.
In machines for high potentials, the use of my invention renders it possible to
employ a larger size of wire for the shunt winding than heretofore, thus enabling
a saving in the cost of winding to be effected.
For electric motors, the field coils may be wound with a conductor the diameter
of which is so proportioned that the coils can be used for a short period (at starting)
in series with a portion of the armature winding, and when the starting has been
effected the remaining portion of the armature winding can be coupled in parallel to
it, whereupon the motor will become essentially a shunt motor. For enabling the field
coils to be thus coupled up, a special switch is provided so constructed and arranged
that upon moving the switch lever for starting, it will connect. one end of the
field coils with the supply main in which the starting switch is placed, the other
end of the field coils being already connected to the intermediate brush; then by
a further movement of the switch lever the supply main and the first mentioned end of
the field coils are both connected with the remaining portion of the armature winding
for continned working.
The field coils when wound as described will have too great an electrical resistance
and an unnecessarily great magnetising force for continuous running as a series motor,
but both the resistance and the large magnetising force are advantageous during
starting. The E.M.F. of the section of the armature to which the field coils are
ultimately connected in parallel or as a shunt should be suitable for producing the
normal magnetising force required for the motor by means of the current flowing
through the said field coils. By the arrangement described I avoid the troublesome
switching arrangements heretofore necessary for starting shunt motors and also the
high inductive effect of the fine sbunt winding of many turns required when high
potentials are used.
Fig. 3 represents diagrammatically an electric motor having its field coils adapted
to be connected up in the manner just described.
S is the field magnet exciting coil which may be wound to act as a shunt coil with
a pressure of about Ith the working pressure applied to the terminals of the motor.
B, B2 are two additional brushes which are adjusted into such a position on the
commutator relatively to that of the main positive brush 6 that the difference of
pressure between the said main brush and the additional ones B1, B2 is about one sixth
of the total back pressure generated by the motor armature. The starting switch
comprises four fixed contacts m, n, o, p, and a movable switch lever one arm q of
which is connected to the positive supply terminal r, whilst the other arm q' is
insulated.
The contact o is connected by a conductor s with one end of the shunt coils the
other end of which is connected with the additional brush B' and the contact m by a
conductor s². The contact n is connected to a second additional brush B2, and
contact p is connected to the positive main brush b. The negative main brush 6' is
connected only to the negative supply terminal r².
With the parts thus arranged, when the switch lever q g' is moved into position No. 1,
the insulated arm g¹ thereof connects, through contacts m, n, the brush B2 in parallel
with the brush B' which is permanently connected to one end of the exciting shunt
coil S, and the arm 9 connects the positive supply main with contact o. The said
exciting coil is then in series with that part of the armature winding which is connected
between the commutator sectors upon which the brushes B' and B2 are bearing and
the brush which is connected to the negative main.
The motor therefore starts as a series motor with the well understood advantage of
very high field excitation. When the motor is started, the switch lever is moved into

page_text: position No. 2. During the movement of the switch lever into this position, connection
between contacts m and n is broken and brush B' is left disconnected while the main
brush is connected to the positive supply main in parallel with the exciting coil S
which becomes a shunt on that portion of the armature winding which is connected
between the commutator sectors upon which brushes b and B bear. The machine
now acts as a shunt inotor, the current which flows around the exciting coil joining
the armature current through brush B'. At very light loads, a local current will be
generated in that portion of the armature winding with which the exciting coil is
connected in shunt and such current will maintain the excitation. The advantages of
this arrangement are that the exciting coil will be composed of a comparatively
few turns of larger wire than would be required if it were adapted to work with
the full pressure of the supply. The coil is consequently cheaper to construct, and the
induced E.M.F. on breaking circuit, and consequent danger of breaking down the
insulation, is greatly reduced.
The brush B is added for the purpose of taking a share of the current and making
both portions of the armature winding operative during starting. The said brush B
may not always be necessary and when this is the case the switch contacts m, n, and
the insulated blade g of the switch are omitted.
When the arrangement shown in Fig. 3 is a lopted for a motor as described, the
main positive brush 6 carries a current which is less than the current carried by the
main negative brush 6 by the amount flowing round the exciting coil, but when
the arrangement is used for a generator the current through the main positive brush b
would be greater by a similar amount, and as in the example taken, the exciting
current will be six times greater than it would be if the exciting coil were wound for
the full pressure, the increased current would cause this brush to spark with a less
load than would cause the brush 6' to spark.
Fig. 4 shows diagrammatically an arrangement in which the main brushes 6 and 6¹
are relieved entirely of the exciting current. B', B' are two additional brushes which;
if the machine is to run singly as a generator, may be connected directly to the
terminals of the exciting coil S so that the machine will excite itself in the ordinary
way. When however the machine is required to work in parallel with others, or to
work as a motor, it may be convenient to excite it in the first case with the full
working E.M.F. instead of with a fraction thereof. In this case I provide two
resistance coils R' and R2 one end of each of which is coupled to an end of the field
exciting coil S and to fixed insulated contacts w, v. The other ends of the resistance
coils are coupled to fixed insulated contacts d, e. The resistance of the coils R', R2 is
such that when coupled in series with the exciting coil S and the full working E.M.F:
is switched on, the current which flows through the exciting coil circuit will be that
which is required to produce normal excitation of the field magnet.
The four contacts d, w, v, e connected as described form part of a commutating
switch which also comprises four movable blades f, g, h, i, and a sliding rod L adapted
to actuate the said blades. The blade f is connected to the positive main or brush b,
the blade g to the brush B', the blade h to the brush B2, and blade i to the negative
main or brush 61. The rod L is so connected to the four blades that in one position
(that shown in full lines). blade fis connected to contact d, and blade i to contact e,
blades and g being then in the "off" positions. With the parts in these positions,
the field magnet will be excited by the full pressure, the current flowing through the
resistance coils R, R and exciting coil S as described. When the rod L is pushed
to bring the blades into the positions shown in dotted lines, blades i and f will be in
the "off" positions and the resistance coils R' R will be out of circuit, but before the
blades & break connexion, blades y and h will make connexion with contacts u and v
respectively and the excitation of the field magnet will be maintained by the current
Howing from brushes B', B. The last mentioned position of the blades is the normal
working position.
If the arrangement shown in Fig. 4 is required to work as a motor, a starting
switch T, connected in the ordinary way, may be used as shown.
When the arrangement is thus used as a motor and it is required to switch off, the

page_text: switch rod L is left in the working position (with the blades f, g, h, i in the positions
shown in dotted lines), and the starting switch T is turned into the "off" position.
The exciting coil S is left connected to the brushes B', B' and the excitation dies away
as the revolution of the armature ceases-thus harmful inductive effects are entirely
obviated.
The pole pieces of the field magnet in each arrangement may have deep grooves G
formed in them in positions corresponding with the position or positions of the
intermediate or additional brush or brushes in order to reduce or avoid sparking.
Usually however the employment of such grooves will be found unnecessary. The
additional brush B or brushes B', B2 may be smaller than the ordinary ones b¹ and
may advantageously be of carbon; they may be fixed to but insulated from the field
magnet, or be carried by a frame mounted on insulated supports independently of the
rocker or other movable support carrying the ordinary brushes.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare. that what I
claim is :-
1. A continuous current dynamo electric inachine. in which the armature winding
and a shunt winding are so arranged that when the machine is working the difference
of potential or electro motive force between the terminals of the shunt winding is less
than that between the terminals of the armature winding substantially as described.
2. The berein described method of making a dynamo electric machine self regulating
by connecting one end of a shunt winding on the field magnet to an additional brush
adapted to bear on the commutator of the machine at a point between the ordinary
brushes, and connecting the other end of the said winding either to one of the said
ordinary brushes or to another additional brush located between the ordinary brushes
the arrangement being such that the said shunt winding will be excited by an E.M.F.
that will increase or decrease, as may be desired, with increase of load.
3. Providing in connection with a dynamo-electric machine having a field magnet
shunt winding adapted to be connected up as referred to in Claim 1 and designed to
run as a motor, a starting switch so constructed and arranged that when moved
into one position will connect the said field magnet winding in series with the armature
winding so that the machine can be started as a series machine, and when moved into
another position will connect the field and armature windings in parallel with each
other so that the machine will then run as a shunt machine, substantially as described.
4. Dynamo-electric machines with shunt windings constructed arranged and
operating substantially as herein before described with reference respectively to and
shown in Fig. 2. in Fig. 3 and in Fig. 4 of the drawings annexed.
Dated this 2nd day of February 1097.
For the Applicant,
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.