Improvements in Dynamo Electric Generators and Motors.
Year: 1895

page_text: Date of Application, 14th Oct., 1895
Complete Specification Left, 23rd June, 1896-Accepted, 12th Sept., 1896
PROVISIONAL SPECIFICATION.
Improvements in Dynamo Electric Generators and Motors.
I, REGINALD Wood, of No. 57 Gower Street, in the County of London,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to the construction of the field magnets, commutator and
brushes of a dynamo electric machine in such a manner as to avoid sparking at the
brushes, which should be fixed in the same position for all loads.
The reaction of the armature current on the magnetic field. whereby the
magnetic flux through the armature induced by a definite magnet excitation is
altered, I counteract by any of the known methods, as by series coils on the field
magnets, definite lead of brushes, or other arrangement of coils carrying currents
from the armature, or other currents, as well as by suitably disposing the iron of
the magnets.
Leaving the above out of consideration, the magnetic flux through the armature
must be increased in a generator and decreased in a motor, to allow for the fall of
pressure due to the resistance of the armature, and this added or subtracted flux
must always be proportional to the current passing through the armature.
The electromotive force required to raise to and maintain at its proper value a
current in an armature coil as it leaves either brush is also practically proportional
to the armature current. I therefore make use of the whole or part of the
electromotive force, induced by the whole or part of this flux added or subtracted
at either brush, in order to raise the current to its proper value in the right
direction in a coil as it leaves either brush.
In the neighbourhood of the neutral or symmetrical line, in a dynamo machine
of the ordinary construction, no lines of magnetic induction pass between the inside
and the outside of the armature, and the armature conductors about that position
are not cutting lines of induction, and are not therefore the seat of electromotive
force. I therefore make the added or subtracted flux pass there by means of an
auxiliary pole piece so that these armature conductors in that position are
cutting lines of induction, and form the seat of an electromotive force of definite
amount per foot length and always proportional to the armature current.
The auxiliary pole piece in the neighbourhood of the neutral line may be
connected by an iron bar among others with the centre of the yoke of the main
magnets, or with the centre of an iron bar connecting, and forming a inagnetic
shunt to the two main pole pieces, or with the auxiliary pole piece diametrically
opposite, or with an adjacent auxiliary pole piece, in which latter case there is a
complete auxiliary horseshoe in the neighbourhood of each end of the symmetrical
line.
In the case in which there is one auxiliary pole piece about each end of the
symmetrical line, joined by an iron bar, the whole of the flux added or subtracted
is operative at each brush; in the other cases mentioned only one half is operative
at ench brush.
The winding on the iron bar connected to the auxiliary pole piece is such that
when there is no load no lines of magnetic induction pass between the auxiliary
pole piece and the arn.ature. Sometimes no winding is required for this purpose;
sometimes a shunt or separate coil would suffice. The configuration of the
machine will usually enable this winding to be settled, and experiment would settle

page_text: it in any case. But the winding on the iron bar must also be such that at any
load the lines of magnetic induction passing between the auxiliary pole piece and
the armature pass in the requisite direction and are in number substantially
proportional to the armature current. This winding again can be determined by
the configuration or by experiment. Series coils may be required, or the current
in the armature conductors may suffice.
In order to prevent sparking, as any segment of the commutator is leaving a
brush, provide for each brush a subsidiary brush, connected to it and so adjusted
that, just when the separation of the segment from the main brush is taking pince,
the subsidiary brush is momentarily in contact with a segment which has already
passed the brush, the segment which is leaving the brush being thus for the
moment rendered neutral so that no spark takes place at the separation. When
the separation of the segment from the subsidiary brush takes place, no spark
occurs, because during the interval of contact, the coil passing the main brush, is
circuited with the other coil or coils between the main and subsidiary brushes.
which coil or coils are then cutting the whole or part of the added or subtracted
flux passing between the subsidiary pole piece and the armature, and forming
therefore the sent of an electromotive force, having built up in it the requisite
current, so that the current passing between the segment and the subsidiary brush
gradually ceases, and it is about the instant when it has ceased that the separation
takes place.
It may obviously be arranged that the coils included momentarily between
the main and subsidiary brushes are cutting that proportion of the added or
subtracted flux which will generate an electromotive force only capable of
maintaining about the half armature current round the coils between and connection
between the main and subsidiary brushes.
For operating in this manner it is preferable to make the contact surface of the
main brush a little narrower than the width of insulator between two adjacent
segments, and, this being so, it is of advantage to construct and mount the brush
in such a manner that its contact surface remains constant in width notwithstanding
wear. I mount each brush ou an arm pivotted on a lever which can turn round
the common axis of the armature and commutator, the brush being pressed
against the commutator by a spring.
The brush itself consists of a number of metal strips fixed obliquely side by side
in a holder, each strip being roughly a segment of a circular annulus, having a
radius about equal to the length of the pivotted arm; thus as the brush wears, the
arm turns on its pivot, and the brush, having its sides concentric with the pivot
has always the same width of surface bearing on the commutator. The subsidiary
brush is made in a similar manner.
In order that the time and duration of contact between the segment and the
subsidiary brush may be determined, it is advisable that the segments should for
this purpose be provided with extensions narrower than the segments, and, in order
that, with change of direction of rotation, the same subsidiary brush may be used,
by rotating it round the main brush, these extensions should be symmetrical.
It will be noticed that the added or subtracted flux passes through the conductors
of the coils circuited between the main and subsidiary brushes. Thus it is evident
that the auxiliary pole piece is forward from the main brush and the subsidiary
brush is forward from or usually under the auxiliary pole piece, and of course
forward from the main brush. When there are two auxiliary pole pieces at each
brush the complementary one is behind the main brush.
The direction of the lines of magnetic induction between the armature and the
auxiliary pole piece is, in a generator, the same direction as that of the lines
between the armature and the main pole piece in advance of the brush, and, on the
contrary, in a motor in the opposite direction.
Both in a generator and motor the electromagnetic energy of the coils circnited
by the main and subsidiniy brushes with the coil leaving the main brush would, at
the making of the circuit, tend to dissipate and assist the raising of the current in

page_text: the latter coil; the energy so dissipated would have to be again stored before the
segment left the subsidiary brush. The time occupied in dissipation might be
different from the time required for restoration. Also as the current carried by
the coil increases, the inductance, being the increase in the number of lines of
magnetic induction enclosed by the coil, owing to an increase of one unit of current
in the coil, decreases, because the permeability of the iron decreases in a generator
and the reverse in a motor.
Hence any tendency to sparking that there might be if it were attempted to
determine the current in the coil by the duration of contact between the segment
and the subsidiary brush is eliminated by determining the current by the electro-
motive force in the local circuit. It is obvious that, if the speed of the machine
is liable to considerable variation, it might be necessary to effect a compromise.
Dated this 14th day of October 1895.
ABEL & IMRAY,
Agents for the Applicant.
Improvements in Dynamo Electric Generators and Motors.
I, REGINALD WOOD, of No. 57 Gower Street, in the County of London,
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 :-
My invention relates to the construction of the field magnets, commutator and
brushes of a dynamo electric machine in such a manner as to avoid sparking at the
brushes, which should be fixed in the same position for all loads.
The reaction of the armature current on the magnetic field, whereby the magnetic
flux through the armature induced by a definite magnet excitation is altered, I
counteract wholly or partially by any of the known methods, as by series coils on
the field magnets, definite lead of brushes, or other arrangement of coils carrying
currents from the armature, or other currents, as well as by suitably disposing the
iron of the magnets.
Leaving the above out of consideration, the magnetic flux through the armature
must be increased in a generator and decreased in a motor, to allow for the fall of
pressure due to the resistance of the armature, and this added or subtracted
Hux must always be proportional to the current passing through the armature.
The electromotive force required to raise to, and maintain ot, its proper value
a current in an armature coil as it leaves either brush is also practically proportional
to the armature current.
I therefore make use of the whole or part of the electromotive force, induced by
the whole or part of this flux added or subtracted at either brush, in order to
raise the current to its proper value in the right direction in a coil as it leaves
either brush.
In the neighbourhood of the neutral or symmetrical line, in a dyname machine
of the ordinary construction, no lines of magnetic induction pass between the inside
and the outside of the armature, and the armature conductors about that position
are not cutting lines of induction, and are not therefore the seat of electromotive
force. I therefore make the added or subtracted Hux pass there by means of an
auxiliary pole piece so that these armature conductors in that position are cutting
lines of induction, and form the seat of an electromotive force of definite amount
per foot length and always proportional to the armature current.
The auxiliary pole piece in the neighbourhood of the neutral line may be
connected by an iron bar among others with the centre of the yoke of the main
magnets, or with the centre of an iron bar connecting, and forming a magnetio

page_text: Ehunt to the two main pole pieces, or with the auxiliary pole piece diametrically
opposite or with an adjacent complementary auxiliary pole piece, in which latter
case there is a complete auxiliary horseshoe in the neighbourhood of each end of
the symmetrical line.
In the case in which there is one auxiliary pole piece about each end of the
symmetrical line, joined by an iron bar, the whole of the flux added or subtracted
is operative at each brush, in the other cases mentioned only one half is operative
at each brush.
The winding on the iron bar connected to the auxiliary pole piece is such that
when there is no load no lines of magnetic induction pass between the auxiliary
polo piece and the armature.
Sometimes no winding is required for this purpose; sometimes a shunt or separate
coil would suffice. The configuration of the machine will usually enable this
winding to be settled, and experiment would settle it in any case. But the winding
on the iron bar must also be such that at any load the lines of magnetic induction
passing between the auxiliary pole piece and the armature pass in the requisite
direction and are in number substantially proportional to the armature current.
This winding again can be determined by the configuration or by experiment.
Series coils may be required, or the current in the armature conductors may suffice.
In order to prevent sparking, as any segment of the commutator is leaving a brush,
I provide for each brush a subsidiary brash connected to it and so adjusted that,
just when the separation of the segment from the main brush is taking place, the
subsidiary brush is momentarily in contact with a segment which has already passed
the brush, the segment which is leaving the brush boing thus for the moment
rendered neutral so that no spark takes place at the separation. When the
separation of the segment from the subsidiary brush takes place, no spark occurs,
because during the interval of contact, the coil passing the main brush, is circuited
with the other coil or coils between the main and subsidiary brushes, which cuil or
coils are then cutting the whole or part of the added or subtracted flux passing
between the auxiliary pole piece and the armature, being therefore the seat of an
electromotive force, having built up in it the requisite current, so that the current
passing between the segment and the subsidiary brush gradually renses, and it is
about the instant when it has ceased that the separation takes place.
It may obviously be arranged that the coils included momentarily between the
main and subsidiary brushes are cutting that proportion of the added or subtracted
Hux which will generate an electromotive force only capable of maintaining about
the half armature current round the coils between and connection between the
main and subsidiary brushes.
For operating in this manner it is preferable to make the contact surface of the
main brush a little marrower than the width of insulator between two adjacent
segments, and, this being so, it is of advantage to construct and mount the brush
in such a manner that its contact surface remains constant in with notwithstanding
wear. I mount each brush on an arm pivotted on a lever which can turn round
the common axis of the armature and commutator, the brush being pressed
against the commutator by a spring. The brush itself consists of a number of
metal strips fixed obliquely side by side in a holder, each strip being roughly a
segment of a circular annulus, having a radins about equal to the length of the
pivotted arm; thus as the brush wears, the arm turns on its pivot, and the brush,
having its sides concentric with the pivot has always the same width of surface
bearing on the commutator.
The subsidiary brush is made in a similar manner.
In order that the time and duration of contact between the segment and the
subsidiary brush may be determined, it is advisable that the segments should for
this purpose be provided with extensions narrower than the segments, and, in order
that, with change of direction of rotation, the same subsidiary brush may be used,
by rotating it round the main brush, these extensions should be syin netrical.
It will be noticed that the added or subtracted flux passes through the conductors

page_text: of the coils circuited between the main and subsidiary brushes. Thus it is evident
that the auxiliary pole piece is forward from the main brush and the subsidiary
brush is forward from or usually under the auxiliary pole piece, and of course
forward from the main brush. When there are two auxiliary pole pieces at each
brush the complementary one is behind the main brush.
The direction of the lines of magnetic induction between the armature and the
auxiliary pole piece is, in a generator, the saine direction as that of the lines
between the armature and the main pole piece in advance of the brush, and, on the
contrary, in a motor in the opposite direction.
Both in a generator and motor the electromagnetic energy of the current in the
coils circuited by the main and subsidiary brushes with the coil leaving the main
brush would, at the making of the circuit, tend to dissipate and assist the raising
of the current in the latter coil; the energy so dissipated would have to be again
stored before the segment left the subsidiary brush. The time occupied in dissipa-
tion might be different from the time required for restoration.
Also as the current
carried by the coil increases, the inductance, being the increase in the number of
lines of magnetic induction enclosed by the coil, owing to an increase of one unit
of current in the coil, decreases, because the permeability of the iron decreases in
a generator and the reverse in a motor. Hence any tendency to sparking that
there might be if it were attempted to determine the current in the coil by the
duration of contact between the segment and the subsidiary brush is eliminated by
It is
determining the current by the electromotive force in the local circuit.
obvious that, if the speed of the machine is liable to considerable variation, it
might be necessary to effect a compromise.
If as the segment leaves the main brush the segment which touches the subsidiary
brush is the one which has just left the main brush the construction is much
simplified.
The accompanying drawing illustrates diagrammatically the application of the
invention to a bi-polar generator. N is the north and S is the south pole of the
main magnets which are excited respectively by the coils H G one of which may
be omitted. A is the armature core, revolving about the centre Q in the ilux
passing from N to S and wound with a coil which may be of the gramme
arrangement as shewn.
The metal segments of the commutator are numbered to 16 arranged in a circle
round with insulation M between them. E indicates the extensions of the
segments by which the segments are connected to the armature coils C. The
neutral or symmetrical line is the line through about perpendicular to N S.
P indicates the positive and B is the negative main brush, and bare the corre-
sponding subsidiary brushes. n is the auxiliary pole piece for the brushes Pp,
connected by the iron bar R to the complementary pole pieces. For the brushes Bb.
is the auxiliary pole piece connected by the iron bar U to the complementary
pole piece n'.
P.
+T is the positive terminal of the machine, and one circuit is from + T through
the coil J exciting R by Por p through both halves of C to B or band so through
the coil K exciting U to T the negative terminal. There is also a circuit from
-
+T through the shunt coils G H to
-
T.
Pp BRU are suitably insulated and fixed to the fraine of the machine.
The brushes P B instead of being narrower than the segments Minay be adjusted
so as just to bridge over them.
For the purpose of explaining the operation it is sufficient to confine attention.
to one brush say B, the action of the other brush P being similar.
it
When the armature is in the position shewn, B has been passing current by 2
to both halves of the armature coil and the coil between 1 and 2 has had in
current in the same direction as the current in the coils on the right hand.
As meet Bif B bridges it, B short circuits the coil between 1 and 2 and its
current dies away. As 2 leaves B, 1 meets B and 3 meets b, so that current still
passes from
T through K by Bb to both sides of the armature coils C, but in
-

page_text: addition there is a circuit from b by its connection to B and by 1 through the coils
between 1 and 3 and 3 to b again. The coil between 1 and 2 has had in it a current
in the same direction as the current in the coils C to the right hand.
If B has bridged M this current has died away. If so or if not a current in the
coil between 1 and 2 is necessarily built up in the same direction as in the coil C
on the left hand in the following way:
The coil between 2 and 3 is cutting lines of induction passing from a through the
ring A to s, and these lines pass in the same direction through the coil between 2
and 3 as the lines from N through A to S pass through the coils on the left hand.
Therefore there is an electromotive force induced in the coil between 2 and 3 in the
same direction as the electromotive force in the armature coils C on the left hand,
and hence the electromotive force in the coil between 2 and 3 builds up in the
coil between 1 and 2 round Bba current in the same direction as the current in
the coils on the left hand.
When 3 leaves the current in the coils between 1 and 3 magnetises U in the
same direction as the current in K.
Similarly the coil between 9 and 10 has a current built up in it in the same
direction as the current in the coils on the right hand. The action is repeated for
ench coil as it passes either brush.
•
In what precedes I have described my invention as applied to bi-polar machines,
but it is to be understood that like arrangements can be made in multipolar
machines.
Having now particularly described and nscertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what
I claim is :-
In a dynamo electric generator or motor, in combination with a subsidiary
magnetic field arranged to act on those parts of the armature which are near the
neutral line, a pair of brushes each having a subsidiary brush extending on to a
segment of the commutator which has already passed the main brush, substantially
as and for the purposes set forth.
Dated this 23rd day of June 1896.
ABEL & IMKAT,
Agents for the Applicant.