An Improved Winding for Dynamos.
Year: 1899

page_text: Date of Application, 18th July, 1899
PROVISIONAL SPECIFICATION.
An Improved Winding for Dynamos.
I, MARK HENRY HURRELL, of 14, Haydon Park Road, Wimbledon,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
The object of this invention is to balance or neutralise the demagnetising and
cross-magnetising effect of the current in the armature coils, and to give, in
generators and motors, a fixed non-sparking position to the collecting brushes.
I obtain the object of this invention by, winding on part of the field magnetic
system a series of compensating coils of suitable magneto-motive force to balance
the distortion, in the poles, caused by the armature coils and current.
This invention relates more particularly to dynamos which have their poles
arranged alternately, that is, which have their adjacent poles of like name when
they are taken circumferentially about and on the same end of the armature;
the same compensating arrangements may be applied to dynamos of the more
usual types.
To assist in the sparkless collection of the current, it is desirable to curve the
leading and trailing ends of the pole pieces: a sine curve gives good results, the
maximum ordinate of the curve varying with the angular breadth of the armature
coils.
The output of dynamos, wound in this manner, being practically limited only
by their heating, I prefer to wind the field exciting coil directly on the armature
core to minimise its CR loss, and I shape oblique radial passages in the excess
of iron in this core so as to sweep the surfaces of the coils, as much as possible,
with a continuous flow of air.
The armature coils are wound on the periphery of the discs or in the slots in
the usual manner.
As is well known the magnetic flux in a generator is increased in the leading
horn and diminished in the trailing horn, or horns, in proportion to the flow of
the armature current, the converse occuring in a motor, this distortion, in the
poles, of the field magnetism requires a certain angle of lead in the brushes for
the collection of the current and this angle of lead causes a further injurious
effect of demagnetisation; to neutralise these effects I place between each adjacent
pair of polar horns, of like name, a compensating or balancing coil with a suit-
able magnetic core wound in such a manner as to form a pole of unlike name at
one horn and a consequent or pole of like name at the other horn.
The series current is passed through these coils which with sufficient turns
gives the requisite magneto-motive force. Each of these coils with its core and the
two adjacent oblique yokes form with the pole pieces a magnetic circuit, in which
is generated a flux in opposition and equal to the cross magnetic flux of the arma-
ture, the effect of compensation is more easily obtained when the pole pieces have
the well known form with a deep gap in the center.
The balance thus obtained allows the magnetic neutral line to coincide with

page_text: the geometric and the armature coils that lie on each side of the line, in the
polar gap, therefore balance and have no demagnetising effect on the pole pieces.
If the compensating coils are wound with a greater number of turns than the
number proportional to the armature turns a backward lead will be given to the
brush, in a generator, and the armature coils in the polar gap will therefore
increase the flux in the field system.
In reversing motors it is desirable to only balance the magnetic effect of the
armature current so that the brushes may remain fixed on the neutral line. When
reversing the motor the direction of the current in the compensating coils must
also be reversed.
These coils may be wound partly on the yokes.
I, MARK HENRY HURRELL, of 14, Haydon Park Road, Wimbledon,
in the County of Surrey, 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 an improved winding for dynamos its object being to
balance or neutralise the de-magnetising and cross-magnetising effects of the
current in the armature coils and to give in generators and motors a fixed non-
sparking position for the collecting brushes.
It is well-known that in a generator the magnetic flux is increased in the lead-
ing horn and diminished in the trailing horn of the pole pieces by an amount
which is proportional to the strength of the armature current, the converse
occurring in a motor. This distortion of the magnetism in the pole pieces neces-
sitates a certain angle of lead in the brushes if the current is to be sparklessly
collected and the angle of lead causes a further injurious de-magnetising effect.
According to this invention the distortion is balanced or neutralised by arranging
compensating coils so that they act between poles of like name. These coils
which are preferably provided with magnetic cores are energised by the main
current, and, owing to their position between similar poles, effect the compensa-
tion in a very efficient way, decreasing in a generator-the density of the mag-
netic lines in the leading horn and decreasing such density in the trailing horn.
and of course acting in the opposite way when the machine is used as a motor.
Compensating coils according to this invention are particularly applicable to
dynamos in which similar poles are adjacent to one another, as for instance in
machines having at one end of the armature an annular series of north poles and
at the other end a similar series of south poles.
The output of dynamos wound with compensating coils according to this inven
tion being practically limited only by their heating and not by heating and
sparking, the exciting coil for the field magnet may in some machines be wound
directly upon the armature core in order to minimise the CR loss and in this
construction oblique radial passages may be formed in the iron forming the
armature core so that a continuous flow of air may sweep the surfaces of the coil.
In order to assist in the sparkless collection of the current it is desirable to shape
the leading and trailing ends of the pole pieces, and it is found in practice that a
shape approximating to that of a sine curve gives good results.

page_text: In the accompanying drawings.
Figure 1 is a perspective view of one construction of field magnet provided with
compensating coils according to this invention,
Figure 2 is a longitudinal section showing diagrammatically a similar field
magnet in position relatively to its armature.
Figure 3 is a perspective view showing another construction of field magnet, and
Figure 4 is a sectional elevation showing a portion of another construction of
field magnet and its relative position with the armature.
Like letters indicate like parts throughout the drawings.
With reference first to Figure 1 the iron portion of the field magnet comprises
a ring A. from which pole pieces A1 and A2 project. All the pole pieces A' on
one side of the ring A are north poles while all the pole pieces A2 on the other
side of the ring are of opposite polarity. Each of the pole piece A is joined to its
neighbour by a connecting piece B of magnetic material around which is wound
a compensating coil C; similar connecting pieces and coils are placed between the
pole pieces A2 The connecting pieces B are attached to the poles by screws B¹.
The exciting coils for the field magnet may be wound as is usual in magnets of
this type, within the annular space A³ between the sets of pole pieces A1 and A2,
or as indicated diagrammatically in Figure 2, these coils may be wound as at D
upon a spider E mounted upon a shaft and carrying the armature discs G.
In the construction illustrated in Figure 2 oblique ventilating passages
E are
formed in the spider E so that a current of air sweeps over the field magnet coil
as the armature rotates.
Supposing the armature to be in place in the field magnets illustrated in
Figure and to be rotated in the direction of the arrow a in that figure the
machine being used as a dynamo, the armature re-actions would, if the compen-
sating coils were not present, cause an increase in the density of the magnetic
lines at the leading side of the pole pieces A A² and a diminution of the density
at the other or trailing side. The compensating coils C are energised by the
armature current and are arranged so as to strengthen the magnetism in the
trailing side of the pole pieces and weaken that in the other side, thus counter-
balancing the distortion caused by the armature re-actions.
In Figure 3 the poles A¹ and A2 are joined by oblique yokes A upon which
the exciting coils A are wound, and the poles A¹ and A2 are so proportioned that
each set covers a peripheral annulus, the breadth of which is approximately equal
to half the length of the armature.
The connecting pieces B with their compensating coils C are arranged across
the gaps formed by the oblique yokes A between the poles.
In a machine having a field magnet of the form shown in Figure 3, the arma-
ture of course rotates within the ring formed by the pole pieces and their yokes:
the position of the end of the armature is indicated by a chain line as at G¹ in
Figure 3. The same general construction however may be employed in an in-
verted form the poles being formed on the outside of a ring outside which the
armature revolves. This construction is found to be suitable for use as a motor
for driving self-propelled vehicles, and its application to that purpose is shown
diagrammatically in Figure 4, in which one of the poles A¹ is seen in section.
The field magnet ring is carried upon a spider one arm of which is shown at H,
the spider being secured to a fixed axle F¹. The armature, which comprises a
number of stamped rings G, is carried upon two discs or casings G2 which are
capable of revolving round the fixed spindle F¹ and are connected by flanges G
so as to be readily detachable. The armature winding, which is indicated at G+,
is joined by connections J to a commutator J. The revolving casing G2 carrying
the armature may conveniently form part of the road wheel of the vehicle. Com-
pensating coils may be fixed between adjacent pole pieces in this construction of
field magnet in a way substantially similar to that illustrated in Figure 3.
If the compensating coils are wound with a greater number of turns than
those required to balance the armature re-actions a backward lead will be given

page_text: to the brushes in a generator and the armature coils in the polar gap will increase
the magnetic flux in the field magnet system.
In compensating coils for motors which are reversed it is of course desirable
to make the number of turns upon the coils such that they merely balance the
armature re-actions so that the line of commutation may remain unchanged in
whichever direction the motor runs. It is of course necessary to reverse the direc-
tion of the current in the compensating coils when the direction of rotation of
the motor is changed.
Although compensating coils according to this invention are more particularly
adapted for use in field magnets such as that illustrated in which all the poles
acting on one end of the armature are of like polarity, yet such coils may be
arranged to operate between poles of like name in other types of machines.
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. In a dynamo electric machine a compensating coil operating between poles
of like name substantially as described.
2. In a dynamo electric machine the combination with adjacent pole pieces of
similar polarity of a compensating coil wound upon a magnetic core connecting
the pole pieces.
3. In a dynamo electric machine compensating coils arranged and operating
substantially as described or illustrated in Figure 1 or Figure 3 of the accom-
panying drawings.
0
PatCAT THIS Jin da
01 May 1900.
MARK HENRY HURRELL.
Boult, Wade & Kilburn,
Agents for the Applicant.