Year: 1888

page_text: Date of Application, 8th Feb., 1888
Complete Specification Left, 31st Oct., 1888
Complete Specification Accepted, 7th Dec., 1888
We GEORGE HOOKHAм of Nos. 7 & 8 New Bartholomew Street, Birmingham in
the County of Warwick, Manufacturer, and ROBERT HOLDEN HOUSMAN of Perry
Hall Bromsgrove in the County of Worcester, Electrical Engineer do hereby
declare the nature of this invention to be as follows:-
Our improvements consist in the first place in the introduction of an intermediate
or subsidiary magnet between the poles of the field-magnets of a dynamo-electric
machine, so placed with its pole close to and facing the armature as to affect that part
of the field in which commutation takes place. It is well known that if commutation
takes place in a field of just such intensity as is sufficient to reverse the current and
no more the reversal is unaccompanied by sparking; but it is also true that if the
intensity of the field at this point is increased in proportion as the armature current
is increased, both the best position of the brushes as regards sparking and the electro-
motive force of the machine remain constant. In order to effect this we wind
the subsidiary magnet with a certain number of turns of the main conductor
carrying the current from the armature to the external circuit. For final adjustment
we either regulate the amount of current circulating in the coils by a shunt, or by
short-circuiting a part of the coils till the best result as regards sparking is obtained;
or we make the magnet adjustable as regards its distance from the arinature and so
obtain a like result. This should be done while the armature is giving its maximum
current, and the adjustment can usually be made once for all, and the brush-holders
permanently fixed; as their best position will then be the same for all currents.
Also if the pole of the intermediate magnet (or, more correctly, its field where cut by
the armature conductor) subtends the same angle at the axis of the armature as is
subtended by a section of the commutator, the electro-motive force will also remain
constant. By increasing this angle the electro-motive force may be caused to rise
with an increase in the armature current practically to any desired degree. This
plan is better than increasing the magnetizing force on the intermediate magnet as
thus the proper strength of field for reversal is not interfered with. We have applied
our device to a dynamo, and have obtained this result in practice.

page_text: The arrangements described are specially applicable to an armature with an
unbroken surface of iron such as that described and claimed in the complete
Specification of Letters Patent granted to one of us, viz. to George Hookham, and
numbered 3212/85 partly because this form allows of the nearest possible approach of
the intermediate magnet to the iron of the armature partly because both in this form
and in the form described and claimed in Letters Patent similarly granted, and
numbered 7533/84, the different layers of the armature conductor are more equally
affected by the subsidiary field. And in order more perfectly to attain this end as
well as to narrow the slots or tunnels in the armature, we may instead of winding two
turns at least of the conductor in each slot as has been the practice hitherto, provide
double the number of slots and place one turn only in each slot.
The intermediate magnet may be entirely separate from the field-magnets or it may
branch from them. In the latter case we prefer to join it to their neutral line; but
we may, especially if the field-magnets are compound-wound, so connect it with a
pole of the field-magnets or with a point intermediate between a pole and a neutral
fine either directly or by means of an adjustable air-space of low magnetic resistance
as to obtain the same or nearly the same effect as that described above without
applying magnetizing coils to the intermediate magnet itself. The movements of a
plain bar of iron placed in the position of the intermediate magnet may be made to
modify sparking and take the place of the movements of the brushes and whether the
condition of least sparking be obtained by the movements of the brushes in the
presence of such bar, or by the movements of the bar, a less delicate adjustment is
required.
The control we obtain over the field of commutation by means of the devices
described enables us not merely to avoid the necessity of moving the brushes, but we
can diminish sparking by producing the right intensity of field at this point. We
may further either in addition to or separately from the arrangements hereinbefore
described connect each section of the commutator with each of the two sections
adjacent to it by wires or other conductors of high resistance and thus absorb the
energy which would otherwise be expended in sparking.
23
We have so far described a single magnet, and in some cases as with armatures of
the drum or Siemens type a single magnet on one side of the armature will be
effective. But in some other cases, as for instance with a Gramme ring, we make use
of two such magnets placed opposite each other in a two-pole dynamo, four in a
four-pole dynamo and so on in a manner that will be readily understood.
The intermediate magnet has the same sign as the magnet-pole which the coil
undergoing reversal is approaching or an opposite sign according as the machine is
being used as a generator or as a motor.
We may substitute for a magnet having an iron core a coil of wire carrying a
similar current but without an iron core placed in the same position. Or we may
dispense with a separate magnet altogether, and instead bring the ordinary magnet-
poles as near together as possible, cut a groove in each near the edge and wind a coil
of wire carrying current from the armature round the two grooves.
Dated this 7th day of February 1888

page_text: COMPLETE SPECIFICATION.
Improvements in Dynamo-electric Machines and in Electro-motors.
We GEORGE HOOKHAм of Nos. 7 and 8 New Bartholomew Street Birmingham in
the County of Warwick Manufacturer and ROBERT HOLDEN HOUSMAN of Perry Hall
Bromsgrove in the County of Worcester Electrical Engineer do hereby declare the
nature of our invention and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:-
Our improvements consist in the first place in the introduction of an intermediate
or subsidiary magnet between the poles of the field magnets of a dynamo electric
machine so placed with one of its poles close to and facing the armature and parallel
to its axis along the whole or greater part of the length of the armature as to affect
that part of the field in which commutation takes place. It is well known that if
commutation takes place in a field of just such intensity as is sufficient to reverse the
current and no more the reversal is unaccompanied by sparking but it is also true that
if the intensity of the field at this point is increased in proportion as the armature
current is increased both the best position of the brushes as regards sparking and the
electro motive force of the machine will remain constant. In order to effect this we
wind the subsidiary magnet with a certain number of turns of the main conductor
carrying the current from the armature to the external circuit.
For final adjustment we either regulate the amount of current circulating in the
coils by a shunt or by short circuiting a part of the coils till the best result as regards
sparking is obtained or we make the magnet adjustable as regards its distance from
the arniature and so obtain a like result. This should be done while the armature is
giving its maximum current and the adjustment can usually be made once for all and
the brush holder permanently fixed as their best position will then be the same for all
currents. Also if the pole of the intermediate magnet (or more correctly its field
were cut by the armature conductor) subtends the same angle at the axis of the
armature as is subtende by a section of the commutator the electro motive force will
also remain constant by increasing this angle the electro-motive force may be caused
to rise with an increase in the armature current practically to any desired degree.
This plan is better than increasing the magnetising force on the intermediate magnet
as thus the proper strength of field for reversal is not interfered with. We have
applied our device to a dynamo and have obtained this result in practice.
The intermediate magnet may be entirely separate from the field magnets or it may
branch from them. In the latter case we prefer to join it to their neutral line. But
we may especially if the field magnets are compound wound connect it with a point
intermediate between a pole and a neutral line.
The control we obtain over the field of commutation by means of the devices
described enables us not merely to avoid the necessity of moving the brushes but we
can diminish sparking by producing the right intensity of field at this point without
forward lead.

page_text: We have so far described a single magnet and in some cases as with armatures of
the drum or Siemens type a single magnet on one side of the armature will be
effective but in some other cases as for instance with a gramme ring we make
use of two such magnets placed opposite each other in a two pole dynamo four
in a four pole dynamo and so on in a manner that will be readily understood by
electricians.
The intermediate magnet has the same sign as the magnet pole which the coil
undergoing reversal is approaching when the machine is used as a dynamo or an
opposite sign when the machine is being used as a motor.
The section of the subsidiary magnets must be such that the intensity in them does
not exceed 10000 lines per squaro centimeter with the maximum current.
We will now proceed to describe with reference to the accompanying Drawings the
manner in which our invention is to be performed.
Figure 1 represents in vertical section partly in elevation the essential parts of a
dynamo-electric machine constructed according to our invention and Figure 2
represents in elevation the electro magnet and subsidiary magnet and diagram of the
armature all unwound.
A is the armature of the dynamo-electric machine B B are the main magnets and
C is the yoke of the magnets. D D is the shunt winding of the main magnets. E is
the subsidiary magnet bolted or otherwise fixed to the yoke C. FF is the series
winding of the subsidiary magnet. When the main polo pieces and the subsidiary
pole are at about the same distance from the iron of the armature as is practically the
case then the best results are obtained both as regards constancy of lead and constancy
of electro-motive force by making the ampère-turns on the subsidiary magnet about
double the ampère-turns on the armature. In this case the change of induction in
the coils undergoing commutation due to cutting the subsidiary field will be equal to
the change of induction due to the reversal of current in them.
When the subsidiary pole pieces subtends a greater angle than is subtended by one
section of the commutator then when the above condition is observed the electro
motive force of the machine may be made to rise with an increase of current or to
remain constant or to fall according to the position of the brushes. If a negative lead
is given to the brushes with reference to the point of constant electro-motive force
then the electro-motive force will rise with an increased current on the contrary if the
lead is positive the electro motive force will fall.
The relative signs of the main and subsidiary pole pieces when the machine is used
as a dynamo are represented in Figure 2 the arrow indicating the direction of the
rotation of the armature. In Figure 3 the relative signs of the main and subsidiary
pole pieces when the machine is used as a motor are represented. The change of
polarity is produced by the change in the direction of the current when the dynamo
is used as a motor.
Figure represents in vertical section partly in elevation an arrangement in which
the subsidiary magnet does not branch from the neutral line as in the machine
represented in Figures 1, 2 and 3 the neutral line having shifted by the current in
the series coils. It will be understood from an inspection of the Drawing that by
this modification the electro motive force may be made to rise through a greater
range for the same current than in the arrangement Figures 1, 2 and 3 but as
will also be seen from an inspection of the Drawing this modification involves the
compound winding of the main magnets and about twice the expenditure of
magnetising force in the series coils. When in either the dynamo or motor a
Gramme ring or disc armature is employed a second subsidiary magnet is fixed
diametrically opposite the one represented.
Having now particularly described and ascertained the nature of our inven-
tion and the manner in which the same is to be performed we declare that we claim
as our invention of "Improvements in dynamo-electric machines and in electro
motors
T
"

page_text: wound with coils carrying the main current or of a subsidiary magnet or subsidiary
magnets in conjunction with compound winding on one side limb of the main magnet
the strength of the said subsidiary magnet or subsidiary magnets being so proportional
and adjusted to that of the principal magnet as to keep the lead of the brushes
constant and thereby to regulate the electro motive force of the machine with
varying currents substantially as herein before described and illustrated in the
accompanying Drawings.
L 011
1
3000
W. T. WHITEMAN,
Agent for the Applicants.