Improvements in and Apparatus for Converting Electric Currents.
Year: 1894

page_text: Date of Application, 31st Mar., 1894-Accepted, 19th May, 1894
COMPLETE SPECIFICATION.
Improvements in and Apparatus for Converting Electric Currents.
I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, (a communi-
cation to me from abroad by André Blondel, and Sautter, Harlé et Cie., of
Avenue Suffren, Paris, in the Republic of France,) 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 :-
Two distinct processes are at present used for converting polyphase alternating
currents into continuous currents.
1. That of motor transformers used in existing distributions.
2. That of transformers with stationary magnetic field and variable secondary
ampère windings, a process superior to the preceding but complicated.
The apparatus forming the object of this invention have for their object to replace
the first process of converting without having recourse to the arrangements of the
second and in a certain measure to improve this latter.
The principle of the motor transformer consists as is known, in arranging two
windings upon one moveable armature.
An ordinary polyphase winding called the primary producing a turning magnetic
field in the armature ring.
An ordinary continuous current dynamo winding, called secondary, formed of
bobbins ending in a Gramme collector fixed to the axle and upon which rub two
fixed brushes.
The armature placed between the fixed inductor poles which are fed by a
coutinuous current, coming from an outside source or from the Gramme collector
itself, rotates by the action of its primary field, synchronously with the alternating
currents which feed it.
The turning primary field thus becomes fixed in space and forms with the
stationary inductor field one resulting stationary field. The secondary winding
rotating in this fixed field acts identically as in a continuous current dynamo aud
thus delivers a continuous current to the brushes.
The power furnished by the primary goes almost entirely to the terminals of the
secondary circuit less a small portion employed to rotate the armature.
The work done in the inductor circuit, serves almost entirely to give rotation to
the armature upon its bearings. Almost the whole of the power consumed by the
inductors, which represents a fairly considerable exciting current, is thus for the
most part lost.
Another grave inconvenience of this way of changing currents is that the brushes
require attention as is the case in ordinary continuous current dynamos.
To replace this system by another not having the same defects, it must be
remembered that the inductor has the two following functions to perform :
To rotate the armature.
To offer to the lines of force produced by the armature a path of less resistance
than the air alone.
These two results may be obtained with a minimum expenditure of energy, the
first by keeping the armature fixed and only rotating the brushes by a small
synchronous motor, the second by replacing the inductor poles by one or two
concentric rings surrounding the whole armature.

page_text: This solution has not been successful in practice for the following reasons:
1. It was necessary to have a considerable gap between the iron parts corresponding
to the thickness of two windings of the ring. The result was an excessive
expenditure of magnetising current.
To obviate this difficulty it has been more recently proposed in order to do away
with the air gaps to form side by side in one structure two Gramine rings each
having its own windings.
By this method the magnetic circuit is apparently well closed for each bobbin
considered separately but if the whole assemblage of the two rings be considered
the magneto motive forces being opposed, the lines of force of the primary are
repelled by those of the secondary: and in a great measure close themselves
through the air either outside the two rings or through the small windows between
them and thus cause considerable magnetic leakage which produces in this kind of
apparatus the same inconveniences as in ordinary transformers.
On the contrary, the magnetic circuit in this apparatus is formed in such a
manner as to do away with the gaps between the iron parts without introducing
any magnetic leakage and this is one of the most important points of our invention.
2. The use of brushes rotating concentrically around a cylindrical collector
cannot be adopted in practice. Centrifugal force prevents proper pressure of the
brushes being maintained it is also impossible to regulate them whilst in motion
and the conditions of this regulation are constantly varying. Thus the several
inventors who are occupied with this question have given up the use of this arrange-
ment to go back to that of a rotating collector taking the partial currents through
a considerable number of rings and rubbing contacts.
3. The adjustment of the brushes not being regulated according to the change in
intensity of the secondary current, there are numerous sparks and the machine is
lighted up just like a continuous current dynamo when the brushes are left to
themselves.
This inconvenience cannot be remedied without constant watching; this system
of conversion is thus not automatic.
The apparatus forming the subject of this invention overcomes these the practical
differences and is a very simple and complete solution of the problem.
This apparatus is characterised by the combination of a revolving closed magnetic
circuit free from leakage, with a special arrangement of rotating brushes and means
for withdrawing and automatically adjusting these brushes.
The invention is shewn in the drawings annexed in which: Figures 1, 2, 3, 4, 5,
6, 7 and 8 show different forms of closed magnetic circuit with rotating field
carrying the primary and secondary windings. The sections Figures 2, 4, 6 and 7
are taken on the lines 1, 1, 2, 2, 3, 3, and 4, 4.
These figures are shown only as examples of many combinations having the same
properties.
A is a magnetic core having teeth on its inner and outer circumference and
formed of a series of insulated sheet iron discs.
A and A3 are two smooth magnetic cores concentric to the former with which
they are rigidly united to form the magnetic circuit; they are formed of insulated
plates.
aaa are the outer teeth of the core A.
a a a² are the inner teeth of the corc A.
a a a³ show the path of the lines of force in the magnetic circuit.
A³ are a series of primary bobbins wound as rings upon the core A and fed
by polyphase currents.
A are a series of secondary bobbins wound upon the same core and the same
teeth as A³ in such a manner as to be traversed without loss by the same field.
A are the conductors feeding the primary bobbins which may be connected in
star, polygon, or mixed and connected in series or in parallel according to the nature
of the source of the polyphase current.
A are the outgoing conductors of the current of the secondary bobbins leading

page_text: to the collector and which may be connected up according to any of the methous
used in continuous current dynamos.
B is a magnetic core toothed on the exterior and formed of superposed plates.
B' is a magnetic ring of smooth plates rigidly adjusted concentric to the former
and in one piece with it and closing completely the magnetic circuit.
b' are the teeth of the core B.
B² are a series of primary bobbins wound according to one or other of the
combinations of the polygonal method upon the core B.
B³ are a series of secondary bobbins polygonally wound upon the core B, upon
the same teeth.
B' are the feed conductors of the primary bobbins connected according to any one
of the methods employed for polyphase currents.
B' are the outgoing conductors of the secondary bobbins leading to the collector
and connected according to any one of the methods of ordinary dynamos.
62 show the path of the lines of force in the magnetic core B.
C is a magnetic core with two sets of radial teeth and formed of a plate wound
on itself.
C¹ and C³ are two smooth magnetic cores similarly formed of wound plates placed
one on each side of the former to make one piece with it.
cc² are the teeth of the core C.
C³ are a series of primary bobbins wound according to any one of the combinations
of the annular method upon the core C.
C* are a series of secondary bobbins wound in a ring upon the core C and between
the same teeth.
C' are the feed conductors of the primary bobbins connected up for polyphase
currents.
Ce are the outgoing conductors of the current of the secondary bobbins connected
up for continuous currents.
C7 C are two series of primary and secondary bobbins wound according to a novel
method which we call oblico-radial.
Figures 9 and 10 are sections on the lines V V, and VI VI respectively-these
sections shew the transformer arranged with a vertical axis.
D is the closed magnetic circuit with rotating field formed of any one of the
combinations shown in Figures 1, 2, 3, 4, 5, 6, 7, 8 or of any other having the same
properties.
Di are the primary bobbins fed by the polyphase currents.
D² are the secondary bobbins connected to the collector D³.
D³ is a fixed flat collector formed of radial bars insulated one from the other in
the same manner as in the collector of a continuous current machine.
Dª a rotating vertical axis carrying the movable current taker d'.
D is the moveable "inductor" of a synchronous motor driven by the rotating
magnetic field developed inside the core D, and fed in series or in parallel from the
continuous current circuit.
I call "inductor" that portion of the motor in which the magnetic flow is only
animated by a relatively weak movement and "armature". that in which the flow
traverses with a rapid movement.
d' is a moveable current taker keyed upon the axle D' so as to rub lightly and
carrying the rings d² d³.
d² dare two conducting rings connected to the carbon rubbers d' d³ by the
insulated conductors de d.
dds are two contact blocks of metal or carbon rotating on the flat collector D³
and forming the positive and negative poles of the continuous current these rubbing
contact blocks being mounted in any suitable manner with spring sheaths for example.
ded are two conducting strips serving to lead the current to the rings d² d³.
d d³ are two fixed brushes collecting the continuous current from the rings ď² d³.
De a supporting bearing for the extremity of the axle D'.
D' is a spring for giving the necessary pressure to the carbon rubbers to hold

page_text: them down on to the collector D³ in case the weight of the current taker d' and of
the rubbing contact blocks is not sufficient to insure contact.
Ds is a lever for lifting the whole of the current taker d' and the rubbing contact
blocks d d upon the axle Dr.
Figure 11 shows the transformer with its axis horizontal and the collector in a
vertical plane; the same letters show the same parts.
do is a flexible cable connecting the rubbing contact block d to the inductor D
of the synchronous motor and putting the circuit of this inductor in series with the
continuous current.
d is a flexible cable connecting the inductor D of the synchronous motor to the
ring d*.
block d to the ring d³ when
d is a conductor connecting the rubbing contact block d³ to the ring d³.
d¹³ is a conductor connecting the rubbing contact
it is wished to feed the inductor D³ in parallel.
D' is a spring pressing upon the current taker d¹.
D is a grooved pulley moved by a lever D and serving as abutment to the
spring Dr.
Figure 12 shows the apparatus formed with the flat collector and synchronous
motor at a distance apart. The same letters indicate the same parts.
D shows the movable inductor of the synchronous motor.
Do the armature fed by ordinary polyphase currents in series or in parallel from
primary conductors or from a branched transformer on the feeding circuit.
D³ the flat collector placed vertically.
D the axle carrying the inductor D and the current taker d'.
D' is a spring to give the necessary pressure to the rubbing contact blocks.
D is a forked lever worked by a screw and hand wheel for shifting the brushes
at starting.
dds are the carbon rubbing contact blocks collecting the continuous current.
Figures 13 and 14 show an arrangement of transformer with rotating field and
coned air space combined with the synchronous motor.
E is the closed magnetic circuit with rotating field carrying the primary and
secondary bobbins the hollow inside of which is of conical shape.
E is the conical moveable inductor of the synchronous motor brush carrier with
its winding.
E is the axle of the synchronous motor and brush carrier.
E is an adjustable bush allowing the width of air space separating the inductor
of the synchronous motor from the magnetic circuit to be regulated.
Figures 15 and 16 show an arrangement which I call a "transformer" with
semi closed rotating field and movable core combined with a synchronous motor
brush carrier.
F is the toothed magnetic ring carrying the primary and secondary bobbins.
F is a laminated core forming the moveable inductor of the synchronous motor
and a portion of the magnetic circuit.
F are the inductor bobbins of the synchronous motor fed in series or in parallel
by the continuous current.
Figure 17 shews the theoretical form of the primary and secondary magneto
motive forces.
H' is the curve of the primary magneto motive force.
H' is the broken line of the secondary magneto motive force.
H³ is a curve entering into the line H².
Figures 18, 19 show the preceding arrangement applied to a transformer with a
stationary field and three branches variable secondary ampère windings each
branch being affected by the conversion of one of the three currents of a combined
three phase system according to the principles stated by Messrs. Kutin & Leblanc.
Figure 18 is a section on the line 7, 7.
G G G are three cores of laminated sheet iron united by two sheet iron
rings C³ G

page_text: G2 G3 are two laminated sheet iron rings uniting the cores G¹ in order to close
he magnetic circuit.
Gare primary bobbins surrounding the cores G' and receiving the polyphase
urrents which in the case shown are three phase currents.
G' are the secondary bobbins concentric with the former the turns in which are
variable in number according to a law sensibly sinuous for each branch.
Ge are the outgoing conductors for the current connecting the secondary bobbins
o the flat star collector G' connected three by three (one from each brauch) so
hat the total number of bobbins coupled to each bar of the collector is kept
constant.
G' is a flat collector carried by the ring G³.
G8 is the movable inductor of the synchronous motor rotating in the central
The different forms of magnetic circuit shown in Figures 1, 2, 3, 4, 5, 6, 7, 8,
13, 14, 15 and 16 and the double series of primary and secondary bobbins, allow by
adopting for each series the polyphase system of coupling, the transformation of
polyphase currents which feed the primary into polyphase currents which are
generated in the secondary.
The primary currents combined in any manner coupled in series, in parallel
according to the polygonal method, star or mixed generate one or more turning
fields in the magnetic core. These turning fields give rise in their turn to a like
number of turning fields in the secondary bobbins, which combining with the first
give rise to as many resulting fields also turning which produce two induced electro
motive forces in reverse directions in the primary and secondary.
Theory and practice show that all that takes place between the two systems of
polyphase currents with turning fields is the same as between the primary and
secondary of an ordinary alternating monophase transformer. Only the resulting
field instead of being stationary is shifting.
The arrangement allows the primary and secondary bobbins to be combined in
any order by varying the number of their coils according to any law.
It differs essentially from all analogous systems in that it allows an apparatus to
be made free from magnetic leakage; which is one of the principal objects of this
invention.
This result is obtained by placing the primary and secondary bobbins either
juxtaposed or concentric in the same teeth as shown at B3 B³, C3 C' in Figures 1,
2, 3, 4, 5, 6, 7, 8. The teeth of the core may moreover be placed upon any one of
the portions A. A' A2 B B' C C'C' forming the magnetic circuit and they may be
of any desired dimensions.
With such constructions by connecting in any suitable manner the outgoing
wires of the secondary, an apparatus with rotating field is obtained which will
allow of any system of polyphase currents being converted into any other system
of polyphase currents or even eventually into a monophase current.
The conversion of polyphase currents into continuous currents or vice versa is
obtained by the combination of the rotating field magnetic circuit with a con-
tinuous current collector and a system of rotating brushes as shown in Figures 9,
10, 11, 12.
On leaving the secondary bobbins D' the currents produced are collected by a
star shaped fixed flat collector formed of insulated bars. Each outgoing conductor
is connected either in series or in parallel with one or several of the collector bars

page_text: according to the form of winding adopted for the secondary circuit. The carbon
or metal brushes d' do rub upon this collector, they may be equal in number to that
of the rotating poles and adjusted to a suitable angle one with respect to the
others, or a smaller number or even two only placed at 180° may be used if the
number of the fields be a multiple of three or at 45° if a multiple of two.
The number of brushes moreover depends as in an ordinary dynamo on the
coupling of the secondary bobbins and on the collector.
By rotating the brushes with a motion synchronous with that of the primary
turning field by a process which will be indicated further on, a continuous current
will be collected upon the collector.
The continuous current thus collected by the rotating brushes d and will pass
by d d to the rings d² d³ upon which rest two fixed brushes d³ 1; these are the
two poles of the outer continuous current circuit.
The advantage of the flat collector is that it allows of easy regulation of the
rotating brushes which operate by their own weight and that of the brush carrier
if its axis be vertical (Figures 9 and 10) or by a spring (Figure 11) if it be
horizontal.
This regulation is therefore independent of wear.
In Figure 9 the current conveyer d' is keyed upon the axle D but can slide
along it with slight friction by sliding it presses by its weight upon the collector.
If the pressure is found to be insufficient the necessary amount could be given by
the spring D'.
The passage of the continuous current in the circuit of the secondary bobbins
causes a reflex field rotating with the brushes through the magnetic core. This
field is no longer sinuous as in the primary field. The small practical importance
of this difference is easily understood.
Let the primary magneto motive force be represented by the sinuous line H' in
Figure 17, the secondary magneto motive force H2 produced by the continuous
current will form a series of triangles.
By applying the Fourier series it will be found that the last field will decompose
forming a principal field of value 1, which combines with the primary field and
forming a series of parasite fields giving rise in the primary to parasite currents
the successive values of which 27 15 he will go on decreasing without altering
the value of the principal current more than 4 to 5%-
Practically the line H2 with angular bends may be replaced by the curved dotted
line H³.
It is the field resulting from these two sinuous lines H and H which produces
the useful energy and the corresponding E.M.F. in our secondary circuit.
The conversion of a polyphase current into a continuous current carried out in
this apparatus may be effected with any one of the forms of magnetic circuit
shown or with any other form, provided it be a closed magnetic circuit sub-
mitted simultaneously without leakage to the primary and secondary magneto
motive forces.
To obtain a sufficient number of contacts in the collector without increasing
the number of phases in the feeding current we employ one or other of the two
following processes.
1. By making up each circuit dephased from the primary not from a single but
from several consecutive bobbins corresponding consequently to several bobbins of
the secondary.
2. By interposing between the teeth which carry the juxtaposed primary and
secondary bobbins, other grooves carrying only secondary bobbins, sufficiently
small in number for the magnetic leakages produced in the space between two
primary bobbins to remain small.
It is preferable to use the first process because it reduces the magnetic loss to a
minimum.
In certain cases the primary and secondary bobbins may be alternately placed in
different grooves.

page_text: Lastly the number of primary bobbins may also be increased by employing the
known method of bisecting the phases by associating bobbins carrying a different
number of turns of winding some in star form others in polygons with the conductors
bringing in the currents; a truly sinuous turning field may thus be obtained
whatever may be the number of phases of the generating current.
The invention is also applicable to converting continuous currents into polyphase
currents by means of the reversibility of the whole system.
If the fixed brusbes d d be fed with a continueus current a polyphase current
will be obtained at the terminals of the bobbins D' in which the number of phases,
the intensity and the E.M.F. will depend upon the method of winding and the
combination of the primary and secondary circuits.
PROCESS FOR GIVING ROTATION AND AUTOMATIC ADJUSTMENT TO
THE BRUSHES.
The rotating movement of the rubbing brushes d and d³ upon the flat
collector D³ is obtained in this system by means of a small synchronous motor
whose moveable inductor D³ possessing a number of poles equal to or less than that
of the magnetic core, is generally driven by a derived turning field produced in the
open space by the presence of iron in this inductor. This latter excited by a
continuous current taken from the rings 2 3 by the conductors do du Figure 11,
moves synchronously with the resulting turning field and by its axle D₁ drives the
current conveyer d' and the rubbing contact blocks d and ds in such a manner that
the line of commutation regulated in the first place on a certain system always
remains perpendicular to the resulting field, a necessary condition for obtaining a
continuous current.
The apparatus thus constituted is very simple and little cumbersome.
The relative value of the derived field required to drive the synchronous motor
is arrived at by suitably proportioning the dimensions of the rotating poles and the
air space.
Figures 9, 10 and 11 show a transformer coupled with a synchronous motor brush
carrier having a vertical or horizontal axis.
The two portions of the apparatus may also be separate.
The magnetic core and the two series of primary and secondary bobbins then
constitute a first apparatus whilst the synchronous motor excited by a shunt taken
from the feed circuit or from a transformer fed by the primary system, and
the flat collector and rotating brushes form a second apparatus distinct from
the first. This is shown in Figure 12 applied to a transformer with horizontal
axis.
This division is however equally applicable to a transformer with vertical axis.
The use of the synchronous motor in one piece with the magnetic circuit has two
advantages.
1. To utilise with a small consumption of energy a portion of the turning field
generated in the ring.
2. To regulate the commutating line of the brushes according to the exact
position of the resulting field and consequently keep it coinciding with the neutral
fine which is adjusted to 90° (angle of phase) behind the line of the rotating
field.
The power of the synchronous motor necessary to drive the brushes can be
varied by altering the dimensions of its moveable inductor, the winding which it
carries and the width of air space which separates it from the magnetic core.
Theoretically the synchronous motor separated from the magnetic circuit should be
excited by the same combination of currents as those generated in the primary and
secondary, in order that its rotating field may be of the same phase as the resulting
field in the core.
It will be readily understood that practically the self induction of the primary

page_text: circuit renders this condition useful and that it is sufficient to directly feed the
stationary armature of the synchronous motor with a shunt taken from the feed
circuit whose voltage presents a nearly constant adjustment of 90° with respect to
the resulting field of the core.
This adjustment once regulated will in practice therefore remain nearly constant.
Figures 13 and 14 show a synchronous inductor E' of conical form placed within
a magnetic core E which is also conical.
By varying the position of the inductor by means of the bush E³ the width of the
air space is modified and consequently its driving couple. This form has the
advantage of relieving by attraction the bush of a portion of the weight of
the synchronous motor.
Hitherto the drawing around of the brushes has been described by supposing
that the adjustment between the line of the brushes and the neutral line remains
zero at all charges.
In reality it is not always so, the self induction of the coils of the secondary may
necessitate the addition of a considerable angle of adjustment between the line of
the rubbing contact blocks d8 do and the neutral line perpendicular to the direction
of the primary field and account must be taken of this adjustment in the position of
the brushes to avoid sparking.
Two cases are therefore to be considered.
If the angle of adjustment does not vary with the intensity of the current
delivered, it is sufficient to be able to alter by hand the collector to a given angle
with respect to the magnetic core by regulating its position until the disappearance
of the sparks.
If the angle of adjustment varies with the charge as is the case in ordinary
dynamos, there may be employed different means to do away with this variation.
One may act upon the secondary bobbins by using a compensating winding of
one or more turns per bobbin, adjusted to a suitable angle around the magnetic
core.
One may also on remarking that the adjustment of the rotating portion of an
alternating current synchronous motor simple or polyphase with respect to the
phase of the current which feeds its armature varies with the excitation of the
inductor, place in the shunt circuit da d¹³ d4 d¹º D³ d¹¹ of the inductor D° a circuit
in series forming a sort of compoundage as is seen in Figure 11 in which the
continuous current in series passes by d³ d' d¹º D³ d" d² in traversing the winding
of the inductor.
The number of turns of winding will be regulated in such a manner as to produce
the desired variation of adjustment within the limits required for each use. These
several processes employed separately or concurrently produce an automatic
adjustment of the brushes and prevent sparking in the collector whatever may be
the variation of the system.
The transformer thus set up will require no further looking after or care except
occasional lubrication.
SETTING THE TRANSFORMER IN ACTION.
To set the transformer in action it is sufficient to start the synchronous motor
brush carrier.
The primary circuit being fed by the polyphase currents coming from the source
of electricity, the brush carrier is lifted by aid of the lever D8 shown in Figures 9,
11, 12 and of the pulley D' or by any other means, the effect of which is to break
the circuit of the inductor.
Foucault currents, which will then be developed in the inductor D³ of the
synchronous motor under the influence of the rotating field, will rotate it and cause
it rapidly to attain synchronous speed. The brushes are then allowed to fall upon
the collector and the apparatus is ready to deliver the continuous current.

page_text: magnetic core to rotate synchronously with the primary field; the portion carrying
the primary and secondary bobbins remaining stationary.
The rotating portion F¹ will serve also for the inductor to the synchronous
motor whose winding it carries. The winding may be according to any system of
armature or inductor of continuous current dynamos and placed in teeth formed
either by grooves equal in number to that of the fields or upon the entire
circumference.
Its function will be two fold; to serve as a rotating inductor to the brush carrier
motor and to close the circuit of the lines of forces generated in the fixed core.
This different combination of the preceding may moreover be carried out with
any one of the closed magnetic circuits and with any one of the windings previously
described.
APPLICATION OF THE SYSTEM OF AUTOMATICALLY ADJUSTED ROTATING
BRUSHES TO TRANSFORMERS WITH STATIONARY MAGNETIC FIELDS AND
VARIABLE SECONDARY AMPERE WINDING.
The system of driving and automatically adjusting the brushes is very applicable
to transformers, with stationary magnetic field and variable secondary ampère
windings for converting polyphase currents into continuous currents and inversely.
In Figures 18, 19 this is shewn applied to the case of a three phase current where
only a single core per phase is used but it can be applied whatever may be the
number of phases by altering the number of cores; this number may be equal to
that of the phases or to a multiple of them by coupling the windings of the cores of
the same phase either in series or in parallel.
With a dephased current this number should be at least four, in order that the
disc may present the two necessary rotating poles.
The three laminated cores G₁ united by two rings G2 G3 carry two windings;
one the primary G fed by the triphase current coming from the source of
electricity, the other secondary G with a variable number of turns of winding
arranged according to the sinuous or other law.
By the effect of the windings there is developed in the terminal rings a rotating
field a shunt from which is employed to drive the moveable inductor G of a
synchron-motor brush carrier excited in parallel or in compound by the continuous
current.
The outgoing conductors Ge of the current of the secondary bobbins are
connected in any suitable manner to the bars of a flat collector G' and the carbon
rubbing contact blocks which rotate upon the collector collect continuous current.
The processes for obtaining automatic adjustment of the brushes can be applied
with the same facility.
The apparatus thus constituted is simpler and more serviceable than the
transformers with stationary fields hitherto employed. It is reversible and may
furnish polyphase currents if fed with a continuous current.
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. The realisation and application in the system of rotating field transformer
for the conversion of polyphase currents into polyphase currents or into continuous
currents or vice versa, of a closed magnetic circuit formed of a magnetic core of
perforated or cut away plates having the general shape of a ring, drum, flat ring or
B

page_text: disc surrounded with a stationary mass of iron and covered with primary and
secondary bobbins concentrically wound and intermixed in a sufficiently intimate
manner to reduce magnetic leakage to a minimum either by winding them together
in the same grooves, or by interposing a small number only of secondary bobbins
between the primary bobbins; the primary bobbins following the annular drum,
disc or oblico radial method and divided into dephased groups, each consisting of
one or more consecutive bobbins; the secondary bobbins in number equal to or
greater than that of the primary bobbins, either similarly connected or coupled to
a collector by any of the methods of winding employed in ordinary dynamos to
furnish a continuous current, the primary bobbins being connected with the supply
conductors according to any of the methods employed for polyphase currents,
either polygonal, star, mixed, in series or in parallel; the secondary bobbins
connected between themselves according to any of these methods and formed of a
constant or variable number of turns according to any law.
2. The realisation and application in the system of transformer with rotating
field of a semi-closed magnetic circuit formed of a magnetic core having one of
the forms mentioned in paragraph 1, wound in the same manner and surrounded
with a mass of iron no longer entirely stationary but moveable in part, the air
space being reduced to the strict minimum, this mass may serve accessorally as
inductor to the synchronous motor brush carrier by means of the addition of an
exciting circuit.
3. The combination with the closed or semi-closed magnetic circuit with rotating
field of one or more star shaped flat collectors connected to the secondary bobbins
according to any of the known methods for continuous current machines, upon the
bars of which rub the moveable brushes turning around the axle, which are in
equal or less in number to that of the rotating poles according to the manner in
which the connections of the collector and the secondary bobbins are made and
which furnish the continuous current.
4. The realisation and application to the system of transformer with rotating
field, of a process of driving and automatically regulating the rotating brushes based
upon the use of a synchronous motor for driving the rubbing brushes with an
inductor excited in series or in parallel by the continuous current produced in the
apparatus and driven either by a just sufficient shunt of rotating field in the interior
of the magnetic core (the space left empty may be of a spherical, cylindrical or
conical shape as most convenient for the air space and in certain cases to relieve
the axle of the weight of a portion of the moveable inductor) either by an
armature separate magnetic core of the transformer but fed by the same currents
or by currents arranged in the same order, taken in shunt from the terminals of the
primary bobbins.
5. The application to the system of automatic regulation of precesses for the
prevention of sparking at the brushes consisting either in the partial or complete
compoundage of the moveable inductor of the synchronous motor, in such a way as
to vary the adjustment according to the secondary intensity or in the diminution
or the prevention of the self induction of the secondary bobbins by the aid of
condensers or otherwise, or by a compensating winding of the secondary circuit in
such a manner as to maintain a fixed angle of adjustment whatever may be the
intensity of the current delivered by the apparatus.
6. The combination of a closed or semi closed magnetic circuit with rotating
field with a flat star collector, a system of rotating brushes driven by a synchronous
motor with automatic regulation whatever may be the charge, for forming a
transformer (with vertical or horizontal axis) of polyphase currents into a continuous
current or of a continuous current into polyphase currents.
These diverse parts
forming a single or two apparatus, the magnetic circuit remaining in the second
case separate from the synchronous motor united with the collector and rotating
brushes; these various combinations being applicable whatever may be the voltage
and intensity of the currents to be converted and obtained, the number of phases,
the nature of the materials employed, the form and the dimensions of the apparatus.

page_text: 7. The application of the closed magnetic circuit with rotating field to the
construction of a fixed transformer of polyphase currents into polyphase currents
with minimum resistance and magnetic leakage whatever may be the voltage
intensity and the number of phases of these currents.
8. The application of the system of flat collector and automatically regulated
rotating brushes with synchronous motor brush carrier driven by a shunt of the
field to transformers with fixed magnetic field and variable secondary ampère
windings for the conversion of polyphase currents into continuous currents or of
continuous currents into polyphase currents whatever may be the voltage intensity
and number of phases of these currents as well as of the number of cores employed
and associated if necessary according to the multipolar form.
9. The construction of converter apparatus substantially as herein before
described and illustrated in the drawings annexed.
Dated this 31st day of March 1894
SYDNEY PITT.