A Method of Exciting Synchronous or Asynchronous Dynamo Electric Machines or Motors Working with Alternating Currents of Constant Potential.
Year: 1896

page_text: Date of Application, 8th Oct., 1896
Complete Specification Left, 10th June, 1897-Accepted, 17th July, 1897
DE LA
FORCE PAR L'ELECTRICITÉ, of 13 Rue Lafayette, Paris, France.]
A Method of Exciting Synchronous or Asynchronous Dynamo
Electric Machines or Motors Working with Alternating Currents
of Constant Potential.
I JOHN IMRAY of No. 28 Southampton Buildings Chancery Lane in the County of
London Consulting Engineer and Chartered Patent Agent do hereby declare the
nature of this invention to be as follows:-
I.
GENERAL CONSIDERATIONS AND OBJECT OF THE INVENTION.
If it he intended to construct a dynamo with certain weights of copper and iron,
and if there be taken into account the amount of energy that is to be allowed to be
lost in heating the machine and the maximum tangential speed of the moving parts,
it will be found that a machine of maximum power can be realised by dividing the
copper equally over the stationary and moving circuits, and making the coiled iron
as light as possible.
Such a machine excited by currents of constant intensity and employed as a
generator would naturally produce currents of practically constant intensity.
If on the other hand, it were desired to make it supply currents of varying intensity
with constant potential the intensity of the exciting current should vary with the
demand for current.
On these grounds most constructors have been led to sacrifice completely economy
of material, making machines in which the number of ampère turns on the armature
is as small as possible relatively to the number of ampère turns on the magnets, and
in which the iron is made very thick notwithstanding the loss of energy in causing
the flux to pass through it; and all this in order to have voltage nearly constant with
equal speed and equal exciting current.
My foreign correspondents have always considered that the simplicity of this
method was only apparent, that the result obtained was too dearly purchased, and
that it would be well to return to machines having great armature reaction, which
cost less and having a better out put than the machines above referred to. As for
constant voltage, that was to be got by automatic variation of the exciting current
and output, such variation being obtained by means purely electric.
For these reasons my correspondents have studied a method of exciting applicable
to all kinds of alternating monophase or polyphase current machines, synchronous or
asynchronous, this method being capable of maintaining constant difference of
potentials between the conductors of the network supplied, whether the machines
operate as generators or motors, whatever be the armature reaction, the intensity of
the currents generated or received and whether they are watted or dewatted.
This new method of exciting and the means employed form the object of the
present invention.

page_text: 2TT
Let the alternator have u inducing circuits traversed by currents of any frequency v
the intensities of which have successive differences of phase each 1/nth of period the
exciter should therefore be capable of developing always n, electromotive forces of
frequency u successively displaced in phase 1/nth of period. This result is obtained
in the following manner. As shewn in Figure 1 the armature of the exciter consists
of an armature A such as that of a continuous current machine provided with its
commutator C. Around C are arranged n brushes F1 F &c. 6 as shewn at angular
intervals apart each The inducing magnets are such as produce a field of constant
intensity which is made to revolve around the axis O with velocity u, while the
armature A is to revolve as fast as possible. It is evident that if the nexternal
circuits C C &c. (6 shewn) are connected to the brushes F F &c. these circuits will
be the seats of n alternating currents of frequency u but successively displaced in
phase by 1/nth period. When O these n circuits are traversed by continuous
currents, the intensities of which vary in passing from each to the next according to
a periodic law depending on their position relatively to the direction of the field i if
1.
=

page_text: the alternator were synchronous with a single inducing circuit two brushes would
suffice.
The system of exciter about to be described therefor applies in all cases.
First the field of constant intensity turning round the armature with velocity u
has to be developed. Let the alternator have tri-phased currents, then the continuous
current armature A should be coiled with 3 separate circuits x. y. zench occupying 1/34
of the ring and connected to 3 collecting rings abe. If there be sent into these
circuits 3 alternating currents of frequency 1/T successively displaced in phase
by 1/3 period furnished by the alternator, a field will be produced revolving round the
armature A with velocity 1/T. If this armature having only two poles, its axis be
connected to that of the alternator through gearing causing it to revolve with N
times the speed of the latter, its speed will be N v. If then it be made to revolve
opposite to the revolving field produced as above set forth, the latter will have an
absolute velocity of 1/T-Nv = since 1/T = N v x u.
1
1
T
This system extends to alternators supplying any number of polyphase currents.
When the alternator supplies only monophase currents, a single circuit with two
poles is arranged on the same ring with the armature A and a current of frequency 1/T
is sent through it. This would tend to produce two fields revolving relatively to the
armature, the one in one direction, the other opposite, their speeds being equal, so
that for the first = N v, for the other u = +Ne. The difference 1/TN vis
small as compared with the sum 1/T + Nv, hence if the armature revolved in the
middle of a stationary conducting cage, the first field would cut the bars with low
speed developing only weak induction, but the other cutting the bars with high speed,
would develop considerable induction, so that this field would be practically destroyed
by the inducing reaction of the cage.
T
Thus there is a general process applicable in all cases allowing development at
every instant in the armature of a field of constant intensity revolving in space with
the velocity u.
Instead of 2 poles, the armature had 2 N, the gearing connecting it to the
alternator would be such as to give it a speed; U.
N
N
The conditions have now to be determined under which the intensity of the flux i
is to vary in order to have currents of constant voltage from the alternator.
When armatures have great self induction, the influence of their resistance may
be neglected as compared with their reactance. Let the line O E (Figure 2) represent
the constant effectual difference of potentials which should be maintained at the ends
of each armature circuit and let O I represent the effectual intensity of the current
in these circuits; the directions 0 E and OI are inclined at an angle k equal to the
product by 2 of the difference of phases between the variations of the difference of
potentials having the effectual value OE and the variations of the intensity
having the effectual value 0 I. The self induction of the armature of the
alternator and that of the circuits of the armature of the exciter traversed by the
same currents develop a total electromotive force proportional to the intensity O'I but
displaced from it in phase by 1/4 period. This electromotive force may be represented
by a line OS perpendicular to Oi and equal to the product of OI by a constant. The
electromotive force necessary for passing the current of intensity O I is proportional
to the resultant OR of the electromotive forces OE and OS. Thus the electromotive
force developed in the alternator is proportional to the intensity of the exciting
currents furnished to it by the exciter. The electromotive forces developed in the
exciter must therefore be proportional to the resultant OR, or supposing for the
moment that the reaction of the armature of the exciter is nil the flux i should be
constantly proportional to the resultant OR. This proportionality may be attained
by applying the method above set forth for producing fluxes of constant intensity
revolving around the axis of the exciter with speed u thus developing in the exciter
two distinct fluxes, the first by circuits such as z. y. z (Figure 1) connected in shunt
with the conductors of the distributing network, the second by similar

page_text: circuits x y z connected in series with those of the armature of the alternator which
is to be excited, making these circuits of the exciter of suitable dimensions.
Referring to Figure 3, the first flux which will remain constant with the voltage at
some given moment a certain direction OG; the second flux has, at the same moment,
an intensity 0 H proportional to the intensity of the currents delivered by the
armature of the alternator. The angle depends, first, on the structional relation of
the circuits producing the first flux to those producing the second, and secondly, to
the difference of phase between the intensity of the currents developed by the
armature of the alternator and the electromotive forces delivered at its terminals.
These conditions may be made such that the angle l O when the currents furnished
by the alternator are completely dewatted. The angle will be 90° when these
currents are completely watted. The angle will always be the compliment of the
angle k in Figure 2. If the circuits producing the fluxes O G and OH are of such
O G он
dimensions that
then the resultant O P is always proportional to O R.
О Е O S
=
It is the resultant OP of OG and O H which determines the production of the
electromotive forces in the exciter, and if it has no reaction of armature, these forces
are always proportional to O P.
The principle above set forth may be practically applied as will now be described
IV.
EXAMPLE OF PRACTICAL APPLICATION.
As the armature A of the exciter has to be the seat of two fluxes, these may be freely
developed by adopting the construction shown in Figures 4 and 5 respectively
longitudinal and transverse sections.
Two rings M M and N N preferably of the Becinatte kind are employed as shewn in
Figure 4. The plates of which they consist have the same profile and the slots in both
are in line with one another. Assuming that a triphase current alternator has to be
excited, then the ring M has a first Gramme coil for triphase currents, the 3 circuits
of which are connected to the rings a b c. The ring N is similarly coiled having the
three circuits connected to the rings f. v. w. The fluxes developed by the circuits of the
rings a b c and t. v. w have no influence on one another. The external plate circles
along which the developed fluxes close themselves are not so thick over N as over M
for a reason hereafter explained. The coils mentioned do not occupy the whole
section of the slots of the rings, besides these the slots contain coils which are the
true armature coils of the exciter. These coils o p qr extend continuously over both
armature rings M and N and constitute as many separate bobbins as there are slots of
the rings which have the entering and leaving ends connected together and to a
commutator C having as many plates as there are hobbins, according to the method
adopted in continuous current machines. The circuit of the armature, properly so
called, of the exciter, is thus the seat of an electromotive force proportional to the
resultant of the two fluxes produced by the cirenits for alternating currents of the
rings M and N. In order to suppress the effects of reaction of the field excited, a
coil o' p q of the same kind is wound in slots within the stationary plate crowns
which surround the armature as near as possible to the iron. The coil of Gramme
kind constitutes n circuits (6 are shewn in Figure 6 marked S¹ $ &c.) corresponding
with a inducing circuits of the alternator and a brushes F P &c. The entering
ends of the circuits S S &c. are arranged in the same radii as the contacts of the
brushes F F &c. with the commutator C and each of the circuits is connected in
series to one of the inducing circuits C C &c. (Figure 6) of the alternator; the
leaving end of each of the circuits S' S² &c. is connected to the entering end of the
next in order.
When the circuits $' S' &c. are the same in number as those of the armature under
them connected to the commutator, they develop the same number of ampère turns
as the latter. When they are wound oppositely, as will always be done, the
magnetising forces developed by these two sets of circuits are equal but of opposite
sign. Consequently the armature circuits cannot produce any flux except those

page_text: When to the first alternator another is to be added having several inducing circuits,
then, after this second machine has attained its normal speed, which always differsa
little from that of synchronism, the rings t, v, w of its exciter are at first connected
to the network as in Figure 7, and if it be found necessary to regulate the voltage,
that can be done by introducing bobbins of variable self induction into the conductors
leading to the rings t, v, w and thereupon the circuits of the second alternator are
closed on the network.
Generally, and especially if the inducing circuits are numerous, the second
alternator does not lend to become synchronised with the first, and its inducing
circuits are traversed by alternating currents of low frequency. Its working however
is not the less uniform for the couple developed on its axis increases and decreases
with the velocity.
When several alternators are coupled, the one that revolves most rapidly is the seat
of a maximum resisting couple, and reciprocally, if the speed of one became too low
it would act as a motor. Finally the coupling of those machines is the same as for
continuous current machines.
When a synchronous alternator having a single inducing circuit acts alone, it acts
as an asynchronous one. When a second synchronous alternator is added, the same
course is pursued as with the asynchronous, but care is to be taken that the two
alternators are coincident in phase when the second is put in circuit with the
network.
The synchronism maintains itself the load of either alternator increasing when it
outruns the other. In like manner any number of alternators might be coupled.
Any alternator whether synchronous or asynchronous, provided with the new
exciter described, may be employed as a motor, taking only the watted currents from
the network which supplies it.
1000
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
A Method of Exciting Synchronous or Asynchronous Dynamo
Electric Machines or Motors Working with Alternating Currents
of Constant Potential.
I, JOHN IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the County
of London, Consulting Engineer and Chartered Patent Agent, 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 :-
I.
. GENERAL CONSIDERATIONS AND OBJECT OF THE INVENTION.
If it be intended to construct a dynamo with certain weights of copper and iron,
and if there be taken into account the amount of energy that is to be allowed to be
lost in heating the machine and the maximum tangential speed of the moving parts,
it will be found that a machine of maximum power can be realised by dividing the
copper equally over the stationary and moving circuits, and making the coiled iron as
light as possible.
Such a machine excited by currents of constant intensity and employed as a
generator would naturally produce currents of practically constant intensity.
If, on the other hand, it were desired to make it supply currents of varying
intensity with constant potential the intensity of the exciting current should vary
with the demand for current.

page_text: On these grounds most constructors have been led to sacrifice completely economy
of material, making machines in which the number of ampère turns on the armature
is as small as possible relatively to the number of ampère turns on the magnets, and
in which the iron is made very thick notwithstanding the loss of energy in causing
the flux to pass through it; and all this in order to have voltage nearly constant with
equal speed and equal exciting current.
My foreign correspondents have always considered that the simplicity of this
method was only apparent, that the result obtained was too dearly purchased, and
that it would be well to return to machines having great armature reaction, which
cost less and have a better output than the machines above referred to. As for
constant voltage, that was to be got by automatic variation of the exciting current
and output, such variation being obtained by means purely electric.
For these reasons my correspondents have studied a method of exciting applicable
to all kinds of alternating monophase or polyphase current machines, synchronous or
asynchronous, this method being capable of maintaining constant difference of
potentials between the conductors of the network supplied, whether the machines.
operate as generators or motors, whatever be the armature reaction, the intensity of
the currents generated or received and whether they are watted or dewatted.
This new method of exciting and the means employed form the object of the
procent invention
An alternator comprises two quite distinct series of circuits.
1. The circuits which may be termed "armature circuits" which are directly
connected to the conductors of the network supplied, and which are 1, 2, 3 &c. in
number according to the currents produced are to be monophase, biphase, triphase &c.
2. The circuits which may be termed "inducing circuits" closed upon themselves
which are traversed by currents froin a source external to the machine, generally of
frequency differing from those in the armature circuits.
The alternator may have any number of identical inducing circuits regularly
arranged around the armature. If they are traversed by alternating currents these
should be regularly displaced in phase by 1/11th of period in passing from each circuit
to the next. If they are traversed by continuous currents, their intensities vary
according to a periodic law in passing from each circuit to the next. Generally if n
denotes the frequency of the inducing currents of an alternator, 2 N the numbers of
its poles, v the speed of rotation and 1/T the frequency of the currents developed in
the armature circuits, there is the relation 1/T=vxNv.
When the alternator has several inducing circuits capable of producing a revolving
field of constant intensity the speed v may be anything, there being no relation
between the speed of the rotation of an alternator and the frequency of the currents
which it gives or receives.
In order to keep this property in view, those alternators which have several
inducing circuits regularly arranged round their armatures may be termed
"asynchronous alternators." But if there is a single inducing circuit whatever be its
arrangement, it cannot produce a revolving field of constant intensity. Such an
alternator, therefore, can act only on the condition that its inducing field shall move
relatively to the armature with the same speed as the field developed in the
apparatus. To keep this in view, those alternators which have a single inducing
circuit excited by a continuous current may be termed "synchronous alternators."
Such an alternator may however be considered only a special case of asynchronous
alternator. Also any method of exciting generally applicable to asynchronous
alternators, having any number of inducing circuits traversed by alternating
currents of any frequency, is applicable also to synchronous alternators. This method
of exciting as applied to asynchronous alternators may be explained as follows.

page_text: PRINCIPLE OF THE METHOD.
In what follows I refer to the drawings accompanying my Provisional Specification.
. Let the alternator have n inducing circuits traversed by currents of any
frequency v the intensities of which have successive differencies of phase each 1/nth
of period, the exciter should therefore be capable of developing always n electromotive
forces of frequency u successively displaced in phase 1/mth of period. This result is
obtained in the following inanner. As shewn in Figure 1 the armature of the exciter
consists of an armature A such as that of a continuous current machine provided with
communicator C. Around C are arranged n brushes F1 F2 &c. 6 as shewn, at angular
2πT.
intervals apart each The inducing magnets are such as produce a field of
constant intensity i which is made to revolve around the axis O with velocity u,
while the armature A is to revolve as fast as possible. It is evident that if the n
external circuits C1 C2 &c. (6 shewn) are connected to the brushes F1 F2 &c. these
circuits will be the seats of 'n alternating currents of frequency w but successively
displaced in phase by 1/nth period. When = 0 these n circuits are traversed by
continuous currents, the intensities of which vary in passing from each to the next
according to a periodic law depending on their position relatively to the direction of
the field i. If the alternator were synchronous with a single inducing circuit, two
brushes would suffice.
22
The system of exciter about to be described therefore applies in all cases.
First the field of contant intensity turning round the armature with velocity u has
to be developed. Let the alternator have tri-phased currents, then the continuous
current armature A should be coiled with three separate circuits x, y, z, each
occuping 1/3 of the ring and connected to 3 collecting rings a, b, c. If there be
sent into these circuits 3 alternating currents of frequency 1/T successively displaced
in phase by 1/3 period furnished by the alternator, a field will be produced revolving
round the armature A with velocity 1/T. If this armature having only two poles, its
axis be connected to that of the alternator through gearing causing it to revolve with N
times the speed of the latter, its speed will be Nv. If then it be made to revolve
opposite to the revolving field produced as above set forth, the latter will have an
absolute velocity of 1/T-Nv=u, since 1/T=Nvxu.
This system extends to alternators supplying any number of polyphase currents.
When the alternator supplies only monyphase currents, a single circuit with two
poles is arranged on the same ring with the armature A and a current of frequency 1/T
is sent through it. This would tend to produce two fields revolving relatively to the
armature, the one in one direction, the other opposite, their speeds being equal, so
that for the first = Nv, for the other u=
–
1
1
T+
Nv. The difference 1/T-Nu
is small as compared with the sum 1/T + Nv, hence if the armature revolved in the
middle of a stationary conducting cage, the first field would cut the bars with low
speed developing only weak induction, but the other cutting the bars with high speed,
would develope considerable induction, so that this field would be practically distroyed
by the inducing reaction of the cage.
Thus there is a general process applicable in all cases allowing development at
every instant in the armature of a field of constant intensity, revolving in space with
the velocity u.
.
.
If instead of 2 poles; the armature had 2N', the gearing connecting it to the
N
alternator would be such as to give it a speedu.
The conditions have now to be determined under which the intensity of the flux i
is to vary in order to have currents of constant voltage from the alternator.
When the armatures have great self induction, the influence of their resistance
may be neglected as compared with their reactance. Let the line OE (Figure 2)

page_text: represent the constant effectual difference of potentials which should be maintained
at the ends of each armature circuit and let OI represent the effectual intensity of
the current in these circuits; the directions OE and OI are inclined at an angle k
equal to the product by 2 of the difference of phases between the variations of the
difference of potentials having the effectual value OE and the variations of the
intensity having the effectual value OI. The self induction of the armature of
the alternator and that of the circuits of the armature of the exciter traversed by the
same currents develop a total electromotive force proportional to the intensity OI but
displaced from it in phase by 1/4 period. This electromotive force may be
represented by a line OS perpendicular to OI and equal to the product of OI by a
constant. The electromotive force necessary for passing the current of intensity OI
is proportional to the resultant OR of the electromotive forces OE and OS.
Thus the electromotive force developed in the alternator is proportional to the
intensity of the exciting currents furnished to it by the exciter.
The electromotive forces developed in the exciter must therefore be proportional to
the resultant OR, or supposing for the moment that the reaction of the armature of
the exciter is nil the flux i should be constantly proportional to the resultant O.R.
This proportionality may be attained by applying the method above set forth for
producing fluxes of constant intensity revolving round the axis of the exciter with
speed u thus developing in the exciter two distinct fluxes, the first by circuits such
as xyz (Figure 1) connected in shunt with the conductors of the distributing
network, the second by similar circuits x1 y1 zl connected in series with those of
the armature of the alternator which is to be excited, making these circuits of the
exciter of suitable dimensions.
Referring to Figure 3, the first flux which will remain constant with the voltage at
some given moment a certain direction O G; the second flux has, at the same moment,
an intensity OH proportional to the intensity of the currents delivered by the armature
of the alternator. The angle depends, first on the structural relation of the circuits
producing the first flux to those producing the second, and secondly, to the difference
of phase between the intensity of the currents developed by the armature of the
alternator and the electromotive forces delivered at its terminals. These conditions
may be made such that the angle 1-0 when the currents furnished by the alternator
are completely dewatted. The angle will be 90° when the currents are completely
watted.
The angle will always be the complement of the angle in Figure 2. If the
circuit producing the fluxes OG and OH are of such dimensions that OG OH
=
OE OS,
then the resultant O P is always proportional to O R.
It is the resultant OP of O G and OH which determines the production of the
electromotive forces in the exciter, and if it has no reaction of armature, these forces
are always proportional to O P.
The principle above set forth may be practically applied as will now be described.
As the armature of the exciter has to be the seat of two fluxes, these may freely
be developed by adopting the construction shewn in Figures 4 and 5 respectively
longitudinal and transverse sections.
Two rings M M and N N preferably of the Becinatte kind are employed as shewn in
Figure 4. The plates of which they consist have the same profile and the slots in
both are in line with one another. Assuming that a triphase current alternator has
to be excited, then the ring M has a first Gramme coil for triphase currents, the 3
circuits of which are connected to the rings a, b, c. The ring N is similarly coiled
having the three circuits connected to the, rings t, v, w. The fluxes developed by
the circuits of the rings a b c and t v w have no influence on one another. The

page_text: external plate circles along which the developed fluxes close themselves are not so
thick over N as over M for a reason hereafter explained.
The coils mentioned do not occupy the whole section of the slots of the rings,
besides these, the slots contain coils which are the true armature coils of the exciter.
These coils o p q r extend continuously over both armature rings M and N and
constitute as many separate bobbins as there are slots of the rings which have the
entering and leaving ends connected together and to a commutator C having as many
plates as there are bobbins, according to the method adopted in continuous current
machines. The circuit of the armature, properly so called, of the exciter, is thus the
seat of an electromotive force proportional to the resultant of the two fluxes produced
by the circuits for alternating currents of the rings M and N. In order to suppress
the effects of reaction of the field excited, a coil o p q 1 of the same kind is wound
in slots within the stationary plate crowns which surround the armature as near as
possible to the iron. The coil of Gramme kind constitutes n circuits (6 are shewn in
Figure 6 marked St S &c.) porresponding with is inducing circuits of the alternator and
n brushes FF &c. The entering ends of the circuits S1 S2 &c. are, arranged in the
same radii as the contacts of the brushes F F &c. with the commutator C and each
of the circuits is connected in series to one of the inducing circuits C' C &c. (Figure 6)
of the alternator; the leaving end of each of the circuits S1 S2 &c. is connected to the
entering end of the next in order.
When the circnits S' S2 &c. are the same in number as those of the armature under
them connected to the commutator, they develop the same number of ampère turns as
the latter. When they are wound oppositely, as will always be done, the magnetising
forces developed by these two sets of circuits are equal but of opposite sign.
Consequently the armature circuits cannot produce any flux except those
corresponding to magnetic leaks which may be rendered negligible by means usually
employed in revolving field motors. The reaction of the armature described
is nil.
If X Y Z Figure 7 be three circuits of the alternator, gghh, and ii being the
three distributing leads connected to the ends of XYZ, the three alternating current
circuits XYZ and X Y of the rings M and N being arranged as triangles,
the circuits X Y Z are closed on those of the armature M by means of the rings a be
and by the rings tv w, the leads g h i are connected in shunt to the circuits of the
armature N.
The sections of wire employed for the several coils should be judiciously chosen...
If difficulties should arise in dealing with machines of very low or very high
tension, these might be overcome by the application of transformers d d as shewn in
Figure 8. The alternating current circuits of the ring M are supplied from the
secondaries of transformers, the primaries of which are connected to X Y Z and the
alternating current circuits of the ring N are similarly supplied from the secondaries
of transformers, the primaries of which are connected in shunt between the leads
g, h, i, and a neutral point.
If the alternator to be excited should not be triphased, but producing a number K
of polyphase currents for the 3 alternating current circuits of the rings M and N with
the 3 rings a, b, c, t, u, ze, would be substituted K similar circuits relatively displaced
and connected to K rings such as a, b, c, t, v, w.
If the alternator were monophase, for the alternating current circuits of M and N
would be substituted a simple bipolar coil connected to two rings. In this case it
would be of advantage to arrange a magnetic screen around the armature of the
exciter. For this purpose there might be lodged in the slots of the external stationary
plate crowns a number of coils wound in the same manner as those of the circuits
intended to resist the reaction of the armature, but. closed on themselves. Thus
there would be around the armature as many coils closed on themselves as there are
slots in the crown.
In what precedes, the exciter has been assumed to be a bipolar machine, so as to
simplify description and drawings. It might however have any number of poles.
Generally, if the alternator has 2 N poles, and the exciter 2 N poles, the axis of the

page_text: V.
OPERATION OF AN ALTERNATOR EXCITED BY THE NEW METHOD.
In a case where there is only one alternator, the least residuary flux developed by
the stationary plates surrounding the armature of the exciter will cause a small current
in the armature which will excite the alternator and thus will produce currents causing
a difference of potential between its terminals. The alternating current circuits of
the armature will develop fluxes which will be added to the first and increase the
electromotive forces produced by the rotation of this armature.. Thus the voltage of
the alternator will go on increasing until the last increment will no longer correspond
with a sufficient increment of flux in the ring N which will happen when the medium
in which this flux is developed has become in one of its parts saturated.
The alternator therefore excites itself like a continuous current machine and its
voltage will arrive at a definite value, but in order that this voltage may be
independent of the output, the fluxes developed in the ring M should always he
proportional to the amount of this output.
Consequently the medium in which these fluxes are developed should always be far
from being saturated, and it is for this reason that the plate crown is shown in Figure 4
thicker where it surrounds M than where it surrounds N.
In fact the exciter furnishes continuous currents and the alternator works as a
synchronous one. If there are several inducing circuits the intensity of the exciting
currents traversing these varies from one circuit to the next according to a periodic
law.
When to the first alternator another is to be added having several inducing
circuits, then, after this second machine has attained its normal speed, which always
differs a little from that of synchronism, the rings tvw of its exciter are at first
connected to the network as in Figure 7 and if it be found necessary to regulate the
voltage, that can be done by introducing bobbins of variable self induction into the
conductors leading to the rings tv w and thereupon the circuits of the second alternator
are closed on the network.
Generally, and especially if the inducing circuits are numerous, the second alternator
does not tend to become synchronised with the first and its inducing circuits are
traversed by alternating currents of low frequency. Its working however is not
the less uniform for the couple developed on its axis increases and decreases with the
velocity.
When several alternators are coupled, the one that revolves the most rapidly is the
seat of a maximum resisting couple, and reciprocally, if the speed of one became too
low it would act as a motor. Finally the coupling of those machines is the same as for
continuous current machines.
When a synchronous alternator having a single inducing circuit acts alone, it acts as
an asynchronous one. When a second synchronous alternator is added, the same course
is pursued as with the asynchronous, but care is to be taken that the two alternators
are coincident in phase when the second is put in circuit with the network.
The synchronism maintains itself the load of either alternator increasing when it
outruns the other. In like manner any number of alternators might be coupled.
Any alternator whether synchronous or asynchronous, provided with the new
exciter described, may be employed as a motor taking only the watted currents from
the network which supplies it.
Having now particularly described and ascertained the nature of this invention and
in what manner the same is to be performed, I declare that what I claim is:-
The herein described method of exciting a monophase or polyphase alternating
current dynamo machine or motor synchronous or asynchronous, by means of a dynamo
having commutator and brushes with its armature revolving within fields developed by

page_text: the passage through special coils on the armature of alternating currents supplied to
or from the main dynamo or coming by shunts from the conductors of the network, or by
secondary currents from transformers having their primaries traversed by the currents
above mentioned, the fields thus developed being either stationary or caused to revolve
with suitable speed, in time with the main dynamo if it is asynchronous-the exciter
armature being also surrounded by suitably arranged stationary circuits connected to
its commutator brushes.
ABEL & IMRAY,
Agents for the Applicant. 1