A Method and Apparatus for Exciting Dynamo Electric Generators.
Year: 1894

page_text: Date of Application, 12th Nov., 1894
Complete Specification Left, 25th July, 1895-Accepted, 31st Aug., 1895
PROVISIONAL SPECIFICATION.
[Communicated from abroad by LA SOCIETE ANONYME POUR LA TRANS-
MISSION DE LA FORCE PAR L'ELECTRICITÉ, of 13 Rue Lafayette, Paris,
France.]
A Method and Apparatus for Exciting Dynamo Electric Generators.
1, 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. This invention has for its object the construction of alternative current
dynamo-electric machines whether monophase or polyphase, capable of working as
generators, without being excited from an external source or being subject to
inductive reaction, and adapted to be coupled in parallel with other machines of
the same kind without being necessarily synchronised with them.
The alternating current machines described in the Specification No. 584 of 1891,
when, from an external exciting alternator, two alternating currents of different
phase are sent into their armatures causing a revolving magnetic field, have the
property of reinforcing these currents without changing their frequency, if at the
same time a motor causes rotation of the field closed on itself, in the same direction
as the revolving field but at greater speed. The same phenomenon can be produced
with a single alternating exciting current acting on the armature of an alternator
In both cases the
having a monophase current and an armature closed upon itself.
function of the alternator can be performed by one or by several condensers, the
combination of which with dynamos renders them self exciting
These properties are utilised in carrying out the present invention in respect of
alternators of monophase and polyphase currents as follows:
II. MONOPHASE CURRENT ALTERNATOR.
This is shewn by Fig. 1 of the accompanying drawings.
1. C is a stationary ring carrying an even number of bobbins all alike. Fig. 2
shews a portion of this ring developed and sectional on a plane perpendicular to
the axis. The laminated iron cores a ẞ are set in a laminated iron ring ab which
surrounds the machine; each of the cores is widened out at its end as shewn at e f.
Fig. 3 is a section such as would be made by a cylindrical surface and developed.
The bobbins are coiled and insulated as in transformers so as to sustain any
tension.
The assemblage of bobbins constitutes the armature of the alternator, the same
as in many known machines.
2. A moveable circuit A, like those of the motors with revolving fields consists of
superposed sheets having holes through which are passed copper bars d, the ends
of which are secured by nuts or by rivetting them on strong copper faces on each
side of the machine, as indicated by the ring of points in Fig. 1. There should be
at least twice as many bars d as there are bobbins, preferably there is a greater
number, as the greater the number the more nearly do the variations of flux
approach the simple law of sines, thus reducing the production of parasite currents
in the conducting masses of the machine. The bars may be fixed as above set
forth or in any other way to form a series of circuits closed themselves.
upon
D17
A

page_text: 1
T
Assuming that there are 2n bobbins; if' a' current of frequence is to be
produced, all the bobbins are connected in one circuit S so that when this is
traversed by a current all the widened ends ef become poles alternately positive
and negative. This circuit S is shewn in Fig. 4 as connecting two conductors u v
andy of the network which has to be supplied with current. At the extremities
of the circuit there is a condenser C or any equivalent apparatus such as
electrolytic condenser, or a thermo-electric chain, its real or apparent capacity r
T2
4.72 L
being
× 10° micro-farads, in which formula T is the period in seconds of
the alternating current desired, and L the coefficient of self-induction of the
armature circuit expressed in quadrants.
It has been proved that under these conditions if the number of revolutions
1
exceeds Ti (n being half the number of poles),
(1) The machine starts itself giving an alternating current of frequency
(2) After a very short time a constant difference of potential, alternating and
effective establishes itself between the terminals, and the magnetic circuits of the
dynamo are sensibly saturated, at least at one of their points.
(3) This effective difference of potential is practically independent of the output
in ampères.
This phenomenon is due to the fact that with increase of intensity of currents
traversing the armature corresponds proportional increase of the currents in their
field. As these currents develop a magnetising force in direction opposite to that
of the armature currents, the flux developed in the dynamo does not vary with the
output of the armature; and the phenomenon called reaction of field does not occur
in these machines.
Similar machines being made to turn with a speed greater than a given speed
may be coupled without having to revolve synchronously.
Indeed when they are connected in parallel, the condensers interposed in shunt
between these terminals are also connected in parallel, the whole then constituting
a single apparatus of capacity which is the sum of the capacities of the coupled
condensers. The external circuit on which is formed this battery of condensers,
may be considered as a single circuit having a determined coefficient of self
induction.
T²
It is this new coefficient of self induction and the new capacity of the coupled
condensers that determines the frequency of current.
farads, T² = 4 Lг.
As r =
4π L
× 10° micro-
If equal machines furnished with equal condensers be coupled, the total
capacity is multiplied by k but the coefficient of self induction of the circuit of all
the parallel coupled armatures is divided by k. Consequently the period T of the
alternating currents produced remains constant.
Of several coupled machines that which revolves most quickly absorbs most
work. If the speed of one falls below above mentioned, it becomes a motor
1
nT
and tends to increase in speed taking work from the others, but without lessening
the intensity of the current supplied.
Finally these dynamos may be coupled like continuous current machines
simultaneously and similarly excited by a special exciting machine for which in the
present case the battery of condensers is substituted.

page_text: Assuming that there are as many monophase machines of the above kind as the
number of currents of different phase desired, each machine may serve to produce
one of these currents.
Preliminary considerations: If an alternating difference of potential is main-
tained at the extremities of any circuit, the alternating current in the circuit may
be considered to be the sum of two currents. The intensity of the first current
has its variations of the same phase as those of the electromotive force. The
intensity of the second current has its variations displaced one quarter of a period
relatively to those of the electromotive force.
The supply current may be considered the first, the exciting current the second
of the two.
The supply current gives energy to the circuit or takes energy from it, but
produces no flux in it.
The exciting current neither gives nor takes energy except momentarily but
it serves to produce in the circuit the magnetic fluxes the variations of which
allow this circuit to give energy to the supply current or to take energy from it.
In the present case it is the condenser introduced in shunt between the terminals
of the dynamo which supplies the exciting current necessary to produce the
magnetic fluxes of which it is to be the seat. The dynamo then develops a supply
current which is superposed on the exciting current traversing its armature.
greater part of this supply current goes to the distributing leads, the rest goes to
the circuit comprising the condenser where it renders disposable the small amount
of energy which the exciting currents consume in overcoming the resistance of
this-circuit.
The
From what precedes it results that the variations of intensity of the supply
current furnished by a dynamo are always displaced one quarter of a period
relatively to those of the intensity of the exciting current. If therefore it is
desired to produce polyphase currents by several dynamos they must be excited
with polyphase currents presenting between them the same difference of phase as
the supply currents desired. It is therefore, for producing the desired exciting
currents, suitable to generate by a single exciter a general exciting current which
is then decomposed into currents displaced in phase relatively to one another.
The polyphase currents thus obtained are then led separately to the terminals of
the dynamos which they have to excite.
Assuming that two supply currents having a quarter of period difference of
phase are to be produced by means of two separate dynamos, Fig. 5 shews
diagrammatically at and 2 the armatures of the two dynamos intended to
supply the currents having the intensities I₁ = A sin 2
t
t
-
T
and I, A cos 2 πT
T
-
common conductor.
The
The return conductors a bare shewn connected to a
producer of the exciting currents consists in a connection in series of a bobbin of
wire having a coefficient A of self induction and a condenser of capacity r or
any other equivent appliance. If currents of frequency T
induction A and the capacity I must be determined according to the formula
г=
(T²
4 m² A
× 10° microfarads.
1
are desired, the self
One of the extremities of this circuit, for example one of the condenser terminals
is connected to the common return a b. The other extremity, the one terminal of
the self induction bobbin is connected to a point P from which there are two
leads, the one comprising a condenser of capacity c₁ and leading to the end of the
armature circuit st, the other comprising a condenser of capacity c, and leading to
the end of the armature circuit s.

page_text: and 52,
$1
R the
If L, and L, express the coefficients of self-induction of
resistance of the circuit comprising the self induction bobbin A and the condenser
of capacity F, the capacities c, and c, are determined by the formulæ
It has been found both theoretically and practically that under these conditions
that the dynamos having the circuits s's start themselves and have each all the
properties of the monophase machine above described, and that they also furnish
currents displaced by one quarter of a period.
Assuming now that there are to be produced & currents displaced relatively
by of a period, Fig. 6 indicates the arrangement for producing 3 alternating
currents differing respectively by of a period, but in what follows k may be
substituted for 3 in determining the arrangement for k currents.
The principal exciting organ consists of a connection in series of a condenser
having capacity F and a bobbin having a coefficient of self induction A. If the
frequency is to be, the condition to be observed is ♫'=
1
T2
x 10 microfarads.
472 A
The apparatus is completed by two transformers m n and p q having identical
primary circuits T, and T. One end of the existing circuit is connected to a point P
whence proceed two leads, the one comprising a condenser of capacity c₁ the other
a condenser of capacity c2. The first lead connects to the entering end of the
primary circuit T₁, the other to that of the primary circuit T₂.
The leaving ends of the primary circuits connect to a common return leading to
the other end of the exciting circuit. R being the resistance of this exciting
circuit and L the apparent coefficient of self induction of each of the primary
circuits T1 and T2 which are supposed the same, the capacities c₁ and c₂ are
determined by the formula

page_text: themselves, and their points of junction are respectively connected to the n wires of
the distribution lead. If the exciting alternator maintains a certain difference of
potential between any two of these wires, it determines the production of magnetic
Hluxes in the circuits of the alternators having field circuits closed on themselves,
branched between the same wires. These fluxes determine in these dynamos the
production of electromotive forces which depend upon their speed. So long as
1
the speed is greater than (where T
nT
denotes the frequency of the currents
developed by the exciter, and n denotes half the number of poles of the dynamo
having field circuits closed on themselves) this dynamo will act as a generator and
will aid in supplying the distributing network. Fig. 7 shews the arrangement for
distributing energy by 3 phase currents. The armatures of the alternators having
field circuits closed on themselves and of the exciter are supposed to have
6 circuits, 1, 2, 3, 4, 5, 6, but 3 of the junction points are connected together. This
arrangement is well known as applied to machines having 3 phase currents.
VII. REMARKS.
All that precedes relates to connecting machines in parallel, which is the most
usual case in practice; they may however be connected in series. In that case at
the moment of connecting there must also be arranged in series the exciting
appliances of the different dynamos if they consist of a system of condensers such
as are described above. If one alternator be employed, each of its circuits should
be arranged in series with the circuits of the dynamos which it has to excite.
Dated this 12th November 1894.
ABEL & IMKAI,
Agents for the Applicant.
A Method and Apparatus for Exciting Dynamo Electric Generators.
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 manuer the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
1. This invention has for its object the construction of alternating current
dynamo-electric machines whether monophase or polyphase, capable of working as
generators, without being excited from an external source or being subject to
inductive reaction, and adapted to be coupled in parallel with other machines of the
same kind without being necessarily synchronised with them.
The alternating current machines described in the Specification No. 584 of 1891,
when, from an 'external exciting alternator, two alternating currents of different
phase are sent into their armatures causing a revolving magnetic field, have the
property of reinforcing these currents without changing their frequency, if at the
same time a motor causes rotation of the field closed on itself, in the same direction
as the revolving field but at greater speed. The same phenomenon can be produced
with a single alternating exciting current acting on the armature of an alternator
having a monophase current and an armature closed upon itself. In both cases the
function of the alternator can be performed by one or by several condensers, the
combination of which with dynamos renders them self exciting. These properties
are utilised in carrying out the present invention in respect of alternators of
monophase and polyphase currents as follows, as I shall describe referring to the
drawings accompanying my Provisional Specification.

page_text: Assuming that there are as many monophase machines of the above kind as the
number of currents of different phase desired, each machine may serve to produce
one of these currents.
Preliminary considerations. If an alternating difference of potential is maintained
at the extremities of any circuit, the alternating current in the circuit may be
considered to be the sum of two currents. The intensity of the first current has
its variations of the same phase as those of the electromotive force. The intensity
of the second current has its variations displaced one quarter of a period relatively
to those of the electromotive force. The supply current may be considered the
first, the exciting current the second of the two.
The supply current gives energy to the circuit or takes energy from it, but
produces no flux in it. The exciting current neither gives nor takes energy except
momentarily but it serves to produce in the circuit the magnetic fluxes the
variations of which allow the circuit to give energy to the supply current or to
take energy from it.
The
In the present case it is the condenser introduced in shunt between the terminals
of the dynamo which supplies the exciting current necessary to produce the
magnetic fluxes of which it is to be the seat. The dynamo then develops a supply
current which is superposed on the exciting current traversing its armature.
greater part of this supply current goes to the distributing leads, the rest goes to
the circuit comprising the condenser where it renders disposable the small amount
of energy which the exciting currents consume in overcoming the resistance of this
circuit.
From what precedes it results that the variations of intensity of the supply
current furnished by a dynamo are always displaced one quarter of a period
relatively to those of the intensity of the exciting current. If therefore it is
desired to produce polyphase currents by several dynamos they must be excited
with polyphase currents presenting between them the same difference of phase as
the supply currents desired. It is therefore, for producing the desired exciting
currents, suitable to generate by a single exciter a general exciting current which
is then decomposed into currents displaced in phase relatively to one another.
The polyphase currents thus obtained are then led separately to the terminals of
the dynamos which they have to excite. Assuming that two supply currents
having a quarter of period difference of phase are to be produced by means of two
separate dynamos. Fig. 5 shews diagrammatically at s' and ' the armatures of

page_text: 1
the two dynamos intended to supply the currents having the intensities A sin
2 πT and I, = A cos 2 π The return conductors ab are shown connected to
t
t
T
a common conductor. The producing of the exciting currents consists in a
connection in series of a bobbin of wire having a coefficient A of self induction and
a condenser of capacity or any other equivalent appliance. If currents of
1
are desired, the self induction A and the capacity I must be determined
frequency T
according to the formula =
T'
4 m² A
× 10° microfarads. One of the extremities of
this circuit, for example one of the condenser terminals is connected to the common
return a b. The other extremity, the one terminal of the self induction bobbin is
connected to a point P from which there are two leads, the one comprising a
condenser of capacity c₁ and leading to the end of the armature circuit s', the other
comprising a condenser of capacity c, and leading to the end of the armature
circuit s².
R the
If L₁ and L, express the coefficients of self induction of s₁ and
resistance of the circuit comprising the self induction bobbin A and the condenser
2 π
f
T
L
datamined h the formulm
It has been found both theoretically and practically that under these conditions
the dynamos having the circuits s's start themselves and have each all the
properties of the monophase machine above described, and that they also furnish
currents displaced by one quarter of a period.
Assuming now that there are to be produced k currents displaced relatively
by of a period. Fig. 6 indicates the arrangement for producing 3 alternating
currents differing respectively by of a period, but in what follows k may be
substituted for 3 in determining the arrangement for k currents.
The principal exciting organ consists of a connection in series of a condenser
having capacity I and a bobbin having a co-efficient of self induction A. If the
frequency is to be the condition to be observed is I =-
T³
4 TA
x 10 microfarads.
.
1
T⁹
The apparatus is completed by two transformers m n and p q having identical
primary circuits T₁ and T2. One end of the existing circuit is connected to a
point P whence proceed two leads, the one comprising a condenser of capacity c
the other a condenser of capacity c₂. The first lead connects to the entering end
of the primary circuit T₁, the other to that of the primary circuit T₂. The leaving
ends of the primary circuits connect to a common return leading to the other end
of the exciting circuit. R being the resistance of this exciting circuit and L the
apparent co-efficient of self induction of each of the primary circuits T₁ and T₂
which are supposed the same, the capacities c₁ and c, are determined by the

page_text: 3. The combination of self induction coils and condensers substantially as and
for the purpose set forth.
Dated this 25th day of July 1895.
ABEL & IMRAY,
Agents for the Applicant.