4. The proportioning of the coils, so that the weight
of metal in each is the same.
Seeing this, it must be thought that this gentleman either does or
will not, understand the subject. Then if Gaulard has succeeded
with his apparatus in obtaining some advantages as proposed in the
above-mentioned clauses, Nos. 1 and 2, these advantages can be obtained
to a much higher degree with non-polar transformers. This has been
proven by Prof. Ferraris.[6]
The improvements mentioned under Nos. 3 and 4 are only to be
attained with bi-polar transformers after difficult and otherwise
disadvantageous arrangements; for instance, the combination of the
primary and secondary wires in a common cable, or, when the coils
consist of ribbon wire, by the winding of the one inside the other.
With non-polar transformers these improvements are already inherent.
The Fuller transformer was just as much without poles as two horseshoe
magnets are, with their like poles laid together.
In all these systems with series connection of the transformers, the
intensity of the current in the primary circuit must be held constant
in order that it may be possible for the induction apparatus to
maintain the secondary electromotive force constant. Notwithstanding
this, constancy was not attained, but only one cause of the variations
annulled. Another cause of the variations of the difference of
potential at the secondary terminals of the coil still remained; this
was the loss of potential due to resistance and self-induction, which
increased with the load. The electromotive force of the secondary, and
therefore of the primary coils, accordingly increases as the current
in the secondary decreases. When no secondary current is flowing, the
electromotive force in the primary and secondary coils is a maximum. We
have consequently this disproportion that the smaller the output of the
apparatus the greater the energy consumed. With the secondary circuit
open and a constant exciting current, the energy used could be as much
as ten times as great as under full load.
The disadvantages of this system are apparent; for, putting aside the
loss of energy arising from the disproportion between produced and
consumed energy, each change of load on the secondary circuit exerted
a great influence on the primary circuit, and again on the secondary
circuits of the other coils in the main circuit.
All the transformer systems already described were intended, as we see,
for subdividing the current, and as fitting therefor we find the series
method of connection universally brought forward. With this method,
owing to a rise in electromotive force which was dangerous to the
lamps, &c., when only a part of those in the secondary circuit were
extinguished, it was compulsory either to run the induction coil
fully loaded or quite empty. Thus, when the number of lamps or other
devices in use was varied, a regulation of the current strength and
uniform working was either quite impossible, or only partly possible
by unreliable and incomplete mechanical means. On this account no one
succeeded with this method in carrying out a rational distribution
of current by means of induction coils such as are required by the
widespread demands for electric current from a central station.
The first to point out the disadvantages of the series method of
connection was Rankine Kennedy, who had devoted himself wholly to the
study of induction apparatus. These disadvantages he published in an
article in the “Electrical Review” of 9th June, 1883. At the end of
this article we find the interesting statement that transformers,
when not connected in the primary circuit in series, as had been
usual till then, but in parallel, form a self-regulating system of
current distribution. Rankine Kennedy expresses this in the following
words:—“In parallel arc, however, the secondary generator is a
beautiful self-governing system of distribution.” At the same time,
however, his article affords proof that the author then possessed only
a limited comprehension of the physical facts concerned, because he
maintained, for instance, that the introduction of an induced counter
electromotive-force in the circuit of an alternating current dynamo
might constitute a means of regulation without loss of energy; however,
it might be allowed, that he meant by these words one of these elements
which must be present in a really rational system of distribution with
the use of transformers, if it were not the case that at that time he
was not aware both of the properties of transformers suiting them for
such a connection as well as those which make them self-regulating in
a system of distribution. Above all this he had at that time never
thought of a transformer in the sense, the word is used to-day, that
is, as an induction apparatus, which converts high into low tension
currents. This is quite clear, as is seen from the end of the sentence
before cited, as he says, “But what about the size of conductors for
such a system? Prodigious!” Kennedy thought to all appearance that
the parallel connection of transformers made possible self-regulation
in the same manner as the simple direct parallel connection of
incandescent lamps. While at the same time he imagined that on account
of the small resistance of each coil the resistance of the net of
leads must nearly vanish, therefore he concluded that the parallel
connection of such induction apparatus as he had in his mind’s eye was
impracticable.
The apprehension of Kennedy’s ideas, as we have here stated, finds
direct confirmation from the leading article in the “Electrical Review”
of 9th June, 1883. At the end of this leader the editors say, that “Mr.
Kennedy’s apparatus is an induction coil pure and simple.” “Messrs.
Gaulard and Gibbs will scarcely deny, nor can they deny, that the
action of this particular construction of the coil is identical with
that of his.” In this sentence it is distinctly stated that the
construction of Kennedy’s induction apparatus is identical with that of
Gaulard and Gibbs’. Kennedy accepted this statement in silence; if it
had been otherwise, he would have protested in his next appearance in
print.
In order to make possible the connection of transformers in parallel,
the advantages of which it may be said Kennedy had augured, there
was still much wanting. Above all there was wanting the idea of a
transformer as meant at present, and an exact knowledge of its action.
F. Geraldy has expressed himself very suitably upon this point in the
introduction to his report upon the trials made with the system of
Messrs. Gaulard and Gibbs.[7]
“La distribution de l’électricité comporte la solution
d’un grand nombre de problèmes. Il ne suffit pas
de se décider en principe et lorsqu’on a choisi la
distribution en quantité (en supposant même, que
l’un des procédés puisse être appliqué d’une façon
exclusive, ce qui n’est pas certain), lorsqu’on
a trouvé le moyen de régler le générateur et les
recepteurs conformément au mode choisi, il reste encore
à lever quantité de difficultés, a créer et disposer
beaucoup d’organes auxiliaires.” Geraldy explained
distinctly that it was not sufficient to determine
only the method of connection, but there were still
a considerable number of obstacles to be surmounted
before the object could be attained.
It has been a costly lesson, before the properties of transformers were
known, which make them form a self-regulating system. Even in the year
1884 do we still find Messrs. Gaulard and Gibbs on the same false track
as previously. It was in the Turin Exhibition where Messrs. Gaulard and
Gibbs carried out their system upon a large scale, and where they also
succeeded in gaining the interest of technical circles, and arousing
general attention.
The transformers installed by Messrs. Gaulard and Gibbs in the Turin
Exhibition were protected by the German patent, No. 28947, and
this time again their transformers were wound with equal primary
and secondary coils. The construction of the apparatus, as already
explained, made it a necessary condition that the transformers be
connected in series, because only by this means could the high tension
current be utilised. It was a necessary corollary of this method of
connection that the converting of the high potential of the primary
circuit into low potential, was performed, not by the ratio of the
number of turns in the coils of the transformers, but in a certain
manner by the subdivision of the electromotive force in the circuit.
[Illustration: FIG. 22.]
The special construction of the transformers used in the Turin
Exhibition differed from the older apparatus in so far that both coils
were formed of stamped out circular copper discs, which were soldered
together by projecting teeth. The insulation was made of stamped-out
paper discs. Both spirals were wound between one another. The building
up of such coils was effected in the following manner (see Fig. 22A):—A
red copper disc was first placed on the core, then insulation, upon
this a black copper disc, then again a red copper disc, and so on. Like
colours of copper discs were then soldered together at the projecting
teeth. In this manner there were produced two spirals running parallel
with one another, there only being one layer of coils. The employment
of such ribbon conductors had some advantages, namely, good use of the
space at disposal for coils, and rapid cooling through the projecting
teeth. They had, also, disadvantages, the chief of which was, that the
conductors were of bare metal, so that a fault in insulation could
easily occur.
[Illustration: FIG. 22A.]
In fact, several faults in the transformers in Turin did arise from
this cause, the action of the coils being disturbed. Further attempts
with similar coils were made, the station houses of Turin, Venaria,
and Lanzo being lit for five consecutive hours. The circuit was about
80 kilometres long, the main lead being of chrombronze wire of 3·7 mm.
diameter. At Turin there were 34 Edison lamps of 16 c.p. each, and a
sun arc lamp; at Lanzo there were nine Bernstein lamps, 16 Swan lamps,
a sun arc lamp, and two Siemens’ arc lamps. In the exhibition itself,
there were nine Bernstein lamps, nine Swan lamps, and a sun arc lamp.
In the Figaro Kiosk nine Swan lamps were fed from a small transformer.
As already related, the trials of Messrs. Gaulard and Gibbs’ system at
Turin had aroused in the widest circles the liveliest interest, and,
consequently, the errors of the system soon became public. Thus we find
in the technical literature of that time influential voices raised
against the system, and pointing out its disadvantages.
Among others, Prof. Colombo read a paper during the course of the
National Exhibition at Turin, the subject being the system of Gaulard
and Gibbs. While doing sufficient justice to the good points of the
system, he also said that although it solved the problem of carrying
the electric current to great distances, it was in no way what it was
represented to be, and what it should be: a system of distribution
allowing the electric current from a distant central station to be led
to meet the demands of any kind of consumer without any one of these
interfering with the supply of current to any other. He characterised
these drawbacks sharply, and very suitably, by the remark, that in the
Gaulard and Gibbs system, each consumer drew properly his supply of
current from his transformer, and not from a common network of leads
always self-regulating, as is the case in every large installation
with continuous currents. Prof. Colombo satisfied himself with this
reference to its disadvantages, mentioning also what should be striven
after to make the system a perfect one, saying that the ideal
electric lead system was one combining the advantages of the Edison
central-station with that of Gaulard and Gibbs.
Prof. Colombo confined himself to these hints, and he must acknowledge
that the means leading to the attainment of this purpose remained still
to be found out.
The reproduction of this lecture by Prof. Colombo is placed before an
article by Depréz in “La Lumière électrique,”[8] in which latter the
system of Gaulard and Gibbs is strongly criticised. Depréz showed that
that system can have no claim to be new. He points also to the wants
of the system, especially that of self-regulation, stating that the
means remain still to be discovered, which would make possible the
self-regulation of a system of distribution with transformers. He also
says that Gaulard’s system of distribution had not solved this problem,
and therefore could not be held to be practically useful.
We find the same view represented in an article by H. Roux,[9] where
he points to the enormous fluctuations which take place when the
resistance in the secondary circuit is altered. Some of the figures
vouching for his opinion we shall now reproduce. They were taken by M.
Pietro Uzel, in Turin, in an observational way.[10]
The observations are only quoted so far that the Watts Δ I at the
secondary terminals are still increasing; were they continued further
the damning fact would reveal itself that as the power put in
increased, the power given out would approach zero.
Taking account of these fluctuations, it is not possible to see how, as
Mr. Roux says with justice, a distribution of current by this system
can be made in an efficient manner. Mr. Gaulard in his reply, virtually
assents to this article, but adds, that these variations could be
prevented, if the cores of the transformers be shifted either by hand
or automatically. Both methods would be expensive, and, besides, the
automatic regulation would be unreliable.
───┬───────────────────┬──────────┬───────────────────┬───────────
│ │ External │ │
│ │Resistance│ │
No.│ Primary │ of │ Secondary │Efficiency.
│ Circuit. │Secondary │ Circuit. │
│ │ Circuit. │ │
───┼─────┬─────┬───────┼──────────┼─────┬─────┬───────┼───────────
│ Δ │ I │ I Δ │ W. │ Δ │ I │ I Δ │ Δ
1 │ 23·4│12·13│ 283·84│ 1·24 │ 15·0│12·02│ 180·30│ 63·52
2 │ 31·4│12·13│ 380·88│ 2·00 │ 24·0│12·00│ 288·00│ 75·62
3 │ 53·0│12·13│ 642·89│ 3·80 │ 45·0│11·83│ 532·35│ 82·81
4 │ 70·0│12·13│ 849·10│ 5·50 │ 65·0│11·75│ 762·45│ 89·80
5 │ 93·0│12·13│1128·09│ 7·53 │ 87·0│11·58│1007·46│ 89·31
6 │107·0│12·13│1297·91│ 9·00 │102·0│11·31│1153·62│ 88·88
7 │126·0│12·13│1518·38│ 10·60 │119·0│11·13│1324·77│ 86·66
8 │145·0│12·13│1758·85│ 12·60 │138·0│10·95│1511·10│ 85·35
9 │159·0│12·13│1928·67│ 14·15 │156·0│10·76│1678·66│ 87·03
───┴─────┴─────┴───────┴──────────┴─────┴─────┴───────┴───────────
It was at once recognised by all those interested in the subject,
that this system made possible a subdivision, but by no means a
distribution of current.
Before proceeding further with the history of the development of the
transformer, let us for a little while take up the question, what
conditions are necessary for a practical and rational system of
current distribution by means of transformers. As we have already
explained in another part of this paper, the method of parallel
connection, i.e., a system in which the difference of potential is
held constant, is alone suitable. Depréz maintained in his time that
the difference of potential between the terminals of the source of
current must be kept constant. Should the distribution be made on this
principle, the resistance of the network of leads must be very small,
in order that with full load only a very small loss of electromotive
force may take place in the leads. In the indirect system of current
distribution, consequently, the tension at the secondary terminals of
the transformers must also be maintained constant.
The question is now before us, “In what manner must the primary
electromotive force vary to effect this?” Consider an iron core,
having on two different parts round it, two rings of wire. This iron
core may now be magnetised by bringing near to it in the line of
its axis a permanent magnet. On drawing the latter quickly away, an
electromotive force will be momentarily produced in both the wire
rings, and the electromotive force will be proportional to the number
of the disappearing lines of force. This number, in consequence of the
dispersion of the lines of force, will be very different at different
parts of the magnetised core. The induced electromotive forces in the
windings of the wire will also be different. The equality of these
electromotive forces, which is so important, can only be attained if
all the windings are in relatively the same position with regard to the
magnetic field. The circuits of both coils being closed, the one having
a current flowing through it, the other through a suitable resistance,
besides the condition mentioned in the last sentence, another must be
fulfilled; this is, the internal resistance must be practically zero,
i.e. the difference of potential between the terminals shall equal to
all intents and purposes the total electromotive force.
We have now to examine how far the already observed constructions
of transformers fulfilled these demands. A transformer in which the
windings lie relatively in the same position to the magnetic field can
quite well be bi-polar. All that is necessary for this is that the
coils be wound on to the core next to one another; this is most simply
managed in a transformer having a ratio of 1:1. This law was first
determined by Maxwell. The apparatus of Strumbo shows such a method of
winding already carried out.
Thus it may be seen that of bi-polar transformers, those which, with
regard to the constancy of the secondary tension, are most suitable,
are quite useless on account of their ratio being 1:1, although they
are destined for the series method of connection.
The connection of proper transformers in parallel can only be made
with such apparatus as, notwithstanding their ratio of transformation,
possess windings having the same relative position to the magnetic
field—this is only the case with non-polar transformers. Besides this
quality of non-polar transformers, their magnetic resistance is so low
that the condition of very low internal resistance is easily fulfilled.
The following conditions of a self-regulating and economical system
of current distribution with transformers result, therefore, from the
foregoing explanations:—
1. The generator of current must give a great
difference of potential as constant as possible at the
terminals of the transformers, and also independent of
the number fed.
2. The transformers must convert the current of
high electromotive force into a current of such
electromotive force as may be desired. The transformers
must have a closed magnetic circuit (that is, they
must be poleless), in order that all the primary and
secondary turns shall possess, relatively to the
magnetic field, a like position, also in order that the
resistances of the primary and secondary coils shall
be so small that they cause practically no loss of
electromotive force.
Through the fulfilment of both these conditions, it is rendered
possible to maintain the secondary tension constant by maintaining
the primary tension constant, indifferently whether it is regulated
automatically or by hand. To suit this, the transformers must also be
arranged into distributive stations of the second order, and derived in
parallel from the main leads.
[Sidenote: Zipernowsky, Déri, Bláthy, 1885.]
In May, 1885, a system of current distribution meeting all the
just-mentioned requirements was publicly brought out, giving an
illustration of a truly self-regulating system of current distribution.
This was the system of Zipernowsky, Déri, and Bláthy.
The first two patents concerning this system date from 18th February,
1885, and are entitled, “Improvements in the means for the regulation
of alternating electric currents,” No. 34,649, by Carl Zipernowsky
and Max Déri, of Budapest; “Improvements in the distribution of
alternating currents,” No. 33,951, by Max Déri, of Vienna. The third
patent is dated 6th March, 1885, and is entitled, “Improvements in
induction apparatus for the purpose of transforming electric currents,”
No. 40,414, by Carl Zipernowsky, Max Déri, and Otto Titus Bláthy, of
Budapest.
The system described in these three patents was immediately afterwards
brought forward in the three exhibitions of Budapest, Antwerp, and
London (Inventions Exhibition), arousing in technical circles a general
and well-earned attention.
In the patent documents as well as in the earliest[11] articles in the
journals concerning the system, two special forms of transformers are
described, viz. that consisting of an iron core with the wire outside,
and, secondly, that consisting of copper coils surrounded by iron wire.
The transformers shown in Figs. 24 to 28 belong to the last of these
classes, that in Fig. 23 to the first. The fundamental principle upon
which all these transformers are constructed is that the subdivisions
of the iron core run perpendicularly to the copper wires. Transformers
such as are shown in Fig. 25 having a ring-shaped iron core wound with
copper wire at first employed, later the inventors used in preference
the form represented in Fig. 23.
[Illustration: FIG. 23.]
In all these forms the principle is generally adhered to, that the
magnetic resistance and the exciting power possess for each part of the
length of the magnetic circuit the same value, and thus the formation
of poles with the resulting dispersion of the lines of force is avoided.
[Illustration: FIG. 24.]
This system procured for itself universal recognition, but especially
in the Budapest Exhibition. There several exhibits within a radius
of 1,300 metres were lit from a common central station. The several
circuits were quite independent of one another, and lamps could be
extinguished or lit in any one of them without anywhere producing a
change in the intensity of the light, which could be perceived.
[Illustration: FIG. 25.]
[Illustration: FIG. 26.]
[Illustration: FIG. 27.]
[Illustration: FIG. 28.]
[Illustration: FIG. 29.]
It was, therefore, in the year 1885 that the problem of current
distribution by means of transformers was solved in a truly practical
manner. The ideas which led the inventors to this thoroughly successful
solution were then so unknown to practical and theoretical electricians,
that it was long ere they were understood and appreciated. Even in
February, 1886, such an electrician as Prof. Forbes maintained in
his Cantor Lectures that the parallel connection of transformers was
quite impracticable. He believed, namely, that a connection such as
shown in Fig. 29 was useless, because the difference of potential
at the generator diminished from the machine outwards, but that a
connection such as shown in Fig. 30 must be used. According to him,
in a direct system of distribution each lamp should have a separate
lead, and having regard to the great number of leads which would thus
be necessary, he concluded that the series method of connection was the
right one. One would suppose that Prof. Forbes was not aware of the
weighty disadvantages of this method. However, that was not the case.
He proposed, that with series connection the strength of current should
be kept constant, and that each transformer should have an especial
regulating apparatus—the raising or lowering of the core; which, by the
way, is an arrangement impracticable in a well designed transformer.
Such a regulating apparatus has lately been made automatic.
[Illustration: FIG. 30.]
“This is,” says Prof. Forbes, “the last triumph, which after a series
of troublesome experiments has brought us year after year nearer to the
solution of the difficulties.” “I am not in a position to explain here
the _modus operandi_,” he says further, “but I have seen the apparatus
working very satisfactorily.”
[Illustration: FIG. 31.]
This apparatus has up till now not become known. The assertion that the
troublesome experiments had brought us year after year nearer to the
solution of the difficulties, is quite inappropriate. Just the opposite
is the case; they have taken us year after year further away from the
solution, until at last all was thrown overboard and a new commencement
made.
Profs. Rühlmann[12] and Esson[13] also gave vent to their opinions
against the connection of transformers in parallel. In a like manner
Messrs. Gaulard and Gibbs for some time after the Zipernowsky-Déri
system was known pleaded for their own method of connection, until
at last they were obliged, on account of the unpleasant experiences
at the Grosvenor Gallery in London, to adopt the system of parallel
connection, which they then at once employed at Tours.
There were, up till very lately, still many electricians who did not
perceive the advantages of parallel connection, just for the simple
reason that they were ignorant of the properties of the non-polar
transformer, suiting the parallel system of connection for a rational
system of distribution. Especially the one property of transformers
remained unknown to the literature devoted to the subject up to the
year 1885, namely, that in transformers properly constructed the
relation between the primary electromotive force and that of the
secondary, remains unaltered notwithstanding any variations in the
current taken out; also that if the primary electromotive force be kept
constant the secondary would likewise remain constant, provided the
transformer be connected in parallel.
It had taken 30 years, until at last the way was found leading to the
desired result. We have already superabundantly explained that this
direction was essentially different from that taken by all electricians
until after Gaulard’s time; that not only the methods of connection,
disposition, and regulation of the system, but also the construction of
the transformers themselves had to be quite departed from, and
apparatus constructed which obeyed totally other laws to those of the
earlier forms.
If indeed earlier inventors proposed for other purposes
magnetically-closed induction coils, the fame due to the birth of
proper non-polar transformers, in which the whole of the primary and
secondary turns have a like position relatively to the magnetic-field,
first invented, carried out, and combined into a self-regulating system
of current distribution, belongs undoubtedly to Messrs. Zipernowsky,
Déri, and Bláthy.
It would have been thought that after the direct distribution of
current to glow-lamps had taken up a determined position, it would
not have been difficult to discover a self-regulating system of
distribution with transformers. However, the fact shows this was
not the case, for after the Edison lighting system was long known,
we find such electricians as Haitzema Enuma, Gaulard, and Kennedy,
experimenting with the series system of connection; indeed the last of
these even deters his colleagues from the attempt to run transformers
in parallel, because he openly held the opinion that this method of
connection was impracticable.
We have here the development of current distribution by means
of transformers, as it completed itself in Europe. The American
electricians however, made the matter somewhat easier. They quietly
waited until the invention gave useful results in Europe, and then
simply imported it.
The field to-day belongs to the parallel method of connection, and
after the installation in the alkali works at Aschersleben was
destroyed by flooding, there only remains a single installation with
series connection, as far as we know; this is that which was fitted
up in Tivoli near Rome in the year 1886. This installation however,
serves only to feed an invariable number of street-lamps, and can
therefore have no claim to the designation of an installation for the
distribution of electric currents by means of transformers.
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,
STAMFORD STREET AND CHARING CROSS.