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.
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.