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.