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.
| No. | Primary Circuit. | External Resistance of Secondary Circuit. | Secondary Circuit. | Efficiency. | ||||
|---|---|---|---|---|---|---|---|---|
| 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.