Edison, His Life and Inventions [346]
circuits of the approximate potential to operate them.
Briefly stated, the principle involved in the three-wire system is to provide main circuits of double the standard potential, so as to operate standard lamps, or other translating devices, in multiple series of two to each series; and for the purpose of securing independent, individual control of each unit, to divide each main circuit into any desired number of derived circuits of standard potential (properly balanced) by means of a central compensating conductor which would be normally neutral, but designed to carry any minor excess of current that might flow by reason of any temporary unbalancing of either side of the main circuit.
Reference to the following diagrams will elucidate this principle more clearly than words alone can do. For the purpose of increased lucidity we will first show a plain multiple-series system.
In this diagram G<1S> and G<2S> represent two generators, each producing current at a potential of 110 volts. By connect- ing them in series this potential is doubled, thus providing a main circuit (P and N) of 220 volts. The figures marked L represent eight lamps of 110 volts each, in multiple series of two, in four derived circuits. The arrows indicate the flow of current. By this method each pair of lamps takes, together, only the same quantity or volume of current required by a single lamp in a simple multiple-arc system; and, as the cross-section of a conductor depends upon the quantity of current carried, such an arrangement as the above would allow the use of conductors of only one-fourth the cross-section that would be otherwise required. From the standpoint of economy of investment such an arrangement would be highly desirable, but considered commercially it is impracticable because the principle of independent control of each unit would be lost, as the turning out of a lamp in any series would mean the extinguishment of its companion also. By referring to the diagram it will be seen that each series of two forms one continuous path between the main conductors, and if this path be broken at any one point current will immediately cease to flow in that particular series.
Edison, by his invention of the three-wire system, over- came this difficulty entirely, and at the same time conserved approximately, the saving of copper, as will be apparent from the following illustration of that system, in its simplest form.
The reference figures are similar to those in the preceding diagram, and all conditions are also alike except that a central compensating, or balancing, conductor, PN, is here introduced. This is technically termed the "neutral" wire, and in the discharge of its functions lies the solution of the problem of economical distribution. Theoretically, a three- wire installation is evenly balanced by wiring for an equal number of lamps on both sides. If all these lamps were always lighted, burned, and extinguished simultaneously the central conductor would, in fact, remain neutral, as there would be no current passing through it, except from lamp to lamp. In practice, however, no such perfect conditions can obtain, hence the necessity of the provision for balancing in order to maintain the principle of independent control of each unit.
It will be apparent that the arrangement shown in Fig. 2 comprises practically two circuits combined in one system, in which the central conductor, PN, in case of emergency, serves in two capacities--namely, as negative to generator G<1S> or as positive to generator G<2S>, although normally neutral. There are two sides to the system, the positive side being represented by the conductors P and PN, and the negative side by the conductors PN and N. Each side, if considered separately, has a potential of about 110 volts, yet the potential of the two outside conductors, P and N, is 220 volts. The lamps are 110 volts.
In practical use the operation of the system is as follows: If all the lamps were lighted the current would flow along P and through each pair of lamps to N, and so back to the source
Briefly stated, the principle involved in the three-wire system is to provide main circuits of double the standard potential, so as to operate standard lamps, or other translating devices, in multiple series of two to each series; and for the purpose of securing independent, individual control of each unit, to divide each main circuit into any desired number of derived circuits of standard potential (properly balanced) by means of a central compensating conductor which would be normally neutral, but designed to carry any minor excess of current that might flow by reason of any temporary unbalancing of either side of the main circuit.
Reference to the following diagrams will elucidate this principle more clearly than words alone can do. For the purpose of increased lucidity we will first show a plain multiple-series system.
In this diagram G<1S> and G<2S> represent two generators, each producing current at a potential of 110 volts. By connect- ing them in series this potential is doubled, thus providing a main circuit (P and N) of 220 volts. The figures marked L represent eight lamps of 110 volts each, in multiple series of two, in four derived circuits. The arrows indicate the flow of current. By this method each pair of lamps takes, together, only the same quantity or volume of current required by a single lamp in a simple multiple-arc system; and, as the cross-section of a conductor depends upon the quantity of current carried, such an arrangement as the above would allow the use of conductors of only one-fourth the cross-section that would be otherwise required. From the standpoint of economy of investment such an arrangement would be highly desirable, but considered commercially it is impracticable because the principle of independent control of each unit would be lost, as the turning out of a lamp in any series would mean the extinguishment of its companion also. By referring to the diagram it will be seen that each series of two forms one continuous path between the main conductors, and if this path be broken at any one point current will immediately cease to flow in that particular series.
Edison, by his invention of the three-wire system, over- came this difficulty entirely, and at the same time conserved approximately, the saving of copper, as will be apparent from the following illustration of that system, in its simplest form.
The reference figures are similar to those in the preceding diagram, and all conditions are also alike except that a central compensating, or balancing, conductor, PN, is here introduced. This is technically termed the "neutral" wire, and in the discharge of its functions lies the solution of the problem of economical distribution. Theoretically, a three- wire installation is evenly balanced by wiring for an equal number of lamps on both sides. If all these lamps were always lighted, burned, and extinguished simultaneously the central conductor would, in fact, remain neutral, as there would be no current passing through it, except from lamp to lamp. In practice, however, no such perfect conditions can obtain, hence the necessity of the provision for balancing in order to maintain the principle of independent control of each unit.
It will be apparent that the arrangement shown in Fig. 2 comprises practically two circuits combined in one system, in which the central conductor, PN, in case of emergency, serves in two capacities--namely, as negative to generator G<1S> or as positive to generator G<2S>, although normally neutral. There are two sides to the system, the positive side being represented by the conductors P and PN, and the negative side by the conductors PN and N. Each side, if considered separately, has a potential of about 110 volts, yet the potential of the two outside conductors, P and N, is 220 volts. The lamps are 110 volts.
In practical use the operation of the system is as follows: If all the lamps were lighted the current would flow along P and through each pair of lamps to N, and so back to the source