The Tesla High-Potential Conductor (Condensed Reprint)

In order to prevent loss by dissipation or interference by induction on line conductors carrying high-potential alternating currents, they have in some instances, such as at Deptford, London, been insulated and enclosed in a continuous conducting sheathing, which is connected with the ground by a good conducting path. The Electrical Engineer of New York states that, while conducing to the safety of the system, Mr. Tesla has found that the use of a conducting sheath or screen around the line conductors and well grounded, or even brought into proximity to external conductors. or large bodies, is attended by an actual, and generally a serious, loss of energy, which is the greater the greater the number of alternations and the higher the potential. He therefore maintains the sheath entirely isolated or connected directly or inductively to the ground, through a path which will practically prevent the passage of currents over it. He has also found that when a continuous isolated sheath or screen is employed, there is greater liability to loss of energy by inductive action; for. unless the sheath or screen be considerably shorter than the current waves passing in the conductor, E.M.F.'s will be set up between different points in the sheath, which will result in the passage between such points of induced currents. Mr. Tesla therefore divides up the sheath or screen into short lengths very much shorter than the wave lengths of the current used, so that the grounding of any one of such lengths or the approach thereto of a large body will result in an inappreciable loss, or at most a small local draining of the energy, while the tendency of currents to flow between different points in the sheath is effectually overcome. The function of the sheath as a static screen for preventing the dissipation of the electric energy, however, requires for its complete effectiveness an uninterrupted conducting partition or screen around the conductor. In the case of a sectional screen this is obtained by causing the ends of the insulated divisions or sections to overlap, and interposing insulating material between the overlapping portions. For transmitting currents of very high potential and very high frequency, Mr. Tesla provides between the sheath and the ground a path of very high ohmic resistance, or one containing a self-induction coil properly determined with respect to the existing conditions so that it will effect the desired result, or a condenser of very small capacity. In such cases the sheathing or screen for practical purposes may be regarded as isolated from the ground, since by the character of the connection employed no appreciable loss results from the passage of current from the sheath to the ground.