Steel conductors for transmission lines

The electrical tests of some steel conductors of moderately large size have been published, and they indicate that there is an opening for the profitable use of steel cables on the branch lines of power systems of all voltages, in the same way that small steel conductors have already been used on branch lines at low voltages. Mechanical weakness or corona loss prohibits the use of small copper or aluminum conductors in many cases, and so steel becomes preferable. Steel cables will not generally be economical on main transmission lines, except for long spans, and for high altitudes where corona is excessive. They may be advisable as bare conductors for direct-current railway feeders. They deteriorate more rapidly than copper conductors. Steel cables for alternating current should be finely stranded and the different groups of wires should be spiraled in opposite directions. Fortunately, medium-priced grades of steel give better results with alternating current than some more expensive grades. The characteristic increase of resistance and reactance with increase of current or frequency may be valuable for limiting lightning and switching surges and short circuit currents. As there are large differences in electrical characteristics between different grades of steel, it is desirable that tests of medium priced steel cables manufactured in America be made and published, so that the data can be used in the designing of transmission lines.