Transmission Line Design Mechanical Design of Spans With Supports at Unequal Elevations

The purpose of this paper is to derive a practical method of design based upon the catenary formulas for spans whose supports are not at the same elevation. It is furthermore intended completely to formulate the method for applying it to any cable which is suspended freely or is uniformly loaded, as well as for obtaining its characteristics after the temperature or loading conditions of the cable have changed. After a brief survey of the present need for more accurate methods of mechanical design of transmission line cables, the several formulas which are adapted to spans with supports at unequal elevations are given, and the method of using them is fully explained. All such special formulas are fully derived in the appendix. The first method given depends somewhat upon interpolated values from the symmetrical span data. A second pure interpolation method is next described which has the advantage of being shorter than the first as well as more accurate, since it depends upon fewer interpolated values from mathematical tables. The use of these two methods is then fully illustrated by the solution of three typical spans. Data for the cable used in symmetrical spans are first given, and from these the solution for the span with supports at unequal elevation is obtained. For the purpose of comparison the computations used in obtaining the desired values by each method are given in full for one of the spans chosen.