The graphic solution of A-G. transmission line problems

The success of the series capacitor in increasing the load capacity, as well as improving the regulation of those a-c. transmission lines on which it has been tried,² promises to lead to its wide adoption. The high loading and excessive short-circuit currents entailed by the series capacitor have to be cared for by safety devices, and in order to be able to design and properly locate such devices, it becomes essential to predetermine the values of current and voltage at every point along the line. A step-by-step method is described for drawing the complete polar vector diagrams of current and voltage in an a-c. transmission line supplying a given load. Its chief novelty consists in the use of cellophane tissue instead of ordinary drawing paper. Such tissue is easily obtained commercially, as it is used chiefly for wrapping candy boxes. It is transparent, thin and flexible and takes ink well. The usual implements, such as scales, protractors, triangles and compasses, are unnecessary. The required vector scales, impedance triangles, and multiplying triangles are laid out in ink upon a sheet of squared paper mounted on a drawing board, and the vector diagram is produced on the superimposed celophane by tracing, the celophane sheet being shifted as required in determining successive points on the vector diagram. It is true that no step-by-step method is as accurate as the mathematical method, but the method described takes only some one or two per cent as much time as the mathematical method and with practise becomes as accurate as working conditions demand.