1923 Volume 43 Issue 415 Pages 79-96
The total self inductance for commercial power frequency of the aerial line with ground return is far greater than the value calculated by the principle of electric image. The experiments with commercial frequency tell that the voltage in the communication line induced electromagnetically by the neighbouring power line with ground return is far greater than the value calculated by the principle of electric image. These facts may be certainly due to the finite conductivity of eartb. K. W. Wagner had developed the theory of electric oscillation of parallel lines with the assumption equivalent to the principle of image, and obtanied the resalts that there exist travelling waves on each parallel line propagating with a velocity equal to the light velocity on both directions.
The author has developed the theory of the same problem for any value of the coefficients of magnetic induction and obtained the results that where there are n wires, n travelling waves of different propagation velocities exist on each wire in general, for the special case of symmetrical three phase line, which is dealt with special interest, the variety of velocity becomes two.
Thus for the symmetrical three phase line, there are two kinds of surge impedance, attention must be paid to this fact. As may be seen in the fundamental equation, the author did not consider the potential drop along the earth, somewhat contradictory to the supposition of the finite conductivity of earth. The validity of the theory must be checked with experiments on the actual transmission line, however, this theory can be applied without reserve to some kind of artificial transmission line. Artificial three phase power transmission line now under construction by the author at the Electrotechnical Laboratory is one example to which the author's theory is applicable.