Corona investigation on an artificial line

Accompanying corona on a transmission line, there has been found, in several cases, an appreciable increase in the line charging current over that indicated by the usual formula. This has been taken to indicate an increased line capacitance resulting from the presence of the corona envelope about the conductors, and has, for this reason, come to be described as the extra-capacity effect of corona. This explanation, by an envelope, however, has not been entirely satisfactory, and the question has arisen as to whether the current increase could not have been equally as well attributed to the current and voltage harmonics which the corona introduces. The paper describes an investigation made of this extra-capacity effect on an artificial transmission line using artificial corona. In avoiding, by means of this method, the glow discharge of real corona, all envelope effects were eliminated. The operation of the artificial corona is described, and the results given of the tests which were made in checking its characteristics against those of real corona. By means of the artificial corona is shown that it is possible to obtain the extra-capacity effect of corona without having present an ionized envelope. The explanation is offered that at least the larger portion of this effect found on transmission lines under corona conditions is apparent only; that it is a result of the approximate method by which the line capacitance is calculated, and the increased admittance which the line offers to currents of harmonic frequencies. The effect of corona leakage in altering potential rise on an open line is shown by representative voltage distribution curves taken on an artificial line with and without the corona leaks operating. From a comparison of these curves it appears that the leakage of corona plays a predominant part in the establishment of the resultant voltage, the harmonics caused by the corona in no case producing unusual resonance effects or extra-potential rises. This is important largely for the indication it gives that the present methods of predetermining voltage distribution on open lines for corona conditions are accurate within the limits of engineering accuracy. Qualitative results are given showing the effectiveness of corona leakage in reducing traveling waves such as result from switching operations. Two oscillograms of the same transient are shown, one taken with the corona leaks operating and the other without. The much shorter duration of the transient in the former case is evidence of the corona's effectiveness in absorbing the energy of the disturbance.