Abridgment of methods used in investigating corona loss by means of the cathode ray oscillograph

Methods of employing the cathode ray oscillograph for investigation of corona loss are described. By deflecting the ray of cathode particles (electrons) in one direction within the tube by a voltage proportional to the applied voltage, and in a transverse direction by a voltage proportional to the current, a closed figure representative of the loss, is thrown upon the screen. Methods of obtaining photographic records of these figures and of calculating therefrom accurate values of the power expended are given. The instrument used is well adapted for this work. Power measurements of 0.1 watt can be measured with an accuracy of 1 per cent. From the volt-ampere cyclograms the characteristics of the positive and negative loss on the a-c. wave are readily observed. The instantaneous voltage of which the loss starts and the instantaneous values of the combined corona and capacity currents can be accurately determined. Measurements of the corona starting point and loss on various conductors check the laws of corona established by Mr. Peek in 1910. The formulas of “critical disruptive gradients” and “visual disruptive gradients” were closely checked. The loss was found to follow a quadratic above the visual critical corona voltage, ev. For cables and roughened conductors the excess loss below ev due to surface irregularities approximately follows the probability law. For smooth, polished conductors the loss suddenly jumps from zero to a definite value at ev and then follows the quadratic. The practical effect of the condition of the conductor surface is forcibly brought out by the following data measured on a 336,400-cir. mil cable at 63.5 in. spacing to neutral plane: