The space charge that surrounds a conductor in corona

A qualitative analysis of the nature of the space charge created about a conductor in corona, particularly with respect to relative magnitudes and polarities, rather than actual quantitative measurement, is described here. This work was the principal work on corona during the past year in the Ryan High-Voltage Laboratory. In tests with the arrangements of a wire and a plane, and of a wire and a cylinder, a decided rectifying effect was discernible in the space about the conductor in corona, in that that region was built up to a unidirectional potential above ground, the magnitude and polarity of this potential depending on the voltage applied. In both of these set-ups, this net rectification, which is evidently caused by some differential action entering into the ionization process, was of a positive sign at the start of corona, but changed over to negative as the voltage was raised. In a test made on two 1.1-in. diameter, parallel concentric strand copper conductors, 10 ft. apart, the space between them was found to have assumed a potential above ground when the conductors were in corona, the sign of this charge being negative at first, and then positive as the voltage increased. Tests were also carried out on a single brush, and on a rod fitted with “artificial” brushes. In a corona-loss curve taken on the two cable conductors it was found that at the same voltage at which the sign of the rectified space charge had reversed, there was a “break” in the curve. This “break” corresponded to the point above which Peek's quadratic law of corona holds, and below which he has suggested the entrance of a probability relation. A final field test was made at a span of the 220-kv. Pit River Lines of the Pacific Gas and Electric Co., in order to ascertain the magnitude and polarity of the charge built up about a high-voltage line in service. A negative polarity was found to be present as far down as 30 ft. below the conductors. Although the voltage was raised to 260 kv., the charge remained negative, indicating that the line at its normal 220-kv. potential was operating at a point on the corona-loss curve appreciably below that where the break occurs in the curve.