Corona Onset Voltage at 60 Hz and at High Frequency for an Isolated Cylindrical Monopole

Corona on electrified conductors (power lines, transmission lines, and antennas) is a significant source of electromagnetic interference to aircraft. The Townsend integral, which describes breakdown in low-frequency nonuniform fields, is derived from the electron continuity equation. Predictions of corona onset are made using published formulas for net ionization. Measurements of 60-Hz corona onset for an isolated cylindrical monopole are compared with predictions. A corona onset criterion, which describes breakdown in nonuniform radio-frequency fields, is also derived from the electron continuity equation. Measurements of corona onset at 300 MHz for the same isolated cylindrical monopole are compared with predictions. The results confirm that the derived breakdown criteria are good predictors of corona onset both at 60 Hz and 300 MHz for cylindrical geometries in the range 0.1 les rp les10 cmldrtorr. A discussion of the transition frequency between power frequency and high-frequency corona onset is also included.