Modeling of corona discharge on a transmission line conductor struck by lightning for FDTD calculations

We have modeled corona discharge from an overhead wire struck by lightning for surge and electromagnetic-pulse calculations using the finite-difference time-domain (FDTD) method. The radial progression of corona discharge from the wire is represented as the radial expansion of conducting region whose conductivity is several tens of micro Siemens per meter. The critical electric field on the surface of a 5-mm-radius wire for emanating corona is set to E₀=1.8 or 2.7 MV/m. The critical electric field at the boundary of radial corona sheath is set to E⁺_c=0.5 MV/m for positive voltage application, and E^-_c=1.5 MV/m for negative voltage application. The calculated waveform of radial corona-discharge current agrees well with the corresponding waveform measured by Noda. Also, the calculated relation between the total charge (charge deposited on the wire and emanated corona charge) and applied voltage (q-V curves) agrees well with the corresponding measured one. Further, the expected increase of coupling between the energized wire and another one nearby due to corona discharge is well simulated.