Tran Huu Thang

A Simplified Model of Corona Discharge on Overhead Wire for FDTD Computations

A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental con- figurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E0 = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E0 = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to Ecp = 0.5 MV/m for positive voltage application, and Ecn = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.

FDTD Simulation of Lightning Surges on Overhead Wires in the Presence of Corona Discharge

A simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along overhead wires with corona discharge. The FDTD computations simulate the experiments of Inoue and Wagner . In Inoues experiment, a 12.65-mm radius, 1.4-km-long overhead wire was employed, and in Wagner s experiment, a 21- or 25-mm radius, 2.2-km-long overhead horizontal wire was employed. The critical electric field on the surface of the 12.65-mm-radius wire for corona initiation is set to E0 = 1.4, 2.4, or 2.9 MV/m, and those for 21- and 25-mm-radius wires are set to E0 = 2.2 and 2.1 MV/m, respectively. The critical background electric field for streamer propagation is set to Ecp = 0.5 MV/m for positive voltage application and Ecn = 1.5 MV/m for negative voltage application. The FDTD-computed waveforms (including wavefront distortion and attenuation at later times) of surge voltages at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms. Also, the FDTD-computed waveforms of surge voltages induced on a nearby parallel bundled conductor agree fairly well with the corresponding measured waveforms.

FDTD Simulation of Insulator Voltages at a Lightning-Struck Tower Considering Ground-Wire Corona

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to the analysis of transient voltages across insulators of a transmission line struck by lightning. In the simulation, three 60-m towers, separated by 200 m, with one overhead ground wire and three-phase conductors are employed. The progression of corona streamers from the ground wire is represented as the radial expansion of cylindrical conducting region around the wire. On the basis of the computed results, the effect of corona discharge at the ground wire on transient insulator voltages is examined. The insulator voltages are reduced by corona discharge on the ground wire. The reduction of insulator-voltage peak due to the ground-wire corona is not very significant: the upper-, middle-, and lower-phase-voltage peaks are reduced by 15, 14, and 13% for a positive stroke with 50-kA-peak and 3-μs-risetime current, and those for the negative stroke with the same current waveform parameters are reduced by 10, 9, and 8%, respectively.

FDTD Simulations of Corona Effect on Lightning-Induced Voltages

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of lightning-induced voltages at different points along a 5-mm radius, 1-km long single overhead wire taking into account corona space charge around the wire. Both perfectly conducting and lossy ground cases were considered. FDTD computations were performed using a 3-D nonuniform grid. The progression of corona streamers from the wire is represented as the radial expansion of cylindrical weakly conducting (40 μS/m) region around the wire. The magnitudes of FDTD-computed lightning-induced voltages in the presence of corona discharge are larger than those computed without considering corona. The observed trend is in agreement with that reported by Nucci et al. and by Dragan et al ., although the increase predicted by our full-wave model (up to 5% and 9% for negative and positive lightning return strokes, respectively) is less significant than in their studies (up to a factor of 2) based on the distributed-circuit model with sources specified using the electromagnetic field theory. The disparity is likely to be related to the use of different charge-voltage diagrams, explicitly assumed by Nucci et al. and Dragan et al . and resulting from our FDTD model with corona in the present study. When corona is considered, there is a tendency for induced-voltage rise time to increase. It appears that the distributed impedance discontinuity, associated with the corona development on the wire, is the primary reason for higher induced-voltage peaks and longer voltage rise times, compared to the case without corona.

FDTD Computation of Lightning-Induced Voltages on Multiconductor Lines With Surge Arresters and Pole Transformers

In this paper, lightning-induced voltages on multiconductor lines with surge arresters and pole transformers have been computed using the 3-D finite-difference time-domain method. This method uses a subgrid model, in which spatial discretization is fine (cell side length is 0.5 m) in the vicinity of overhead wires and coarse (cell side length is 5 m) in the rest of the computational domain. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. The 1-cm-radius overhead conductors are represented by placing a wire having an equivalent radius of about 0.12 m (≈ 0.23 × 0.5 m) in the center of an artificial rectangular prism having a cross-sectional area of 1 m × 1 m (2 cells × 2 cells) and the modified (relative to air) constitutive parameters: lower electric permittivity and higher magnetic permeability. The computed lightning-induced voltage waveforms agree reasonably well with the corresponding ones measured in the small-scale experiment of Piantini et al. (2007).

Lightning-Induced Voltages in the Presence of Nearby Buildings: FDTD Simulation Versus Small-Scale Experiment

In this paper, we have computed lightning-induced voltages on overhead distribution lines in the presence of nearby buildings using the 3-D finite-difference time-domain method. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. It appears that the presence of nearby buildings causes reduction of lightning induced voltages, as expected. The observed trend is in general agreement with that reported from the small-scale experiment by Piantini et al.

FDTD computation of lightning surges on overhead wires in the presence of corona discharge

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analyzing a lightning surge propagating along a 12.65-mm-radius and 1.4-km long overhead horizontal wire, which simulates the experiment of Inoue (1983). The critical electric field on the surface of the 12.65-mm-radius wire for corona initiation is set to E0 = 1.4, 2.4 or 2.9 MV/m. The critical background electric field for streamer propagation is set to Ecp = 0.5 MV/m for positive voltage applications, and Ecn = 1.5 MV/m for negative voltage applications. The FDTD-computed waveforms of surge voltage at different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms.

FDTD simulation of back-flashover at the transmission-line tower struck by lightning considering ground-wire corona

In this paper, we have simulated back-flashover at transmission line tower struck by lightning in the presence of corona emanated at the ground wire. In the simulations, three two-circuit 60-m high towers, separated by 400 m, with two overhead ground wires, and six phase conductors (two three-phase circuits) are employed. A simplified (engineering) model of corona discharge is applied to the analysis of transient voltages across insulators of transmission line. Back-flashover is assumed to occur at upper-, middle-, or lower phase. On the basis of computed results, the effect of corona space charge emanated from ground wires on transient voltages across insulators in the presence of back-flashover is discussed.

2D FDTD simulation of LEMP propagation considering the presence of conducting atmosphere

In this paper, we have computed vertical electric field Ez, and azimuthal magnetic field Hφ at different distances from the vertical lightning channel using the finite-difference time-domain (FDTD) method in the 2D cylindrical coordinate system. The presence of conducting atmosphere up to 110 km above ground level was considered. The fields are computed on the ground surface at distances ranging from 50 to 500 km. One-hop and two-hop skywaves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights.

FDTD computations of lightning-induced voltages in the presence of nearby buildings

In this paper, we have computed lightning-induced voltages on distribution lines in the presence of nearby buildings using the 3D finite-difference time-domain (FDTD) method. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. It appears that the presence of nearby buildings cause reduction of lighting induced voltages, as expected. The observed trend is in general agreement with that reported from the small-scale experiment by Piantini et al. (2007).