• Energy Research

The division of return stroke current among the arresters and groundings of two unenergized test distribution lines, one horizontally configured and the other vertically configured, was studied at the International Center for Lightning Research and Testing in Florida. The division of return stroke currents for the vertically configured line was initially similar to the division on the horizontally configured line: at the time the return stroke current reached peak value (after one microsecond, or so) the two closest arresters/grounds on both lines passed about 90% of the total current. However, the time during which the return stroke current flowed primarily through the closest arresters to the neutral conductor was significantly shorter on the vertically configured line. On that line, the arrester current was about equally divided among all four arresters after several tens of microseconds. The arrester current division as a function of time measured on the vertical line was successfully modeled using the published VI-characteristic, while the division on the horizontal line after some tens of microseconds was only successfully modeled if the residual voltage of the two arresters closest to the current injection point was reduced by 20%. Based on the triggered lightning current division observed on our line, the minimum energy absorbed in each of the two arresters closest to the strike point during a typical natural first stroke is estimated to be 40 kJ.

In this paper, a simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along a 25 or 21 mm radius, 2.2 km long single overhead horizontal wire, which simulates the experiment of Wagner et al. [1954]. The critical electric field on the surface of the 25 mm radius wire for corona initiation is set to E 0 =1.3, 2.1 or 2.5 MV/m, and E 0 =2.2 MV/m for 21 mm radius wire. The critical background electric field for streamer propagation is set to E cp =0.5 MV/m for positive voltage application and E cn =1.5 MV/m for negative voltage application. The FDTD-computed waveforms of surge voltage at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms.

Various parameters of lightning discharges will be reviewed. Both common negative and less frequent but potentially more destructive positive and bipolar flashes will be covered. Direct lightning current measurements on instrumented towers will be discussed. Properties of first and subsequent strokes will be compared. The average number of strokes per flash and multiple channel terminations on ground will be considered. Parameters of subsequent strokes in natural lightning will be compared to their counterparts in rocket-triggered lightning. New insights into the lightning processes gained from triggered-lightning experiments will be discussed.

This paper intends to relate high frequency earthing impedance measurements made on the earthing systems installed at Camp Blanding Florida to the sharing of current measured during triggered lightning tests at the facility.

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 Inoue's 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.

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 E 0 =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.

We present CiLIV (Circuit for Lightning Induced Voltage), a new tool for lightning induced voltage calculations. The tool can be integrated into power systems simulators, and is based on the theory proposed by Andreotti et al. (2001, 2009, 2013). The accuracy, stability and efficiency of the new tool has been demonstrated by comparison with other solutions/codes found in the literature and with experimental data.

A triggered-lightning experiment was conducted during Summer 2000 at the International Center for Lightning Research and Testing (ICLRT) in north-central Florida for the purpose of studying the lightning current division in an 829-m-long, 18-pole, three-phase plus neutral, unenergized, overhead distribution line equipped with six arrester stations. Eight lightning flashes containing a total of 34 recorded return strokes, as well as low amplitude, long duration steady currents, were artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique, and the flash currents were directed to phase C (one of the two outer conductors of the three-phase cross-arm-configured line). Six of the eight triggered lightning flashes caused damage to one of the two closest phase C arresters. In the case when no arrester was damaged or was not yet damaged by current in the flash, it is inferred that about 40% of the return stroke peak current and about 25% or more of the return stroke charge transferred in the first millisecond passed to the neutral conductor through each of the two closest arresters located about 70 m away on either side of the strike point. The bulk of the peak current then flowed from the neutral conductor to ground through the groundings of the two closest arresters. The charge transferred in the first millisecond from the neutral to the eight system groundings, six at arrester stations, and one at each of the two line-end poles, appears to be distributed inversely to the low-frequency, low-current grounding resistances. From our measurements of return stroke current division and in view of the available data on the currents of first strokes in natural lightning, we estimate that over half of natural first strokes would result in an arrester failure in our test distribution line, which is representative of some distribution lines in service, within about 450 /spl mu/s of the initiation of the first return stroke current flow, in the absence of flashovers and other alternative current paths that might be provided by transformers or underground cable connections to allow the stroke current to bypass the arrester. Additional first stroke current flow beyond about 450 /spl mu/s and currents associated with subsequent strokes and potentially other processes should further increase the likelihood of arrester damage.

The above-named article [ibid., vol. 28, no. 2, pp. 1213-1223, Apr. 2013] had an incorrect equation (11b). It is shown in the correct form here, using the same equation number as in the paper. All of the results in the article were obtained by using the correct equation and, therefore, are not affected.