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The results of experimental observations and mathematical modeling of corona formation on the tips of grounded rods are presented as a function of their tip height, curvature radius, the magnitude and polarity of the applied electric field producing corona. The investigations demonstrate that corona current depends on the active volume of zone in which electric field strength exceeds the breakdown criteria for air. The mathematical model was verified with the experimental data, enabling dependence of corona current on rod tip height, tip radius and applied electric field strength to be quantified with the need for a plethora of experiments.

This paper presents the results of an investigation into the influence of corona formation processes at the tips of grounded rod electrodes on the probability of those rods being “struck” by high-voltage discharges. Experiments simulating the final stage of the attachment process were carried out with a composite voltage comprising a simultaneously applied impulse and DC potential of different levels to grounded rod electrodes simulating lightning rods, featuring either a spherical or pointed (conical) tip. The experiments show that corona does not influence the probability of the electrode being struck until a critical electric field (EF) strength is reached.

Research on the attachment processes in competition tests can provide insights into the influencing factors involved in the selection process that determines the lightning strike point. In this paper, a series of competition tests with a rod-rod gap configuration are designed and carried out. The test results indicate that the strike mechanism is decided by two discharge processes, namely the free development of the downward-propagating discharge and the interception process of the upward and downward discharges. If the first process prevails, the strike probabilities for different grounded rods will tend to be equal. For the second process, the strike probabilities reflect the different performances of the grounded rods for intercepting downward discharges. As the scale of the discharge gap increases, the development of the downward leader becomes more and more dominant in selecting the strike point. In natural lightning strikes, the scale of the downward leader is normally more than 90% of the discharge gap, hence the protective effect of lightning rods with different tips will not be significant for low rod heights and small lightning currents. To reflect the effect of the downward leader development on the choice of the strike point, a minimum discharge air gap of 10 m is suggested.

Traditional methods for shielding substations against direct lightning strokes were first published in IEEE Std. 998 in 1996. Several new methods were added to the ensuing 2012 edition. This paper provides an exposition of the key principles and practical implementation of one of those methods, viz. the “leader inception theory”. A novel software implementation of the method is described and the output is illustrated with a case study. Since the efficient interception of lightning involves not only the method used to position protective air terminals but also the characteristics of the air terminals themselves, the paper addresses the importance of space charge and the necessity for minimizing corona discharges during the pre-stroke phase of a thunderstorm. The results of corona discharge measurements made on sharp and blunt air terminals at a state-of-the-art HV facility are presented and discussed.

Oral Diseases (2011) 17, 298–303 Background: This study aimed to analyse a case series of microinvasive (tumour thickness

An important consideration in the design of any air termination system is the maximum distance at which the terminations can be placed from the “vulnerable points” on structures, i.e., typically those points that create the highest degree of electric field intensification. This paper extends a previous, preliminary analysis of the problem in three significant ways. Firstly, the height range of the air terminations has been extended by a factor of 4 with a series of additional calculations. Secondly, account is taken of the material of construction of the building on which the air terminations are installed. Thirdly, and most importantly, a field study has been carried out in a high-lightning area as real check on the model results. All of the results are compared and some quantitative guidelines are provided for the maximum distance at which air terminations should be installed from the vulnerable points of structures.

A new methodology, the Collection Volume Method, is given for the placement of lightning rods or “air terminals” for the protection of structures against lightning. Each air terminal is assigned an “attractive radius”, which is calculated as a function of its height, radius of curvature, location on the structure, structure dimensions, and a set of site, atmospheric and lightning-related parameters. In a similar manner, an attractive radius is assigned to all “competing features” on the structure which can also capture a lightning strike, e.g., building edges, corners, parapets, flagpoles, lift motor rooms, etc. The calculations of the attractive radii also depend on the upward leader inception criterion employed, in the present case a critical breakdown field of ∼ 3 MV / m over an effective space charge or corona radius of ∼ 0.3 m , both taken from laboratory experiments of previous investigations. The attractive radius computations involve three-dimensional calculations of the electrostatic field on the surface and immediately around the structure, i.e., the degree of electric field intensification created by the penetration of the structure into the ambient field of the thunderstorm. The structure is regarded as being protected if the combined attractive areas of the various air terminals overlap those of the competing features. The Collection Volume Method is shown to be a new, practical, physically based technique for the efficient placement of air terminals on structures. It can both complement and replace existing placement methods as the need arises.

This paper describes two unprecedented experiments that will answer two of the most fundamental and outstanding questions that remain today regarding the lightning attachment process, namely: (1) Ultra-long, free-ranging sparks that replicate typical “sneak” lightning discharges are used to evaluate and quantify the interception efficiency of the most common LPS's used around the world, and (2) Lightning flash counters and high-speed video cameras are used to make optical observations of natural lightning strikes to a tall structure in order to measure the striking distance and to compare it with current and past models of the lightning attachment process. The quantified outcomes expected from the test campaigns are both profound and of great importance to lightning protection practice, particularly with respect to quantifying the effectiveness of air terminals and lightning protection systems.