Chernukhin O. Corona discharge from lightning rods in conditions of action of strong electric field of thundercloud

Українська версія

Thesis for the degree of Candidate of Sciences (CSc)

State registration number

0421U100167

Applicant for

Specialization

  • 05.09.13 - Техніка сильних електричних та магнітних полів

15-01-2021

Specialized Academic Board

Д 64.050.08

National Technical University "Kharkiv Polytechnic Institute"

Essay

The dissertation deals with solution of the topical scientific-practical problem of granting permission to use new types of lightning rods that realize mechanism of Early Streamer Emission (ESE). To use the newest devices in practice of lightning protection, it is necessary to have confidence that properties announced by a manufacturer correspond to the facts. Quality control is proposed to be carried out according to the procedure regulated by France standard NF17-102:2011. But this standard is recognized only in some countries besides France including Spain, Kazakhstan, Lithuania, and some others. In the dissertation it is proved that it is necessary to change the requirement of the standard to the value of dispersion of function of distribution of lead time which ensures lightning interception with predicted probability taking into account the time at which the distribution has the maximal value. Method of measuring the velocity of propagation of leader in interelectrode space, which is based on comparative analysis of oscillograms of voltage between the electrodes and current from the electrode that forms discharge has been developed. It is shown that leader velocity increases by square law as his head propagates. It is proved that velocity of streamer propagation in the interelectrode space with length 1.2 m is no more than 1,14·106 m/s, and the average value over the time of propagation is equal to 1.3 105 m/s. The relationship between the value of constant electric field strength at which corona discharge begins, and height of rods of different forms of cross-section (square, circle, hexagon) with flat top, and round cross-section with pointed top, was determined. For air gaps that are more than 1 m it is experimentally proved that in the range of electric field strength from 4 kV/m to 120 kV/m, corona discharge is formed by pulses of individual electron avalanches that have front duration of units of nanoseconds and half-decay duration of tens of nanoseconds. And the time parameters practically do not depend on the value of electric field strength. It was determined that frequency of occurrence of current pulses depends uniquely on the level of electric field strength. This aspect supplements results obtained by Trichel and Kipp (1938) for short gaps (up to 10 cm). Functional dependence of frequency of corona streamers on electric field strength was used as a basis for creating a number of indicators used as a device for warning against thunderstorm hazard. The investigation was performed by experimental methods with the use of created specialized high-voltage complex ВВС-1.2 and the corresponding mathematical models. According to the results of the performed investigations, a number of important conclusions concerning the possibility of introduction of France standard NF C 102-17:2011 in Ukraine, also concerning creation of the new type of lightning hazard indicators, were made. It is proved that breakdown of air gap rod-plane with the use of rod of square section (dimensions 12x12 mm2) has the most stable characteristics among the considered variants, including the traditional pointed rod. This fact indicates appropriateness of the use of rod with square section in lightning protection practice. The requirement, which deals with assessment of results of certification of lightning rods by the procedure of France standard NF C 102-17:2011, to the value of dispersion of function of distribution of lead time was improved, which provides increase of reliability of advantages in relation to interception of lightning with predicted probability. Relationship between the value of constant electric field strength, at which corona discharge begins, and height of rods of different form of cross-section (square, circle, hexahedron) with flat top was determined. The obtained functional dependence of streamer frequency on electric field strength was used as the basis for creation of a number of indicators to use as the device of warning against lightning hazard.

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