Experimental study of leader tortuosity and velocity in long rod-plane air discharges

Abstract

Long air gap electrical discharges are of particular interest among scientists and engineers working on high voltage techniques and lightning research. In the present work we report experimental results obtained while testing a long rod-plane air gap with positive switching-like voltage impulses to study the velocity and tortuous progression of the leader discharge. Voltage and current waveforms were recorded. Two still digital cameras were used to track the leader tortuous path. By using a fast digital camera, the leader temporal evolution was recorded and its propagation velocity was estimated. Three angles were used to describe the leader tortuous progression.

A Contribution to the Investigation of Leader Tortuosity in Positive Long Rod-Plane Air Discharge

“…Following the methodology presented in [29], the original full-color and high-resolution images from the two still cameras were processed using the Matlab@ Image Process- ing Toolbox to find the leader path between the rod tip and the ground plane. Projective geometry was applied to the data pairs of each image (from the views of two orthogonally arranged static cameras) to obtain the Cartesian orthogonal three-dimensional location for each discharge (each segment equals ca.…”

“…By the method in the previous section, all the coupled images of the two still cameras and the corresponding photos at the initiation of the final jump from CCD were processed to reconstruct the leader progression paths of 17 recorded shots of the breakdown events. As the methodology was presented in [20], [29], the leader tortuosity was described using three different angles between consecutive leader segments s i and s j , as it is shown in Fig. 4, which can be described as: • αbetween two adjacent leader segments (0, π ) • θ -leader segment inclination with respect to the gap axis; also known as polar angle (0, π )…”

“…• ϕ -leader segment projection on a reference plane (e.g. XY), also known as azimuthal (−π , π ) For the sake of comparison, the statistical approach of the three angles is the same as [29]. Once the coordinates of the leader propagation path were obtained and the three angles were calculated using Matlab@, probability density functions -PDF-were fitted with Origin@, including data from all tests for each angle.…”

“…With the development of observation devices and digital data record and processing techniques, Chinese scholars have carried out a series of long air gap experiment for the construction of China UHV power grid in recent years [20]- [28], and propose the third method for the three-dimensional (3-D for short) representation of leader tortuosity by three different angles (α, θ , and ϕ) [21]. In 2016, Diaz and Cooray use the same characterization method to study the leader tortuosity by setting up 7m and 8m rod-plane air gaps subjected to positive switching impulse voltage [29]. In 2016 and 2018, based on their test data, Diaz, Arevalo and Cooray study and establish a numerical model for positive long air gap, considering the 3-D geometries of leader path [30], [31].…”

Modeling of Positive Switching Impulse Discharge of UHV Transmission Line Air Gaps

“…In the 1980s, some scholars established a typical gap breakdown voltage calculation model based on the leader discharge mechanism [9,10]. Since the 21st century, with the continuous progress of technology, scholars have carried out long air gap breakdown voltage prediction calculation and observation tests [11][12][13][14][15][16][17][18][19], further promoting the research process of long air gap discharge. At present, scholars mainly adopt real tower discharge tests to obtain the positive switching impulse discharge characteristics of air gaps in UHV transmission lines.…”