Critical condition of DC flashover on a circular sector model

Abstract

In order to find the electrical size which determined the critical condition of flashover, the authors have examined the propagation of the discharge on surface under dc voltage in a new laboratory model which has a continuous and radial current distribution. This model is a vat having a circular sector form of variable angles, radiuses and depths filled by an electrolyte. The obtained results on this model show that for a given resistivity of electrolyte: -If the current distribution in the horizontal plane is uniform according to the sector angle, the applied critical voltage and the critical current per unit of angle (1°) are constant for all sectors of various angles. -If the current distribution in the vertical plane is uniform according to the depth, the critical flashover voltage and the critical current per unit of the electrolyte depth (1mm) are constant for all the depths. These results lead to the critical conditions of flashover to be determined by the current per unit of angle and per unit of electrolyte depth (A/°/mm).

Refinement of residual resistance calculation dedicated to polluted insulator flashover models

“…The validation of the dynamic flashover model presented in the previous section was validated using the experimental model of the figure 3 which was used in previous studies [33,39]. The critical flashover voltage of this experimental model was obtained using the experimental set up presented on the figure 11.…”

DC flashover criterion and discharge elongation mechanism in an air–electrolyte interval

“…4. It is a circular vat [19, 24] which has a radius of r = 137 mm, a depth of e = 12 mm, filled to a certain thickness by an electrolyte (NaCl + H 2 O) of a given resistivity. A high‐voltage (HV) rod electrode of 10 mm in diameter, 60 mm in length and 2 mm of point radius was placed at the top of the vat centre at a constant height ‘ h ’ of 3 mm of electrolyte surface.…”

“…The particular characteristics of this laboratory model at initial conditions, that is, after the ignition of initial discharge between HV rod electrode and electrolyte of a few hundreds of milliamperes, are as follows: The distribution of the current around the foot of the discharge is continuous and radial. The distribution of the current density, and that of the potential and its gradient along a radius, are the same for all the radii [24]. …”

“…The distribution of the current density, and that of the potential and its gradient along a radius, are the same for all the radii [24].…”

“…They take part in the creation of another electrical parameter, which has a physical significance and direct final influence on the discharge elongation. This parameter is the electric field distribution in the air near the electrolyte surface, between the discharge and the ground electrode [24]. Based on this conclusion, we proposed the following flashover criterion: ‘Flashover is possible if the electric field distribution along the leakage distance is sufficient for discharge elongation by a progressive breakdown between the discharge and the electrolyte’ [22].…”