A. Nekahi

Excitation temperature determination of an arc formed over an ice surface using optical emission spectroscopy

Optical emission spectroscopy has been used to study an arc formed over an ice surface. DC positive voltage was applied to a flat ice surface with a 6 cm air gap to initiate electric discharge. Time-resolved spectra were recorded during the propagation of arc along the surface. Excitation temperature was measured using copper and oxygen lines and employing the relative line intensities method. Deviation from the local thermodynamic equilibrium was considered using the Burton and Blade correction factor. The investigation results showed that the excitation temperature does not vary monotonically with the discharge current.

Rotational temperature measurement of an arc formed over an ice surface

Rotational temperatures were calculated versus current variation during dc discharge propagation on an ice surface. Strong diatomic molecular band of OH, N₂⁺ 1^st negative system and NH were observed from the captured spectra. In order to determine the rotational temperature, an optical emission spectroscopy (OES) analysis was carried out using the OH A-X (0, 0) transition band. Also, the rotational temperature was evaluated using the N₂⁺ 1^st negative system.

Arc Energy and Temperature During Its Propagation Over Ice-Covered Surfaces

The voltage and current waveforms during the propagation of an arc over an ice surface were measured and analyzed. The V-I characteristics of the discharge driven by ac power supply were studied. The instantaneous and per-cycle energy delivered to the arc column were calculated. The spectra of the emitted light during the arc propagation were collected and analyzed using a spectroscopic system. The rotational temperature was derived from the relative intensities of two groups of rotational lines corresponding to the peaks of the OH (A-X) (0, 0) vibrational band. The rotational temperatures of the experimental spectra for different current levels were derived. The relationship between the delivered energy to the arc column and the rotational temperature was studied and discussed.

Effect of dry band location on electric field distribution along a polymeric insulator under contaminated conditions

To study the effect of dry band location on electric field distribution of polymeric insulators, simulations were carried out using Comsol Multiphysics. The effect of dry band along a polymeric insulator at shed, core and junction of core and shed regions on the electric field distribution was investigated. Pollution was modelled as a 2-mm uniform conductive water layer on the insulator surface. Conductivity of pollution layer was set at 500μS/cm to simulate medium pollution conditions. Simulation was carried out by considering a 2-cm dry band at the shed, core and junction of shed and core regions respectively. The highest electric field strength was observed when the dry band was considered at the junction of shed and core region while the electric field strength was minimum along the dry band at the shed regions. The result of this study will help scientists and engineers to improve the design of weather sheds for high voltage insulators so that the possibility of dry band formation at the junction of shed and core is minimized.

Effect of pollution severity on electric field distribution along a polymeric insulator

To study the effect of pollution level on electric field distribution of polymeric insulators, simulations were carried out using Comsol Multiphysics. The effect of light, medium, heavy and very heavy pollution on the electric field and potential distribution was investigated. Pollution was modelled as a uniform conductive water layer on the insulator surface. Electric field analysis was carried out by changing the conductivity of the pollution layer. Simulation results show that electric field strength is high at the junction of the sheath and shed and minimum at the top of the shed. It was also observed from simulations that electric field stress increases with increasing pollution level. The result of this study will help scientists and engineers in the design and selection of outdoor insulators for different polluted environments.

Mechanisms and processes of arc propagation over an ice-covered surface

The general objective of this paper is to investigate the physical mechanisms and processes involved in the propagation of arc over the surface of ice. In the present research work, high-speed imaging and optical emission spectroscopy techniques were synchronized with the electrical measurements to study the various parameters of arc on an ice surface, i.e. channel radius, propagation velocities, arc column temperature and electron density. These results, together with observation of the propagation patterns and arc foot geometries, calculation of arc energy and the examination of the state of thermal equilibrium provide background information for understanding the ice-covered insulator flashover phenomenon. Arc root structure, current profile, propagation pattern and velocity were investigated under different type of applied voltage and different polarities. Water film conductivity and thickness, relative air humidity and the direction of arc propagation were also analyzed as influencing parameters of arc propagation. The effects of different possible mechanisms, e.g. collision and thermal ionization, buoyancy force and electrostatic force, on different stages of arc propagation has been discussed.

Time-resolved spectroscopic observation of surface flashover across an ice surface

Results of the first studies of arc on an ice surface by time-resolved spectral analysis with a good time and wavelength resolution have been obtained and are reported in this paper. Time-resolved spectra were recorded at different stages of arc propagation on an ice surface in order to obtain information on the occurring ionization processes. Moreover, the emission features of Hydrogen Balmer series Hα and Hβ were observed and found to be distinctly different from those of singly ionized species. The sodium-D lines, which result from the production of sodium ions from dissolution of NaCl in water, due to their low ionization energy were observed at high intensity level during the early stages of arc development.

Investigating flashover behaviour of silicone rubber insulators under contaminated conditions

Flashover behaviour of silicone rubber insulators were analysed under contaminated conditions in this paper. The modified IEC 60507 Standard was used to simulate pollution deposition on the insulator surface. Experiments were carried out at different pollution level and changing leakage distances to investigate the behaviour of silicone rubber insulators. It was shown experimentally that flashover voltage is highly dependent on pollution level and leakage distance. The result of this study can be used to investigate the ageing of silicone rubber insulators and their selection for contaminated and wet environments.

Local thermodynamic equilibrium of an arc over an ice surface

A study of the emission spectra from discharges on an ice surface and a discussion of its implication on local thermodynamic equilibrium are presented. Rotational temperatures were measured using OH (A-X) emission bands. The variation of rotational temperature, which is similar to that of gas temperature with discharge current, was studied. The excitation temperature of the arc column was determined using the ratio of spectral line intensities as well as the Boltzmann method. Electron densities were estimated by analyzing the Balmer line Hα profile, broadened by the Stark effect. Differences between the rotational and excitation temperatures showed that the arc formed over an ice surface is not in a state of thermal equilibrium.

Electron Density Measurement of DC Positive Arc Propagating Over an Ice Surface Based on

Results of spectroscopic investigation of an arc formed over an ice surface are presented. Direct-current positive voltage is applied to a flat ice surface with a 6-cm air gap to initiate electric discharge. Time-resolved spectra are taken during the propagation of arc along the surface. From the emission spectra, the profile of hydrogen-alpha from Blamer series is used to measure the electron density of the arc column. A method based on broadening of the Hα line considering instrumentation broadening is employed. The electron densities obtained by optical emission spectroscopy show an increase from 1 to 2 × 1017 cm-3 corresponding to current increase from 200 to 700 mA. The electron density at the flashover instant is calculated to be about 2.5 × 1017 cm-3.