Ice-covered Insulators Research Articles

Dynamics and modeling of AC arc on surface of ice

A self-consistent dynamic model allowing the prediction of AC discharge activities leading to flashover on ice-covered insulator surface is presented. This model takes into account the effects of a number of parameters including insulator geometry and applied water conductivity. The instantaneous variations of major parameters are discussed in order to develop a sequential time-dependent simulation of the flashover. The temporal evolution of arc current and axial arc velocity are determined in a consistent manner. The critical flashover voltage characteristics, as a function of surface conductivity, insulator length, and insulator diameter, calculated by the model are quite satisfactory when compared to the experimental results from empirical models reported in the literature

Artificial Neural Networks Approach to the Modelling of AC Arcs Maintenance Conditions on Ice-covered Insulators

Artificial Neural Networks Approach to the Modelling of AC Arcs Maintenance Conditions on Ice-covered Insulators

Effect of insulator diameter on AC flashover voltage of an ice-covered insulator string

The effect of the diameter of an insulator covered with ice on its flashover voltage was investigated. The insulator diameter was simulated and varied by controlling the width of a layer of ice artificially accreted on a short string of 5 IEEE standard units. The 50% withstand voltage (V/sub 50/) was experimentally determined using the method described in IEC 60507. The results show that the V/sub 50/ decreases as the width of the ice layer increases. Moreover, a mathematical model for predicting the critical flashover voltage of ice-covered insulators is proposed, and is validated against the experimental results. The model is then applied to ice-covered industrial insulators with different diameters yielding good concordance between the results from the model and the experimental ones.

Potential and electric-field calculation along an ice-covered composite insulator with finite-element method

A two-dimensional finite-element model for potential and electrical-field calculation along an ice-covered composite insulator is presented. To find the influence of the ice on the potential and electrical-field distribution, various thicknesses of the ice and various lengths of the icicles are simulated in the condition of dry ice and wet ice, respectively. In addition, the present study investigates the influence of the discrete water film and the dry band on the potential and electrical-field distribution of the iced composite insulator. Finally, a comparison between the electric-field distribution along the ice-covered composite insulator and that of ice-covered ceramic insulator string is presented.

Potential and electric-field distributions around an ice-covered post-type insulator

To facilitate the study of phenomena preceding the flashover of an ice-covered station post insulator during a melting period, the potential and electric-field distributions along the insulator have been numerically calculated. Commercial software based on the boundary element method was used for this purpose, and a simplified three-dimensional model of the ice-covered insulator was developed and validated experimentally. Then, a station post insulator covered with wet-grown ice under a melting regime was numerically simulated on the basis of experimental results. The presence of a conducting water film at the ice surface, the shedding of ice deposits, and the presence of a partial electric arc along an air gap were taken into account in the simulations. The results obtained have made it possible to show that the water film, the number of intervals of air, and the presence of partial arcs have a considerable effect on the distribution of the potential and the electric field along the insulator. In the same way, the appearance of a partial arc as well as the occurrence of ice shedding lead to a redistribution of the potential along the ice deposit, either supporting or inhibiting the flashover process. The results obtained will help to improve insulator geometry for cold climate regions.

Modelling of flashover performance of an ice-covered resistive glazed post station insulator in presence of an air gap

The main objective of this paper is to study the electric field distributions around a standard post insulator for the power frequency, lightning impulse (1.2/50 µs) and switching impulse (250/2500 µs) voltages under icing conditions, and these were computed numerically using the finite element method. Thin glaze coating on the insulator requires a very large number of elements for finite element analysis because of the open boundary around the ice-covered insulator. To reduce the number of elements and hence computation time, the region between the domain of interest and infinity was modelled by a form of Kelvin transformation. The simulation results, confirmed by laboratory experiments, show that while a lightning impulse is the limiting factor in the design of a resistive glazed insulator under clean conditions, a switching impulse is the limiting factor under icing conditions.

Three-Dimensional Modeling of Potential and Electric-Field Distributions Along an EHV Ceramic Post Insulator Covered With Ice—Part I: Simulations of a Melting Period

The main objective of this paper is to determine the potential and electric-field distributions along a typical ceramic extremely-high-voltage post insulator covered with atmospheric ice during a melting period. Commercial software, Coulomb 3D, based on the boundary element method (BEM), was used for all of the three-dimensional modeling and simulations. It was demonstrated that the BEM is well suited for evaluating the effect of ice shedding on the potential and electric-field distributions along an ice-covered insulator during a melting period. The results obtained show that the length and number of ice free zones, also called air gaps, are the major parameters that affect the applied voltage distribution along an ice-covered insulator. The mean electric field per arcing distance, affected mainly by the air-gap lengths, can provide a good indication of the presence of partial arcing along the different air gaps.

Effects of low air pressure on ac and dc arc propagation on ice surface

The effects of air pressure on the AC and DC arc process on an ice surface, including velocity, parameters and flashover voltage, were studied. The results obtained showed that air pressure has an obvious influence on the arc propagation velocity, arc constant A, electrode voltage drop Ve and consequently on the flashover voltage of the ice surface, Vf. This decrease in Vf is explained by the decrease in the E-I arc characteristics and arc propagation velocity, and by the relatively higher density of Na atoms in the arcs at pressures below standard air pressure. Based on these results, the mechanism underlying the decrease in the flashover voltage of ice-covered insulators at high altitude was analyzed

Impulse flashover performance of semiconducting glazed station insulator under icing conditions based on field calculations by finite-element method

The flashover performance of a semiconducting glazed standard post insulator for lightning impulse and switching impulse stresses under icing conditions is studied. The flashover performance can be predicted by calculating the potential distribution along the station post insulator. The potential distribution is computed numerically using the finite-element method. The thickness and conductivity of the semiconducting glaze are varied and their effects on the potential distribution have been studied, to improve electrical performance under icing conditions. Thin semiconducting glaze requires a very large number of elements for finite-element analysis because of the open boundary around the ice-covered insulator. To reduce the number of elements and hence computation time, the region between the domain of interest and infinity is modelled simply by adding a circular boundary, connected to a second mesh of the same size, and boundary constraints to force equivalent boundary potentials to be identical. Infinity lies at the centre of the second mesh. Simulation results are confirmed by laboratory experiments, and it has been found that switching impulse is the limiting factor for the design of a semiconducting glazed insulator under icing conditions. This is contrary to clean conditions, where it has been found that lightning impulse is the limiting factor for the design of a semiconducting glazed insulator.

Electrical performance of ice-covered insulators at high altitudes

This paper presents results on the flashover of ice-covered insulators at low air pressure. The flashover performance of two different types of insulators covered with polluted ice was experimentally determined and the effects of several determining factors, such as the air pressure, ice severity, and pollution rate, were discussed. Based on the laboratory investigations, a mathematical model for predicting the critical flashover voltage of ice-covered insulators at low air pressure was established. There is optimal agreement between the calculated and experimental results.

Propagation of ac and dc arcs on ice surfaces

Using a high-speed camera, the fundamental behavior of arcs on ice surfaces, including propagation velocity and root radii were studied under both ac and dc voltages. It was found that the arc may propagate randomly inside or outside of the ice with a relatively low velocity before the critical length is reached, and then at a much higher velocity. Moreover, the relationship between the radius of the arc root and leakage current was determined. The results obtained allowed us to improve our previous model dealing with insulators. There is a good concordance between the critical flashover voltage of ice-covered insulators calculated from the model and laboratory results.

Modelling of DC arc discharge on ice surfaces

Using a triangular ice sample, the characteristics of the DC arc appearing on ice surfaces was investigated. Based on the results obtained, a model for predicting the 50% flashover voltage of ice-covered insulators energised with DC was presented. The model takes into account the ice surface conductivity, voltage polarity, and arc root radius. Moreover, to validate the model, the 50% flashover voltage of a short string of five IEEE standard insulators covered with artificial ice under both DC– and DC+ was measured. There was an excellent concordance between the experimental results and those calculated from the mathematical model.

DC characteristics of local arc on ice surfaces

In this research work, the characteristics of the dc local arc appearing on ice surfaces near the cathode was investigated and the corresponding arc constants A and n were determined. The difference between the arc characteristics under dc and ac voltages were also analyzed. These results present a particular interest in the modeling of the dc arc discharge on ice-covered insulators.

Flashover performance of ice-covered insulators

The presence of ice on the surface of insulators is sometimes the cause of severe problems in power networks. In fact, the presence of ice reduces the electrical performance of insulators in ways that can, in some circumstances, lead to flashover, resulting in power outages. The maximum withstand voltage of ice-covered insulators is distinctly inferior to that of clean insulators. The electrical performance of insulators also depends on atmospheric conditions during the formation and development of ice deposits. Temperature liquid water content, wind speed, water droplet size, conductivity of precipitation, as well as the nature and strength of the electric field are major factors influencing the type, quantity and uniformity of ice. This paper gives an account of the research carried out on the electrical behaviour of ice-covered insulators, particularly in relation to laboratory ice simulation, voltage application methods and the major intervening factors. The paper also reports on the work being done in laboratories around the world, and highlights the results obtained at the High Voltage and Atmospheric Icing Laboratory of the University of Quebec in Chicoutimi (UQAC).

Modeling of the AC arc discharge on ice surfaces

A model for predicting the flashover voltage of ice-covered insulators energized with AC voltage is presented in this paper. The model takes into account the variation of ice surface conductivity as a function of freezing water conductivity. The effects of the length of the arc on its own characteristics, as well as the AC arc reignition condition, were determined in a laboratory investigation using triangular ice samples. The model is applied to a short string of 5 IEEE standard insulator units. There is an excellent concordance between the 50% flashover voltage calculated from the mathematical model and the experimental results.

AC flashover performance of insulators covered with artificial ice

A field observation of ice accretion on Hydro-Quebec HV insulators was carried out, as well as a laboratory investigation of the AC flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8/spl times/2.8 m/spl times/3.8 m climate room using a HV transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V/sub WS/) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V/sub WS/ of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm/sup 2/ on the same insulators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

AC Flashover Tests at Project UHV on Ice-Coated Insulators

This paper presents results of experimental studies on the flashover strength of ice-coated insulators. Two types of flashover have been found on ice-covered insulators. One is caused by hard and dry ice formed in temperatures lower than 15 °F. Another is caused by mixed conditions of ice and misty rain in relatively high temperatures of 20 to 30 °F. The flashover voltages of 25 units of 53/4- by 10-inch insulators were 288 kV (phase to ground) in the former condition and 246 kV in the latter. These results were obtained for uncontaminated insulators. Nonuniform voltage distribution along the insulator string produces these low flashover voltages. These tests were conducted at General Electric's Project UHV in the winter season of 1968-1969.