Contamination flashover theory and insulator design

Jolly, David C.

doi:10.1016/0016-0032(72)90099-3

Cited by 46 publications

(23 citation statements)

References 7 publications

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“…After an abnormally dry autumn in 1962, Jolly [7] noted that accumulation of hoar frost, followed by melting on the evening of January 23, 1963, caused 130 flashovers on the UK 275-kV system, causing isolations that dropped 17% of the total system load. Overall, there were 281 line flashovers and 122 station flashovers in December 1962 and January 1963 as a result of the pollution accumulation and winter fog.…”

Section: Kv Hoar-frost Event 1962-1963mentioning

confidence: 98%

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Insulator Leakage Distance Dimensioning in Areas of Winter Contamination using Cold-fog Test Results

Chisholm

2007

IEEE Trans. Dielect. Electr. Insul.

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Electrical utilities have adapted insulator leakage distances to a wide range of contamination environments. This has led to development of guidelines for unified specific creepage distance, for example in IEC 60815. Under freezing conditions, a number of factors change. The surface conductivity of ice is much lower than that of water, but there is the countervailing possibility of accumulating a significant amount of ice. One of the crossover points between applications occurs when a very light layer of hoar frost or freezing fog, simulated in a "cold fog" test, fully wets a precontaminated insulator. The leakage distance requirements for these conditions are compared with those suggested for conventional clean-fog requirements. The possibility of treating fog accretion as a form of non-soluble deposit density is explored.

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Section: Kv Hoar-frost Event 1962-1963mentioning

confidence: 98%

“…The first evidence of this actually was noted in the UK 275 kV transmission system, with widespread flashovers after hoar frost accumulated on insulators that had been exposed without rain for a month [7]. Ice flashover was also tested at Project UHV using water of 2.9 mS/m conductivity [8].…”

Section: Field Experience In Cold Fogmentioning

confidence: 99%

Insulator Leakage Distance Dimensioning in Areas of Winter Contamination using Cold-fog Test Results

Chisholm

2007

IEEE Trans. Dielect. Electr. Insul.

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“…Furthermore, the surrounding temperature of icecovered insulator is too low to melt the remaining ice. From the arc propagation, it was observed that the positive partial arc lies close to the surface [133] and is strongly cooled by the cold surface, resulting in a thin and hot arc column [134], [135]. In contrast to a positive arc, these bright spots in a negative arc are floating away from the surface.…”

Section: Volume Flow Rate and Water Film Conductivitymentioning

confidence: 99%

Two-arc dynamic modeling of AC and DC flashovers of EHV post station insulators covered with ice based on laboratory experiments /

Ledari¹

2014

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Ice and snow accretion on insulators has been recognized as a significant risk factor in the reliability of overhead transmission lines and substations. Accumulated ice on insulators can initiate corona discharge along ice-free zones, often called air gaps. In the presence of a highly conductive water film on the surface of the ice, while applied voltage is sufficiently high, corona discharge activity may be initiated and developed into partial arcs. Under certain conditions, these partial arcs may result in complete flashover.The general objective of this research is to study the flashover phenomenon on icecovered extra-high-voltage (EHV) post insulators. Hence, a two-arc dynamic model based on the existing mathematical models was proposed to predict the parameters of AC and DC flashovers. The model considers the arc as time-dependent impedance constituted of a resistance in series with an inductance. The residual ice layer is defined in terms of an equivalent resistance, where the equivalent surface conductivity is calculated by taking into account the water film flowing along the ice surface. The present contribution proposes a novel approach to determine the equivalent surface conductivity, based on fluid mechanics and the Navier-Stokes equations, as well as on a series of experiments carried out to measure the water film flow rate and conductivity.Moreover, the mechanisms of discharge initiation and arc development on the surface of the ice accumulated on the insulators were studied. Special attention was paid to evaluate the effect of the volume conductivity of the ice surface on the arc propagation velocity for different freezing water conductivities, using high-speed video camera techniques.The proposed models were successfully validated in laboratory using station post insulators -typically used in Hydro-Quebec 735 kV substations -under AC and DC voltages. The maximum AC and DC withstand voltages were experimentally determined based on IEEE Std 1783. Furthermore, the influence of the number and position of air gaps on the flashover performance of ice-covered insulators was investigated experimentally. Experimental results revealed that the air gap configuration affects the maximum withstand voltage significantly. The main characteristics of flashover, including minimum flashover voltage and leakage current, derived from the proposed two-arc dynamic model, respond properly to the variation of major parameters, namely, insulator length and freezing water conductivity.Finally, in order to interpret the performance of insulators under different air gap positions, the voltage and electric field distributions along the ice-covered insulator were simulated numerically during the melting period, using the Finite Element Method (FEM). Simulations results confirm that increasing the number of air gaps improves the maximum withstand voltage and uniformity of voltage distribution of EHV post insulators. Based on the results, the use of booster sheds and grading rings to improve the insulating performance of...

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“…One of the most important factors influencing the performance of outdoor insulators is air pollution. It is revealed in literature that in the United State insulators that performed well at 60 kV in clean air, failed at 11 kV near the coastline [1]. The stable and reliable operation of power system is dependent on the pollution flashover performance of outdoor insulators.…”

Section: Introductionmentioning

confidence: 99%

Flashover Characteristics of Silicone Rubber Sheets under Various Environmental Conditions

et al. 2016

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Silicone rubber insulators are replacing the conventional ceramic and porcelain insulators rapidly in power transmission and distribution industry. Very limited field knowledge is available about the performance of silicone rubber insulators in polluted and contaminated environments and therefore need further investigation. A comprehensive analysis of silicone rubber sheets (intended for coating outdoor insulators) was carried out in this paper based on experimental results. The main performance parameters analyzed were arc inception voltage and flashover voltage. Dependence of these parameters on equivalent salt deposit density (ESDD), non-soluble salt deposit density (NSDD), relative humidity, ambient temperature, fog rate, dry band formation, dry band location and number of dry bands were investigated extensively. Insulator orientation and its effect on performance were also studied. The authors believe that this paper will provide a comprehensive knowledge about the flashover characteristics of silicone rubber insulators under humid, contaminated and dry band conditions. These results could be used in the selection and design of silicone rubber insulators for polluted environments.

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Contamination flashover theory and insulator design

Cited by 46 publications

References 7 publications

Insulator Leakage Distance Dimensioning in Areas of Winter Contamination using Cold-fog Test Results

Insulator Leakage Distance Dimensioning in Areas of Winter Contamination using Cold-fog Test Results

Two-arc dynamic modeling of AC and DC flashovers of EHV post station insulators covered with ice based on laboratory experiments /

Flashover Characteristics of Silicone Rubber Sheets under Various Environmental Conditions

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