Improving electrical performance of ehv post station insulators under severe icing conditions using modified grading rings

Akkal, H.; Volat, Christophe; Farzaneh, M.

doi:10.1109/tdei.2013.6451361

Cited by 17 publications

(9 citation statements)

References 15 publications

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“…Concerning the effect of the air gaps on the voltage distribution along ice-covered insulators, several solutions consisting in the addition of booster sheds [24] and grading rings [97] to improve the insulating performance of insulators under icing conditions have been offered. The applications of the booster sheds (BS) and grading rings provide several air gaps along the insulator covered with the ice.…”

Section: Effect Of Air Gapsmentioning

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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Section: Effect Of Air Gapsmentioning

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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“…Even though uniform icing indicates satisfactory field grading, they can cause unsatisfactory electrical performance under icing conditions, because ice bridges the sheds of the insulator more quickly. Figure 2.1-Ice accretion on 500-kV polymer insulator with grading ring [48] A modified grading ring is proposed in [49] that also improves electrical performance under heavy icing conditions (Figure 2.2). It is a standard grading ring that includes a fine metallic mesh.…”

Section: Reliability Of Insulators In Icing Conditionsmentioning

confidence: 99%

“…(a) (b) Figure 2.2-Physical appearance of ice-covered insulators with modified grading rings after 15-mm/60 min ice accretion .a) one modified grading ring b) two modified grading rings [49] Creepage extenders are applied to insulators to increase the creepage (or leakage) distance and shed diameter [2], [45]. They are bonded with an adhesive to the outside edge of the shed.…”

Section: Reliability Of Insulators In Icing Conditionsmentioning

confidence: 99%

“…Moreover, regular/modified grading rings lead to significant improvements of the electric field stress on EHV insulators [49] . Thus, an effective design to make use of these mitigation options simultaneously can lead to a practical guideline in order to benefit their positive effects altogether.…”

Section: Recommendations For Future Workmentioning

confidence: 99%

“…The proposed test can be used not only in the area of BS designs and applications under icing conditions but also for other designs of ice-covered insulators with similar large air gaps. For example, it may provide better estimation of the breakdown voltage along the large air gaps for modified grading rings in [49]. Using equation (3.35) as a primary approximation, a transformer in the range of 198 kV or higher is required to perform the proposed test for its typical values (Figure 7.2).…”

Section: Recommendations For Future Workmentioning

confidence: 99%

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Design of booster shed parameters for improving the electrical performance of post insulators under icing conditions /

Ale-Emran¹

2013

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The optimized design of outdoor insulators that consider heavy icing and pollution conditions is a significant concern for the reliability of power networks. Based on field observations, the probability of flashover of EHV post insulators is higher than line insulators under the same heavy icing conditions. The flashover along the insulators is caused mainly by the presence of a water film on the ice surfaces (melting period) and partial arcs in ice-free zones (air gaps).One of the mitigation options is the use of booster sheds (BSs) to create air gaps along the iced insulator. A booster shed (BS) is a flexible c-shape device made of highquality insulating materials. Since BSs are easy to use, they seem to be simpler alternatives to upgrading insulators to those designed for cold climate regions. Despite the promising results of BS applications, still an important work must be achieved to propose optimized design of BS configurations.This project aims to provide a generic design approach to the use of BSs by optimizing their main parameters (number, diameter, inclination angle, position, and permittivity) on post insulators under heavy icing conditions. This approach is based on analyzing previous BS tests in CEGELE, an improved hypothesis of BS effects, numerical analysis using commercial software (e.g. Comsol Multiphysics™, Matlab, and Minitab), geometric modeling of ice-covered post insulator with BSs, and finally experimental validation tests. IllThe improved hypothesis states that the major effect of BSs is the creation of air gaps and their minor effect is the increase in dry arcing distance. Moreover, among total length of the air gaps, dry arcing distance, and total ice-free leakage distance (IFLD to t), the IFLD to t is a good indicator to quantify the BS effects on standard post insulators. Simulation analyses of BS configurations during the melting period demonstrate that the optimized relative permittivity of BS is an arbitrary value in its feasible variation range (2-15). The

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Optimization of high voltage electrodes for 765 kv bus post insulators

Nayak¹,

Radhika

Devulal

et al. 2021

Sustainable Energy Technologies and Assessments

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Improving electrical performance of ehv post station insulators under severe icing conditions using modified grading rings

Cited by 17 publications

References 15 publications

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

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

Design of booster shed parameters for improving the electrical performance of post insulators under icing conditions /

Optimization of high voltage electrodes for 765 kv bus post insulators

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