Icing flashover characteristics and discharge process of 500 kV AC transmission line suspension insulator strings

Liu, Yunpeng; Gao, Song; Huang, Daochun; Yao, Takeshi; Xiong, Wenjing; Hu, Yi; Cai, Wei

doi:10.1109/tdei.2010.5448098

Cited by 33 publications

(17 citation statements)

References 14 publications

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“…Jiang et al [81], [82], Su et al [83] and Liu et al [84] confirmed the influence of pollution on ice-covered insulator flashover.…”

Section: Effect Of Applied Water Conductivitymentioning

confidence: 90%

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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“…Jiang et al [81], [82], Su et al [83] and Liu et al [84] confirmed the influence of pollution on ice-covered insulator flashover.…”

Section: Effect Of Applied Water Conductivitymentioning

confidence: 90%

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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“…AT THE HV END ON U mf When the freezing water conductivity γ 20 is 370, 640, 1000 and 1500 μS/cm and d is fixed at 10 mm, U mf of types A and B with different GRs (including without GR) only at the HV end Previous studies [7,17,19] have shown that U mf decreases rapidly with the increase of γ 20 under the given ice thickness and other identical conditions. The decrease can be expressed by a power-law curve which follows the relation:…”

Section: Influence Of Different Grading Ringsmentioning

confidence: 92%

“…In order to simulate the ice deposited on the actual insulators effectively, the operating phase voltage is applied to the HV end during the icing period [17,[20][21]. The densities of glaze on the samples are about 0.78-0.90 g/cm 3 , some icecovered composite insulators with or without GRI are presented in Figure 3.…”

Section: Ice Accretion Methodsmentioning

confidence: 99%

“…Under severe icing condition, GR might even lead to the decrease of icing flashover voltage [16]. For composite line insulators under heavy icing condition and the pollution degree of SDD=0.1 mg/cm 2 , the test results [17] have shown that the given GR had, however, a negative effect on the flashover performance of ice-covered composite insulator. All these existing research reveal the general disagreement on the effect of GR on the electrical performance of ice-covered insulators.…”

Section: Introductionmentioning

confidence: 97%

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Influences of grading ring arrangement on AC flashover performance of 220 KV ice-covered composite insulators

Shu

Wang

Jiang

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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The grading ring (GR) can adjust the potential distribution along the composite insulator and reduce the electric field (E-field) strengths near its end fittings. However, little research has been conducted about the effects of GR on the insulation performance of composite insulators under icing condition. Therefore, the ac icing flashover performance of two kinds of 220 kV composite insulators under different GR arrangement patterns are tested in the artificial climate chamber. Combining with the numerical simulation, the effects are analyzed. The results indicate that when GR is installed at the high voltage (HV) end, the E-field strength close to the end fitting and the icing uniformity on the whole insulators are both improved. These cause the effect of icing degree on the icing flashover voltage to be larger than that without GR at the HV end. When GR is installed at the grounded end, the perpendicular icicles on the GR will impact the flashover arc path, which causes the icing flashover voltages to be lower than that without GR at the grounded end. When different GRs are only installed at the HV end, the characteristic exponents b (characterizing the influence of freezing water conductivity on icing flashover voltage) are all larger than that without GR. Moreover, the value of b increases with the decrease of GR's diameter and with the raise of GR's height. But b changes slightly when there are variations in GR's pipe diameter and structure. The research can provide reference for the application of GR for 220 kV composite insulators in icing regions.Index Terms -Grading ring, composite insulator, ice accretion, icing flashover voltage, potential distribution.

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“…Experimental investigations and field observations indicated that the flashover of ice-covered insulator string typically occurs during the ice-melting period [6][7][8]. Reasons are as follows.…”

Section: Introductionmentioning

confidence: 99%

Ion Migration in the Process of Water Freezing under Alternating Electric Field and Its Impact on Insulator Flashover

et al. 2017

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Abstract:Ice flashover threatens the security and reliability of power transmission. However, the ice flashover mechanism of insulators remains poorly understood. This study analyses water droplet freezing and ion distribution in ice layer under alternating electric field. It also investigates ion migration during icing process of insulator string under alternating electric field and its effects on insulator flashover. Results showed that the average freezing time of water droplets was related to electric field strength. The extent of ion migration during freezing decreased with increasing electric field strength. The maximal melting water conductivity of the ice layer and icicle of the insulator formed under energized condition was higher than the corresponding freezing water conductivity but lower than that under non-energized condition. Furthermore, the hanging location of each insulator significantly affected the melting water conductivity of the ice layer. The surface conductivity of the ice layer increased because of the conductive ion migration in freezing water during freezing, which was an important factor that decreased the flashover voltage of the ice-covered insulator. The existence of alternating electric field would impact the extent of ion migration. This study may serve as a reference for updating prediction flashover model of ice-covered insulators during the melting period.

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Icing flashover characteristics and discharge process of 500 kV AC transmission line suspension insulator strings

Cited by 33 publications

References 14 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 /

Influences of grading ring arrangement on AC flashover performance of 220 KV ice-covered composite insulators

Ion Migration in the Process of Water Freezing under Alternating Electric Field and Its Impact on Insulator Flashover

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