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The power outage caused by decay-like fracture of composite insulators significantly impacts the power grid. In this paper, a decay-like fractured insulator of 500 kV transmission line is taken as a research object. The detailed observation of core rod and silicone rubber housings, discharge results, temperature rises, and electric field distribution are obtained. (a) The fractured insulator has abnormal heating on the exposed core rod and sheath surface, and the ambient temperature and humidity significantly influence the temperature rise. (b) It is proposed that one of the most obvious characteristics of decay-like insulator is abnormal temperature and temperature rise (such as T > 50°C, ΔT > 30 K). (c) Under the same conditions, temperature rises, electrical discharge, and electrical field strength of decay-like insulator are higher than those of other insulators, and the discharge at the bare core rod is intense. (d) The electric field strength distribution and discharge distribution of decay-like insulator are different from other aging and new insulators. However, the measurement results are significantly affected by test conditions. Therefore, it is difficult to determine whether the composite insulators are decay-like using electric field distribution and UV measurement on site. [ABSTRACT FROM AUTHOR]

The possibility of insulator flashover would be higher with the increase in icing degree. Therefore, the method of monitoring the icing weight of the insulator is of vital importance. In this study, the estimation method of icing weight on composite insulator in rime icing was proposed. By quite a few experiments under different rime icing conditions, results showed good agreement between estimated value and measured icing weight. Therefore, the estimation method of icing weight proposed by this study was effective and may be used for predicting icing weight. Based on the estimation method, this study discusses the effect of key structural parameters of composite insulator under different rime conditions on icing weight. In order to better apply the composite insulator to electric transmission line in icing area, several suggestions on design optimisation of structural parameters are proposed. [ABSTRACT FROM AUTHOR]

Transferring the current of bundled sub-conductors through smart switching modules is a promising de-icing method. This study explores the application of line impedance modulation to line de-icing. The control requirements of the de-icing method by transferred current are illustrated according to the characteristics of the method, and two key parameters, namely, critical ice-melting current and ice-melting time, are introduced. The analytical expression for the critical ice-melting current is deduced theoretically. On this basis, the effect of icing shape on the critical ice-melting current is analysed and discussed, along with the calculation of the critical ice-melting current when icing on the windward surface of conductor. A simplified method for calculating ice-melting time is presented on the basis of the heat balance equation during the ice-melting process. With the control requirements of this method as a framework, the calculation and selection of the grouping mode and current duration for the sub-conductors are discussed, and the control scheme of the de-icing method by transferred current is established. The control scheme is preliminarily validated by laboratory investigations conducted in an artificial climate chamber. The results can serve as a reference for obtaining the ice-melting scheme when de-icing via the transferred current of bundled conductors. [ABSTRACT FROM AUTHOR]

In China external discharge accidents caused by heavy rain is growing. However, the rain effect is not considered in atmospheric correction for external insulation design in IEC 60071‐1(Edition 8.1, 2011) or domestic standard. Hence, a series of experiments are implemented with positive switching impulse, a typical kind of overvoltage of power grid, to analyse the discharge performance of rod‐plane short air gap under rain conditions. The effects of rain and its intensity, rain conductivity and ambient temperature on the discharge voltage are explored, and the theory behind them, which can help in the development of discharge mechanism of air gap under rain condition, are respectively given. The results show that under the experimental rain condition, the discharge voltage can be up to −10.9, −9, −8.5, −3.2 and −2.3% lower than under dry condition for clearance distance of 0.1, 0.2, 0.3, 0.4 and 0.5 m, respectively. Besides, it decreases with increase in rain intensity, rain conductivity and ambient temperature, respectively. Among them, the rain intensity is the most significant one, next is temperature, whereas rain conductivity is the minimum and trifling. Finally, a correction formula for breakdown voltage (positive switching impulse) of rod‐plane air gap under rain condition is proposed for reference. [ABSTRACT FROM AUTHOR]

In the construction or reconstruction of transmission lines for cold climate region, selection of ice thickness design criterion is an important factor to improve the lines anti‐icing performance. Indeed if the designed ice thickness selection is excessively thin, it is hard for the conductors to keep safe and stable operation under icing conditions; and if the designed ice thickness selection is excessively large, the investment of the construction or the reconstruction can several times increase. Hence, how to determine the reasonable ice thickness design criterion and make it meet the economy and safe demands is an important problem to the construction and reconstruction project of the lines. The influence mechanism of diameter on conductors icing is analysed in this study. Based on the results of icing accretion on conductors at several natural ice observation stations in recent years, the diameter correction coefficient (Kφ) of icing thickness on conductors is proposed. The Kφ can meet the demand of the ice thickness design of the lines for observed regions. Moreover, the influence of height on ice thickness on conductors is analysed. The results may provide invaluable reference for engineering applications designing reliable power transmission lines for cold climate region. [ABSTRACT FROM AUTHOR]

The pollution flashover performance of insulators is generally tested by the steam fog method. However, environmental temperature in tests differs greatly, so the dispensability of test results is high. Moreover, the influence of fog‐water conductivity has not been taken into account. Compared with the steam fog method, the cold‐fog method simulating natural fog is more consistent with the actual operating conditions of transmission line insulators. This deals with the influence of salt deposit density (SDD) and fog‐water conductivity on pollution flashover performance. The influence of the two factors is determined by analysing the results of laboratory experiments where polluted insulators were tested by using the cold‐fog method. The results show that the 50% AC pollution flashover voltage (U50) decreases as SDD and fog‐water conductivity increase. The correction coefficient (K) indicating the influence of fog‐water conductivity on U50 can be expressed as an exponential function, where the factors are 0.0476, 0.0587 and 0.0567 for samples A, B and C, respectively. [ABSTRACT FROM AUTHOR]

Carbon foam templates were prepared from a mixture of mesophase pitch (MP) and Si particles, followed by foaming and carbonization. Subsequent molten Si infiltrated into the carbon foam at 1500°C for 4 h in an inert atmosphere resulted in the formation of porous SiC ceramics. Micrographs were investigated by a scanning electron microscope (SEM), and phase identification of porous SiC ceramics was performed by X-ray diffraction (XRD). The flexural strength and bulk density of porous SiC ceramics were also measured and calculated. The results revealed that the flexural strength of porous SiC ceramics increases with increasing Si content and decreasing porosity. The addition of Si in MP results in an increased densification of porous SiC struts. With 50 wt% Si, porous SiC ceramics with a high flexural strength of 23.9 MPa and a porosity of 55% were obtained. [ABSTRACT FROM AUTHOR]