Abstract This paper presents a new type of poly(dimethylsiloxane)/modified nano-silica (PDMS/modified nanosilica) hybrid superhydrophobic coating to reduce ice accumulation on insulators. The PDMS/modified nano-silica hybrid coating and a room temperature vulcanized (RTV) silicone rubber coating were formed on glass insulators for ice accumulation experiments in the laboratory. The hydrophobicity of the two coatings was measured and compared. Average water contact angle on the PDMS/modified nano-silica hybrid coating reached 161°. The microstructures and functional groups on the surfaces of both coatings were investigated using field-emission scanning electron microscopy (FE–SEM) and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy, respectively. Analysis results show that both multiscale microstructure and low surface energy contributed to the superhydrophobicity of the PDMS/modified nano-silica hybrid coating. Finally, experiments on ice accumulation on insulators were carried out to investigate the anti-icing properties of the PDMS/modified nano-silica hybrid coating on insulators. Significantly smaller rate of ice accumulation was observed for the insulators treated with the PDMS/modified nano-silica hybrid coating, relative to that treated with the RTV silicone rubber coating.
Icing experiments on three units of XP4-160 insulator string are conducted to reveal the influence of the crystallisation effect of conductive ions during phase transition on melting water conductivity and ice flashover voltage, and to analyse the motion of conductive ions and its spatial distribution. The influence of different parameters, such as freezing water conductivity, electric field and pollution, on crystallisation effect is examined and analysed. Results of the tests indicate that the melting water conductivity of the ice layer and icicles is considerably greater than that of freezing water, particularly for a polluted insulator, because of the crystallisation effect. The electric field has a significant influence on the crystallisation effect, that is, the melting water conductivity under a non-energised condition is higher than that under an energised condition. Finally, through 35 kV insulator flashover tests, the reason for the propagation of partial arcs over icicles is determined, and the flashover process is illustrated. The crystallisation effect during phase transition changes the ion distribution in a solid ice layer, thereby increasing water film conductivity, and is also a critical reason for the decline of ice flashover voltage.
Lightning is the main reason that endangers the safety and reliability of transmission line today, but the existing models of estimating shielding failure outage rates can not be in agreement with field experience at present. Based on electromagnetism field, the paper studies on the striking distance factor for higher tower, the simulation results by self programming show that the striking distance factor(β) will reduce with the height(H) of tower increasing, and the value of lightning current does not affect on the striking distance factor and gets the relation equation between β and H :β=1.18?H/108.69, furthermore, the striking distance factor is introduced to the improved electric-geometry model to analyze the lightning protection performance of shielding failure for ultra high voltage transmission line. Taking 500kV Yafu transmission line as example, the improved electric- geometry model gets the result in agreement with field experience. At the same time, the paper analyzes the influence of the height of tower, the grounding obliquity, the shielding angle and the electrical stress of insulators on the lightning performance of the transmission line.
In this paper, a model based on dynamic electric field analysis has been developed to predict the flashover voltage of the ice-covered HV insulators, under dc voltage. The potential and electric field calculation models before and after air gap breakdown are built respectively based on finite element method (FEM). The arc initiation process is determined based on the model before air gap breakdown. The critical applied voltage and leakage current to maintain an arc with certain length are obtained based on the electric field calculation model after air gap breakdown and the U-I characteristic of the arc. Moreover, the improved Hampton criterion has been employed to determine the critical flashover of the ice-covered insulator. The results obtained from the dynamic electric field analysis model have been compared with other mathematical and experimental results of other researchers and got a great agreement.
Tower surge impedance is an important parameter in the prediction of HV and EHV lightning outage rates. Several attempts have been made to measure it experimentally on full scale towers, and formulas to calculate this parameter have been proposed by Jordan, Wanger and Sargent, etc. However, the values of surge impedance calculated using these relationships are in poor agreement with each other and, in general, with the various measured values. This paper presents a simulation model of uneven distributing parameter for determining the surge impedance of towers by the Electromagnetic Transients Program (EMTP). This paper also demonstrates that the values so obtained describe the response of the tower adequately when a transmission line is struck by lightning, Furthermore, the simulation value of tower surge impedance is close to the actual test value and the relative error is ten percent.
According to the laboratory investigations carried out on the positive switching impulse discharge performance of rod-plane short air-gaps less than 500 mm simulated the atmospheric pressures of the altitude of 4000 m and above in the artificial climate chamber, this paper discusses the effects of the altitude and the atmospheric conditions on the positive switching impulse discharge performance of rod-plane short air-gaps of 200/spl sim/450 mm, and puts forward that the discharge voltage of the air-gaps is related to the relative air density and the temperature and the absolute humidity, and that the 50% positive switching impulse discharge voltage of a rod-plane short air-gap is the power function of the product of relative air density and the absolute humidity, and that the characteristic index of the effect of atmosphere on the discharge voltage is about 0.41 for the short air-gaps less than 500 mm. Based on the analysis of the tested results, it puts forward the atmospheric correction factor of discharge voltage of the short air-gaps at the positive switching impulse voltage.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
