Electric Field Distribution of Soluble Salt Deposition on the Surface of Insulators in Railway Overhead Lines

Different constituents of soluble salts have different effects on the insulation performance of insulators.To study the electric field distribution of soluble salt deposition on the surface of high-speed railway insulators,a two-dimensional model of the cantilever insulator electrostatic field and constant-current field with soluble salt deposition is constructed.The simulation results indicate that the relative dielectric constant of dry pollution is the main factor that affects the electric field distribution on the surface of the insulator.The electric field intensity is arranged in the following order:CaSO_(4)>KNO_(3)>NaNO_(3)>K_(2)SO_(4)>NaCl>MgSO_(4),and the conductivity of each dirty liquid in the wet state becomes a key factor affecting the electric field distribution,which is specifically shown as sodium chloride>nitrate>sulfate.The simulation results are compared with existing test results to verify that they were correct.It is also found that the electric field intensity of the insulator with good hydrophobicity is slightly greater than that of the insulator without hydrophobicity.The results provide a theoretical basis for the classification of regional pollution levels and the testing of insulator contamination in the laboratory.

Contribution of underlying terrain to sand dunes: evidence from the Qaidam Basin, Northwest China

Underlying terrain strongly influences dune formation.However,the impacts of underlying terrain on the dune formation are poorly studied.In the present research,we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin,Northwest China.We quantified the dunes'sediment characteristics on different types of underlying terrain and the terrain's effects on the surface quartz grains by analyzing grain-size distribution,soluble salt contents and grain surface micro-textures.Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution,whose peak corresponded to the saltation load.Linear dunes were mainly composed of fine sands with a bimodal frequency distribution,whose main peak represented the saltation load,and whose secondary peak represented the modified saltation or suspension load.Sand was transported from source area by running water(inland rivers)over short distances and by wind over relatively longer distances.Thus,quartz grains had poor roundness and were dominated by sub-angular and angular shapes.Surface micro-textures indicated that dune sands were successively transported by exogenic agents(glaciation,fluviation and wind).Soluble salt contents were low in dunes that developed in the alluvial fans,which represented a low-energy chemical environment,so the grain surface micro-textures mainly resulted from mechanical erosion,with weak micro-textures formed by SiO2 solution and precipitation.However,soluble salt contents were much higher in dunes that developed in the dry salt flats,which indicated a high-energy chemical environment.Therefore,in addition to micro-structures caused by mechanical erosion,micro-textures formed by SiO2 solution and precipitation also well developed.Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin,China.