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In order to provide reference for the operation and maintenance of porcelain insulators on DC transmission lines, the test method for electrolytic corrosion of iron caps was studied in National Engineering Laboratory for Ultra High Voltage Engineering Technology (Kunming) of China, with XZP2-300 porcelain insulators that had no protection zinc collar. The results indicated that the spray water method could simulate the field corrosion condition when the conductivity and volume flow rate were 12 mS/cm and 6-12 L/h respectively, and the differences in the length, width and depth of corrosion area between the test results and the field condition were less than 8%. Besides, the differences in the test results with spray water method from two experimenters were less than 7%. Our study demonstrated that the spray water method proposed in this paper had good equivalence and repeatability, which could be used to research the electrolytic corrosion problem of iron caps of porcelain insulator on HVDC transmission line. [ABSTRACT FROM AUTHOR]

The space charges produced by the corona discharge of the DC voltage divider's high-voltage electrode can move under the effect of the electric field force, and parts of them can attach to the surface of the insulation sheds. Because of the influence of the space charges and the charges on the insulator sheds' surface, the electric field around has a big difference with the situation in the electrostatic field. In the paper, a 2-D axisymmetric upwind finite element method (upwind FEM) is used to calculate the electric field distribution on the surface of the DC voltage divider's insulation sheds. The space charge density inside the insulation sheds is set to be 0, and the charge density on the surface of the sheds is calculated by the iterative process. The ionized field of a 3-D sphere electrode model is calculated, and the 2-D axisymmetric upwind FEM is verified by comparing the numerical results with the analytical results. In the end the ionized field of the 500 kV voltage divider is calculated. The simulation results show that the existence of space charges affect evidently on the electric field distribution characteristic, and hence improve the uniformity of the electric field intensity along the sheds surface. [ABSTRACT FROM AUTHOR]

The backflashover rate (BFR) of typical 220/110 kV quadruple-circuit transmission lines due to direct negative first and subsequent return strokes and the effects of common lightning protection measures are quantified. The method based on ATP-EMTP and IEEE electro-geometric model (EGM) is adopted. The results show that the peak current distribution of the first and subsequent stroke has great influence on the BFR. The subsequent strokes propagate along the first stroke channel may lead more multi-circuit trip-out than the first stroke. The influence of tower foot resistance on single and double circuit BFR due to the first stroke is more serious than that due to subsequent strokes. The protection measures of unbalanced insulation, insulation strengthen and coupling ground wire are effective for BFR due to first and subsequent strokes. [ABSTRACT FROM AUTHOR]

Composite cross-arms have been developed to take place of the steel cross-arm in the power system. In order to suit the environmental impact factors in the long-term operation, superior comprehensive properties of the internally insulated materials for composite cross-arm are required. In the present study, a syntactic foam based on hollow polymer microsphere (HPM)-filled siliconized epoxy resin (SER) was prepared for satisfying these requirements. First, the SER was synthesized using poly (methylphenylsiloxane) and an epoxy resin via a graft reaction. The as-synthesized SER was characterized via Fourier transform infrared, 1H nuclear magnetic resonance (NMR), and 13C NMR spectroscopies. Subsequently, a series of SER-based syntactic foams were fabricated using HPM with five different mass fractions. According to the thermogravimetric analysis results, the thermal stability of the composites considerably improved because of the introduction of the siloxane bond. The dielectric constant and dielectric loss of the composites simultaneously decreased with increasing HPM content. The dielectric strength of the composites remained 10.08–21.31 kV/mm after hydrothermal treatment, indicating excellent electrical insulation reliability. Notably, after water diffusion pre-stressing, the leakage current properties of the composites only slightly differed as the HPM content increased. These results further support their application as an internally insulated material for a composite cross-arm. Image 1 [ABSTRACT FROM AUTHOR]