Applied Mechanics and Materials Vols. 672-674

Abstract: Grounding grid was considered as a pure-resistor network and its inner information was obtained through limited grounding leads. A set of diagnostic equations was established based on Tellegen’s theorem. Iteration method and Nonnegative Least Squares method (NNLS) were used to solve it. To verify this method, corrosion diagnosis of single-branch and two-branch was simulated. An optimal plan was proposed in the simulating calculation, which diagnosed step by step and added measurement nodes according to the result of each step. This method is able to determine the corrosion position and degree reliably and the optimal plan has higher efficiency and less workload.

Abstract: Defects inside the gas-insulated switchgear (GIS) will produce ultra-high frequency (UHF) electromagnetic waves. The waves will be affected by the shell of GIS when propagating inside the GIS cavity. In the 0-3GHz frequency range, propagation characteristic of electromagnetic which is excited by partial discharge in GIS is simulated based on the method of finite difference time domain (FDTD). This paper designs the GIS simulation models with and without insulator according to the size of a 220kV single phase GIS bus and sets a metal protrusion defect on the bus as the PD source. The transmission characteristics of model waves inside typical GIS structures, and the influence of the insulator to the propagation of electromagnetic wave was studied via setting the different directions of electromagnetic, comparing the time and frequency domain results of electromagnetic wave in different structures and measurement angles.

Abstract: When the HVDC works in mono-polar operation or bipolar unbalanced operation, DC flows through the neutral point and causes DC bias magnetic of transformer around HVDC grounding electrode, which influences the operation security of transformers. Beside highly saturated core, it also causes the distortion of exciting current, increasing harmonics and leakage magnetic flux, and thus the losses, which in turn results in the structures of transformer overheating and insulation aging. Based on the principle of transformer DC bias magnetic and UMEC of transformer in PSCAD/EMTDC, electromagnetic transient simulation platform of transformer DC bias magnetic is built. Considering the effect of DC bias magnetic on different structure of transformer, three kinds of typical transformer that has been widely applied are selected including three-phase three-limb transformer, three-phase five-limb transformer, three-phase bank transformer. After comparing the differences between these three kinds of transformer, related parameters are set such as the core structure and mode of winding connection and so on.

Abstract: Lightning overvoltage often leads to transmission lines trip, which is the weak link of power system. In this paper, 110-kV transmission line model is studied on the basis of the EMTP software. Several simulation models are established for back flashover lightning, induced lightning, shield failure. The transient process of lightning stroke is studied. According to the contrast of simulation results of three kinds of lightning, a set of discriminant basis to distinguish lightning on transmission line is put forward.

Abstract: According to two typical COT bushing faults, three typical 220kV cable-conductor bushings (COT, TOM and BRDLW) widely used in the power grid are analyzed about bushing compact structure. Bushing pressing structure, installation clamping force, deformation deviation and sealing system are discussed in the paper. The study found that the installation clamping force and the reeds adjustment range of COT bushing is smaller than others. The manufacturability deviation and the poor condition will cause hidden trouble to the bushing sealing system. Last, several suggestions about bushing maintenance are given for the COT bushing.

Abstract: This article is one of the series of papers about the Cross-linked polyethylene cable partial discharge on-line monitoring and positioning system. Design and application, which is about the Cross-linked polyethylene cable partial discharge on-line monitoring and positioning system software, is discussed from the run analysis , log record and PC control, etc. Basing on the field running effect of the Cross-linked polyethylene cable partial discharge on-line monitoring and positioning system, it manifests the correctness and effectiveness of the above methods.

Abstract: According to the wind vibration shape of HVDC tower Under icing,the reason of guyed HVDC tower galloping is analysised.The mathematical model of icing guyed galloping and the vibration equation of HVDC tower is established .Using the measured wind data, the galloping dynamic characteristic of guyed HVDC tower under icing condition is completed in soft. The structure vibration situation drawing close to reality, the research results has been possible to provide the reference for wind disaster prevention.

Abstract: Based on the analysis of the influence of the reactive power flow in transmission lines and system on the net losses, the definition of the unbalanced reactive power of lines is given. Then the important impact of the unbalanced reactive power on the net loss is illustrated. Thanks to the flexible zeroing function, the apply of controllable reactor can lay a solid foundation for minimize the net loss. The actual grid example shows that the high-voltage controllable reactor system has an important impact on net loss. Compared with ordinary reactors, controllable reactors can effectively reduce the system losses.

Abstract: This article is one of the series of papers about research and development of partial discharge monitoring and positioning systems in cross-linked polyethylene(XLPE) cable. We discuss the design of hardware principle diagram which belongs to partial discharge on-line monitoring and positioning system in XLPE cable in terms of the system block diagram, power management module and control processing module and so on, the operation effect of partial discharge on-line monitoring and positioning system in XLPE cable shows the correctness and effectiveness of the above methods.

Abstract: This paper studies about the influence of main components in PM2.5 on insulator pollution flashover characteristics. A paper written by Institute of Atmospheric Physics Chinese Academy of Sciences presents the main components in Beijing’s PM2.5. Basing on that, an artificial pollution test in our lab. The test result shows that components in PM2.5 have no significant effect on insulator pollution flashover characteristics. But, in haze weather, insulators are easier to be polluted. As a result, the probability of insulator flashover become higher.