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Live working is important for the continuity of electricity supply in power system. Experiment results of 50% switching impulse sparkover voltages (U50) for different live working entering routes on a real tower are presented. The potential and electric-field distribution around the 750 kV straight tower window with a line worker inside, was analyzed via an approach combing charge simulation method and indirect boundary element method. The comparison demonstrates the close relationship between electric-field distribution and (U50). The sparkover voltage and the maximum electric-field strength change synchronously for a specific structure. Generally speaking, the higher the electric filed strength is, the lower the sparkover voltage will be. Thus, the experiment procedure for deciding the best entering route can be simplified according to the electric-field distribution calculation. [ABSTRACT FROM AUTHOR]

This paper presents the study on the potential distribution of the ac 1000-kV ultra-high voltage metal-oxide arrester (MOA). Based on the idea of field-circuit combination, the 3-D finite-element method (FEM) and circuit-analytic method are applied to analyze and improve the potential distribution of the 1000-kV MOA. The 3-D FEM is used to obtain the 1000-kV MOA's potential distribution and stray capacitances to build the equivalent circuit of the MOA. With the equivalent circuit, the method to improve the potential distribution of the MOA by adding parallel capacitors is analyzed. A scheme to obtain the recommended values of parallel capacitors is achieved to improve the potential distribution coefficient within ±5%. In addition, the influences of the grading ring and mounting height of the MOA on the potential distribution are also discussed. The potential distribution of the developed 1000-kV surge arrester was tested by the photoelectricity measurement method, which is close to the analysis results. [ABSTRACT FROM AUTHOR]

The impulse characteristics of frozen soil are the fundament for the lightning protection design of the overhead transmission lines in frozen soil environments. In this paper, the conductivity and lightning impulse breakdown characteristics of the frozen soil were experimentally studied, and those key factors influencing the impulse breakdown characteristics of the frozen soils such as temperature, water content and salinity were analyzed systematically. Comparing with the normal soil, some important conclusions on the impulse breakdown characteristics of the frozen soil were proposed. The electric breakdown process accompanied by a thermal thaw process was proposed to explain the impulse breakdown mechanism of the frozen soil. [ABSTRACT FROM AUTHOR]

When dc current is injected into the earth through the grounding electrodes of an HVDC system, transformers in an ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a circuit model is presented to calculate the dc current distribution in an ac power system caused by the ground return current of a dc system. A complex image method is used to calculate the ground potential rise of each substation in multilayer earth. An indirect boundary element method is used to take into account the effects of mountains, rivers, and sea. The circuit equations are used to take into account the effects of the transmission lines. By using the method, the dc current distribution and the effectiveness of restraining measure in an ac power system are analyzed. The method and the results are not only useful for analyzing the influence of the ground return current from an HVDC ground electrode on ac power systems, but also useful for analyzing the effectiveness of the restraining measure. [ABSTRACT FROM AUTHOR]

In this paper, the electric-field distribution around the composite insulators and the heads of transmission towers is calculated by a model coupling the indirect boundary-element method to the moment method. The heterogeneous media, such as the composite insulators and the filament metal structures such as the transmission towers and the transmission lines, are considered altogether. The method can take into account not only the permittivity but also the resistivity of the media by using the complex resistivity in the frequency domain. The electric-field distribution around a three-phase 330-kV transmission tower with composite insulators was analyzed. The electric fields on the surfaces of the grading rings and the phase subconductors and at the ends of the composite insulators are analyzed. Both the method and the results are useful for the design of high-voltage transmission lines. [ABSTRACT FROM AUTHOR]

The grounding systems are simply handled as lumped resistances with constant values in traditional lightning transient analysis of substation. A complete transmission line model is proposed to consider the actual transient process of power network and the grounding grid of the substation and the grounding devices of transmission towers. A loss transmission line model with time-variable parameters is proposed to calculate the transient characteristics of grounding systems under lightning current in which the soil ionization phenomena around the ground conductors are considered. The analyzed results by the proposed model have large differences with those obtained by the traditional simplified method. The transient characteristics of grounding systems have strong influence on the lightning transient process of substation. [ABSTRACT FROM AUTHOR]

In a high soil resistivity area, counterpoise wires are applied to decrease the grounding resistance of tower grounding devices. If the conductor of counterpoise wire is very long, although the power frequency grounding resistance of the tower grounding device ii decreased, the lightning protection performance of the transmission line is still not good. The influences of the length of grounding electrodes on the lightning transient characteristic were analyzed. The dynamic and nonlinear effect of soil ionization around the grounding electrode was considered in the analysis model of transient characteristics for the grounding electrodes under lightning impulse. The counterpoise wire has an effective length when lightning passes through it. When the length of a grounding electrode exceeds the effective length, the grounding conductor will not be utilized effectively. The simulating experiments were performed to analyze influences of the length of the counterpoise wire on the impulse characteristics. The formulae to calculate the impulse effective lengths of counterpoise wires were proposed. The model proposed in the paper has been validated by comparing the numerical results with experimental tests. [ABSTRACT FROM AUTHOR]