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SUMMARYTo solve a grounding problem which describes a grounding system with floating metallic conductors buried in vertical multilayer earth model under a high voltage a.c. substation, a new mathematical model for accurately computing currents flowing along conductors of the grounding system has been developed in this paper, which is hybrid of Galerkin's type Boundary Element Method and conventional nodal analysis method. Propagation effect of electromagnetic wave within the substation has been neglected due to its limited area. A quasi-static complex image method and new closed form of Green's function for the vertical multilayer earth model are introduced into this model to accelerate mutual impedance and induction coefficients calculation. The model is then implemented in a computer program, which can be used to calculate currents distribution of any configuration of grounding system, and with or without floating metallic conductors buried in the vertical multilayer earth model.

The corona onset voltage (COV) for bare overhead bundle conductors for transmission lines has been investigated using numerical calculations and the gas discharge theory. First, an accurate numerical method, the charge simulation method, was used to calculate the electric field distribution in the vicinity of bare sub-conductors in bundles. Then the electric field values and a criterion from the gas discharge theory were used to evaluate the onset voltage for negative coronas on the bare sub-conductors. The COVs obtained are in good agreement with literature data for laboratory models and full-scale test lines. Some numerical results for the COV for six-bundle conductors are also discussed.

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Abstract-Based on quasi-static electromagnetic field theory, recently grounding system under alternative currents (AC) substation has been studied with equal potential and unequal potential models. In these numerical models, the closed form of Green's function for a point source within a horizontal multilayered earth model and its quasistatic complex image method have been fully discussed. However, less information about how to achieve the closed form of Green's function through Matrix Pencil method is presented in these references. In this paper, we discuss how the kernel of the Green's function can be expanded into a finite exponential series.