A fractal-based approach is presented for the direct-stroke shielding analysis of high-voltage substations. The proposed method considers the effect of lightning polarity and the stochastic nature of the lightning attachment phenomenon. An application to a typical 69 kV substation reveals that shielding failures may occur even if the shielding design is realized with IEEE Std 998-2012 methods. This can be explained by the fact that the shielding design methods adopted by IEEE Std 998 do not consider the effects of lightning polarity and object height on striking distance. In addition, IEEE Std 998 methods adopt a deterministic approach on shielding failure analysis neglecting the branched and tortuous behavior of lightning discharges. Fractal-based simulation results show a considerable dispersion of striking distance and a significantly higher shielding failure probability for downward positive lightning than negative lightning. This work forms a discussion framework on shielding failure analysis following a stochastic approach; this approach may explain unexpected shielding failures, such as those reported in IEEE surveys, and can be used for the direct-stroke shielding design of mission-critical high-voltage substations.

Shielding Failure of High-Voltage Substations: A Fractal-Based Approach for Negative and Positive Lightning

This paper presents the analysis of lightning overvoltage for the new coming 115 kV CMU (ChiangMai University) GIS (Gas Insulated Switchgear) substation applying simplified models. The GIS being considered here is connected to an overhead line through XLPE underground cables. The sensitivity analysis of lightning overvoltage have been evaluated using ATP-EMTP. Factors including, pole footing resistance, cable length and additional surge arrester installed which gives the variation of overvoltages in GIS have also been considered. Finally, means to reduce the lightning overvoltages for the new coming 115 kV CMU GIS substation will be recommended.

Studies of lightning overvoltages of 115 kV CMU GIS substation

Electrical substations of 220−750 kV are objects of critical infrastructure with a complex branched technical system, various communications, and expensive equipment. Current regulations provide only general concepts and calculation methods for the simplest objects; however, the issue of arranging a lightning protection system with a combination of mesh, cable, and rod lightning rods for complex power facilities has not been considered. The aim of this study was to systematize the parameters and determine the directions of research on the development of risk assessment methods for determining the level of lightning protection of existing substations with a voltage class of 220−750 kV. Using analysis and synthesis methods, the parameters influencing the risk components were identified and systematized to determine the level of lightning protection, which was performed using the risk assessment method. It has been shown that two components should be considered when determining the level of lightning protection using the risk assessment method for energy facilities: the risk of loss of human life and the risk of loss of services to the public. Areas of research with further development of the risk assessment methodology for 220−750 kV substations are outlined. The parameters for the risk assessment were grouped according to the characteristics of the energy facility, such as location, dimensions, mode of operation of personnel, and line characteristics. The transition from generalized concepts for basic parameters of the risk assessment method to terminology of power plants and substations is performed, and components and parameters that are not considered are identified, which simplifies the determination of the level of lightning protection for existing electrical substations with a voltage class of 220−750 kV

The Problem of Determining the Level of Lightning Protection for Electrical Substations by the Risk Assessment Method

Lightning risk assessment of a 170 kV GIS substation connected to the Hellenic transmission system through underground cables has been performed Fast-front overvoltages impinging on the substation due to shielding failure and backflashover of the incoming overhead transmission lines have been computed with the aid of ATPEMTP simulations and evaluated with respect to the insulation level of the substation equipment The mean time between failures of the substation is greatly reduced for higher tower grounding resistance and varies significantly among lightning attachment models employed for the evaluation of the lightning performance of the incoming overhead transmission lines Implementation of the IEEE Std 1243:1997 in lightning risk assessment of substations imposes high requirements on protection against incoming fast-front overvoltage surges (5 pages)

Lightning risk assessment of a 170 kV GIS substation connected to the Hellenic transmission system through underground cables

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Lightning risk assessment of a 170 kV GIS substation connected to the Hellenic transmission system through underground cables