Abstract
Since high voltage transmission line towers or wind turbines structures are installed in high-altitude areas, it is essential to achieve a high overvoltage protection system against direct and indirect lightning strikes collisions. The lightning current must be discharged quickly into the protective earth, to prevent the dangerous over-voltages formation and define a reference voltage node. This paper presents a novel model to assess the behavior of the grounding system, based on Pocklington integral equations under lightning magnetic fields and variations in soil ionization, in which an explicit circuit-based vector fitting RLC admittance branches are proposed. The frequency-dependent behavior of grounding system frequency response and soil ionization effect is modeled in time domain, straightly to implement into the electro-magnetic transient program (EMTP). The model verification contains horizontal, vertical, and their combinations of grounding grids to represent the complete investigations under lightning strikes. The harmonic impedance mathematical formulations and principles are derived based on a rational function, that could be applicable on ground potential rise (GPR) investigation.
Highlights
Grounding systems, or the buried electrodes under the soil, are essential and significant to provide the health and safety for the staff occupied at high-voltage substations, power plants and industrial areas
When the high-frequency lightning strokes collide to the ground as a shock wave and excite it, the Earth high-frequency components emerge from the ground, causing soil ionization
Afterwards, the soil particles properties cause the non-linearization of the transient state of buried grounding grid under the soil
Summary
The buried electrodes under the soil (either individually or in combination and interconnected with regular arrangements), are essential and significant to provide the health and safety for the staff occupied at high-voltage substations, power plants and industrial areas. If these equipments are buried in multilayer soils with different special resistances and with different geometries such as cylindrical or spherical soils, the modeling of its electrodes, in order to analyze power networks in software packages, is practically impossible. This paper presents a novel technique to investigate all these phenomena, in order to investigate the electromagnetic transient states of lightning strikes by fast relaxed vector fitting (FRVF) algorithm Using this method, each arbitrary grounding system can be implemented and evaluated with just a few simple RLC admittance branches with a low-order state-space transfer function and frequency response in a very wide frequency range. Another feature of this process is its high precision and computational speed
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