Numerical Calculation And Measurement Of Parameters Of Large Gronding Grids In Industry Frequency

The substation grounding grid can provide a reference ground for various electric devices within the substation. During a fault of an electric power system, the failure current drains quickly to the ground. The maximum ground potential rise can be controlled to ensure adequate safety for people and to protect the installation. Therefore, an effective grounding grid is very important for the safe operation of the electric power system.Along with the development of electric power system capacity, the value of failure current flowing into ground has been increased greatly. Particularly, after the construction of the three gorge power plant, 34kA can be reached. In order to control ground potential rise, the area of the grid may be very large and maximum diagonal of the grid can be above a kilometer. When a fault is happened in a power system, the failure current flows along the conductors and leakage current drains quickly to the surrounding earth. Before the total current drains to the ground, the great potential fall may be generated as longitudinal current flows through the resistance and inductance of the conductors. The great potential differences are generated between points of the grounding grid. It shakes the currently used grounding design method based on the ground electrode equipotential. Efficient simulation numerical calculation methods and software are developed in this paper based on electromagnetic field and basic electric theory to improve the level of grounding system design. The grounding resistance measurement in non-uniform soil and grounding impedance measurement for large grounding systems are also studied.The study of the dissertation includes calculation of grounding parameters of large grounding grids in industry frequency, design of large substation grounding electrodes, analysis of grounding grids intertied with buried conductors, calculation of grounding parameters in industry frequency after consideration of iron nonlinear permeability, grounding resistance measurement in non-uniform soi} and grounding impedance measurement for large grounding systems.The calculation method for substation grounding systems regarded as an equipotential is the basis of the calculation method for substation grounding systems regarded as a nonequipotential. First of all, the method for calculating stationary current field produced by a point current source in multiplayer media is discussed. A complex image concept is introduced on the basis of the classical image method. An efficient method based on a complex image is derived for calculating Green's function of horizontal three-layer soil. Thesoftware is more efficient. Comparing with the results in some literature, the equipotential software is testified.Based on method of moment and field-circuit coupling theory, a numerical calculation method of substation grounding grids is presented. The resistance and self-inductance of conductors as well as mutual inductance between conductors are taken into account. It can be used to calculate grounding parameters in industry frequency. The calculating method is verified, comparing with the results of the famous software. The short circuit experiment of 500kV shuanghe substation in the early 80's last century is analyzed. The calculating results are in agreement with the experiment results. Therefore, the method in this paper is very practical.Based on the software developed in this paper, many practical engineering problems such as the choice of grounding materials, the difference between the grounding impedances in industry frequency and the grounding resistances with the euipotential grounding electrode, touch voltages and step voltages, potential differences within the grounding grids, the choice of grounding conductor radius, short circuit current flowing multi-points into ground as well as efficient area are analyzed. The principals for the design of large grounding grids are renewed.In order to decrease the grounding impedance, it is usual to use a main grounding grid that is intertied with anot...