Theoretical Study On Impact Impedance Of Grounding Grid

Grounding of the power system is a very complex and important issue,which has a direct influence on electrical equipment and personal security. Grounding grid of the substation can provide a reference ground for electric equipment within the substation by draining the fault current to ground quickly while an electric fault is occurred, the maximum ground potential rise can be controlled to protect the equipment and to ensure adequate safety for people. Therefore,an effective grounding grid is very important for the safe operation of the electric power system. In this paper, some existed analysis methods for ground system home and abroad have been introduced, in which their advantages and disadvantages are analyzed in detailBased on method of point matching theory, the resistance and self-resistance of conductors caused by the leakage current of the conductors is analyzed, the grounding resistance of the grounding grid by direct current and low frequency current is calculated. Due to the characteristics of the inductance of conductors by high frequency current, the self-inductance of conductors and mutual inductance between conductors are taken into account to calculate the unequal potential of grounding grid. Then program for calculating the grounding parameters is compiled. Comparing with the results in other literature, its correctness is verified.As the grounding impedance in industry frequency, the impact grounding impedance becomes an important parameter to evaluate a grounding grid. Because of the importance of grounding for lightning,a improved method for calculating the lightning impact grounding impedance is presented, in which firstly the spectrum of lightning is obtained by Discrete Fourier Transform, then the frequency domain characteristics of the potential of grounding grid is calculated by using the unequal potential model, and the response of grounding grid in time domain is calculated by Inverse Discrete Fourier Transform.The method discussed above was applied to calculate the impact grounding impedance by different radius, conductivity, permeability of conductors, conductivity of soil, lightning wave and the characteristics of impact grounding impedance effected by various factors are analyzed . It is useful for designing and improving grounding grid.