Research On Fast Computational Model And Method Of Grounding Transients

When lightning strikes a substation or transmission lines, high currentsgenerated by the stroke will flow into the grounding system and dissipate in thesoil. The electromagnetic fields generated by such high current may causedamage to equipment and may be dangerous to personnel working nearby. It isvery important to establish a transient computation model of grounding systemsunder lightning strike correctly. With the wide use of sensitive electronicdevices and digital electricity in electrical systems, the interference and damagecaused by spatial electromagnetic fields are more and more clear. One of themis the voltage between core and sheath of a cable, which is caused by thelightning or fault current conducted to the ground.Because the frequency of surge current is very high, the transientcharacteristics of grounding systems are different with those under lowfrequency. The inductance and capacitance between conductors becomes largerand the metallic impedance of conductors is larger because of skin effect. Theseall make the equivalent-potential model incorrect, which is a correct modelunder low frequency. Otherwise, the methods of segmentation are often used intransient computation. Many scholars ignored the effects of mutual-admittancebetween conductors when doing transient computation for the complexity.In this paper the mutual-admittance is proved very important and cannot beignored when doing transient computation of grounding systems. Havingconsidered the effects of skin effects, whirling current in the soil and themutual-admittance between conductors, the writer establish a model fortransient computation of grounding systems under lightning, and a computingmethod based on EMTP according to the characteristic of this model.The grounding potential rising (GPR), contact voltage and page voltage areanalyzed in the paper. The relationships between the GPR, contact voltage, pagevoltage and the current decanting point, current frequency, depth of groundingnetwork, relative permittivity are discussed respectively.The interference produced on secondary cable is discussed in this paper.The effects of soil resistivity, relative permittivity, the density and area ofgrounding network are described. Except the conductive interference, theradiant interference due to mutual inductance caused by current in groundingnetwork is also sketch out. The results show that the wiring modes of cableshave important effects on the interference produced on the cable. Better wiringmode can decrease the interference.In this paper, a new model of cable, parallel multi-conductors model isproposed. The theoretical base, computing methods of the parameters andrealization of program are introduced detailed.