Risk Assessment Of Substation Grounding Systems

The power grid has developed rapidly towards long distance,large capacity,extra high voltage,and high intelligence.The area of the substation grounding network and the fault short-circuit current have also increased continuously,and security accidents caused by it have also occurred from time to time.The rise of the ground network potential and the potential difference caused by the short circuit or lightning strike failure pose a certain threat to the safety of the staff and equipment in the station.Therefore,the evaluation and optimization about the safety performance of the newly-built or operating substation grounding system is an indispensable part of the entire process which contains the design,construction,operation and maintenance.This thesis mainly calculates the risk probability of the substation grounding systems from the perspective of personal safety when a ground fault occurs based on the comparison and evaluation method of the traditional characteristic parameter threshold value of the substation grounding systems and evaluates the safety performance of the substation grounding system based on the principle of " As low As Reasonably Practically ".And then,corresponding risk treatment measures are given according to the evaluation results.At the same time,on the premise of ensuring the safety performance of power frequency grounding faults in the substation grounding system,the impact of transient ground potential rise on the equipment in the station under lightning strike faults and the electric shock effect of the step voltage on the human body are studied,which makes power plants and substations operate more safely and reliably.The human current and voltage tolerance characteristics of different body currents and body impedance factors in electric shock scenarios are studied,and the principles of a global risk management framework including risk identification,risk analysis,and risk assessment are explained.The personal risk probability calculation method and risk assessment process of the substation grounding system are introduced from the perspective of personal safety.And the risk grading and early warning technology under grounding fault are described.The general design and performance evaluation procedure of the substation grounding system incorporating risk probability analysis is summarized.Taking the grounding system of a 500 k V substation as a research example,the simulation model of the grounding system of the substation is established with the help of CDEGS software to obtain the distribution of soil inversion model and the distribution of characteristic parameters such as grounding resistance,ground potential rise,contact voltage and step voltage.The risk probability is analyzed and evaluated,and the corresponding early warning measures are given according to the evaluation results.The evaluation results are compared with the results in the existing literature to verify the accuracy and feasibility of the proposed risk probability evaluation method.The effects of transient ground potential rise on secondary equipment in the station under lightning strike fault and the shielding effect of the secondary cable shielding layer on the transient ground potential rise were studied through field test and PSCAD simulation calculation.The electric shock effect of the step voltage on the human body is analyzed to realize the safety analysis of the grounding system under the lightning transient fault.