DEVELOPMENT OF SOFTWARE FOR GROUNDING DESIGN OF EHV SUBSTATION

Abstract

The objective of grounding system in a substation is to provide in and around the substation a uniform potential at near zero , or absolute ground potential. With this it is ensured that no human being in and around the substation is subjected to shock or injury on occurrence of abnormal conditions. If this is ensured then the grounding design is "safe" grounding. In this thesis work this has been kept in mind while designing the safe grounding grid for substation. Keeping in view of importance of grounding, there are several standards that deal with various aspects. ANSI/IEEE standard 80 addresses the impact of grounding system design on safety of personnel in the power station, ANSI/IEEE standard 81 addresses measuring of earth resistivity, ground impedance, earth surface potentials of a ground system and ANSI/IEEE std. 367 addresses to practice for determining the electrical power station ground potential rise and induced voltage from a power fault. While designing the grounding grid, these standards have been extensively used and limits and levels have been fully adhered. In this thesis work, methods for design of grounding systems have been reviewed in detail and grounding system for EHV substations has been designed by using these methods. A step to step designing procedures has been included. Also algorithms have also been included for easier understanding and then two software SSGNU and SSG80 have been developed for design of grounding for EHV substation. SSGNU program is based on numerical method and where as SSG80 is based on ANSI/IEEE Std. 80 and its updates. The designs obtained from . these programs have been validated by comparison with the results obtained from other published works. A case study has also been included for design of grounding system for 400 KV EHV AC substation. A comparison with existing design and that carried out by computer program SSG80 has been included and critically discussed.