Abstract
This chapter contains safety criteria according to IEEE Standards, step and touch voltage criteria, reduction factor, simplified equations for mesh and step voltage, application of step and mesh potential in safe earthing system design, safety criteria, IEC 479-1 STD, permissible touch and step voltage according to IEC 479-1, Optimum Compression Ratio (OCR), test and verify, approximated analysis to calculate voltage profile using apparent soil resistivity, Scaling factor, test and verify the approximated method—Ground Potential Rise (GPR) of faulty substations having equal and unequal spacing grounding grids conductors. This chapter draws attention also to the following points: Infinite Series Potential (I.S.M.) expressions in three dimensions and calculations of three dimensions potential rise.
TopIntroduction
Since the early days of the electric power industry, safety of personnel in and around electric power installations have been a prime concern.
Over the years and after many investigations on the effects of electric current on humans, safe limits have been established and standards have been developed which provide permissible values of body currents to avoid electrocution. Two such standards are IEEE 80 (1961) and the IEC60 479-1(1984). The purpose of both standards is to establish safe (permissible) body currents.
Since IEEE Standards 80 publication in 1961, Guide For Safety In AC Substation Grounding, has been favorably received by the industry and gained a broad acceptance worldwide, this chapter presents the improvements in a broader context of the Guide’s development to this date.
This chapter is organized as follows: first the safety criteria as stated in the two documents, IEEE Standards (2000) and IEC 60479-1 (1984), are described in detail and evolution of IEEE standard. A common basis for comparison is developed in terms of permissible touch and step voltages.
A detailed analysis of potential profile at a surface above energized unequally spaced grounding grid has been carried out, for soils with multiple layers. Exact and approximated algorithms are used to obtain the voltage profile and then to calculate the step and touch voltages.