PART III- Voltage Surges, Over- voltages, Circuit Interrupters and Grounding Practices
Chapter 22. Grounding practices
• Grounding electrodes
• Resistivity of soil (r)
• Measuring the ground resistance
• Metal for the grounding conductor
• Jointing of grounding conductors
• Maintenance of grounding stations
• Grounding practices in a power generating station
• Tolerable potential difference at a location
• Voltage gradients
• Determining the leakage current through a human body
• Measuring the average resistivity of soil
• Improving the performance of soil
• Determining the ground fault current
• Designing a grounding grid
Grounding electrodes for buildings, industrial installations and substations
The following are a few types of grounding electrodes commonly used for the grounding of buildings, industrial installations, equipment grounding or small and medium-sized substations. Power generating stations and large switchyards may experience large ground fault currents accordingly, grounding electrodes demand a lot more safety considerations and are discussed in Section II.
Grounding practices in a power generating station
This is a vast subject, on which extensive research has been done by many authors and field engineers over the years. The grounding stations in such areas are normally spread over the entire station, and sometimes may even extend beyond its boundary to achieve the desired results. Here we discuss briefly, the basic criteria behind the elaborate requirement of a grounding system in a power station and its design considerations.
The magnitude of ground voltage in such areas in the event of a ground fault is very high, due to high system voltage. On a ground fault, the ground path resistance may become a source of a high potential gradient across the grounding conductors at a particular location. It may become high enough to prove fatal to a human operator coming into contact with it. To limit this potential difference at all locations within a tolerable value and achieve an equipotential distribution of a ground conductor over the station is the basic criterion on which is based the design of a grounding system for a power generating station. Our discussion is also applicable to outdoor switchyards and large substations. For detailed working, it is advisable to refer to IEEE-80.