Earthing Module

Grounding Module

7 Hours of Training

In this module, you will learn: 

1. Human safety

• Distinction between earthing and grounding 
• Average Resistance of Human Body 
• Potential difference and Electric shock 
• Tolerable body current as a function of time 
• Role of PPE (Personal Protective Equipment) when working on energized circuits 
• Advantage of fast clearance of fault from human safety point of view 
• Application of Earth Leakage Circuit Breakers (ELCBs)

2. Soil Resistivity

• Definition of Soil Resistivity and comparison with metals such as Copper and GI 
• Effect of moisture content on soil resistivity 
• Effect of salt on soil resistivity, corrosion allowance for electrode sizing, Soil classification based on corrosion intensity 
• Non-corrosive materials for treating earth pits – Coke, Charcoal, Bentonite clay 
• Effect of temperature on soil resistivity 
• Wenner’s four probe Method for soil resistivity measurement

3. Electrode Resistance to Earth

• Definition of Electrode Resistance to earth, Resistance to earth of hemispherical electrode, 
• Concept of Resistance area of soil and the area of soil influencing electrode resistance 
• Formulae for the resistance of tube or rod electrode and horizontal strip electrode; influence of length, cross section, and material 
• Discussion on Plate electrode

4. Grounding Grid Resistance

• Effective Resistance of two and three electrodes in parallel and minimum separation distance between electrodes 
• Sverak formula for overall Grounding grid resistance with numerical examples 
• Influence of Area of grid and electrode material on grounding grid resistance 
• Grounding grid resistance measurement at site using Fall of potential method, 90 degree connection for potential electrode 
• Procedure for electrode sizing (cross section), Design current density for copper, Aluminium and GI for electrode sizing, 0.5sec and 1sec duty.

5. LV and MV System Earthing

• Role of bonding conductor or earth continuity conductor in reducing shock hazard 
• Key features of Low Voltage system earthing 
• IEC classification of LT distribution in utilities based on bonding between Neutral Conductor and Earth Continuity conductor, TN-S, TN-C-S, Modified TN-C-S, TT 
• Earthing of Medium Voltage systems (grounded and ungrounded) and NGR enclosure earthing 
• Mis-interpretation of IE rules regarding neutral and body earthing 
• Guidelines for earthing of Lightning Arrestors

6. Miscellaneous Topics

• Introduction to Clean Earth (Electronic Earth) and recommendations for interconnection with Power Earth 
• Earthing of Fuel tanks and Lightning protection measures for fuel tanks 
• Busduct enclosure earthing 
• Earthing grid for solar farms, Early Streamer Emission (ESE) Air Terminations for lightning protection; Inverter earthing 
• CT secondary earthing, risks of multiple earthing 
• Recommendations for cable insulation grade (earthed or unearthed) based on type of system grounding (Ungrounded, solidly grounded, Resistance / Reactance grounded)

7. Switchyard Grounding Grid Design concepts

• Definition of Ground Potential Rise (GPR) 
• Split Factor (SF) and its Relationship to Fault Current, current discharged to earth, and GPR 
• Shield wire in overhead line – current diversion by induction and conduction, Influence of Tower footing resistance and Ruling Span 
• EHV Cable – Sheath Cross Bonding, path of fault current returning to source, Split Factor 
• Site measurement of current through shield wire and cable sheath during faults 
• Definition of Step Potential and Touch Potential, values near the boundary of grid o Numerical example showing the need for meshed grid to reduce Step and Touch potentials (Comparison of 6 x 9 grid vs 2 x 2 grid). 
• Effective foot resistance involved for Step and Touch potentials, deciding criterion Touch potential 
• Comparison between Uniformly spaced and non-uniformly spaced grids 
• Effect of thin layer of gravel over native soil in EHV Switchyards 
• Formulae for Allowable Safe Step and Touch Potentials based on Body Resistance, Tolerable body current, surface layer(gravel) resistivity and native soil resistivity. 
• Calculation of design Step and Touch Potentials for assumed grid geometry as per IEEE Std – 80. 
•  Influence of electrode Cross Section on Step and Touch Potentials 
• Examples of earthing grid design using software with color coded output showing safe and unsafe areas from Step and Touch potential point of view. 
• Earthing of special Areas in AIS – Isolator Handle and Fence

8. Reference and Applicable Standards

Duration: 7 Hours