Handbook on Electrical Earthing


CONTENTS

1.0 INTRODUCTION 01
1.1 ADVANTAGES OF EARTHING 02
1.2 TERMINOLOGY 03
1.3 EARTH AS CONDUCTOR 05
1.4 IMPORTANT INDIAN ELECTRICITY
RULE RELATED TO EARTHING 05
1.5 GENERAL REQUIREMENT
FOR EARTHING 07
1.6 DIFFERENCE BETWEEN
GROUNDING AND EARTHING 10
1.7 HUMAN ELEMENT & ELECTRIC
SHOCK 11
1.8 FACTORS WHICH DETERMINE
RESISTIVITY OF SOIL 13
1.9 LOCATION OF EARTH ELECTRODE 19
2.0 DESIGN, SIZE AND TYPES OF EARTH
ELECTRODE 20
2.1 ELECTRODE RESISTANCE TO EARTH 20
2.2 INFLUENCING FACTORS FOR
ELECTRODE RESISTANCE 21
2.3 ELECTRODE SIZE 22
2.4 DESIGN OF EARTH ELECTRODES 22
2.5 EARTH ELECTRODE 
2.6 TYPES OF ELECTRODES 26
2.7 TYPES OF EARTHING 32
2.8 EARTHING LEAD 35
 3.0 EARTHING SYSTEM 35
3.1 CLASSIFICATION OF EARTHING 35
3.2 EARTHING SYSTEM IN SUB STATION 41
3.3 EARTHING OF VARIOUS EQUIPMENT IN
 THE SUB-STATIONS 43
3.4 DISTRIBUTION TRANSFORMER
 STRUCTURE EATHING 47
3.5 EARTHING OF DISTRIBUTION LIENE
 STRUCTURES 51
3.6 EARTHING AT CONSUMER’S PREMISES 53
3.7 EARTHING IN INDUSTRIAL PREMISES 56
3.8 DANGERS OF IMPERFECT EARTHING 57
3.9 PRECAUTIONS 58
4.0 TESTING & MAINTENANCE 59
4.1 TESTING OF EARTHING SYSTEM 59
4.2 MAINTENANCE SCHEDULES 62
5.0 MAINTENANCE FREE EARTHING 65
5.1 EARTH RESISTANCE 66
5.2 APPLICATIONS 66
5.3 MAINTENANCE FREE EARTHING SYSTEM 66
6.0 DO’S & DON’TS 77
6.1 DO’S 77
6.2 DON’T 78
REFRENCES 

INTRODUCTION

Earthing is a connection done through a metal
link between the body of any electrical appliance, or neutral point, as the case may be, to the deeper ground
through these metal links, normally of MS flat, CI flat,GI wire penetrated to the earth grid. Object of earthing is that all parts of apparatus other than live parts shall be at earth potential.

Earthing eliminates the possibility of any
dangerous potential rise on the body of electrical equipment. It drains away the charge on the equipment through an earth connection. When an earth fault is
occurres such as winding insulation failure etc. causes a heavy current flow into the general mass of the earth.

This causes blowing out of fuse or operation/ tripping of protective devices. The potential under and around of the object shall be uniform nearly to zero w.r.t. earth.
Apart from this it is to ensure that operators or working personnel shall be at earth potential at all times, so that there will be no potential difference to cause shock or injury to a person, whenever any short
circuit takes place.

The primary requirements of a good earthing
system are:

a. It stabilizes circuit potential with respect to
ground potential and limits the potential rise.

b.It protects men & materials from injury or
damage due to over voltage or touching. 

c. It provides low impedance path to fault currents to ensure prompt & consistent operation of protective devices during earth fault.

d. It keeps the maximum voltage gradient along the surface inside & around the substation within safe limits during earth fault.

e. It protects underground cables from overall
ground potential rise & voltage gradient during
ground fault in the system

ADVANTAGES OF EARTHING

For efficient/effective operation of any power
system, it is essential to connect the neutral to suitable
earth connection. The following are the few advantages:

• Reduced operation & maintenance cost

• Reduction in magnitude of transient over voltages.

• Improved lightning protection.

• Simplification of ground fault location.

• Improved system and equipment fault protection.

• Improved service reliability

• Greater safety for personnel & equipment

• Prompt and consistent operation of protective devices during earth fault

Handbook on Electrical Earthing

The Handbook on Electrical Earthing is a comprehensive guide designed to provide detailed insights into the principles, design, installation, and maintenance of earthing systems. Electrical earthing, also known as grounding, is a critical aspect of electrical engineering that ensures the safety, reliability, and performance of electrical systems by providing a path for fault currents to dissipate into the ground.

1. Importance of Electrical Earthing

  • Safety: Protects people and equipment from electric shocks during faults.
  • Fault Current Management: Provides a low-resistance path for fault currents to safely discharge.
  • Voltage Stabilization: Maintains the voltage levels of electrical systems under normal and fault conditions.
  • Lightning Protection: Dissipates lightning surges into the earth to protect buildings and systems.
  • EMI Reduction: Reduces electromagnetic interference (EMI) in sensitive equipment.

2. Types of Earthing Systems

  1. System Earthing:

    • Ensures proper operation of the electrical system.
    • Examples: Neutral earthing in power systems.

  2. Equipment Earthing:

    • Protects non-current-carrying parts of equipment (e.g., frames, enclosures).
    • Connects the equipment body to the earth to prevent shock hazards.

  3. Functional Earthing:

    • Ensures correct operation of sensitive equipment (e.g., telecommunication systems).

3. Components of an Earthing System

  1. Earth Electrode:

    • Conductors buried in the soil to provide a path for fault currents.
    • Types: Rods, plates, pipes, and mats.

  2. Earthing Conductors:

    • Connect the electrical system to the earth electrode.
    • Materials: Copper, aluminum, or galvanized steel.

  3. Earth Pit:

    • Accessible point for testing and maintenance of the earthing system.

  4. Bonding:

    • Connection between different conductive parts to ensure uniform potential.

4. Methods of Earthing

  1. Plate Earthing:

    • A metal plate (copper or galvanized iron) is buried vertically in the ground.
    • Suitable for high-capacity earthing systems.

  2. Pipe Earthing:

    • A hollow pipe is used as the earth electrode.
    • Commonly used in industrial and domestic applications.

  3. Rod Earthing:

    • A copper or galvanized iron rod driven vertically into the ground.
    • Suitable for areas with limited space.

  4. Strip or Wire Earthing:

    • A strip or wire buried in trenches.
    • Used for extensive grounding systems.

  5. Grid or Mesh Earthing:

    • A network of interconnected conductors buried in the ground.
    • Common in substations and power plants.

5. Design of Earthing Systems

Key Design Parameters:

  • Soil Resistivity: Determines the effectiveness of the earthing system.
  • Fault Current Capacity: The system must handle maximum expected fault currents.
  • Earth Resistance: Target value is typically less than 1 ohm for critical systems.
  • Material Selection: Durable and corrosion-resistant materials (e.g., copper).

Calculation of Earth Resistance:

  • Formula (using a single rod electrode):

    R=ρ2πL⋅ln⁡4LdR = \frac{\rho}{2\pi L} \cdot \ln{\frac{4L}{d}}

    Where:

    • RR: Earth resistance.
    • ρ\rho: Soil resistivity (ohm-meters).
    • LL: Length of the electrode.
    • dd: Diameter of the electrode.

  • For complex systems, software tools like ETAP or manual grid design methods are used.

6. Installation Practices

  • Selection of Site: Choose low-resistivity soil areas, away from underground utilities.
  • Depth of Electrode: Ensure sufficient depth to avoid seasonal variations in resistivity.
  • Jointing and Bonding: Use proper connectors and welding techniques to ensure low resistance.
  • Backfilling: Use materials like bentonite or charcoal to enhance soil conductivity.

7. Testing and Maintenance

  1. Earth Resistance Measurement:

    • Performed using an earth resistance tester (e.g., Megger).
    • Common methods: Fall-of-potential, clamp-on method, and three-point method.

  2. Visual Inspections:

    • Check for corrosion, loose connections, and mechanical damage.

  3. Periodic Testing:

    • Conduct regular tests to ensure the system maintains desired resistance levels.

  4. Record Keeping:

    • Maintain logs of resistance values, test dates, and maintenance activities.

8. Standards and Codes for Earthing

  • IEEE 80: Guide for safety in substation grounding.
  • IEC 60364: Electrical installations of buildings.
  • IS 3043: Code of practice for earthing in India.
  • NEC (National Electrical Code): Earthing requirements in the USA.

9. Applications of Earthing

  • Domestic Installations: Protect appliances and residents from electric shocks.
  • Industrial Systems: Safe operation of heavy machinery and protection from faults.
  • Power Systems: Grounding of transformers, generators, and substations.
  • Data Centers: Reduce EMI and ensure reliable operation of IT equipment.

10. Challenges and Solutions in Earthing

  1. High Soil Resistivity:

    • Solution: Use multiple electrodes, backfill materials, or chemical grounding.

  2. Corrosion:

    • Solution: Use corrosion-resistant materials like copper or stainless steel.

  3. Space Constraints:

    • Solution: Employ compact designs like rod or deep-well electrodes.

Conclusion

The Handbook on Electrical Earthing serves as an essential reference for engineers, technicians, and safety professionals to design, implement, and maintain effective earthing systems. Proper earthing ensures safety, protects equipment, and enhances system performance, making it a cornerstone of electrical engineering practices.


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