Effect of Integrity of the Earthing System on the Rise of Earth Potential

This paper investigates the effects of breaks in bonds,
breaks in the earthing system and breaks in earth wire on the rise of
the earth potential (EPR) in a substation and at the transmission tower
bases using various models of an L6 tower. Different approaches
were adopted to examine the integrity of the earthing system and the
terminal towers. These effects were investigated to see the associated
difference in the EPR magnitudes with respect to a healthy system at
various locations. Comparisons of the computed EPR magnitudes
were then made between the healthy and unhealthy system to detect
any difference. The studies were conducted at power frequency for a
uniform soil with different soil resistivities. It was found that full
breaks in the double bond of the terminal towers increase the EPR
significantly at the fault location, while they reduce EPR at the
terminal tower bases. A fault on the isolated section of the grid can
result in EPR values up to 8 times of those on a healthy system at
higher soil resistivities, provided that the extended earthing system
stays connected to the grid.

Authors:

• N. Ullah
• A. Haddad
• F. Van Der Linde

Keywords:

• Bonding
• earthing
• EPR
• integrity
• system.

References:

[1] IEEE Std-80-2000, “IEEE Guide for Safety in AC Substation
Grounding”, The Institute of Electrical and Electronic Engineers, New
York, 2000.
[2] EA-TS 41-24, “Guidelines for the Design, Installations, Testing and
Maintenance of the Main Earthing Systems in Substations”, Electricity
Association, Technical Specifications, 1992.
[3] National Grid Transco Research Project, “Quantification of the Effect of
the Earth Wire Isolation on Hazard Limitation and System
Performance”, High Voltage Group, Cardiff University August 2005.
[4] N. Ullah, H. Griffiths, A. Haddad, A. Ainsley, “Effect of Earth Wire
Connection on Hazard Limitation at Often Frequented Towers”, 41st
International Universities Power Engineering Conference September
2006, (IUPEC 2006), University of Northumbria, UK.
[5] Safe Engineering Services: “Current Distribution Electromagnetic
Grounding Analysis Software (CDEGS)”, Canada, 2004.