TITLE:
Analysis of a Large Grounding System and Subsequent Field Test Validation Using the Fall of Potential Method
AUTHORS:
Huan Huang, Hualin Liu, Hong Luo, Hao Du, Yi Xing, Yexu Li, Farid P. Dawalibi, Haijun Zhou, Longhai Fu
KEYWORDS:
Ground Resistance; Fall-of-Potential; Ground Impedance Measurement; Ground Potential Rise; Ground Potential Difference; Touch Voltage; Step Voltage; Steel Conductors
JOURNAL NAME:
Energy and Power Engineering,
Vol.5 No.4B,
November
18,
2013
ABSTRACT:
This paper examines various aspects of the design
process and subsequent field test measurements of a large and complex
substation grounding system. The study and measurements show that soil
layering and lead interference can have a significant impact on the appropriate
test location that yields the exact substation ground impedance. Applying a specific
percentage rule such as the 61.8% rule for uniform soils to obtain the true
ground impedance may lead to unacceptable errors for large grounding systems.
This poses significant problems when attempting to validate a design based on
raw test data that are interpreted using approximate methods to evaluate
substation ground impedance, and determine ground potential rise (GPR), touch
and step voltages. Advanced measurement methodologies and modern software
packages were used to obtain and effectively analyze fall of potential test
data, compute fault current distribution, and evaluate touch and step voltages
for this large substation. Fault current distribution between the grounding
system and other metallic paths were computed to determine the portion of fault
current discharged in the grounding system. The performance of the grounding
system, including its GPR and touch and step voltages, has been accurately
computed and measured, taking into account the impedance of the steel material
used of the ground conductors and circulating currents within the substation
grounding system.