The field problem
Benban MV Substation
Ground-grid measurements were produced with a normal fixed-probe assumption and without validating the potential-probe position for the large site.
why the obvious answer can be misleading
Large grids and high-resistivity sites can have broad influence zones. A single assumed percentage point may not represent remote earth.
Why it failed
Large grids and high-resistivity sites can have broad influence zones.
A single assumed percentage point may not represent remote earth.
Follow the engineering
Switch between the field condition and the engineering concept. Trace the path and examine what changes.
Inspect the engineering detail
What changes
Extend the test line appropriately and use a slope/curve-based method where needed to identify a representative potential-probe location.
Correction & verification
Extend the test line appropriately and use a slope/curve-based method where needed to identify a representative potential-probe location.
Verification recorded in the case
- Plot the measurement curve and demonstrate a defensible stable/derived result rather than presenting one meter reading.
- Record as-built topology and connection points.
- Repeat the measurement or functional test under a defined condition.
- Confirm continuity and mechanical integrity of the corrected path.
- Document instrument/setup, environmental condition and test method.
- Close the NCR/case only when evidence supports the conclusion.
References & project context
References are reproduced from the PIS casebook. Select the governing edition and project acceptance criteria before using them for a design. The diagrams explain the concept, rather than define construction dimensions.
Large grounding-grid test methodology; IEC 61557-5 principles; project utility procedure.
PIS reviewed field handbook · PIS-CS-031
View the original social cardThe engineering lesson
Large-grid testing is a geometry problem before it is a meter-reading problem.
Take the lesson into your next design review.