A Novel Evaluation Method for the Integrity of Grounding Grids in High Voltage Substations Based on Magnetic Field Measurements

The safety in the high voltage substations relies on the integrity of its grounding grid. A single
discontinuity at any part of the grounding grid may cause an increase in touch or step potentials,
resulting in the exposure of the personnel to a hazard of critical electric shock. In addition,
such a discontinuity may lead to malfunction of the protection devices leading to the gratuitous
tripping of circuit breakers.
In this paper, a cost-effective, reliable and meticulous measurement will be presented for the
evaluation of the integrity of an existing substation grounding grid. The method involves injecting
a sinusoidal current (in the order of few Amps) into the grounding grid at a frequency of 400
Hz and the operator walks along different magnetic field profiles while holding an electromagnetic
sensor. To verify the correctness of the measurement readings, a comparison is performed
with simulation results in the CDEGS software for the same location and profiles.
A mathematical analysis of the grounding grid was undertaken to calculate the expected magnitude
of currents and magnetic fields, when damaged or integrated elements are present within
the grounding grid. It was found that the current distribution of damaged horizontal elements
is uneven in comparison with elements without failure and/or mechanical degradation. Also,
the magnetic field along the profile of a damaged element shows a noticeable dip compared to
an expected peak for elements without failure and/or mechanical degradation. Considering all
these factors, the integrity of an existing substation grounding grid can be evaluated. Finally, a
flowchart for the sequence of steps that should be followed during grounding grid investigations
will also be presented.