Summary
In substations, low grounding resistance is not enough to state that the system is safe. Step and touch voltages make it possible to evaluate the real risk to people during a fault.
What step voltage is
It is the potential difference that can appear between a person's feet during a ground fault.
It matters in electrical yards, fences, rooms, towers and areas where relevant fault currents circulate.
What touch voltage is
It is the potential difference between a structure touched by a person and the point where that person is standing.
It can appear on enclosures, fences, equipment, panels, transformers or structures connected to the grid.
Variables that influence it
Fault current, clearing time, resistivity, grid geometry, surface layer, joints and equipotential bonding change the result.
That is why the analysis must be specific to the site and to the real electrical network.
Measurement, calculation and mitigation
In some cases they are calculated; in others they are measured or verified in the field according to scope.
Measures can include grid improvement, surface layer, equipotential bonding, access control and protection review.
Frequently asked questions
Why is measuring ground resistance not enough?
Because safety depends on surface and touch potentials during a fault, not only on a global value.
Does it apply only to high voltage?
It is especially relevant in medium and high voltage, substations and systems with high fault currents.
Does protection coordination influence it?
Yes, clearing time affects energy and exposure during the fault.
Can it be evaluated in an existing substation?
Yes, with background information, inspection, measurements and/or modeling according to scope.
If you need technical support applied to this topic, review our industrial grounding service.