Schrittspannungen

Schrittspannungen, also known as step voltages, are a significant hazard associated with electrical grounding systems, particularly in high-voltage substations. They arise when current flows through the earth, typically during a fault condition such as a ground fault. This current causes the earth itself to act as a conductor, and because the earth's resistance is not uniform, a potential difference develops across the surface.

When a person stands on the ground within the influence of this fault current, their feet are at different points on the earth's surface, experiencing a difference in electrical potential. This difference is the Schrittspannung. The magnitude of this voltage depends on the fault current, the resistivity of the soil, and the distance between the person's feet. A larger distance between the feet, or higher soil resistivity, generally leads to a higher Schrittspannung.

The danger of Schrittspannungen lies in their ability to cause electric shock. If the potential difference is sufficiently high, current can flow through the body, potentially leading to muscle contractions, burns, respiratory paralysis, and cardiac arrest. Safety measures in substations are designed to minimize the risk of Schrittspannungen. These include installing effective grounding grids that distribute fault current over a wide area, using insulating materials for surfaces, and establishing safety zones where personnel are not permitted during fault conditions. Grounding grids are carefully designed to keep the Schrittspannungen within acceptable limits, often referred to as "safe touch voltages."