Step tension

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Here a conductor cable lying on the floor forms a potential funnel. The red curve represents the electrical potential of the ground; the higher the slope between two points on this curve, the greater the tension between the points above it on the ground.

As a step voltage is defined as the voltage between two points is one of strong current -carrying bottom portion. The name is based on the fact that this tension affects a person when he touches the ground at different points during one step . It can be life-threatening for humans and animals.

An essential step stress takes place there where a high electric current flows into the ground, which for example, when ground impact of a flash , but also in ground fault of a fallen to the ground power line occurs. Particularly in the case of high-voltage lines that are operated with earth fault compensation , the line is not switched off immediately in the event of a simple earth fault, but remains live for a while.

Emergence

If a high electrical current is introduced into the ground (in the event of a lightning strike, it can briefly be several 10,000  amperes ), this current generates an electrical voltage at the electrical resistance of the ground according to Ohm's law . A body that touches two points of different potential in the area of ​​the floor through which current flows , bridges a voltage that can amount to a few 1,000 volts and thus lead to an electrical accident . The electrical potential, which drops evenly outwards from the point of impact, is imagined as a so-called potential funnel .

The step voltage between two contact points depends on:

  • the current density in the area of ​​the contact points (the closer to the point of introduction, the higher the current density)
  • the resistance of the floor (the higher the resistance, the higher the [" falling "] voltage that arises at the same current flow )
  • the absolute applied current
  • Position and distance of the contact points

Avoidance

Torn off overhead lines as a result of storm damage. Dangerous step voltages can occur on the ground near the contact points.

The risk of a dangerous flow through the body is largely ruled out if the body only touches the ground at a single, as small as possible, point. It is safest to stand with closed feet in the area of ​​a potential funnel. This is why you should crouch down with your feet together during a thunderstorm (so as not to attract the lightning yourself), but never sit down or even lie down - then you would experience a potentially life-threatening step voltage if lightning strikes nearby.

Lying flat on the floor in the potential funnel is considered to be even more dangerous than standing with legs apart, as there is good contact with the floor due to the large area covered and an even higher current flow through the entire body is to be feared.

The step tension also endangers animals in the open air, for example grazing cows, as they naturally stand on the ground with four legs and large distances between their legs.

literature

  • Gerhard Kiefer: VDE 0100 and practice. 1st edition, VDE-Verlag GmbH, Berlin / Offenbach 1984, ISBN 3-8007-1359-4 .

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