Pillars with wires of overhead power lines have become such a familiar attribute of the landscape of the modern world that many simply do not notice them. Despite the high location of the conductors to prevent accidental contact, they nevertheless conceal a potential danger. Everyone remembers the situation from childhood, when parents, seeing such a torn wire lying on the ground, tried to get around this place "tenth road." Due to this, electrical injury can be avoided, since the step voltage decreases with distance. We all know that it is impossible to approach a dangling wire. However, that such a step voltage is known only to people with an electrical education. In the article we’ll try to understand this issue in more detail, explaining, literally, “on the fingers”.
So, the step voltage is the potential difference between the legs or, which is also true, between two (or more) points located one from another at a step distance. In explaining many processes in electrical engineering, they often resort to the analogy with water. Indeed, in some cases, a comparison of electric current and water is quite acceptable, as it simplifies the understanding of the processes taking place. So let's do it.
Imagine that on one of the poles of the power line it broke off and one end of the wire that fell under the voltage fell to the ground. If the wire is a pipe, and the current is water, then a puddle will appear at the point of contact with the ground. Its diameter is a spreading zone in which a person can wet his legs. A puddle is formed because water cannot be completely absorbed into the soil instantly. The size of the spreading zone depends on the amount of water passing through the pipe per unit time.
Now back to electricity. The voltage source creates a potential difference between the two points of the line, and the higher the voltage and the effective current value, the wider the danger zone around the broken wire. The appearance of a "puddle" is due to the high ohmic resistance of the soil: with the current grounding circuit (according to the PUE 4 Ohms), the spreading zone is minimal or completely absent.
Imagine that a person is standing next to a dangling wire. Due to the distance between the feet, a potential difference appears. And due to the presence of resistance of the body - and electric current. In fact, this means getting an electric shock. Moreover, if after an electric shock a person falls (completely or on hand), then this only exacerbates the situation, since the step voltage increases. In addition, if in the vertical position of the body the current flows along the “leg-to-leg” contour, then after a fall other chains form that can pass through the heart, presenting an immediate danger to life. It is easy to understand that animals (cows, bears, horses) that fall into the current spreading zone are in greater danger than humans, since they have a greater distance between the front and rear legs, which means that step voltage is much more dangerous.
From the foregoing, several conclusions can be drawn:
- in the event that current from a broken wire (or other malfunction) falls into the zone of action, in no case should panic and run. When running, the distance between the soles becomes greater than when walking, respectively, the potential increases. Moreover, since a person tries to move away from the current source, the step voltage becomes even more dangerous;
- the shape of the spreading zone may differ from the circle due to differences in soil conductivity.
You can leave the zone of step voltage by a non-conductive material (for example, a thick dry board); jumping on one leg (in this case there is no potential difference); or slowly go out with your feet together.