When you fall down due to high-voltage wires, don’t run. The standard life-saving posture is so funny?

High-voltage wires are dangerous. It is common sense not to touch them. But if a high-voltage wire falls to the ground nearby, what should you do?

Remember these four words: Don't run. There is only one way to walk that can save your life. Today we will learn the correct way to act in case there is a grounded high-voltage wire next to you.

Error demonstration. Image source: Elektroschutz in 132 Bildern

High voltage electricity is closely related to our daily life and industrial production, and can be said to be the "blood" of human society.

The power supply station and the substation are connected by a 60,000-500,000 volt transmission line. At the substation, the voltage of the high-voltage electricity is reduced and then transported to thousands of households. Generally speaking, the voltage of high-voltage wires on the street is between 4-25 kilovolts.

This H-shaped transmission line is an older transmission system, and is more common in old residential areas. The voltage of the transmission line at the top is high, and the communication line is at the bottom. Image source: hsseworld

The danger of high-voltage wires is self-evident. Once an electric shock occurs, the heat generated by the current passing through the human body can burn the internal organs, and the current can also cause cardiac arrest. But what many people don't know is that there is a "barrier" near high-voltage wires, and the "barrier" is actually very dangerous.

When a high-voltage wire directly or indirectly contacts the earth, the electric potential (which you can simply think of as voltage) at the contact point spreads out like water waves. The closer to the contact point, the higher the electric potential, and the more dangerous it is. This form of electric potential spreading and weakening in a ripple-like manner along the contact point is called earth potential rise, which is equivalent to expanding the scope of harm of high-voltage wires.

The ground potential rises when the wire is in direct contact with the ground. Image source: Western power

How large is the range of the "barrier" formed by this high-voltage area?

If a 60,000-volt high-voltage wire falls to the ground, the area within a 10-meter radius with the point of contact as the center is as dangerous as the high-voltage wire. If you don't want to get an electric shock, you must stay at least 10 meters away from the point of contact. If it is a higher-voltage high-voltage wire, then the range of this circle is even larger.

Of course, if anything conductive is placed in the area (such as tree branches), it can become just as dangerous as high-voltage wires and can cause electric shocks to humans.

The ground potential near the substation increases. Image source: Wikipedia

In the field of electrical engineering, the hazards of ground potential rise have long been known to everyone, and many international organizations have protection standards for ground potential rise, such as the Institute of Electrical and Electronics Engineers (IEEE)'s relevant standard IEEE Std. 80-2000. The U.S. Occupational Safety and Health Administration (OSHA) also classifies ground potential rise as a "known hazard" and has proposed corresponding management and disposal regulations.

So, what should you do if a high-voltage wire really falls nearby?

Once again, do not run at this time. Running means death. According to the regulations of the U.S. Occupational Safety and Health Administration, there are only two correct actions at this time: it is best to stay where you are unless necessary. If you must leave, you should take the "Geisha Step", that is, walk with your legs rubbing against each other, moving a few centimeters each time, and your feet cannot leave the ground.

How to move in areas of increased ground potential: Geisha Step. Image credit: SCGA

Why is this? High school physics knowledge tells us that electric current is caused by potential difference. If there is a potential difference between two points on the human body, then the person will be electrocuted.

In the field of power safety production, the potential difference between two steps is called step potential. In the area of ​​increased ground potential, the larger the step, the greater the step potential, and the easier it is to be struck by electricity.

Imagine that one of a person's legs is stepping on the contact point between 60,000 volts of high voltage electricity and the earth, and the other leg is 10 meters away. The potential difference between his two feet reaches 60,000 volts. Pikachu's critical hit is inevitable. Unless you are Satoshi, don't try it.

Conversely, reducing the step potential can reduce the possibility of "pika pika", which is also the principle of the "geisha step": keeping the two feet in contact at all times and moving by rubbing the legs can reduce the potential difference between the two feet.

In addition to step potential, another danger is called touch potential, which refers to a person standing on the ground with low potential, and at the same time a part of the body touches an object with high potential, such as an excavator connected to a high-voltage wire. Of course, at this time, the current will flow from the high potential through your feet to the low potential ground.

The principle of contact potential sounds simple enough, but what should you do if you really encounter such a situation, such as when you are sitting in a car that is in contact with high-voltage power lines?

This is the second important suggestion.

At this time, the most critical self-rescue measure is not to try to leave the car. Because as long as you stay in the car and your body is not in contact with the low-potential ground, no current will be generated and you will be safe.

The U.S. Occupational Safety and Health Administration recommends that if you must abandon your vehicle, the best position is to keep your feet together, your hands close to your body, and bounce away from the vehicle like an inchworm. The goal is to do this so that you don't touch the ground as you exit the vehicle.

Of course, once you leave the car, you will need to use the geisha steps you learned earlier.

At this point, you might think that as long as high-voltage wires touch the ground, it is dangerous, but in fact this happens because of human settings: the neutral wire of most high-voltage transmission lines is grounded, that is, it is connected to the earth.

In other words, if the neutral wire is not grounded, then you won't get an electric shock if you stand on the ground while touching the hot wire of a high-voltage power line. But does such a system exist?

Yes, it is called floating ground, or suspended ground. The neutral line of the floating ground transmission system is not grounded, and the purpose of doing so is mainly for safety and to prevent electromagnetic interference caused by the current loop generated by the grounding.

Since floating grounding seems safer than grounding, why don't we usually use this power transmission system?

The reason is that the voltage of floating ground is not very stable, especially when users turn appliances on and off. When appliances are turned on and off, overvoltage may appear in the ungrounded loop, which may damage the appliances. Therefore, floating ground is mainly used in large factories and places where the neutral wire cannot be grounded, such as on airplanes.

After seeing the safe positioning and floating grounding near high-voltage power lines, careful children may ask a question: Since the neutral wire of a general transmission line is grounded, can I directly use the earth as the neutral wire?

There is indeed such an operation. This kind of transmission system that uses the earth directly as the neutral wire is called a single wire earth return system. Sometimes, the neutral wire is not the earth, but water. Of course, such a system has very high requirements for the insulation of the live wire, otherwise Pikachu will really go crazy everywhere.

Obviously, the main reason for using the earth as the neutral wire is to save the cost of manufacturing and laying the neutral wire, so single-wire ground loops are mostly used in sparsely populated areas and isolated power consumption sites.

In 1981, a single-line ground-loop transmission line was built between Bethel and Napak in Alaska, USA. Some developing countries also use such systems as their main power transmission facilities, such as Laos, Mozambique and South Africa. The tingling sensation when stepping on the ground in these countries may not be an illusion.

It's like a flash of lightning. Do you understand?