Prof. Valentin Kolev from TU Sofia: Lightning is among the least studied phenomena

08.09.2021

• Modeling a lightning strike is impossible
• During a storm, you should curl up into a ball
• Lightning rods do not guarantee complete protection

- Recent tragic incidents have once again brought the topic of protection against lightning strikes into focus. Does the Technical University of Sofia have any specialty that trains specialists in this field?
- There is one discipline called high voltage engineering, and in it, one of the questions in the students' exam summary is related to lightning protection.
- Does Bulgaria have a laboratory where lightning can be simulated? Such a laboratory existed in the Romanian city of Craiova.
- No. In our high voltage engineering laboratory, the impulse voltage generator creates a standard impulse wave, which results from the effect of a lightning strike. It is physically impossible to model a lightning strike.
- Do lightning rods guarantee complete protection?
- It is more than clear that we cannot stop lightning. In populated areas, there are lightning rods, and in addition, many tall buildings that can attract lightning. Unfortunately, however, lightning has a random nature and does not always orient itself towards the lightning receptor. Sometimes it manages to penetrate the protection and falls into the protected zone.If caught in an open field or mountain during a thunderstorm, we should crouch and curl up into a ball to be at the lowest possible level. It is not advisable to lie down, as this may create a high potential difference between the limbs. The most severe injuries from lightning occur between the hand and foot, because the electric charge passes between these two limbs through the sternum, where the fibrillation of the heart is most strongly affected. We also know that during a storm, one should not hide under a tree, because when wet, it becomes a conductor of electricity and can more easily attract lightning.
- Some advise turning off mobile phones during a storm. What is your opinion on this?
- Regarding this claim, I would need to consult with my colleagues from the telecommunications field. The physics of lightning attraction is related to the presence of an element with a sharp point, which increases the field intensity, thereby increasing the likelihood of attracting lightning. I do not know how a phone increases the field intensity around it. There is no more random phenomenon than exactly where a lightning bolt will strike. In the case of the footballer who died a few days ago, a fatal role could have been played by the metal bracelet on his wrist or an involuntary gesture of raising his hand high, thereby attracting the lightning.
- In that case, what is the solution?
- Only a Faraday cage can provide protection from lightning. This is a cube made of metal.
- Do cars with metal bodies create similar protection?
- Yes, but it is not certain.
- Are lightning bolts dangerous for airplanes and other manned aircraft?
- Special measures are taken. For a lightning bolt to strike an object, the circuit must always be completed. The greatest risk for an aircraft is when lightning strikes it and then discharges to the ground. In effect, the aircraft becomes a conductor through which the lightning current flows to the ground.
Years ago, we had cases where parts of an aircraft's electronic systems were damaged after being struck by lightning, and we were called upon to provide an opinion.
- Some say that the Sofia metro creates a magnetic field that attracts lightning. Is such a claim true?
- No. It is underground and cannot produce such an effect.
- What is the power of a lightning bolt?
- The electricity generated by a lightning bolt amounts to thousands of amperes. The higher the altitude, the lower the current. The current is highest at sea level. When lightning strikes the ground, depending on the resistance it passes through, a voltage drop is formed, which can reach several thousand or even millions of volts. However, no precise measurement of lightning voltage has ever been made, as such manipulation is dangerous. These values are largely theoretical. Lightning is still very poorly studied. We can only observe its effects. I have seen a hole burned through a steel door of a transformer substation by a ball lightning. It was about ten centimeters in diameter, as if cut with an oxy-acetylene torch. The round opening showed signs of melted metal.
- What work do active lightning rods do? They have been very modern lately.
- Early streamer emission lightning rods have a protection zone of about 150 m. However, there are quite a few publications in the scientific literature that indicate a higher percentage of lightning strikes bypassing them and hitting within the protection zone. No lightning rod provides 100% protection.
- Have studies been conducted on the percentage of these lightning strikes bypassing the area covered by lightning protection structures?
- Such studies have not been conducted. In the city, when there is a thunderstorm, one simply needs to find shelter. One should not stay outside. If thunder is heard in the sky, one should get indoors as soon as possible.
- Besides lightning rods, is additional protection for electrical installations in buildings against the effects of lightning necessary?
- Naturally. There is also a regulation for lightning protection of buildings and structures, and it must be followed. Surge protection devices, so-called, are installed on the electrical installations inside the buildings. Some call them surge arresters, others call them arrestors. Their task is to equalize the potential between the phase and the neutral of the installation when necessary. This reduces the risk of damaging electrical appliances - a refrigerator or a TV, for example. There are devices that are even plugged into the socket to which the appliance itself is connected. Surge-protected power strips are already being sold on the market.
- Are such measures suitable for buildings located in remote areas?
- Yes. This applies to buildings that do not fall within the protection zone of lightning rods on other taller structures.
- What are the risks for overhead internet cable lines and for subscribers' computers?
- The same as for all types of networks. In cable internet, if lightning strikes the wire, it cannot withstand the voltage and will break down somewhere. Thus, there is a risk that this voltage will reach users' homes.
- In such a case, during a storm, is it advisable for subscribers connected to such networks to unplug the cable from their computer?
- Yes, it should be unplugged or appropriate overvoltage protection should be installed on the cable itself.
- Does this protection in this case automatically disconnect the internet line to the computer?
- No. In this case, this protection safeguards the input of devices connected to the internet from dangerous overvoltage.
- How are large long-distance power lines protected from lightning?
- With lightning protection wires. They are installed between the tops of the poles and are mandatory for networks carrying electricity with a voltage above 110 kilovolts.
- Which countries are most advanced in lightning research and have the highest achievements in lightning protection?
- It is difficult to say.
BIOGRAPHY: Prof. Valentin Kolev was born on April 11, 1959. Dean of the Faculty of Electrical Engineering at TU-Sofia. Doctor in the specialty "High Voltage Engineering". Lead lecturer in "High Voltage Engineering", "Coordination and Diagnostics of Electrical Insulation", "Economics of Energy", "Legal Regulation and Market of Electrical Energy".He has been the Executive Director of ESO EAD, Deputy Chairman of the Board of the Branch Chamber of Energy Professionals in Bulgaria.

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Mmonitor.bg, 08.09.2021