The third webinar of a series "Grounding and lightning protection: IEC 62305 standard"
Webinar text. Page 3
Quick navigation through slides:
1. International electro technical standard IEC 62305 Part 3
2. Configuration of IEC standards
3. Main standard series
4. Risk calculation
5. Classification of lightning protection systems (LPS)
6. Diagram of the process of lightning protection design
7. Design of lightning protection systems LPS
8. Description of lightning rod system
9. Image of the possible lightning protection system
10. Geometric model of rolling sphere radius
11. Chart of protection zone dependence
12. Dependence of rolling sphere radius on the building’s height
13. Data chart of various protection methods
14. Example of conical-shaped protection
15. Parameters of protection zone
16. Examples of rolling sphere use
17. Example of mesh method use
18. Funny devices used in different countries
19. Classification and result of lightning strikes
20. Types of natural lightning rods
21. Table of sizes for natural lightning rods
22. Lightning rod geometry
23. Insulated lightning protection system
24. Non-insulated lightning protection systems
25. Calculation of distance between lightning rods
26. Grounding of lightning protection system
27. Types of electronic devices
28. A type of electronic device
29. B type of electronic device
30. Installation of ground electrodes
31. Table of materials for lightning protection
32. Internal lightning protection systems
33. Equipotential bonding systems
34. Grounding system scheme
35. Example of a system with a dead-earthed neutral
36. Example of circular grounding network
37. Calculation formula of a safe zone
38. Table of Ki coefficient values
39. Table of Kc coefficient values
40. Detailed calculation of Kc coefficients
41. Image of lightning current distribution
42. Touch voltage
43. Step voltage
44. Lightning protection systems maintenance
45. Table of lightning protection maintenance
46. Questions and answers
Chart of materials for lightning protection
— Here there is a table, in which we described the materials, which can be used for lightning protection systems, for components of lighting protection systems, for lightning rods, lightning arresters, ground electrode systems. We have copper, hot galvanized steel, electro-deposited copper - it is coating made of copper, stainless steel, which is very expensive, in some cases we even use aluminium, for example, for lightning rods. If we use components on air, if we use components of lightning protection systems in the ground and concrete, all of them will act differently and it is necessary to see what type of wires to use. And the second part of the chart - possible corrosion, resistance of corrosions. The second column is why corrosion may increase, become stronger. And also corrosion may lead to destruction due to galvanic connections with specific elements and all this is given in the chart. But it basically happens because of copper. The use of copper and possible corrosions is well described in this part. I haven't told before, but in the first part of the webinar, there is a certain set of standards, which refers to lightning protection systems made of copper and sizes and requirements are well described there.
Internal lightning protection systems
— The net part refers to the internal systems of lightning protection. Let's switch to questions now. I will try to read and answer your questions. The first question from Mr. Kudakov.
— "Why more than one lightning rod should be used?"
— "What is the safe distance from a free-standing mast of a lightning rod to the building?". The separating distance depends on different parameters. And we can count it by the formula; you can see it on this slide. The separating distance is counted by the formula. Here we use different parameters. Please wait, I will tell about it in detail a bit later. Another thing, if there is a tank with flammable substances on the building or inside it, say, oil or petrol, it's another question then. Question from Mr. Norenko. You probably meant two down conductors. Yes, we will not stop here. It's a good idea which is written in the question from Mt. Krivulits. The minimal distance between lightning rods should be less than 50 meters. I don't understand. Depending on lightning protection class. I will get back to the table. I hope I am not wrong. Here are the typical distances between lightning rods for class II - not more than 10 meters, for class III - not more than 15 meters and for class IV - not more than 20 meters. 50 - I did not have it in my table, the distance of 50 meters.
— The next question about my report in Novosibirsk in 2005. Let me read it. It is a question about corrosions, if we use hot galvanized steel. Here are the materials which can be used.
— Question from Mr. Valkovich. "Circular conductors should be performed only in case, when safe distance from the down conductor to metal parts of the building is less the safe distance s or always?". When we use circular conductors, electrodes, it is of course recommended. You understand that circular conductors create equipotential bonding between every free standing lightning rod. And if it is technically possible, because there are objects and cases when circular conductors can't create a required protection, but it is recommended.
— "How to make lightning protection of oil tanks (1 category) 15-20 meters high, if installation of lightning rods on the tank roof is not allowed? The sphere with the radius of 20 meters won't close the whole tank".
— "Is it correct to place lightning rods on high technological columns of oil refinery, where there is the process of separation of heated oil to petrol, kerosene and mixture of hydrocarbon gas?". The requirements can be found in the amendments of the series of standards. The methodology is practically the same. The requirements to sizes are stricter there. Usually in such cases, we use the first or second class of lightning protection system. There are some answers of my colleagues, I won't comment on them, only questions.
— Let's switch to the final part, it is shorter. External lightning protection system. This part refers to the problems which appear with the objects or buildings which are subject to lightning strikes. We need to protect building from possible blinking, which may get into the building or appear within the immediate vicinity of these buildings. They may appear between different metal structures, in the internal systems of the building or external conductive parts and lines connected with the building. In some cases it is a system of telecommunications or electric wires, and in these cases it will be necessary to use additional protection systems. All this will be studied at the next seminar, but in this part I will tell that equipotential bonding and separating distance between the electric parts is required.
Equipotential bonding system
— What can we use for equipotential bonding? It is achieved outside the building or inside the buildings. We can use metal structures, internal systems, if we don't have active conductors, no installations and in these cases we use protective devices between the active conductors and elements of lightning protection systems, connecting elements or use of insulating standards. The system of arresters of pulse voltages is applied for grounding. This grounding is sometimes not allowed for the use at gas pipelines or power supply lines. Erection of such systems should be studied together with builders, who can present you a lot of information of the systems applied for the construction of the building.
Grounding system circuit
— If we have insulated external lightning protection systems, then we can achieve equipotential bonding on the ground level only. For external lightning protection systems which are not insulated, they can be installed on the level of basements or at the ground level within the immediate vicinity of the building. Connecting conductor must be connected with the closing device. And it should be installed in the place where it is easy to get access for inspection. And of course the closing device should be connected with the grounding system.
Example of a system with a death-grounded neutral
— At the next diagram we see an example of connection in the buildings with multiple entry points of external conductive parts using the circular electrode for the connection with the closing device. In this case, there are two points. In each place, we put connections, additional electrodes, ground electrodes, individual closing devices. If we have installations of existing connections, then we need to install surge protection devices. There are systems with low voltage, for example, systems with a death-grounded neutral. Then in such cases, protective ground electrodes or united zero working protective conductors will be used, but they must be connected directly or through the surge protection system with a closing device.
Example of circular grounding network
— On the next example we see a case with several input points of external conductive elements, and on the previous slide we saw external. A circular electrode was used here, but there was no external electrode. In this case, it is necessary to create a circular grounding network inside the building. It means that it is best of all to introduce such a system on the level of the basement or ground level. If the building is tall-40,50,100 meters, such internal connections, internal grounding is recommended inside the buildings or at least 20 meters high from the ground.
Safe zone calculation formula
— Here we see the possibilities, if we can't connect metal closing devices, then there is a possibility to create safe space by electric insulation between lightning rod and lighting arrester and also metal structures of the building, metal installations and internal systems. The coefficients given in the bottom are Ki, Km, Kc were shown on the previous slides, L - I would like to stop here, it is length in meters, which goes along the lightning rod from the nearest point of equipotential bonding or grounding. This way, we can make a formula here.
Ki coefficient values chart
— In the next chart, you see the values of coefficients of Ki, they depend on the class of lighting protection system, coefficient Km depends on the material.
Kc coefficient values chart
— And finally, Kc coefficient - it is quite a complex calculation of this coefficient. In our standards two cases are studied: simplified approach giving approximate values, includes the number of lightning rods only in cases of insulated, it is applied only in cases of insulated lightning protection systems, if we have more than 2 lightning rods. And the detailed approach is more complex.
Detail calculation of Kc coefficient
— If the distribution of lightning current goes in case of meshed lightning protection system and the use of a great number of lightning rod systems. Here the data depend on the number of lightning rods, lightning arresters, and the formula is more complex here. It includes various components Kc1, Kc2.
Lightning current distribution image
— You see more information here, on this image. You see the number of lightning rods, for example 24 and various parts of lightning current distribution. Here the formula and the approach are more detailed.
— A special topic which should be studied in these standards is protective measures, directed at the prevention of injuries of people, living beings from touch and step voltage. If there are people in the building, there are common rules, which refer to the protection and it is necessary to achieve the admissible level of life and health threat. It is very important, that at the normal work conditions, people should not be closer than 3 meters to lightning rods. At least 10 lightning rods should be used for a better protection of people and animals. The contact resistance of the surface ground layer at the distance of 3 meters from lightning rods is important. It should be not less than 100 kOhm. How can we achieve it? We can put a layer of asphalt, 5 cm thick or 15 cm of gravel. Of course outside the building. Within the building, we can put some artificial non-conductive materials on the floor. The layer of the insulating material, for example asphalt should be 5 cm, and for gravel - 15.
— Protective measures against step voltage. In fact they are almost the same as from touch voltage. People should not be closer than 3 meters from rods. Sorry I forgot here, that the requirements are the same for touch voltage and equipotential bonding and resistance of the surface ground layer, it's all the same. But what is different here, is that it is possible to carry out some potentialization here by using mesh grounding system. There are preferences of using mesh lightning protection system outside the building. This way, we minimize the probability of step voltage, which can be dangerous for animals and people.
Lightning protection systems maintenance
— Now we come to the last topic, which refers to the maintenance of lightning protection systems. The standards give recommendations o the regulation of inspection, which are one of the main conditions of a safe maintenance of lightning protection systems. In fact, the owners should be aware of all possible failures, which may appear and they should be corrected instantly. It is also important, that lightning protection system corresponds to the design project based on these standards, all lightning protection components must be in a good working state, and there should be no corrosion.
Lightning protection maintenance chart
— Inspections must be held at least once a year. Such a more detailed inspection must be held at least once in two years, if there are some critical situations, for example, use of explosives, or there is flammable substances in the building, then the inspection should be held once a year. For III and IV protection level, the checks should be held once a year, but for a complete check it is enough to hold inspection once in 4 years. It is important to track the condition of metal parts, so they are not subject to corrosion, inspection of such parts of lightning protection systems which are in the air - it means there can be corrosion and the resistivity of elements drops. Usually corrosion appears due to electrochemical connections and when there happens a connection with other metals, all this should be observed.
Questions and answers
— In fact it was the final part of our presentation, the last slide. Thanks very much for your attention! This beautiful picture was made in the laboratory of Tesla. It was possible to make such a lightning out of Tesla's generator. I know there are similar generators in Russia. Thanks very much for your attention and for your patience. I want to see if you have any questions and answer them.
— Another question from Mr. Valkovich, it relates to lightning rods. People should not come to lightning rods closer than 3 meters, but in some cases there are recommendations. Sorry I did not understand what you mean. We are talking about the height of lightning rods. If a lightning rod is not less than 2,5 meters, then the bottom parts of lightning rods must be using insulating materials. This way, we will increase the insulation conductivity. In general, we should, but if there is a thunderstorm, it's raining, and then we should not come closer than 3 meters to lightning rods.
— The next question refers to the use of copper: "Use of grounding devices made of copper or copper-bonded will influence the existing grounding systems made of hot-galvanized steel and operation of electrochemical protection system".
— " Does IEC allow using lightning protection mesh without rod lightning rods for the protection of buildings? How effective this solution is?" Yes, of course, it all depends on the possibility of creating a protective volume. If the building is covered or the volume under protection is created by a lightning protection mesh, then we don't need to put additional lightning rods. But we need to remember, that the most vulnerable parts of the building, which are subject to a direct strike, they are in great danger and some designers in such cases put additional lightning rods on these angles. But if we have a protective zone properly made, there is no need in that.
— "Why don't you study the regulatory documentation of the Russian Federation to talk to the Russian audience?"
— Thank you very much again. We've talked for more than 1,5 hours. I would like to thank Anastasia, out interpreter, who is very tired and she knows nothing about lightning protection, so please excuse me for possible mistakes, 2 hours is terribly hard. I hope Marek will talk about it in May. I hope we will hold another webinar in May and will talk about lightning protection standards. Thanks a lot! Best Regards!
Thank you, Marek! Thank you, Anastasia. Yes, the webinar lasted longer than we expected. But anyway, it was useful and for the next webinars to be useful too, please help us to make them better and fill in the questionnaire. I sent the link to the chat. Do not forget about the next webinars, sign up for them. You can see the link in the chat too. I think we're done for now. Thank you very much, sign up for the next webinars.
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