FAQ on modern lightning protection methods
Questions from the "Modern lightning protection methods" webinar series with the representatives of Lightning Eliminators & Consultants, Inc (LEC), USA
- Tell us more about the side effects of lightning strike (Video, timecode 27:04)
Here you can see that the upper part of the cloud is positively charged and its bottom part is negatively charged. The negative charge coming from the bottom of the cloud creates a positive charge on the ground surface, and these charges accumulate on trees and power transmission supports. In this specific example, we can see conductors — the wires running between buildings. These wires are laid underground at a depth of 0.5 to 1 meters. The wires are surrounded by positively charged particles. When the lightning strikes into a tree, all positive charges that are in the ground are very quickly transformed into the current; it goes up towards the tree in one-thousandth of a second and the positive charge is transferred from the wire to the tree. The induced current is generated, creating a voltage surge in the wires.
- What are the special features of lightning protection of skyscrapers rising above the clouds? (video, timecode 28:11)
Buildings over 100 meters high are more prone to lightning strikes than lower structures; it is also necessary to avoid the strikes of lightning into the walls of the building at different heights. To protect skyscrapers, dissipation array devices (DAS) are installed on their roofs. It is also necessary to mount additional devices along the building walls at appropriate intervals.
- Do US standards allow the use of active lightning? (video, timecode 53:01)
In the US, there is one basic standard — NFPA (The National Fire Protection Standard). It covers the operation of air terminals based on Benjamin Franklin's system (the lightning rods). But we can do whatever we want in the US: this is called a decision at your own risk. Typically, building owners in the US are not restricted in their choices. They can choose a lightning protection system, air terminals and technology at their discretion. They have the freedom to choose their own lightning protection methods for their buildings, but the standards recommend the use of lightning rods.
- What types of lightning protection are most effective at storage tank yards? (video, timecode 55:20)
In fact, many types of lightning protection are effective for tank yards. It is important to remember that air terminals actually attract the lightning. Instead of conventional lightning rods, we recommend protecting tanks with DAS systems, which prevent the occurrence of the streamer.
- Is there a publicly available method of calculating the DAS lightning protection system? (video, timecode 57:24)
No, there isn't. We prepare the method and adapt it for Russian-speaking users.
- What is the service life of ionizers? (video, timecode 1:09:02)
The service life depends on the metal used to manufacture DAS. If it is stainless steel, it will serve for a very long time, about 50 years.
- Is the system certified in Russia? (video time code: 1:11:50)
No, it isn't. At the present moment, the system is not certified.
- Can the ionizer be mounted on a process column with an explosive medium? (video time code:1:12:09)
Yes, it can. The ionizer can be placed in an explosive medium.
- Are there plans to certify DAS systems in CIS countries? (video time code: 1:13:04)
As far as Peter Carpenter knows, such certification is planned, and research is carried out in Russia.
- Will the active lightning protection system be effective for positively charged lightning strikes? (video time code: 1:23:47)
Yes, the system will be effective for both positively and negatively charged lightning strikes.
- What is the advantage of DAS systems compared to technologies and systems manufactured by DEHN, OBO Bettermann, or Galmar? (video, timecode: 01:24:09)
These companies use traditional lightning protection — conventional and ESE lightning rods, as well as mesh cages (including surge protection devices). The difference is that the DAS system isolates the facility from lightning rather than attracts it, as the said systems do.
- What is the effectiveness of such systems in open-type high voltage step-up/down substations? (video, timecode: 01:24:48)
You can use these systems at any substations. The efficiency will definitely be high.
- How are explosive mixture-releasing pipes protected? The protection is usually needed within a radius of 5 meters above the edge of the pipe. (video time code: 1:25:38)
Of course, they can be protected. The protection radius should be two meters or more. Since the pipes contain liquid mixtures and do not have oxygen inside, the risk is lower.
- Should DAS lightning protection systems be made individually for each facility, or are there a number of off-the-shelf solutions suitable for different facilities?(video, time code: 1:27:27)
Actually, both approaches are used. There are a number of off-the-shelf solutions made under the same pattern, but the system is built for each individual facility because it all depends on the size of the protected building. They are adjusted and customized for each facility.
- Are there any requirements for the grounding device to ensure the quality of operation? (video time code:01:29:11)
Yes, there are requirements for the grounding device. They depend on the facility to be protected. The main requirement is to ensure the resistance of up to 5 ohms, and it is desirable that the grounding device takes the greatest possible area.
- Do these requirements depend on the type of facility to be protected or the type and size of the device? What minimum resistance should be achieved? (video time code: 1:31:37)
In fact, there are a lot of factors that depend on the types of object to be protected: what building needs to be protected specifically, the geometry of the building etc. This is a broad topic
- What is the physical background of the process in terms of the origin of the leader which starts from the DAS air terminal? (video time code: 51:56)
The process is this: the downward leader and at the same time the upward streamer, which in the process of formation, join together and a discharge occurs.
You see several upward streamers here. The one that goes from the middle of the tree, joins the downward leader, and discharge occurs right here.
- That means that the DAS system does not attract lightning leader, but creates a field that just pushes the leader away from the developing lightning channel? So how to calculate the structure of DAS air terminal and its protection zone then? As far as I can understand from the photographs, DAS air terminal design is different at different facilities. How do you calculate it? (video time code: 54:40)
You're right; dissipation array systems have different shapes. There are systems that look like an umbrella; there are flat and conical systems. The shape of dissipation array system depends on the shape of the protected facility. For example, the "umbrellas" are used for factory chimneys; and flat dissipation array systems are used on flat-roofed buildings.
- What is the distance from the test sensor to the DAS air terminal? (video time code: 56:51)
Here we have one sensor under the dissipation array system. The second sensor is at a distance of 200 meters from the protected structure.
- The DAS air terminal on the picture with UPS is on the lower level of the roof, not on the top. It is not immediately visible. I do not understand why. (video time code: 1:00:17)
It is fairly difficult to see the DAS system here. But it is here. Here it is.
- How will the system work in an open field with no other nearby objects that are high enough? (video time code:1:01:54)
If we place the DAS system on a low tower located in the open field, we will prevent the occurrence of streamers on the tower and around it. But they can occur in other parts of the field.
- Are there cases of lightning strikes into the protected facilities, whatever they were? At least one case? (video time code: 1:03:52)
As I've already said, our successful operation rate exceeds 99%, but it is not 100%. Yes, there were several failures. This happened because ionization at the DAS system was not sufficient, so no discharge occurred.
- How do American colleagues design the system? Are there any formulas or regulations? What is the basis of the project, the choice of structural elements and their location? (video time code: 1:05:51)
When a customer calls us, we ask him about the structure to be protected by the DAS system. There are no standard solutions that can be offered to all customers. If the client wants a lightning protection system complying with a specific standard, we can offer different types of dissipation array systems.
- How to calculate the DAS air terminal protection zone (or the surface area of the ground, if there are several buildings to be protected)? (video time code: 01:08:37)
The calculation of protection zone depends on the facility or structure where the DAS system is installed. When installed on a tower, the system resembles a dome. In the case of a building, the zone resembles a cone.
- What types of this system are used to protect overhead power lines, including their sections in the spans between supports? (video time code: 1:10:35)
In fact, DAS system is rarely used to protect such lines, because it is very expensive in the United States. Although there is a certain type of the system that can be used. We also use a certain type of ionizer, which hangs over the wires and protects the wires beneath it. But it is rarely used for protection as well.
- Is there a permission to use DAS air terminals in NFA 780 standard? (video time code:1:12:43)
DAS system does not comply with the NFA 780, but we also have other types of ionizers that can be used. And they comply with the standard.
- What formula and what calculations do you use to select the height and position for the system?(video, time code: 1:14:07)
Here, at the test track, one sensor is located on the roof of the building, and the second sensor is in the field (at a sufficient distance). That is, a degree of accuracy may not be exactly the one you might expect. DAS system influences a large area. An ionizer located on the roof of the building has 50,000 tips, and the sensor can be placed anywhere.
- What resistance of grounding device is necessary for the reliable operation of the system? (video time code: 01:17:11)
We try to achieve 5 ohms or less.
- Do you use data from one test only or the tests are carried out regularly? (video time code: 01:20:10)
We do not perform tests on each facility to be protected against lightning. Nevertheless, we have a general proof, and we've carried out a general test that was verified by the Japanese government, the Singapore Ministry of Defense and the Indian government. They all came to the same conclusion.
- What factors are determining for the DAS system protection zones? Is it the analysis of test results, or mathematical calculations, or the laws of electrical discharge physics? (video time code: 01:22:12)
We use calculations for our new projects. The calculations take into account physical processes occurring during the lightning discharge, which is described by the theory. In addition, we take into account the numerous and long-term practical studies of lightning discharges conducted in the laboratory, as well as outdoors during real thunderstorms, including the use of DAS.
- LEC stated that the number of lightning strikes had decreased after the DAS system installation in the protected area and that their number increased around the DAS-protected area. Some online resources also translate "DAS system" as lightning repulsion or thunderstorm dissipation system. So, the question is does an installed DAS system increase the number of lightning strikes over the facilities or in the immediate vicinity of the protected area. If we set a DAS system to cover the protection area of facility A, will the number of lightning strikes increase over facility B? (video time code: 38:55)
DAS system covers structures from lightning, i.e. a high-rise facility with the DAS system installed is almost indistinguishable from the ground surface for lightning. At the same time, the lightning attraction radius is decreased, so not only the number of potential lightning strikes into to the facility is decreased, but also the number of strikes at a certain distance from it falls as well.
Thus, if we assume that facilities A and B are located, say, 100 meters from each other and facility A is protected by DAS, but facility B is not protected, then the number of potential lightning strikes into facility B will also descrease.
Let me explain this point. For an unprotected facility with a height of 50 meters or a facility protected with a traditional lightning rod, the lighting attraction radius described by 3h formula will be 150 m, and the radius of protection at ground level for such a facility is 60 m (with a reliability of 0.9).That is, an elevated facility, no matter whether it is protected by a conventional lightning rod or not, will accept lightning strikes and protect closely adjacent low objects, but facilities B located 100 meters further on will be subject to more frequent lightning strikes because facility A will attract lightning within a radius of 150 m, and its protection does not extend to 100-150 meters.
As for the figure with the number of lightning strikes presented at the webinar, I will present the data in the form of a table.
Lightning strikes measurement radius Number of strikes before installing DAS Number of strikes after installing DAS After/before ratio 500 meters 40 13 0.325 3 miles 2630 4327 1.64 6 miles 11277 18688 1.66 10 miles 33685 55199 1.64
- Why do DAS systems look like umbrellas, and conventional air terminal masts cannot be used in this technology? (video time code: 40:53)
LEC has empirically proved that the rounded shape in the form of an umbrella allows to better achieve the ionization effect and form upward streamers. A right angle is set under the umbrella, which facilitates all the processes.
- Can the DAS system create a secondary pickup in the supply circuit during the thunderstorm, as the classical lightning protection system do? (video time code: 42:01)
No secondary effects occur, as lightning strikes simply do not appear in the protected area. For this reason, the power supply circuits are not affected in the protected area. However, they may be exposed to the secondary effects of lightning outside the protected area.
- Does the DAS system need a power supply? (video time code: 42:45)
DAS system is passive; it is not connected to anything and is powered by the storm currents.
- What grounding device resistance must be obtained for the DAS system to operate? (video time code: 44:05)
Less than 5 ohms, if possible.
- What is the advantage of the DAS system over other passive and active lightning protection systems? (video time code: 45:10)
The main and the most important advantage is that lightning simply does not occur above the protected facility, so there is neither direct damage nor secondary effects of lightning.
- If the soil has a high resistivity, then is it allowed to exceed the level of 5 ohms for the grounding device? (video time code: 46:40)
We had the experience of work with high resistivity soils. We use special ground electrodes called electrolytic grounding. And, of course, it is allowed to increase the level of grounding resistivity.
- Is there any physical explanation for the reduction of the number of lightning strikes? (video time code: 49:57)
This slide shows the lightning activity analysis: the number of lightning strikes into the protected facility has decreased after the DAS system installation. DAS technology reduces the number of lightning strikes due to ionization. During a thunderstorm, the lightning looks for a charged facility. The DAS system creates a neutral zone, over which the lightning is formed.
Response from the chat: Ionization occurs due to the increase in intensity as we approach the downward lightning leader since charges are transferred from the ground into the air. A counter streamer goes from a conventional air terminal. In the DAS system, the corona discharge is spread over its surface, so the streamers are not formed. This allows avoiding the lightning strike into the DAS.
- To ionize the air, an enormous amount of energy is needed (video time code: 57:24)
Yes, an enormous potential is required to ionize the air. This is exactly what occurs during a thunderstorm.
Questions and answers are to be added soon
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