Non-Conventional Lightning Protection System – Part Six


In Article " Types Of Lightning Protection Systems LPS ", I list the main types of Lightning Protection Systems as follows:




Types of Lightning Protection Systems LPS

Lightning protection systems for buildings and installations may be divided into three principal types as follows:

1- LPS for Protection for buildings and installations against direct strike by lightning, which includes:

A- Conventional lightning protection system, which includes:

  1. Franklin Rod LPS,
  2. Franklin/Faraday Cage LPS.


B- Non-Conventional lightning protection system, which includes:

a- Active Attraction LPS, which includes:

  1. Improved single mast system (Blunt Ended Rods),
  2. Early streamer Emission System.


b- Active Prevention/Elimination LPS, which includes:

  1. Charge Transfer System (CTS),
  2. Dissipation Array System (DAS).


2- LPS for Protection against overvoltage on incoming conductors and conductor systems,

3- LPS for Protection against the electromagnetic pulse of the lightning.





And, I explained the Conventional Lightning Protection System parts and components in the following Articles:



And, I explained the Non-Conventional Lightning Protection System parts and components in the following Articles:




Today, I will explain The Claimed Advantages for Dissipation Array System (DAS) And Arguments against Them.







The Claimed Advantages for Dissipation Array System (DAS) And Arguments against Them





Claimed Advantage #1

The proponents of Dissipation Array Systems claimed that the space charge generated by the array will silently discharge the thundercloud.


Argument against Claimed Advantage #1

  • The mobility of small ions at ground level is about (1 – 2) x 10-4 m2 V-1 s-1 [1] and in the background electric fields of 10 – 50 kV/m the drift velocity of these ions may reach 1 to 10 m/s.
  • Even if the array can generate charge of sufficient quantities to neutralize the cloud charge, in the time of regeneration of charge between lightning flashes in the thundercloud of about 10 s the space charge can move only a distance of about 10 to 100 m. Thus, the space charge would not be able to reach the cloud in time to prevent the occurrence of lightning.
  • Facing this challenging and convincing opposition from lightning researchers the proponents of lightning eliminators accepted that the arrays are not capable of neutralizing the cloud charge [2]. In turn they suggested that the function of the dissipation array is to neutralize the charge on the down coming stepped leaders


References:

[1] Chalmers, J. A., Atmospheric Electricity, Pergamon Press, London, 1967.
[2] Zipse, D. W., Lightning protection methods: An update and a discredited system vindicated, IEEE Trans. on industry applications, vol. 37, no. 2, pp. 407- 414, 2001.





Claimed Advantage #2

  • The proponents of dissipation arrays made the following argument to show the effectiveness of the array in generating sufficient quantity of charge to neutralize the stepped leader [3].
  • According to Zipse [3] a 12 point array (four sets of three points) located on a 20 m pole can produce about 1 - 2 mA as the storm sets in (no details as to how these measurements were carried out are given in the paper). Thus, a typical array with 4000 points can inject a charge comparable to that of a stepped leader in about 10 s, the time interval between lightning strikes.



Argument against Claimed Advantage #2

  • Firstly, the proponents of dissipation arrays do not explain the physics behind this claimed neutralization process. For example, since the charge generated by the array is distributed in space the stepped leader has to move into this space charge region before it could be neutralized. Recall that the bulk of this space charge is located in the near vicinity of the dissipation array.
  • If the stepped leader channel, which is at a potential of 50 to 100 MV, moves into this space charge region, a critical potential gradient of about 500 kV/m could easily be established between the stepped leader and the dissipation array (which is at ground potential) leading to an imminent lightning strike.
  • Secondly, in making the above claim proponents of dissipation arrays have assumed that the current generated by a multi point array is equal to the current generated by a single point multiplied by the number of points.
  • Cooray and Zitnik [4] conducted experiments to investigate how the corona currents produced by an array of sharp points or needles vary as a function of number of needles in the array. The experimental setup consists of a parallel plate gap of length 0,3 m with 1.0 m diameter, Rogowski profiled electrodes. The bottom electrode of the gap was prepared in such a way that a cluster of needles can be fixed onto it. The needles used in the experiment were pointed, 2 cm long and 1 mm in diameter. The needles were arranged at the corners of 2x2 cm adjacent squares. A constant voltage was applied to the electrode gap and the corona current generated by the needles is measured as a function of the background electric field and the number of needles in the cluster using a micro ammeter. The lower limit of the corona current that could be measured in the experiment was about 1 mA. The results obtained are shown in Fig.1. Observe first that the corona current increases with increasing electric field and for a given electric field the corona current increases with increasing number of needles. Note, however, that for a given electric field the corona current does not increase linearly with the number of needles. Even though the conditions under which dissipation arrays are supposed to be working are different to the conditions under which this laboratory experiment was conducted, this experiment clearly demonstrates that the corona current does not increase linearly with increasing number of needles. The reason for this could be the screening of one needle from the other in a multiple needle array.



Fig.1: The corona current as a function of the background electric field from clusters of needles. The number of needles in the cluster is shown in the diagram.



References:

[3] Zipse, D. W., Lightning protection methods: An update and a discredited system vindicated, IEEE Trans. on industry applications, vol. 37, no. 2, pp. 407- 414, 2001.
[4] V. Cooray, M. Zitnik, On attempts to protect a structure from lightning strikes by enhanced charge generation, In Proc. Intern. Conf. Lightning Protection ICLP, France, 2004.


Another Argument against Claimed Advantage #2

  • According to the Draft Standard regarding charge transfer systems submitted to the IEEE (IEEE P1576/ D2.01 2001) by their proponents, a 12-point array will produce a corona current of 700 mA under a thunderstorm.
  • Zipse (2001) reported on a corona current of 500 mA from four sets of three points installed on a 20-m pole, apparently measured in the absence of lightning in the immediate vicinity of the pole.
  • It is not clear who performed these measurements or how.
  • More important, it is not clear if the reported value is average or peak current.
  • The actual corona current from a large number of points depends on the spacing between the points since the corona from each point reduces the electric field at adjacent points and hence their individual current output (e.g., Chalmers 1967, 239–262). Thus, many closely spaced points do not necessarily emit more corona current than several well-separated points.
  • Ette and Utah (1973), in perhaps the best study to date of corona current from grounded objects under thunderstorms, found the average corona current from a 10-m metal point to be about 0.5 mA, while palm trees of 13- and 18-m height produced between 1 and 2 mA.
  • IEEE P1576/ D2.01 (2001) states that the appropriate array design should consist of a sufficient number of corona points so that the array will emit a charge equal to that on a stepped leader, apparently taken as 5 C, in a time of 10 s, the cloud-charge regeneration time noted in the previous paragraph. If, for example, a current of roughly l mA were emitted from a 10-point array, as stated in IEEE P1576/D2.0 (2001) without adequate experimental evidence, then a charge of 10−2 C would flow into the air in the 10-s charge regeneration time.
  • To emit 5 C to the air in 10 s, the array would require 5000 well-separated points. According to Zipse (2001), a typical array contains 4000 points, although usually located in close proximity to each other.
  • There are no well-documented data in the literature on corona current that could be extrapolated to a large array and certainly no evidence that several coulombs of corona charge can be released in 10 s or so from an array of any practical dimensions.





Claimed Advantage #3

More recently, proponents of the dissipation arrays claimed that the dissipation arrays work by suppressing the initiation of upward leaders by screening the top of the structure by space charge. This claim was based on the study conducted by Aleksandrov et al. [5]. In that study Aleksandrov et al. showed that the electric field redistribution due to space charge released by corona discharges near the top of a high object hinders the initiation and development of an upward leader from an object in a thunderstorm electric field.


Argument against Claimed Advantage #3

  • It is important to recognize, however, that the corona charge issued from the terminal would not screen the sides of the terminal or the tower. Thus, as the stepped leader approaches the dissipation array a connecting leader could be issued from the sides of the terminal which is not screened by the space charge.
  • The main question is whether the space charge from the needles can counter balance the increase in the electric field caused by the down coming stepped leader at the tip of the structure to such an extent that the formation of a connecting leader is inhibited.
  • Calculations done in [6] show that a tower without the space charge produced by the needles will launch a connecting leader before a tower with similar geometry but with space charge, generated during the descent of the leader, at the tower top.
  • However, the space charge controlled field does not lag far behind the field that would be present in the absence of the space charge. For example, the difference in the stepped leader tip height from the tower top when the electric field at the tower top is large enough to launch a connecting leader in the presence and in the absence of space charge is no more than two meters [5].
  • This study indicates that the reduction in the striking distance caused by the space charge may not be more than a few meters.



References:

[5] N. L. Aleksandrov, E. M. Bazelyan, Y. P. Raizer, Initiation and development of first lightning leader: the effects of coronae and position of lightning origin, Atmospheric Research, 2005.
[6] V. Cooray, M. Zitnik, On attempts to protect a structure from lightning strikes by enhanced charge generation, In Proc. Intern. Conf. Lightning Protection ICLP, France, 2004.





Claimed Advantage #4:

  • The proponents of dissipation arrays claim that according to the anecdotal evidence of the users there is a reduction in the cases of lightning damage after the installation of arrays.
  • Golde (1977) [7] has suggested that dissipation arrays installed on tall structures, typically towers, will inhibit upward lightning flashes (initiated by leaders that propagate upward from the tall structure into the cloud) by modifying the needlelike shape of the structure tops to a shape that has a less pronounced field enhancing effect.
  • For example: study was made in the Browns Ferry Nuclear Power Plant (BFN). In 1998 a DAS was installed on the off-gas stack, replacing a traditional LPS. Prior to DAS installation, lightning was repeatedly collected by the LPS on the off-gas stack and equipment on the stack and around its base was routinely damaged. A number of safety and financial issues ensued. As part of an internal review process, BFN consulted a database of lightning activity to determine the number and location of lightning strikes around the off-gas stack in the three years before and after DAS implementation. They compared the number and location of lightning strikes around the off-gas stack for these periods. The weighted data for strikes showed that although lightning frequency increased a nearly uniform 65% in 3, 6 and 10-mile radii around the stack, in the 3 years after DAS implementation there was an 80% reduction in lightning strikes within 500-meters of the off-gas stack. The result has been no lightning strikes to the off-gas stack since installation.



Argument against Claimed Advantage #4:

  • First: While Golde (1977) suggestion is not unreasonable, there are no measurements to support it. However, this does not necessarily mean that the array has prevented any lightning strikes.
  • Second: Upward lightning discharges occur from objects greater than 100 m or so in height (above flat terrain) and most lightning associated with objects of height above 300 m or so is upward (Eriksson 1978; Rakov and Lutz 1988).
  • In this view, dissipation arrays would inadvertently reduce the probability of occurrence of these upward flashes, which represent the majority of flashes to very tall towers. The upward flashes contain initial continuous current and often contain subsequent strokes similar to those in normal cloud-toground lightning (e.g., Uman 1987; Rakov 2001), thus having the potential for damage to electronics.
  • The reduction of the electric field at the tower top due to the increase of its effective radius of curvature, discussed above, does not require either the release of space charge to provide shielding or the dissipation of cloud charge.
  • The view of Golde (1977) has been expanded on by Mousa (1998) [8], who argues that the suppression of upward flashes will be particularly effective for towers of 300-m height or more and that dissipation arrays will have no effect whatsoever on the frequency of strikes to smaller structures such as power substations and transmission line towers.
  • Mousa (1998) has reviewed lightning elimination devices that are claimed to employ corona discharge from multiple points. Mousa (1998) shows drawings of six so-called dissipaters produced by five different manufacturers. One of these, the umbrella dissipater, has been described by Bent and Llewellyn (1977) as about 300 m of barbed wire wrapped spirally around the frame of a 6-m-diameter umbrella. The barbed wire has 2-cm barbs with four barbs separated by 90° placed every 7 cm along the wire. The umbrella dissipater described by Bent and Llewellyn (1977) was mounted on a 30.5-m tower in Merritt Island, Florida.
  • Mousa (1998) also describes a ball dissipater, a barbed power line shield wire, a conical barbed wire array, a cylindrical dissipater, a panel dissipater (fakir’s bed of nails), and a doughnut dissipater.
  • Third: since the array is well grounded, it provides a preferential path for the lightning current to go to ground. This itself will reduce the damage due to lightning strikes even if it does not prevent a lightning strike. Mousa (1998) also discusses the extensive grounding procedures used by the manufacturers and installers of lightning elimination devices (see also Zipse 2001).
  • The leading manufacturer (see Carpenter and Auer 1995) typically uses a buried ground ring (the ground current collector in Fig. 2) that encircles the structure with 1-m-long ground rods located at 10-m intervals around the ring.
  • In poorly conducting soil, the same manufacturer uses chemical ground rods of its own design, hollow copper tubes filled with a chemical that leaches into the soil in order to reduce the soil conductivity surrounding the grounding system.
  •  In addition to the structural lightning protection, this same manufacturer highly recommends the installation of surge protective devices on sensitive electronics at the same time that the dissipation array system is installed.



References:

[7] Golde, R. H., Lightning Protection, Edward Arnold, 1977.
[8] A. M. Mousa, The applicability of lightning elimination devices to substations and power lines. IEEE Trans. Power Delivery, 13, 1120-1127, 1998.





Claimed Advantage #5


Fig. 2: Principle of Operation of Dissipation Arrays 

  • Carpenter and Auer (1995) give their view of the operation of the dissipation array marketed by the leading manufacturer. This array, schematically shown in Fig. 2, consists of:

  1. an “ionizer” with many hundreds of points,
  2. a “ground current (or charge) collector,” which is essentially a grounding system,
  3. Conductors (labeled “service wires” in Fig. 2) connecting the ionizer to the grounding system.

  • The ground charge collector is said to “neutralize” the positive charge on the ground that would otherwise accompany the negative cloud charge overhead. It is further stated that “millions of ionized air molecules” from the ionizer are drawn away from the site (presumably related to the positive charge “neutralized” on the ground) toward the thundercloud by the high electrostatic field, and, in the process, “a protective ‘space charge’ or ion cloud is formed between the site and the storm.” According to Carpenter and Auer (1995), “many consider the space charge the primary protective mode, saying its function is much like a Faraday shield providing a second mode of protection.”


Argument against Claimed Advantage #5:

  • Carpenter and Auer (1995) do not support their description of the principle of operation of dissipation arrays with quantitative arguments.
  • In a comment accompanying the paper of Carpenter and Auer (1995), Zipse (see also Zipse 1994) points out that trees and blades of grass generate corona discharge, often exceeding that of dissipation arrays, without apparently inhibiting lightning.
  • This same point has been previously made by Zeleny (1934) and by Golde (1977). Zeleny (1934) observed that “during a storm in Switzerland the top of a whole forest was seen to take on a vivid glow, repeatedly, which increased in brilliance until a lightning bolt struck.”
  • Ette and Utah (1973) reported that the average corona currents from a metal point and from palm trees of comparable height were similar.
  • Zipse (2001) has referred to the conclusions of Zipse (1994) as “erroneous,” stating that corona on trees is incapable of producing as much charge as the charge transfer system. Zipse (2001) also states that the lightning elimination system may fail to eliminate lightning, and, in this case, it acts as a conventional lightning protection system.
  • Also, Several such studies have been conducted which are:

  1. R. B. Bent, S. K. Llewellyn, An investigation of the lightning elimination and strike reduction properties of dissipation arrays. Review of Lightning Protection Technology for Tall Structures, J. Hughes, Ed., Publ. AD-A075 449, Office of Naval Research, pp. 149-241, 1977.
  2. Federal Aviation Administration, 1989 Lightning protection multipoint discharge system tests: Orlando, Saratosa and Tampa, Florida, Final Rep. FAATC TI6 Power Systems Program, ACN-210, 1990.
  3. Kuwabara, N., T. Tominaga, M. Kanazawa and S. Kuramoto, Probability occurrence of estimated lightning surge current at lightning rod before and after installing dissipation Array System DAS), Proceeding of the IEEE-EMC Symposium, pp.1072-107, 1998.
  4. W. Rison, W., Evaluation of the lightning dissipation array at the WSMR lightning test bed, Final report for the US army research lab, Contract DAAD07- 89-K-0031, WSMR, NM, 1994.


All these studies show that Charge Transfer systems CTS were struck by lightning as well as the control structure. No reduction in the frequency of lightning strikes to structures has been observed.





History and Current Situation for the Dissipation Array System (DAS)

  • The DAS was invented in 1973 and was claimed to be able to prevent lightning from striking the facility it was installed on. However, the claim was short lived since American scientists who were called in by the US government to investigate the claims were able to photograph several lightning bolts striking on the DAS itself.
  • In spite of this, the DAS is still being sold in the US market since its prohibition would have been a violation of the American constitution.
  • Since the inventor of the DAS still claimed that the air terminal can prevent lightning strikes, other scientists and engineers have examined his claim and found them to be false. Due to the adverse publicity on the DAS terminology, the inventor had introduced a new concept to describe his invention in the 1990s and named it as the Charge Transfer System (CTS). However, other studies revealed that the DAS and CTS systems could not prevent lightning strikes.
  • The NFPA refused to issue the proposed NFPA-780 ESE standard in 2000. It should be noted that the NFPA is not expected to issue a new lightning protection standard until the physics of protection is clearly defined and agreed upon by an appropriate group. The IEEE is the most likely and the obvious source of those data.
  • In 2001, the inventor had applied for a proposed standard for the CTS from the IEEE. However, due to the absence of any scientific theory for the invention, the proposed standard had stalled but the vendors still continued to sell the system worldwide with the claim that an IEEE standard is being developed.



In the next Article, I will explain Design Calculations of Lightning Protection System. Please, keep following.





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