Non-Conventional Lightning Protection System – Part One


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:




For more information, you can review the following Articles:




Today, I will explain the Non-Conventional Lightning Protection System.


Non-Conventional Lightning Protection System





1- Components of Non-Conventional Lightning Protection System

Non-Conventional lightning protection system includes (2) main types as follows:

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- General Information About
Non-Conventional Lightning Protection System

  • In the 1970s, two types of unconventional air terminals had been commercially reinvented and introduced in the world market under a variety of trade names. They are:


1- The lightning Active Attraction air terminal: 

the lightning attracting air terminal is claimed to be able to attract the lightning to it (and hence away from the building) in order to protect the building that it was installed on.

 2- The lightning Active Prevention/Elimination air terminal:

 the lightning prevention air terminal is claimed to be able to prevent lightning from occurring and hence protect the building.

  • Some of the trade names for of unconventional air terminals are as follows:



Product Name
Country
Dynasphere
Australia
Prevectron
France
EF
Swiss
St. Elmo
France And Italy
Pulsar
France
DAT Controler
Spain
Paratonerre
France
Preventor
France And UK
EF33
Australia


  • In reality, the inventors of these un-conventional air terminals have never been able to provide any scientific basis for their invention. None of the “scientific papers” that they have published in the last 30 years have been independently verified by the scientific community.
  • In addition to this, these inventors have never been able to provide any independently validated proof that their inventions work. However, they have provided plenty of anecdotal (i.e. hearsay) evidence which had been obtained from “satisfied customers” and some insurance carriers will accept them as equivalent for the conventional techniques.
  • These Non-conventional air terminals are claimed to be superior to the conventional lightning protection but neither experimental data nor theory supports these claims.

  • For these reasons, these inventors and manufacturers have not been able to get their unconventional air terminals approved by the standards bodies like:

  1. NFPA,
  2. IEEE,
  3. IEC,
  4. US Military,
  5. UL.


  • Hence the LPS that used these Non-conventional air terminals have been classified as Non-standard LPS by academics, scientists and the various standards bodies around the world.
  • The Non-standard LPS are usually easier and cheaper to install when compared to the conventional system but the protection that it provides is very limited i.e. equivalent to that of a single Franklin rod! Hence these vendors had to rely on some very creative marketing to sell their non-scientific and unproven products.





Important Note

The volume or zone of protection afforded by the air termination system shall be determined only by the real physical dimension of the air termination system. Typically if the air rod is 5m tall then the only claim for the zone of protection afforded by this air rod would be based on 5m and the relevant Class of LPS and not any enhanced dimension claimed by some non-conventional air rods.




3- Active Attraction LPS





3.1 Improved Single Mast System (Blunt Ended Rods)

  • In Article " Types Of Lightning Protection Systems LPS ", I explained the first type of the Conventional Lightning Protection System which is Franklin Rod LPS and I listed Other names for this type as follows:


  1. Sharp pointed rods,
  2. Single mast system,
  3. Franklin Cone / protective Angle cone.




Fig.1: Blunt and Sharp Ended Rods

  • Today, I introduce another type of lightning rod or air terminal or a single mast called improved single mast system or Blunt Ended Rods (see fig.1), although this type is lying under Conventional LPS category, its working principle is the same as Active Attraction LPS category, Therefore, it is explained as Active Attraction LPS type.
  • Following tradition, sharp-tipped Franklin rods are widely installed than the Blunt Ended rod, although the Blunt Ended rod is more effective in lightning protection than the sharp-tipped Franklin rods. 

  

why the Blunt Ended rod is more effective in lightning protection than the sharp-tipped Franklin rods?

this is for the following reasons:

  • Observations In recent tests of various tip configurations to determine which were preferentially struck by lightning, several hemispherically tipped, blunt rods were struck but none of the nearby, sharper rods were ‘‘hit’’ by lightning.
  •  As Franklin found, the application of strong electric fields to an exposed, sharp electrode such as a lightning rod causes an electric current to flow into the air; this current is a result of ionization processes in the air around the tip. The space charge formed by the ions created around the tip of a rod, however, acts to weaken the applied electric field. This weakening causes a problem for lightning protection efforts because very strong electric fields are required above a lightning rod to establish the upward going leaders to connect to approaching lightning.
  • Laboratory measurements of the emissions from a wide range of electrodes exposed to strong, normal polarity thunderstorm electric fields show that positive ions are formed and move more readily over sharp-tipped electrodes than over blunter ones. From these findings, it appears that the electric field rates of intensification over sharp rods must be much greater than those over similarly exposed blunt rods for the initiation of upward going leaders.
  • Calculations of the relative strengths of the electric fields above similarly exposed sharp and blunt rods show that although the fields, prior to any emissions, are much stronger at the tip of a sharp rod, they decrease more rapidly with distance. As a result, at a few centimeters above the tip of a 20-mm-diameter blunt rod, the strength of the field is greater than that over an otherwise similar, sharper rod at the same height. Since the field strength at the tip of a sharpened rod tends to be limited by the easy formation of ions in the surrounding air, the field strengths over blunt rods can be much stronger than those at distances greater than 1 cm over sharper ones.
  • Different Studies show that moderately blunt Franklin rods with tip height–to–tip radius of curvature ratios of about 680:1 are more likely to furnish return strokes and therefore to provide better protection against lightning than can either very blunt ones or the traditional, sharp rods.





3.2 The Early Streamer Emission Air Terminals

Early Streamer Emission (ESE) Concept:

  • These systems are designed to attract the lightning strike to a known and preferred point therefore protecting nearby non-preferred points.
  • The attractive effect of an air terminal would be enhanced by a longer upward-connecting leader (according to Rakov and Lutz 1990); the longer the leader, the greater the enhancement.
  • The most common way this is done is to have an ESE terminal which equipped with a discharge triggering device that initiates a streamer from the terminal in an attempt to increase the probability of inception of a pre-ionized path (upward leader) from the terminal during the approach of a downward lightning leader (see fig.2).


fig.2: Active Attraction LPS Concept

  • The ESE air terminal made use of proprietary designed metal enclosures around the ordinary lightning rods to create the ionisation that can generate the artificial streamers earlier than the natural ones. Different manufacturers will provide different shaped enclosures to distinguish their branded products as shown in fig.3.




Fig.3: Different Shapes of Early Streamer Emission Air Terminals





3.2.1 Claimed Advantages Of ESE Over Conventional Air Terminal According To The Proponents Of ESE
And Arguments Against These Claimed Advantages

Claim#1:
  • Early streamer emission ESE air terminals emit a positive upward-moving connecting leader (intended to meet the downward-moving negative stepped leader that initiates the usual cloud-to-ground lightning flash) at an earlier time, by a time interval Δt, than would a conventional air terminal having similar geometry and installed at the same height. This earlier initiated leader occurs in a smaller electric field than is required for the initiation of a leader by a conventional rod.


Arguments Against Claim#1:
  • According to Mackerras et al. (1997), once the upward-connecting leader propagates into the space remote from the air terminal, its farther progression depends upon the supply of energy from the electric field in the space near the tip of the leader and upon the dielectric properties of the air undergoing breakdown, neither of these factors being influenced by the air terminal.
  • Using this and geometrical arguments, Mackerras et al. (1997) conclude that “it is not possible to gain a significant improvement in lightning interception performance by causing the early emission of a streamer from an air terminal.”



Claim#2: 
  • The claimed time advantage Δt transferred into a length advantage, ΔL, for the earlier initiated leader via ΔL = vΔt, where v is the speed of the upward-connecting leader. So, the initiated leader generated by an ESE terminal can travel a longer distance in comparison to that from a conventional air terminal. ESE proponents assume that the speed of the upward connecting leader v is of the order of 106 m/s. This length advantage, ΔL able to provide a significantly larger zone of protection than the upward-connecting leader from a conventional air terminal of the same height.


Arguments Against Claim#2: 
  • This value of leader speed v is arbitrary, since it is not supported by experimental data. Actual field measures from multiple investigators have documented streamer speeds ranging as follows:

  1. McEachron: 5.2 x 104 to 6.4 x 105 m/s
  2. Yokoyama: 0.8 to 2.7 x 105 m/s
  3. Laboratory propagation speeds 104 m/s

  • for a value of Δt of about 100 ms in order to claim a significant length advantage ΔL of 100 m for the upward-connecting leader from an ESE rod over that from a conventional rod. If the value of v = 105 m/s, which is consistent with the available experimental data were used instead, even allowing a 100 ms time advantage and even assuming that the leader could propagate in the lower field in which its initiation is claimed to occur, the length advantage would be only ΔL = 10 m, which is not likely to be significant in most practical situations.


Claim#3: 
  • Based on the above claims, it would follow that a single early streamer emission air terminal could replace many conventional air terminals, because ESE air terminal can protect a larger volume of space (i.e., can attract a lightning to itself from farther away) than can a similarly placed and grounded conventional rod of the same height.


Notes:
  • This is the primary claim of ESE proponents without this claim, ESE systems would be indistinguishable from conventional systems.
  • Based on calim#3 as per proponents of ESE, Only one early streamer emission air terminal is usually installed centrally on the roof of a building. However, for buildings with a larger roof area, two or more un-conventional air terminals may be installed and they are normally spaced at some distance apart from one another.



Arguments Against Claim#3: 
  • There is no experimental evidence that an ESE air terminal can protect a larger volume of space (i.e., can attract a lightning to itself from farther away) than can a similarly placed and grounded conventional rod of the same height. An upward-connecting leader speed of 106 m/s is required to produce the “length advantage” of 100 m claimed by the proponents of ESE systems in order to demonstrate the superiority of the ESE technique over the conventional method of lightning protection. The typical measured upward positive leader speed is an order of magnitude lower, 105 m s−1, inconsistent with this claim. Given the lack of evidence of the superiority of ESE systems over conventional systems, adequate lightning protection would require that each of them have a similar number of air terminals.



  


3.2.2 How ESE Proponents Support The Efficacy Of The ESE Technique?
And What Is The Argument Against This Support?

ESE Proponents Support The Efficacy Of The ESE Technique by the following points:

Support#1:
  • A laboratory experiment conducted in France and described by done by Eybert-Berard et al. (1998) where the ESE terminal was located closer to the rocket launcher than the conventional one and the downward moving leader got attached to the ESE terminal before conventional terminal.

Argument Against Support#1:
  • Unfortunately, in this A laboratory experiment, the positions of the rods were not interchanged to validate the claimed enhanced attractive range of the ESE terminal. Thus, this experiment does not provide evidence for the claimed superiority of the ESE terminals against the conventional ones.


Support#2:
  • Another triggered-lightning test of a commercial ESE system conducted in Florida, where particular ESE system had several spark gaps at the tip of the air terminal that were intended to be activated in a sufficiently high electric field. 

Argument Against Support#2:
  • This test proves nothing relative to ESE system validation. However, we do not believe that laboratory sparks can adequately simulate the natural-lightning attachment process, as discussed in the section “General information and theory.”


Support#3: 
A French Standard (1995) and a Spanish Standard (1996) for the laboratory qualification of early streamer emission systems for lightning protection of structures.


    Argument Against Support#3:
    • Strong arguments can be made that no laboratory spark test can be extrapolated to describe the case of natural lightning, For example:

    1. the length of individual steps in the lightning stepped leader is of the order of tens of meters, a distance considerably larger than the length of laboratory spark gaps, of the order of a meter, specified to test and certify ESE systems [e.g., French Standard (1995) that requires a gap no smaller than 2 m with the air terminal being between 0.25 and 0.5 times the gap size]. It is not likely that one can adequately simulate the natural-lightning attachment process in a 2-m laboratory gap.(see fig.4)
    2. in natural lightning the downward negative leader from the cloud has a length of many kilometers while the positive upward-connecting discharge from the ground or from elevated objects is generally much shorter, some tens to hundreds of meters long. On the other hand, in laboratory spark studies intended to simulate lightning strikes to grounded objects, positive leaders are always much longer than negative leaders.


    Fig.4: Laboratory Spark Test





    3.2.3 Summary For Comparison Between ESE And Conventional Techniques

    • There is, in fact, no support for the proposed ESE technique in the results of any experimental study involving either triggered or natural lightning. On the contrary, natural-lightning studies have shown that ESE systems do not work as their proponents claim.
    • Hartono and Robiah (1995, 2000; HR99), Moore et al. (2000a,b) conclude that there is no advantage in using an ESE system relative to conventional systems.






    3.2.4 Types of Early Streamer Emission ESE Air Terminals

    There are several types of early streamer emission systems as follows:

    1. Radioactive,
    2. Pulsed voltage,
    3. Sparking-controlled leader trigger (CLT).


    All these types employ specially designed air terminals that are claimed to create enhanced ionization near the air terminal.





    3.2.4.1 Radioactive Air Terminals



    Fig.5: Radioactive Air Terminals

    • In the 1970s, the first early streamer emission devices were so-called radioactive air terminals, The various types of radioactive air terminals were constructed like the Franklin air terminal except that they had radioactive isotopes added to the terminal. The radioactive materials employed are weak alpha particle emitters with relatively long lifetimes.
    • The radioactive isotopes were claimed to be able to ionize the terminal which can assist in the launch of the streamers.
    • In this method, the inventors claimed that The radioactive air terminal can attract lightning up to 100 m away, hence providing large protection coverage of about the same radial distance. Therefore, only one centrally located radioactive air terminal is required to protect a large building as compared to the dozens of Franklin rods in a standard LPS.
    • However, these claims were disproved in 1985 when some academics from Australia and Singapore conducted a study of buildings that had been installed with the radioactive lightning rods. In that study that was conducted in Singapore several buildings were found to have been struck and damaged by lightning within the claimed protection radius of the radioactive air terminal.
    • At the same time, the radioactive air terminals were also found to be hazardous since the radioactive material can disintegrate in the weather and can enter the human body through the food chain or through inhaling radioactive dust in the air (see fig.6). Consequently, the use of the radioactive air terminal was banned worldwide in 1987. However, in the late 1980s, the inventors provided a new generation lightning attracting air terminal, the ESE air terminal.



     Fig.6: Ban on Radioactive Air Terminals Using





    3.2.4.2 Pulsed Voltage ESE Air Terminals Type



    Fig.7: Pulsed Voltage ESE Air Terminals Type

    • The Voltage Pulsing ESE are air terminals that contain an auxiliary powered apparatus that produces voltage pulses. The voltage pulses produce positive ions around the point of the terminal. The frequency of the pulses is designed to limit the formation of space charge (corona) around the air terminal.
    • These ESE contain a tapered rod fixed to a shaft containing the high voltage transformer and an electronic module which detects the increase in field strength. These units are typically powered by batteries and photo cells. The corona produced is supposed to provide a channel of positive ions before a streamer is emitted.
    • It is known that most commercial ESE devices operate by application of a pulsed voltage to a pointed termination.


    Example For Pulsed Voltage ESE Air Terminals Type:

    Pulsar 7:(see fig.7)

    • this device consisted of a rod, 0.75 m long, tapering to a tip of radius l mm approximately. The rod surmounted a cylindrical ‘can’, containing a power unit.
    • This was sealed, self-contained and integral with the device. It was evident, therefore, that the energy required for the high voltage pulses must be derived from the corona set up at the tip of the rod in the enhanced electric field existing throughout a lightning storm. The energy is stored until the power unit discharges to produce a pulse of high voltage which then, presumably, produces a more energetic corona.





    3.2.4.3 Sparking-Controlled Leader Trigger (CLT) ESE Air Terminals Type



    Fig.8: Sparking-Controlled Leader Trigger (CLT) ESE Air Terminals Type


    Special Shapes and Sparking ESE can be described as:

    • Air terminals that are designed to have an increased protective radius due to the specific shape of the terminal, or
    • Air terminals that discharge sparks at the point of the terminal when the air terminal is under the influence of a high electric field. These sparks are said to cause increased ionization to occur at the tip of the air terminal.


    Examples of Sparking-controlled leader trigger (CLT) ESE Type:


    The Prevectron: (see fig.8)

    this device is said to operate as a capacitor gathering charge as the electric field increases. According to product literature, when the leader is approaching the area, the electric field increases significantly; this causes the device to spark, creating corona and initiating a collective streamer. It is interesting to note that other ESE are designed to discourage the formation of corona. They claim that the presence of corona suppresses the formation of a collective streamer

    The Dynasphere: (see fig.8)

    this device can be described as a floating spheroid with earthed central rod, the floating sphere being grounded via a very high impedance static drain. The floating sphere appears grounded to the static electric fields which are in existence prior to leader approach. In this mode, its geometric shape creates minimal field intensification and there is little corona formed to distort the near electric field. The unit becomes active only in the few milliseconds of downward leader approach. At this time the outer sphere will rise in voltage due to capacitive coupling to the approaching leader and will create a spark discharge between itself and the nearby earthed rod.



    In the next Article, I will explain The Active Prevention/Elimination LPS. Please, keep following.

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