The LPI GuardianTM CAT series are Controlled Advanced Triggering devices which intercept lightning discharges for the safe passage to a low impedance down-conductor system. The GuardianTM terminals have been designed to emit a “streamer” of ionised air at precisely the right time so that an approaching “down leader” is intercepted and brought under control.
The concept of controlled triggering is important because if a “streamer” is launched too early the median or ambient field will not be strong enough to sustain propagation and the “streamer” will stall or die. This will leave space charge behind which may inhibit future “streamer” development. An electric field of ~3MV/m is essential at the tip of the air terminal to initiate a corona streamer but an electric field of ~300KV/m is needed in the region between the air terminal and the down-leader to convert the streamer into an up-leader and to sustain propagation.
The dynamic response of the Guardian terminals to the approach of a lightning down leader is the key – detrimental space charge generation prior to leader approach is suppressed and the GuardianTM launches its streamer at the correct time to ensure both electric field criteria are met thus giving the greatest possible area of protection. How does an LPI Guardian Terminal operate
A Guardian CAT terminal consists of a grounded blunt lightning rod surrounded by electrically floating metal panels. Rounded or blunt tips have now been proven to be more efficient than sharp points because of a reduced space charge effect. This has been clearly proven in tests conducted at South Baldy Peak in central New Mexico, USA. (Source: “The Measurement of Lightning Rod Responses to Nearby Strikes” by C.B.
Moore, G.D. Aulich and W. Rison / 2001.)
During the static thunderstorm phase when the electric fields are steady at 5-15 KV/m the panels present as a relatively low field intensification surface aided by the blunt configuration of the finial tip. This restricts the production of “corona” or “point discharge” ions and is critical because excessive production of ions (corona) results in a “space charge cloud” above the air terminal which tends to mask the electrical field and inhibit the formation and progression of an up-leader. (See step 1).
The panels are isolated from each other as well as from the lightning rod to allow the panel facing the down-leader to rise in voltage due to capacitive coupling with the approaching down-leader. The electric field increases as the lightning downleader approaches closer causing increased voltage difference between the facing panel and the lightning rod. Eventually the voltage rises to the point where a triggering arc is generated between the facing panel and the lightning rod. (See step 2).
By design and appropriate terminal placement this arc occurs at the right time to ensure the resulting streamer will form a stable progressive up-leader. (See step 3).
The triggering arc has two key effects, namely:
(i) It produces a large number of ions to aid the initiation of an up-leader.
(ii) It causes a large increase in the electric field at a critical distance from the air terminal, aiding propagation through this critical area. This ensures a more efficient mode of protection with an enhanced area of protection.
Downconductors
Following the successful interception of a lightning discharge by the Guardian terminal, the installation of LPI IS High Volatge Shielded Cable allows for the safe passage of the lightning energy to the dedicated lightning earth with reduced risk of side flashing.
HVSC is a high integrity low impedance cable which is particularly effective on structures containing high density human occupancy and those which contain sensitive electronic equipment, volatile liquids and other sensitive applications.
LPI also offers a range of conventional downconductors of all types such as copper tape and stranded cable, bare aluminium, galvanised steel cable and tapes or any of the above in PVC insulated form.
Ground Resistance ImprovementPowder (GRIP)
Ground Resistance Improvement Powder is a ground enhancing material which is applied in and around an earthing system to reduce the soil resistivity and lower ground impedance. GRIP is supplied in 10kg and 40kg kits and is particularly useful in difficult sites such as sandy soils and rocky ground. LPI recommends the installation of a radial lightning earth to aid in the efficient dissipation of the lightning energy.
Contact LPI or an authorised representative for design assistance and for further details on LPI IS complete range of earth enhancing compounds.
Application
LPI IS Guardian CAT series terminals come in three sizes which permits the user to select a terminal which suits his particular application. See the accompanying chart for an indication of the model which best suits your requirements. For a more accurate design for your project, LPI uses a software based program which accurately takes into consideration important factors relating to your project such as thunderdays per year, height above sea level, level of protection desired / recommended (Standard – High – Very High), physical dimensions of your structures and materials used. Such additional care ensures that competing features (which themselves also have the ability to create streamer development) are taken into consideration.
Unlike other lightning terminal suppliers, LPI consider the development of competing structural features as particularly critical on very tall buildings and on sites that comprise more than one major structure.
Such designs are certified by LPI and therefore offer additional security with regard to the provision of satisfactory lightning protection levels particularly in relation to the lightning activity.
| Structure height +installed CAT terminal(typically 5m aboveStructure) | Protection Level -Very High | Protection Level -High | metres mProtection Level -Standard | ||||||
| 10 | 38 | 44 | 54 | 52 | 60 | 72 | 69 | 80 | 88 |
| 20 | 46 | 54 | 66 | 63 | 73 | 89 | 74 | 99 | 109 |
| 30 | 52 | 62 | 75 | 73 | 84 | 118 | 77 | 113 | 120 |
| 50 | 75 | 92 | 102 | 124 | 128 | 134 | |||
| 80 | 75 | 92 | 115 | 124 | 128 | 134 | |||
| 100 | 75 | 92 | 115 | 124 | 128 | 134 | |||
| 120 | 75 | 92 | 115 | 124 | 128 | 134 | |||
| 150 | 75 | 92 | 115 | 124 | 128 | 134 | |||
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