Real lightning conditions research
PREVECTRON® : On-site testing in real lightning conditions
Over the past fifteen years, Indelec has been working on unprecedented tests on PREVECTRON® in real lightning conditions in order to establish a link between tests carried out in a high voltage laboratory and tests on site.
The C.E.A. (Atomic Energy Commission French Nuclear Power Board) in Grenoble was initially brought in to carry out the testing and their results are outlined below. A full copy of their report is available on request.
Real lightning testing sites have been successively installed in the USA, in France, in Japan and more recently in Brazil. Due to the wide interest of the scientific community for these type of real lightning tests, INDELEC test sites have been visited by numerous universities and research organizations from USA, Canada, France, Brazil or Japan.
Object of on-site tests
There are four main objectives to the tests :
1. Ratify the PREVECTRON®’s performance as measured in the laboratory
For this, both a PREVECTRON® and a single rod were exposed to natural lightning in identical conditions and their reactions were measured, in particular, at the moment just before the lightning struck i.e. the moment when the upward leader begins to form. To achieve this, lightning produced naturally in the vicinity was used as well as triggered lightning, so as to increase the occurrence of worthwhile activity for the lightning rods. The triggering procedure consisted of waiting for a suitable moment during the storm and then firing up a rocket toward the clouds. The rocket carried a thin, Kevlar-coated copper wire which unravelled as it climbed. In this way it was possible to «short-circuit» the cloud to the ground. So that the flashes produced were as similar to the natural phenomena as possible, the wire contained an isolating section («Lightning Rocket System-Altitude Grounded» technique). In this way, more usable lightning strikes were produced and could more easily be centred around the lightning conductors under test.
2. Check that the PREVECTRON® performs correctly
The unique feature of the PREVECTRON®’s operation is its «trigger» system, which senses the rate at which the electric field is increasing and sets off the discharge device at precisely the right moment. A series of instruments enables the trigger operation to be monitored as the electric field increases during the build up to a real lightning strike.
3 Check the resistance of the PREVECTRON® to real lightning strikes
The PREVECTRON® was subjected to a large number of direct lightning strikes in conditions identical to - and occasionally more severe than - those likely to be encountered over the product’s life. Thus it was possible to check :
- its mechanical robustness
- its resistance to electrodynamic effects
- the ability of the triggering system to withstand induced excess voltage
4. Support INDELEC R&D programs
As per the HV Laboratory, the real lightning testing facilities represent a unique opportunity to test our future product developments in real lightning conditions (real lightning phenomenon, actual thunderstorm conditions, actual voltage, intensity or timing characteristics).
Test site
Lightning strike
Launch pad
Test Procedures
Two main types of tests have been conducted by INDELEC and its partners during these campaigns in real lightning conditions :
Naturally occurring lightning strikes
The air terminal to be tested are installed in high lightning density level areas. The parameters of naturally occurring lightning discharges are then recorded.
- On Cachoeira Paulista test site in Brazil, four air terminals have been fixed (two Franklin rods and two Prevectron ESE air terminals). Each lightning strike on one of the four rods is recorded with a lightning event counter. The guy wires are made of non conductive Kevlar wires to ensure that the full lightning current is dissipated through the down conductor and the counter.
- On Nadachi site in Japan, the Prevectron ESE air terminal is fixed on the top of a 60 meter high tower in a very high lightning density area. A special optical and mechanical twin-shutter camera allows the lightning to be photographed very quickly.
- In Bandung (Indonesia), two air terminals have been installed on top of two communication towers on a building. The lightning intensity is very high in this area of Central Java. The lightning discharges on the air terminals are recorded using lightning event counters.
Lightning triggered test campaigns
The lightning conductors tested are placed on three vertical masts fixed to the ground for this type of campaigns such as the current campaign conducted in Brazil (Cachoeira Paulista).
The three masts are placed equidistant from the rocket firing system but close enough together so as to be exposed to the same electric field conditions generated by the discharge. Each lightning rods have a coaxial shunt and are linked by optic cable to the measuring system, which monitors and records electrical activity at the top of the lightning rods as the electric field changes.
Lightning strike pictures in real conditions
The lightning strikes are triggered either by fully grounded rockets (named LRS – G, the cable between the rocket and the ground is made of fully conductive copper cable) or by partially grounded rockets (named LRS – A, the cable is made of 600m of conductive copper and 100m of non conductive Kevlar cable). In thunderstorm electrical field conditions, the rockets are launched towards the clouds and establish a “short-circuit” between the base of the clouds and the ground. The lightning discharge is then conducted through the cable fixed between the rocket and the ground. The rockets are fired with engines allowing a full speed of 220 m/s.
The rocket speed as well as the length of the conductive and non conductive cables are essential to allow the stepped-leader to naturally developed into several steps from the cloud base to the air terminal under test. The average length of a step is around 20 meters.