A University of Queensland researcher has undertaken the most realistic simulations yet of multiple lightning strokes in a quest to improve protection for power system equipment.
Professor Mat Darveniza of the University's Electrical and Computer Engineering Department has taken his realistic laboratory lightning simulations one step further with a series of rocket-initiated lightning experiments in the field at Florida, during a recent special studies program.
Rockets were fired trailing fine metallic wire to heights of about 250-450 metres, triggering lightning strikes to objects such as overhead and underground power system equipment.
Data from the experiments are still being analysed, but findings are expected to lead to further refinements in equipment such as surge arresters, used to suppress surge over-voltages and keep voltages at a safe value in power systems when lightning is around.
Professor Darveniza, using facilities provided by Dr Martin Uman and Dr Vladimir Rakov, recently conducted the experiments at the University of Florida's $4 million Cape Blanding facility for research into lightning effects and into many aspects of lightning protection.
The work was part of a University of Queensland research project conducted in conjunction with the world's major electro-technology manufacturer ASEA Brown Boveri (ABB) of Switzerland, which has developed arresters for more robust handling of multiple stroke lightning flashes.
Several different sets of experiments are used in Florida; one one set triggering multiple lightning strikes directly to the launch test site using a rocket trailing 250 metres of metallic wire to the ground. The wire burns in a straight line and this causes the triggering.
A second set of experiments uses rockets trailing about 250 metres of metallic wire into the air, and a further 200 metres of insulating line connected from the lower end of the wire to the ground. The lofted wire burns, triggering multiple lightning strokes, which then create 'natural' paths to the ground. Normally, less than half of the lightning strikes created using this technique hit the launcher. The remainder strike points on the ground up to 100 metres from the launcher.
Preliminary data indicated that power equipment tested in the Florida experiments appeared to have performed well, Professor Darveniza said.
He said the rocket-initiated lightning experiments were a further development in the University's research to advance high voltage engineering and lightning studies.
Lightning has been studied since the time of Benjamin Franklin, but much remains a mystery. Researchers are still examining the physics of lightning, and the effect of lightning on ground systems such as power and telecommunications networks.
The University's Electrical and Computer Engineering Department has made a significant contribution to lightning research for more than 40 years with facilities such as its high-voltage laboratory, which was the first of its kind in Australia.
The laboratory can simulate the currrents and voltages that appear at the terminals of electrical equipment (such as power transformers) following a lightning strike. This allows researchers to predict effects on electrical networks such as powerlines, and to test equipment for external clients.
In the early 1990s, with University colleagues, Professor Darveniza developed equipment giving the first realistic laboratory simulations of the multiple stroke nature of lightning - the first major advance in lightning simulation equipment in more than 50 years.
'When a lightning flash occurs to ground, it sounds like a single event, but it is, in fact a large number of discrete strokes,' Professor Darveniza said.
'An average lightning flash has four to five strokes, and up to 30 strokes have been recorded in one flash. A single stroke flash is a fairly rare event.'
Professor Darveniza is a world leader in high voltage insulation engineeering and lightning protection, and the author of several books and more than 150 scientific and engineering publications in this field. He has been associated with lightning protection research since the 1960s. His important contributions have included better understanding of damage to electrical equipment such as transformers, leading to a reduced transformer failure rate by a factor of 10.
His group's laboratory studies of multiple strike lightning to older types of surge arresters showed that 50 percent commonly failed during sextuple impulse testing. This equipment had already passed standardised laboratory testing with single stroke lightning impules. Modern arresters perform better.
Joint experiments between the University and ABB between 1992 and 1995 using the University's multi-pulse generator led to the development of an improved polymer-housed metal oxide distribution arrester.
'This equipment is sufficiently robust to withstand the effects of multi-pulse lightning currents,' he said.
Born in Innisfail, Professor Darveniza is a graduate of the University of Queensland (bachelor of engineering, 1953, doctor of engineering, 1980) and the University of London, (PhD 1959) and was awarded an honorary doctorate of science in engineering by Chalmers University of Technology, Sweden (1990). He has worked in the electricity supply and manufacturing industries and has been invited as a visiting professor at universities on several continents.
Professor Darveniza chairs EL24, the Standards Australia committee responsible for maintaining and re-issuing the lightning protection standard for Australia. He also represents Australia on the International Electro-Technical Commission (IEC) technical committee 81, which sets the world-wide standards for lightning protection.
Professor Darveniza said the new set of experiments also continued a long association between the University of Queensland and the University of Florida in lightning research. Both universities worked on a major research project on lightning protection of distribution systems in association with the General Electric Company and Jet Propulsion Laboratory between 1976 and 1981.
Subsequently, the Electric Power Research Institute commissioned Power Technology Inc. to design and construct a rocket-triggered lightning facility in Florida. In 1995, control of the Camp Blanding facility was handed over to Dr Uman of the University of Florida. Research teams using the facility now include US universities and defence groups, and universities from Norway, Sweden, France, Italy and Australia.
For further information, contact Professor Darveniza, telephone 07 3365 3775.
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