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They say there are two things that are inevitable: death and taxes. We would add a third: lightning! We cannot control it, we cannot even make use of it. But we can be ready for it and plan to at least minimise the effects of its incredibly destructive power. By ROSS TESTER LPATS: Striking a Blow Against Lightning 4  Silicon Chip Lightning photo by MICHAEL BATH C ONSIDER THIS SCENARIO: you are in charge of an electricity distribution network and the weather forecast is not good. “Thunderstorms”, it says. Now thunder is no great problem – ear muffs can stop the noise. But it is the immense power behind the thunder that has you worried – lightning. You know that lightning is by far the number one cause of electricity supply failure. The problem is that you don’t know how bad the lightning will be. Or where it will strike. Or when it will strike. Do you put your maintenance crews on standby – just in case? Or do you cross your fingers and hope this storm will miss your area altogether? And then the lights go out... Now consider this: same person, same situation. But instead of casting an anxious eye to the heavens, you are looking instead at your computer screen. What you see doesn’t look good: stroke after stroke of lightning, advancing at an alarming rate in your direction. You get on the 2-way to the maintenance crew chief: get the crew ready to move as soon as you give the all-clear. They’ll be needed at suchand-such grid coordinates because that’s where the lightning will strike in the next 15 minutes. Sure, the lights still go out. But you smile as they come on again after a minimal delay. Move that same storm to a busy airport. Everyone knows that planes don’t land or take off during lightning. Lightning damage, either by direct hit or by a struck tree bringing down lines is by far the most significant cause of power supply faults. Reducing the costs associated with lightning damage is therefore of major importance to electricity supply authorities. (Photo courtesy Integral Energy). But when does the air traffic controller say “stop” and “go”? When he can see the lightning? It could be 50km away – more than enough time to get many flights in or away. What about the all-clear? Again, the controller looks at his screen. He can see exactly where the lightning is striking, in real time. He can see when the storm is going to hit, or even if it is going to hit, and when it has passed. Another example: a bush fire control centre. At least 30% of bush fires are caused by lightning strikes. If only you knew exactly where the lightning was a problem, you could have fire fighters there before the small blaze became a conflagration. The screen tells you exactly where they have to go! The same scenario could be repeat- ed over and over across the country. Sports arenas, building sites, mines, oil rigs, the military, shows and exhibitions, ports and so on – all benefit from having accurate data on the direction, speed, severity and likely duration of storms containing lightning. Critical processes in industry, radio & TV stations, hospitals and the like could have their emergency generation equipment up and running before Somewhere under this kaleidoscope lies the Sydney metropolitan area being belted by a violent storm during the night of February 8, 1996. The LPATS screen dramatically shows one hour's worth of a storm front crossing the Northern Suburbs. Every dot is a lightning stroke: the grey dots occurred in the last 10 minutes, ranging back to one hour previously. The time graph (bottom left) shows a massive build in intensity as time passes. This screen, which stretches from roughly Palm Beach in the north to Botany Bay in the south, could be zoomed i­n much closer if required. If you think the southern suburbs were spared, the same LPATS file some two hours earlier shows another two massive storm fronts, one passing between Sydney city and Sutherland and the other hitting the greater Wollongong area with even greater fury! November 1996  5 HYPERBOLAS Fig 1: time-of-arrival lightning stroke positioning depends on gaining a very accurate time "fix" from three or more special receivers, widely spaced. This gives a single, unambiguous position accurate to within a few hundred metres. the storms hit: proactive instead of reactive. How it is done Back in September 1991, SILICON CHIP readers were told of an exciting new method of tracking thunderstorms by detecting the intense electromagnetic (e-m) field generated when lightning occurs. Readers would be aware of the static they hear on ordinary AM radio receivers when a thunderstorm is even some distance away. That static is the direct result of that e-m field and basically lightning tracking systems are “listening” for that “static”. The e-m field is generated over a very, very wide frequency range – almost “from DC to daylight”, as amat­eur operators put it. However, by tailoring the frequency response of the receiver, the system can be made dramatically more sensitive to lightning only. In 1991, two methods were under Fig 2: how lightning is located by time of arrival: (a) The signal will be detected at each receiver at a different time relative to the stroke, depending on the distance from the stroke. (b) Time is measured at each site with a resolution of 100 nanoseconds (±50 nanoseconds). (c) Each receiver has a 10MHz timebase which is typically synchronised 20 times each second from the precise time signals of the Global Positioning System satellites. (d) A minimum of three receivers is required for a solution. Achievable accuracy is 1 microsecond and within 200 metres, depending on the distance from the lightning stroke to the receivers. 6  Silicon Chip investigation – direction finding and time-of-arrival. As its name implies, the direction finding method uses trad­ itio­nal radio direction finding methods and is reasonably accurate if enough data is available. What has really captured the imagination, however, is the other meth­od reported at the time, although then in its infancy (and not then available in Australia). Now things have changed: time-of-arrival detection is not only VISIT OUR WEB SITE OUR COMPLETE CATALOGUE IS ON OUR SITE. A “STOP PRESS” SECTION LISTS NEW AND LIMITED PRODUCTS AND SPECIALS. 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OATLEY ELECTRONICS PO Box 89 Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: branko<at>oatleyelectronics.com major cards with phone and fax orders, P&P typically $6. November 1996  7 TRACKING A STORM WITH It formed over the Channel Country in the early evening. By 9.37 LPATS had record­ ed 174 strokes in the past hour. here but is proving its worth continuously. If you missed the earlier article, a brief recap is in order. Basically, a number of sensitive radio receivers pick up the extremely strong electromagnetic field generated by the lightning discharge. The exact time of arrival (to 100ns) is compared to the extremely accurate time signals from the Global Positioning Satellite (GPS). If two radio receivers separated by some distance detect the emf of a lightning strike at precisely the same moment, it stands to reason that the strike was somewhere along a straight line between those two receivers – see Fig.1. But if one receiver detects the strike at a slightly different time than the other, the differences between the times can be used to work out two hyperbolas about the receivers on which the strike could have occurred. These hyperbolas will intersect in two places; one of these two places is the location of the lightning strike. Add a third receiver to the system and by using the time differences between each of the three pairs, three hyperbolas can be drawn. However, there will only be one point where all three hyperbolas intersect: this is the location of the lighting strike. This point can be located with quite impressive accuracy: within 200 metres of the actual strike location within the baseband of the receivers, and within 500 metres outside (and 8  Silicon Chip Half an hour later further cells had developed and more than 500 strokes had been recorded in the past 50 minutes. By midnight it had moved southeast but had reduced in intensity – under 300 strokes in the hour. Was it dying out? remember, the actual location can be thousands of kilometres from the receivers). The accuracy of the GPS “commercial” signal is only ±100 metres, so the fix is very close indeed. Fig.2 shows the system graphically. As we said, a minimum of three receivers is necessary to calculate an accurate position. Add a fourth and subsequent receivers and the accuracy can be further increased. Under the acronym of LPATS, the Lightning Positioning and Tracking System is provided in Australia by Kattron, a company based on the central coast of NSW. As an aside, whether by luck (bad!) or design, Kattron’s head office just happens to be located in one of most active storm belts on the East Coast. “It is incredible”, said Kattron’s Ken Tice­hurst, “to see the number of storms which come through this area and then affect Sydney.” Ken is not just speaking from anecdotal evidence: Kattron now has five years of historical data to demonstrate the effectiveness of the LPATS method of lightning tracking. Not only does the data correlate perfectly with weather bureau data, it actually surpasses it in many respects. In fact, the Bureau of Meteorology has been using Kattron data since April 1992 for general forecasting as well as upper air reports for commercial aircraft flight paths. LPATS operation As mentioned, it takes three LPATS receivers to obtain an accurate “fix”. At present, there are six receivers in place, ranging from Rockhampton in central Queensland to East Sale in Victoria. Other receivers are located at Moree, Cobar, Coffs Harbour and Power Network Faults Faulty Type Percentage Lightning 58.98 Other Weather 6.49 Trees 2.12 Personnel Error 2.95 Equipment Failure 6.35 Other Misc. Causes 5.56 Unknown Causes 17.56 This table, from the records of Minnesota Power in the USA, clearly shows the overwhelming proportion of problems to the power network caused by lightning. LPATS helps to minimise the effects and the costs. LPATS The night of September 24, 1992 was not one to be outdoors. A huge storm made its way from southwest Queensland down through northern NSW, finally crossing the NSW central coast. These Australia-wide "screen grabs" (which could in fact be much smaller areas) track its path in real time by recording lightning strokes. The grey strokes are the most recent (previous 10 minutes) ranging back to one hour before. It was just fooling everyone. By 2am it was recording a massive 2000 strokes per hour. No one slept over half the state! By 4am it was crossing the coast between Newcastle & Sydney, still recording 1000+ strokes per hour. That's some storm . . . As dawn broke it was moving out into the Tasman and people over a 2000km path were counting the cost. Nowra. This gives more than enough receivers to ensure the three-receiver fix but also gives a very high level of built-in redundancy. As more and more users come on line, so more receivers will be added to the LPATS network. The receivers themselves use a simple whip antenna to receive the lightning signal and a helix antenna to receive the GPS satellite timing signals. The receivers monitor the 2-450kHz radio band; ie, the spectrum below the AM broadcast band. AM detection is used. When a lightning stroke is detected, the receivers digitise 100 microseconds of the stroke information and store it in memory. At the very first peak of the received signal a very accurate time stamp is used to measure rise time and to provide the essential time-of-arrival reference, which is derived from the Global Positioning Satellite and accurate to 100 nanoseconds. Embedded in the digitised information is the polarity (positive or negative) and the peak stroke current which determines the size (and therefore the damage capability) of the stroke. This information is then sent to a “Central Analyser” computer via a modem and continuous data link. Various algorithms are used to not only reject false strokes but also determine the exact location of the stroke. The central computer also generates the lightning stroke data to be both disseminated to system users and also stored for later evaluation and use. With the location of the six LPATS receivers, lighting can be detected across a very wide area – virtually the whole of Australia. For Perth and Darwin, strokes with an amplitude of 50kA and greater can be detected. To demonstrate the effectiveness of the system, LPATS regularly records lightning strokes in Japan, Indonesia and way out into the Pacific Ocean. Indeed, New Zealand can be more-than-adequately covered using the current setup, though accuracy would be increased with an LPATS receiver or two in the Shaky Isles. Distributing the information It’s fine for Kattron to know about lightning approaching but how do customers find out about it? Many larger organisations go “on line” to Kattron’s Central Analyser computer and obtain their lightning If you believe, as do many people, that lightning strikes occur mostly at night, look again: these graphs from LPATS data record the number of strikes per hour in central western NSW over each of three months: November, December 1995 and January 1996 (coincidentally, the peak lighting period in NSW). November had most strikes around midday, December was all over the place while January peaked very much in the early evening, with very little at other times. November 1996  9 The one that got away . . . or that we got away from! Two much more recent screens (from September 19/20 last) demonstrate the fickle nature of lightning. The first screen taken at 7.30pm on September 19, shows a truly massive line of thunderstorms virtually unbroken from central Queensland to the Victoria/NSW border. More than 1400 strokes had been recorded in the previous hour. The second screen, showing the same storm at 6am next morning and "zoomed in" on the central NSW coast, shows just a few isolated strokes in the Hunter Valley and the mountains northwest of Sydney, with just 153 strokes recorded in the hour. data in as much detail as they want it, any time of the day or night. Organisations such as electricity supply authorities and similar “must know” bodies have become major customers. The software enables customers to utilise the data in a variety of ways to suit their particular needs. Most users are of course interested in their local area(s) and this information is available constantly. Sometimes, however, the “broader picture” is required and information is also available over a larger area by zooming out – even to the whole of Australia. It’s fascinating watching the buildup of a storm near Indonesia and eventually seeing the lightning strike Sydney! But Kattron has a much wider distribution (and lower cost) network available to anyone who can receive a television picture from any station in the Seven network (including Prime and other affiliates). If your local TV 7 affiliate station transmits Teletext, it also transmits Datacast. Like Teletext, Datacast is transmitted during the vertical blanking interval (VBI) – the black lines you see on a TV screen when the picture rolls. Through the use of a suitable decoder, various LPATS data can be displayed on any personal computer. When this service commenced in January 1993, it was a world first for Australia – no other country had 10  Silicon Chip lightning data available via Datacast. The data is also available in report form for such bodies as insurance companies and assessors. With the accuracy of the lightning data now beyond question, Kattron has been called on many times to verify (or alternatively to dispute) insurance claims. With bogus claims costing the industry many, many millions of dollars a year, insurance companies are glad to pay $150 for a report. For example, take the claimant who insisted his freezer was damaged by lightning between a certain Friday night and Sunday night when he was away from home. He said that all the frozen food was of course spoiled and therefore the claim was quite significant. Unfortunately for the claimant, the insurance company purchased a report from Kattron which proved that there was no strike within 50km of his house that weekend, nor even a few days either side. Faced with the black and white data, the claim was withdrawn. Conversely, individuals having a fight with their insurance companies can also purchase a report to back their claim. There have been many instances where claims have been accepted with lightning data after they were initially rejected. But by far the biggest users of the lightning data are power supply au- thorities, telecommunication companies, oil companies and airports. Figures produced for one of the major power distributors showed savings of more than $50,000 per annum in maintenance costs alone, simply because the controllers knew exactly where the trouble spots were. Add to that the dramatically quicker restoration of power from lightning damage – and its almost incalculable savings to the community – and it’s not hard to see why authorities are so enthusiastic about LPATS. Power outages have become something of a political football of late. Anything that helps get the power back on sooner is sure to be a winner! Contact: Ken Ticehurst Kattron Phone/Fax (043) 89 2024 Footnote: Michael Bath, the photographer who captured the lightning strike on page 4, is also the editor of the severe weather newsletter “Storm News”. For more information, contact Michael on (02) 9625 9700 (ah) or visit his web sites at: http://www.geocitites.com/capecaneral/1801/ (lightning photos).­ http:/atmos.es.mq.edu.au/AMOS/weather­ watch/photos.htm (storm photos). http:/www.ozemail.com.au/~jimmyd/news.htm (storm news). What do you know about lightning? Everyone has experienced static electricity, caused when two insulated objects rub across each other. Lightning is simply the most violent manifestation of a static electricity charge which has become too high to be maintained. The amount of static electricity generated between objects depends on several factors, not the least of which are the amount of movement creating friction and the insulation between the objects. In a storm cloud enormous amounts of unstable air are constantly on the move. This movement picks up ice crystals within the cloud, forcing them upwards until they are too heavy and fall back down again. Back near the base of the cloud the crystals may again be forced upwards, the cycle repeating over and over. This movement creates friction and hence static charge. Eventually, the charge builds to such a high level that the insulation of the air is insufficient to prevent some electrons “jumping the gap” to a point of a lower potential. That may be another point on the same cloud or another cloud altogether (cloud to cloud or C-C strokes). Or it can be between a cloud and ground or earth (C-G strokes). The latter is the type of major interest to humans, as C-G strokes have the most potential – no pun intended – to cause damage, injury and death. In a C-G stroke, as the insulation begins to break down a stepped leader begins to zig-zag from the cloud, ionising the air in its way and thus creating a very low impedance path. When the electron path is about 200 metres from the ground it “searches” for a point or points which form the easiest path to ground: a mountain, a tall building, an electricity tower, a tree, a person standing on a golf course... When a suitable point is found a massive return stroke occurs from the ground up. The electrons blast towards the cloud at half the speed of light. The circuit is completed and the huge amount of energy stored in the cloud is then virtually “short circuited” to ground, resulting in a rapid and spectacular electron flow from cloud to ground – the phenomenon we know as lightning. And all this in a few millionths of a second! The amount of energy involved boggles the imagination: all lightning strokes have peak currents of thousands of amperes while the very largest strokes can easily exceed a quarter of a million amps! The potential difference between the cloud and ground can be millions of volts. The huge discharge also results in a very large electromagnetic field being generated (which we can hear as static on an AM radio, even from a storm hundreds of kilometres away). Lightning may be either positively or negatively charged – or, more accurately, the cloud which contains the energy may be either positively or negatively charged. In fact, in a large, anvil-shaped thunderstorm cell, there will be areas of positive charge and areas of negative charge (which is why C-C strokes occur). Recorded lightning data suggests that both the leading and trailing edges of the cloud are usually positively charged, resulting in positive lightning strokes. To some degree, these can be used to pinpoint the start and finish of the storm cell. The centre of the storm cell is more likely to result in negative strokes. There is a difference between a lightning flash and lightning stroke. A flash will typically contain more than one stroke – on average two to three, but up to 20. Each stroke will normally last only 20-50µs and strokes will be about 20-50ms apart. The area covered by all the strokes can be quite large: a 10km radius is not unknown. Because we humans cannot differentiate such small periods (and also because of persistence of vision), we tend to see this multiplicity of strokes as one flash, lasting up to say half a second. So where does the thunder come from? As the air is ionised by the electrons (creating the flash of light) it is violently heated to around thirty thousand degrees. This massive influx of energy causes the air to expand extremely rapidly, creating a shock wave which we hear as thunder. The closer you are to the lightning stroke, the shorter and sharper the shock wave. If you are very close, all you will hear is one mighty “K-ER-A-C-K!” – and if you’re still alive afterwards, you might think to yourself “goodness gracious me . . .”, or words to SC that effect! November 1996  11