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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
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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
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