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A lightning simulator based on a simple pendulum could help engineers
to prevent blackouts and stop voltage surges, caused by natural lightning,
damaging electrical equipment.

Devices known as surge arresters currently protect power lines, computers,
telephones, and other equipment from excess voltage triggered by lightning
strikes. But when the Australian inventor of the new lightning simulator
tested commercially available surge arresters, he found that half of them
failed. All of them had performed well when tested with existing equipment
and all conform to international standards.

Lightning causes billions of pounds of damage to the world’s power systems
every year, according to Tony Wilson, general manager of the State Electricity
Commission of Victoria’s power grid. ‘All electricity utilities need to
take very expensive precautions against lightning,’ he says.

Mat Darveniza, an electrical engineer at the University of Queensland
in Brisbane, developed the new simulator which, rather than creating actual
bolts of artificial lightning, simulates the voltage surges that lightning
causes. He believes the reason his machine caused the surge arresters to
fail is that it mimics the effects of lightning more closely than previous
devices.

The Swedish electrical manufacturer ASEA Brown Boveri supplied Darveniza
with surge arresters for testing. David Roby, manager of the company’s surge
arrester and breakers division, hopes Darveniza will boost the power of
his existing equipment from 7500 to 15 000 amps so that heavy duty arresters
can be evaluated. ‘What we are doing is to establish a minimum standard
(of arrester performance),’ he says. ‘We want to find out what’s adequate
and what should be rubbished.’

Although a lightning flash appears to be a single bolt, Darveniza says
it usually consists of four or five individual strokes. As many as 30 strokes
have been recorded in one flash. Darveniza’s device produces up to six impulses,
as close as 15 milliseconds apart, while conventional generators produce
just one stroke.

The new simulator also reproduces the ‘cold’ and ‘hot’ electrical currents
flowing in real lightning. A cold current lasts only millionths of a second,
but can shatter trees, masonry or equipment because it converts moisture
in the object to steam. The high pressure of the steam ruptures the object.
It is called a cold current because there is no evidence of charring or
burning. Conversely, a hot current flows through an object for several thousandths
of a second and raises its temperature high enough to burn it.

According to Darveniza, it is the cumulative effect of numerous ‘quick
blows’ of high voltage together with hot and cold currents which cause lightning
damage. Even the most powerful single pulse generators, up to 10 million
volts per hit, cannot replicate these effects.

Darveniza’s lightning simulator uses six large capacitors, which are
stores of electrical charge. These are charged from a high-voltage supply
which takes roughly a minute for each capacitor.

Darveniza creates voltage surges by connecting each capacitor circuit
to an output circuit in quick succession. He arranges the capacitors horizontally
with a gap between the capacitor circuits and the output circuit. A 2-metre-long
pendulum swings past the row of capacitors, bridging the gap in each circuit
as it passes.

The weight of the pendulum is adjusted, much like a metronome, to vary
the speed of the pendulum’s swing and, consequently, the time interval between
successive pulses. The pulses can range from 15 to 150 milliseconds apart.
Darveniza can shape the current flow into various hot and cold currents
by putting inductors, resistors, and capacitors between the main capacitors
and the output circuit.