Laboratory tests are performed using a generator to produce a
standardized voltage wave. This wave reproduces the conditions required to initiate
a rising tracer from a lightning conductor when a negative falling tracer approaches.
This enables rising tracers generated by the lightning conductor to be characterized
and early streamer emission lightning conductors to be compared with standard lightning
rods.
Sufficient space is needed to suspend a plate that is used to
simulate the electric field generated by a cloud positionned above the lightning
conductor and the field generated by a falling tracer as it approaches the ground.
A complex high voltage (dc level with superimposed impulse) is applied between the
ground and the plate in order to create a discharge allowing lightning current to
pass in the air between the point and the plate.
There are very few laboratories in the world able to perform this type of test.
The photo on the left shows the IREQ laboratory in Canada.
The initiation time is measured either by recording the current passing through the
lightning conductor, or by recording the current of a photomultiplier (light emitted at the point).
The operation is carried out first using a standard lightning rod, and then with an
early streamer emission lightning conductor. The time difference between the two
measurements is called the initiation advance. It indicates the effectiveness of
an early streamer emission
system.
A large number of measurements are used to create a graph.
This shows the typically large difference between the values
recorded during the two type of tests.
It can be clearly seen that not only does the early
streamer emission device provide an initiation advance,
but its operation is also much more regular than a simple point.
A test protocol in compliance with NF C 17 102 must be defined in
order to obtain reliable and reproducible results in the laboratory.
The diagram on the right shows a comparison of the rising tracer currents emitted
by a standard lightning rod (PTS) and an early streamer emission lightning rod (PDA)
placed in the same electrical and geometrical conditions.
It can be seen that the PTS current is pulsed, unlike that of the PDA. Further,
the PDA current is higher than that of the PTS at the instant the rising tracer is
propagated.
