Balisor is a system of illuminated
beacons for high voltage power lines using a cold-cathode low-pressure neon
lamp
Description
High voltage power cables,
particularly those close to airports, need to be visible day and night. During
the day, brightly coloured balls positioned along the length of the cables are
sufficient, but during the night, lighting is necessary. These beacons which
emit a red glow (the standard colour used in aviation for warning beacons) are
used to provide this lighting.
The system is extremely simple,
efficient and reliable and is considered the most economically viable
solution[citation needed]. Its working principle is attractive because it uses
a phenomenon usually considered as a weakness. However a large disadvantage is
that it does not work when the line is switched-off. It cannot also be used on
HVDC-powerlines, but similar devices may be also used on mast radiators.
Operating principle
The interest of the system lies in
the way it obtains a power supply directly from the single cable on which it is
mounted. It is difficult to obtain a very small amount of energy from a line
which transports an enormous amount.
System diagram
Each high voltage cable creates an
electric field around itself, in the same way as any live electrical conductor.
When the electric potential of such a cable is sufficiently high, its electric
field causes a significant voltage difference between the cable and its
immediate neighbour. (It is the strength of the electric field that makes it
difficult use low powers.)
As a result, a second conductor a
few metres long, insulated from but parallel to the high voltage cable, will
have a potential different from that of the main cable. Together the conductors
make a capacitor charged across an air gap (dielectric).
Under certain conditions, the
accumulated charge (and hence the potential difference) is sufficient to
trigger a discharge lamp. This what is used in practice, giving a reliable and
robust beacon.
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