beacon
A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
neon lamp
A neon lamp (also neon glow lamp) is a miniature gas-discharge lamp. The lamp typically consists of a small glass capsule that contains a mixture of neon and other gases at a low pressure and two electrodes (an anode and a cathode). When suffi ...
,David F. Rider '' Jane's airport equipment fifth edition'', Jane's Pub. Co., 1986 page 92 used as an
aircraft warning light
Aviation obstruction lighting is used to enhance the visibility of structures or fixed obstacles which may conflict with the safe navigation of aircraft. Obstruction lighting is commonly installed on towers, buildings, and even fences located in ...
.
Description
High voltage power cables, particularly those close to
airport
An airport is an aerodrome with extended facilities, mostly for commercial Aviation, air transport. They usually consist of a landing area, which comprises an aerially accessible open space including at least one operationally active surf ...
s, 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 provide this lighting by glowing red, the standard colour used in aviation for warning beacons.
The system is extremely simple, efficient and reliable and is considered the most economically viable solution. 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
A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems. Most HVDC links use voltages betwe ...
powerlines, but similar devices may be also used on
mast radiator
A mast radiator (or radiating tower) is a radio mast or tower in which the metal structure itself is energized and functions as an antenna. This design, first used widely in the 1930s, is commonly used for transmitting antennas operating at l ...
s.
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.
Each high voltage cable creates an electric field around itself, in the same way as any live
electrical conductor
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. The flow of negatively c ...
. When the
electric potential
Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...
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
An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...
that makes it difficult to 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
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
charged across an air gap (
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...
).
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.
Overhead wire marker
Overhead wire markers are safety instruments applied to the overhead power lines marking transmission lines and ropeways along the flight path during the day.Rogowski coil, a device that gets energy from the magnetic field, instead of the electric field