Marker lamps for high-voltage lines
Marker lamps for high-voltage lines are special flight safety lights that are attached to high-voltage lines and serve as a visual indication of the obstacle for low-flying aircraft . The various processes have been described in various patents since the 1930s.
General
Overhead lines with large spans, which is typical for high-voltage lines , represent barely visible obstacles for low-flying aircraft such as helicopters . One way to mitigate the problem is to mark the lines with warning lights.
A simple solution is to attach the lights directly to the lines. The electrical power required to operate the warning light is taken directly from the overhead line, which avoids technical difficulties in supplying energy to the light. The disadvantage of this "self-sufficiency" is that when the high-voltage line is switched off, for example during maintenance work, the warning lights are not in operation.
Implementation principle
In principle, there are two ways of extracting the necessary power in the range from fractions to a few watts for operating the signal lamp from a high-voltage line .
Electrical coupling
The energy is taken from the electric field and the decrease in the electric field strength in the vicinity of the conductor. An example of this system is Balisor . The advantage of this method is that the power is available regardless of the current flow through the line. The disadvantage is that the power that can be drawn is low and can only supply small gas discharge lamps such as glow lamps with low power. This means that it can only be seen well in the dark.
Warning lights with electrical coupling can only be used in the area of high-voltage networks in the range of 220 kV or 400 kV, because at lower voltage the decrease in the electric field strength in the vicinity of the conductor is too small.
Inductive coupling
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The energy is taken from the magnetic field , since the magnetic flux density spreads in a circle around the conductor cable when a current flows through the conductor. A current transformer , which is also used to suspend the lamp on the rope, allows the power required to operate the lamp in the range of a few watts to be taken from the line. The disadvantage is that a sufficiently high current must flow through the conductor to operate the lamp. If the overhead line is switched on, but no or only a very low current flows through the line, for example because little power is being drawn, the luminaire will fail.
Inductively coupled warning lights are independent of the voltage level, but for practical reasons are only used in the high voltage area. The process also requires alternating current - the use of inductively coupled warning lights is not possible on lines that transmit direct current, such as high-voltage direct current transmission (HVDC).
Since the power that can be drawn is higher with this principle, the lamp can consist of several brightly shining light-emitting diodes (LEDs) that are controlled by an integrated electronic circuit and, for example, flash regularly. A sufficiently high current through the conductor cable, which ranges from approx. 8 A to approx. 1 kA, is important for operation. However, inductive warning lights also have to cope with the high power losses that occur with high currents and current surges, especially with electrical short circuits .