electric fence
An electric fence is a fence with which animals or people are prevented from entering or leaving a property by the frightening, shocking, injuring or killing effect of an electrical voltage . As a rule, the fence forms one pole of an open circuit, the earth the other. If animals or people touch the fence, the circuit is closed. The best-known type of electric fence, which is approved in most states , is the electric pasture fence .
Electric pasture fence
An electric pasture fence is a special type of pasture fence in which one or more electrical conductors with insulators are attached to the fence posts . On posts made of wood rich in resin, for example fir wood, the insulator may be unnecessary. The same applies to plastic posts.
construction
The electrical conductors used to be bare wires made of galvanized steel or aluminum, later thin strands (approx. 0.2–0.3 mm thick) were woven into a plastic cord or a plastic rope (6–8 mm thick). Today one often uses clearly visible plastic fabric tape (mostly 20–50 mm wide) with woven metal braid.
The electronic device uses 12 volts to generate pulses of up to 15,000 volts of very short duration (0.1 to 0.3 milliseconds). This limits the energy - depending on the size of the animal to be guarded and the length of the fence - to 0.1 to 5 joules and is harmless to animals and humans. An accumulator , possibly supported by solar cells , or a power supply unit serves as the energy source . A flyback converter increases the voltage to around 600 V. The energy is stored in a capacitor, chopped up into short pulses by an electronic switch and released every 1 to 2 seconds. A transformer then increases the impulse to around 15,000 volts. In the past, the electromechanical principle of Wagner's hammer was used to generate pulses.
One pole of the device is connected to the electric fence wire using pliers or clamps. The other pole is connected to a pile driven into the earth. As soon as the animal touches the fence wire, it short-circuits the circuit between the wire and the earth with its body and the impulse flows through the animal via the earth back to the device. The body resistance of the animal is 500 to 1000 ohms.
safety
In order to avoid voltage loss, blades of grass and other conductive objects must not touch the tapes and wires (voltage dissipation). The hat voltage must be at least 2 kV at every point on the fence, but should not exceed 10 kV. According to DIN EN 60335-2-76 Appendix E and VDE0131, there must be a pause of at least one second between the individual pulses. The pulse duration must be less than 10 ms. The energy per pulse in the 500 ohm portion of the standard load must not exceed 5 joules. The standard load practically represents the animal's body. The device is allowed to deliver more energy in order to overcome the fur resistance and / or parallel dissipating vegetation. Both cases are taken into account by the standard in that a further resistor is connected in parallel or in series with the 500 ohm resistor for testing . Its size and type of switching must be selected so that the maximum energy occurs in the 500 ohm resistor. The complexity is explained by the fact that, on the one hand, a high level of safety should be achieved and, on the other hand, maximum safety for humans and animals is necessary. Accordingly, modern devices adapt to the load conditions (see section Operation and Features ). The maximum output current is already 1A with the above-mentioned limit values and may be higher for shorter pulses.
Barbed wire fences must not be energized, as they could get caught. B. on clothing and thus a permanent end of the circuit would be possible.
Operation and features
The devices are also called electric fence devices, and in Switzerland they are also called cattle keepers . Electric fence devices operated with batteries generate an electrical voltage of up to 10 kV at 9–12 V battery voltage . Depending on the intended use, the energy per pulse is up to 6 joules . The minimum capacity of the battery can be calculated using the pulse energy E, the repetition frequency f (e.g. 1 Hz corresponding to 1 pulse per second) and the operating time t
can be roughly estimated. It is better to measure the actual average power consumption of the device or to take it from the data sheet.
In good conditions, fence lengths of up to 25 km can be effectively energized. Electric fence devices operated with mains voltage are known with energies per pulse of over 30 joules, which is sufficient for fence lengths of up to 150 km. However, the supplyable fence length is reduced very quickly depending on the vegetation on the fence and should therefore be kept short. With medium vegetation 45 km and with heavy vegetation a maximum of approx. 25 km fence length are available.
A voltage of at least 3 kV is considered to be fouling, i.e. H. the tips of regrowing blades of grass are destroyed when they touch the fence and therefore do not represent an unwanted discharge.
The high voltage is largely harmless for larger animals, as the energy per pulse and the pulse length are limited and the pause> 1s is required. When they come into contact with the wires, the animals receive a brief electrical shock, which flows through the animal's body to the earth, and they back off. Smaller animals such as snails, spiders or geckos can be killed in the area of the isolators.
The advantages of electric pasture fences over other pasture fences are the low workload involved in erecting them, the ease with which they can be changed and expanded, and the low risk of injury to people and animals. A closed circuit does not have to be set up for the function, which keeps the construction effort very small. Any "ramifications" are possible during construction - the circuit is only closed when an animal (or something else) touches the fence and thus establishes a connection with the earth.
Modern electric fence devices are self-regulating in that they independently adapt their pulse energy to the conditions of the fence (length or capacity to the earth). You care e.g. B. also in the event of malfunctions (branches, etc.) that the necessary fence tension is maintained. Other functions available today are call and notification systems (telephone dialers, signal lamps and sirens) that notify the fence operator in the event of such malfunctions. Some devices also enable monitoring of interruptions by connecting the live wire at its end to a return connection of the electric fence device (fence loop). In this way, the devices can inform the user of any interruptions or breaches of the fence.
One source of error when erecting an electric fence is inadequate earthing of the second pole of the fence device. Since currents in the ampere range already flow through the fence capacity to the earth, but especially when it is touched, it has a great influence on the function of a pasture fence. If the earth resistance is too high due to dry earth or too short an earth electrode, energy is lost and high voltages occur on the earth electrode, which can also cause electric shocks. Manufacturers specify how the grounding must be designed on the respective fence energiser. A connection to a house earthing (protective conductor) is not permitted, the minimum distance to the house earthing is 10 m. The reason is to avoid introducing interference pulses into the electrical installation.
There is calculation software to help with fence planning and the choice of the right fence components. There are regulations for the safe erection and operation of an electric pasture fence. a. at the Association of Electrical, Electronics and Information Technology (VDE) and the Agricultural Employer's Liability Insurance Association.
criticism
Mobile electric pasture and herding fences can pose a danger to wild animals that should not be underestimated, especially when they are switched off and therefore do not have a deterrent effect. Animals with horns or antlers can get entangled in the wires and ligaments and in extreme cases die. Anyone who erects mobile electrical pasture and herding fences should be aware of this fact, constantly check the systems and clear them when not in use.
Electric fence device on net fence
Electric pasture fence: isolator
Electric fence device with built-in accumulator
Electric fence device with external accumulator
Electric fence energizer operated with solar cells
Deadly electric fences
In the case of electric fences with life-threatening electrical energy (also called high-voltage fences), the wires of the fence are, as in the case of pasture fences, under a high voltage of 1 kV to 20 kV; however, the currents are higher and longer when touched, since there is no or only a slight voltage drop. This means that significantly larger amounts of energy are transported during the exposure period. The currents flowing through the body when touched or through voltage flashovers cause , among other things, cardiac arrest , ventricular fibrillation and severe burns such as in electrical accidents .
The first use of high voltage electric fences took place in Belgium during World War I. There, in 1915, German troops erected a high-voltage fence connected to 2 kV (officially: border high-voltage obstacle) along the border between occupied Belgium and the Netherlands over a length of about 180 km in order to prevent unwanted border crossings (see high-voltage fence in Belgium ).
Electric fences were also used to fence off concentration camps . Outside the fence there was also another fence made of barbed wire . The inner, high-voltage fence was often unprotected.
Similar barriers protect sensitive facilities abroad (restricted military areas, ammunition stores, etc.), especially in the former states of the Eastern Bloc .
In the GDR, high-voltage fences about 1.8 m high with a voltage of 10 kV were common to protect high-security systems (e.g. military air surveillance systems). In these fences, both high voltage and earthed wires ran on porcelain insulators, the position of which changed at irregular intervals along the fence. The high-voltage fence was located between two chain-link fences, which were supposed to protect against unintentional contact with the fence, including by game. A monitoring system was usually connected to the fence, which signaled a voltage drop when the fence was touched.
In the 1980s, South Africa fortified sections of its state border with high-voltage fences in order to prevent or deter civil war refugees and armed forces of the anti-apartheid movements from entering from neighboring countries . This type of state territorial security on the border with Mozambique , for example, has gained international recognition .
Signal fence
Electrical signal fences are used to signal the violation of a restricted area - through contact with the wires or contactlessly as a result of the change in the electrical field when people approach. The voltage used is not fatal. So were z. B. set up the border signal fences on the western border of the GDR and West Berlin . Electric barriers as climbing protection for buildings or climbing protection for walls also work in this way. They were z. B. attached to many security-relevant buildings of the GDR (state security, police). They consisted of wires attached to fiberglass rods protruding from the building in a V shape and running around the building above the ground floor.
From the end of the 1960s until 1989 there was an approximately 240-kilometer-long signal fence ("electronic signal system SZ-100"), a product from the Soviet Union , on the Hungarian-Austrian border (at that time the border between the Eastern Bloc and the West and part of the Iron Curtain) . Elsewhere there was a combination of barbed wire and minefields, see death strip . There was also a piece of SZ-100 between Hungary and the ČSSR , near Pressburg (Bratislava).
In Graz - Messendorf , the 2.5 m high fence (wire mesh, barbed wire) at the storage area for loading cars from local production onto car transporters is equipped on its inside with numerous horizontal signal wires at a horizontal distance of about 10 cm from the fence grille.
See also
Web links
Individual evidence
- ↑ Günter Herkert: Requirements for achieving a high level of security with electric fences. (PDF) patura KG, 2010, p. 14 , archived from the original on June 27, 2015 ; Retrieved December 20, 2015 .
- ↑ Austrian Electrotechnical Association: Safety for household and similar purposes. (PDF) Part 2-76: Special requirements for electric fences. ÖVE / EN, November 1, 2002, p. 13 , archived from the original on June 27, 2015 ; Retrieved December 20, 2015 .
- ↑ Wilma Rücker: Roebucks in agony. burgschwalbach.de (taken from the Rhein-Lahn-Zeitung Diez), July 30, 2010, accessed on June 19, 2015 .
- ↑ Deer strangles itself on pasture fence. main-netz.de, accessed on June 19, 2015 .
- ↑ a b c Burkhard Pohler: High-voltage safety system. In: www.bunker-wollenberg.eu. 2013, accessed June 19, 2015 .
- ↑ Chris McMichael: The re-militarization of South Africa's borders . on www.opendemocracy.net (English)
- ↑ Wolfgang Freitag: So much for the beginning of the end »Die Presse«, print edition of June 20, 2009