EP0103763B1 - Insulator, and installation of the insulator on a capacitive fence - Google Patents

Description

The invention relates to an insulator with the features mentioned in the preamble of claim 1, and an arrangement of the insulator on a capacitive protective fence.

For perimeter security, i.a. wired detection systems, capacitive protective fences are used, which work in the low frequency range (e.g. at 10 kHz) in an open-air climate. The detection is based on a transmission and reception method with which changes in the capacitance of a tension wire arrangement (electrode wires) are evaluated. For example, in a four-wire basic configuration of the detection system, a capacitive protective fence is formed by four tension wires. With air as the dielectric, the tension wires form capacities with each other and with the earth, whereby for example the partial capacities are measured and evaluated. For example, two wires can serve as transmit wires, the other two serve as receive wires. An intruder changes the partial capacitance and thus the reactive current through this arrangement due to its dielectric constant deviating from the air when the protective fence is approached. This change is evaluated according to size, speed and duration and an alarm is derived from it.

Capacitive fences that are exposed to extreme environmental conditions, such as desert sand and near the sea, pose particular problems. Salt, sand, wind, salt water, Spray and moisture or rain act on the capacitive protective fence and influence its susceptibility to faults. Such disturbing influences have a particular effect, the insulator surfaces of such a capacitive protection system. Known insulators used have, for example, a bell-shaped, rotationally symmetrical insulating body made of ceramic or plastic. In the upper area, such an insulator has an annular constriction for fastening the wire. On the underside of the insulator, a retaining bracket is attached centrally in the axial direction, which can be bent, for example, in a U-shape and is attached to the fence pole of the capacitive protection system. If extreme environmental conditions now prevail, salt and sand deposits on the insulator surfaces in damp and wet conditions lead to changes in the capacity of the protective fence and thus to faults and false alarms. In addition, since a bare wire is often used for the electrode wire instead of an insulated wire, because the plastic insulation of the wires is not sufficiently resistant to gases, acids and UV radiation, the insulator surface increases with the deposits described above, which form small interfering surfaces , a change in the capacity of the protective fence. Especially when the humidity or the wetness of sea spray or rain is added, the interfering surfaces on the insulator surface cause sudden changes in capacitance.

One remedy is the very maintenance-intensive cleaning or washing of the insulators several times a year in order to free them from salt and dirt, but this is very disadvantageous.

In addition, large insulators also have large surfaces that no longer contribute significantly to the insulation effect, because the insulation effect lies in the creepage distance (Labyrinth) at the bottom of the isolator. On the contrary, conductive interference surfaces such as salt, dirt and moisture form on the insulator surface due to such extreme environmental conditions. This leads to various interference effects. On the one hand, the bare wire is contacted with a conductive interfering surface via the air humidity, on the other hand two or more conductive interfering surfaces grow together or separate due to moisture or drying, which leads to changes in capacity, namely capacity increase or capacity reduction. Furthermore, the interference surfaces become generally conductive when the air humidity increases. The first-mentioned disruptive effect is much stronger and more disruptive than the other two disruptive effects.

In the case of a large number of insulators with many conductive small interference surfaces - the insulation surface is therefore inhomogeneous - within a monitoring area of a capacitive protective fence, the above-mentioned interference effects increase and decrease the capacitances measured, so that statistically a "noise floor" similar to that of the carbon microphone arises, which Makes the system very susceptible to failure in practical use. This leads to frequent false alarms, especially when the first-mentioned interference occurs.

In order not to let conductive, interfering surfaces that form on the insulator surface adversely affect the capacity due to salt, dirt and moisture, it has already been proposed to provide the outside of the jacket (surface) of the insulator with an electrically conductive layer (FR-A-1 014 790). The insulator on a capacitive protective fence can either be attached to the mast of the capacitive protective fence with the outside of the jacket and the electrode wire can be connected to the bracket, or the insulator can be attached to the mast with the bracket and the electrode wire can be connected to the outside of the conductive jacket.

The object of the invention is to develop an isolator as described in the introduction, such as is known, for example, from FR-A-1 014 790, in such a way that it functions smoothly even under extreme environmental conditions.

This object is achieved in an isolator mentioned above with the characterizing features of claim 1.

The insulator according to the invention has an electrically conductive layer on its outside, which is formed by a metal cup fitted over the insulator with a snug fit, which has a fastening web on one side, the retaining bracket having a fastening device for the electrode wire at its free end, and in which a plurality of annular recesses are arranged concentrically on the underside of the insulator. The metal cup can advantageously be drawn from stainless steel sheet or punched and folded, and then slipped over the insulator or the insulator can be fitted into the metal cup. It is particularly advantageous to form the fastening web for attaching the insulator to the mast of the capacitive protective fence when producing the metal cup. The mounting bracket, which is attached in the center to the underside of the insulator, is also made of rustproof, corrosion-resistant stainless steel and is provided with a fastening device for the electrode wire at one free end. The fastening device can be designed differently in order only to guide the electrode wire, to anchor it firmly or to tension it.

The metal cup is expediently adapted to the shape of the insulator, a preferred embodiment being formed by a cuboid which is open towards the bottom. This can be produced particularly well by punching and bending or folding from sheet steel. The fastening web can be punched out and bent into two U-shaped legs in the same step. In addition to the U-shaped legs, there is a breakthrough in the metal cup of the insulator. A hose tie can be pulled through these breakthroughs, and the insulator according to the invention can thus be fastened in an electrically conductive manner to the grounded fence pole without additional grounding elements being necessary.

In a further embodiment of the invention, the U-shaped retaining bracket of the insulator has at least one approximately circular spring turn. This has the advantage that for the length compensation, which is necessary for the electrode wire because the electrode wire changes its length due to temperature fluctuations, the tensioned electrode wire does not require an additional tension spring. A commercially available tension spring cannot be used anyway for the extremely unfavorable climatic conditions. An extremely corrosion-resistant tension spring would have to be provided. A further advantage is also given in that the weight load of the electrode wire is lower with the elimination of the tension spring, and the natural vibration of the electrode wire is thereby reduced. In addition, the capacitive conditions of the protective fence improve because the wire is brought directly to the insulator because there is no areal enlargement of the electrode wire by the tension spring.

A fastening device for the electrode wire at the free end of the holding bracket can be expediently produced in a very simple manner in that a bore is made diametrically through which the electrode wire is drawn and wound with several turns around the free end of the holding bracket.

A further developed embodiment of the fastening device is provided by a wire tensioning device placed directly on the free end of the holding bracket. This wire tensioning device eliminates the need for a hot-dip galvanized turnbuckle, which is disadvantageous due to the lack of corrosion resistance. In addition, there is no further weight load on the electrode wire. The wire tensioning device expediently has a wire winding drum and a crank with which the wire can be tensioned. The crank can then be removed. The drum is locked in a simple manner with a split pin, which is inserted through the drum and through the hole in the bracket.

Further details, arrangements and advantages of the invention emerge from the subclaims and the drawing, which is explained in more detail below.

Fig. 1

eine bekannte Anordnung der Isolatoren an einen kapazitiven Schutzzaun,

Fig. 2

einen bekannten Isolator, teilweise im Schnitt,

Fig. 3

einen Isolator in Draufsicht, vergrößert dargestellt mit den Störflächen,

Fig. 4

einen bekannter Isolator mit Metallschicht

Fig. 5

eine Anordnung eines Isolators am kapazitiven Schutzzaun mit geerdeter Mantelaußenseite und Elektrodendrehtanschluß am Haltebügel,

Fig. 6

eine Anordnung mit Elektrodendrahtanschluß an der leitenden Mantelaußenseite und Befestigung des Isolators über den Haltebügel am Mast,

Fig. 7

eine zweckmäßige Ausführungsform des erfindungsgemäßen Isolators im Schnitt mit einem U-förmig gebogenen Haltebügel,

Fig. 8

einen Isolator ähnlich Fig. 7 im Schnitt mit senkrecht nach unten herausgeführtem kurzen Haltestift,

Fig. 9

den Isolator nach Fig. 8 an einem Zaunmast,

Fig. 10

den Isolator nach Fig. 9 in Draufsicht,

Fig. 11

einen Isolator mit U-förmig gebogenen Haltebügel mit einer Federwindung,

Fig. 12

den Isolator nach Fig. 11 in Draufsicht und

Fig. 13

eine Drahtspannvorrichtung auf dem freien Ende des Haltebügels eines Isolators gemäß Fig. 7 oder 11.

Show

Fig. 1

a known arrangement of the insulators on a capacitive protective fence,

Fig. 2

a known isolator, partly in section,

Fig. 3

an insulator in plan view, shown enlarged with the interference surfaces,

Fig. 4

a known insulator with a metal layer

Fig. 5

an arrangement of an insulator on the capacitive protective fence with grounded outer jacket and rotating electrode connection on the bracket,

Fig. 6

an arrangement with an electrode wire connection on the outside of the conductive jacket and fastening of the insulator via the retaining bracket on the mast,

Fig. 7

an expedient embodiment of the insulator according to the invention in section with a U-shaped bracket,

Fig. 8

7 shows an insulator similar to FIG. 7 in section with the short holding pin led out vertically downwards,

Fig. 9

8 on a fence pole,

Fig. 10

9 in top view,

Fig. 11

an insulator with a U-shaped bracket with a spring turn,

Fig. 12

11 in top view and

Fig. 13

a wire tensioning device on the free end of the bracket of an insulator according to FIG. 7 or 11th

In Fig. 1, a mast 6 of a capacitive protective fence is shown, which is electrically conductive and grounded. The insulator 1 is fastened to the masts 6 by means of a holding bracket 4. In the upper area of the insulator 1 is the Electrode wire 5 connected. The arrangement of several tension wires (electrode wires) one above the other forms the capacitive protective fence, whereby - as shown here - one electrode is connected as the receiving electrode, the lower wire, the other electrode, the wire arranged above it, as the transmitting electrode. For example, the partial capacitance between the transmitting and receiving electrodes, the actual useful capacitance C _{N, is} measured. The approach of an intruder changes this capacity. If conductive interference surfaces are now formed on the surface of the insulator, these likewise lead to changes in capacitance, shown in the drawing C _S as interference capacitance, which can trigger an alarm. In this case, this leads to a false alarm because the interference capacity C _S and not the change in capacity caused by the intruder causes the alarm.

2 shows an insulator 1 known per se, one half of which is shown in section. The isolator 1 has e.g. approximately a bell shape and has a constriction 11 in the upper area for the attachment of the electrode wire 5. The retaining bracket 4 is fitted centrally in the axial direction. The main insulation effect is formed by the recess 10 on the underside in the insulator 1, which is arranged centrally around the holding bracket 4 and which represents a long leakage current path 12. This is little affected by the environmental conditions.

In Fig. 3, the insulator is partially shown in section when viewed from above. The electrode wire 5, which is fastened in the constriction 11 of the insulator 1, is a bare wire. If, for example, conductive interference surfaces 13 are formed on the surface 2 of the insulator 1 by salt, dirt and moisture the interference surface 13a, which has arisen close to the electrode wire 5, for making contact with the bare wire 5, thereby causing a disturbing change in capacitance. Likewise, two interfering surfaces 13b and 13c can grow together or separate again, so that this also causes jumps in capacity. In general, the interfering surfaces 13 can become conductive with increasing air humidity or with the onset of rain and thereby change the capacitance conditions in a disruptive manner.

A known isolator is shown in FIG. It shows on the surface, i.e. the outer side 2 of the insulator 1, an electrically conductive layer 3, e.g. an applied metal layer.

Conductive interfering surfaces 13 on a conductive surface 3 do not cause this surface to change, and an inhomogeneous surface can no longer form.

If this conductive surface is grounded, interfering surfaces 13 which become conductive can form without these having a disruptive effect on the capacitive behavior of the protective fence itself, since the electrode wire 5 is fastened to the holding bracket 4 of the insulator 1. The insulation of the electrode wire 5 from earth is given by the insulation path or leakage current path 12 on the underside of the insulator 1. This insulation section 12 is arranged in the region of the insulator 1 which is protected from the weather by the insulator and is therefore hardly touched by disturbing salt and dirt.

If the conductive surface 3 is galvanically connected to an electrode wire 5, interfering surfaces 13 also no longer have a disruptive effect on the capacitive behavior of the protective fence (FIG. 6).

The insulation of the bare wire 5 and the conductive insulator surface 3 from earth is also given here by the insulation path or leakage current path 12 on the underside of the insulator 1; as already mentioned, it lies in the protected area of the isolator.

5 shows an arrangement of the insulator according to FIG. 4 on the capacitive protective fence similar to that shown in FIG. 1, with the difference that the insulator 1 is fastened to the fence pole 6 with a holding device 8. As a result, the metallized insulator surface 3 is electrically conductively connected to the grounded mast 6. The electrode wire 5 is connected to the bracket 4 of the insulator 1 with a fastening device 7, not shown here, on the insulator.

6 shows a further arrangement of the insulator according to FIG. 4 on the capacitive protective fence similar to that shown in FIG. 1, with the difference that the insulator 1 is electrically connected to the bare electrode wire 5 with the electrically conductive surface 3 and the insulator 1 is attached via its bracket 4 to the grounded fence pole 6.

In contrast to Fig. 5 - there is a reduction in field sensitivity due to the large grounded areas - the arrangement according to Fig. 6 increases the field sensitivity in the vicinity of the isolators, so that the generally present reduction in field sensitivity due to the grounded mast 6 near the mast by them Arrangement is partially compensated.

The insulator 1 shown in FIG. 7 with a U-shaped retaining bracket 4 is shown in section. The insulator 1 can be made of ceramic or plastic. It expediently has the shape of a cuboid. Centrally in the middle, the U-shaped bracket 4 is fitted from the bottom into the body of the insulator. In the insulator body, the holding bracket 4 can additionally be anchored in the insulator body 1 with a cross pin 4a. The cross pin 4a is inserted through a hole in the bracket 4 and thus secures the insulator against twisting. The metal cup 14 according to the invention has the shape of a cuboid open at the bottom, into which the body of the insulator 1 is fitted. In order to give the metal cup 14 an additional hold on the insulator body, a window-like recess 14b is provided on one side of the metal cup 14, into which a snap-in lug 1b engages on the insulator 1. On its underside, the insulator has a plurality of recesses 15 which are provided concentrically around the holding bracket 4. The ribs 15a formed in this way form a very long leakage current path 12 between the holding bracket 4 and the metal jacket 14 of the insulator 1. The free end 18 of the U-shaped holding bracket 4 here has a bore 19 through which the electrode wire 5 can be inserted. The electrode wire is wound in several turns 5a around the free end 18 of the retaining bracket 4, inserted through the bore 19 and, for example, to a junction box, not shown here, which is arranged on the mast above the insulator. The electrode wire 5 can then be tensioned and carried on to the next insulator and there to the junction box. On one side of the metal cup 14, the fastening web 8 'is formed, which consists of two U-shaped legs, as can be clearly seen in a later figure.

FIG. 8 shows a cut away form of the isolator according to the invention. Instead of the retaining bracket, a retaining pin 4 'is pressed into the insulator body 1 and led out vertically downwards. The holding pin 4 'has only a short length and has a slot 26 at its free end 18'. This slot introduced radially into the holding pin 4 'extends at least to the middle, i.e. the axis of the holding pin 4 '. In this slot 26, the electrode wire 5 is inserted and freely movable. To prevent the wire 5 from jumping out, this fastening device 7 'is secured with a clamping sleeve 27 which can be displaced along the holding pin 4' and can thus be pushed over the slot 26 when the electrode wire 5 is inserted. The wire 5 is still freely movable in its longitudinal direction in order to be able to take part in the changes in length that are present due to temperature fluctuations. The body of the insulator 1 also has concentrically arranged annular recesses 15 on its underside 1a. The fastening web 8 ′ can be seen on one side of the metal cup 14. The body of the insulator 1 has a recess 1c in the immediate vicinity of the fastening web 8 '. Through this and through the openings 9 in the metal jacket 14, the hose tie 16, as can be seen in FIGS. 9 to 12, can be inserted for fastening the insulator 1 to the mast 6. For additional fastening of the insulator body 1 in the metal cup 14, instead of the window 14b and the lug 1b according to FIG. 7, a screw 14a can be simply rotated through the metal jacket 14 into a hole in the insulator 1.

In FIG. 9 the insulator 1 according to FIG. 8 is shown arranged on the fence pole 6. The insulator 1 is fastened to the mast 6 with a hose tie 16 as described above. This can be seen better in FIG. 10, in which the insulator 1 on the mast 6 is shown in a top view. The insulator 1 is due to the mast 6 at a certain distance the U-shaped leg of the fastening web 8 'held. The hose tie 16, which is guided through the openings 9 in the metal jacket 14 and through the recess 1c in the body of the insulator 1, is looped around the mast 6 and is fastened in a known manner with a worm gear.

FIG. 11 shows the isolator 1 according to the invention according to FIG. 7 with the U-shaped bracket 4 and with the circular spring turn 17 of the bracket 4. The free end 18 of the retaining bracket corresponds to the illustration in FIG. 7 for the attachment of the electrode wire 5. The insulator 1 is attached to the mast 6 with the hose tie 16. The metal cup 14 has a greater height than the body of the insulator 1, so that the insulator underside 1c is better protected against the weather by the outstanding metal jacket (14). In this area, the metal cup (14) is roof-shaped 14c on two opposite sides, so that in the case of an insulator according to FIG. 9, when it rains, the water cannot drip directly onto the electrode wire (5). This arrangement is shown in plan view in FIG. 12.

In Fig. 13 the wire tensioning device (20) is shown as a detailed view in section. The free end 18 of the U-shaped bracket (4) has a bore 19. The wire tensioning device 20 is placed on the free end. In this exemplary embodiment, it consists of a drum 21 with which the electrode wire 5 is wound and tensioned. The detachable assembly crank 22 is used to tension the wire 5. The split pin 23 is used to lock the drum 21 on the free end 18 of the retaining bracket (4).

Claims (9)

1. Insulator (1), which has a fixing bracket (4), arranged centrally in the axial direction on its underside (1a), and at least one annular recess (15), which is concentric with the fixing bracket (4) and forms a creepage current insulating clearance (12) and to the outer lateral surface (2) of which insulator a holding device (8) can be attached, the outer lateral surface (2) of the insulator (1) having an electrically conductive layer (3), characterised in that the conductive layer (3) is formed by a metal can (14) slipped over the insulator (1) with a snug fit, which has a fastening bar (8') on one side, in that the fixing bracket (4) has at its free end (18) a fastening device (7) for an electrode wire (5) and in that a plurality of annular recesses (15) are arranged concentrically on its underside (1a).
2. Insulator according to Claim 1, characterised in that the metal can (14) has approximately the shape of the insulator (1).
3. Insulator according to Claim 1, characterised in that the metal can (14) has the shape of a cuboid open downwards.
4. Insulator according to Claim 1, characterised in that the metal can (14) has the shape of a prism open downwards.
5. Insulator according to one of Claims 1 to 4, characterised in that the fastening bar (8') is formed from two U-shaped legs and the metal can (14) has an opening (9) next to the leg, in each case.
6. Insulator according to Claim 1, characterised in that the fixing bracket (4) is bent in a U-shaped fashion and has at least one spring winding (17) of approximately circular construction.
7. Insulator according to Claim 1 or 6 , characterised in that the fastening device (7) is formed either directly by a bore (19) inserted diametrically into the fixing bracket (4) or by a wire clamping device (20) set up on the free end (18) of the fixing bracket (4), the wire clamping device (20) having a wire take-up drum (21) known per se with a detachable crank (22) and a split pin (23) that can be pushed through the drum (21) and through the bore (19) in the fixing bracket (4) and can be located in position.
8. Insulator according to Claim 1, characterised in that the fixing bracket (4) is formed by a short holding pin (4') projecting perpendicularly downwards from the insulator (1) and the fastening device (7) is formed by a slot (26) introduced radially into the holding pin (4') at the free end (18') thereof and a clamping sleeve (27) which can be displaced along the holding pin (4').
9. Arrangement of the insulator according to Claim 5 on a capacitive protective fence, characterised in that the insulator (1) with the outer lateral surface (2) is fastened to the pole (6) of the capacitive protective fence by means of the fastening bar (8') and a hose clamp (16), the conductive layer (3) or the pole (6) being earthed, and in that the electrode wire (5) is connected to the fixing bracket (4, 4' or 18).

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