EP3074984B1 - High-voltage cable - Google Patents

Description

The invention relates to a high-voltage cable, in particular for electrostatic coating agent charging in a coating system.

FIG. 1 1 shows a conventional high-voltage cable 1 with a cable core 2 made of a copper strand or copper wires, a field straightener 3 made of electrically conductive polyolefin surrounding the cable core 2, an insulating jacket 4 of electrically insulating polyolefin surrounding the field straightener 3 in the manner of a shell, and an outer jacket 5 made of polyurethane ( PU), wherein the outer jacket 5, in addition to an additional electrical insulation for sufficient abrasion resistance and chemical resistance of the high voltage cable 1 provides.

A disadvantage of the known high-voltage cable 1 described above is the very low electrical resistance, which is due to the fact that the cable core 2 consists of copper, which has a very low electrical resistivity. The low electrical resistance of the high-voltage cable 1 can namely lead to strong current oscillations when used in an electrostatic coating system during a discharge, which is undesirable.

FIG. 2 shows a correspondingly improved high voltage cable 1, as in EP 0 829 883 A2 is described. This high voltage cable 1 is partly true with that described above and in FIG. 1 shown high voltage cable 1 to avoid repetition, reference is made to the above description, wherein like reference numerals are used for corresponding details.

A special feature of this high-voltage cable 1 is that the insulation jacket 4 consists of two coaxial and superimposed in the radial direction layers 4.1, 4.2.

Another special feature of this known high-voltage cable 1 is that the cable core 2 consists of an electrically insulating plastic (eg polyester) and therefore does not conduct electricity. The thread-like and electrically insulating cable core 2 serves as a mechanical support for a conductor layer 6, which may consist for example of filled with soot particles polyethylene (PE). However, the conductor layer 6 has a much greater electrical resistance than the conductive cable core 2 of copper according to FIG. 1 , This is advantageous because the high voltage cable 1 according to FIG. 2 Thus, having a greater electrical resistance, which are attenuated when used in an electrostatic coating system, the unwanted current oscillations during discharge operations.

A disadvantage of the high voltage cable 1 according to FIG. 2 However, it is the fact that on contact with Vaseline or insulating oils (eg transformer oil), the electrical conductivity can be lost. In the conventional plug-in technology of high voltage cables namely a filling with Vaseline is provided. This vaseline can penetrate from the cable ends of the high-voltage cable 1, starting in the high-voltage cable 1, wherein the high-voltage cable 1 due to the capillary effect from the cable end starting with vaseline can soak. The penetrating vaseline has the consequence that the conductive layer 6 becomes electrically insulating due to the vaseline which diffuses in, the high-voltage cable 1 becoming inoperative.

Out US 3 792 409 A a high voltage cable according to the preamble of claim 1 is known.

However, this known high voltage cable is also not optimal.

The invention is therefore based on the object to provide a correspondingly improved high-voltage cable, which is particularly suitable for use in an electrostatic coating system.

On the one hand, when used in an electrostatic coating system, the high-voltage cable according to the invention is intended to damp the unwanted current oscillations which occur when the known high-voltage cable is used FIG. 1 occur during loading and unloading operations.

On the other hand, however, the high-voltage cable according to the invention should also prevent the electrical conductivity from being influenced or even lost by the contact with petroleum jelly or insulating oils (for example transformer oil).

This object is achieved by an inventive high voltage cable according to the main claim.

The invention initially provides a correspondence with the prior art that the high-voltage cable has a centrally arranged cable core, which is surrounded by an electrically insulating insulating jacket. The invention differs from the conventional ones described above High voltage cables in that the cable core has a medium electrical resistance.

In contrast to the known high-voltage cable according to FIG. 1, the cable core is therefore not highly electrically conductive, whereby unwanted current oscillations during charging and discharging operations are avoided.

In contrast to the conventional high voltage cable according to FIG. 2 the high voltage cable according to the invention is insensitive to vaseline or insulating oils and barely changes its electrical resistance.

The term of an average electrical resistance used in the invention is to be distinguished from an electrical conductor (eg copper) on the one hand and an electrical insulator on the other hand and preferably has the meaning that the electrical resistance in the range of 1kΩ / m relative to the length of the high voltage cable -1mΩ / m, 2kΩ / m-500kΩ / m, 5kΩ / m-200kΩ / m or 10kΩ / m-50kΩ / m. The electrical resistance of the conductive cable core is therefore preferably in a range which is suitable for use in an electrostatic coating system for electrostatic coating agent charging.

According to the invention, the cable core consists of twisted nonwoven strips, which in turn are composed of several filaments and are themselves electrically conductive or made electrically conductive. In this case, a single nonwoven strip can be twisted and then form the cable core. However, it is within the scope of the invention also possible that several nonwoven strips are twisted in several strands and then form the cable core.

In a variant of the invention, the individual fibers or filaments of the nonwoven strips consist of an electrically conductive plastic, for example polyethylene (PE), the filled with soot particles, as is made EP 0 829 883 A2 is described.

In another variant of the invention, however, the individual fibers of the nonwoven strip consist of an electrically insulating plastic which is rendered electrically conductive by a surface coating with an electrically conductive material.

It has already been mentioned above that in the conventional high-voltage cables, the penetrating vaseline can cause the electrical conductivity to be lost. This disturbing effect, the invention can counteract in two different ways.

On the one hand, the invention can prevent vaseline from ever penetrating into the high voltage cable due to the capillary effect.

On the other hand, however, the invention can also prevent the penetrated petroleum jelly or insulating oils from influencing or even resulting in a loss of electrical conductivity, this effect resulting from the design of the high-voltage cable according to the invention.

The penetration of vaseline into the high voltage cable can be prevented in the invention in turn in two different ways.

On the one hand, the cable core can be so coarse-grained that the spaces between the individual fibers of the cable core are so large that the capillary force is insufficient to suck petroleum jelly into the intermediate spaces. In this way, it is thus prevented that Vaseline ever penetrates into the high-voltage cable according to the invention.

On the other hand, penetration of vaseline into the high-voltage cable can also be prevented by eliminating the gaps between the fibers of the cable core, so that the cable core can not absorb any vaseline at all. For example, the fleece strips of the cable core can be twisted so much that the spaces between the individual fibers are almost completely eliminated. Alternatively, however, there is the possibility that the interstices between the fibers of the cable core may be filled in order to prevent vaseline from penetrating into the intermediate spaces.

It should also be mentioned that the electrically conductive cable core in the high-voltage cable according to the invention can be surrounded by a so-called field smoothing device, as is already known from the prior art. Such a field straightener may for example consist of electrically conductive plastic, such as polyolefin, as it is made EP 0 829 863 A2 is known. It should be mentioned here that the field smoother also preferably has an average electrical resistance, the meaning of this term having already been explained above. However, the electrical resistance of the field trowel is preferably greater than the electrical resistance of the cable core in order to effect a field smoothing can. However, the electric resistance of the field trowel is preferably smaller than the electrical resistance of the insulation jacket. The field smoother is arranged between the cable core and the insulating jacket, as it is already known from the prior art. It should be mentioned that the field straightener rests preferably without an intermediate layer directly on the cable core or on the conductive coating of the cable core.

Furthermore, the high-voltage cable according to the invention preferably has a shielding jacket in accordance with the prior art in order to electrically shield the high-voltage cable, wherein the shielding jacket is preferably of low resistance. For example, the shielding jacket made of a copper braid or a combination of a copper braid with a plastic. In any case, the resistance of the Abschirmmantels is preferably smaller than the resistance of the cable core and the Feldglätters.

It should be mentioned that the dielectric strength of the high-voltage cable depends, inter alia, on the field distribution within the high-voltage cable. The field strength should therefore be as small as possible at the conductor layer. However, the field strength depends on the ratio of the diameter dA of the shielding shell to the diameter dS of the cable core, wherein the diameter ratio dA / dS should be in the range of 1.5-5, 2-4 or 2-3.4.

Finally, the high-voltage cable according to the invention in accordance with the prior art may still have an electrically insulating outer jacket, wherein the outer shell may for example consist of plastic, in particular of polyurethane (PU). The outer jacket preferably has a greater mechanical abrasion resistance compared to the insulating jacket, is less flammable and / or acid-resistant.

It should also be mentioned that the high-voltage cable according to the invention preferably has sufficient dielectric strength for use in an electrostatic coating system. The dielectric strength of the high voltage cable is therefore preferably at least 1kV, 2kV, 5kV, 10kV, 20kV, 50kV, 100kV or even 150kV.

It should also be mentioned that the high-voltage cable preferably has an electrical capacitance which allows use in an electrostatic coating system. The electrical capacity of the high voltage cable is therefore preferably in the range of 1pF / m-1000pF / m, 10pF / m-500pF / m, 20pF / m-250pF / m, 50pF / m-100pF / m or 70pF / m-100pF / m ,

In addition, it should be mentioned that the electrically moderately conductive cable core can be electrically surrounded with field straightener at connection points along the high-voltage cable. Preferably, these connection points do not extend over the entire length of the high-voltage cable, but are only punctiform.

The electrical contacting of the high voltage cable to the cable ends can be done for example by a metallic connecting pin which is axially inserted or screwed into the end face of the cable core to electrically contact the high voltage cable. Other connection techniques, such as Cutting and clamping technology are also applicable.

Furthermore, it should be mentioned that the invention not only comprises the high-voltage cable described above as a single component. Rather, the invention also includes the novel use of such a high voltage cable for electrostatic Coating agent charging in a coating plant, in particular in a paint shop for painting automotive body components and in the parts painting in the general or supplier industry.

Finally, the invention also encompasses an electrostatic coating agent charge which can be used, for example, in a painting installation in order to electrostatically charge the coating agent to be applied (for example paint, powder paint).

The coating agent charging according to the invention initially has a high voltage generator which generates the required high voltage for charging the coating agent. Furthermore, the coating agent charging according to the invention comprises a high-voltage electrode in order to electrostatically charge the coating agent to be applied. Such high voltage electrodes are known per se from the prior art and may be formed, for example, as external electrodes of a rotary atomizer. However, within the scope of the invention, there is also the possibility of direct charging within a rotary atomizer.

In the case of the coating agent charging according to the invention, the electrical connection between the high-voltage generator and the high-voltage electrode takes place at least over part of the connection length through the high-voltage cable according to the invention, as described above.

Figur 1

eine Querschnittsansicht eines herkömmlichen Hochspannungskabels mit einer Kabelseele aus Kupfer,

Figur 2

eine Querschnittsansicht eines herkömmlichen Hochspannungskabels mit einer elektrisch isolierenden Kabelseele, die elektrisch leitfähig beschichtet ist,

Figur 3

eine Querschnittsansicht eines erfindungsgemäßen Hochspannungskabels mit einer elektrisch leitfähigen Kabelseele,

Figur 4

eine Abwandlung von Figur 3 mit einem zusätzlichen Abschirmmantel, sowie

Figur 5

eine schematische Darstellung einer erfindungsgemäßen Beschichtungsmittelaufladung.

Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to FIGS. Show it:

FIG. 1

a cross-sectional view of a conventional high voltage cable with a cable core made of copper,

FIG. 2

a cross-sectional view of a conventional high-voltage cable with an electrically insulating cable core, which is coated electrically conductive,

FIG. 3

a cross-sectional view of a high-voltage cable according to the invention with an electrically conductive cable core,

FIG. 4

a modification of FIG. 3 with an additional shielding coat, as well

FIG. 5

a schematic representation of a coating agent charge according to the invention.

FIG. 3 shows a preferred embodiment of a high voltage cable 1 according to the invention, which partially with the above described and in FIG. 2 shown high voltage cable 1, so reference is made to avoid repetition of the above description, wherein the same reference numerals are used for corresponding details.

A special feature of this embodiment according to the invention consists in the design and construction of the cable core 2. Thus, the cable core 2 consists here of twisted nonwoven strips, each consisting of several filaments (fibers) and are made electrically conductive. The cable core 2 thus consists of plastic as a carrier material, which is made electrically conductive, for example by filling or coating with Rußteilchen. The cable core 2 therefore has a mean electrical resistance in the range of 10kΩ / m-100kΩ / m.

The design of the cable core 2 of twisted nonwoven strips prevents in comparison to the conventional high voltage cable 1 according to FIG. 2 advantageous that penetrating vaseline affects the electrical conductivity of the high voltage cable 1.

The average electrical resistance of the cable core 2, in comparison to the conventional high-voltage cable 1 according to FIG. 1, ensures that no excessive current oscillations occur during discharging operations in an electrostatic coating system.

FIG. 4 shows a modification of FIG. 3 In order to avoid repetition, reference is made to the above description, wherein the same reference numerals are used for corresponding details.

A special feature of this embodiment is that between the outer sheath 5 and the outer layer 4.2 of the insulation sheath 4, a shielding shell 7 is additionally arranged, which may consist of a copper braid.

Finally shows FIG. 5 in a highly simplified manner a coating agent charging according to the invention with a high voltage generator 8, which is connected via the high-voltage cable 1 according to the invention with an electrostatic atomizer 9, as it is known per se from the prior art.

The electrostatic atomizer 9 is a spray 10 of an electrostatically charged coating agent (eg Paint) on an electrically grounded motor vehicle body component 11 from.

The average electrical resistance of the high-voltage cable 1 advantageously ensures that no excessive current oscillations occur during discharging operations.

The above-described structural design of the high-voltage cable 1, however, has the advantage that penetrating vaseline does not lead to a change or even to a loss of electrical conductivity of the high-voltage cable 1.

The invention is not limited to the preferred embodiments described above. Rather, a variety of variants and modifications is possible, which also make use of the inventive idea and therefore fall within the scope. In particular, the invention also claims protection of the subject matter and the features of the dependent claims independently of the claims in each case.

LIST OF REFERENCE NUMBERS

1

High voltage cables

2

cable core

3

polyolefin

4

insulation jacket

4.1

Layer of insulation jacket

4.2

Layer of insulation jacket

5

outer sheath

6

conductor layer

7

shielding jacket

8th

High voltage generator

9

atomizer

10

spray

11

Motor vehicle body part

Claims (12)

1. A high-voltage cable (1), in particular for electrostatically charging a coating agent in an electrostatic coating plant, comprising

   a) a centrally arranged cable core (2) and

   b) an electrically insulating jacket (4, 4.1, 4.2), which sheaths the cable core (2),

   c) wherein the cable core (2) has a moderate electrical resistance and includes fibres,

   characterized in that

   d) the fibers of the cable core (2) form a nonwoven fabric,

   e) at least one nonwoven-fabric strip of the nonwoven fabric is twisted and forms the cable core (2), and

   f) the nonwoven-fabric strips each consist of a plurality of filaments of the fibers.
2. The high-voltage cable (1) according to claim 1, characterized in that at least part of the cable core (2) is made of an electrically conductive plastics material.
3. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the cable core (2) is made of such coarse fibers, and the gaps between the individual fibers of the cable core (2) are so large, that the capillary force is not sufficient to draw petroleum jelly into the gaps, or

   b) the gaps between the fibers of the cable core (2) are completely filled so that the cable core (2) cannot draw up any petroleum jelly.
4. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the electrically conductive cable core (2) is sheathed by a field-smoothing element(3), and

   b) the field-smoothing element (3) is made of a plastics material, in particular is made of polyolefin, and

   c) the field-smoothing element (3) has a moderate electrical resistance, and

   d) the electrical resistance of the field-smoothing element (3) is greater than the electrical resistance of the cable core (2), and

   e) the electrical resistance of the field-smoothing element (3) is less than the electrical resistance of the insulating jacket (4, 4.1 4.2), and

   f) the field-smoothing element is arranged between the cable core (2) and the insulating jacket (4, 4.1, 4.2) and

   g) the field-smoothing element(3) lies directly on the cable core (2) without any intermediate layer.
5. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the high-voltage cable (1) comprises a shield (7) for electrical shielding, and

   b) the shield (7) has a moderate electrical resistance or a low resistance, and

   c) the shield (7) surrounds the insulating jacket (4, 4.1, 4.2), and

   d) the resistance of the shield (7) is less than the resistance of the cable core (2) and/or of the field-smoothing element (3), and

   e) the shield (7) has a diameter dA, and the cable core (2) has a diameter dS, where the diameter ratio dA/dS is greater than 1.5 or 2, and/or is less than 5, 4 or 3.4.
6. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) an electrically insulating outer jacket (5) sheaths the cable core (2), the field-smoothing element (3), the insulating jacket (4, 4.1, 4.2) and/or the shield (7), and

   b) the outer jacket (5) is made of a plastics material, in particular is made of polyurethane, and

   c) compared with the insulating jacket (4, 4.1, 4.2), the outer jacket (5)

   - has a greater wear resistance,

   - is of lower flammability and/or

   - is more resistant to acid.
7. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the moderate electrical resistance of the conductor element and/or of the field-smoothing element (3) per unit length equals

   - at least 1kΩ/m, 2kΩ/m, 5kΩ/m, 10kΩ/m and/or

   - at most 1MΩ/m, 500kΩ/m, 200kΩ/m, 100kΩ/m, 50kΩ/m or 20kΩ/m, and

   b) the high-voltage cable (1) has a dielectric strength of at least 1kV, 2kV, 5kV, 10kV, 20kV, 50kV, 100kV or 150kV, and

   c) the high-voltage cable (1) has an electrical resistance per unit length that equals

   - at least 1kΩ/m, 2kΩ/m, 5kΩ/m, 10kΩ/m and/or

   - at most 1MΩ/m, 500kΩ/m, 200kΩ/m, 100kΩ/m, 50kΩ/m or 20kΩ/m, and

   d) the high-voltage cable (1) has an electrical capacitance per unit length that equals

   - at least 1pF/m, 10pF/m, 20pF/m, 50pF/m, 70pF/m and/or

   - at most 1000pF/m, 500pF/m, 250pF/m, 100pF/m.
8. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the insulating jacket (4, 4.1, 4.2) is made of a plastics material, in particular is made of polyolefin, and

   a) the insulating jacket (4, 4.1, 4.2) comprises a plurality of coaxial layers (4.1, 4.2), and

   c) the layers (4.1, 4.2) of the insulating jacket (4, 4.1, 4.2) have a different electrical resistance.
9. The high-voltage cable (1) according to any of the preceding claims, characterized in that

   a) the cable core (2) is electrically connected to the field-smoothing element (3) at junctions, and/or

   b) the junctions do not extend over the entire length of the high-voltage cable (1), and/or

   c) the junctions are discrete points.
10. The high-voltage cable (1) according to any of the preceding claims, characterized in that at at least one end of the high-voltage cable (1), a metallic connecting spike is pushed or screwed axially into the end face of the cable core (2) in order to make electrical contact with the high-voltage cable (1).
11. A use of a high-voltage cable (1) according to any of the preceding claims for electrostatically charging a coating agent in an electrostatic coating plant, in particular in a paint shop for painting motor vehicle body components.
12. An apparatus for electrostatically charging a coating agent, in particular in a coating plant, which apparatus comprises

    a) a high-voltage generator (8) for generating a high voltage,

    b) a high-voltage electrode for electrostatically charging the coating agent to be applied, in particular on or in an atomizer (9), and

    c) a high-voltage cable (1) for electrically connecting the high-voltage generator (8) to the high-voltage electrode,

    characterized in that

    d) the high-voltage cable (1) is embodied according to any of claims 1 to 10.

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