EP1515806B1 - Leadthrough for electric high-voltage through a wall separating an environment area from a process area - Google Patents

Abstract

In a leadthrough for an electrical high voltage conductor through a wall which separates a process area from an ambient area, comprising a body of a dielectric high voltage resistant material, two axially adjacent geometric base structures are provided, a cylinder and a truncated cone having a smaller diameter end adjacent the cylinder so that the cylinder has a radial annular surface area adjacent the truncated cone, and the cylinder includes axially extending gas supply bores arranged uniformly distributed over the circumference of the cylinder and having exit openings at the radial annular face of the cylinder such that gas supplied to the gas supply bores at the ambient area end of the cylinder is discharged from the gas supply bores onto the outer surface of the truncated cone to form a gas envelope around the truncated cone.

Description

The invention relates to a high voltage electrical feedthrough through a wall separating a surrounding area from a process area. The process area has at least one atmosphere in its entrance area. Liquid droplets (aerosols) and / or soot / dust particles loaded / contaminated and is therefore kept separate from the environment.

To clean the process atmosphere of such polluting aerosols or solid particles, it is passed through cleaning facilities in the process area. Such devices are electrostatic precipitators or electrostatic wet cleaners. With them, such impurities are removed from air / gases. The process of precipitation is effected by electrostatic charging and collection of the charged particles on grounded electrodes. For this purpose, electrical high voltage must be conducted from a source in the environment to corresponding high-voltage equipment in the process area. Such electrostatic precipitators and electrostatically enhanced wet scrubbers remove particles from flue gas. Many devices have been developed in recent years, in which a reduction in size was accompanied by the extension of the long-term stability. Often high voltage feedthroughs are routed through the wall or attached to an annex.

A high voltage electrostatic shield may be used to prevent particle deposition on the insulator (see WO 00/30755). In such a case, the conductive sheath is connected to the same high voltage source as the discharge electrode, so that the high electric field is generated in the area between the sheath and the nearby grounded surface of the housing. Accordingly, the existing in the gas charged droplets or Particles precipitate on the grounded surface and not on the high voltage insulator. In order to prevent the insulator from steam condensation, the insulator is heated because condensation can cause a reduction in the high voltage on the electrical connection. An electrostatic heater is connected to the insulator to keep it at a temperature 10 ° C or more higher than the surrounding gas temperature. This also, to avoid steam condensation, usually some degrees C are sufficient.

The heating of the insulator is also effected by an injection of dry, warm cleaning gas into the shield surrounding the insulator (US 6,156,098 or WO 00/47326). The movement of airflow around the insulator is used to keep the insulator on its surface free from moisture build-up and dust deposits, helping to keep the insulator clean and generally free of flashovers. When air is supplied by a blower or other air pressure generating means, air cooling and controlled heating as well as cleaning associated with air conditioning in the failure device are provided to some degree.

The self-cleaning venturi insulator for an electrostatic precipitator is described in US 5,421,863. The insulator is made of a dielectric material in which an arc / flashover is very difficult to burn. The effect of directing the airflow through a Venturi nozzle is used to protect the surface of the isolator from the deposition of contaminants from flue gas.

The effectiveness of gas cleaning depends on the working reliability of the high voltage device. For this purpose, good electrical high-voltage insulator materials, which are versatile, and suitable for the environment and the process area suitable and in particular produced geometries of paramount importance. During the In operation, the high voltage insulator is exposed to the charged / uncharged particles suspended in the gas as well as any condensable vapor that may be present. For a long time, the accumulation of condensed material on the insulator affects its insulating property. Therefore, the insulator must be kept free from deposits of impurities and consequent rollovers. Furthermore, the cleaning intervals must be extended. In addition, the cost of manufacturing must be reduced while maintaining or even improving the insulating properties.

This concerns a system component in particular, namely the high-voltage bushing, which is installed in the wall between the environment and the process area and with which the necessary for the electrostatic cleaning device high voltage can be safely and long-term reliable. Thus, the object underlying the invention is also formulated.

The object is achieved by a high-voltage bushing with the features of claim 1 in principle. It consists of a dielectric, high-voltage resistant and kriechspurresistenten material such as glass or PTFE (P oly t etra f luor e Thylen) or glazed ceramics, on the one hand in his / n Aussgangssubstanz / s readily pourable (glass) or well ductile (ceramic ) On the other hand machinable (PTFE) is machinable.

The body of the high voltage feedthrough consists of two coaxially related geometric basic structures: a cylinder and a truncated cone. The cylinder merges into the truncated cone with a smaller end face on its one end face facing the process area. This end face of the cylinder and the attached truncated cone are fully exposed in the process area, the free end face of the cylinder in the environment. The outer radius of the cylinder is greater than that of this smaller end face of the truncated cone.

Through the body passes a central bore, through which the high voltage is passed through a close-fitting electrical conductor.

Geometrically on a coaxial circle within the cylinder at least two evenly distributed, axially parallel holes go through the cylinder. Through it air or gas is forced out of the environment during operation with a pump or a fan and the lateral surface of the truncated cone flows.

The high-voltage feedthrough sits with its lateral surface tight in the wall, which separates the environment from the process area.

With this basic structure, on the one hand, with the suitable insulator material, there is a reliable insulation of the high voltage passing through the central hole and tightly embedded conductor. On the other hand, at the part of the high voltage feedthrough exposed in the process area, the geometry is sufficient for distances to other potential electric fields than that High voltage potential available.

In the dependent claims 2 to 4 embodiments are described at the non-centrally located holes that affect the flow of the lateral surface of the truncated cone targeted and effective. Thus, according to claim 2, the clear width of such a bore over the length is not constant, in particular for air / gas outlet in the process environment towards larger, the truncated cone already at its approach to the cylinder, depending on the distributed around the circumference axial bores as completely as possible to inflate the scope.

The clear width is at the outlet of the bore at most so far that it does not enter the jacket wall of the truncated cone (claim 3). Equally effective is when these holes open in the ground in an axis concentric with the annular groove with at least the inner radius equal to the radius of the local front of the truncated cone.

According to claim 4, the bores are provided at their respective output with a lip, in particular when the opening angle of the truncated cone / cone is less than 20 °, which directs the air / gas flow through the inclination to the axis correspondingly strong toward her. Depending on the atmospheric conditions in the process area, it may be of decisive influence for the safe electrical operation, especially in the long term, that the approach area of the truncated cone on the cylinder flows safely and to avoid dead-end zones.

Claims 5 to 11 describe measures which reliably suppress creeping discharges along the surface of the truncated cone exposed in the process area during nominal operation

In order to relax the electric field conditions along the surface at the truncated cone are exposed according to claim 5 in the process area exposed edges.

The large, exposed in the process area face of the truncated cone (2) is in a kind of basic structure plan or funnel-shaped or conical in the process environment (claim 6).

If the spatial situation permits, the large end face of the truncated cone can extend to extend the creepage path coaxially and with at least the clear width of the electrical conductor to be performed by a predetermined length in the process environment (claim 7).

The large end face of the truncated cone can be provided for electrical strength with at least one groove concentric to the axis with u- or v-shaped cross-section (claim 8). For just this reason, this can also be extended to the coaxial extension (claim 9).

In the lateral surface of the truncated cone according to claim 10 at least one u- or v-shaped annular groove is recessed. For example, an axial creepage would then meander and is thus considerably longer. If the edges of the annular gap or round (claim 11) then deposits that can be electrically problematic or are easier to rinse off.

The recessed approach of the truncated cone on the cylinder is described in claim 12 and may be the isolationstechnisch effective solution for space saving reasons. For this purpose, the end of the cylinder exposed in the process area is recessed frustoconically. The truncated cone is now at the bottom of this depression under with the cylinder funnel-shaped gap formation. This gap remains constant or widens towards the process area. The holes in the cylinder about the axis open in this embodiment, the ring bottom of this funnel-shaped gap. This also avoids an inflow-related dead zone.

At high humidity in the process area, liquid precipitation or problematic steam condensation, the high-voltage problem is further mitigated if the outer edge of the projecting into the process area end of the cylinder around the circumference of an annular lip is attached, which forms a groove with the wall (claim 13). With horizontal installation of the implementation and thus vertical position of this groove forming a ring running down the wall liquid is passed around the implementation and can drain to deeper zones.

Technically more complex is provided with a heater high-voltage bushing, but can be an acceptable solution because of difficult process circumstances and, for example, space constraints. According to claim 14 is an electric heater in the form of built-in insulator material / retracted heating rods or a recessed fluid-flow channel into consideration.

The high voltage feedthrough has advantages:
Depending on the modification of the basic structure of cylinder and truncated cone, it can be selected according to the problematic environmental conditions in the process area. This ranges from a little risk of flashover environmental conditions or almost such and thus smooth coat of the conical part to high risk of flashover atmosphere in which then the conical part is provided with annular grooves.

It works in flue gas with solid particles and liquid droplets.

The high-voltage bushing is a single body, which is produced by casting or cutting from a solid body. Both manufacturing techniques can be automated and thus perform economically.

The conical part is flown through the paraxial bores with air or gas, natural or conditioned. Of course, the simplest case scenario is meant that the incoming air has ambient conditions, such as temperature or humidity, and is, for example, a fan in the process area. By conditioned, the technically more complex system case is meant that the air / gas is cooled or heated, for example above the dew point, and / or dried and more or less forced flows into the process area. This prolongs the operating time and prolongs the cleaning intervals considerably.

The invention will be explained in more detail with reference to the drawing. The drawing consists of the figures 1 to 9.

• Figur 1 den Schnitt durch die Achse der Hochspannungsdurchführung,
• Figur 2 die Hochspannungsdurchführung mit kleinem Öffnungswinkel des Konus,
• Figur 3 Mündung der achsparallelen Bohrungen in einer konzentrischen Ringnut,
• Figur 4 den Kegelstumpf mit freier Stirn und abgerundetem Rand,
• Figur 5 den Kegelstumpf mit freier, trichterförmiger Stirn,
• Figur 6 die Hochspannungsdurchführung mit u-und v-förmiger Ringnut,
• Figur 7 den Einbau der Hochspannungsdurchführung in die Trennwand,
• Figur 8 die in den Prozessbereich exponierte, kegelstumpfförmig vertiefte Stirn des Zylinders,
• Figur 9 die in den Prozessbereich exponierte, kegelstumpfförmig vertiefte Stirn des Zylinders mit umlaufender Rinne,
• Figur 10 die Hochspannungsdurchführung für 15 kV.

It shows:

• 1 shows the section through the axis of the high-voltage feedthrough,
• 2 shows the high-voltage bushing with a small opening angle of the cone,
• 3 mouth of the axis-parallel holes in a concentric annular groove,
• 4 shows the truncated cone with a free forehead and rounded edge,
• 5 shows the truncated cone with free, funnel-shaped forehead,
• FIG. 6 shows the high-voltage leadthrough with U-shaped and V-shaped annular groove,
• FIG. 7 shows the installation of the high-voltage bushing in the partition,
• FIG. 8 shows the frustum-shaped forehead of the cylinder exposed in the process area,
• FIG. 9 shows the truncated cone-shaped forehead of the cylinder with circumferential groove exposed in the process area,
• Figure 10, the high voltage bushing for 15 kV.

A suitable dielectric, high-voltage resistant and kriechspurresistentes material from which the body is the high-voltage bushing is PTFE (P oly t etra f luo r ethylene). The body consists, as can be seen in section from Figure 1, from the cylindrical part 1 and the conical, frusto-conical part 2. The conical part has the forehead with the smaller diameter D1 and goes with this forehead concentric in the cylinder with the diameter D3 over. The other, free end of the truncated cone with the larger diameter D2 is exposed in the process area. The axially parallel bores 4, here for example 16 are indicated by the cylinder 1 (see section AA below), through which air is flowed here, are concentric with the central bore 3 for passage of the electrical conductor for the high voltage. This tightly inserted in the bore 3 metallic conductor itself is not indicated.

Depending on the value of the creeping stress, the angle α, the half opening angle of the truncated cone, can vary, which also determines the geometric size of the bushing. Depending on the conditions of the technical process, the mass L1 (height of the truncated cone 2 or length of the cone 2) and the length L2 of the cylindrical part 1 vary as well as the diameters D1, D2 and D3. The high-voltage bushing is adapted geometrically from case to case to meet the requirements and optimally adapted to the plant conditions.

At a small opening angle, α ≤ 20 °, the outputs of the axis-parallel holes in the process area are each closed with the lip 5 according to magnification and plan view in Figure 2 on it. This helps to direct the airflow at the respective outlet to the foot of the truncated cone shell.

In order to avoid dead areas in the flow of the foot of the truncated cone, the axis-parallel holes open through the cylinder 1 in the concentric annular groove 6 in his exposed in the process area end (see Figure 3, section B-B). The inner radius of the annular groove 6 is at least equal to the there attaching end of the truncated cone 2. As a result, the air currents begin to unite and are distributed to a homogeneous hollow cylindrical air flow, which flows around the jacket of the truncated cone already in his foot.

In order to avoid the influence of the sharp edge on the high-voltage leadthrough during operation, the edge concentric with the axis at the free end of the truncated cone 2 is rounded off (see FIG. 4). To increase the arc distance, the free end of the truncated cone is funnel-shaped (see Figure 5). Although the peripheral edge of this forehead is sharply drawn here, it can also be rounded as in FIG. 4.

The creepage distance is longer for heavy process conditions than for moderate ones. An effective measure is the introduction of juxtaposed concentric annular grooves 8, 4 pieces of Figures 6a and 6b. To avoid the sharp edge, all edges of these annular grooves 8 are rounded. Figure 6a shows a U-shaped, Figure 6b V-shaped annular grooves 8, so annular grooves 8 with constant width H, or annular grooves 8mit outward expectant width H. If the High-voltage bushing is installed in a system with electrostatically enhanced wet scrubbers, the gap width H of the annular grooves 8 is greater than the present in the gas flow to be cleaned liquid droplets, or forming on the surface. In particular, the annular grooves 8 of Figure 6b reduce the accumulation of impurities on the mantle surface in the case of wet scrubbers, namely, the liquid that condenses flows on the side walls of the annular grooves 8 in the direction of the jacket wall of the truncated cone 2 and thereby ensures the self-cleaning effect of the high-voltage feedthrough.

The high voltage bushing is tightly installed / inserted with its cylindrical part 1 in the wall 9 between the environment and process area. From the installation structure forth that is shown schematically in Figure 7, 8 and 9 in exemplary variants. In all cases, however, the axis-parallel holes 4 are completely free, from the environmental side to the process area there is a free passage.

During the process, air is blown from the surroundings through the openings 4, which are axially parallel in the cylinder 1, onto the jacket surface of the truncated cone 2, thus preventing the deposition of solid or liquid particles from flue gas there. The air, also gas, cold or at ambient or warm, is supplied with a technical device, such as a fan or a pump (nowhere indicated in the drawing). The purpose of heating the air or gas above the dew point in the process area is to avoid liquid condensation on the process area exposed surface of the duct to prevent the tendency of reducing the high voltage strength of the electrical connection.

In the event that there is lower atmospheric pressure in the process area than in the environment, the air / gas is naturally sucked in from the environment via the bores 4 and blown onto the lateral surface 2.

This eliminates the need for a pump or fan that forces the air / gas through the holes.

If the high-voltage feedthrough projects into a process atmosphere with high humidity, liquid-water overflow could occur under critical process conditions and provoke or lead to electrical flashovers. In order to avoid flashovers, this can be achieved by modifying the concentric annular groove 6 according to FIG. 3 to the conical, concentric annular gap 10 in the end of the cylinder 1 according to FIG. 8 exposed to the process area. This annular gap 10 has here along its depth constant width, and only to the extent that retains the ground at the bottom by the holes 4 therethrough entering air / gas flow so much speed that herendurchgeblasen penetrating liquid or moisture, or prevents penetration at all becomes. This avoids flashovers under such difficult conditions. The peripheral edge of this annular groove 10 towards the process area is additionally rounded in order to avoid the sharp edge effect (see enlargement in FIG. 8).

If the condensation of water / liquid vapor on the inner wall in the process area be very intense, the resulting liquid flow on the inner wall can be redirected by a flange 11 around the exposed in the process area end of the cylinder 1, it forms with the cylinder and the inner wall a channel which deflects the liquid flowing in from the region of the high-voltage bushing (FIG. 9).

FIG. 10 shows by way of example the high-voltage feedthrough made of PTFE in its dimension for a maximum of 15 kV. Except for the coaxial hollow cylindrical extension into the process environment and the two coaxial annular groove in the lateral wall of the truncated cone, it has a structurally simplest design. Their over-all length is only 75 mm, their largest diameter only 48 mm. It is flush with its cylindrical part in a 30 mm thick wall can be used. The around the Scope equally distributed here 12 holes 3 ends with a steady transition at the base of the frustoconical part 2 of the high-voltage bushing, so that this approach is immediately blown around. For mechanical, in particular weight reasons, the centrally performed electrical conductor made of titanium. Tests for hours with water vapor saturated, condensing process atmosphere to be cleaned were carried out at highest rated voltage without electrical flashovers.

LIST OF REFERENCE NUMBERS

1

cylinder

2

truncated cone

3

drilling

4

drilling

5

lip

6

ring groove

7

Funnel-shaped forehead

8th

ring groove

9

wall

10

annular gap

11

flange

Claims (14)

1. Feedthrough for high electric voltage through a wall that separates a surrounding area from a process area, consisting of:

   - An element of dielectric, high-voltage-resistant, and creep-resistant material, which is made up of two coaxially arranged geometric structures: A cylinder (1) and a truncated cone (2), with the latter (2) being joined to the cylinder (1) with its smaller front surface, and this feedthrough being characterized by:

   - The outer radius of the cylinder (1) being larger than that of this smaller front surface and the truncated cone (2), together with that front surface of the cylinder (1) to which it is joined, being exposed completely in the process area,

   - a central borehole (3) passing the element for the feedthrough of the electric conductor,

   - at least two boreholes (4) passing the cylinder (1) and being arranged on a circle around the axis having a radius that is smaller than that of the cylinder in a uniformly distributed and axis-parallel manner, with both front openings of the boreholes being free and serving for blowing air or gas from the surroundings towards the lateral surface of the truncated cone (2), with the feedthrough being installed tightly into the wall (9) with the lateral surface of its cylinder (1) and the free front surface of the cylinder (1) being exposed to the surroundings.
2. High-voltage feedthrough according to Claim 1, characterized by the clear widths of the boreholes (4) being constant or varying locally over their lengths.
3. High-voltage feedthrough according to Claim 2, characterized by the boreholes (4) opening out into the process area with a clear width exceeding the diameter of the borehole (4), but not that of the onset of the truncated cone (2), or with the boreholes at the bottom opening out in an annular groove that is concentric to the axis and the inner radius of which at least equals the radius of the front surface of the truncated cone located there.
4. High-voltage feedthrough according to Claim 2, characterized by the boreholes (4), in their outlet ranges towards the process area, being equipped with a lip inclined towards the axis that partly closes the clear width and that inclines the direction of the air/gas flow towards the axis.
5. High-voltage feedthrough according to one of Claims 3 or 4, characterized by the large front surface of the truncated cone (2) that is exposed to the process area being rounded off at its circumference.
6. High-voltage feedthrough according to one of Claims 3 through 5, characterized by the large front surface of the truncated cone (2) that is exposed to the process area being plane or funnel-shaped or cone-shaped towards the surroundings.
7. High-voltage feedthrough according to Claim 6, characterized by the large front surface of the truncated cone (2) extending by a given length into the process surroundings in a coaxial manner and in the form of a hollow cylinder having at least the clear width of the electric conductor to be fed through.
8. High-voltage feedthrough according to Claim 6, characterized by the large front surface of the truncated cone (2) being provided with at least one groove of u- or v-shaped cross section that is concentric to the axis.
9. High-voltage feedthrough according to Claim 7, characterized by the large front surface of the truncated cone (2) and/or the outwards directed lateral surface of the hollow cylinder extension being provided with at least one groove of u- or v-shaped cross section that is concentric to the axis.
10. High-voltage feedthrough according to one of Claims 3 through 9, characterized by the lateral surface of the truncated cone (2) being provided with at least one u- or v-shaped annular groove.
11. High-voltage feedthrough according to Claim 10, characterized by the edges of the annular groove or annular grooves being round.
12. High-voltage feedthrough according to one of Claims 3 through 7, characterized by the front surface of the cylinder (1) that is exposed to the process area being depressed in the form of a truncated cone and the truncated cone (2) at the bottom of this depression forming a funnel-shaped gap with the cylinder (1), with this gap being constant or extending towards the process area and the boreholes (4) opening out into the annular bottom of this funnel-shaped gap.
13. High-voltage feedthrough according to Claim 12, characterized by an annular lip being installed around the circumference at the outer edge of the cylinder's front surface protruding into the process area, which forms a duct with the wall.
14. High-voltage feedthrough according to Claim 13, characterized by this high-voltage feedthrough being equipped with a heating system, such as integrated electric heating rods or a channel that can be passed by a fluid, by means of which this feedthrough can be thermostated.

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