High voltage direct current energy transmission (HVDCT) air-core inductor, and method for manufacturing the HVDCT air-core inductor

Abstract

A high voltage direct current energy transmission (HVDCT) air-core inductor includes at least one concentric winding layer having electric terminals are formed at its ends, and includes an electrostatic shield that has a layer of electrostatically dissipative material having a surface resistance ranging from 109 to 1014 ohm/square, wherein at least one end of the layer is provided with a collector electrode that extends essentially along the circumference of the end of the layer and that is to be connected to one of the terminals, and where the layer is designed as a spray coating on an outer surface of an exterior winding layer.

Claims

1. A high voltage direct current energy transmission (HVDCT) air-core inductor, comprising: at least one concentric winding layer having electrical terminals formed at ends thereof; an electrostatic screen, comprising an outermost layer made of electrostatically dissipative material which has a surface resistance in a region of 10.sup.9 to 10.sup.14 ohm/square, the layer being provided at least at one end with a collector electrode extending over a periphery of the layer for connection at one terminal of the electrical terminals; wherein the outermost layer is formed as a continuous circumferentially arranged coating disposed along a longitudinal axis of the air-core inductor, said coating having no abutment site or circumferential overlap on a lateral surface of an externally arranged winding layer.

2. The air-core inductor as claimed in claim 1, wherein the outermost layer has a layer thickness of between 80 μm and 120 μm.

3. The air-core inductor as claimed in claim 1, wherein the outermost layer comprises a polymer matrix with embedded filler materials comprising one of (i) an epoxy resin, (ii) a polyurethane, (iii) a silicone and (iv) a polyester.

4. The air-core inductor as claimed in claim 3, wherein the filler materials are formed by particles made from one of (i) metal oxide and (ii) silicon carbide.

5. The air-core inductor as claimed in claim 3, wherein the filler materials are formed by particles made from one of (i) doped metal oxide and (ii) doped silicon carbide.

6. The air-core inductor as claimed in claim 3, wherein the filler materials are formed by particles made from undoped silicon carbide and tin oxide doped with antimony.

7. The air-core inductor as claimed in claim 1, wherein the outermost layer is covered with a cover layer.

8. A method for producing a high voltage direct current energy transmission (HVDCT) air-core inductor, comprising: providing at least one concentric winding layer; and coating the at least one concentric winding layer on an outer lateral surface of the at least one concentric winding layer via a spray coating method in which an outermost layer made of a semiconducting paint which is formed from an electrostatically dissipative material having a surface resistance in a region from 10.sup.9 to 10.sup.14 ohm/square; wherein the outermost layer is formed as a continuous circumferentially arranged coating disposed along a longitudinal axis of the air-core inductor, said coating having no abutment site or circumferential overlap on the outer lateral surface of the at least one concentric winding layer.

9. The method as claimed in claim 8, wherein the outermost layer is formed via a low pressure (HVLP) spraying method.

10. The method as claimed in claim 8, wherein the outermost layer has a layer thickness of between 80 μm and 120 μm.

11. The method as claimed in claim 9, wherein a compressed air with an air pressure of 3-4 bar is utilized during the low pressure spraying method to atomize the material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For the further explanation of the invention, in the following part of the description, reference is made to drawings in which advantageous embodiments, details and developments of the invention are disclosed on the basis of a non-restrictive exemplary embodiment, in which:

(2) FIG. 1 is an HVDCT air-core inductor in accordance with the invention in a side view;

(3) FIG. 2 is a detail representation taken from FIG. 1 with a view of the upper end side of the HVDCT air-core inductor, such that a part of the winding arrangement is seen in a perspective illustration;

(4) FIG. 3 is the electrostatic screening of the HVDCT air-core inductor of FIG. 1 in a perspective view;

(5) FIG. 4 is a sectional representation through the winding arrangement of FIG. 2, wherein the layered structure on the outer winding layer is shown enlarged; and

(6) FIG. 5 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(7) FIG. 1 shows an HVDCT air-core inductor 1 such as those typically used for high voltage direct current transmission (HVDCT) as smoothing reactors. The operation of such an HVDCT air-core inductor 1 typically occurs outside, and it is therefore also exposed to the prevailing outdoor weather conditions. The drawing in FIG. 1 shows the air-core inductor 1 in a vertically arranged position that is supported by insulators 13 and a steel construction 15 on a base or on the ground 15.

(8) During operation, the air-core inductor 1 is at a high electrical potential relative to earth, for example, 500-800 kV and carries a current of up to 4000 A. The voltage drop across the air-core inductor 1, i.e., between the electrical connections 11 and 12 is lower in comparison thereto and corresponds approximately to the residual ripple of the voltage to be smoothed, typically approximately 100 V up to a few kV. Only in the event of transient events, such as switching processes or a lightning strike, can there be a significant voltage drop across the air-core inductor 1 itself, which the insulation of its windings must be able to withstand.

(9) As shown in FIG. 2, the air-core inductor 1 comprises an electrical winding arrangement with a coil conductor 10 wound helically about the axis 18. The individual layers 2, 3, 4 and 4′ of the conductor 10 are held at a radial spacing by a spider 7, 8. Provided at each end, on each spider 7, 8, is a screening cap 16 so that the action of points effect is reduced.

(10) Due to the high electrical potential of the air-core inductor 1, a strong electrostatic field forms between the exterior of the air-core inductor 1 and the ground 15. This potential can lead to charge carriers from the surroundings 9 forming on the lateral surface of the choke 1 with the consequences, as set out in the introduction, of an electrostatic contamination or the formation of “black spots”. In order to counteract this “black spot phenomenon”, the air-core inductor 1 is provided with an electrostatic screening. This electrostatic screening has conventionally been realized with a self-adhesive semiconducting foil which, however, is now replaced in accordance with the invention with a layer 22 that is sprayed directly onto the outer winding layer and is described in detail below.

(11) FIG. 2 shows a detailed view taken from FIG. 1, looking toward the upper end side of the HVDCT air-core inductor, so that a part of the winding arrangement is visible in a spatial representation. The semiconducting layer 22 is sprayed onto the outer lateral surface 21 in the form of a paint coating (see also FIG. 4). It is evident from FIG. 2 that the individual winding layers 2, 3, 4, 4′ of the air-core inductor 1 are separated from one another by air gaps 6. The spider 7 holds these winding layers 2, 3, 4, 4′ at a spacing. Spacers 5 define the spacing of the individual winding layers 2, 3, 4, 4′ from one another. At the end side, the spiders 7 are provided with a screening cap 16.

(12) FIG. 3 shows the electrostatic screening 17 of the HVDCT air-core inductor separately therefrom. The electrostatic screening 17 consists substantially of the hollow cylindrical layer 22 and at the end side, collector electrodes 19, 20 encircling the circumference. The layer 22 was/is manufactured by spraying. Using a spray pistol, a semiconducting polyurethane paint was/is atomized in a spray pistol and sprayed at an air pressure of 3-4 bar externally onto the lateral surface of the winding layer 4′. During the spraying process, the spacing between the spray pistol axis 18 and the coil 1 was/is kept constant. In this way, with an automated spraying apparatus, an electrically semiconducting coating 22 with an even layer thickness of 80-120 μm can be created on the outer circumferential surface of the winding layer 4′.

(13) The coating 22 has collector electrodes 19, 20 on the end side, each extending around the circumference. These collector electrodes 19, 20 are conductively connected to the electrical terminals 11, 12 of the air-core inductor 1.

(14) The semiconducting layer 22 comprises a polymer substance that contains a filler material, in the form of electric semiconducting solid particles or pigments that are embedded in the polymer material. The electric conductivity of the particles can be varied within broad limits by doping their material. Through doping or bringing together particles and matrix material, a resistive coating 22 with a surface resistance in a range between 10.sup.9 and 10.sup.14 ohm/square can be made. The layer 22 acts, as mentioned, as electrostatic screening. With the electrically semiconducting layer 22, it is achieved that the charge carriers impinging upon the air-core inductor 1 from the exterior 9 pass “dissipatively” by the shortest route to the nearest collector electrode 19 or 20 and from there are conducted away to one of the terminals 11 or 12. By conducting away these charge carriers, the risk of the formation of a conductive structure on the exterior of the air gap choke 2 and therefore of a surface leakage current is lessened. The disadvantages mentioned in the introduction can thus be largely prevented.

(15) FIG. 4 shows a sectional representation through the winding arrangement of FIG. 2, where the layered structure on the outer winding layer 4′ is shown enlarged. The lateral surface 21 of the outer winding layer 4′ is coated with the semiconducting spray coating 22. The spray coating 22 contains a filler material. In FIG. 4, particles of the filler material are identified with the reference character 23. The filler material is composed of particles 23 of different materials. In the present exemplary embodiment, the composition of the filler material consists of a mixture of particles 23 of different materials formed from undoped silicon carbide and with antimony-doped tin oxide. Toward the exterior environment 9, the spray coating 22 is covered with a protective or covering layer 24 which consists of an RTV silicone.

(16) FIG. 5 is a flowchart of a method for producing a high voltage direct current energy transmission (HVDCT) air-core inductor. The method comprises providing at least one concentric winding layer 2, 3, 4, as indicated in step 510.

(17) Next, the at least one concentric winding layer is coated on an outer lateral surface 21 via a spray coating method in which a layer 22 made of a semiconducting paint that is formed from an electrostatically dissipative material having a surface resistance in a region from 109 to 1014 ohm/square, as indicated in step 520.

(18) Although the invention has been described and explained in detail on the basis of the two exemplary embodiments set out above, the invention is not restricted to these examples. Other embodiments and variations are conceivable without departing from the underlying concept of the invention.

(19) Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.