Patent Publication Number: US-8969729-B2

Title: High-voltage bushing with conductive inserts for DC voltage and method for producing the bushing

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2012 204 052.8, filed Mar. 15, 2012; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a high-voltage bushing with conductive inserts for a DC voltage with a bushing body surrounding a high-voltage conductor and containing paper insulation. The bushing body tapers conically, at least at one end region thereof, from a ground-potential-side location to a high-voltage-side end and is surrounded by an insulation barrier. 
     A high-voltage bushing of this type is known from the book entitled “Hochspannungstechnik” (High-Voltage Engineering) by A. Küchler, 2 nd  edition, 2005, pages 100 and 101. In particular, the lower illustration from FIG. 2.4-28 shows a high-voltage bushing of this type, in which the insulation barrier consists of individual pressboard barriers. In conjunction with oil which is conductive compared to the conductivity of the bushing body and the pressboard barriers, a high-voltage bushing which has a relatively good potential distribution is obtained. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a high-voltage bushing with conductive inserts for a DC voltage and a method for producing the bushing which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which is distinguished by an even better potential distribution. 
     With the foregoing and other objects in view there is provided, in accordance with the invention a high-voltage bushing for a DC voltage. The bushing contains conductive inserts, a high-voltage conductor, an insulation barrier, and a bushing body surrounding the high-voltage conductor and contains a paper insulation. The bushing body tapers conically, at least at one end region thereof, from a ground-potential-side location to a high-voltage-side end and is surrounded by the insulation barrier. The bushing body has an outer side coated at least in a region of the at least one end region with a coating forming a coating layer. The coating layer has a greater electrical conductivity than the bushing body. 
     In order to solve this problem in the case of a high-voltage bushing of the type mentioned at the outset, according to the invention the outside of the bushing body is coated at least in the region of the at least one end region with a coating to form a coating layer, which has a greater electrical conductivity than the bushing body. 
     A significant advantage of the high-voltage bushing of the invention consists in that, even at exposed locations in the interior of the bushing, the applied coating layer has the effect that peak loads caused by concentrations of the electrical field do not occur. Furthermore, a material saving is made because the high-voltage bushing of the invention can have smaller dimensions for a certain voltage loading than the known high-voltage bushing can at the same voltage loading. In this case, these advantages are achievable in an inexpensive way by the coating layer simply being applied to the outside of the bushing body. 
     In the case of the high-voltage bushing of the invention, the coating layer may have no connection to high and ground potential. However, it is considered to be particularly advantageous for the coating layer to be connected to the high voltage at the high-voltage-side end of the at least one end region of the bushing body and to be connected to ground potential at the ground-potential-side location. In this case, a particularly good and regular potential distribution over the entire high-voltage bushing results. 
     Furthermore, with regard to a regular potential distribution, it has proven to be particularly advantageous for the electrical conductivity of the coating layer to be approximately two orders of magnitude greater than that of the bushing body. 
     As is known per se, for the high-voltage bushing of the invention, the paper insulation of the bushing body is likewise a paper insulation impregnated with epoxy resin, which is advantageously distinguished by a high insulation resistance. 
     The invention also relates to a method for producing a high-voltage bushing with conductive inserts for DC voltage with a bushing body surrounding a high-voltage conductor and containing paper insulation, which bushing body tapers conically, at least at one end region thereof, from a ground-potential-side location to a high-voltage-side end and is surrounded by an insulation barrier; a method of this type can be taken from the aforesaid book. 
     It is an object of the invention to specify a method for producing a high-voltage bushing, with which a high-voltage bushing having a particularly good potential distribution can be produced in a simple manner. 
     In order to achieve this object in the case of a method of the type mentioned above, according to the invention the outside of the bushing body is coated at least in the region of the at least one end region with a coating to form a coating layer, which has a greater electrical conductivity than the bushing body. 
     A particular advantage of the method of the invention consists in that, simply by applying a coating layer to the outside of the bushing body, it is possible to produce a high-voltage bushing which has the advantages specified above for high-voltage bushings. 
     For the reasons already mentioned above, it is advantageous in the case of the method of the invention for the coating layer to be connected to high voltage at the high-voltage-side end of the at least one end region of the bushing body and to be connected to ground potential at the ground-potential-side location. 
     It is also advantageous for a coating having a conductivity which is approximately two orders of magnitude greater than that of the bushing body to be used as the coating layer. 
     It is likewise advantageous for a paper insulation impregnated with epoxy resin to be used as the paper insulation of the bushing body. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a high-voltage bushing with conductive inserts for a DC voltage and a method for producing the bushing, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, side view of an exemplary embodiment of a high-voltage bushing for a transformer according to the invention; 
         FIG. 2  is a diagrammatic, side view of a detail of the exemplary embodiment of  FIG. 1 ; 
         FIG. 3  is a diagrammatic, sectional view of an excerpt of a section through a further exemplary embodiment of the high-voltage bushing of the invention to illustrate the basic mode of operation of the coating layer on the bushing body; and 
         FIG. 4  is a diagrammatic, sectional view of an identical configuration to that shown in  FIG. 3 , only without a coating layer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a high-voltage bushing  1  which provides an electrical transition from a non-illustrated transformer to an outdoor high-voltage connection  2 . As can also be seen in  FIGS. 1 and 2 , the high-voltage bushing  1  has a bushing body  3 , which extends from the high-voltage or transformer-side end  4  thereof (the lower end in  FIG. 1 ) through a support flange  5  to the outdoor high-voltage connection  2 . On the support flange  5  is an annular housing part  6  and on the housing part  6  is an outdoor-side part  7  of the high-voltage bushing  1  with screens  8 . 
     As is also shown in  FIGS. 1 and 2 , the outside of the bushing body  3  is provided with a coating layer  9 , which has a greater electrical conductivity than the bushing body  3 , for example a conductivity which is two orders of magnitude greater. The bushing body  3  is wound from paper, conductive inserts  10  being wound in during the winding in a known manner to form a capacitor-controlled high-voltage bushing  1 . The bushing body  3  formed in this manner is impregnated with casting resin. A high-voltage conductor  11  runs inside the bushing body  3 . 
     As is evident from  FIG. 1  in particular, the bushing body  3  has an end region  12 , which tapers conically from a location  13  on the ground-potential side to the high-voltage-side end  4  with an electrode  15 . The coating layer  9  is galvanically connected to the electrode  15 ; on the other side, there is also a connection between the coating layer  9  and the support flange  5  or the annular housing part  6 , which are at ground potential. 
       FIG. 2  indicates that both the electrode  15  and the bushing body  3  are surrounded on the outside by an insulating oil  16  of the transformer. In this case there is also an insulation barrier (not shown in  FIGS. 1 and 2 ) in the insulating oil. 
       FIG. 3  shows a high-voltage bushing  20  with a high-voltage conductor  21 , which carries a bushing body  22  of wound paper with conductive inserts  23 . A high-voltage-side end  24  of the bushing body  22  is opposite an electrode  25 , which is connected to the high-voltage conductor  21  in a manner which is not shown and is provided with a coating layer  27  on an outer surface  26  thereof. The coating layer  27  has a conductivity which is approximately two orders of magnitude greater than that of the bushing body  22 . The high-voltage bushing  20  is closed to the outside by a housing  28 . 
     Individual barrier elements  29  of an insulation barrier  30  are partially applied in close contact and partially arranged cylindrically around the high-voltage conductor  21 . As a result of this, together with the coating layer  27 , a very regular potential distribution is created, as indicated by the marked field lines  31 . 
     In comparison with this,  FIG. 4  shows how the potential distribution appears when the coating layer  27  is not present on the same arrangement as in  FIG. 3 .