CONDENSER CORE, BUSHING, HIGH VOLTAGE APPLICATION AND METHOD OF PRODUCING BUSHING

Abstract

A condenser core for being positioned around a high voltage main electrical conductor, the condenser core including an electrically insulating body; a longitudinal through hole for accommodating the main electrical conductor; a plurality of electrically conductive foils encircling the through hole and being surrounded by the body such that each foil is insulated from any other of the foils; a potential electrical conductor for establishing an electrical connection between one of the foils and the main electrical conductor when the main electrical conductor is accommodated in the through hole; and a fastening device configured to mechanically connect the potential electrical conductor to the main electrical conductor when the main electrical conductor is accommodated in the through hole. A bushing, a high voltage application and a method of producing a bushing are also provided.

Claims

1. A condenser core (24) for being positioned around a high voltage main electrical conductor (18), the condenser core (24) comprising: an electrically insulating body (26); a longitudinal through hole (28) for accommodating the main electrical conductor (18); a plurality of electrically conductive foils (32) encircling the through hole (28) and being surrounded by the body (26) such that each foil (32) is insulated from any other of the foils (32); and a potential electrical conductor (36) for establishing an electrical connection between one of the foils (32) and the main electrical conductor (18) when the main electrical conductor (18) is accommodated in the through hole (28); characterized in that the condenser core (24) further comprises a fastening device (38) configured to mechanically connect the potential electrical conductor (36) to the main electrical conductor (18) when the main electrical conductor (18) is accommodated in the through hole (28).

2. The condenser core (24) according to claim 1, wherein the fastening device (38) comprises a fastener (40) constituted by a screw.

3. The condenser core (24) according to claim 1 or 2, wherein the fastening device (38) comprises a fastener (40) and a washer (42) for being pressed by the fastener (40) such that the washer (42) presses the potential electrical conductor (36) against the main electrical conductor (18).

4. The condenser core (24) according to claim 3, wherein the washer (42) comprises a laterally outer rounded edge (56).

5. The condenser core (24) according to claim 3 or 4, wherein the washer (42) is countersunk.

6. The condenser core (24) according to any of the preceding claims, further comprising an electrically insulating compressive layer (34), wherein the body (26) is wound onto and around the compressive layer (34) and wherein the potential electrical conductor (36) passes through the compressive layer (34).

7. The condenser core (24) according to any of the preceding claims, wherein the body (26) comprises resin impregnated paper or resin impregnated synthetics.

8. A bushing (12) for a high voltage application (10), the bushing (12) to comprising a condenser core (24) according to any of the preceding claims and a main electrical conductor (18), wherein the potential electrical conductor (36) is electrically connected between one of the foils (32) and the main electrical conductor (18), and wherein the potential electrical conductor (36) is mechanically connected to the main electrical conductor (18) by means of the fastening device (38).

9. The bushing (12) according to claim 8, wherein the body (26) is shrink-fitted around the main electrical conductor (18).

10. A high voltage application (10) comprising a condenser core (24) according to any of claims 1 to 7 or a bushing (12) according to claim 8 or 9.

11. A method of producing a bushing (12) for a high voltage application (10), the method comprising: providing a main electrical conductor (18) in a through hole (28) of an electrically insulating body (26); and establishing an electrical connection between an electrically conductive foil (32) and the main electrical conductor (18) by means of a potential electrical conductor (36); characterized in that the method further comprises: mechanically connecting the potential electrical conductor (36) to the main electrical conductor (18); arranging the foil (32) to encircle the through hole (28); winding at least one sheet of an insulating material over the foil (32); and impregnating the body (26) to form a condenser core (24) wherein the mechanical connection comprises connecting the potential electrical conductor (36) to the main electrical conductor (18) by means of a fastening device (38).

12. The method according to claim ii, further comprising cutting through an inner portion (53) of the body (26) to the main electrical conductor (18), opening the inner portion (53) of the body (26), electrically and mechanically connecting the potential electrical conductor (16) to the main electrical conductor (18), and closing the inner portion (53) of the body (26) over the connection between the potential electrical conductor (16) and the main electrical conductor (18).

13. The method according to claim 11 or 12, further comprising electrically connecting the potential electrical conductor (36) to the main electrical conductor (18) by means of electrically conductive glue (54) prior to mechanically connecting the potential electrical conductor (36) to the main electrical conductor (18).

14. The method according to any of claims 11 to 13, further comprising pressing the potential electrical conductor (36) against the main electrical conductor (18) by means of a washer (42).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:

[0045] FIG. 1: schematically represents a high voltage application comprising a bushing;

[0046] FIG. 2: schematically represents the bushing in FIG. 1 comprising a condenser core and a main electrical conductor; and

[0047] FIG. 3: schematically represents a partial enlarged view of the bushing in FIG. 2.

DETAILED DESCRIPTION

[0048] In the following, a condenser core for being positioned around a high voltage main electrical conductor, a bushing for a high voltage application, which bushing comprises a condenser core, a high voltage application comprising a condenser core, and a method of producing a bushing for a high voltage application, will be described. The same reference numerals will be used to denote the same or similar structural features.

[0049] FIG. 1 schematically represents a high voltage application 10 comprising a bushing 12 according to the present disclosure. The high voltage application 10 is here exemplified as a transformer 14 arranged in a tank 16. The bushing 12 is for conducting an electrical current in a main electrical conductor 18 through a wall 20 of the tank 16 to the transformer 14.

[0050] The tank 16 is at least partly filled with an electrically insulating fluid 22, in this example a dielectric oil, such as a mineral oil or an ester-based oil. The bushing 12 extends from the insulating fluid 22 to the outside of the tank 16. In this example, the high voltage application 10 is surrounded by air. The bushing 12 thus constitutes an oil-to-air bushing.

[0051] The transformer 14 may be a high voltage power transformer, e.g. having a rating or operating voltage of at least 1 kV, such as at least 10 kV, such as at least 35 kV, e.g. within the range of 50-200 kV. Thus, a high voltage current is passed from the transformer 14 through the bushing 12 via the main electrical conductor 18 passing through the through hole of the bushing 12. The bushing 12 may, by means of its associated main electrical conductor 18, conduct current from e.g. a winding of the transformer 14, through the wall 20 of the tank 16 and to e.g. an air-borne line of a power distribution network. The bushing 12 insulates the current from the wall 20, which constitutes a grounded plane, and any other external structures.

[0052] FIG. 2 schematically represents the bushing 12 in FIG. 1. The bushing 12 comprises the main electrical conductor 18 and a condenser core 24 positioned around the main electrical conductor 18.

[0053] The condenser core 24 comprises an electrically insulating body 26 and a longitudinal through hole 28 through which the main electrical conductor 18 passes. The body 26 includes insulation material, for example combinations of oil and paper, resin and paper, or resin and synthetics. FIG. 2 further shows a longitudinal axis 30 of the main electrical conductor 18.

[0054] The condenser core 24 further comprises a plurality of electrically conductive foils 32a, 32b, 32c coaxially encircling the through hole 28 and the main electrical conductor 18 (each foil 32a, 32b, 32c is also referred to with reference numeral “32”). Any or all of the foils 32 may be of any suitable conductive material, e.g. aluminium or copper. Each foil 32 is surrounded by the body 26 such that each foil 32 is insulated from any of the other foils 32. Although the condenser core 24 in FIG. 2 comprises three foils 32, the condenser core 24 may comprise only two foils 32, or more than three foils 32.

[0055] The condenser core 24 of this example further comprises an optional electrically insulating compressive layer 34. The compressive layer 34 may for example comprise cork rubber and Teflon ®. The body 26 is wound onto and around the compressive layer 34. As shown in FIG. 2, the innermost foil 32a is in this example spaced from the compressive layer 34 by means of an inner part of the body 26.

[0056] The condenser core 24 further comprises two potential electrical conductors 36. The condenser core 24 may however comprise only one, or more than two potential electrical conductors 36. Each potential electrical conductor 36 is arranged to establish an electrical connection between the innermost foil 32a and the main electrical conductor 18. Each potential electrical conductor 36 passes through the compressive layer 34 and through a part of the body 26 radially inside of the foil 32a (with respect to the longitudinal axis 3o of the main electrical conductor 18). In this example, the potential electrical conductors 36 are constituted by braided copper wires.

[0057] As shown in FIG. 2, the condenser core 24 further comprises a fastening device 38. The fastening device 38 is configured to mechanically connect each potential electrical conductor 36 to the main electrical conductor 18 to secure an electrical connection therebetween.

[0058] FIG. 3 schematically represents a partial enlarged view of the bushing 12 in FIG. 2. In the example in FIG. 3, the fastening device 38 comprises a fastener 4o, here constituted by a self-tapping screw, and a washer 42. FIG. 3 also shows a longitudinal axis 44 of the fastener 40. The fastener 40 is engaged in a hole 46 in the main electrical conductor 18. The washer 42 and a head 48 of the fastener 40 are seated in an aperture 50 of the main electrical conductor 18. The aperture 50 has rounded edges in order to reduce the local electric field enhancement.

[0059] One example of a method of producing the bushing 12 according to the present disclosure will now be described. The optional electrically insulating compressive layer 34 is wound around the main electrical conductor 18. One or more sheets of an insulating material, such as paper, are then wound around the compressive layer 34. A hole 52 is cut for each potential electrical conductor 36. As shown in FIG. 3, each hole 52 is cut through the compressive layer 34 and through an inner portion 53 of the body 26 inside of the foil 32a. The holes 52 form part of a slit through the compressive layer 34 and the inner portion 53 of the body 26. The slit may be generally U-shaped, in a circumferential direction of the compressive layer 34, such that a flap of the compressive layer 34 and the inner portion 53 of the body 26 can be folded open. The hole 46 and/or the aperture 50 in the main electrical conductor 18 may be produced after having folded open the flap, or prior to winding the compressive layer 34 around the main electrical conductor 18.

[0060] The contact surfaces of the aperture 50 in the main electrical conductor 18 and of the potential electrical conductor 36 may be cleaned, e.g. with acetone, wiped dry, and polished to remove oxides. One end of each potential electrical conductor 36 is glued onto the main electrical conductor 18 by means of electrically conductive glue 54 such that each potential electrical conductor 36 is electrically connected to the main electrical conductor 18. Each potential electrical conductor 36 is glued on both sides. Electrically conductive glue 54 is also applied to the contact surface in the aperture 50 of the main electrical conductor 18. The electrically conductive glue 54 may be to applied in thin layers.

[0061] The washer 42 is then placed on top of the ends of the potential electrical conductors 36 and the fastener 40 is inserted through the washer 42 and fastened in the hole 46 of the main electrical conductor 18. The fastening device 38 is thereby used to mechanically connect each potential electrical conductor 36 to the main electrical conductor 18. In this example, the fastener 40 is a screw that is screwed into the hole 46 such that the head 48 of the screw presses the washer 42. The washer 42 in turn presses the electrically conductive glue 54 and the potential electrical conductors 36 against the main electrical conductor 18. When tightening the fastener 40, the washer 42 tightly presses the potential electrical conductor 36 and the electrically conductive glue 54 against the main electrical conductor 18.

[0062] In FIG. 3, the outer surface of the head 48 of the fastener 40 and the outer surface of the washer 42 extend radially outside (with respect to the longitudinal axis 30) of the outer surface of the main electrical conductor 18. A small play may exist between the outer surfaces of the head 48 and the washer 42 and the compressive layer 34 prior to shrinkage of the body 26. The play may for example be approximately 0.5 mm. The washer 42 further comprises a laterally outer rounded edge 56 which reduces the local electric field enhancement.

[0063] The potential electrical conductors 36 are then lead up through the holes 52.

[0064] The flap is then folded back and the potential electrical conductors 36 are glued to the foil 32a. The foil 32a is then folded over the flap. Each potential electrical conductor 36 is connected to the foil 32a by means of electrically conductive glue 54. The remaining layers of insulating material and further foils 32b, 32c may then be wound over the foil 32a.

[0065] The body 26 is then impregnated with a resin, such as epoxy, followed by curing of the resin to form the condenser core 24. Due to the shrinkage of the body 26 during curing, the end of each potential electrical conductor 36 (the upper ends in FIG. 3) is self-locked to the foil 32a. Furthermore, the shrinkage of the body 26 causes the fastening device 38 (e.g. the fastener 40 and/or the washer 42 thereof) to be pressed against the main electrical conductor 18 to secure the electrical contact between the potential electrical conductor 36 and the main electrical conductor 18.

[0066] Each potential electrical conductor 36 may be formed with an excess bow or slack, for example of 10 mm. In this way, tension in the potential electrical conductor 36, due to the shrinking of the body 26 when cured, can be reduced or avoided.

[0067] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed.