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EP-4062437-B1 - CONDENSER CORE WITH CONDUCTIVE SHEETS EARTHED IN A CABLE FEEDTHROUGH OR TERMINATION

EP4062437B1EP 4062437 B1EP4062437 B1EP 4062437B1EP-4062437-B1

Inventors

  • KANJE-NORDBERG, Jens
  • SJÖBERG, Peter
  • JOHANSSON, KENNETH

Dates

Publication Date
20260506
Application Date
20201027

Claims (12)

  1. A condenser core (3) configured for surrounding an electrical conductor (2), the condenser core comprising an insulation material (4) and a plurality of electrically conducting capacitive layers (5) for modifying electrical fields formed by a current flowing in the electrical conductor; wherein at least one of the electrically conducting capacitive layers (5) comprises a first foil (5a) and a second foil (5b); wherein each of the first and second foils (5a, 5b) of an outermost capacitive layer is individually connected with a respective grounding arrangement (10a, 10b) for grounding the foils.
  2. The condenser core of claim 1, wherein the respective grounding arrangement (10a, 10b) comprises a measuring tap.
  3. The condenser core of claim 1, wherein the first and second foils (5a, 5b) are overlapping by an overlap (o) at a first edge (7a) of the first foil and a second edge (7b) of the second foil.
  4. The condenser of claim 3, wherein the first and second foils (5a, 5b) are of equal length (l).
  5. The condenser core of claim 4, wherein the first and second foils (5a, 5b) are arranged such that the overlap (o) is at respective longitudinal edges (7a, 7b) of the foils and has a length corresponding to the length (l) of the first and second foils.
  6. The condenser core of claim 5, wherein a length (L) of a sheet (20) formed by the overlapping first and second foils of the capacitive layer (5) is greater than the length (l) of the first and second foils.
  7. The condenser core of any preceding claim 3-6, wherein the overlap (o) comprises a joint (6) via which the first and second foils (5a, 5b) are electrically connected.
  8. The condenser core of claim 7, wherein the joint comprises a conductive adhesive (30).
  9. The condenser core according to any of claims 3-8, wherein the first and second foils (5a, 5b) are each individually grounded on both sides of the overlap.
  10. An electrical device (1) comprising the condenser core of any preceding claim.
  11. The electrical device of claim 10, wherein the electrical device comprises any one of a bushing and a cable termination.
  12. The electrical device of any claim 10-11, further comprising the electrical conductor (2) passing through the condenser core (3).

Description

TECHNICAL FIELD The present disclosure relates to a condenser core, e.g. of a bushing or cable termination, having electrically conductive foils for modifying electrical fields formed by a current flowing in an electrical conductor passing through the condenser core. BACKGROUND A condenser core is used for insulating an electrical conductor and modifying the electrical field formed around the electrical conductor when an electrical current is flowing there through. The condenser core is made up of an electrically insulating material interleaved with capacitive layers, e.g. of aluminium foil. Condenser cores are e.g. used in bushings and cable terminations. There is a move towards using larger diameter condenser cores. Due to the increase in diameter, the outermost capacitive layers may need to be created from joined foils, e.g. aluminium foils, since there are no aluminium foils available of the needed dimensions. This may cause problems of heating, difference in potential in the different foils of the capacitive layer and other issues during operation. US3793475, US3484679, US3600502, WO80/00762 and US3875327 disclose conventional capacitive layers arranged around (high-voltage) conductors. The conductive layers may be grounded or connected to a potential. CN104089569 relates to a multifunctional transformer signal sensor based on capacitive coupling. The multifunctional transformer signal sensor comprises a circle of thin metal band, a socket and a fixing clamp, wherein the socket is used for being connected with an external cable, the external cable is used for transmitting scanning signals, the socket is electrically connected with the thin metal band, the external cable is electrically connected with the thin metal band through the socket, and the fixing clamp is used for fixing the thin metal band and the socket. In the measurement process, the sensor is wrapped in the position, close to a flange, of a tap on the outer surface of a transformer bushing. The multifunctional transformer signal sensor based on the capacitive coupling principle can be conveniently installed on existing coil type devices such as operation transformers to be used for detecting deformation of winding devices through an on-line frequency response CN200968968 relates to a can-type capacitance-voltage mutual inductor that is composed of an airproof can, a high voltage electrode, a medium voltage electrode, an outgoing wire sleeve and electromagnetic cells and is insulated with SF6 gas. The airproof can, the high voltage electrode and the medium voltage electrode are in coaxial column structure. A high voltage arm capacitance C1 is formed between the high voltage electrode and the medium voltage electrode, a medium voltage arm capacitance C2 is formed between the medium voltage electrode and a cylinder of the airproof can; the high voltage arm capacitance C1 and the medium arm capacitance C2 form a capacitance voltage divider. SUMMARY It is an objective of the present invention to provide a condenser core having a capacitive layer made up from two overlapping foils with reduced risk of potential difference between the foils and/or heat forming at a joint of the overlap. According to an aspect of the present invention, there is provided a condenser core of claim 1 configured for surrounding an electrical conductor. The condenser core comprises an insulation material and a plurality of electrically conducting capacitive layers for modifying electrical fields formed by a current flowing in the electrical conductor. At least one of the electrically conducting capacitive layers comprises a first foil and a second foil. Each of the first and second foils of an outermost capacitive layer is connected with a grounding arrangement for grounding the foils. According to another aspect of the present invention, there is provided an electrical device of claim 10. In accordance with the present invention, each of the foils of the outermost electrically conducting capacitive layer is grounded by means of respective grounding arrangements (also called measuring taps since the grounding conductor thereof may also be used for performing measurements, e.g. of capacitance). Thus, the different foils are individually grounded (i.e. on both sides of the overlap) and not dependent on a good electrical connection between the foils at their overlap for ensuring equal electrical potential and low resistive heat formation at the overlap e.g. at transient events such as a lightning strike. A capacitive layer is herein defined as an electrically conducting layer comprising one or more foils arranged at a substantially constant radius around a longitudinal axis of the condenser core. Two foils located at different radii from the longitudinal axis of the condenser core therefore belong to different capacitive layers. Generally, different capacitive layers are not galvanically connected. An outer capacitive layer consisting of two or more foils may be joined to