DE-102024132857-A1 - Sensor for detecting partial discharges in cables

Abstract

A sensor for detecting partial discharge in a cable, wherein the sensor comprises a flux concentrator made of highly permeable material, which is wrapped with a measuring coil. The flux concentrator has two legs that span a surface open on one side. The spanned surface is designed such that it can accommodate at least one section of the cross-sectional area of the cable, wherein the section of the cross-sectional area of the cable comprises a conductor of the cable.

Inventors

• Bastian Zimmer
• Frank Jenau

Assignees

• Dipl. -Ing. H. Horstmann GmbH

Dates

Publication Date

20260513

Application Date

20241111

Claims (6)

1. Sensor (1) for detecting a partial discharge in a cable (2), wherein the sensor (1) has a flux concentrator (3) made of magnetically highly permeable material, which is wound with at least one winding of a coil (4), characterized in that the flux concentrator (3) has a first and second leg (3a, 3b) which span an area (3d), wherein the spanned area (3d) is designed such that it can accommodate at least a section of the cross-sectional area of the cable (2), wherein the section of the cross-sectional area of the cable has a conductor of the cable (2), and wherein the distance between the ends of the two legs (3a, 3b) is greater than a diameter of the cable (2).
2. Sensor (1) after Claim 1 , wherein the first and second limbs (3a, 3b) of the flow concentrator (3) are arranged in a U or V shape or in a circular segment shape.
3. Sensor (1) after Claim 1 , wherein the flow concentrator (3) has only the first and second limbs (3a, 3b).
4. Sensor (1) according to one of the preceding claims, wherein the cable (2) has a cable diameter and the distance between the ends of the legs (3a, 3b) is less than 1.25 times the cable diameter, preferably less than 1.1 times.
5. Sensor (1) according to one of the preceding claims, wherein the coil (4) comprises fewer than 20 windings, preferably fewer than 15 and particularly preferably 10 or fewer windings.
6. Sensor (1) according to one of the preceding claims, wherein the flow concentrator (3) is formed in one piece.

Description

The invention relates to a sensor for detecting a partial discharge in a cable, in particular in a cable for voltages greater than 1000 volts. Partial discharges in faulty high-voltage insulation are small, spatially confined electrical discharges that occur in small cavities in the insulation, such as voids, when a critical electric field strength is exceeded. These discharges induce a short, high-frequency current pulse in the conductor that carries the voltage for the electric field. With prolonged exposure or repeated occurrences in such a cavity, the discharges can damage the insulation and subsequently lead to a complete breakdown, causing the insulation to fail and high voltages and currents to leak into an adjacent electrical conductor. Therefore, the continuous testing of insulation for partial electrical discharges is important for operational safety. A suitable known method for testing insulated cables is the continuous measurement of whether partial discharges occur within the insulation. It is known that a partial discharge outside the insulation of a cable can be detected and measured as a short, high-frequency electrical pulse. A sensor based on a closed toroidal core made of highly permeable ferrite material is known from the prior art. This core is placed around the cable or around the ground conductor of a cable shield and essentially completely encloses the cable circumferentially; these are known as HFCTs (High Frequency Current Transformers). The toroidal core acts as a flux concentrator and is wound with an electrical conductor, forming a coil through which the magnetic flux in the toroidal core flows. A partial discharge in the cable insulation causes a high-frequency primary current in the cable, which produces a corresponding magnetic flux in the flux concentrator and thus induces a corresponding voltage in the coil. The ferrite core serves as the flux concentrator for the magnetic flux. It is also known that the ferrite core has at least one thin air gap, allowing the toroidal core to be made in two parts and thus easily wrapped around a cable and mounted. A closed toroidal core increases the sensitivity of the measurement; however, the core material quickly saturates at high currents, and the transmission capacity for high-frequency pulses is lost, resulting in inaccurate measurements in the saturation range. Small air gaps in the toroidal core can remedy this, but the gap width must be known for the measurement. However, such toroidal cores have the disadvantage of being more complex to mount. It is also known that, as an alternative to a toroidal core with a coil wound around it, an air-core coil, i.e., a coil without a soft magnetic core, can be used as a sensor to detect partial discharges. Measurement distortion due to saturation in the core material does not occur because the air-core coil has no core, and air has a permeability of 1. However, the use of an air-core coil typically requires an amplifier because only a very small secondary voltage is induced in the coil. The task is therefore to propose an improved sensor for detecting partial discharges in cables. This problem is solved by a sensor comprising a flux concentrator made of a highly magnetically permeable material, wherein the flux concentrator is wound with at least one winding of a measuring coil. The sensor is characterized in that the flux concentrator has a first and second leg, such that the first and second legs define an area, the distance between the two legs being greater than the diameter of the cable. The cable to be monitored is positioned between the first and second legs, i.e., within the area defined by the legs. The defined area is designed such that it encompasses at least a portion of the cable's cross-sectional area, and this portion includes a conductor of the cable. Typically, the flux concentrator is designed such that the defined area encompasses at least half the cross-sectional area of the cable to be monitored. Typically, the first and second legs of the flow concentrator are arranged in a U- or V-shape, or as a circular segment, for example, a semicircle, so that the area between the two legs is defined. This allows the sensor, i.e., in particular the sensor's flow concentrator, to be easily mounted radially on a cable. The flow concentrator can, in particular, be formed from a single piece. A sensor with a flux concentrator designed in this way enables the detection of partial discharges in a cable. The sensor is designed so that it can be easily attached to the cable from one side. It is not necessary to attach a flux concentrator section to the side of the cable opposite the attached sensor section. At the same time, the sensor has the property that the flux concentrator does not saturate even at very high currents. The invention is explained below with the aid of figures. These show: 1 a schematic overview of sensors in a measurement setup, 2 A schematic cross-sectional view throug