Magnetic closure system for Rogowski buckle

Abstract

A current sensor closing system based on the Rogowski loop principle, characterized in that it comprises a winding (1), the shape of which allows it to surround a conductor (2) subjected to the passage of a current to be measured. The ends of the winding (1) are provided with permanent magnets (3a) and (3b) ensuring precise closing while allowing easy opening. The magnets (3a) and (3b) have a magnetic permeability close to that of air and a high coercive field. Figure for abstract: [Fig 1]

Description

Title of the invention: Magnetic closure system for Rogowski buckle

[0001] The present invention relates to a device for measuring electric currents without requiring opening of the circuit which implements the principle of Rogowski loops.

[0002] This principle is well known for measuring alternating electric currents. These sensors are often used connected to portable network analyzers, or integrated into fixed electricity meters.

[0003] It will be briefly recalled that Rogowski sensors are transformers without magnetic cores which comprise a primary conductor and a secondary coil. The current flowing through the primary conductor generates a magnetic field whose variations cause, in the secondary coil, an electromotive force. The integration of this electromotive force then provides an image of the current flowing through the primary conductor.

[0004] The principle of Rogowski loops makes it possible to produce flexible sensors of all sizes which adapt to the shape of the conductors to be measured, facilitating their installation.

[0005] The present invention relates to the closing system of such a sensor, to allow its rapid installation on an electrical circuit without disassembly. One application of such a sensor is the detailed measurement of electricity consumption in electrical cabinets.

[0006] Rogowski loops must have a constant turn surface density over their entire length, so as to obtain a response that is independent of the position of the conductor to be measured, as long as it is surrounded by the loop, and zero if it is placed outside the loop. The requirements for producing such an openable loop are particularly high at the junction, which should maintain a turn density that deviates little from the ideal. The locking mechanism in the closed position must be simple, robust, easy to handle, and not lead to a higher section, which would make the sensor more difficult to slide into tight spaces.

[0007] The current art of achieving the best compromise on these requirements consists of aligning the ends leaving as little space as possible, or of overlapping the ends of the loop. If necessary, turns are added to compensate for their absence in the area between the ends.

[0008] In patent EP2009453A1, the use of a body with high magnetic permeability makes it possible to reduce the distance constraint between the two ends of the buckle, but the sensor's closing mechanism remains difficult to use with one hand.

[0009] Other commonly used solutions use locking levers or friction devices that require one hand to direct the end toward the device, and one hand to operate the lever.

[0010] In order to increase ease of use, the invention relates to a Rogowski current sensor characterized in that the ends of the loop are provided with permanent magnets oriented so as to exert an attraction from one end to the other. Opening is easy, and the attraction of the magnets then helps to close the loop around the conductor to be measured.

[0011] The permanent magnets chosen have a high remanent magnetization to obtain a significant attractive force, a sufficient coercive field so as not to be demagnetized by the alternating field to be measured, and a stable and low relative magnetic permeability, i.e. preferably between 0.9 and 10, so as not to increase the flux in the turns surrounding the magnets, and thus not to affect the measurement accuracy. Magnets produced from Neodium (NdFeB) or Samarium Cobalt (Sm-Co) meet these conditions.

[0012] The winding is carried out precisely so that the entire sensor in the closed position achieves a good approximation of an ideal Rogowski coil, that is to say for which the value of the measured current does not depend on the position of the primary conductor in the sensor or on the conductors external to the sensors. A winding machine is used to position the turns along the core, on one or more layers, with a return conductor if necessary so as not to create a turn with a large surface area in the plane of symmetry of the loop.

[0013] According to a variant of the invention, the sensor can be produced from two or more Rogowski loops arranged end to end, and equipped with permanent magnets at at least one junction between two loops. This configuration facilitates the production of the sensor, in particular its toroidal shaping after linear winding of the turns, in particular for small toroid diameters.

[0014] The invention is now explained in detail by the description of various embodiments, with reference to the accompanying drawings.

[0015] [Fig. 1] shows an embodiment of the sensor according to the present invention in a slightly open position. The sensor is composed here of a regular winding (1), made on a flexible polymer core, the shape of which approximates a torus. A torus is understood here as the volume obtained by the revolution of a disk, or of another surface around an axis located in the plane but outside this surface.

[0016] Permanent magnets (3a) and (3b) are integrated at the ends of the winding, preferably inside. By permanent magnet is meant a body having a remanent magnetization such that opposite poles are subject to an attractive force, and a high coercive field to suffer only negligible loss of magnetization when subjected to an external magnetic field, such as from currents flowing in nearby conductors.

[0017] The attraction of the magnets makes it possible to obtain a force to hold the loop in the closed position, while retaining the possibility of opening it easily for placement around a conductor (2).

[0018] The permanent magnets (3a) and (3b) are made from a material having a magnetic permeability close to that of air, so as not to modify the flux to which the portion of the winding located around these magnets is subjected. This characteristic is necessary to maintain the continuity of the Ampere path and guarantee the measurement accuracy of the sensor. Materials such as Neodium (NdFeB) or samarium-cobalt (Sm-Co) have a relative magnetic permeability close to 1.05, a high remanent magnetization and a coercive field of several hundreds of thousands of kA / m, and are suitable for this use.

[0019] In an advantageous embodiment of the present invention, the sensor has an overall diameter of 30 mm and can accommodate a sheathed wire to be measured up to 25 mm2 of conductor cross-section. The winding comprises 3000 turns of enameled wire of 0.1 mm diameter, wound in 4 layers and the area of ​​the turns, all perpendicular to the magnetic field to be measured, is approximately 10 mm2. The sensor thus allows the precise measurement of currents in a range from 10 mA to 1000 A in low frequency alternating current such as 50 or 60 Hz public networks.

[0020] When the position and shape of the turns are well controlled by the winding machine, the sensor thus produced remains insensitive to conductors outside the sensor, that is to say it indicates less than 0.5% of the value that it would indicate if the same conductor were placed inside the loop.

[0021] The internal section of the sensor can be enlarged by the use of an extension made of a material with high magnetic permeability (6), introduced between the ends of the Rogowski loop, and which remains in place due to the attraction exerted by the permanent magnets.

[0022] [Fig. 1] shows the sensor which is the subject of the present invention, in a slightly open position.

[0023] [Fig.2] shows the prior art.

[0024] [Fig.3] illustrates the sensor in the closed position.

[0025] [Fig.4] shows the sensor in the open position with the addition of an extension (6) made of a material with high magnetic permeability, i.e. greater than 1000, to allow measurements on a conductor of larger diameter.

[0026] [Fig.5] describes a sensor consisting of 2 loops (4a) and (4b) arranged in series so as to surround the conductor (5).

Claims

Claims

1. System for closing a current sensor flowing through an electrical conductor (2) comprising at least one Rogowski loop (1) characterized in that the ends of the loop are provided with permanent magnets (3a) and (3b) having a stable magnetic permeability close to 1, arranged so as to provide a restoring force in the closed position of the loop, the closing system being configured to be opened by moving one end away from the other, to allow the introduction of the electrical conductor (2) whose current is to be measured.

2. Closing system according to claim 1 characterized in that the permanent magnets (3a) and (3b) have a relative magnetic permeability of between 0.9 and 10.

0.

3. Closing system according to claim 1 characterized in that the permanent magnets are made from Neodium (NdFeB) or Samarium Cobalt (Sm-Co).

4. Closing system according to claim 1 characterized in that the Rogowski loop is provided with a deformable body which tends to return the loop to the closed position.

5. Current sensor consisting of one or a plurality of Rogowski loops (4a) (4b) arranged in series, characterized in that it comprises at least one closing system according to claim i

6. 1. Device for extending a flexible current sensor comprising one or more Rogowski loops provided with at least one closing system according to claim 1, characterized in that the extension device (6) is made of a material whose magnetic permeability is greater than 1000.

Images