FR3132953A1 - Magnetic closure system for Rogowski buckle - Google Patents

Abstract

System for closing a current sensor based on the principle of Rogowski loops, characterized in that it comprises a winding (1), the shape of which makes it possible to surround a conductor (2) subjected to the passage of a current at measure. The ends of the winding (1) are fitted 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

Magnetic closure system for Rogowski buckle

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

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.

We will briefly recall that Rogowski sensors are transformers without magnetic cores which include a primary conductor and a secondary coil. The current passing 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 passing through the primary conductor.

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

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

The Rogowski loops must have a constant density of turn surface over their entire length, so as to obtain a response which 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 creating such an openable loop are particularly high at the junction, which should maintain a density of turns that does not stray far 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 places.

Today's art to best compromise these requirements is to align the ends leaving as little space as possible, or to overlap the ends of the loop. If necessary, turns are added to compensate for their absence in the area between the ends.

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 loop, but the sensor closing mechanism remains difficult to use with one hand.

Other commonly used solutions use locking levers or friction devices which require one hand to direct the end towards the device, and one hand to operate the lever.

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.

The permanent magnets chosen have a high remanent magnetization to obtain a significant force of attraction, 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 precision. Magnets produced from Neodium (NdFeB) or Samarium Cobalt (Sm-Co) meet these conditions.

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

According to a variant of the invention, the sensor can be made 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 shaping into a toroid after linear winding of the turns, particularly for small diameters of toroids.

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

There represents an embodiment of the sensor according to the present invention in a slightly open position. The sensor here is composed 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 another surface around an axis located in the plane but external to this surface.

Permanent magnets (3a) and (3b) are integrated at the ends of the winding, preferably inside. By permanent magnet we mean a body presenting a remanent magnetization such that the opposite poles are subjected to an attractive force, and a high coercive field so as to suffer only a negligible loss of magnetization when they are subjected to a magnetic field external, such as coming for example from currents circulating in nearby conductors.

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 installation around a conductor (2).

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 winding portion located around these magnets is subjected. This characteristic is necessary to maintain the continuity of the Ampère path and guarantee the measurement precision of the sensor. Materials such as Neodium (NdFeB) or samarium–cobalt (Sm-Co) have a relative magnetic permeability close to 1.05, high remanent magnetization and a coercive field of several hundred thousand kA/m, and are suitable for this use.

In an advantageous embodiment of the present invention, the sensor has an overall diameter of 30 mm and can accommodate a sheathed wire to measure up to 25 mm² of conductor section. The winding includes 3000 turns of enameled wire 0.1 mm in 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 10mA to 1000A in low frequency alternating current such as 50 or 60Hz public networks.

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

The interior section of the sensor can be enlarged by the use of an extension made of 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.

shows the sensor which is the subject of the present invention, in the slightly open position.

presents the prior art.

illustrates the sensor in the closed position.

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

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

Claims (6)

System for closing a current sensor running 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), arranged so as to ensure a restoring force in the closed position of the loop. The opening is done by moving one end away from the other, to allow the introduction of the electrical conductor (2) whose current is to be measured. 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. Closing system according to claim 1 characterized in that the permanent magnets are made from Neodium (NdFeB) or Samarium Cobalt (Sm-Co). Closure 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. Current sensor consisting of one or a plurality of Rogowski loops (4a) (4b) arranged in series, characterized in that it comprises at least one closure system according to claim (1). Device for extending a flexible current sensor comprising one or more Rogowski loops provided with at least one closure system according to claim 1, characterized in that the extension device (6) is made of a material whose permeability magnetic is greater than 1000.