Ring-core type current transducer for magnetic flux detection

Abstract

A current transducer for measuring magnetic flux from a current carrying conductor, comprising a sensor core for concentrating magnetic flux from the current carrying conductor, the sensor core being shaped as a loop interrupted by a gap. The current transducer further comprises a fluxgate ring core for sensing the magnetic flux, and two excitation coils for generating an excitation flux in the ring core and detecting the magnetic flux of the current carrying conductor. There is a driving means for driving an excitation current through the excitation coils, together with a detection circuit, connected to the excitation coils for detecting an electronic signal of the excitation coils. The fluxgate ring core is disposed within the gap of the sensor core, and the excitation coils are wound around first and second portions of the fluxgate ring core, respectively. In some embodiments, the first and second fluxgate ring cores have serially connected excitation coils mounted within the first and second gaps, which are disposed directly opposite each other in the sensor core of the current transducer.

Description

[Technical field]

[0001] The present invention relates to the field of current sensing, and more particularly to the field of current sensing by magnetic flux sensing. [Background technology]

[0002] Current transducers are known for detecting the current in a current-carrying conductor, such as a wire or busbar, without the need to establish a direct electrical connection. The current transducer determines the primary current of the current-carrying transducer by determining the strength of the magnetic field emanating from the current-carrying transducer.

[0003] Known current transducers of the fluxgate type typically comprise a core of a high magnetic permeability material shaped as a continuous loop that can be placed around a current carrying conductor. Typically such fluxgate current transducers further comprise two excitation coils for inducing a magnetic field in the core, and a sensor coil for detecting the net magnetic flux in the core.

[0004] In a typical fluxgate current transformer, the core forms a continuous loop that can be placed around a current carrying conductor, but such a configuration requires that the transformer be loaded before the current carrying conductor is connected to its power source. A split core current transformer, which can be opened and closed in this structure, solves this problem by allowing the transformer to be placed around one current carrying conductor and moved to another current carrying conductor without having to de-energize the current carrying conductor.

[0005] Although split-core current transducers are practical for use with multiple current carrying conductors, current transducers that can be opened and closed pose several challenges. Splitting the core poses the risk of variability in the way the loop is formed when it is closed again, which affects detection sensitivity. Some systems attempt to solve this by having multiple magnetometer cores mounted separately within the current transducer to avoid splitting the magnetometer core itself, but the use of multiple separate magnetometer cores makes the current transducer more vulnerable to external fields and complicates the construction of the device. Summary of the Invention

[0006] It is an object of the present invention to provide a tool for reliably determining the current in a current-carrying conductor by measuring the magnetic flux from that conductor.

[0007] The above objects and advantages, together with numerous other objects and advantages which will become apparent from the description of the invention, are set forth below. a sensor core for concentrating magnetic flux from a current carrying conductor, the sensor core being shaped as a loop interrupted by a gap; a fluxgate ring core for sensing magnetic flux, the fluxgate ring core being disposed within the gap of the sensor core; a first excitation coil wound around a first portion of the flux-gate ring core for generating an excitation magnetic flux in the ring core and for detecting a magnetic flux of a current-carrying conductor; a second excitation coil wound around a second portion of the flux-gate ring core for generating an excitation flux in the ring core and for detecting a magnetic flux of a current-carrying conductor; a driving means for driving an excitation current through the first excitation coil and the second excitation coil; a detection circuit connected to the first excitation coil and the second excitation coil for detecting electronic signals of the first and second excitation coils; Equipped with According to a first aspect of the invention there is provided a current transducer for measuring magnetic flux from a current carrying conductor.

[0008] By loop is understood a structure whose beginning part is connected to its end part to form an enclosure. In one preferred variant the loop may be circular, but in other preferred variants it may have other shapes, such as a square. In a preferred variant the loop of the sensor core is of regular shape, i.e. a circle or a geometric shape in which all angles are equal.

[0009] By loop interrupted by gap is understood a structure forming a loop but with a segment removed. In a preferred variant, the removed segment is at most one fifth of the contour length of the sensor core, such as one tenth of the contour length of the sensor core. By gap is understood the area between the first end of the sensor core and the second end of the sensor core, such that the gap is the volume of the missing segment of the sensor core if the sensor core were a closed loop with a continuous cross-sectional area from the first end of the sensor core to the second end of the sensor core.

[0010] By the term fluxgate ring core arranged in the gap of the sensor core, it is understood that the fluxgate ring core is located between the first end of the sensor core and the second end of the sensor core. In preferred variants, the fluxgate ring core is contained within the volume of the gap, i.e. the cross section of the fluxgate ring core is smaller than or equal to the cross section of the sensor core. In some of such preferred variants in which the fluxgate ring core does not extend beyond the gap, the first and second excitation coils wound around the fluxgate ring core may extend outside the volume of the gap, even if the fluxgate ring core itself does not. In another variant, the fluxgate ring core may be arranged between the first end of the sensor core and the second end of the sensor core, extending beyond the gap in a direction perpendicular to the end faces of the first end of the sensor core and the second end of the sensor core.

[0011] Having the fluxgate ring core mounted within the gap of the sensor core provides several advantages. The sensor core can be positioned around the current carrying conductor such that the current carrying conductor is within an opening enclosed by the loop formed by the sensor core. The sensor core, which is made of a magnetic material, concentrates the magnetic field of the current carrying conductor. The magnetic field is guided by the sensor core to the fluxgate ring core, thereby increasing sensitivity. Furthermore, since the sensor core concentrates the magnetic field, it also reduces vulnerability to external fields and non-center alignment of the current carrying conductor within the sensor core opening. Having the fluxgate ring core located within the gap rather than being an integral part of the sensor core reduces the amount of noise from the excitation flux induced by the first and second excitation coils that may enter the sensor core.

[0012] Furthermore, having the fluxgate ring core disposed within the gap of the sensor core allows the same fluxgate ring core structure to be used with various sizes of sensor cores. The sensor core may be enlarged or reduced to allow current carrying conductors of different sizes to be enclosed by the sensor core opening. Preferably, the gap height, i.e., the distance between the first end of the sensor core and the second end of the sensor core, may be the same between different variations of the current converter so that the same fluxgate ring core configuration can be used with different sensor core dimensions, thereby simplifying the creation of a current converter that can be adapted to different current conductors.

[0013] In a preferred variant, the driving means is a modulator for controlling the current driven through the first and second excitation coils.

[0014] Having a detection circuit directly connected to the first and second excitation coils allows the magnetic flux of the current carrying conductor to be measured based on the electrical signals of the first and second excitation coils. The primary current may be calculated based on the measured magnetic flux, and the magnetic flux may be determined by monitoring the difference between the electrical signals of the first and second excitation coils, i.e. the current and voltage. In a preferred variant, the current converter therefore does not have a dedicated sensor coil. By determining the magnetic flux directly from the signals of the first and second excitation coils, the system is simplified, since a sensor coil can be eliminated. Measuring the magnetic flux directly on the fluxgate ring core increases the signal strength, compared to either a measurement on the sensor core or, if necessary, a measurement further away with a sensor coil wound around the outside of the first and second excitation coils.

[0015] In a preferred variant, the first excitation coil and the second excitation coil are wound around the fluxgate ring core such that they are equally spaced on the fluxgate ring core, in other words the distance from one end of the first excitation coil to the nearest end of the second excitation coil is the same.

[0016] According to a further embodiment of the first aspect of the present invention, the detection circuit comprises a second harmonic detector for demodulating the difference between the currents of the first and second excitation coils, respectively.

[0017] The use of second harmonic detection to determine the difference in the electrical signals from the first and second excitation coils allows the magnetic flux of a current carrying conductor to be detected even when a current transformer having a low sensitivity is used. Second harmonic detection reduces the adverse effects of noise in the current transformer. Furthermore, the symmetry of second harmonic detection, which is performed at full saturation in both directions, reduces temperature drift in the current transformer.

[0018] In another variation of the current converter, the detection circuit comprises an edge time difference detector. In yet other variations, other known methods of demodulating the current signals of the first and second excitation coils may be used.

[0019] According to a further embodiment of the first aspect of the present invention, the fluxgate ring core is made of a magnetic material having a relative permeability of at least 100.000.

[0020] By constructing the fluxgate ring core of a magnetic material with high relative permeability, the magnetic resistance is low in the fluxgate ring core. Also, the small dimensions of the fluxgate ring core provide only a short path through the magnetic material. These features help to confine the excitation flux within the fluxgate ring core. It is preferable to confine the excitation flux to the fluxgate ring core, since the excitation flux traveling into the sensor core is a noise source for the magnetic flux picked up from the current carrying conductor.

[0021] The magnetic material of the fluxgate ring core is further made of a low-loss material to minimize power loss at the excitation frequency. High magnetic permeability contributes to localizing the excitation flux, while minimizing flux loss into the material of the fluxgate ring core allows the use of high excitation frequencies, thereby increasing the bandwidth over which the primary current can be detected. In a preferred variant, the excitation frequency is at least 32 kHz. In another preferred variant, the excitation frequency is 128 kHz or greater.

[0022] Some variations of the current converter may include a filter to suppress excitation noise in the system electronics.

[0023] According to a further embodiment of the first aspect of the present invention, the fluxgate ring core is made of a cobalt-based amorphous metal alloy.

[0024] According to a further embodiment of the first aspect of the invention, the sensor core is made of a magnetic material having a relative permeability lower than the relative permeability of the fluxgate ring core.

[0025] Although it is preferable for the sensor core to have a high magnetic permeability, there are some advantages to selecting the magnetic material of the sensor core such that its relative permeability is lower than that of the fluxgate ring core.

[0026] First, magnetic materials with lower relative permeability are usually cheaper than those with higher relative permeability, and by making a larger sensor core of cheaper material, the cost of the current transducer can be kept low.

[0027] Second, having a higher relative permeability in the fluxgate ring core further helps confine the excitation flux to the fluxgate ring core, thereby minimizing excitation flux noise penetrating the sensor core. Additionally, the primary flux from the current carrying conductor picked up by the sensor core follows the path with the least reluctance to the fluxgate ring core, from where it is measured by the detection circuitry.

[0028] According to a further embodiment of the first aspect of the present invention, the sensor core is made of Mu metal.

[0029] According to a further embodiment of the first aspect of the present invention, the current transducer comprises a shield to provide protection from external magnetic fields and reduce noise, the shield enclosing the sensor core, the fluxgate ring core, the first excitation coil and the second excitation coil together.

[0030] The system is sensitive to external magnetic fields, such as the magnetic fields of nearby electronic devices as well as the earth's magnetic field. The current converter components may be enclosed to reduce sensitivity to such unwanted magnetic fields. The sensor core, fluxgate ring core, and first and second excitation coils are enclosed together with a shield so that the exchange of magnetic flux between those components is not restricted by the shield, and so that if any external field does enter the current converter, the shield is used to guide it away from the sensor and fluxgate ring core.

[0031] In some variations of the first aspect of the present invention, the shield includes an inner shield core, an outer shield core, a top shield plate, and a bottom shield plate.

[0032] According to a further embodiment of the first aspect of the invention, the shield is made of a material having a lower relative permeability than both the material of the sensor core and the material of the fluxgate ring core.

[0033] In a preferred variant, the shield is made of a material that has a higher saturation flux density than both the material of the sensor core and the material of the fluxgate ring core.

[0034] In order for the shield to provide effective protection from external magnetic fields, it must be made of a material with suitable properties. A high saturation flux density of the shield ensures that the shield can shield against strong external magnetic fields, since the magnetic field can pass through the shield when the material is saturated. Materials with high saturation flux density generally have low relative permeability. Furthermore, materials with low relative permeability are often less expensive than those with higher relative permeability, so choosing a material with low relative permeability contributes to lowering the cost of the current converter.

[0035] In preferred variations, the shield and the sensor core are spaced apart so that they are not in direct physical or electrical contact. In some variations, the distance between the shield and the sensor core and the distance between the shield and the fluxgate ring core is at least half the thickness of the shield material. In other preferred variations, the distance between the shield and the sensor core and the distance between the shield and the fluxgate ring core is at least 1 mm.

[0036] If the distance between the shield and the sensor core and / or fluxgate ring core is too small, external magnetic fields may transfer from the shield to the sensor core and / or fluxgate ring core. Therefore, a minimum distance is required for the shield to provide effective protection from external magnetic fields.

[0037] According to a further embodiment of the first aspect of the invention, the shield is made of magnetic steel sheet.

[0038] By electrical steel is understood iron and iron alloys containing up to 7% silicon.

[0039] According to a further embodiment of the first aspect of the invention, the current transducer comprises a compensation coil for inducing a cancelling current and maintaining a near zero magnetic flux in a flux-gate ring core, the compensation coil being wound around the shield around the sensor core.

[0040] The compensation coil allows the current converter to operate with zero magnetic flux. The compensation coil is connected to the detection circuit and current is directed through the compensation coil such that the magnetic flux generated by the compensation coil exceeds the magnetic field from the primary current to leave the magnetometer output at zero. Operating with zero net magnetic flux ensures that the magnetic material of the fluxgate ring core avoids saturation even when the magnetic field of the current carrying conductors would otherwise be large enough to saturate the magnetometer. The compensation coil thus contributes to increasing the dynamic range of the current converter.

[0041] By wrapping a compensation coil around the shield, the shield is also affected by the compensation current and therefore also contributes to the offset magnetization of the shield.

[0042] The shield has the added advantage of acting as a hollow transformer core for high frequencies for the compensation coil wound around it.

[0043] According to a further embodiment of the first aspect of the present invention, the current transformer comprises a degaussing circuit connected to the compensation coil for eliminating residual magnetic flux in the current transformer.

[0044] By degaussing circuit is understood a circuit for controlling the activation of a degaussing signal driven through the compensation coil. By degaussing signal is understood an alternating current high enough to cancel residual magnetic flux in the magnetic material of the current converter. The magnetic material may retain residual magnetic flux after being subjected to a magnetic field. The stronger the magnetic field the material is subjected to, the more likely residual magnetic flux will be retained in the material, even with a compensation system such as a compensation coil and shielding in place. A degaussing circuit is particularly advantageous when the compensation coil is experiencing problems and / or is temporarily switched off, or in situations where the current converter is subjected to a magnetic field that exceeds the magnitude of the magnetic field that can be compensated for by the compensation coil.

[0045] In some variations, the current converter includes a first spacer and a second spacer to space the fluxgate ring core from the sensor core, the first spacer being positioned between a first end of the sensor core and the fluxgate ring core, and the second spacer being positioned between a second end of the sensor core and the fluxgate ring core.

[0046] By spacer is understood any component that does not put the sensor core in direct contact with the fluxgate ring core. In one preferred variant, the spacer may be part of a holder for mounting the fluxgate ring core in the gap of the sensor core. In another preferred variant, the spacer may be part of a shielding structure. In yet another preferred variant, the first and second spacers may be separate components whose sole purpose is to create additional spacing. However, it should be understood that the first spacer and the second spacer may also be connected, for example on opposite sides of the holder.

[0047] The excitation flux induced in the fluxgate ring core by the first and second excitation coils is a noise source relative to the detected flux from the current carrying conductor. Having the first and second spacers between the fluxgate ring core and the sensor core helps to contain the excitation flux within the fluxgate ring core, thereby minimizing any excitation flux penetrating into the sensor core.

[0048] In some variations of the current transformer, the effect of the first and second spacers may complement the advantage of the sensor core and the fluxgate ring core being made of different materials. In other variations of the current transformer, the first and second spacers may provide suitable decoupling of the sensor core and the fluxgate ring core while being made of the same material.

[0049] According to a further embodiment of the first aspect of the present invention, the first spacer has a thickness of at most 50 μm and the second spacer has a thickness of at most 50 μm.

[0050] The spacing between the sensor core and the fluxgate sensor core results in a reduction in the magnetic coupling between the sensor core and the fluxgate core sensor. This contributes to the containment of the excitation flux within the fluxgate ring core, which also results in a reduction in the amount of sensed flux from the current carrying conductor moving from the sensor core to the fluxgate ring core. It is therefore important that the first spacer and the second spacer each have a minimum thickness, i.e., the distance between the fluxgate ring core and the sensor core is small. The thickness of each of the first spacer and the second spacer, which is 50 μm or less, is suitable to guide the magnetic flux into the fluxgate ring core while keeping the noise from the excitation flux to a minimum.

[0051] In some preferred variations, the current transducer does not include a spacer between the fluxgate ring core and the sensor core, which may be considered to be equivalent to having first and second spacers each having a thickness of 0 μm.

[0052] In the absence of a spacer, the coupling between the sensor core and the fluxgate ring core sensor is improved. In such a variation, the material selection and the resulting differences in the magnetic properties of the materials are sufficient to avoid the adverse effects of the excitation flux leaking into the sensor core.

[0053] According to a further variant, the current transducer comprises two or more fluxgate ring cores, said fluxgate ring cores being evenly distributed along the sensor core.

[0054] By the term fluxgate ring cores being evenly distributed along the sensor core, it is understood that the portions of the sensor core between each fluxgate ring core are of equal length.

[0055] In a preferred variant, the sensor core comprises two fluxgate ring cores located directly opposite each other, in other words, a fluxgate ring core is located at each end of the diameter of the sensor core. In such a configuration, the sensor core comprises two gaps and the fluxgate ring cores are mounted within the gaps.

[0056] It should be understood that each of the two or more fluxgate ring cores is configured as a fluxgate ring core as described above, for example each of the fluxgate ring cores including a first excitation coil and a second excitation coil wound around the fluxgate ring core, and in the case of a shield, all of the fluxgate ring cores are surrounded by the shield of the current transformer.

[0057] The inclusion of two or more fluxgate ring cores has the advantage that variations in the current transformer can be detected and compensated for, further mitigating the effects of external magnetic fields.

[0058] According to a further embodiment of the first aspect of the present invention, the current transducer comprises: a second fluxgate ring core for sensing magnetic flux, the second fluxgate being disposed directly opposite the fluxgate ring core and located within a second gap of the sensor core; a third excitation coil for generating an excitation magnetic flux in the second ring core and detecting the magnetic flux of a current-carrying conductor; a fourth excitation coil for generating an excitation magnetic flux in the second ring core and detecting the magnetic flux of a current-carrying conductor; Equipped with.

[0059] The fluxgate rings position the cores at either end of a diameter of the sensor core, and the other fluxgate ring core, also referred to as the first fluxgate ring core, is spaced 180 degrees from the second fluxgate ring core along the loop of the sensor core.

[0060] The mounting of the second fluxgate ring core into the second gap is the same as the previously described mounting of the fluxgate ring core into the gap.

[0061] Having the first and second fluxgate ring cores directly opposite each other in the path of the sensor core has the advantage of reducing the influence of external magnetic fields that would otherwise cause noise in the measurement. Having the first and second fluxgate ring cores directly opposite each other means that the external magnetic field affects the first and second ring cores differently, thus reducing the influence caused by the external field. In the ideal case where the external field is a large uniform magnetic field, it affects the first and second fluxgate ring cores with a magnetic field of the same magnitude, even though the magnetic field is applied in opposite directions. Hence, the external fields sensed by the first fluxgate ring core and the second fluxgate ring core cancel each other out. At the same time, the magnetic field generated by the current carrying conductor picked up by the sensor core is detected by both the first flux core current transducer and the second flux core current transducer without canceling each other out, since the magnetic flux is directed in one direction around the sensor core.

[0062] In a preferred variant, the fluxgate ring cores, also referred to as the first and second fluxgate ring cores, are made of the same material and have the same proportions as each other, thereby providing measurement symmetry. In such a preferred variant, the third and fourth excitation coils are the same as the first and second excitation coils, e.g. they have the same number of turns and are made of the same type of wire.

[0063] In a preferred variant, the first and third excitation coils are electrically connected in series, and the second and fourth excitation coils are electrically connected in series. Such a connection allows the excitation coils of the first and second fluxgate ring cores to be electrically driven simultaneously and in the same way. This simplifies the operation of the current converter and minimizes the required equipment.

[0064] According to some preferred variants, a sensor core for concentrating magnetic flux from a current carrying conductor, the sensor core being shaped as a loop interrupted by first and second gaps located directly opposite one another; a first fluxgate ring core for sensing magnetic flux, the first fluxgate ring core being disposed in the first gap of the sensor core; a first excitation coil wound around a first portion of the flux-gate ring core for generating an excitation magnetic flux in the first ring core and detecting a magnetic flux of a current-carrying conductor; a second excitation coil wound around a second portion of the flux-gate ring core for generating an excitation magnetic flux in the first ring core and detecting a magnetic flux of a current-carrying conductor; a second fluxgate ring core for sensing magnetic flux, the second fluxgate ring core being disposed in the second gap of the sensor core; a third excitation coil wound around a first portion of the second flux-gate ring core for generating an excitation flux in the second ring core and detecting a magnetic flux of a current-carrying conductor; a fourth excitation coil wound around a second portion of the second flux-gate ring core for generating an excitation magnetic flux in the second ring core and detecting a magnetic flux of a current-carrying conductor; a driving means for driving an excitation current through the first excitation coil, the second excitation coil, the third excitation coil and the fourth excitation coil; a detection circuit connected to the first excitation coil, the second excitation coil, the third excitation coil, and the fourth excitation coil for detecting electronic signals of the first and second excitation coils; There is a current transducer for measuring magnetic flux from a current carrying conductor comprising:

[0065] According to a further embodiment of the first aspect of the present invention, the current transformer is a split-core current transformer.

[0066] By split core current transducer, it is understood that the closed loop of the sensor core and the fluxgate ring core are reattachably separated so that the current transducer can be placed around a current carrying conductor and then the loop of the current transducer can be opened to reattach a portion of it around the current carrying conductor. Thus, having a split core current transducer allows the current transducer to be placed around a current carrying conductor without having to reposition the current carrying conductor itself. This also makes it easy to move the current transducer from one current carrying conductor to another, and therefore easy to use the same current transducer to measure the primary current of a variety of different current carrying conductors.

[0067] In a preferred variant, the split core current converter comprises a first split and a second split for dividing a portion of the split core current converter, both the first split and the second split being located above the sensor core.

[0068] By the term first and second splits located within the sensor core, it is understood that both the first and second splits have the sensor core on either side. Thus, both the first and second splits are located away from the fluxgate ring core so that the splits do not increase the size of the gap. Having the first and second splits located within the sensor core away from the gap allows for an enclosure shield to be maintained around the fluxgate ring core whenever the current transducer is in use, including when the split core current transducer is opened and closed to place it around a current carrying conductor, for example.

[0069] The sensor core is less sensitive than the fluxgate ring core to imprecision in the reattachable closure mechanism, and therefore sensing the magnetic field within the gap of the sensor core rather than surrounding the current carrying conductor with the fluxgate ring core allows for the inclusion of splits without changing the properties of the fluxgate ring core.

[0070] In such variations of the current transducer with multiple fluxgate ring cores, each of these fluxgate ring cores is located away from the split of the split core current transducer, for example in a preferred variation with two fluxgate ring cores, the fluxgate ring cores are located directly opposite each other at 180 degrees from each other along the sensor core, and the splits are also directly opposite each other and located approximately 90 degrees away from the fluxgate ring cores.

[0071] In variations with three or more fluxgate ring cores, the fluxgate ring cores are not equidistant with respect to the split, but in preferred variations the splits are positioned to maximize the distance between the fluxgate ring cores and the splits.

[0072] In another preferred variant, the split core current converter comprises a first split and a second split for dividing a portion of the split core current converter, the first split being located between the fluxgate ring core and the sensor core.

[0073] In such variations with two fluxgate ring cores, the first split is located between the first fluxgate ring core and the sensor core and the second split is located between the second fluxgate ring core and the sensor core. In variations with three or more fluxgate ring cores, at least the first split is located between the fluxgate ring core and the sensor core and the second split may be located elsewhere within the sensor core.

[0074] According to a further embodiment of the first aspect of the present invention, the current transducer comprises a feedback coil to increase the accuracy of said current transducer.

[0075] The feedback coil is suitable for sensing alternating magnetic flux, i.e. magnetic flux generated from alternating current. The inclusion of the feedback coil enhances the accuracy of the mid-frequency range. In the data processing of the detection circuit, the signal measured by the feedback coil is added to the signal of the magnetometer, thereby enhancing the accuracy of the mid-frequency range of the final output of the detection.

[0076] In a preferred variation, the feedback coil is wrapped around a shield around the sensor core.

[0077] It is another object of the present invention to provide a method for determining the current in a current carrying conductor by measuring the magnetic flux from that conductor.

[0078] According to a second aspect of the present invention, the above objects and advantages are achieved by: Providing a current carrying conductor for carrying the primary current; providing a current converter comprising a sensor core, a fluxgate ring core, a first excitation coil and a second excitation coil; disposing a sensor core around a current-carrying conductor such that the sensor core can sense magnetic flux emanating from the current-carrying conductor; connecting the first excitation coil and the second excitation coil to a driving means and driving an excitation current through the first and second excitation coils such that an excitation flux is induced in the fluxgate ring core; connecting the first excitation coil and the second excitation coil to a detection circuit and determining a difference in current through the first excitation coil and the second excitation coil using second harmonic detection; Calculating the primary current of a current-carrying conductor based on second harmonic detection of the current difference The present invention is obtained by a method for detecting a primary current flow through a current carrying conductor, comprising:

[0079] Applying a second harmonic detection to the excitation current increases the accuracy of the detection method where the primary current is determined based on the difference in current of the excitation current through the first and second excitation coils.

[0080] According to a further embodiment of the second aspect of the present invention, the method further comprises driving an excitation current through third and fourth excitation coils provided in a second fluxgate ring core of a current transformer, such that an excitation flux is induced in said second fluxgate ring core, and connecting said third excitation coil and said fourth excitation coil in series with said first excitation coil and said second excitation coil, such that said third excitation coil and said fourth excitation coil are connected to said detection circuit, thereby determining a current difference between a first combined system of said first excitation coil and said third excitation coil and a combined system of said second excitation and said fourth excitation coil.

[0081] Forming a first combined system of the first and third excitation coils and a second combined system of the second and fourth excitation coils by serial connection of the respective excitation coils has several advantages: the first and second fluxgate ring cores may be driven by the same driving means, thereby simplifying the electrical connections; furthermore, the same detection circuit may be used to detect the combined measurements of the first and second fluxgate ring cores, thereby simplifying the required circuitry and the necessary calculations to be made on the collected measurements are not complicated by the presence of multiple fluxgate ring cores.

[0082] According to a further embodiment of the second aspect of the present invention, the excitation current driven through the first and second excitation coils is an alternating current.

[0083] In a preferred variation, alternating excitation currents drive the first and second excitation coils to drive the magnetic material of the fluxgate ring core into deep saturation in both directions. Driving the fluxgate ring core in alternating deep saturation minimizes any thermal offset drift in the fluxgate ring core, thereby increasing the reliability of measurements made by the current transducer.

[0084] According to a further embodiment of the second aspect of the present invention, the method comprises providing a compensation coil around the sensor core and driving a compensation current through the compensation coil, determining the compensation current based on an output of the detection circuit such that a primary magnetic flux of the primary current is compensated by the compensation magnetic flux of the compensation current through the compensation coil.

[0085] According to a further embodiment of the second aspect of the present invention, a demagnetizing signal is sent via the compensation coil in order to eliminate residual magnetic flux present in the material of the current transformer.

[0086] Magnetic materials may retain residual magnetic flux after being subjected to a magnetic field. The stronger the magnetic field the material is subjected to, the more likely it is that residual magnetic flux will be retained in the material, even with compensation systems such as compensation coils and shielding in place. By demagnetizing signal is understood an alternating current high enough to cancel the residual magnetic flux in the magnetic material of the current transformer.

[0087] In a preferred variant, the degaussing signal may be activated manually by the user, such that it is introduced when the user observes the need to counteract residual magnetic flux. In another preferred variant, the degaussing signal is activated automatically when the output offset current exceeds a predefined threshold.

[0088] In the following, examples of embodiments according to the present invention will be described. [Brief description of the drawings]

[0089] [Figure 1]FIG. 2 is a schematic diagram of a cross-sectional view of a current transformer disposed around a current carrying conductor. [Diagram 2] 1 is a schematic diagram of current converter components and circuits. [Diagram 3] FIG. 2 is a schematic diagram of a current transducer shown in partial cutaway view. [Figure 4] 1 is a schematic diagram of a cross section of a current transformer having two fluxgate ring cores arranged around a current carrying conductor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0090] The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

[0091] However, the present invention may be embodied in forms other than those shown below and should not be construed as limited to any examples set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Thus, like elements will not be described in detail with respect to the description of each figure. Detailed descriptions of embodiments of ring core fluxgate current converters as well as methods for using such systems are provided.

[0092] FIG. 1 shows a schematic diagram of the components of a current transducer 1 in its simplest form shown in cross section.

[0093] The sensor core 10 is made of a magnetic material and forms a loop interrupted by a gap 13. By loop is understood a structure whose beginning is connected to its end to form an enclosure. By loop interrupted by a gap is understood a structure that forms a loop but from which a segment has been removed. By gap 13 is understood the area between the first end 11 of the sensor core and the second end 12 of the sensor core such that gap 13 is the volume that the missing segment of the sensor core would occupy if the sensor core 10 were a closed loop with a continuous cross-sectional area from the first end 11 of the sensor core to the second end 12 of the sensor core. In a preferred embodiment, the cross-sectional area of ​​the sensor core 10 is constant along the length of the sensor core 10.

[0094] The sensor core 10 is arranged around the current-carrying conductor 5 such that a portion of the current-carrying conductor 5 is located within an opening 15 of the sensor core 10. By opening 15 of the sensor core 10 is understood the area bounded by the loop of the sensor core 10.

[0095] In a preferred variation, the current carrying conductor 5 is centered in the sensor core opening 15 during measurement. For example, this may be the case when the diameter of the current carrying conductor 5 matches the diameter of the sensor core opening 15, or the current transducer 1 may be mounted on an external support (not shown) that holds it in a preferred position. While it is optimal to have the current carrying conductor 5 centered relative to the sensor core opening 15, the current transducer 1 will also function in less optimal positions, such as when the sensor core portion of the current transducer is suspended above the current carrying conductor so that it is off-center.

[0096] In a preferred embodiment, the sensor core 10 is circular. In other embodiments, the sensor core 10 may have another shape, such as a square or hexagon. In a preferred variant, the shape of the sensor core is regular.

[0097] The fluxgate ring core 50 is arranged in the gap 13 of the sensor core 10. By the term fluxgate ring core arranged in the gap of the sensor core, it is understood that the fluxgate ring core is located between the first end 11 of the sensor core and the second end 12 of the sensor core. In a preferred variant, the fluxgate ring core is contained within the volume of the gap 13.

[0098] In FIG. 1, the fluxgate ring core is shown oriented with its loops parallel to the loops of the sensor core. This is an illustration of one possible orientation. In another preferred embodiment of the current transformer, the fluxgate ring core is oriented such that the loops of the fluxgate ring core are perpendicular to the loops of the sensor core, thereby causing the first and second excitation coils to be equidistant to the current carrying conductor. In yet other preferred embodiments, the fluxgate ring core 50 may be oriented at any other angle to the orientation of the sensor core 10, i.e., between parallel and perpendicular.

[0099] The fluxgate ring core 50 forms a closed loop. In a preferred embodiment, the loop of the fluxgate ring core 50 is elliptical as shown in FIG. 1. The fluxgate ring core 50 may have other shapes forming a loop. In some preferred embodiments, the fluxgate ring core 50 comprises two substantially parallel elongated portions around which the first excitation coil 61 and the second excitation coil 62 are wound, respectively. Such a shape may be stadium-like, or it may be rectangular with rounded corners, but not semicircular. In yet another preferred variant, the fluxgate ring core 50 may be a loop formed by a square or a rectangle. In another embodiment, the fluxgate ring core is circular. In a preferred embodiment, the elongated portions around which the first excitation coil 61 and the second excitation coil 62 are wound are oriented along the magnetic field of the sensor core 10 when the fluxgate ring core is mounted in the gap 13. In other words, the portion of the fluxgate ring core 50 around which the first excitation coil 61 and the second excitation coil 62 are wound extends substantially in a direction from the first end 11 of the sensor core to the second end 12 of the sensor core.

[0100] In a preferred embodiment, the fluxgate ring core 50 together with any attachment means 20 mechanically connects the sensor core first end 11 and the sensor core second end 12 such that the current transducer 1 forms a loop configuration.

[0101] The first excitation coil 61 is wound around a first portion of the fluxgate ring core 50, and the second excitation coil 62 is wound around a second portion of the fluxgate ring core 50 such that the first coil 61 and the second excitation coil 62 do not overlap. In a preferred embodiment, the first excitation coil 61 and the second excitation coil 62 are located opposite each other, i.e. the spacing between the first excitation coil 61 and the second excitation coil 62 is the same on both sides of the excitation coil, in other words they are evenly spaced on the fluxgate ring core 50. In a preferred embodiment, the number of turns in the first excitation coil 61 is the same as the number of turns in the second excitation coil 62.

[0102] Although not shown in the schematic diagram of FIG. 1, in a preferred embodiment of the current transformer 1, the fluxgate ring coil 50 is mounted in the gap 13 by mounting means 20. Such mounting means 20 may be a holder surrounding the fluxgate ring core 50, it may be a small support covering only a part of the fluxgate ring core 50, or it may be a spacing element that ensures a friction fit of the fluxgate ring core 50 in the gap 13. In some preferred variants, the mounting means 20 are also used as bobbins for the first coil 61 and the second excitation coil 62. In preferred variants, the mounting means 20 are made of a non-magnetic material so that they do not interfere with the magnetic flux.

[0103] In some embodiments of the current transformer 1, there is a first spacer located between the first end 11 of the sensor core and the fluxgate ring core 50, and a second spacer located between the second end 12 of the sensor core and the fluxgate ring core 50. In a preferred variant of the current transformer 1, the first spacer and the second spacer are part of the holding means. In other variants, the first and second spacers may be separate components for controlling the distance between the fluxgate ring core 50 and the end 11 of the first sensor core and the end 12 of the second sensor core, respectively. In a preferred variant of such an embodiment, the thickness of the first spacer does not exceed 50 μm, and the thickness of the second spacer does not exceed 50 μm. In some preferred variants, the thickness of the first spacer is the same as the thickness of the second spacer.

[0104] In other embodiments, the current transformer 1 does not include a spacer. In such embodiments, the retaining means 20 is positioned so as not to separate the fluxgate ring core 50 and the sensor core 10. For example, the retaining means may be connected to the shield and / or the center of the fluxgate ring core 50.

[0105] In some variations, the current transducer 1 may not require a retaining means 20 because the fluxgate ring core 50 is mounted within the gap 13 of the sensor core 10 by direct contact between the fluxgate ring core 50 and the first and second ends 11, 12 of the sensor core.

[0106] The combined system of the fluxgate ring core 50 and the first and second excitation coils 61, 62 connected to the driving means and detection circuitry is considered a magnetometer since it can detect magnetic fields. Other components of the current converter 1 contribute to improving the output of the magnetometer.

[0107] The current carrying conductor 5 carries a primary current and the current transducer 1 is intended to determine the primary current. The primary current generates a primary flux, also called primary magnetic flux. The primary flux is measured by a magnetometer in the current transducer 1 and the primary current can then be calculated based on the detected magnetic flux.

[0108] A magnetic field is generated as the primary current travels along the current carrying conductor 5. The sensor core 10, made of a magnetic material, receives the primary magnetic flux, which then travels along the sensor core 10. As the primary magnetic flux travels along the sensor core 10, it reaches the fluxgate ring core 50, which is located within the gap 13 of the sensor core 10.

[0109] In a preferred embodiment, the fluxgate ring core 50 is made of a material with a high relative permeability of at least 100.000, which is low loss at the excitation frequency of the first excitation coil 61 and the second excitation coil 62. In a preferred variant, the fluxgate ring core 50 is made of a cobalt-based amorphous metal alloy having such characteristics of low loss and high relative permeability. Furthermore, the dimensions, e.g. diameter or cross-sectional area, of the fluxgate ring core 50 are small compared to the diameter or cross-sectional area of ​​the sensor core 10, when it is required to position the fluxgate ring core 50 in the gap 13 of the sensor core 10.

[0110] In a preferred embodiment, the current driven through the fluxgate ring core 50 is sufficient such that the excitation flux drives the fluxgate ring core 50 into deep magnetic saturation. In a preferred embodiment, an alternating current is used to drive the excitation flux, and the induced saturation thereby also alternates. The alternating direction of saturation results in low thermal offset drift in the fluxgate ring core 50.

[0111] Due to the material and dimensions of the fluxgate ring core 50 which result in low reluctance in the fluxgate ring core 50, the magnetic flux in the sensor core 10 flows to the fluxgate ring core in a manner that concentrates the primary magnetic flux in the fluxgate ring core 50. In a preferred embodiment, the relative permeability of the sensor core 10 is lower than that of the fluxgate ring core 50, thereby further enhancing the effect of concentrating the magnetic flux in the fluxgate ring core 50. The sensor core may be made of, for example, Mu metal.

[0112] 2 is a schematic diagram of the current transducer 1 with further components. The figure shows a portion of the sensor core 10 in the region of the gap 13, where the fluxgate ring core 50 is shown and positioned in a tangential cross section. The coils and the circuit are shown as electronic circuit diagrams.

[0113] The current transducer 1 of Fig. 2 still comprises a sensor core 10 and a fluxgate ring core 50 located in the gap 13 of the sensor core 10. An excitation flux is induced in the fluxgate ring core 50 via a first excitation coil 61 and a second excitation coil 62 driven by a driving means 35, which in a preferred variant is a modulator for modulating a signal. The first excitation coil 61 and the second excitation coil 62 are further connected to a detection circuit 30, which is able to determine the difference in the currents in the first excitation coil 61 and the second excitation coil 62 by using a second harmonic detection.

[0114] Both the first excitation coil 61 and the second excitation coil 62 are connected to a drive means 35. In a preferred embodiment, the drive means 35 is a modulator that controls the amplitude and frequency of the alternating current driven through the first excitation coil 61 and the second excitation coil 62, respectively. The current driven through the first excitation coil 61 and the second excitation coil 62 generates an excitation flux that is induced in the fluxgate ring core 50. Due to the symmetry of the magnetometer system, the first portion of the fluxgate ring core around which the first excitation coil 61 is wound will reach saturation at the same time as the second portion of the fluxgate ring core around which the second excitation coil 62 is wound in the absence of primary magnetic flux. When the magnetic flux from the primary current in the current carrying conductor 5 is conducted from the sensor core 10 into the fluxgate ring core 50, the magnetic flux from the primary current is added to the excitation magnetic flux in one of the excitation coils 61, 62 and subtracted from the excitation magnetic flux in the other of the excitation coils 61, 62, causing the first excitation coil 61 and the second excitation coil 62 to reach saturation at different times.

[0115] When the fluxgate ring core 50 is subjected to a primary magnetic flux, the alignment of the primary magnetic flux is different with respect to the excitation magnetic flux induced by the first excitation coil 61 and the second excitation coil 62. Due to the difference in alignment, the primary magnetic flux increases the total magnetic flux in one portion of the fluxgate ring core 50 and decreases it in another portion of the fluxgate ring core 50, resulting in a difference in the time it takes before achieving deep saturation on each side.

[0116] Both the first excitation coil 61 and the second excitation coil 62 are connected to the detection circuit 30. The detection circuit uses second harmonic detection to detect the difference in the current in the first excitation coil 61 and the second excitation coil 62. The second harmonic detection increases the sensitivity of the current transformer 1 while minimizing the effects of temperature drift. When the first excitation coil 61 and the second excitation coil 62 operate on the same fluxgate ring core 50, temperature induced characteristic changes are nullified when the two signals are subtracted.

[0117] In a preferred variant, the detection circuit 30 comprises further processing capabilities acting as a processing device capable of calculating the primary current based on the second harmonic detection.

[0118] It is an advantage of the present disclosure that sensor cores having different sizes may be used with the same magnetometer components, i.e., fluxgate ring core 50 and excitation coils 61, 62, so that the magnetometer components can be used and fabricated in a similar manner for current transducers that can be used to measure primary currents in various types of current carrying conductors.

[0119] Sensor cores 10 may be available in many different sizes capable of enclosing different current carrying conductors 5. In a preferred embodiment, the diameter of the sensor core opening 15 is in the range of 0.1 to 5 m, more preferably in the range of 0.2 to 1 m, such as about 0.5 m.

[0120] In a preferred embodiment, the dimensions of the fluxgate ring core 50 are small compared to the dimensions of the sensor core 10 because this reduces the sensitivity of the magnetometer to noise. In a preferred embodiment, the diameter of the fluxgate ring core 50 is in the range of 0.5-50 mm, such as 1-10 mm, more preferably in the range of 5-10 mm, such as 7 mm.

[0121] In the preferred embodiment of the current transformer 1 shown in FIG. 2, the sensor core 10, the fluxgate ring core 50, and the first and second excitation coils 61 and 62 are surrounded by a shield 70. In the schematic cross-section of FIG. 2, an inner shield core 71 and an outer shield core 72 are shown. It should be noted that the schematic is not to scale and that, for example, the thickness of the shield cores 71, 72 relative to the sensor core 10 and the spacing between the shield 70 and the sensor core 10 may differ from those shown, just as they may differ for different preferred embodiments of the current transformer 1. It should be understood that the shield 70 further comprises a top shield plate and a bottom shield plate so that the sensor core 10, the fluxgate ring core 50, and the first and second excitation coils 61 and 62 are completely surrounded. In one variant, the shield 70 may be made of four parts that can be fixedly or removably attached around the previously mentioned components. In other variations, some of the parts of the shielding 70 may be fixedly connected, while others, for example the inner shielding core 71 and top shielding plate formed by integral molding, may be removable, as may the outer shielding core 72 and bottom shielding plate, and these two parts may be removably mounted around the sensor core 10, the fluxgate ring core 50 and the first and second excitation coils 61, 62 so that the shielding 70 can be removed to access the shielded components, for example for maintenance.

[0122] The shield 70 is intended to protect the other components from external magnetic fields, such as magnetic fields from other electronic devices and / or the Earth's magnetic field, so that the magnetic field sensed by the magnetometer is the magnetic field generated by the primary current.

[0123] In a preferred embodiment, the shield 70 is made of a material with a high saturation magnetic flux density. If the shield 70 is fully saturated by an external magnetic field, magnetic flux may pass through the shield 70 and disturb the magnetometer, so it is preferred to make the shield from a material with a saturation magnetic flux density high enough to withstand the external magnetic field without reaching saturation. Very often, materials with high saturation magnetic flux density have low relative permeability, so in some preferred variants of the current transducer 1, the shield 70 is made of a material with a relative permeability lower than that of the sensor core 10 and that of the fluxgate ring core 50. Such a preferred material used in some variants is magnetic steel sheet. In some variants, the shield 70 is made of multiple materials, for example top and bottom shield cores made of different materials than the inner and outer shield cores 71 and 72, such as top and bottom shield cores cut from a plate, and the inner and outer shield cores made of wound ribbons.

[0124] In preferred embodiments, the shield is mounted such that the distance between the shield 70 and the sensor core 10 and / or fluxgate ring core 50 is at least twice the thickness of the shield (note that FIG. 2 is not to scale). In some preferred embodiments, the distance between the shield 70 and the sensor core 10 and / or fluxgate ring core 50 is at least 1 mm. In some variations, the distance is achieved by at least two distance pieces made of a non-magnetic material, which are placed between the shield 70 and the sensor core 10 to maintain a fixed distance between the shield 70 and the sensor core 10. The distance between the shield 70 and the sensor core 10 and / or fluxgate ring core 50 limits the risk of magnetic flux transferring from the shield 70 to the sensor core 10 and / or fluxgate ring core 50, which would otherwise make the shield 70 inefficient.

[0125] In a preferred embodiment shown in FIG. 2, the current transformer 1 further comprises a compensation coil 65. The compensation coil 65 is wound around the shield 70. In a preferred embodiment, the compensation coil 65 is wound around all the sensor cores such that the shield is covered with evenly spaced turns of the compensation coil 65. In a more preferred embodiment, the compensation coil 65 is wound evenly around the shield in the region of the fluxgate ring core 50. The turns of the compensation coil may be less evenly distributed around the region of the sensor core, for example such that the spacing between the turns is greater around the region of the sensor core than around the region of the fluxgate ring core 50. In some embodiments where the current transformer 1 is a split-core current transformer, it may be necessary to increase the distance between the turns of the compensation coil 65 that are close together in the first and second splits, respectively, to be able to open up the split-core current transformer.

[0126] In a preferred embodiment, the compensation coil is connected to the detection circuit 30 to determine that the compensation current driving the compensation flux of the compensation coil 65 is proportional to the calculated primary current. By determining the compensation current based on the calculated primary current, it is possible to match the compensation flux to the primary flux so that it exceeds the primary flux so that the total flux sensed is zero. Operating the magnetometer with zero flux allows the magnetometer to function when it detects the primary flux, which would otherwise be too high and saturate the magnetometer and be unable to detect flux. The compensation coil 65 is particularly important for magnetometers operating with a fluxgate ring core 50 because such magnetometers are non-linear and saturate more quickly than, for example, a linear magnetometer core.

[0127] In the preferred embodiment shown in FIG. 2, the current converter 1 further comprises a feedback coil 67. In a preferred variant, the feedback coil 67 is wound around the shield 70. The feedback coil 67 senses the alternating magnetic flux combined in the system. The detected signal from the feedback coil 67 is added to the magnetometer signal, thereby amplifying the signal of the alternating magnetic flux. The feedback coil 67 thereby increases the accuracy of the magnetic flux detected at mid-frequency with fluctuations. The magnetometer is limited to detecting magnetic flux, where the primary current is a direct or alternating current fluctuating at low frequency, since it cannot detect the primary flux if the fluctuations are too fast with respect to the frequency of the excitation current driving the excitation flux. The frequency of the excitation flux is further limited by the saturation flux density and the amplitude of the excitation current, since the fluxgate ring core 50 needs to reach saturation in each direction within each period.

[0128] In one embodiment with both the compensation coil 65 and the feedback coil 67 wrapped around the outside of the shield 70, the compensation coil 65 may be divided into two spaced apart segments, with the feedback coil 67 wrapped around the shield in the area between the segments of the compensation coil 65. In another embodiment with both the compensation coil 65 and the feedback coil 67 wrapped around the outside of the shield 70, the compensation coil 65 may be wrapped around the shield 70 first, and the feedback coil 67 may be wrapped around both the shield 70 and the compensation coil 65 such that the feedback coil 67 is wrapped over the compensation coil 65. In yet another embodiment, the feedback coil 67 may be wrapped around the shield first, and the compensation coil 65 may be wrapped around both the shield and the compensation coil 67 such that the compensation coil 65 is wrapped over the compensation coil 67.

[0129] In all embodiments in which both a compensation coil 65 and a feedback coil 67 are present, the coils are kept electrically separated even when the coils are in physical contact.

[0130] In other embodiments, it is possible to have only one or some combination of the additional components, for example only the shielding 70 without the compensation coil 65 or the feedback coil 67, or a shielding combined with the compensation coil 65 but not including the feedback coil 67.

[0131] In a preferred embodiment, not shown in any of the figures, the current transducer 1 comprises a demagnetizing circuit. The demagnetizing circuit is connected to the compensation coil 65 and allows to activate and drive a demagnetizing signal via the compensation coil 65. The demagnetizing signal is an alternating current with a high amplitude capable of cancelling the residual magnetic flux in the magnetic material of the current transducer 1. In a preferred variant, the demagnetizing signal is activated manually by the user, since the user can decide when the demagnetizing signal is needed and when it has little negative effect on the use of the current transducer 1, for example when it is not important for monitoring the primary current.

[0132] In some embodiments, the current transducer 1 may include an outer shell 80 of a non-magnetic material, such as a plastic material. This outer shell encloses the components of the current transducer 1 to protect it from mechanical wear from the environment as well as electrical signals, and to facilitate user handling of the current transducer 1. The outer shell may enclose, for example, the sensor core 10, the fluxgate ring core 50, the shield 70, and all coils and circuitry. The outer shell may further include a display device for reading the output of the current transducer 1, and a port for connecting to the current transducer for remote display and / or control, such as to initiate a degaussing signal.

[0133] In a preferred embodiment, the current transformer 1 is a split-core current transformer. By split-core current transformer, a system is understood in which the closed loop of the sensor core 10 and the fluxgate ring core 50 are separated so as to be reattachable. This allows the opening of the loop of the current transformer 1, which can then be placed around the current-carrying conductor 5. The current transformer 10 can then be closed around the current-carrying conductor 5. In one variant, the open end of the sensor core may be structured to increase the surface area, where the parts on either side of the split are connected. In other variants, the split may comprise a simple plane. In some preferred variants, the shield and / or the outer shell may comprise connection means, such as snap connections or latches, to releasably secure the split-core current conductor in the closed configuration.

[0134] FIG. 3 shows the split-core current transformer 1 in a partially cut-away view, illustrating the various components and how they are arranged relative to each other.

[0135] FIG. 3 reveals how the sensor core 10 is mounted such that it is surrounded by a shield 70, which in turn is surrounded by a shell 80. The sensor core 10 is mounted such that it is spaced apart from the shield 70 so that there is no direct physical contact between the sensor core 10 and the shield 70. In a preferred embodiment, the compensation coil 65 is mounted wrapped around the shield 70 and is therefore located between the shield 70 and the shell 80. In a preferred embodiment, the feedback coil 67 is mounted wrapped around the shield 70 and is therefore located between the shield 70 and the shell 80. In a more preferred embodiment, the current transformer 1 comprises both the compensation coil 65 and the feedback coil 67 located between the shield 70 and the shell 80.

[0136] The fluxgate ring core with the first excitation coil 61 and the second excitation coil 62 wound therearound is mounted within the gap of the sensor core 10 and held in place by mounting means 20.

[0137] The current transducer 1 shown in FIG. 3 is a split core variant in a closed configuration. A single split 2 is visible in the cutaway view, where parts of the current transducer 1 can be separated and reattached, thus allowing the current transducer to be opened. In the preferred embodiment shown, the split 2 is located away from the magnetometer. The split 2 therefore separates the sensor core 10, shield 70 and shell 80 without disturbing the magnetometer components.

[0138] FIG. 4 shows a schematic diagram of the components of a current transformer 1 with both a first fluxgate ring core 50 and a second fluxgate ring core 50' shown in cross section.

[0139] The sensor core 10 is made of a magnetic material and forms a loop interrupted by a first gap 13 and a second gap. The first and second gaps are located directly opposite each other, i.e. at diagonally opposite ends of the sensor core 10. By loop is understood a structure whose beginning is connected to its end to form an enclosure. By loop interrupted by a gap is understood a structure that forms a loop but from which a segment has been removed. By gap is understood the area between the first end 11 of the sensor core and the second end 12 of the sensor core such that gap 13 is the volume that would be occupied by the missing segment of the sensor core if the sensor core 10 were a closed loop with a continuous cross-sectional area from the first end 11 of the sensor core to the second end 12 of the sensor core. This applies to both the first and second gaps, which are the volumes occupied by the segments of sensor core 10 occupying the space between the third and fourth ends of sensor core 10, as the sensor core is divided into two symmetrical segments by the first and second gaps.

[0140] The sensor core 10 is arranged around the current carrying conductor 5 such that a portion of the current carrying conductor 5 is located within an opening 15 of the sensor core 10. By opening 15 of the sensor core 10 is understood the area bounded by the loop of the sensor core 10.

[0141] In a preferred embodiment, the sensor core 10 is circular. In other embodiments, the sensor core 10 may have another shape, such as a square or hexagon, as long as the sensor core 10 is of a regular shape that can be divided into two symmetrical parts by a first and a second gap disposed directly opposite each other, such that the effect of the external fields applied to the sensor core by the first fluxgate ring core 50 disposed in the first gap 13 of the sensor core 10 and the second fluxgate ring core 50' disposed in the second gap of the sensor core is reduced.

[0142] The preferred placement and orientation of the first and second fluxgate ring cores within the first and second gaps is the same as discussed for other embodiments of the current transformer.

[0143] In a preferred embodiment, the first fluxgate ring core 50 and the second fluxgate ring core 50' are constructed in a similar manner, including the geometry, materials and placement of the excitation coils. In such an embodiment, the first fluxgate ring core 50 and the second fluxgate ring core 50' with the excitation coils on the respective fluxgate ring cores may be of the same construction as described for other embodiments of the present current transformer.

[0144] In a preferred embodiment, the first fluxgate ring core 50 and the second fluxgate ring core 50' together with any attachment means mechanically connect the ends of the segments of the sensor core 10 such that the current transducer 1 forms a loop configuration. The attachment of the first fluxgate ring core 50 and the second fluxgate ring core 50' may be done in the same manner or in any of the ways described for the other embodiments of the invention.

[0145] Some embodiments of the current converter having first and second fluxgate ring cores may be of the split core type current converter variety. In such embodiments, the split is preferably located as far away as possible from the first and second fluxgate ring cores and rotated 90 degrees along the loop of the current converter relative to the fluxgate ring cores so that the split is equidistant from the fluxgate ring cores. This is preferred when the shield is separated at the split, and therefore the beneficial effect of the shield is most important in the fluxgate ring core when it remains uninterrupted in that area.

[0146] The operating principle behind the present current converter embodiment with two fluxgate ring cores is the same as described for the other embodiments of the present invention. The excitation coils may be connected in series, for example a first excitation coil of a first fluxgate ring core may be connected in series with a third excitation coil of a second fluxgate ring core while a second excitation coil is connected in series with a fourth excitation coil, so that they may be connected to a common drive means and detection circuit to form a common magnetometer. An excitation current is driven through the first and second fluxgate ring cores in the same manner as described for the other embodiments of the present invention, preferably in an amount sufficient to drive the first and second fluxgate ring cores into deep magnetic saturation.

[0147] List of References 1 Current transducer 5 Current-carrying conductors 10 Sensor Core 11 First end of sensor core 12 Second end of sensor core 13 Gap 15 Opening 30 Detection circuit 35 Driving means 50 Fluxgate Ring Core 50' 2nd Fluxgate Ring Core 61 First exciting coil 62 Second exciting coil 63 Third excitation coil 64 4th excitation coil 65 Compensation coil 67 Feedback coil 70 Shield 71 Inner shield core 72 Outer shield core

Claims

1. a sensor core shaped as a loop interrupted by a gap for concentrating magnetic flux from a current-carrying conductor; a fluxgate ring core for sensing the magnetic flux, the fluxgate ring core being disposed within the gap of the sensor core; a first excitation coil wound around a first portion of the flux-gate ring core for generating an excitation magnetic flux in the ring core and for detecting the magnetic flux in the current-carrying conductor; a second excitation coil wound around a second portion of the flux-gate ring core for generating an excitation magnetic flux in the ring core and detecting the magnetic flux in the current-carrying conductor; a driving means for driving an excitation current through the first excitation coil and the second excitation coil; a detection circuit connected to the first excitation coil and the second excitation coil for detecting electronic signals of the first and second excitation coils; 1. A current transducer for measuring magnetic flux from a current-carrying conductor, comprising:

2. 2. The current converter of claim 1, wherein the detection circuit comprises a second harmonic detector for demodulating a difference between the currents in the first excitation coil and the second excitation coil.

3. 2. The current transformer of claim 1, wherein the fluxgate ring core is made of a magnetic material having a relative permeability of at least 100,000.

4. 4. The current transformer of claim 3, wherein the fluxgate ring core is made of a cobalt-based amorphous metal alloy.

5. 2. The current transducer of claim 1, wherein the sensor core is made of a magnetic material having a relative permeability lower than that of the fluxgate ring core.

6. The current transducer of claim 5 , wherein the sensor core is made of Mu metal.

7. 2. The current converter of claim 1, further comprising a shield to provide protection from external magnetic fields and reduce noise, the shield surrounding the sensor core, the fluxgate ring core, the first excitation coil, and the second excitation coil together.

8. 8. The current transducer of claim 7, wherein the shield is made of a material having a relative permeability lower than the relative permeability of both the sensor core and the fluxgate ring core.

9. 9. The current transformer of claim 8, wherein the shield is made of magnetic steel sheet.

10. 8. The current converter of claim 7, further comprising a compensation coil for inducing a canceling current and maintaining near-zero magnetic flux in the flux-gate ring core, the compensation coil being wrapped around the shield around the sensor core.

11. 11. The current transformer of claim 10, wherein the current transformer comprises a degaussing circuit for removing residual magnetic flux in the current transformer, the degaussing circuit being connected to the compensation coil.

12. a second fluxgate ring core for sensing the magnetic flux, the second fluxgate being disposed directly opposite the fluxgate ring core and located within a second gap of the sensor core; a third excitation coil for generating an excitation magnetic flux in the second flux-gate ring core and detecting the magnetic flux in the current-carrying conductor; a fourth excitation coil for generating an excitation magnetic flux in the second fluxgate ring core and detecting the magnetic flux in the current-carrying conductor; The current transducer of claim 1 , comprising:

13. The current transformer of claim 1 , wherein the current transformer is a split-core current transformer.

14. 10. The current transformer of claim 1, wherein the current transformer comprises a feedback coil to increase the accuracy of the current transformer.

15. providing a current-carrying conductor for carrying the primary current; providing a current transducer comprising a sensor core, a fluxgate ring core, a first excitation coil and a second excitation coil; disposing the sensor core around the current-carrying conductor so that the sensor core can sense magnetic flux emanating from the current-carrying conductor; connecting the first excitation coil and the second excitation coil to a driving means and driving an excitation current through the first and second excitation coils such that an excitation flux is induced in the fluxgate ring core; connecting the first excitation coil and the second excitation coil to a detection circuit and determining a difference in current through the first excitation coil and the second excitation coil using second harmonic detection; calculating the primary current in the current-carrying conductor based on a second harmonic detection of the current difference; 1. A method for detecting a primary current flow through a current-carrying conductor, comprising:

16. 16. The method of claim 15, further comprising: driving an excitation current through third and fourth excitation coils provided within a second fluxgate ring core of the current transformer such that an excitation flux is induced in the second fluxgate ring core; and connecting the third and fourth excitation coils in series with the first and second excitation coils such that the third and fourth excitation coils are connected to the detection circuit, thereby determining a current difference between a first combined system of the first and third excitation coils and a second combined system of the second and fourth excitation coils.

17. The method of claim 15 , wherein the excitation current driven through the first and second excitation coils is an alternating current.

18. 16. The method of claim 15, further comprising providing a compensation coil around the sensor core, driving a compensation current through the compensation coil, and determining the compensation current based on an output of the detection circuit such that a primary magnetic flux of the primary current is compensated by the compensation magnetic flux of the compensation current through the compensation coil.

19. 20. The method of claim 18, further comprising transmitting a degaussing signal through the compensation coil to eliminate residual magnetic flux present in the material of the current transformer.

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