Device for measuring a current in a conductor, method for producing such a device and method for measuring a current in a conductor

Abstract

The invention relates to a device for measuring a current in a conductor, wherein the device comprises at least a first and a second coil, wherein the at least two coils have an identical coil body and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the at least two coils are arranged spatially one above the other in an electrically connected series and differ in the orientation of their turns, so that the at least two coils form a super coil, wherein the conductor is guided through the super coil to measure the current.

Description

[0001] The invention relates to a device for measuring a current in a conductor, a method for producing a super coil for measuring a current in a conductor and a method for measuring a current in a conductor.

[0002] Coils are used to measure alternating currents. The induced voltage, which is caused both by the time-varying magnetic field of the current to be measured, for example the current in a primary conductor, and by external time-varying magnetic fields such as external fields, is used as the sensor variable. Rogowski coils are usually constructed as ring-shaped structures and arranged around the primary conductor in such a way that the magnetic field of the primary current perpendicularly penetrates as many turns as possible. Turns refer to the areas spanned by the turns of the coil. The closed ring-shaped structure with a constant product of cross-sectional area and turns density minimizes the influence of external magnetic fields as much as possible. In general, both the cross-sectional area and the turns density are constant along the Rogowski coil.

[0003] In contrast to the magnetic field of the measuring current or primary current, the external magnetic fields can have any spatial orientation. Due to its symmetry, an ideal Rogowski coil would be virtually insensitive to external fields. In practice, real Rogowski coils exhibit significant sensitivity to time-varying external magnetic fields. Depending on the winding pattern of the Rogowski coil, time-varying magnetic field components parallel to the Rogowski coil's rotation axis and not originating from the primary current can lead to a significant output signal from the Rogowski coil. This then results in an inaccurate current measurement.

[0004] In simple winding schemes, such as those used for very small Rogowski coils due to limitations of manufacturing technology, time-varying external fields aligned parallel to the primary current axis have the greatest influence on the Rogowski coil's output signal. However, for measuring alternating currents with an RMS value of less than 100 A in low-voltage applications, very small Rogowski coils are necessary to meet the requirements for a compact design of the measuring devices.

[0005] In addition to inductive coupling, capacitive coupling, which is caused by time-varying electric fields, also plays an important role. In general, the conductive winding of the Rogowski coil forms a more or less complex capacitive structure with all the conductive surfaces in the surrounding area. Due to the relatively large distances between the winding of the Rogowski coil and the conductive surfaces, such as the surface of the primary conductor, the coupling capacitances are usually very low. However, since the potential difference between these surfaces is very large compared to the measuring voltage at the ends of the Rogowski coil, even normal operating conditions in low-voltage networks can lead to significant measurement errors when measuring current with Rogowski coils.

[0006] Typically, the described problem has been solved by specific winding schemes for Rogowski coils. These winding schemes involve a certain amount of effort and significantly increase the complexity of the manufacturing process. However, for very small, multi-layer Rogowski coils, it is currently technically impossible to implement these winding schemes with sufficient quality due to their increased manufacturing complexity. Accordingly, Rogowski coils with an outer diameter of less than approximately 30 mm exhibit significantly increased measurement errors in the presence of corresponding interference fields.

[0007] In general, alternating currents with an effective value of less than 100 A can also be measured with a toroidal transformer in low-voltage applications. While these have some advantages over Rogowski coils, they also have some disadvantages, such as higher costs, greater weight, and a larger design or significantly larger volume.

[0008] The problem of capacitive interference was solved in the past by integrating shielding surfaces into the design of Rogowski coils. These shielding surfaces were kept at the coil's measuring potential, thus providing the necessary countercharges on the surface to shield the electric field. Since good shielding must not influence the time-varying magnetic field in the Rogowski coil, while simultaneously avoiding a significant increase in the space required for the Rogowski coil, the use of capacitive shields in small Rogowski coils is subject to certain limitations.

[0009] It is therefore an object of the invention to provide an alternative device for measuring a current which compensates for or improves the disadvantages described.

[0010] The object is achieved according to the invention by the device for measuring a current in a conductor according to claim 1. Alternative embodiments of the device according to the invention are specified in subclaims 2 to 4. The object is also achieved by the method for producing a super coil for measuring a current in a conductor according to claim 5. Advantageous embodiments of the method according to the invention are specified in claims 6 to 13. The object is also achieved by the method for measuring a current in a conductor according to claim 14.

[0011] The device for measuring a current in a conductor according to claim 1 comprises at least a first and a second coil, wherein the at least two coils have an identical coil body and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the at least two coils are arranged electrically connected in series spatially one above the other and differ in the orientation of their turns, so that the at least two coils form a super coil, wherein the conductor is guided through the super coil to measure the current.

[0012] The advantage here is that the device according to the invention can reduce interference coupling and, overall, allow for more precise current measurements. Another advantage is that the device according to the invention has a small installation space and a small volume, making it particularly advantageous for use in low-voltage applications.

[0013] In one embodiment, the coils have inputs and outputs and these inputs and outputs are rotated by 180° relative to each other.

[0014] In a further embodiment of the device according to the invention, the at least two coils are electrically connected to one another in their outer winding layers and the total signal is determined between the inner winding layers.

[0015] In a further embodiment, the connection of the outer winding layers is earthed.

[0016] The inventive method for producing a super coil for measuring a current in a conductor according to claim 5 comprises the steps: - Winding a first coil; - Winding a second coil, wherein the two coils have an identical coil body and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the two coils differ in the orientation of their turns; - Combining the first coil and the second coil to form a super coil, wherein the two coils are arranged spatially one above the other and electrically connected in series.

[0017] In one embodiment of the method, the first coil is wound right-handed counterclockwise, and the second coil is wound right-handed clockwise, wherein during assembly the inputs and outputs of the second coil are swapped or the second coil is tilted by 180°.

[0018] In one embodiment of the method, the first coil is wound right-handed counterclockwise and the second coil is wound left-handed clockwise, whereby during assembly the inputs and outputs of the second coil are swapped and the second coil is tilted by 180°.

[0019] In one embodiment of the method, the first coil is wound right-handed clockwise and the second coil is wound right-handed counterclockwise, whereby during assembly the inputs and outputs of the second coil are swapped and the second coil is tilted by 180°.

[0020] In one embodiment of the method, the first coil is wound right-handed clockwise and the second coil is wound left-handed counterclockwise, whereby during assembly the inputs and outputs of the second coil are swapped and the second coil is tilted by 180°.

[0021] In one embodiment of the method, the first coil is wound left-handed clockwise and the second coil is wound left-handed counterclockwise, wherein during assembly the inputs and outputs of the second coil are swapped or the second coil is tilted by 180°.

[0022] In one embodiment of the method, the first coil is wound left-handed clockwise and the second coil is wound right-handed counterclockwise, whereby during assembly the inputs and outputs of the second coil are swapped and the second coil is tilted by 180°.

[0023] In one embodiment of the method, the second coil is wound counterclockwise in a left-handed manner and the second coil is wound clockwise in a left-handed manner, wherein the inputs and outputs of the second coil are swapped during assembly or the second coil is tilted by 180°.

[0024] In one embodiment of the method, the first coil is wound counterclockwise in a left-handed manner and the second coil is wound clockwise in a right-handed manner, whereby the inputs and outputs of the second coil are swapped during assembly and the second coil is tilted by 180°.

[0025] The method for measuring a current in a conductor according to claim 14 comprises the steps: - Providing a super coil according to any one of the preceding claims; - Passing a conductor through the super coil; and - Measuring the current in the super coil.

[0026] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the description of the embodiments which are explained in more detail in connection with the figures.

[0027] Showing: Fig. 1A coil right-handed counterclockwise, Fig. 1B coil right-handed clockwise, Fig. 1C coil left-handed counterclockwise and Fig. 1D coil wound left-handed clockwise; Fig. 2 super coil made of first coil and second coil and conductor; Fig. 3 Equivalent circuit of a coil with four winding layers; Fig. 4 first coil and second coil with electrically connected outer winding layers; Fig. 5 Equivalent circuit of the two coils according to Fig. 4; Fig. 6 first coil and second coil with electrically connected outer winding layers which are grounded; and Fig. 7 Methods for measuring a current in a conductor.

[0028] Fig. 1A to 1D shows coils 110; 120; 130; 140. The coil 110 is from the Fig. 1A is wound right-handed in a counterclockwise direction. This means that starting from an input 111, the wire is guided below the coil body 151, upwards inside and then again above the coil body 151 until the output 112 is reached. The right-handed winding results in the representation of the Fig. 1A, that the windings move counterclockwise. If one looks at the coil body 151 of the coil 110 from the side, so that the windings are wound towards the observer, it can be seen that the windings are oriented counterclockwise. In the illustration of the Fig. 1A, this view is the top view of the side of the coil 110.

[0029] Fig. 1B also shows a coil 120 comprising a coil former 152 and windings from an input 121 to an output 122. The winding is again right-handed, so that the windings move counterclockwise on the coil former 152. If the observer again looks at the coil from the side, so that the windings move toward the observer, the profile of the coil former 152 shows that the windings are arranged clockwise around it.

[0030] In the Fig. 1C and Fig. 1D shows the coils 130; 140, each wound left-handed. Fig. 1C the winding is oriented left-handed counterclockwise and in the Fig. 1D the turns are oriented left-handed clockwise.

[0031] The coil 110 of the Fig. 4A can be inserted into the coil 130 of the Fig. 1C either by swapping inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 or by tilting by 180°. The same applies to coil 120 of the Fig. 1B and the coil 140 of the Fig. 1D.

[0032] The problem of inductive and capacitive interference is solved by using at least two Rogowski coils 110; 120; 130; 140. It should be noted that the at least two coils 110; 120; 130; 140 used should be constructed as identically as possible. The at least two coils 110; 120; 130; 140 have an identical coil body 151; 152; 153; 154 and were wound with the same wire type, the same number of windings, and the same number of windings.

[0033] To compensate for inductive interference, at least two coils 110; 120; 130; 140 are combined to form a super coil 200, as described in the Fig. 2. At least two coils 110; 140 are electrically connected in series and arranged one above the other, with the two coils 110; 140 differing in the orientation of their windings. To measure the current in a conductor 500, the current must be passed through the super coil 200. The output 142 of the coil 140 is connected to the input 111 of the coil 110, thereby creating the series connection. The coil body 151; 152; 153; 154 is toroidal, and the wire is, for example, passed through the torus and then around the outside and in the opposite direction to the corresponding coil partner, i.e., first around the outside and then back inside. The other windings are placed in the same direction around the coil body 151; 152; 153; 154. Subsequently, one of the coils is tilted by 180°, which, for example, creates a right-handed clockwise combination according to Fig. 1B coil 120 and left-handed counterclockwise accordingly Fig. 1C coil 130 is created.

[0034] In the other case, the direction of the winding of the torus-shaped coil body 151; 152; 153; 154 is varied. The winding direction of the individual turns is maintained. The wire is fed through the inside of both coils and returned to the outside. However, the subsequent turns are wound in different directions around the torus. For example, the combination right-handed counterclockwise is created, as shown in the illustration. Fig. 1A coil 110 and left-handed clockwise as shown in 1D in coil 140.

[0035] In Rogowski coils with one winding layer, the winding schemes are right-handed counterclockwise ( Fig. 1A) and left-handed counterclockwise ( Fig. 1C) can be converted into one another by reversing the polarity or tilting by 180°. The same applies to the right-handed winding pattern pair in a clockwise direction ( Fig. 1B) and left-handed clockwise ( Fig. 1D). With multiple winding layers, these pairs of winding schemes differ in terms of external field sensitivity and capacitive coupling. These properties can be used to compensate for the respective interference couplings. Polarity reversal refers to the swapping of input and output.

[0036] According to the Fig. 2 Two Rogowski coils, whose windings have the same orientation, but whose coil bodies are wound in different directions (e.g., first coil 110 right-handed counterclockwise and second coil 140 left-handed clockwise) mounted one above the other, for example, on the top and bottom of a circuit board. Both coils 110; 140 are rotated by 180° relative to each other as shown in the Fig. 2, a good compensation of the interference couplings caused by inaccuracies in manufacturing by external magnetic fields is achieved when both coils 110; 140 are connected in series.

[0037] By mounting the two coils 110; 140 one above the other, interference from magnetic fields oriented parallel to the current is reduced, as a right-handed coil is combined with a left-handed coil. Rotating the terminals (inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142) by 180° reduces interference from magnetic fields perpendicular to the conductor axis.

[0038] If, in addition to the magnetic and inductive couplings, the electrical and capacitive couplings are also to be compensated, it is important that the two coils 110; 120; 130; 140 are also manufactured and connected in such a way that the potential difference is always measured between the inputs of the windings of the two coils of the inner layers or the ends of the two coils. Measurement between the inputs is particularly advantageous. Since in a multi-layer coil only the first layer is wound directly onto the coil body 151; 152; 153; 154 and the subsequent layers onto the respective preceding layers, the outer layers shield part of the electric field. The outer layers themselves are most exposed to the electric field, so that - assuming an equal number of windings per layer - the outer layers have a greater coupling capacitance to the primary conductor, see the circuit diagram of the Fig. 3 with the layer L1 on the coil body and the layers L2, L3 and L4 built on it.

[0039] The advantage here is that at least two coils 110; 120; 130; 140 are electrically connected to each other in their outer winding layers L4, and the total signal is determined between the inner winding layers L1. Furthermore, the connection of the outer winding layers L4 can be grounded. This is described in the Fig. 5 and Fig. 6, where Fig. 5 the electrical equivalent circuit of the two coils 110; 140 of the Fig. 6 is shown with the grounding of the connection of the outer bonding layers L4.

[0040] It is important that the second coil is wound, for example, with the opposite winding direction to the first coil but in the same winding direction. Next, the input and output of the second coil are swapped, and both coils are mounted one above the other. Now, the output of coil 1 is connected to the new input of coil 2, as shown in the Fig. 3 and Fig. 4, the signals of the measuring current are added, but the capacitive and inductive interference couplings of both coils are subtracted. The compensation of the capacitive interference couplings in the output signal of the coil arrangement can be achieved by grounding the connecting line between the two coils, as shown in Fig. 5 and Fig. 6, can be further improved. The effect of reducing capacitive interference by combining coils with symmetrical coupling capacitances can be seen from the Fig. 5. The effect of reducing capacitive interference by combining coils with the shielding of the grounded outputs can be clearly seen from Fig. Both effects can also be combined.

[0041] The inventive method 1000 for producing a super coil 200 for measuring a current in a conductor 500 comprises the steps: - Winding a first coil 110; 120; 130; 140; - Winding a second coil 110; 120; 130; 140, wherein the two coils 110; 120; 130; 140 have an identical coil body 151; 152; 153; 154 and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the two coils 110; 120; 130; 140 differ in the orientation of their turns; - Assembling the first coil 110; 120; 130; 140 and the second coil 110; 120; 130; 140 to form a super coil 200, wherein the two coils 110; 120; 130; 140 are arranged spatially one above the other, electrically connected in series.

[0042] The first coil 110; 120; 130; 140 can be wound right-handed counterclockwise and the second coil 110; 120; 130; 140 can be wound right-handed clockwise, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped or the second coil 110; 120; 130; 140 is tilted by 180°.

[0043] Likewise, the first coil 110; 120; 130; 140 can be wound right-handed counterclockwise and the second coil 110; 120; 130; 140 can be wound left-handed clockwise, whereby when joining the second coil, the inputs and outputs are swapped and the second coil is tilted by 180°.

[0044] Likewise, the first coil 110; 120; 130; 140 can be wound right-handed clockwise and the second coil 110; 120; 130; 140 can be wound right-handed counterclockwise, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped and the second coil is tilted by 180°.

[0045] Likewise, the first coil 110; 120; 130; 140 can be wound right-handed clockwise and the second coil 110; 120; 130; 140 can be wound left-handed counterclockwise, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped and the second coil is tilted by 180°.

[0046] Likewise, the first coil 110; 120; 130; 140 can be wound left-handed clockwise and the second coil 110; 120; 130; 140 can be wound left-handed counterclockwise, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped or the second coil is tilted by 180°.

[0047] Likewise, the first coil 110; 120; 130; 140 can be wound left-handed clockwise and the second coil 110; 120; 130; 140 can be wound right-handed counterclockwise, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped and the second coil is tilted by 180°.

[0048] Likewise, the first coil 110; 120; 130; 140 can be wound counterclockwise in a left-handed manner and the second coil 110; 120; 130; 140 can be wound clockwise in a left-handed manner, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped or the second coil is tilted by 180°.

[0049] Likewise, the first coil 110; 120; 130; 140 can be wound counterclockwise in a left-handed manner and the second coil 110; 120; 130; 140 can be wound clockwise in a right-handed manner, whereby when joining the second coil 110; 120; 130; 140, the inputs and outputs 111, 112; 121, 122; 131, 132; 141, 142 are swapped and the second coil is tilted by 180°.

[0050] In Fig. 7 shows the method 2000 according to the invention for measuring a current in a conductor 500 between the start 2001 and the end 2999. The method 2000 comprises the steps: - Providing 2010 a super coil 200 according to the previous; - Lead 2020 of a conductor 500 through the super coil 200; and - Measure 2030 the current in the super coil 200.

[0051] In general, it should be noted that by rotating the connection of both coils 110; 120; 130; 140 by 180°, interference caused by magnetic fields perpendicular to the axis of the conductor is reduced.

Claims

[1] Device (100) for measuring a current in a conductor (500), characterized by , that the device (100) comprises at least a first and a second coil (110; 120; 130; 140), wherein the at least two coils (110; 120; 130; 140) have an identical coil body (151; 152; 153; 154) and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the at least two coils (110; 120; 130; 140) are arranged spatially one above the other, electrically connected in series, and differ in the orientation of their windings, so that the at least two coils (110; 120; 130; 140) form a super coil (200), whereby to measure the current the conductor (500) is passed through the super coil (200). [2] Device (100) according to claim 1, in which the at least two coils (110; 120; 130; 140) have inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) and these inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) are rotated by 180° relative to each other. [3] Device (100) according to claim 1 or 2, wherein the at least two coils (110; 120; 130; 140) are electrically connected to one another in their outer winding layers (L4) and the total signal is determined between the inner winding layers (L1). [4] Device (100) according to claim 3, wherein the connection of the outer winding layers (L4) is grounded. [5] Method (1000) for producing a super coil (200) for measuring a current in a conductor (500) comprising the steps: - winding a first coil (110; 120; 130; 140); - Winding a second coil (110; 120; 130; 140), wherein the two coils (110; 120; 130; 140) have an identical coil body (151; 152; 153; 154) and are wound with the same wire type with the same number of winding layers and the same number of turns, wherein the two coils (110; 120; 130; 140) differ in the orientation of their turns; - assembling the first coil (110; 120; 130; 140) and the second coil (110; 120; 130; 140) to form a super coil (200), wherein the two coils (110; 120; 130; 140) are arranged spatially one above the other, electrically connected in series. [6] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound right-handed counterclockwise, and wherein the second coil (110; 120; 130; 140) is wound right-handed in a clockwise direction, wherein during assembly the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged or the second coil (110; 120; 130; 140) is tilted by 180°. [7] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound right-handed counterclockwise, and wherein the second coil (110; 120; 130; 140) is wound left-handed in a clockwise direction, wherein during assembly the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged and the second coil (110; 120; 130; 140) is tilted by 180°. [8] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound right-handed in a clockwise direction, and wherein the second coil (110; 120; 130; 140) is wound right-handed counterclockwise, wherein, during assembly, the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are swapped or the second coil (110; 120; 130; 140) is tilted by 180°. [9] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound right-handed in a clockwise direction, and wherein the second coil (110; 120; 130; 140) is wound left-handed counterclockwise, wherein, during assembly, the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged and the second coil (110; 120; 130; 140) is tilted by 180°. [10] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound left-handed in a clockwise direction, and wherein the second coil (110; 120; 130; 140) is wound left-handed counterclockwise, wherein, during assembly, the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are swapped or the second coil (110; 120; 130; 140) is tilted by 180°. [11] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound left-handed in a clockwise direction, and wherein the second coil (110; 120; 130; 140) is wound right-handed counterclockwise, wherein, during assembly, the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged and the second coil (110; 120; 130; 140) is tilted by 180°. [12] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound left-handed counterclockwise, and wherein the second coil (110; 120; 130; 140) is wound left-handed in a clockwise direction, wherein during assembly the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged or the second coil (110; 120; 130; 140) is tilted by 180°. [13] Method (1000) according to claim 5, wherein the first coil (110; 120; 130; 140) is wound left-handed counterclockwise, and wherein the second coil (110; 120; 130; 140) is wound right-handed in a clockwise direction, wherein during assembly the inputs and outputs (111, 112; 121, 122; 131, 132; 141, 142) of the second coil (110; 120; 130; 140) are interchanged and the second coil (110; 120; 130; 140) is tilted by 180°. [14] Method (2000) for measuring a current in a conductor (500) comprising the steps: - Providing (2010) a super coil (200) according to one of the preceding claims; - guiding (2020) a conductor (500) through the super coil (200); and - Measuring (2030) the current in the super coil (200).

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