WO2025202178A1

WO2025202178A1 - Method and system for rogowski coil current measurements

Info

Publication number: WO2025202178A1
Application number: PCT/EP2025/058086
Authority: WO
Inventors: Tycho van van LEERSUM; Elise MORSKIEFT; Bram POSTHUMA
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2024-03-26
Filing date: 2025-03-25
Publication date: 2025-10-02
Anticipated expiration: 2026-09-26
Also published as: GB2639873A; GB202404293D0

Abstract

Disclosed herein is a system comprising a conductor and a Rogowski coil. The Rogowski coil is configured to measure a current through the conductor, wherein the current measured by the Rogowski coil comprises a first component and a second component, wherein the first component is the current through the conductor. The system further comprises a voltage measuring device configured to measure a voltage across of the conductor, wherein the second component of the current depends on the measured voltage in accordance with a pre-defined relationship. The system further comprises a processing means configured to receive the measured current and the measured voltage, and wherein the processing means is configured to calculate a corrected current measurement from the measured current, wherein the corrected current measurement is generated by subtracting the second component of the current from the measured current to obtain the first component.

Description

Method and system for Rogowski coil current measurements

Field

This relates to a Rogowski coil, used to measure the current through a conductor, and in particular to an approach for correcting for errors in the current measured by the Rogowski coil.

Background

A Rogowski coil is used to measure the current flowing in a conductor. In the presence of strong external electric fields or high voltages, an additional current will be induced, leading to an error in the current measured by the Rogowski coil. A typical method to prevent the undesirable effects of such interference is to shield the Rogowski coil.

Shielding a Rogowski coil requires a large amount of specific materials. Therefore, a Rogowski coil with shielding requires additional materials for manufacture. Moreover, the process of shielding a Rogowski coil is a delicate task, which requires a high degree of precision. Therefore, manufacturing a Rogowski coil with shielding will also require additional time.

Therefore, it would be desirable to provide a Rogowski coil without shielding, and in which the effects of induced errors in the measured current can be mitigated.

Summary

Described herein is a system used for correcting errors in the current measured by a Rogowski coil. A method for operating the system is also disclosed.

The system disclosed comprises a conductor. The system also comprises a Rogowski coil configured to measure a current through the conductor. The current measured by the Rogowski coil comprises a first component and a second component, wherein the first component is the current through the conductor. The system further comprises a voltage measuring device configured to measure a voltage of the conductor, wherein the second component of the current depends on the measured voltage in accordance with a pre-defined relationship. The system also comprises a processing means configured to receive the measured current and the measured voltage, and further configured to calculate a corrected current measurement from the measured current. The corrected current measurement is generated by subtracting the second component of the current from the measured current to obtain the first component. Typical alternative approaches to prevent errors in current measurements made using Rogowski coils involve shielding the Rogowski coil. Shielding Rogowski coils requires additional time and additional materials during manufacture. In contrast, the described system for calculating the corrected current measurement obviates the need to shield the Rogowski coil, and therefore the system may be easier and quicker to manufacture.

In some implementations, the processing means of the system further comprises a storage means, in which the pre-defined relationship is stored. Optionally, the predefined relationship is based on at least one of: empirical data, and/or one or more simulations.

In some implementations, the system further comprises a communication module, which is configured to provide the corrected current measurement to an external device. In some implementations, the processing means may be remote from the conductor, the Rogowski coil, and the voltage measuring device. Optionally, the remote processing means may further comprise a communication module, which is configured to provide the measured current and the measured voltage to the remote processing means.

In some implementations, the processing means is also configured to perform a Fourier transform of the measured current through the conductor and the measured voltage of the conductor. In some implementations, the processing means is further configured to calculate a first angle between the measured current and the measured voltage based on the Fourier transforms. In some implementations, the subtraction of the second component of the current from the measured current is based on the calculated first angle between the measured current and the measured voltage and a second angle between the second component and the measured voltage, wherein the second angle is defined by the pre-defined relationship.

Also disclosed herein is a method for operating the system for calculating a corrected current measurement of a current measured by a Rogowski coil, wherein the Rogowski coil measures the current through a conductor, and wherein the measured current comprises a first and second component. The method further comprises measuring, using a voltage measuring device, a voltage of the conductor, wherein the second component of the current depends on the measured voltage in accordance with a predefined relationship. The method also comprises receiving, at the processing means, the measured current and the measured voltage. The method further comprises subtracting, using the processing means, the second component of the current from the measured current to obtain the first component.

The features of the system can be combined in any suitable combination. The features described with reference to the system can be combined with the described method, and vice versa.

List of Figures

The detailed description is with reference to the followings Figures.

Fig 1 : Schematic illustration of a system for correcting a current measurement by removing phantom current.

Fig 2: Example illustration of a method of subtraction of phantom current from a measured current.

Fig 3: Schematic illustration of a method for calculating a corrected current measurement.

Fig 4: Schematic illustration of another method for calculating a corrected current measurement.

Detailed Description

An approach for correcting for errors in the current measured by the Rogowski coil is described with reference to Figure 1, which shows an example schematic illustration of a system 100 for correcting a current measurement by removing phantom current.

The system 100 comprises a conductor 104 and a Rogowski coil 102. The Rogowski coil 102 is configured to measure the current through the conductor 104. The current measured by the Rogowski coil 102 comprises a first component and a second component. The first component of the measured current is the actual current flowing through the conductor 104 (i.e. the current supplied by a load).

The system further comprises a voltage measuring device 106. The voltage measuring device 106 is configured to measure a voltage of the conductor 104 (e.g., as compared to ground). The voltage of the conductor 104 is constant along the whole length of the conductor 104 and the voltage of the conductor 104 is measured compared to ground or neutral by the voltage measuring device to obtain the measured voltage. The second component of the measured current is an induced current (also referred to herein as a phantom current). The second component can be induced in the Rogowski coil 102 itself, and/or in any other part of the circuit used for processing the measured current, by an external electric field. In some implementations, an electric field produced by the voltage of the conductor 104 induces the second component of the current in the conductor. The second component thus depends on the voltage of the conductor 104. The dependence of the second component on the voltage is in accordance with a pre-defined relationship.

In some examples, the pre-defined relationship between the voltage of the conductor 104 and the second component of the measured current (phantom current) is at least based on empirical data and/or one or more simulations. In some examples, the predefined relationship between an amplitude of the measured voltage and an amplitude of the second component of the current may be a linear relationship.

The system further comprises a processing means 108. The processing means 108 is configured to receive the current measured by the Rogowski coil 102. The processing means 108 is also configured to receive the measured voltage of the conductor 104. The processing means 108 of the system 100 is further configured to calculate a corrected current measurement from the measured current based on the pre-defined relationship. In some examples, the processing means 108 may be able to access a storage means (not shown), in which the pre-defined relationship is stored. In some implementations, the processing means 108 may be configured such that the predefined relationship can be overwritten and/or updated.

The corrected current measurement is generated by subtracting the second component of the measured current from the measured current to obtain the first component (i.e. to obtain the actual current through the conductor 104). This calculation will be discussed below in more detail with reference to Figure 2.

The described system calculates a corrected current measurement which can mitigate errors in the measurement caused by induced currents (or phantom currents). Typical alternative approaches involve shielding a Rogowski coil to prevent errors in the current measurements made using the Rogowski coil. The described system obviates the need to shield the Rogowski coil, and therefore removes the additional time and specifical additional materials required during manufacture. Hence, the described system may be quicker and cheaper to manufacture, with fewer input resources required.

In some examples, the system 100 may further comprise a communication module (not shown). The communication module can be configured to provide the corrected current measurement to an external device (not shown). In some examples, the processing means 108 of the system 100 may be remote from the conductor, the Rogowski coil, the voltage measuring device (for example, located in or provided within an external computing device). For example, the processing means can be located in a central unit which is communicatively coupled to a plurality of systems 100, each having a separate conductor 104 and Rogowski coil 102. The central unit may have an embedded microprocessor or any other processing means to implement processing means 108 as described herein.

In such an arrangement, the communication module may be configured to provide the measured current and the measured voltage to the remote processing means 108.

Any suitable wireless communication protocol can be used by the communication module to communicate with an external device and/or the remote processing means 108, including, but not limited to, any cellular connection (e.g., 2G, 3G, 4G, 5G), a WiFi connection, a Bluetooth connection, a Bluetooth Low Energy BLE connection, a Zigbee connection, or the like. Additionally or alternatively, a wired connection could be used. The communication unit can be configured to periodically send the measured current and voltage to the remote processing. This can provide a trade-off in terms of accuracy of the corrected current and computational resources used by the system 100 (e.g. battery life, bandwidth usage, etc).

In some examples, the processing means 108 may be further configured to perform a Fourier transform of the measured current through the conductor 104, and a Fourier transform of the measured voltage of the conductor 104. In further examples, the processing means is also configured to calculate a first angle between the measured current and the measured voltage, wherein the calculation is based on the Fourier transforms of the measured current and the measured voltage. The first angle between the measured current and the measured voltage may represent the phase difference between the measured current through the conductor 104 and the measured voltage of the conductor 104.

In some implementations, the pre-defined relationship may also be used to determine a second angle between the second component of the measured current and the measured voltage of the conductor 104. The corrected current measurement is generated by subtracting the second component of the current from the measured current based on the first angle and the second angle. The use of the first and second angles will be discussed below in more detail with reference to Figure 2. Figure 2 shows an example illustration of subtraction of the second component (phantom current) from the measured current to determine the first component of the current (the actual current through the conductor in the absence of any induced or phantom current components). The example illustration of Figure 2 depicts a phasor representation with a real axis, denoted by "Re", and an imaginary axis, denoted by "Im". In other example illustrations, the axes labels may be interchanged, or any other suitable representation of the measured current and voltage may be used.

Figure 2 shows a phasor representation of the measured current 204 through the conductor 104, as measured by the Rogowski coil 102. Figure 2 also shows a phasor representation of the measured voltage 210 of the conductor 104, as measured by the voltage measuring device 106. The voltage can be normalised to lie along the real axis Re, as shown in Figure 2, though other approaches may also be used.

The measured current 204 comprises a first component 206 and a second component 208. The first component of the measured current 204 is the current through the conductor 104. The second component of the current 208 depends on the measured voltage in accordance with a pre-defined relationship (phantom or induced current). In some examples, the second component 208 is induced (i.e., contributes to the current measured by the Rogowski coil 102) by an electric field produced by the voltage of the conductor 104. The second component 208 can be induced in the Rogowski coil 102 itself, or in any other part of the circuit used for processing the measured current.

In some examples, the processing means 108 is configured to perform a Fourier transform of the measured current through the conductor 104 and a Fourier transform of the measured voltage 210 of the conductor 104. The processing means calculates, based on the Fourier transforms, a first angle 214 between the measured current 204 and the measured voltage 210. The first angle between the measured current and the measured voltage is the phase difference between the measured current 204 and the measured voltage 210.

Using the pre-defined relationship, the second component 208 of the measured current 204 may be determined from the measured voltage 210 of the conductor 104. The pre-defined relationship may determine the amplitude of the second component 208a based on the amplitude of the measured voltage 210. In other words, the amplitude of the measured voltage may be scaled by some pre-defined relationship to determine the amplitude of the induced current component 208. The pre-defined relationship may also determine a phase difference between the measured voltage 210 and the second component 208a. In this example, a second angle 212 represents a phase difference between the measured voltage 210 and the second component 208a. In other words, the measured voltage may be shifted or rotated by the second angle 212 to infer the induced current component. The pre-defined relationship may comprise the second angle (i.e. the second angle can be known).

In Figure 2, a translated second component 208b is shown, which is a translation of the second component 208a, and which depends on the measured voltage 210 according to the pre-defined relationship. The measured current 204 through the conductor 104 is the sum of the first component 206 and the second component 208, wherein in the phasor representation the summation is based on both the amplitudes and phase difference of the first 206 and second 208 components. This summation in the phasor representation is illustrated by the addition of the first component 206 and the translated second component 208b.

Therefore, to calculate a corrected current measurement and obtain the first component 206 (i.e. the actual current), the second component 208 is subtracted from the measured current 204. This subtraction is based on the first angle 214 and the second angle 212 in accordance with the vector representation of the current components in Figure 2. It will be understood that the relative orientations and lengths in the phasor representation of Figure 2 are for illustration purposes only. In other example illustrations, different phase differences and angles may be shown, and alternative lengths and orientations of phasor representations of the measured current 204, measured voltage 210, first component 206, and second component 208 may be illustrated.

With reference to Figure 3, an example method 300 for using or operating the system 100 is described. At operation 302, the method comprises measuring the current through the conductor 104 using the Rogowski coil 102. At operation 304, the method further comprises measuring the voltage 210 of the conductor 104 using the voltage measuring device 106. At operation 306, the method further comprises receiving, at the processing means 108, the measured voltage 210 and the measured current. At operation 308, the method further comprises calculating a corrected current measurement by subtracting the second component of the measured current from the measured current. This method calculates a corrected current measurement for the current measured by the Rogowski coil. Typical alternative approaches involve shielding a Rogowski coil such that strong external electric fields may not induce an additional current and lead to an error in the current measured by the Rogowski coil. However, shielding a Rogowski coil requires a large amount of additional specific materials and requires extra precision during manufacture. The method described allows for a Rogowski coil with less shielding while still providing a corrected current measurement, and so reducing time and resources required during manufacture, as well as reducing production costs.

The example method 300 for using or operating the system 100 described, and shown in Figure 3, can be used when a particular set of conditions are satisfied.

One condition is that the voltage 210 of the conductor 104 is known. This is satisfied by the operation 304 of the example method 300, in which the example method 300 comprises measuring the voltage 210 of the conductor 104 using the voltage measuring device 106. Another condition is that the voltage 210 of the conductor 104 and the second component 208 of the measured current have a known relationship. In other words, the second component of the current depends on the measured voltage 210 in accordance with a known, or pre-defined, relationship. In some examples, the pre-defined relationship may be stored in a storage means of the processing means 108.

In some examples, the pre-defined relationship may be based on at least one of: empirical data and/or one or more simulations. For example, a plurality of known voltages may be applied to the conductor in the absence of any applied current, and the induced currents measured using the Rogowski coil 102. Additionally or alternatively, the system 100 may be simulated and a plurality of voltages applied to the simulated conductor and the induced currents determined. The resulting currents can then be plotted against the applied voltage to the conductor and a trend line found. The equation describing this line is the relation between the amplitude of the phantom current and the amplitude of the voltage (i.e. the scaling factor).

An additional condition is that the angle between the voltage 210 of the conductor 104 and the second current component 208 (phantom current) is known. The second angle 212 is the angle between the measured voltage and the second component. The second angle 12 is known in accordance with the pre-defined relationship and can be obtained using empirical data and/or one or more simulations. For example, a voltage may be applied to the conductor in the absence of any applied current, and the induced current measured using the Rogowski coil 102. Additionally or alternatively, the system 100 may be simulated and a voltage applied to the simulated conductor and the induced current determined. By measuring the voltage and the phantom current, it is possible to calculate the angle between them (second angle 212). This can be done through several methods like zero crossing detection, peak detection and taking the Fourier transform and subtracting the voltage angle from the phantom current angle.

A further condition is that the measured current 204 is the sum of the first component 206, which is the current through the conductor 104, and the second component 208. This condition is known in accordance with the pre-defined relationship (i.e. by using a known voltage and known phantom current, it can be determined if a sum of the applied current and the known phantom current equals the current measured by the Rogowski coil). At operation 308 of the example method 300, since the measured current 204 is sum of first component 206 and the second component 208, subtracting the second component 208 from the measured current 204 allows for the calculation of a calculated current measurement, which is the current through the conductor 104.

In this way, the current through the conductor can be obtained through the abovedescribed calculations in post-processing.

Another condition is that the frequency of the voltage 210 of the conductor 104 and the current through the conductor 104 is the same. This condition is assumed to be satisfied for most electrical circuits.

With reference to Figure 4, an example method 400 for using or operating the system 100, which further illustrates additional operations of example method 300.

Operations 402, 404, and 406 correspond to the operations 302, 304, and 306 of example method 300. At operation 402, the method comprises measuring the current through the conductor 104 using the Rogowski coil 102. At operation 404, the method further comprises measuring the voltage 210 of the conductor 104 using the voltage measuring device 106. At operation 406, the method further comprises receiving at the processing means 108 the measured voltage 210 and the measured current.

Operations 408, 410, 412, 414 further define operation 308 of Figure 3. At operation 408, the method comprises performing, using the processing means, a Fourier transform of the measured current through the conductor 104 and a Fourier transform of the measured voltage 210 of the conductor 104. At operation 410, the method further comprises calculating, using the processing means 108 and based on the Fourier transforms, a first angle between the measured voltage and the measured current.

In some implementations, the Fourier transform performed using the processing means may be a Complex Fast Fourier Transform (CFFT). The calculation at operation 410 may further comprise obtaining, using the CFFT, the DC component of the measured current and measured voltage and their harmonics. One or more of the harmonics may be used to calculate the angle of the measured voltage and the measured current. The calculation can further comprise obtaining real and imaginary components of one or more harmonics (optionally each harmonic), and further calculating, using the complex representation of each respective harmonic, the angle of the measured voltage and the measured current. For example, a vector representation of the real and imaginary parts may be used to find the angle. The first angle between the measured voltage and the measured current may be calculated as the phase difference between the angle of the measured voltage and the angle of the measured current.

In some implementations, the first angle may be used to determine the direction of electrical power flow (i.e. the orientation of the measured current 204 in the phasor representation of Figure 2).

At operation 412, the method further comprises determining, using the processing means 108 and the pre-defined relationship, a second angle between the measured voltage 210 and second component 208 of the measured current 204. The amplitude of the second component of the measured current has a known relationship with the amplitude of the voltage of the conductor 104 (i.e. there can be a known scaling factor or function). This relationship is known in accordance with the pre-defined relationship. The angle between the second component and the voltage of the conductor is also known in accordance with the pre-defined relationship, wherein the angle represents the phase difference between the second component and the voltage. In other words, the pre-defined relationship defines how the voltage of the conductor can be shifted (or rotated) by the first angle and scaled to find the second component of the current. After operation 412 in the example method 400, the complex phasors of the measured current, measured voltage, and the second component are known. Figure 2 depicts example illustrations of the complex phasors of the measured current, measured voltage, and the second component.

At operation 414, the method further comprises subtracting the second component of the measured current from the measured current. The subtraction is based on the first angle and the second angle (as discussed with reference to operation 308) in that these first and second angles 212, 214 are required to formulate the appropriate phasor representation of the current components. This subtraction, which calculates a corrected current measurement, follows from the measured current being the addition of the first component and the second component.

Mathematically, this subtraction is given by /corrected /first component /measured /second component < in which : /corrected is the calculated corrected current measurement and which is equal /first component (i.e. the first component of the measured current); /measured is the current through the conductor 104 as measured by the Rogowski coil 102; and /second component is the second component of the measured current (phantom current).

Specifically, since the subtraction is based on both the amplitude and phase difference of the current components, and the pre-defined relationship between the voltage and the phantom current, mathematically the subtraction is given by:

/corrected /first component — Re{/_measured} f (V) cos(<p) + i (Im{/_measured} f(V^ sin^p)) , in which Re{} and Im{} are functions which return the real and imaginary part of the argument respectively, where i is the imaginary unit, and where f(V) is the relationship between the amplitude of the second component and the measured voltage in accordance with the pre-defined relationship, and cp is the second angle between the measured voltage and the phantom current, which is known from the pre-defined relationship.

In some examples, the relationship between the amplitude of the second component and the measured voltage in accordance with the pre-defined relationship is a linear relationship, and so the measured voltage may be divided by a scaling factor (e.g., in one particular example f(V) = V/3, so for each volt, the second component is 0.333A). In this way, the measured current may be corrected in a simple and efficient manner, without the need for shielding of the Rogowski coil. An effective current correcting system may therefore be provided, which is quicker and cheaper to manufacture than existing arrangements.

Claims

1. A system (100) comprising: a conductor (104); a Rogowski coil (102) configured to measure a current through the conductor (104), wherein the current measured (204) by the Rogowski coil (102) comprises a first component (206) and a second component (208), wherein the first component is the current through the conductor (104); a voltage measuring device (106) configured to measure a voltage (210) of the conductor (104), wherein the second component of the current depends on the measured voltage in accordance with a pre-defined relationship; and a processing means (108) configured to receive the measured current and the measured voltage, and wherein the processing means (108) is configured to calculate a corrected current measurement from the measured current, wherein the corrected current measurement is generated by subtracting the second component of the current from the measured current to obtain the first component.

2. The system (100) of any preceding claim, wherein the pre-defined relationship is stored in a storage means accessible to the processing means (108).

3. The system (100) of any preceding claim, wherein the pre-defined relationship is based on at least one of: empirical data, and one or more simulations.

4. The system (100) of any preceding claims, wherein the processing means (108) is configured to perform a Fourier transform of the measured current (204) and the measured voltage (210) of the conductor (104).

5. The system (100) of claim 4, wherein the processing means (108) is further configured to calculate, based on the Fourier transforms, a first angle (214) between the measured current (204) and the measured voltage (210).

6. The system (100) of claim 5, wherein subtracting the second component (208) of the current from the measured current (204) is based on the first angle (214) and a second angle (212) between the second component and the measured voltage, the second angle defined by the pre-defined relationship.

7. The system (100) of any preceding claim, wherein the system (100) further comprises a communication module, wherein the communication module is configured to provide the corrected current measurement to an external device.

8. The system (100) of any preceding claim, wherein the processing means (108) is remote from the conductor, the Rogowski coil and the voltage measuring device.

9. The system of claim 8, wherein the system (100) further comprises a communication module, wherein the communication module is configured to provide the measured current and the measured voltage to the remote processing means (108).

10. A method for calculating a corrected current measurement of a current (204) measured by a Rogowski coil (102), wherein the Rogowski coil (102) measures (302) the current through a conductor (104), and wherein the measured current comprises a first (206) and second (208) component, wherein the method further comprises: measuring (304), using a voltage measuring device (106), a voltage (210) of the conductor, wherein the second component of the current depends on the measured voltage in accordance with a pre-defined relationship; receiving (306), at the processing means (108), the measured current and the measured voltage; and subtracting (308), using the processing means (108), the second component of the current from the measured current to obtain the first component.