Current transformer for measuring the current flowing through an electrical conductor, and method for outputting a measurement value in a current transformer, including outputting the direction of energy flow in an alternating current

Abstract

The invention relates to a current transformer for measuring the current flowing through an electrical conductor, said current transformer having a current sensor (12) which picks up the current intensity through the electrical conductor, and an evaluation device (14) for evaluating the measurement values picked up by the current sensor (12). Furthermore, in the current transformer (10) according to the invention, the energy flow direction is determined and the current intensity is output in the positive or negative range of the output unit depending on the determined energy flow direction. The invention also relates to a method for outputting measurement values in a current transformer, including the output of the energy flow direction in an alternating current.

Description

Technical Field

[0001] This invention relates to a current transmitter for measuring the current flowing through an electrical conductor. The invention also proposes a method for outputting measured values ​​in the current transmitter, including outputting the direction of energy flow in the alternating current. Background Technology

[0002] In known current transmitters for alternating current, the current intensity value is typically output only proportionally.

[0003] There exists an energy measuring instrument that can measure and indicate the direction of energy flow, but it cannot output proportional current.

[0004] Document US2009315566A1 discloses an AC current sensor that generates a pulse output signal, which can be used to provide the phase angle and polarity, thereby determining the direction of energy flow. The current intensity is indicated by a lamp (LED), specifically by controlling the lamp with the generated pulse. In this case, a brighter lamp indicates a larger current. In one embodiment, the direction of energy flow is also output and indicated digitally. Therefore, this sensor can provide an indication of which direction of energy flow, for example, a relevant short circuit would occur relative to the current sensor, because the direction indication provided is recorded over a measurement time span prior to the impending short circuit.

[0005] However, the drawback of known solutions is that they cannot provide current intensity and energy flow direction to a control unit to control the machine or process. Summary of the Invention

[0006] Therefore, there is a need for an improved current transmitter that avoids the aforementioned drawbacks. This can be achieved within the scope of this invention.

[0007] The solution of the present invention to achieve the above-mentioned objective is a current transmitter for measuring the current flowing through an electrical conductor according to claim 1, and a method for outputting current intensity in such a current transmitter according to claim 9.

[0008] The dependent claims contain advantageous further embodiments and improvements of the invention based on the following description of these measures.

[0009] This invention describes a current transmitter having an input terminal for measuring a primary alternating current at the output terminal. For this purpose, a suitable current sensor is installed. Furthermore, the current transmitter includes an energy flow direction identification device, which allows detection of the current direction of the primary alternating current. A suitable processing unit combines the level of the primary alternating current and the energy flow direction into an analog output signal, which can be either positive or negative.

[0010] The current transmitter of this invention includes a current sensor for acquiring the current intensity passing through an electrical conductor, and an analysis device for analyzing the measured values ​​acquired by the current sensor, and for determining the energy flow direction. In the current transmitter of this invention, the current intensity in the output current is output as positive or negative according to the measured energy flow direction. An advantage over known current transmitters is that the energy flow direction is also acquired, and the output is designed in a way that simultaneously outputs the energy flow direction and current intensity. Control equipment can acquire this output signal and control or adjust the machine or process accordingly.

[0011] Advantageously, the current transmitter also includes a voltmeter, which acquires the voltage level across the conductor to determine the phase. In this case, it is advantageous to determine the energy flow direction by analyzing the measured values ​​of the current and voltage across the conductor, thereby performing a phase shift angle measurement for the phase shift between voltage and current. This generates an output signal, wherein when the phase shift angle is in the range of -90° to +90°, the current intensity is output in the positive output range; otherwise, the current intensity is output in the negative output range. By measuring the phase shift angle, the energy flow direction can be easily determined.

[0012] In a preferred embodiment of the current transmitter, the current intensity is output proportionally in both positive and negative output ranges, wherein the corresponding output ranges are defined such that the output current passes through zero in proportion to the measured current.

[0013] The analysis device generates the output signal of the acquired measured current in such a way that the output value can be output with a sign along the vertical axis according to the measured energy flow direction. The output value can be equivalent to an analog DC signal. The energy flow direction determines the current direction.

[0014] In another technical variant, the output of the measured current is always positive, meaning it is output via another output port in the same current and energy flow direction.

[0015] Furthermore, in this variant, the output of the measured current is always positive, the energy flow direction is output via another output port, and the output signal also has an offset value. In a preferred example, this offset value can be 4mA.

[0016] To facilitate information access for operators, the current transmitter is advantageously equipped with two additional indicating elements, particularly light-emitting diodes, for indicating the direction of energy flow.

[0017] In another configuration, the present invention relates to a method for outputting a measured value in a current transmitter, wherein, in addition to the current intensity, the energy flow direction of the alternating current flowing through the conductor is measured, and the current intensity is output in the positive or negative output range of the output unit according to the measured energy flow direction.

[0018] Advantageously, the voltage level on the electric conductor is measured, and the direction of energy flow is determined by analyzing the measured values ​​of current and voltage, wherein the phase shift angle is measured for the phase shift between voltage and current, and the current intensity is output in the positive output range when the phase shift angle is in the range of 90° to +90°, otherwise the current intensity is output in the negative output range.

[0019] If the measured primary current needs to be output at the output terminal without polarity conversion, then the polarity can be output through another output terminal.

[0020] The standard current can be 0-20mA or 4-20mA.

[0021] Furthermore, advantageously, in addition to current measurement, the voltage level across the conductor is also measured, and the apparent power S can be calculated using S = U·I. In this case, this apparent power can be output proportionally to the current measurement. Using the measured phase shift angle φ, active and reactive power can also be obtained and output using specific active factor cosφ and specific reactive factor sinφ. The formula for active power P is P = S·cosφ, and the formula for reactive power QL is QL = S·sinφ. Different technical variations are mentioned. In one variation, the analog output of the microcontroller is used as the output unit to output a standard current ranging from, for example, 0-20mA, or a standard voltage ranging from, for example, -10V…+10V or 0-10V.

[0022] In one technical variant, a current transmitter is used to measure the current and a voltmeter is used to measure the voltage, wherein the measured current is output as a voltage in proportion to the measured current, instead of being output as the current.

[0023] In another scheme, a current transmitter is used to measure the current and a voltmeter is used to measure the voltage. The active power obtained is output within the positive and negative output range of the output unit, which is used as a substitute for the current intensity.

[0024] In the next scheme, a current transmitter is used to measure the current and a voltmeter is used to measure the voltage. The reactive power obtained is output within the positive and negative output range of the output unit, which is used as a substitute for the current intensity.

[0025] In another scheme, a current transmitter is used to measure the current and a voltmeter is used to measure the voltage. The apparent power is output within the positive output range of the output unit, which is used as a substitute for the current intensity.

[0026] In another scheme, a current transmitter is used to measure the current and a voltmeter is used to measure the voltage. As a substitute for the current intensity, a specific power factor or the measured phase shift angle is output within the positive and negative output range of the output unit.

[0027] In another scheme, a current transmitter is used to measure the current, and as a substitute for the current intensity, a specific frequency is output within the positive output range of the output unit.

[0028] Of course, the maximum power factor or the highest frequency to be measured corresponds to, for example, a maximum output current of 20mA, or a maximum output voltage of, for example, 10V.

[0029] This also applies to phase shift angles, except that the phase shift angles are also output with a sign. Attached Figure Description

[0030] The accompanying drawings illustrate several embodiments of the present invention, which are described in detail below in conjunction with the drawings.

[0031] in:

[0032] Figure 1 This is a first block diagram of a current transmitter used to measure the current flowing through an electrical conductor.

[0033] Figure 2 A wiring diagram is shown to illustrate the characteristics of alternating current in the presence of inductance;

[0034] Figure 3 In accordance with Figure 2 In a circuit, there is a signal diagram showing the current curves and voltage curves at the active resistance and reactance points.

[0035] Figure 4 This is a second block diagram of a current transmitter used to measure the current flowing through an electrical conductor.

[0036] Figure 5 This is a first embodiment of the current transmitter of the present invention, which outputs current intensity and energy flow direction in an analog form;

[0037] Figure 6 This is a second embodiment of the current transmitter of the present invention, which outputs the current intensity and energy flow direction in an analog form;

[0038] Figure 7 This is a third embodiment of the current transmitter of the present invention, which outputs current intensity and energy flow direction in an analog form;

[0039] Figure 8 This is a flowchart of an analysis algorithm used to determine the direction of energy flow and to preprocess data used to simulate the output current intensity and direction of energy flow. Detailed Implementation

[0040] This specification explains the principles of the disclosed contents of the present invention. It is understood that those skilled in the art can design different arrangement schemes, which, although not explicitly described herein, embody the principles of the disclosed contents and their scope should also be protected.

[0041] Figure 1 A block diagram of a current transmitter 10 for measuring the current flowing through an electrical conductor is shown. The single-phase cable 5 shown consists of a phase line L and a neutral line N. Optionally, the cable 5 may also include a protective grounding wire (not shown). The current on the conductor needs to be monitored. For this purpose, a current transmitter 10 is used. The current transmitter is connected between the phase line L and the neutral line N. In this technical variant, the current is guided through the current transmitter 10 internally. In another type of current transmitter, the current is not guided through the current transmitter, but is measured indirectly. For this purpose, a current transmitter 10 with a Rogowski coil can be used, for example. This is an air-core coil placed around the conductor. The changing magnetic field generated around the conductor in the alternating current induces a voltage in the Rogowski coil, which is then measured.

[0042] In the current transmitter 10 shown, reference numeral 12 denotes a current sensor. This current sensor quantitatively acquires the current flowing through the conductor. The current transmitter 10 is also connected to the neutral line N. The two conductors, namely the phase line L and the neutral line N, are re-leaded out at the output and connected to the load 20. A typical current sensor, often referred to as a current transformer, is a small-power transformer that converts large currents into easily measurable values. In one technical variant, the input winding is connected to the conductor of the phase line L and is through which the current to be measured flows. For example, a conventional ammeter is connected to the output winding. The primary winding has only a few turns or even only one turn, while the secondary winding has a much larger number of turns, thus allowing the acquisition of larger current values ​​of hundreds of amperes using conventional measurement techniques (ammeters). Another technical variant of the current sensor is the so-called through-hole current transformer, where the conductor through which the current to be acquired is inserted and passed. This also includes a Rogowski coil. This allows even larger current values ​​to be acquired. This is advantageous, for example, for conductors associated with the busbar but no longer easily wound. A third technical variant of the current sensor 12, which can also be applied to the described device, is a Hall effect current sensor. Here, the Hall effect is utilized, including generating a voltage in a conductor through which current flows in a static magnetic field. Such Hall generators are typically implemented as planar devices, generating a magnetic field that is as uniform as possible, perpendicular to the planar conductor. A Hall voltage is acquired transversely to the current direction at the outer edge of the planar conductor. For this purpose, in one technical variant, the Hall effect current sensor is inserted into a slotted magnetic toroidal core.

[0043] The electronic analysis device 14 of the apparatus acquires and temporarily stores the measured values ​​for analysis. The electronic analysis device 14 can be implemented as a microcontroller. This microcontroller is equipped with an A / D converter and a sampling unit to acquire continuous measured values. The controller also includes a memory (e.g., CMOS-RAM memory) to temporarily store the measured values. The main component is a programmable microcomputer that executes the analysis algorithm. This microcomputer also includes a D / A conversion unit that generates analog output signals. The output unit is preferably implemented by the D / A conversion unit integrated in the microcomputer. An analog output signal is emitted via output port 18. A separate wire can be connected to this output port 18, and this signal can be transmitted to the control device 24. For example, the signal can be transmitted to a programmable logic controller (PLC) 24. Measured values ​​are acquired at a specific sampling rate, which can be in the range of kS / s. The electronic analysis device 14 also acquires the voltage between the phase line L and the neutral line N. For this purpose, a voltmeter 16 is connected to the phase line L and the neutral line N. The measured voltage value is received by the electronic analysis device 14 and written to its memory.

[0044] The current transmitter 10 also measures the direction of energy flow. This is done by measuring the phase of the current relative to the voltage. Figure 2 The circuit shown illustrates the measurement principle. The reference symbol for the AC generator is 30. The current I points in one direction. In the circuit shown, the load 20 consists of a coil 32 and an ohmic resistor 34. The current I is correspondingly divided into two parts, I0 and I1. bl and part of I w As is well known, coil 32 has the same function as reactance, but it causes a phase shift between voltage U and current I.

[0045] Figure 3 The precise signal curve is shown. The left side shows the vector diagram, and the right side shows the signal curve. Voltage through coil 32. Current and the current through ohmic resistor 34 The peak value is shown as the corresponding vector length in the vector diagram. The superposition forms the total current i, whose signal curve is also visible. Figure 3 Both sections show the phase difference φ between voltage u and current i. A phase difference φ of approximately 40° is generated through specific wiring. The phase difference φ can be measured, thereby analyzing the signal curves of u and i. In both cases, the rising zero-crossing points of the signal curves of u and i are measured. Subsequently, the time difference is correlated with the period length to determine the phase difference φ.

[0046] The energy flow direction is determined as follows: if the phase difference between u and i is 90° and +90°, the energy flow direction is defined as positive, that is, from generator 30 to load 20. In other cases, the energy flow direction is defined as negative, that is, from load 20 to generator 30.

[0047] Figure 4 A second technical variant of the current transmitter 10 is shown. The same reference numerals denote the same components. The difference lies in that two output lines are led out from the current transmitter 10. One output line leads to output port 18. The other output line leads to output port 17. The wire on output port 18 is then connected to the D / A output of a microcomputer. The other output line leading to output port 17 can also be connected to the D / A output of the microcomputer. In another technical variant, the output lines can alternatively be connected to the digital output of the microcomputer. That is, both output lines lead to the control device 24.

[0048] Figure 5 A variation of the technique, combining the measured current intensity and energy flow direction from the analog output, is shown. The analog output signal is presented as a graph of the secondary current relative to the primary current. The primary current corresponds to the current flowing through the conductor. Figure 5 The given value is -400A to +400A. The secondary current refers to the current measured in the analysis device 14, and is within the range of -25mA to +25mA. In the case shown, a peak value of approximately 20mA is generated. This value corresponds to a primary current of approximately 300A. The conversion is proportional. As shown, considering the energy flow direction, the current intensity is output in a simulated form. That is, if the measured energy flow direction is positive, it is output as a straight line in the first quadrant of the coordinate system. A DC current is output. Therefore, the direction of its current is from the electronic analysis device 14 to the control device 24. Conversely, if the measured energy flow direction is negative, it is output as a straight line in the third quadrant of the coordinate system. In this case, the direction of its current is in the opposite direction from the control device 24 to the electronic analysis device 14. Figure 5 The diagram shows two straight lines that are continuous.

[0049] Figure 6 A second technical variant is shown, illustrating the measured current intensity and energy flow direction at the output, which is suitable for... Figure 4 A technical variant of the current transmitter 10 is described. In this variant, the direction of energy flow is indicated only by the difference between the positive and negative states of the additional output terminal 17. For secondary current, a positive polarity signal is emitted in both cases, meaning the current direction remains the same.

[0050] Figure 7 This is a third embodiment showing the current intensity and energy flow direction measured by analog output. The energy flow direction is... Figure 6 The same applies. For the secondary current intensity, a positive value is indicated in both cases. However, the straight line does not originate from the coordinate system origin. Instead, a specific offset of approximately 4 mA is shown. The straight line extends from this offset point at 0 A towards the currently measured peak value. Further, this form of measured current output can still achieve secondary current even when no primary current flows. This allows monitoring of the measurement system itself when no primary current is flowing. The on / off signal of the output polarity is shown again.

[0051] Figure 8 An embodiment of the analysis algorithm executed in the electronic analysis device 14 is shown in the flowchart. The program begins with reference numeral 50. In program step 51, the measurement value of the current through the conductor of phase line L is acquired. In program step 52, the measurement value of the voltage across the conductor of phase line L relative to the neutral line is acquired. The signal emitted by the current sensor 12 is provided to the A / D input of the microcontroller of the electronic analysis device 14. This A / D input acquires the input signal and writes the digital value into memory. Similarly, the measurement signal from the voltmeter is acquired via another A / D input of the microcontroller, and the digital value is also written into memory. In program step 53, the phase difference φ between voltage U and current I is measured. (The above is in conjunction with...) Figure 3 The measurement is performed as described. The signal curves of U and I are analyzed. In one technical variant, the rising zero-crossing points of the signal curves of u and i are determined in both signals. Subsequently, the time difference between these two points is measured. This time difference is then correlated with a specific period length T of the signal to determine the phase difference φ. In the presence of inductance, the alternating current is proportional to the alternating voltage. In program step 54, the determined phase shift angle φ is analyzed. If φ is within the range [90°, +90°], the energy flow direction is positive, i.e., energy flows from the alternating current generator 12 to the load 20. If the phase shift angle φ is determined to be outside this range, the energy flow direction is reversed, i.e., the load provides energy and this energy flows back to the generator. In program step 55, the positive energy flow direction is determined. Subsequently, in program step 57, based on the input current intensity, as shown... Figure 5 , Figure 6 or Figure 7 The output current intensity is linear, as shown in the first quadrant. This also indicates the direction of energy flow. Furthermore, the output... Figure 6 and Figure 7 The on / off signal is shown. If the phase shift angle φ is outside the range [90°, +90°], then the energy flow direction is determined to be negative in program step 56. Accordingly, in program step 58, the on / off signal is determined as follows: Figure 5 The third quadrant or Figure 6 or Figure 7 The output current intensity is linear, as shown in the second quadrant. Similarly, an on / off signal can be output at output port 17.

[0052] This should be understood as meaning that the proposed methods and corresponding apparatus can be implemented in different forms of hardware, software, firmware, dedicated processors, or combinations thereof. In a preferred embodiment, a microcontroller with integrated RAM memory and integrated I / O interfaces is used. The processor may include application-specific integrated circuits (ASICs), reduced instruction set computers (RISCs), and / or field-programmable gate arrays (FPGAs). The proposed methods and apparatus are preferably implemented as a combination of hardware and software. The software is preferably installed as an application program on a program storage device. This typically refers to a computer platform-based machine with hardware such as one or more central processing units (CPUs), a random access memory (RAM), and one or more input / output (I / O) interfaces. An operating system is also typically installed on the computer platform. The various processes and functions described herein may be part of the application program or part executed through the operating system.

[0053] The disclosure is not limited to the embodiments described herein. There is room for various adjustments and modifications that a person skilled in the art, based on their expertise, would consider to be part of the disclosure.

[0054] The table below summarizes several different technical variations of the input measurement options and output options of the current transmitter of the present invention. The output options are listed in separate columns according to analog and digital options.

[0055] Table 1 should be understood as allowing all input measurement options to be arbitrarily associated with analog and digital output options. That is, for each input measurement option, one can choose whether it should be provided to the control device as an analog current output or a digital voltage output.

[0056] For example, different output ranges can be selected, such as a current output of 4 to 20mA or a voltage output of 1 to 5V. Information given in the table can be output digitally via corresponding controlled LEDs. The abbreviation THD stands for Total Harmonic Distortion, which in signal analysis is equivalent to a parameter used to quantify the magnitude of the nonlinear distortion portion of a signal.

[0057] Table 1

[0058]

[0059]

[0060] Explanation of reference numerals in the attached figures

[0061] AC wire 5

[0062] Current Transmitter 10

[0063] Current sensor 12

[0064] Electronic analysis equipment 14

[0065] Voltmeter 16

[0066] Output port 17

[0067] Second output port 18

[0068] AC load 20

[0069] Control device 24

[0070] AC generator 30

[0071] Coil 32

[0072] Resistor 34

[0073] Different program steps in a computer program (50-59)

[0074] Phase line L

[0075] Neutral line N

[0076] Current I

[0077] Voltage U

[0078] reactive current I bL

[0079] Active current I w

[0080] Total peak current

[0081] Peak reactive current

[0082] Peak active current

[0083] Peak voltage

[0084] Phase angle α

[0085] Phase shift angle φ

Claims

1. A current transmitter for measuring current flowing through an electrical conductor and for determining the direction of energy flow, the current transmitter comprising a current sensor (12) for acquiring the current intensity flowing through the electrical conductor, and an analysis device (14) for analyzing the measured values ​​acquired by the current sensor (12), characterized in that, The current intensity is output in the positive or negative output range of the output unit according to the measured energy flow direction, wherein the current transmitter has a voltmeter (16) for acquiring the voltage on the conductor, wherein the energy flow direction is determined by analyzing the measured values ​​of current and voltage, thereby performing a phase shift angle measurement for the phase shift between voltage and current, and wherein the current intensity is output in the positive output range when the phase shift angle (φ) is in the range of -90° to +90°, otherwise the current intensity is output in the negative output range.

2. The current transmitter of claim 1, wherein the current intensity is output proportionally in the positive and negative output ranges, wherein the corresponding output ranges are defined such that the output current passes through zero in proportion to the measured current.

3. The current transmitter according to claim 2, wherein the analysis device (14) generates the output signal of the acquired measurement current in such a way that the output value can be output with a sign along the vertical axis according to the measured energy flow direction.

4. The current transmitter according to claim 1, wherein the output of the measured current is always positive, and the energy flow direction can be output via another output port (17).

5. The current transmitter according to claim 4, wherein the output of the measured current is always positive, the energy flow direction can be output via the other output port (17), and the output signal has an offset value of 4 mA.

6. The current transmitter according to claim 1, wherein the current transmitter has one or two additional indicating elements for indicating the direction of the energy flow.

7. The current transmitter according to claim 6, wherein the indicating element is a light-emitting diode.

8. The current transmitter according to claim 1, as an alternative to outputting the measured current, outputs a voltage in proportion to the measured current.

9. A method for outputting a measured value in a current transmitter according to any one of the preceding claims, characterized in that, In addition to the current intensity, the energy flow direction of the alternating current flowing through the electrical conductor is also measured, and the measured current intensity is output in the positive or negative output range of the output unit according to the measured energy flow direction. The voltage level of the voltage on the electrical conductor is measured, and the energy flow direction is determined by analyzing the measured values ​​of the current and voltage. The phase shift angle between the voltage and the current is measured. When the phase shift angle (φ) is in the range of 90° to +90°, the measured current intensity is output in the positive output range; otherwise, the current intensity is output in the negative output range.

10. The method of claim 9, wherein active power is measured, and as an alternative to the measured current intensity, the measured active power is output in the positive and negative output ranges.

11. The method of claim 9, wherein reactive power is measured, and as an alternative to the measured current intensity, the measured reactive power is output in the positive and negative output ranges.

12. The method of claim 9, wherein the apparent power is measured, and as an alternative to the measured current intensity, the measured apparent power is output within the positive output range.

13. The method of claim 9, wherein the power factor is measured, and as an alternative to the measured current intensity, the measured power factor or the measured phase shift angle is output in the positive and negative output ranges.

14. The method of claim 9, wherein the frequency of the alternating current is measured, and the measured frequency is output within the positive output range as an alternative to the measured current intensity.

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