Current transducer for measuring the current flowing through an electrical conductor and method for outputting measured values ​​from a current transducer with output of the energy flow direction for alternating currents

Description

[0001] The invention relates to a current transmitter for measuring the current flowing through an electrical conductor. The proposal further relates to a method for outputting measured values ​​from a current transmitter, including the output of the energy flow direction for alternating currents.

[0002] With conventional current transmitters for alternating currents, typically only the value of the current intensity is output proportionally.

[0003] There are energy meters that can determine and display the direction of energy flow, but cannot output the proportional current.

[0004] Document CN 110 224 491 A discloses a monitoring device for an automatic switch of a distributed energy distribution network.

[0005] Document DE 11 2014 002840 T5 teaches a power meter which measures electrical energy supplied to or supplied by each current transformer CT, based on a current measured by an ammeter and a voltage measured by a voltmeter.

[0006] Document US2009315566A1 relates to an AC current sensor that generates a pulsed output signal. This signal can indicate both the phase angle and polarity, allowing the direction of energy flow to be determined. The current is displayed by a lamp (LED) that is driven by the generated pulses. Brighter light indicates a stronger current flow. In one embodiment, the direction of energy flow is also digitally output and displayed. This sensor can thus provide an indication of the direction of energy flow relative to the current sensor, for example, when a potential short circuit occurred, because the direction indicator is recorded during the measurement period immediately preceding the short circuit.

[0007] However, the known solution has the disadvantage that current intensity and energy flow direction cannot be given to a control unit in this way to control a machine or a process.

[0008] Therefore, there is a need for an improved current transmitter that avoids these disadvantages. This was recognized within the scope of the invention.

[0009] This problem is solved by a current transmitter for measuring the current flowing through an electrical conductor according to claim 1, and a method for outputting the current intensity from such a current transmitter according to claim 9.

[0010] The dependent claims include advantageous further developments and improvements of the invention in accordance with the following description of these measures.

[0011] The invention describes a current transmitter with an input for measuring a primary alternating current. A suitable current sensor is integrated for this purpose. The current transmitter also includes a suitable energy flow direction detection system that allows the direction of the primary alternating current to be detected. A suitable processing unit combines the magnitude of the primary alternating current and the energy flow direction to generate an analog output signal, which can assume both positive and negative values.

[0012] The current transmitter according to the invention comprises a current sensor that detects the current through the electrical conductor and an evaluation unit for evaluating the measured values ​​acquired by the current sensor and for determining the direction of energy flow. Depending on the determined direction of energy flow, the current transmitter according to the invention outputs the current as a positive or negative output current. Compared to known current transmitters, the advantage is that the direction of energy flow is also detected, and the output is designed such that the direction of energy flow and the current are displayed simultaneously. A control unit can acquire this output signal and control or regulate the machine or process accordingly.

[0013] Advantageously, the current transmitter also includes a voltmeter, which measures the voltage level on the electrical conductor to determine the phase angle. It is then advantageous if the energy flow direction is determined by evaluating the measured current and voltage values ​​on the conductor using the evaluation unit, such that a phase shift angle is determined for the phase shift between voltage and current. This generates an output signal in which the current is displayed in the positive range if the phase shift angle is between -90° and +90°, and in the negative range otherwise. The energy flow direction can be easily determined by measuring the phase shift angle.

[0014] In a preferred embodiment of the current transmitter, the current is output proportionally in the positive and negative output ranges, wherein the respective output range is defined such that the output current passes through the zero point proportionally to the measuring current.

[0015] The evaluation unit can generate the output signal for the measured current in such a way that the output values ​​can be displayed with a sign along the ordinate, corresponding to the determined direction of energy flow. The output signal can correspond to an analog DC signal. The direction of energy flow determines the current direction.

[0016] In another variant, the output of the measuring current is always positive, i.e., with the same current direction, and the energy flow direction is output via a further output terminal.

[0017] In this variant, it can additionally be provided that the output of the measuring current is always positive, the energy flow direction is output via the additional output terminal, and the output signal also has an offset value. In a preferred example, this offset can be 4 mA.

[0018] To better inform the operating personnel, it is advantageous if the current transmitter is equipped with two additional display elements, in particular light-emitting diodes, which serve to indicate the direction of energy flow.

[0019] In another embodiment, the invention consists of a method for outputting measured values ​​from a current transmitter in which, in addition to the current intensity, the direction of energy flow of the alternating current flowing through the electrical conductor is measured, and the current intensity is output in a positive or negative output range of an output unit depending on the determined direction of energy flow.

[0020] For this purpose, it is advantageous to measure the voltage level on the electrical conductor and to determine the direction of energy flow by evaluating the measured values ​​of current and voltage, whereby a phase shift angle determination is carried out for the phase shift between voltage and current, and the current is output in the positive output range if the phase shift angle is in the range of 90° to +90°, and otherwise the current is output in the negative output range.

[0021] If the measured primary current is to be measured without polarity switching at the output, the polarity can be output via a separate output.

[0022] The standard current can be 0-20mA or 4-20mA.

[0023] It is also advantageous to measure the voltage across the electrical conductor in addition to the current measurement, and to determine the apparent power S using S = U·I. This apparent power can then be output proportionally to the current measurement. With the determined phase shift angle ϕ, it is possible to determine and output the active and reactive power using the determined power factor cos ϕ and the determined reactive power factor sin ϕ. The formula for active power P is P = S·cos ϕ, and the formula for reactive power QL is QL = S·sin ϕ. Several methods are mentioned for this. An analog output of a microcontroller is used as the output unit, which outputs a standard current in the range of, for example, 0-20 mA or a standard voltage in the range of, for example, -10 V to +10 V or 0-10 V.

[0024] In one variant, the current is measured by the current transmitter and the voltage with a voltmeter, whereby instead of the output of the measured current, an output in the form of a voltage proportional to the measured current is given.

[0025] In another variant, the current is again measured by the current transmitter and the voltage with a voltmeter, whereby instead of the current, the specific active power is output in the positive and negative output range of the output unit.

[0026] In the next variant, the current is again measured by the current transmitter, and the voltage with a voltmeter, whereby instead of the current, the specific reactive power is output in the positive and negative output range of the output unit.

[0027] In another variant, the current is again measured by the current transmitter, and the voltage with a voltmeter, whereby instead of the current, the specific apparent power is output in the positive output range of the output unit.

[0028] In another variant, the current is again measured by the current transmitter, and the voltage with a voltmeter, whereby instead of the current, the specific power factor or the specific phase shift angle is output in the positive and negative output range of the output unit.

[0029] In another variant, the current is again measured by the current transmitter, and instead of the current intensity, the specific frequency is output in the positive output range of the output unit.

[0030] It is understood that the highest power factor, or the highest frequency to be measured, corresponds to the highest output current, e.g. 20 mA, or the highest output voltage, e.g. 10 V.

[0031] The same applies to the phase shift angle, except that the phase shift angle is also output with a sign.

[0032] Several embodiments of the invention are shown in the drawings and are explained in more detail below with reference to the figures.

[0033] They show: Fig. 1 a first block diagram of a current transducer for measuring the current flowing through an electrical conductor; Fig. 2 a circuit diagram to illustrate the behavior of an alternating current in the presence of an inductor; Fig. 3 a signal diagram showing the current waveforms across resistance and reactance and the voltage waveform for the circuit according to Fig. 2Fig. 4 shows a second block diagram of a current transmitter for measuring the current flowing through an electrical conductor; Fig. 5 shows a first embodiment of an analog output of current and energy flow direction from the current transmitter according to the invention; Fig. 6 shows a second embodiment of an analog output of current and energy flow direction from the current transmitter according to the invention; Fig. 7 shows a third embodiment of an analog output of current and energy flow direction from the current transmitter according to the invention; and Fig. 8 shows a flowchart for an evaluation algorithm for determining the energy flow direction and for processing the data for an analog output of current and energy flow direction.

[0034] The present description illustrates the principles of the inventive disclosure. It is therefore understood that those skilled in the art will be able to design various arrangements which, although not explicitly described here, embody principles of the inventive disclosure and which are also intended to be protected in their scope.

[0035] Fig. 1Figure 1 shows a block diagram of a current transmitter 10 for measuring the current flowing through an electrical conductor L. A single-phase cable 5 is shown, consisting of phase L and neutral N. Optionally, a protective conductor can also be included in the cable 5 (not shown). The current on conductor L is to be monitored. For this purpose, a current transmitter 10 is used. It is connected between phase L and neutral N. In this configuration, the current is passed internally through the current transmitter 10. In another type of current transmitter, the current is not passed through the transmitter but is determined indirectly. For example, a current transmitter 10 with a Rogowski coil can be used. This is an air-core coil that is placed around conductor L. The effect of the changing magnetic field that arises around conductor L during alternating current is such that a voltage is induced in the Rogowski coil, which is then measured.

[0036] In the illustrated current transmitter 10, the reference number 12 denotes a current sensor. This sensor quantitatively measures the current flowing through conductor L. The current transmitter 10 is also connected to the neutral conductor N. Both conductors, phase L and neutral N, are brought out to outputs to which the load 20 is connected. Typical current sensors, often also called current transformers, are low-power transformers that convert high currents into easily measurable values. In one variant, the input winding is connected to the phase conductor L and carries the current to be measured. A conventional ammeter, for example, is connected to the output winding.Because the primary winding has only a few turns or even just one, while the secondary winding has a significantly larger number of turns, high current values ​​of several hundred amperes can be measured using conventional measuring technology (ammeters). Another type of current sensor is the so-called through-hole current transformer, through which the conductor whose current is to be measured is inserted. Rogowski coils are one example of this type. These allow even higher current values ​​to be measured. This is advantageous for conductors, such as those used in busbars, which cannot be wound easily. A third type of current sensor, which can also be used in the described device, is the Hall effect current sensor.These devices utilize the Hall effect, which occurs when a current-carrying conductor located in a stationary magnetic field generates an electrical voltage. Such Hall generators are typically designed as flat surfaces, generating a magnetic field that is as homogeneous as possible and oriented perpendicular to the flat conductor. The Hall voltage is measured at the outer edges of the flat conductor, perpendicular to the current direction. In one version, the Hall effect current sensor is inserted into a slotted magnetic ring core.

[0037] The measured values ​​are acquired by the evaluation electronics 14 of the device and temporarily stored for evaluation. The evaluation electronics 14 can be implemented as a microcontroller. This is equipped with an analog-to-digital converter (ADC) and a sampling unit to acquire successive measured values. It also includes a memory (e.g., CMOS RAM) to temporarily store the measured values. The main component is a programmable microcomputer that executes the evaluation algorithm. The microcomputer also includes a digital-to-analog converter (DAC) unit that generates an analog output signal. The output unit is preferably implemented by an integrated DAC unit within a microcomputer. The analog output signal is output via the output terminal 18. A separate line can be connected to this output terminal 18 and forwards this signal to a control unit 24.The signal can be routed to a programmable logic controller (PLC) 24. Measurement data is acquired at a specific sampling rate, which can be in the range of kS / s. The evaluation electronics 14 also acquire the voltage between phase L and neutral N. For this purpose, a voltmeter 16 is connected to phase L and neutral N. The measured voltage values ​​are received by the evaluation electronics 14 and written to its memory.

[0038] The direction of energy flow is also determined by the current transmitter 10. This is done by determining the phase angle of the current relative to the voltage. To illustrate the measuring principle, the following is shown in Fig. 2A circuit is shown. The AC generator has reference number 30. The current flow I is shown in one direction. In the circuit shown, the load 20 consists of an inductor 32 and a resistor 34. The current I is divided accordingly into a component Ibl and a component Iw. As is known, the inductor 32 acts like a reactance, but leads to a phase shift between voltage U and current I.

[0039] The exact signal waveforms are in the Fig. 3 The diagram is shown on the left and the signal waveforms on the right. The peak values ​​of voltage u, current î bl through coil 32, and current î w through resistor 34 are represented in the diagram as the corresponding phasor lengths. The superposition of these values ​​results in the total current i, the waveform of which is also shown. The phase difference ϕ between voltage u and current i is shown in both parts of the diagram. Fig. 3The diagram shows the phase difference ϕ of approximately 40° resulting from the specific circuit configuration. This phase difference can be determined by evaluating the signal waveforms of u and i. In both cases, the rising zero crossing of the signal waveforms of u and i is identified. The time difference is then related to the period T to determine the phase difference ϕ.

[0040] 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, i.e., from generator 30 to load 20. In the other cases, it is defined as negative, i.e., from load 20 to generator 30.

[0041] The Fig. 4Figure 1 shows a second variant of the current transmitter 10. The same reference numbers denote the same components. One difference is that two output lines lead out of the current transmitter 10. One output line leads to output terminal 18. The other output line leads to output terminal 17. The line at output terminal 18 is connected to a D / A output of the microcomputer. The other output line to output terminal 17 can also be connected to a D / A output of the microcomputer. In another variant, the output line can alternatively be connected to a digital output of the microcomputer. Thus, two output lines lead to the control unit 24.

[0042] Fig. 5This shows a combined version of an analog output of the measured current and the direction of energy flow. The analog output signal is displayed as a secondary-to-primary current diagram. The primary current corresponds to the current through conductor L and is shown in Fig. 5The secondary current is specified from -400 A to +400 A. The secondary current is the current measured in the evaluation unit 14 and ranges from -25 mA to +25 mA. In the illustrated case, this results in a peak value of approximately 20 mA. This value corresponds to a primary current of approximately 300 A. The conversion is directly proportional. The current is output in analog form, as shown, taking the energy flow direction into account. Therefore, if the energy flow direction is determined to be positive, the output is a straight line in the first quadrant of the coordinate system. This represents a direct current. Its current flow is thus in the direction from the evaluation electronics 14 to the controller 24. Conversely, if the energy flow direction is determined to be negative, the output is a straight line in the third quadrant of the coordinate system. The current flow is then in the opposite direction, from the controller 24 to the evaluation electronics 14. Fig. 5 shows both straight lines in the form of a continuous line.

[0043] Fig. 6 shows a second variant of the output of the measured current and the direction of energy flow, which is for the variant of the current transmitter 10 according to. Fig. 4 This is valid. The energy flow direction is indicated only by the fact that the additional output 17 assumes a different state for the positive range than for the negative range. For the secondary current, a signal with positive polarity is output in both cases, i.e., the current direction remains the same.

[0044] Fig. 7 This shows a third embodiment of the analog output of the measured current and the direction of energy flow. The direction of energy flow is displayed as in Fig. 6The display shows positive values ​​for the secondary current in both cases. However, the lines do not originate from the origin of the coordinate system. Instead, a specific offset of approximately 4 mA is shown. The lines run from this offset point at 0 A primary current to the currently measured peak value î. This form of current output allows for secondary current flow even when no primary current is flowing. This enables the measuring system to be monitored even without primary current. The switching signal for polarity output is also shown again.

[0045] Fig. 8Figure 1 shows an exemplary implementation of a flowchart for an evaluation algorithm that is executed in the evaluation electronics 14. The program start is designated by the reference number 50. In program step 51, the current through the conductor of phase L is measured. In program step 52, the voltage on the conductor of phase L relative to the neutral conductor is measured. The signals output by the current sensor 12 are fed to an A / D input of the microcontroller of the evaluation electronics 14. This microcontroller samples the input signal and writes the digital values ​​to memory. The measurement signal from the voltmeter is also sampled via another A / D input of the microcontroller, and the digital values ​​are likewise written to memory. In program step 53, the phase difference ϕ between voltage U and current I is determined. This determination is performed as described previously in connection with the Fig. 3The process is described. The signal waveforms of U and I are evaluated. In one variant, the rising zero crossing of the signal waveforms of U and I is determined for both signals. Then, the time difference between these two points is determined. This difference is then related to the determined period T of the signals to calculate the phase difference ϕ. If inductors are present, the alternating current follows the alternating voltage. In program step 54, the determined phase shift angle ϕ is evaluated. If ϕ lies within the range [90°, +90°], it is concluded that the energy flow direction is positive, i.e., energy flows from the AC generator 12 towards the load 20. If it is determined that the phase shift angle ϕ lies outside this range, it is concluded that the energy flow direction is reversed, i.e., the load supplies the energy and it flows back to the power plant.In program step 55, it is specified that the energy flow direction is positive. Then, in program step 57, the output current is displayed as a function of the input current, using the straight line as in the first quadrant of the diagram. Fig. 5 , the Fig. 6 or the Fig. 7 shown. The direction of energy flow is also shown. Additionally, this is shown in the Fig. 6 and 7 The displayed switching signal is output. If the phase shift angle ϕ lies outside the range of [-90°, +90°], it is determined in program step 56 that the energy flow direction is negative. Accordingly, in program step 58, the output current is calculated using the straight line as shown in the 3rd quadrant of the Fig. 5 , or in the 2nd quadrant of the Fig. 6 or 7 Output. The switching signal can also be output at output terminal 17.

[0046] It should be understood that the proposed method and the associated apparatus can be implemented in various forms of hardware, software, firmware, specialized processors, or a combination thereof. In a preferred embodiment, microcontrollers with integrated RAM and integrated I / O interfaces are used. Specialized processors can include application-specific integrated circuits (ASICs), reduced instruction set computers (RISCs), and / or field-programmable gate arrays (FPGAs). Preferably, the proposed method and apparatus are implemented as a combination of hardware and software. The software is preferably installed as an application program on a program storage device.Typically, this is a machine based on a computer platform that includes hardware such as one or more central processing units (CPUs), 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 here may be part of the application program or part that is executed by the operating system.

[0047] The disclosure is not limited to the embodiments described here. There is scope for various adaptations and modifications that a person skilled in the art would consider based on their expertise and in relation to the disclosure itself.

[0048] The following table lists some possible input and output options for the current transmitter according to the invention. The output options are listed separately for analog and digital options in different columns.

[0049] Table 1 should be understood to mean that all input measurement options can be arbitrarily linked to the analog and digital output options. In other words, for each input measurement option, it can be selected whether it should be provided to the control system as an analog current output or an analog voltage output.

[0050] Various output ranges can be selected, e.g., 4 to 20 mA for current output or 1 to 5 V for voltage output. The digital output options allow the information specified in the table to be displayed, for example, via appropriately controlled LEDs. The abbreviation THD stands for Total Harmonic Distortion, which, in signal analysis, is a measure used to quantify the proportion of a signal caused by nonlinear distortion. Table 1 Input measurement options Analog output options Digital output options RMS value of the alternating current for electricity output Polarity of energy flow direction RMS value of the AC voltage 0 to 20 mA Polarity of the conduction factor Active power 4 to 20 mA Polarity of the deviation from the target value Reactive power -20 to +20 mA Load type (inductive / capacitive) Apparent power for voltage output Performance factor 0 to 10 V frequency 2 to 10 V Crest factor -10 to +10 V THD power 0 to 5 V THD voltage 1 to 5 V Direct current -5 to +5 V DC voltage 0 to 10 V Load type (inductive / capacitive) 2 to 10 V Phase angle Deviation from the target value of one of the aforementioned quantities Reference symbol list

[0051] alternating current line 5 Current transmitter 10 Current sensor 12 Evaluation electronics 14 Voltage meter 16 1. Output port 17 2. Output port 18 AC load 20 Control unit 24 AC generator 30 Sink 32 Resistance 34 various program steps of a computer program 50 - 59 phase L Neutral conductor N Electricity I Tension U Reactive power I bL Active current I w Peak value total current î Peak value reactive power î bL Peak value active current î w Peak voltage û Phase angle α Phase shift angle ϕ

Claims

1. A current measuring transducer for the measurement of the current flowing through an electrical conductor (L), comprising: a current sensor (12) that captures the current intensity through the electrical conductor (L) and an evaluation device (14) for the evaluation of the measured values captured by the current sensor (12), and for the determination of the energy flow direction, characterized in that the output of the current intensity in a positive or negative output range of an output unit occurs depending on the determined energy flow direction, and a voltage meter (16) that captures the voltage on the electrical conductor (L), wherein the determination of the energy flow direction is performed by evaluating the measured values of current and voltage such that a determination of the phase shift angle between voltage and current occurs, and wherein an output of the current intensity occurs in the positive output range if the phase shift angle (ϕ) lies in the range from -90° to +90°, otherwise an output of the current intensity occurs in the negative output range.

2. The current measuring transducer according to claim 1, wherein the output of the current intensity in the positive and negative output range occurs proportionally, wherein the respective output range is defined such that the output current runs proportionally to the measured current through the zero point.

3. The current measuring transducer according to claim 2, wherein the evaluation device (14) generates the output signal for the captured measured current such that along the ordinate, according to the determined energy flow direction, the output values can be output with a sign.

4. The current measuring transducer according to claim 1, wherein the output of the measured current is always positive and the energy flow direction can be output through an additional output terminal (17).

5. The current measuring transducer according to claim 4, wherein the output of the measured current is always positive and the energy flow direction can be output through the additional output terminal (17) and the output signal has an offset value of 4 mA.

6. The current measuring transducer according to any of the preceding claims, with one or two additional display elements, particularly light-emitting diodes (LEDs), which serve to display the energy flow direction.

7. The current measuring transducer according to any of the preceding claims, wherein instead of the output of the measured current, an output in the form of a voltage proportional to the measured current occurs.

8. A method for the output of measured values in a current measuring transducer according to any 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 (L) is measured, and that the measured current intensity is output in a positive or negative output range of an output unit depending on the determined energy flow direction, wherein a measurement of the voltage amplitude on the electrical conductor (L) is carried out and the determination of the energy flow direction is performed by evaluating the measured values of current and voltage, wherein a determination of the phase shift angle for the phase shift between voltage and current is carried out, and the measured current intensity is output in the positive output range if the phase shift angle (ϕ) lies in the range from 90° to +90°, otherwise the current intensity is output in the negative output range.

9. The method according to claim 8, wherein the active power is determined and instead of the measured current intensity, the measured active power is output in the positive and negative output range.

10. The method according to claim 8, wherein the reactive power is determined and instead of the measured current intensity, the measured reactive power is output in the positive and negative output range.

11. The method according to claim 8, wherein the apparent power is determined and instead of the measured current intensity, the measured apparent power is output in the positive output range.

12. The method according to claim 8, wherein the power factor is determined and instead of the measured current intensity, the measured power factor or the measured phase shift angle is output in the positive and negative output range.

13. The method according to claim 8, wherein the frequency of the alternating current is measured and instead of the measured current intensity, the measured frequency is output in the positive output range.