Universal measuring input for connecting a small signal converter and electrical device with such a measuring input

Description

[0001] The invention relates to a measuring input for connecting a small-signal converter to an electrical device, having an electrical input for connecting a connecting cable of the small-signal converter, an electrical output for outputting a measuring signal to the electrical device, and having a correction element which has a digital filter whose filter transfer function is adapted to the small-signal converter.

[0002] The invention also relates to an electrical device with such a measuring input.

[0003] Electrical devices in use today, such as automation, measurement, control, or protection devices in a technical system (e.g., a power grid), typically have one or more measurement inputs to which a secondary side of transformers or sensors can be connected in order to record measured variables such as currents or voltages in the technical system. These measurement inputs are usually specifically adapted to the type and special design of the transformer. For decades, inductive transformers were commonly used for both current and voltage measurement. With the advent of so-called low-power instrument transformers (LPITs), which are designed, for example, according to the IEC 61869 standard, the number of new sensor types and thus the effort required to provide suitable measurement inputs is increasing significantly.Examples of small-signal converters include Rogowski coils, inductive converters with integrated load, capacitive dividers, resistive dividers, and compensated RC dividers. Furthermore, CR dividers with passive integrators (see, for example, IEC 61869-11 Annex 11C, Figure 11C.1) or simple measuring capacitors for displacement current measurement (so-called "field probes") can be used for voltage measurement. In addition to the passive small-signal converters described in IEC 61869-10, sensors based on the magnetoresistive effect or the Hall effect can also be used for current measurement. These sensors, in turn, are divided into direct imaging and compensation types.

[0004] If a device manufacturer wanted to offer a separate, specific measuring input for each sensor type, a large number of different modules would have to be developed and maintained in order to cover all possible combinations of sensor types and sensor designs.

[0005] For comparison, it should be noted that for conventional inductive transducers, a single standardized measurement input is sufficient to ensure compatibility between the current or voltage transducers and the respective device signal inputs. For the new small-signal transducers, various current sensor types exist (e.g., Rogowski coils, low-power current transformers ("Low Power CTs") with integrated load resistors) and various voltage sensor types (capacitive dividers, resistive dividers, compensated RC dividers, field probes, and CR dividers with passive integrators). Each of these sensor types can be designed for different load impedances, and each of these variants would require its own measurement input, so a variety of different measurement inputs would be required to cover each of these variants.

[0006] DE 103 46 356 A1 discloses a voltage input for connecting a small-signal converter in the form of a capacitive divider. To correct the transfer function of the capacitive divider, a filter with a correction function that is inverse to the transfer function is used. To enable the known measurement input to also be connected to a conventional inductive converter, the filter can be bridged.

[0007] Further state-of-the-art measurement inputs are described in US 9 917 662 B2 and US 2019 / 383859 A1.

[0008] Starting from a measuring input of the type mentioned at the outset, the object of the invention is to provide a measuring input with which all possible types of small-signal converters, in particular those small-signal converters designed according to the IEC 61869 standard, can be connected to an electrical device and thus the variety of measuring inputs to be provided can be reduced.

[0009] To solve this problem, a generic measuring input is proposed in which the filter transfer function of the correction element is defined by means of a parameter set, whereby the parameter set can be variably specified specifically for the small-signal converter.

[0010] The advantage of the measuring input according to the invention is that the adjustment is essentially carried out via a correction filter whose transfer function can be variably specified using a parameter set. This allows the measuring input to be universally and easily adapted specifically for each of the different sensor types using the parameter set. The parameter set can contain parameters that can be used to define the filter transfer function. Examples of such parameters are the properties of the connected small-signal converters, any adapters used, and the connecting cables. These sensor properties can be described, for example, for current sensors with the rated values ​​specified in Table 1004 "Designation of a passive CT" of IEC 61869-10. For voltage sensors, these properties can be described with the rated values ​​from Table 1106 "Designation of a passive LPCT" of IEC 61869-11.Alternatively, the properties of a small-signal converter can be described by specifying the values ​​of the equivalent circuit diagram of the sensors, adapters, and cables. From these parameters, the required filter transfer function can be determined if the desired resulting overall transfer function is known.

[0011] According to the invention, the parameter set can be specified specifically for different types of small-signal converters, on the one hand for current measurement and on the other hand for voltage measurement.

[0012] Thus, one and the same measuring input can be used variably not only for the measurement of current or voltage signals, but - depending on the specified parameter set - it can also be used for the measurement of both currents and voltages without the need for a different hardware module.

[0013] A further advantageous embodiment provides that the filter transfer function of the correction element is designed to compensate for a sensor path transfer function of a transmission path formed by the small-signal converter, the connecting cable and at least one component of the measuring input.

[0014] According to this embodiment, the accuracy of the measurement is increased by the fact that the correction is not only performed with regard to the transfer function of the small-signal converter. Rather, the correction also includes the connecting cable with which the small-signal converter is connected to the measuring input, as well as essential components of the measuring input itself. The latter components can also have a significant influence on the transmission of the measurement signals. With regard to the connecting cables, aspects of the connection technology (sensor connection to a device terminal) can also influence the required correction: for example, cables of different lengths, different cable types, and various adapters can have a significant influence on the required correction.

[0015] A further advantageous embodiment of the measuring input according to the invention also provides that the filter transfer function is designed such that an overall transfer function resulting from the superposition of the sensor path transfer function and the filter transfer function corresponds to a transfer characteristic that would be present when using a (conventional) inductive converter as a sensor.

[0016] This ensures that the measurement input connected to a small-signal converter behaves, from the perspective of the electrical device, as if a "normal" inductive converter were connected. This allows all functions using the measurement signal to continue to be used without additional adjustments.

[0017] Within the scope of a further advantageous embodiment, it can be provided that the pole points of the filter transfer function are determined as a function of the position of the zero points of the sensor path transfer function and the zero points of the filter transfer function are determined as a function of the position of the pole points of the sensor path transfer function.

[0018] In this way, the filter transfer function used for correction can be generated particularly advantageously, since the zero and pole points of the sensor path transfer function, which are easy to determine analytically, are used as anchor points for determining the filter transfer function.

[0019] According to a further advantageous embodiment, it is provided that the sensor-specific parameter set is stored in a data memory as part of a configuration of the measuring input.

[0020] Specifically, in this context, it can be provided that a sensor model describing the small-signal converter, a cable model describing the connecting cable and a measurement input model describing at least one component of the measurement input are provided in the data memory of the measurement input or in a configuration tool for configuration, from which the sensor-specific parameter set is derived.

[0021] The respective models can represent a mathematical simulation of the respective frequency-dependent transfer functions of the individual components. Each of the components is viewed as a block, for example, a so-called "four-terminal network," with its own properties. The sensor path transfer function is formed by linking the individual blocks. From this, the parameter set used to define the filter transfer function can ultimately be derived.

[0022] A further advantageous embodiment provides that an impedance matching circuit designed as a voltage divider is arranged downstream of the electrical input.

[0023] This allows the measurement input to be designed to provide the required input impedance. For example, the IEC 61869-10 or IEC 61869-11 standards specify input impedances for measurement inputs for small-signal converters, which can be maintained using such an impedance matching circuit.

[0024] Furthermore, it can be provided that a signal conditioning unit is connected downstream of the impedance matching circuit, which can be switched between a first mode according to a low-pass characteristic or a PI element and a second mode according to a proportional characteristic.

[0025] The signal conditioning unit allows the measurement input to be adapted to the type of small-signal converter, thus simplifying the filter transfer function. Furthermore, the required dynamic range is compressed across the frequency, for example, as the transfer behavior of the signal conditioning unit compensates for a large dynamic range of the frequency-dependent gains of the sensor path transfer function within the passband of interest to a value that is as frequency-independent as possible. This is achieved in sensors with differentiating behavior, for example, with a low-pass filter above the cutoff frequency of the low-pass filter.

[0026] Specifically, in this context, it can be provided that the mode of the signal processing unit is determined depending on the position of a zero point of the transfer function of the small-signal converter.

[0027] For example, it can be provided that the signal conditioning unit operates in the first mode when the transfer function of the small-signal converter has a zero point at f=0Hz in order to compensate for a differentiating characteristic of the converter used (e.g. Rogowski coil).

[0028] A further advantageous embodiment of the measuring input according to the invention provides that a programmable amplifier is connected downstream of the signal processing unit.

[0029] This allows the varying gains of various small-signal converters to be adapted to the measuring range of the downstream A / D converter. The gain stages of the programmable amplifier are advantageously graded logarithmically to achieve optimal adaptation of the measurement input to the gain of the small-signal converters. In other words, small-signal converters with different transformation ratios can exist (i.e., different secondary nominal values ​​will result depending on the primary nominal current). To accommodate this, different measuring ranges / gain switching are required, which can be implemented with the amplifier.

[0030] Finally, to digitize the measurement signal, a sampling device or an AD converter can be connected downstream of the programmable amplifier.

[0031] The invention also relates to an electrical device with at least one measuring input according to one of claims 1-12. Such an electrical device can be, for example, an automation, measuring, control, or protection device of a technical system, for example, a power grid.

[0032] With regard to the device according to the invention, all statements made above and below regarding the measuring input according to the invention apply accordingly, and vice versa. In particular, the device according to the invention can be operated with the measuring input in any desired embodiment or a combination of desired embodiments. Regarding the advantages of the device according to the invention, reference is also made to the advantages described for the measuring input according to the invention.

[0033] According to an advantageous embodiment of the electrical device, it can be provided that the electrical device, in addition to the at least one measuring input, has at least one further measuring input for connecting an inductive converter.

[0034] In particular, in the case where the measuring input connected to a small-signal converter simulates the characteristics of a "conventional" measuring input connected to an inductive converter, it can be ensured that all downstream device functions of the electrical device can operate without further adaptation and within the specified specifications to the type of converter.

[0035] The invention is explained in more detail below using an exemplary embodiment. The specific embodiment of the exemplary embodiment is in no way intended to limit the general design of the measuring input according to the invention and the device according to the invention; rather, individual design features of the exemplary embodiment can be freely combined with one another and with the features described above in any way.

[0036] To this end, Figure 1 shows an electrical device connected to a technical system by means of a small-signal converter, having a measuring input; Figure 2 shows a schematic representation of individual components of transfer functions of a measuring section; Figure 3 shows an exemplary embodiment of a measuring input; Figure 4 shows an electrical device connected to a technical system by means of a small-signal converter on the one hand and an inductive converter on the other; and Figure 5 shows examples of a sensor section transfer function and a filter transfer function.

[0037] In the figures, identical or corresponding units are identified by the same reference numerals.

[0038] Figure 1shows an electrical device 10, which can be, for example, an automation, measuring, control or protection device. Such devices are usually used to observe, control, protect or monitor technical systems. For this purpose, the devices are connected to the technical system via sensors, which record measurement signals that indicate the status of the technical system. The technical system can be, for example, an electrical power supply network. To monitor such an electrical power supply network, measurement signals of currents and voltages are usually recorded. While inductive measuring transducers have been used as sensors for this purpose for a long time, the use of small-signal measuring transducers is now becoming more and more widespread. Sensors that output a low electrical power (compared to conventional inductive transducers) at their output are considered small-signal measuring transducers.Examples of small-signal converters for measuring currents or voltages include Rogowski coils, capacitive dividers, resistive dividers, compensated RC dividers, CR dividers with passive integrators, or low-power current transformers with integrated burden. Such small-signal converters usually exhibit different transfer characteristics than inductive converters, which is particularly evident in high and low frequency ranges.

[0039] In the example of Figure 1 The electrical device 10 is connected to the technical system 12 via a small signal converter 11. The technical system 12 is, for example, an electrical power supply network, from which Figure 1For the sake of clarity, only one line is shown. The small-signal converter 11 is connected to a measuring input 14 of the electrical device 10 via a connecting cable 13, which can be, for example, a double-shielded pair of wires with a length customary in technical systems (e.g., substations) (e.g., a few meters in medium-voltage switchgear up to several hundred meters in high-voltage switchgear). The measuring input 14 can, for example, represent an integrated board of the electrical device 10. Alternatively, it can also be a separate module located outside the device 10. The measuring input 14 is designed to interact with any small-signal converter.For this purpose, it has a digital filter whose transfer function compensates the characteristics of a sensor path transfer function formed by small-signal converter 11, connecting cable 13 and at least one module of the measuring input 14 in the desired manner.

[0040] This shows Figure 2 A schematic representation of the individual components of a measuring path 20, including their various transfer functions. The measuring path consists of the small-signal converter 11, the connecting line 13, and the measuring input 14, with the measuring input having at least one module 21 and a correction element 22 with the aforementioned digital filter. The at least one module 21 of the measuring input 14 comprises all analog circuits of the measuring input 14 up to an analog-to-digital conversion. These analog circuits serve for preprocessing (e.g., filtering, amplification) of the measuring signal.

[0041] Each of the components of the measuring section 20 has its own transfer function, i.e., in the frequency domain, a characteristic of how currents and voltages are transferred in a frequency-dependent manner with regard to their amplitude (attenuation) and their phase angle (phase shift). Specifically, the small-signal converter 11 has a transfer function g Sensor (f), the connecting line 13 has a transfer function g Cable (f), and the at least one module 21 of the measuring input 14 has a transfer function g Input (f). These components together form a sensor section and have a sensor section transfer function g total (f) composed of the three individual transfer functions. The correction element 22 with the digital filter has a transfer function g Filter (f), which serves to correct the sensor section transfer function, so that the characteristics of the individual components of the sensor section, e.g.The type and design of the small-signal converter, the nominal termination impedance (design burden) of the small-signal converter, and the type and length of the connecting cables do not affect the measurement result. To enable the use of any small-signal converter with any connecting cables as sensors for current or voltage measurement, the filter transfer function g Filter (f) can also be arbitrarily adapted to the respective sensor path transfer function.

[0042] Figure 3shows a schematic view of the measuring input 14. The measuring input 14 has an electrical input 30 and an electrical output 31. The electrical input 14 is designed for electrical connection to the connecting lines 13 in order to connect the measuring input 14 to the small-signal converter. An impedance matching circuit 32 is arranged downstream of the electrical input 30 and serves to match the input impedance of the measuring input 14. Input impedances for measuring inputs operated with small-signal converters are specified, for example, in the IEC 61869 standard. The impedance matching circuit 32 can be constructed as a resistive voltage divider and, in this context, can have, for example, an upper resistance value of 1.8 MΩ and a lower resistance value of 200 kΩ.

[0043] A signal processing unit 33 can be arranged downstream of the impedance matching circuit 32. The signal processing unit 33 can, for example, be designed as a low-pass filter or PI element. In a design as a low-pass filter, it can, for example, be an RC combination of a resistor and a capacitor, which forms a first-order low-pass filter whose cut-off frequency is set below the nominal frequency of the technical system. In a design as a PI element, for example, an operational amplifier in an inverting basic circuit with a resistor from the input of the circuit to the inverting OPV input and a resistor in parallel with a capacitor in the feedback branch can be used. The signal processing unit 33 can, for example, serve to limit the frequency-dependent amplification of the analog signal chain within the used frequency range. The signal processing unit 33 can (e.g.via software that controls the measurement input) be switchable between two modes, the first mode having a low-pass characteristic or a PI characteristic and the second mode a proportional characteristic. The switching between the two modes serves to compensate for the differentiating behavior of a Rogowski coil before the analog-to-digital conversion. The mode of the signal processing unit 33 can be determined depending on the position of a zero of the transfer function g sensor (f) of the small-signal converter 11. If the transfer function g sensor (f) has a zero at a frequency of 0 Hz in the zero-pole representation, as is the case with a Rogowski coil, for example, the signal processing unit 33 is operated in the first mode.This has the advantage that the downstream analog-to-digital converter can be operated with high accuracy, since no or only a small headroom of the AD converter needs to be maintained for transient pulse peaks of the Rogowski coil.

[0044] A programmable gain amplifier (PGA) 34 is connected downstream of the signal conditioning unit 33. This amplifier serves to adjustably boost the signal level. The gain g PGA of the programmable amplifier can be set, for example, according to the following equation: g PGA = V IO − inp − max V ADC − max ⋅ g Div V IO − inp − max = 2 ⋅ g SigChain f n ⋅ X Nom ⋅ Clip

[0045] Here, the following means: g SigChain (fn ): transfer function of the connected small signal converter (including connecting cable) folded with the transfer function of at least one module 22 of the measuring input 14 at the nominal frequency of the technical system; X Nom : nominal voltage or nominal current of the technical system (depending on the sensor type); Clip: ratio between the full scale and the nominal value of the voltage or current; V ADC-max : full scale of the input voltage of the analog-to-digital converter; g div : transformation ratio of the signal transmission chain; quotient of the output voltage of the signal transmission chain and the applied input signal (current or voltage depending on the sensor) at nominal frequency.

[0046] The programmable amplifier 34 is followed by a sampling device or analog-digital converter 35, which digitizes the measurement signal output by the amplifier 34 and transmits it via an internal bus to the correction element 22 (cf. Figure 2). In the example of the Figure 3 the impedance matching circuit 32, the signal conditioning unit 33 and the programmable amplifier 34 form the analog part of the measuring input 14 and thus the at least one module 21 according to Figure 2 .

[0047] The correction element 22 comprises a digital filter 36 and a data memory 37. In the data memory 37, a Figure 3A schematically indicated parameter set 38 is provided, which determines the filter transfer function g Filter (f) of the digital filter. The parameter set is variable and can be specifically adapted to the type and design of the small-signal converter 11, the connecting cable 13, and the at least one module 21 of the measuring input 14. For this purpose, model descriptions 39 are stored in the data memory, which analytically describe the transfer functions g Sensor (f), g Cable (f), and g Input (f) of the individual components of the sensor transmission path. Alternatively, the model descriptions 39 can also be stored in a configuration tool, e.g., configuration software. The model descriptions specify the modeling of two-terminal or four-terminal networks, with which the transfer functions of the "small-signal converter," "connecting cable," and "measuring input module" components can be described.These model descriptions use predefined equivalent circuits and their parameters for the respective small-signal converter types, connecting cable types and module types of the measuring input in order to describe the frequency-dependent transfer behavior. The equivalent circuits of the individual four-terminal networks are modeled, for example, in a chain matrix representation of a four-terminal network using four individual transfer functions. The transfer functions of the chain matrix elements are determined in a known manner by comparing coefficients from the respective equivalent circuit of the four-terminal network. From the combination of the individual modeled transfer functions, the sensor path transfer function g total (f) can be determined, and the filter transfer function g filter (f) is designed to correct this. The type of combination can be achieved, for example, by multiplying the chain matrices of the individual four-terminal networks connected in series.From the resulting chain matrix elements, the output voltage to input voltage or output voltage to input current transfer function (depending on the sensor type) of the resulting four-terminal network can then be formed in a known manner, given the transfer function of the load impedance of the four-terminal network.

[0048] The transfer function g result (f) resulting from the superposition of the sensor path transfer function g total (f) and the filter transfer function g filter (f) can be selected such that it would correspond to a transfer characteristic that would be present when connecting a conventional inductive current or voltage transformer to a conventional measuring input. This makes it possible to retain unchanged the evaluation functions of the electrical device 10 downstream of the measuring input 14, which were previously designed for the use of inductive transformers and adapted to their characteristics. Of course, any other form of the resulting transfer function is also possible, so that, for example, completely flat curves of the resulting transfer function can also be realized.To calculate the corrective filter transfer function based on the sensor-path transfer function, the sensor-path transfer function is advantageously transformed into a product form using an eigenvalue calculation of the characteristic matrix of the transfer function polynomial (so-called "zero, pole gain representation"). The poles and zeros of the sensor-path transfer function are sorted by their frequency. Only poles and zeros that lie within the frequency range of interest for correction are considered (typically the frequency range from 0 Hz to half the sampling frequency of the AD converter).To achieve the flattest possible resulting overall transfer function after correction, zeros of the sensor-path transfer function in the frequency range of interest are used as poles in the filter transfer function, and the poles of the sensor-path transfer function are used as zeros of the filter transfer function. The gain of the filter transfer function is selected such that the product of the gains of the sensor-path transfer function and the filter transfer function at the nominal frequency corresponds to the desired value (e.g., 1.0 times the nominal value). To adapt the filter transfer function to a given reference characteristic of an inductive transducer, the poles and zeros of the reference characteristic are inserted into the filter transfer function of the flat characteristic as additional product terms.

[0049] Figure 4shows an electrical device 40 that is connected to a small-signal converter 11 via a measuring input 14 and to an inductive converter via another (conventional) measuring input 41. Particularly in such a mixed configuration, it is advantageous if the resulting transfer function of the measuring input 14 is designed such that it corresponds to the characteristics of a transmission path with an inductive converter.

[0050] Figure 5Finally, shows diagrams with example transfer function curves when using a small-signal converter in the form of an RC divider for voltage measurement. The upper diagram shows the amplitude transfer functions and the lower diagram the phase angle transfer function. In the upper diagram, curve 50 shows the sensor path transfer function g total (f) when using the RC divider. Curve 51 indicates the corrective filter transfer function g filter (f) of the digital filter, which must be used to achieve the desired resulting overall transfer function g result (f), which is shown as curve 52. It can be seen that in a zero-pole representation of the transfer function, dependencies between zeros and poles of the filter transfer function g filter (f) and the sensor path transfer function g total (f) must be created in order to design the filter transfer function.

[0051] For example, it can be provided that in a frequency range between 0Hz and half the sampling frequency fa of the AD converter, the poles of the filter transfer function (e.g. position 53 in Figure 5 ) at the zero points of the sensor path transfer function (e.g. position 54 in Figure 5 ) and vice versa the zeros of the filter transfer function (e.g. position 55 in Figure 5 ) at the poles of the sensor path transfer function (e.g. point 56 in Figure 5 ) lay.

[0052] In the case of a Rogowski coil, a zero of the sensor path transfer function at f=0Hz is compensated with a pole of the filter transfer function at a frequency corresponding to a time constant of a conventional inductive current or voltage transformer.

[0053] In the case of other transformer types where there is no zero at 0Hz, an additional pole is inserted in the filter transfer function at a frequency corresponding to a time constant of a conventional inductive current or voltage transformer.

[0054] In the lower diagram, with regard to the phase rotation, curve 57 indicates the sensor path transfer function for a small-signal converter in the form of an RC divider, curve 58 indicates the corrective filter transfer function and curve 59 indicates the resulting overall transfer function.

[0055] The measuring input 14 is designed to interact with any type of small-signal converter and to exhibit the desired characteristics as the resulting transfer function. To do so, the parameter set 38 stored in the data memory 37 simply needs to be adapted to the small-signal converter as explained above. This is done as part of a configuration. For this purpose, the required information about the individual transfer functions can be determined from the models 39 for the components of the measuring path. This can be done directly in the measuring input or in an external configuration tool. In the latter case, the model descriptions are stored in the configuration tool instead of in the measuring input. The obtained parameter set also takes into account the transfer characteristics of the connecting cable, which are determined in particular from its type and length. The configuration can be performed before the measuring input is put into operation.Standard settings for different types and designs of small signal converters can also already be calculated and stored (e.g. in the data memory of the measuring input), so that only the correct type of small signal converter needs to be selected for configuration.

[0056] Although the invention has been illustrated and described in detail above by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the following claims.

Claims

1. Measurement input (14) for connecting a small signal transformer (11) to an electrical device (10), having - an electrical input (30) for connecting a connection line (13) of the small signal transformer (11); - an electrical output (31) for outputting a measurement signal to the electrical device (10); and - a correction element (22) which has a digital filter (36), the filter transfer function of which is adapted for the small signal transformer (11); wherein - the filter transfer function of the correction element (22) is defined by means of a parameter set (38), wherein the parameter set (38) is able to be variably preset specifically for the small signal transformer (11), characterized in that - the parameter set (38) is able to be preset specifically for different types of small signal transformers (11) on the one hand for current measurement and on the other hand for voltage measurement.

2. Measurement input (14) according to Claim 1, characterized in that - the filter transfer function of the correction element (22) is designed for compensating a sensor path transfer function of a transfer path formed by the small signal transformer (11), the connection line (13) and at least one assembly (21) of the measurement input (14).

3. Measurement input (14) according to either of the preceding claims, characterized in that - the filter transfer function is designed in such a way that a total transfer function resulting from the superposition of the sensor path transfer function and the filter transfer function corresponds to a transfer characteristic which would be present when using an inductive transformer as a sensor.

4. Measurement input (14) according to one of the preceding claims, characterized in that - the pole points of the filter transfer function are defined depending on the position of the zero points of the sensor path transfer function and the zero points of the filter transfer function depending on the position of the pole points of the sensor path transfer function.

5. Measurement input (14) according to one of the preceding claims, - the parameter set (38) is stored in a data storage device (37) in the context of a configuration of the measurement input (14) .

6. Measurement input (14) according to Claim 6, characterized in that - a sensor model describing the small signal transformer (11), a cable model describing the connection line (13) and a measurement input model describing at least one assembly (21) of the measurement input (14) are provided, from which the parameter set (38) is derived, in the data storage device (37) of the measurement input or in a configuration tool for configuration.

7. Measurement input (14) according to one of the preceding claims, characterized in that - an impedance matching circuit (32), which is designed as a voltage divider, is connected downstream of the electrical input (30) .

8. Measurement input (14) according to Claim 7, characterized in that - a signal conditioning unit (33), which is able to be switched between a first mode according to a low-pass characteristic or a PI element and a second mode according to a proportional characteristic, is connected downstream of the impedance matching circuit (32).

9. Measurement input (14) according to Claim 8, characterized in that - the mode of the signal conditioning unit (33) is defined depending on the position of a zero point of the transfer function of the small signal transformer (11).

10. Measurement input (14) according to Claim 9, characterized in that - a programmable gain amplifier (34) is connected downstream of the signal conditioning unit (33).

11. Measurement input (14) according to Claim 10, characterized in that - a scanning device (35) is connected downstream of the programmable gain amplifier (34).

12. Electrical device (10) having at least one measurement input (14) according to one of the preceding claims.

13. Electrical device (10) according to Claim 12, characterized in that - the electrical device is a measurement, control or protection device of a technical system.

14. Electrical device according to Claim 12 or 13, characterized in that - the electrical device, in addition to the at least one measurement input (14), has at least one further measurement input (41) for connecting an inductive transformer (42).