METHOD FOR MEASURING ELECTRICAL CURRENTS AND VOLTAGES, AND ENERGY METER

Abstract

A method for measuring electric currents and a method for measuring electrical voltages. The method uses a mathematical model of the measuring system to compensate for error effects of the real system compared to an ideal system, thereby enabling a highly accurate measuring system. An energy meter compensates for the error effects of the real measuring system.

Claims

1-28. (canceled)

29. A method for measuring electric currents, wherein a primary current flowing through a primary conductor is converted into a secondary current of smaller magnitude using an inductive current converter that has a primary side and a secondary side that is DC-isolated from the primary side, comprising the steps of: measuring the secondary current using a measuring apparatus; loading from a memory device at least one compensation table based on a mathematical model of the current converter for magnitude and/or phase of the measured secondary current or generating the at least one compensation table from the mathematical model of the current converter; using the at least one compensation table to at least partly compensate for a deviation of the measurement signal in magnitude and/or phase; and reconstructing a primary current flowing through the primary conductor based on the compensated secondary current.

30. The method for measuring electric currents according to claim 29, wherein the mathematical model of the current converter is based on an electrical equivalent circuit diagram of the current converter.

31. The method for measuring electric currents according to claim 29, wherein the mathematical model of the current converter takes into account the actual burden on the current converter in terms of the input impedance of the measuring apparatus and/or line resistance of a line from the current converter to the measuring apparatus.

32. The method for measuring electric currents according to claim 29, wherein an error effect of the connected current converter is at least partly compensated for in an energy meter.

33. The method for measuring electric currents according to claim 29, including measuring the current on the secondary side of the current converter.

34. The method for measuring electric currents according to claim 29, including reading out a type-related coding of the current converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, downloading the mathematical model of the respective current converter from a web server onto the transmission apparatus using the coding read out, transmitting the mathematical model of the respective current converter to the energy meter via an interface, and storing the mathematical model of the current converter in a memory device of the energy meter.

35. The method for measuring electric currents according to claim 29, including reading out a type-related coding of the current converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, downloading the mathematical model of the current converter from a web server onto a transmission apparatus using the coding read out, generating at least one compensation table from the mathematical model of the current converter using the transmission apparatus, transmitting the at least one compensation table to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

36. The method for measuring electric currents according to claim 29, including reading at a type-related coding of the current converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, accessing the mathematical model of the current converter on a web server using the coding read out, generating at least one compensation table from the mathematical model of the respective current converter on the web server, downloading the compensation table onto the transmission apparatus, transmitting the at least one compensation table from the transmission apparatus to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

37. The method for measuring electric currents according to claim 34, wherein the mathematical model of the current converter is stored on the web server in a digital file.

38. The method for measuring electric currents according to claim 34, wherein the type-related coding of the current converter contains a download link for downloading the mathematical model or the compensation table of the current converter from the web server.

39. The method for measuring electric currents according to claim 29, including reading out a type-related coding of the current converter connected to an energy meter or to be connected to said energy meter out using a transmission apparatus, accessing the mathematical model of the current converter on a PC or selecting the mathematical model on the transmission apparatus using the coding read out, generating at least one compensation table is generated from the mathematical model of the respective current converter on the PC, and downloading the at least one compensation table onto the transmission apparatus or generating the compensation table from the mathematical model selected on the transmission apparatus, transmitting the at least one compensation table from the transmission apparatus to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

40. The method for measuring electric currents according to claim 34, including supplementing the mathematical model of the current converter using the transmission apparatus with an impedance of a line between the current converter and the energy meter and/or an input impedance of the measuring apparatus of the energy meter.

41. The method for measuring electric currents according to claim 29, wherein the mathematical model of the current converter is determined using a secondary voltage method.

42. A method for measuring electrical voltages, wherein a primary voltage applied to a primary conductor is converted into a secondary voltage of smaller magnitude using an inductive voltage converter that has a primary side and a secondary side that is DC-isolated from the primary side, comprising the steps of: measuring the secondary voltage using a measuring apparatus; loading at least one compensation table based on a mathematical model of the voltage converter for magnitude and/or phase of the measured secondary voltage from a memory device or generating the at least one compensation table from the mathematical model of the voltage converter; using the at least one compensation table to at least partly compensate for a deviation of the measurement signal in magnitude and/or phase; and reconstructing a primary voltage applied to the primary conductor based on the compensated secondary voltage.

43. The method for measuring electric voltages according to claim 42, wherein the mathematical model of the voltage converter is based on an electrical equivalent circuit diagram of the voltage converter.

44. The method for measuring electric voltages according to claim 42, wherein the mathematical model of the voltage converter takes into account an actual burden on the voltage converter in terms of an input impedance of the measuring apparatus and/or line resistance of a line from the voltage converter to the measuring apparatus.

45. The method for measuring electric voltages according to claim 42, wherein an error effect of the connected voltage converter is at least partly compensated for in an energy meter.

46. The method for measuring electric voltages according to claim 42, including measuring voltage on the secondary side of the voltage converter.

47. The method for measuring electric voltages according to claim 42, including reading out a type-related coding of the voltage converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, downloading a mathematical model of the voltage converter from a web server onto the transmission apparatus using the coding read out, transmitting the mathematical model of the respective voltage converter to the energy meter via an interface, and storing the mathematical model of the voltage converter in a memory device of the energy meter.

48. The method for measuring electric voltages according to claim 42, including reading out a type-related coding of the voltage converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, downloading a mathematical model of the respective current converter from a web server onto the transmission apparatus using the coding read out, generating at least one compensation table from the mathematical model of the respective voltage converter using the transmission apparatus, transmitting the at least one compensation table to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

49. The method for measuring electric voltages according to claim 42, including reading out a type-related coding of the voltage converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, accessing a mathematical model of the respective voltage converter on a web server using the coding read out, generating at least one compensation table from the mathematical model of the respective voltage converter on the web server, downloading compensation table onto the transmission apparatus, transmitting the at least one compensation table from the transmission apparatus to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

50. The method for measuring electric voltages according to claim 47, wherein the mathematical model of the voltage converter is stored on the web server in a digital file.

51. The method for measuring electric voltages according to claim 47, wherein the type-related coding of the voltage converter contains a download link for downloading the mathematical model or the compensation table of the current converter from a web server.

52. The method for measuring electric voltages according to claim 42, including reading out a type-related coding of the voltage converter connected to an energy meter or to be connected to said energy meter using a transmission apparatus, accessing a mathematical model of the respective voltage converter is accessed on a PC or selecting the mathematical model on the transmission apparatus using the coding read out, generating at least one compensation table is generated from the mathematical model of the respective voltage converter on the PC, downloading the at least one conservation table onto the transmission apparatus or generating the at least one compensation table from the mathematical model selected on the transmission apparatus, transmitting the at least one compensation table from the transmission apparatus to the energy meter via an interface, and storing the at least one compensation table in a memory device of the energy meter.

53. The method for measuring electric voltages according to claim 47, including supplementing the mathematical model of the voltage converter using the transmission apparatus with an impedance of a line between the voltage converter and the energy meter and/or an input impedance of the measuring apparatus of the energy meter.

54. The method for measuring electric voltages according to claim 42, wherein the mathematical model of the voltage converter is determined using a secondary voltage method.

55. An energy meter for measuring energy consumption of at least one consumer connected to at least one primary conductor, comprising: at least one current measurement input and at least one voltage measurement input for measuring a current or a voltage in each case; a compensation unit for compensating for an error effect of a current converter connected to the current measurement input onto at least one measured current signal and/or an error effect of a voltage converter connected to a voltage measurement input onto at least one measured voltage signal, wherein the at least one measured current and/or voltage signal is compensated by virtue of at least one compensation table for compensating the respective measurement signal in magnitude and/or phase based on a mathematical model of the respective current converter or voltage converter being able to be loaded or generated using the compensation unit, and wherein the at least one compensation table for compensating for the respective measurement signal in magnitude and/or phase is applied to the respective measurement signal.

56. The energy meter according to claim 55, wherein the mathematical model of the current converter and/or the voltage converter takes into account an actual burden on the current converter or the voltage converter in terms of input impedance of a measuring apparatus and/or line resistance of a line from the current converter or the voltage converter to the measuring apparatus.

Description

[0093] The following drawings show exemplary embodiments of the methods according to the invention and an application example for an energy meter. In the drawings:

[0094] FIG. 1: shows a schematic representation of a measuring apparatus that can be used for a method according to the invention,

[0095] FIG. 2: shows a schematic representation of the electrical equivalent circuit diagram of a current converter,

[0096] FIG. 3a: shows an exemplary compensation table for the current measured on the secondary side in relation to the magnitude of the current,

[0097] FIG. 3b: shows an exemplary compensation table for the current measured on the secondary side in relation to the phase of the current,

[0098] FIG. 4: shows a representation of the measured and the compensated secondary current,

[0099] FIG. 5: shows a schematic representation of the metrological scanning of the secondary-side current signal,

[0100] FIG. 6: shows a schematic representation of the electrical equivalent circuit diagram of a voltage converter,

[0101] FIG. 7: shows a flow chart of a method according to the invention for measuring electric currents and

[0102] FIGS. 8a and 8b: show a schematic representation of the method for installing a mathematical model of a current or voltage converter on an energy meter.

[0103] FIG. 1 shows a schematic representation of the application example for a measuring apparatus (1) with a current measurement input (2) and a voltage measurement input (3), such as the measuring apparatus (1) of an energy meter (100), for example.

[0104] A first supply line (4) is connected to the current measurement input (2) with the input impedance Z1, via which supply line the current measurement input (2) can be connected to the secondary side of a current converter (10), not shown in this figure. On the primary side, the current converter (10) can be coupled to a primary line through which the current Ito be determined flows. A second supply line (5) is connected to the voltage measurement input (3) with the input impedance Z2, via which supply line the voltage measurement input (3) can be connected to the secondary side of a voltage converter (20), not shown in this figure. The primary side of the voltage converter (20) can be coupled to the primary line on which the voltage U to be determined is applied.

[0105] The measurement data for current and voltage detected using the measuring apparatus (1) can be stored at least temporarily using a memory device (6) so that the measurement data can be compensated for using the compensation unit (7) in order to determine the compensated primary variables I and U.

[0106] The input impedance Z1 of the current measurement input (2) is low. In the exemplary embodiment shown, the input impedance Z1 of the current measurement input (2) is 1 ohm. The supply line resistance ZL of the first supply line (4) is a total of 1.5 ohms (2×0.75 ohms). The input impedance Z2 of the voltage measurement input (3) is high and in the example is 10 MOhm.

[0107] FIG. 2 shows an electrical equivalent circuit diagram of a current converter (20) as an example of how the mathematical model of a current converter (20) is based in a method according to the invention.

[0108] The voltage U.sub.1 is the primary voltage and the voltage U.sub.2 is the secondary voltage of the current converter (20). The core voltage of the current converter (20) is denoted by U.sub.0. The voltage across the secondary winding of the current converter (20) is denoted by U.sub.W. Regarding the currents, I.sub.1 denotes the primary current, I.sub.2 the secondary current, I.sub.1′ the ideally transformed primary current, I.sub.0 the magnetizing current, I.sub.μ the inductive component of the magnetizing current I.sub.0 and I.sub.R the ohmic component of the magnetizing current I.sub.0. P.sub.1 and P.sub.2 are used to denote the primary terminals, while S.sub.1 and S.sub.2 are used to denote the secondary terminals. N.sub.1 denotes the number of primary turns and N.sub.2 the number of secondary turns of the current converter (20). The turns ratio is given by N.sub.1/N.sub.2. L.sub.2σ denotes the secondary leakage inductance, R.sub.CT denotes the secondary winding resistance, X.sub.B denotes the inductive component of the burden impedance, R.sub.B denotes the resistive component of the burden impedance, X.sub.H denotes the main inductance of the core of the current converter (20) and R.sub.Fe denotes the resistance representing the iron losses of the current converter (20).

[0109] FIG. 3a shows an exemplary compensation table for compensating for the magnitude of the measured current, as used in a method according to the invention for measuring electric currents according to advantageous embodiments. In the course of designing the system, a rated power is specified for the current converter (20).

[0110] In an application example explained in detail below, the primary rated current is 100 A, the secondary rated current is 1 A, the rated power is 10 VA, the accuracy class of the current converter (20) is 0.5 and the rated frequency of the primary current is 50 Hz. The primary current to be detected is 10 A. The supply line resistance of the supply line (4) between the current converter (20) and the current measurement input (2) of the measuring apparatus (1) is twice 0.75 ohms and the input impedance Z1 of the current measurement input (2) is 1 ohm. According to the formula P=I.sup.2×R, the rated power for the example current converter is then: (1 A).sup.2×(2×0.75 ohm+1 ohm)=2.5 VA.

[0111] Based on the current value measured on the secondary side, which is 0.10039 A for example, and the rated power, which is 2.5 VA as calculated above in the example, the error value for the measured current value can be read from the compensation table shown. In the example, the nominal transmission ratio of the current converter (20) is 100:1, such that, from the compensated current value measured on the secondary side, which is quantified as 0.1 A after compensation for the error of 0.39%, it can be calculated at 10 A, which corresponds to the primary current actually currently flowing through the primary conductor according to the example.

[0112] FIG. 3b shows an analog compensation table for the phase error of the measured current. The phase error is compensated for here in the same way as for the compensation of the magnitude error, in that the phase error is read from the compensation table using the previously determined rated power and the measured current value.

[0113] FIG. 4 shows the sine waves of the secondary current of the current converter (20) from the example defined above. The profile of the actually measured secondary current and that of the subsequently compensated current signal are shown. The measured current signal was compensated for here in magnitude and phase using the compensation tables shown in FIGS. 3a and 3b.

[0114] FIG. 5 shows the actual treatment of the secondary current by the measuring apparatus (1). Using said measuring apparatus, the secondary current is sampled at discrete points in time, which are represented in the figure by the black lines with a circular head. The actual profile of the current can be reconstructed from the sampled values. A direct correction of the discrete sampled values is in this case not possible in embodiments of the invention since the current values are present as RMS values in the corresponding compensation tables. In order to then carry out a subsequent correction of the sampled values, the relevant RMS value is calculated in the measuring apparatus over a complete sinusoidal oscillation. For this purpose, the sampled values of the current measurement input (2) of the measuring apparatus (1) are stored with the associated sampled values of the voltage measurement input (3) using a storage apparatus (6). In other embodiments of the invention, the RMS value is estimated over a shorter interval. It is now possible to read from the compensation table, for example, that at an RMS value of the current measured on the secondary side of 0.10039 A and a rated power of 2.5 VA, there is ultimately a nominal secondary current of 0.1 A. The phase error or the compensation of the phase error must then be dealt with in the same way using the corresponding compensation table.

[0115] FIG. 6 shows the electrical equivalent circuit diagram of a voltage converter (30) as used as the basis of a mathematical model of a voltage converter (30) in embodiments of a method according to the invention. In this case, U.sub.1 denotes the primary voltage, U.sub.2 denotes the secondary voltage and U.sub.0 denotes the core voltage of the voltage converter (30). I.sub.1 denotes the primary current, I.sub.2 denotes the secondary current, I.sub.2′ denotes the transformed primary current, I.sub.0 denotes the magnetizing current, I.sub.μ denotes the inductive component of the magnetizing current I.sub.0 and I.sub.R denotes the ohmic component of the magnetizing current I.sub.0. The primary terminals are marked A/A and N/B and the secondary terminals are marked a/a and n/b. N.sub.1 indicates the number of primary turns and N.sub.2 indicates the number of secondary turns of the voltage converter (30). The turns ratio of the voltage converter (30) is given by N.sub.1/N.sub.2. L.sub.1σ denotes the primary leakage inductances, R.sub.1 denotes the primary winding resistance, L.sub.2σ denotes the secondary leakage inductances, R.sub.2 denotes the secondary winding resistance, X.sub.B denotes the inductive component of the burden impedance, R.sub.B denotes the resistive component of the burden impedance, X.sub.H denotes the main inductance of the core, and R.sub.Fe denotes the resistance representing the iron losses of the voltage converter (30).

[0116] FIG. 7 shows a schematic representation of the method steps for installing the mathematical model of a current converter (20) on an energy meter (100). The coding (21) applied to the current converter (20) is read out using a transmission apparatus (40), which is designed as a smartphone in the example. In the example, the coding (21) of the current converter (20) contains a manufacturer identification and a serial number of the current converter (20). The data relating to the current converter (20) read out using the transmission apparatus (40) are transmitted via an Internet connection to a server (50), from which the mathematical model of the corresponding current converter (20) is retrieved using the transmission apparatus (40). The mathematical model of the current converter (20) and/or the associated compensation tables are then transmitted from the transmission apparatus (40) to the energy meter (100) via a suitable interface and stored in a memory apparatus (6) of the energy meter (100).

[0117] The sequence of a method according to the invention for the example of a compensation for a current converter (20) and a voltage converter (30) is shown schematically in FIGS. 8a and 8b. After the corresponding converters have been produced, mathematical models of the corresponding converters are generated using suitable measurements, which can be given, for example, by their electrical equivalent circuit diagrams. These mathematical models of the converters are stored in the form of a file on a server or a similarly accessible data memory. By coupling the mathematical models of the corresponding converters to the respective unambiguous designations, for example the serial number and/or a manufacturer identification, the mathematical models are correspondingly retrieved using suitable transmission apparatuses (40), which can be in the form of a smartphone, tablet or PC, for example. For this purpose, suitable software applications are installed on the corresponding transmission apparatuses (40) in embodiments of the invention. The model of the current and/or voltage converter retrieved using the transmission apparatus (40) can then be transmitted to the measuring apparatus (1) using the transmission apparatus (40) via a suitable data interface, such as USB, Bluetooth, etc. In a particularly advantageous embodiment of the method according to the invention, the mathematical models of the current converter (20) and/or the voltage converter (30) are expanded by entering the corresponding resistances of the supply lines and the input impedance of the measuring apparatus (1) using the transmission apparatus (40) or at the measuring apparatus (1) itself in order to achieve increased accuracy of the compensation. The appropriately configured measuring apparatus (1) compensates for the secondary signal coming from the respective converter using the compensation unit (7) by using the respective compensation tables in terms of amplitude and/or phase. The compensated measured values are highly accurate in interaction with the electronics of the measuring apparatus (1). By compensating for the error effects caused by the converter, it is no longer absolutely necessary to use high-precision converters, with the result that correspondingly more cost-effective converters can be used. The accuracy of the measurement results ultimately depends on the accuracy of the mathematical models.