POWER CONVERTER

Description

[0001] The invention relates to a current transformer for monitoring power grids with direct and alternating currents or mixed currents and to a method for measuring currents with such a current transformer.

[0002] In particular, the invention relates to current transformers for high- and medium-voltage networks. In alternating current networks, inductive current transformers based on the transformer principle are generally used. However, these inductive current transformers cannot detect direct currents or the direct current components of mixed currents. The detection of direct currents and direct current components is particularly necessary for monitoring power grids with high-voltage direct current transmission lines. Such power grids are becoming increasingly important, especially for transporting electrical energy over long distances with low losses.

[0003] US 2015 / 0331015 A1 discloses a flux-gate type contactless current measuring device for measuring a current by detecting an electromagnetic field around a conductive wire in which the current flows. The current measuring device can detect a DC component of the current by changing an oscillating signal for magnetizing two cores with opposite polarities and an AC component of the current using another core.

[0004] The invention is based on the object of providing a current transformer and a method for measuring currents which are improved in particular with regard to the detection of alternating and direct currents.

[0005] The object is achieved according to the invention by a current transformer having the features of claim 1 and a method having the features of claim 9.

[0006] Advantageous embodiments of the invention are the subject of the subclaims.

[0007] A current transformer according to the invention enables the detection of both alternating currents or alternating current components of mixed currents and direct currents or direct current components of mixed currents.

[0008] In order to detect alternating currents and alternating current components of mixed currents, the current transformer has, in particular, an inductive alternating current sensor which is based on the transformer principle: an alternating current or alternating current component flowing through the primary conductor generates a time-varying primary magnetic field which induces a secondary voltage and a secondary current in the secondary coil, via which the alternating current or alternating current component flowing through the primary conductor can be detected.

[0009] In addition, the current transformer has a compensation current sensor, which can be used to detect, in particular, direct currents and direct current components of mixed currents: a primary current flowing through the primary conductor generates a primary magnetic field in the vicinity of the primary conductor; a compensation current is set in the compensation coil, which generates a compensation magnetic field that compensates for the primary magnetic field at the location of the magnetometer and via which the primary current is detected.

[0010] A current transformer according to the invention can therefore be used particularly advantageously for monitoring power grids with direct and alternating currents or mixed currents, in which separate direct and alternating current transformers would otherwise have to be used. The compensation coil of the compensation current sensor is installed in the same housing as the at least one secondary coil of the inductive alternating current sensor, so that a housing design known from and proven to be effective in conventional inductive alternating current transformers can be used to construct a current transformer according to the invention. A current transformer according to the invention can be implemented separately or as part of a combined current and voltage transformer.

[0011] One embodiment of the invention provides that the inductive AC sensor has at least one measuring core and at least one protective core. A measuring core or protective core is understood to be a soft magnetic core of a secondary coil. Measuring and protective cores do not differ fundamentally from each other, but only in their design for measuring and protective purposes. The use of measuring cores and protective cores enables the primary magnetic field generated by the primary conductor to be concentrated at the locations of these cores.

[0012] The invention provides that the magnetometer is a fluxgate magnetometer. In particular, the fluxgate magnetometer has two compensation cores arranged in the housing, running annularly around the primary conductor, and an excitation winding wound in opposite directions around the two compensation cores. Compared to other magnetometers, such as Hall sensors, fluxgate magnetometers have the advantage of delivering signals with little or no offset. Furthermore, they can be manufactured from essentially the same components and materials as inductive AC sensors, so that no separate, complex protective devices need to be provided to protect their components in the housing. Fluxgate magnetometers with two compensation cores, on which an excitation winding is wound in opposite directions, also have the advantage that the effects of the compensation cores on the primary conductor largely compensate each other.

[0013] Furthermore, in addition to the two compensation cores, the fluxgate magnetometer is provided with an additional core arranged in the housing, which runs in a ring around the primary conductor, and an additional secondary winding. The additional secondary winding and the compensation coil are wound around the additional core. Thanks to the additional core and the additional secondary winding, the compensation current sensor can also be used to detect alternating currents or alternating current components, for example, to detect alternating currents or alternating current components that the inductive AC sensor is not designed to measure and that cannot be detected by the two compensation cores.

[0014] In an embodiment not claimed, the compensation current sensor can comprise a magnetometer with a Hall sensor instead of a fluxgate magnetometer. For example, the compensation current sensor can comprise a magnetic core arranged in the housing, extending annularly around the primary conductor, around which the compensation coil is wound and which has an air gap in which the Hall sensor is arranged. This makes it possible to use the Hall sensor to detect the sum of the primary magnetic field generated by the primary conductor and the compensation magnetic field generated by the compensation coil at the location of the Hall sensor and to adjust the compensation current flowing in the compensation coil so that this sum disappears. By arranging the Hall sensor in the air gap of a magnetic core wound with the compensation coil, the magnetic field is advantageously concentrated at the location of the Hall sensor.

[0015] A further embodiment of the invention provides a winding housing arranged in the housing, in which the at least one secondary coil and the compensation coil are arranged. The winding housing, also referred to as the core shell, can be used to establish an electrical potential in the vicinity of the secondary and compensation coils, for example, by grounding the winding housing.

[0016] The winding housing is preferably electrically insulated from the housing. For example, the housing is filled with an insulating gas, an insulating liquid, or an insulating compound. This prevents an electrical voltage, particularly a high voltage, applied to the housing from being transmitted to the winding housing.

[0017] Further embodiments of the invention provide that the inductive AC sensor has a first measuring circuit arranged outside the housing and electrically connected to each secondary coil, and / or that the compensation current sensor has a second measuring circuit arranged outside the housing and electrically connected to the compensation coil and the magnetometer. These embodiments of the invention provide for the arrangement of the measuring circuits of the current transformer outside the housing. This allows the measuring circuits to be advantageously arranged in protected and easily accessible locations, for example, in a control cabinet.

[0018] A further embodiment of the invention provides that the compensation current sensor can be deactivated, with the compensation coil, in particular, being short-circuitable. This embodiment of the invention takes into account that a compensation current sensor requires electrical energy to supply the compensation coil and the magnetometer. Therefore, it is advantageous to design the compensation current sensor so that it can be deactivated only when needed, particularly when a direct current or direct current component is to be detected. This advantageously reduces the energy consumption and operating costs of the current transformer. Furthermore, the acquisition costs or initial acquisition costs for the current transformer can be reduced by purchasing a measuring circuit for the compensation current sensor only when needed and possibly only later.

[0019] A further embodiment of the invention provides a support insulator on which the housing is mounted. This embodiment of the invention is particularly advantageous when a high voltage is applied to the primary conductor, in order to arrange the housing and the primary conductor at a sufficient height and electrically insulated from the ground.

[0020] In the method according to the invention for measuring currents with a current transformer according to the invention, an alternating current flowing in the primary conductor or an alternating current component of a current flowing in the primary conductor is detected with the inductive alternating current sensor and a direct current flowing in the primary conductor or a direct current component of a current flowing in the primary conductor is detected with the compensation current sensor.

[0021] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings. FIG 1 schematically shows an embodiment of a current transformer, FIG 2 schematically shows a sectional view of a current transformer head of the Figure 1 current transformer shown, FIG 3 schematically shows the Figure 1 shown current transformer with deactivated compensation current sensor, FIG 4 schematically shows an embodiment not according to the invention of a compensation current sensor with a Hall sensor.

[0022] Corresponding parts are provided with the same reference numerals in the figures.

[0023] Figure 1shows schematically an embodiment of a current transformer 1. The current transformer 1 has a current transformer head 3, a support insulator 5 on which the current transformer head 3 is arranged, and a base 7 on which the support insulator 5 is arranged and on which a terminal box 8 is arranged.

[0024] Figure 2 shows a schematic sectional view of the current transformer head 3. The current transformer head 3 has a housing 9 through which a primary conductor 11 is guided. A torus-shaped winding housing 10 is arranged in the housing 9 and is arranged around the primary conductor 11.

[0025] The current transformer 1 has an inductive alternating current sensor 13 and a compensation current sensor 15.

[0026] The inductive AC sensor 13 of this embodiment has two annular protective cores 17 and two annular measuring cores 19, on each of which a secondary coil 21 is wound and which each run around the primary conductor 11 within the winding housing 10.

[0027] The compensation current sensor 15 has a compensation coil 23 and a magnometer 25. The magnometer 25 is designed as a fluxgate magnetometer and has two soft magnetic compensation cores 27, a soft magnetic additional core 29, an excitation winding 31, and an additional secondary winding 33. The compensation cores 27 and the additional core 29 are each ring-shaped and run around the primary conductor 11 within the winding housing 10. The excitation winding 31 is wound in opposite directions around the two compensation cores 27. The additional secondary winding 33 is wound around the additional core 29. The compensation coil 23 is wound around the two compensation cores 27 and the additional core 29. During operation of the compensation current sensor 15, an alternating excitation current is generated in the excitation winding 31, which periodically drives the compensation cores 27 into magnetic saturation.Since the excitation winding 31 is wound in opposite directions around the two compensation cores 27, the magnetic fields generated by the compensation cores 27 are opposite to each other. The compensation cores 27 and their windings by the excitation winding 31 are identical except for the winding directions, so that the magnetic fields of the compensation cores 27 are also equal in magnitude when no external magnetic field acts on the compensation cores 27. However, if an external magnetic field acts on the compensation cores 27, this leads to different magnetic fields of the compensation cores 27, the difference between which is a measure of the magnetic field strength of the external magnetic field. The external magnetic field acting on the compensation cores 27 is the sum of a primary magnetic field generated by a primary current in the primary conductor 11 and a compensation magnetic field generated by a compensation current in the compensation coil 23.The compensation current in the compensation coil 23 is adjusted so that the compensation magnetic field compensates for the primary magnetic field in the compensation cores 27, or the magnitudes of the magnetic fields of the compensation cores 27 are equal. The current intensity of the compensation current is therefore a measure of the primary current intensity and enables its measurement. The compensation cores 27 serve to measure direct currents or direct current components flowing in the primary conductor 11.

[0028] The additional core 29 is used for additional measurement of alternating currents or alternating current components flowing in the primary conductor 11, for example, for measuring alternating currents or alternating current components for which the measuring cores 19 of the inductive alternating current sensor 13 are not designed. The compensation current in the compensation coil 23 also compensates for primary magnetic fields generated in the additional core 29 by alternating currents or alternating current components flowing in the primary conductor 11. AC components of the primary current and the compensation current generate changes in a magnetic field in the additional core 29, which induce a secondary current in the additional secondary winding 33. The AC component of the compensation current is therefore set such that no secondary current is induced in the additional secondary winding 33.

[0029] The inductive alternating current sensor 13 has a first measuring circuit 35 for detecting secondary currents flowing in the secondary coils 21, which are induced by an alternating current or alternating current component flowing in the primary conductor 11. The compensation current sensor 15 has a second measuring circuit 37 for generating the excitation current flowing in the excitation winding 31, generating and adjusting the compensation current flowing in the compensation coil 23, and optionally for detecting the secondary current flowing in the additional secondary winding 33. The first measuring circuit 35 is connected to the secondary coils 21 via first connecting lines 39. The second measuring circuit 37 is connected to the excitation winding 31 and the compensation coil 23, as well as to the additional secondary winding 33, via second connecting lines 41.The connecting lines 39, 41 extend from the winding housing 10 and the housing 9 and through the post insulator 5 to the terminal box 8 and from there to the measuring circuits 35, 37. The compensation current sensor 15 can be deactivated. For this purpose, the parts of the second connecting lines 41 that connect the terminal box 8 to the second measuring circuit 37 are detachably connected to the terminal box 8, for example via a plug connection. After these parts of the second connecting lines 41 are detached from the terminal box 8, the excitation winding 31, the additional secondary winding 33, and the compensation coil 23 can each be short-circuited, for example with a short-circuit plug 43 that can be connected to the terminal box 8 instead of these parts of the second connecting lines 41.

[0030] Figure 3shows the current transformer 1 with a short-circuit plug 43, which short-circuits the excitation winding 31, the additional secondary winding 33 and the compensation coil 23, respectively.

[0031] The support insulator 5 is designed as a hollow insulator and has a plurality of insulating shields 6, each of which extends in a ring shape around a longitudinal axis of the support insulator 5. The support insulator 5 is made, for example, of a ceramic material or is designed as a tube made of a glass-fiber-reinforced plastic, on which insulating shields 6 made of silicone are arranged.

[0032] The winding housing 10 is electrically insulated from the housing 9. For this purpose, the housing 9 is filled with an insulating gas, for example, sulfur hexafluoride or nitrogen, or with an insulating liquid, for example, an insulating oil, or an insulating compound, for example, a silicone insulating compound.

[0033] The exemplary embodiment shown in the figures can be modified in various ways not according to the invention. For example, the inductive AC sensor 13 can have a different number of protective cores 17 and / or measuring cores 19. In particular, it can have no protective core 17 or no measuring core 19 at all. Furthermore, the compensation current sensor 15 can have a magnometer 25 other than a fluxgate magnetometer, for example, a magnometer 25 with a Hall sensor 49 (see Figure 4 ).

[0034] Figure 4shows a schematic illustration of a non-inventive embodiment of a compensation current sensor 15, which has a magnetic core 45 arranged in the winding housing 10, extending annularly around the primary conductor 11, around which the compensation coil 23 is wound, and which has an air gap 47 in which a Hall sensor 49 is arranged. The Hall sensor 49 detects the sum of the primary magnetic field generated by the primary conductor 11 and the compensation magnetic field generated by the compensation coil 23 at the location of the Hall sensor 49, and the compensation current flowing in the compensation coil 23 is adjusted so that this sum disappears.

[0035] Although the invention has been illustrated and described in detail 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 claims.

Claims

1. Current converter (1) for monitoring of high- and medium-voltage grids having direct and alternating currents or mixed currents, comprising: - a primary conductor (11); - a housing (9) through which the primary conductor (11) is led; - an inductive alternating current sensor (13) having at least one secondary coil (21) which is disposed in the housing (9) and - a compensation current sensor (15) having a compensation coil (23) disposed in the housing (9) for producing a compensation magnetic field, compensating a primary magnetic field produced by the primary conductor (11), and a magnetometer (25) for sensing a sum of the primary magnetic field and the compensation magnetic field, - wherein the inductive alternating current sensor (13) has at least one measuring core (19) and at least one protective core (17), - wherein the magnetometer (25) is a fluxgate magnetometer, - wherein the fluxgate magnetometer has two compensation cores (27) arranged in the housing (9), annularly extending about the primary conductor (11), and an excitation winding (31) wound in an inverse direction about the two compensation cores (27), and - wherein the fluxgate magnetometer has an additional core (29) and an additional secondary winding (33) arranged in the housing (9), annularly extending about the primary conductor (11) and the additional secondary winding (33) and the compensation coil (23) are wound about the additional core (29).

2. The current converter (1) according to claim 1, characterized in that a winding housing (10) is arranged in the housing (9), in which the at least one secondary coil (21) and the compensation coil (23) are arranged.

3. The current converter (1) according to claim 2, characterized in that the winding housing (10) is electrically insulated vis-à-vis the housing (9).

4. The current converter (1) according to one of the preceding claims, characterized in that the housing (9) is filled with an insulating gas or an insulating fluid, or an insulating compound.

5. The current converter (1) according to one of the preceding claims, characterized in that the inductive alternating current sensor (13) has a first measuring circuit (35), which is arranged outside the housing (9) and is electrically connected to each said secondary coil (21).

6. The current converter (1) according to one of the preceding claims, characterized in that the compensation current sensor (15) has a second measuring circuit (37), which is arranged outside the housing (9) and is electrically connected with the compensation coil (23) and the magnetometer (25).

7. The current converter (1) according to one of the preceding claims, characterized in that the compensation current sensor (15) is deactivable.

8. The current converter (1) according to one of the preceding claims, characterized in that the housing is arranged upon a post insulator (5).

9. Method for measuring currents with a current converter (1) according to one of the preceding claims, wherein - with the inductive alternating current sensor (13) an alternating current flowing in the primary conductor (11) or an alternating current component of a current flowing in the primary conductor (11) is sensed and - with the compensation current sensor (15) a direct current flowing in the primary conductor (11) or a direct current component of a current flowing in the primary conductor (11) is sensed.