PROTECTION OF AN AC DEVICE

Description

[0001] The invention relates to an energy transmission system comprising a protective device for protecting an AC device electrically connected to an AC line, as well as a method in the energy transmission system and its use.

[0002] In the following, power lines carrying alternating current and alternating voltage are referred to as AC lines, and power lines carrying direct current and direct voltage are referred to as DC lines. DC lines are used in particular for transmitting energy over long distances at high direct voltages using what is known as high-voltage direct current (HVDC) transmission. In order to lay AC lines and direct current lines of power grids efficiently, AC lines and direct current lines can be suspended as overhead lines, at least in sections, between the same pylons and run parallel to each other between these pylons. Ionization of the air surrounding the DC lines can occur, particularly on DC lines carrying high direct voltages.If an AC line runs adjacent to a DC line, such ionization can cause ion currents to flow to the AC line, causing DC currents to flow in the AC line. Such DC currents in an AC line can typically reach currents of around 100 mA. During normal operation of an AC system, these DC currents can flow away, for example, via a power transformer connected to the AC line. However, if the AC line is connected to the primary winding of an inductive voltage transformer and has been switched off without being grounded, or if there is no power transformer, or if the power transformer is switched off, the DC currents flow via the primary winding of the voltage transformer, driving the voltage transformer into magnetic saturation, causing thermal overload and destruction.

[0003] From US 3 240 957 A a protective device for an AC device electrically connected to an AC line is known, the protective device comprising at least one current diverting coil connected to the AC line in parallel with the AC device and a magnetic core for each current diverting coil with a first magnetic core section around which the current diverting coil runs.

[0004] From DE 10 2016 205 118 A1 a method for expanding the electrical transmission capacity of an overhead line pylon system as part of a high-voltage grid is known, wherein the overhead line pylon system is designed as a hybrid system for alternating current and direct current.

[0005] The invention is based on the object of specifying an energy transmission system comprising a protective device and a method for protecting an AC device electrically connected to an AC line, in particular an inductive voltage transformer, from damage caused by direct currents flowing in the AC line, in particular when a direct current line, for example an HVDC line, runs adjacent to the AC line.

[0006] The object is achieved according to the invention by an energy transmission system having the features of claim 1, a method in the energy transmission system having the features of claim 9 and its use having the features of claim 10.

[0007] Advantageous embodiments of the invention are the subject of the subclaims.

[0008] An energy transmission system according to the invention with a protection device for a voltage transformer electrically connected to an alternating current line comprises at least one current diverting coil connected to the alternating current line in parallel with the voltage transformer and, for each current diverting coil, a magnetic core with a first magnetic core section around which the current diverting coil runs.

[0009] The parallel connection of the at least one current-discharge coil of the protective device and the voltage transformer to be protected results in a distribution of the current between the at least one current-discharge coil and the voltage transformer.

[0010] This results in a lower current flowing through the voltage converter. In particular, direct currents flowing through the voltage converter, which could damage or destroy the voltage converter, are reduced. Each magnetic core is preferably designed such that it is not driven into magnetic saturation even at relatively small direct currents. The protective device can, in particular, comprise a plurality of current-discharge coils, each of which is connected in parallel with the voltage converter and extends around a magnetic core section of a magnetic core.

[0011] One embodiment of the protective device provides that at least one magnetic core has at least one air gap. In particular, the first magnetic core section of at least one magnetic core can have at least one air gap. Furthermore, at least one magnetic core can have a second magnetic core section that is not surrounded by the current diverting coil and has at least one air gap. The design of at least one magnetic core with at least one air gap advantageously ensures that the magnetic saturation of the magnetic core only occurs at significantly higher magnetic field strengths than with an otherwise identical magnetic core without an air gap. To achieve the same effect with a magnetic core without an air gap, the cross-section of the magnetic core would have to be significantly increased, which would increase material costs and the space required for the measuring arrangement.In particular, it can advantageously be provided that at least one magnetic core has at least one air gap in the first magnetic core section surrounded by a current-discharge coil and at least one air gap in a second magnetic core section. This allows access to an air gap in the second magnetic core section to optimize the magnetic properties of the magnetic core.

[0012] In the method according to the invention for protecting an inductive voltage transformer electrically connected to an alternating current line, each current discharge coil of a protective device according to the invention is accordingly electrically connected to the alternating current line in parallel to the voltage transformer.

[0013] An energy transmission system according to the invention with a measuring arrangement for measuring an alternating voltage on an alternating current line comprises an inductive voltage transformer with a primary winding having a first primary winding end electrically connected to the alternating current line, and at least one protective device according to the invention, wherein each current-discharge coil of the protective device is connected in parallel with the primary winding of the voltage transformer, and the protective device has a lower electrical resistance than the primary winding of the voltage transformer. For example, the effective resistance of the protective device is at most half the effective resistance of the primary winding of the voltage transformer.Because the protective device has a lower effective resistance than the primary winding of the voltage transformer, most of the current flows through the protective device and the primary winding of the voltage transformer is particularly well protected against damage by direct currents.

[0014] One embodiment of the measuring arrangement provides that a second primary winding end of the voltage transformer's primary winding is connected to ground potential. This connects the second primary winding end to a defined reference potential.

[0015] An energy transmission system according to the invention comprises a direct current line, an alternating current line running adjacent to the direct current line, and a measuring arrangement according to the invention, the first primary winding end of which is electrically connected to the alternating current line. For example, the direct current line and the alternating current line are overhead lines and / or are suspended at least in sections between the same line pylons.

[0016] Such an energy transmission system enables, in particular, high-voltage direct current transmission via the direct current line without the above-mentioned risk to the voltage transformer connected to the alternating current line by ion currents caused by the direct current line, since direct currents that would otherwise flow via the voltage transformer essentially flow via the current diverting coil of the measuring arrangement and do not drive the voltage transformer into magnetic saturation.

[0017] Accordingly, the invention provides in particular the use of an energy transmission system according to the invention for high-voltage direct current transmission via the direct current line.

[0018] 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 shows a block diagram of an embodiment of an energy transmission system, FIG 2 shows a broken perspective view of an embodiment of a protective device.

[0019] Corresponding parts are provided with the same reference numerals in the figures.

[0020] Figure 1 (FIG 1) shows a block diagram of an embodiment of an energy transmission system 1 according to the invention. The energy transmission system 1 comprises a direct current line 3, an alternating current line 5 and an embodiment of a measuring arrangement 7 according to the invention for measuring an alternating voltage on the alternating current line 5.

[0021] The direct current line 3 and the alternating current line 5 are suspended at least in sections between the same line masts 9, 10. In Figure 1 For example, only one section each of the direct current line 3 and the alternating current line 5 is shown, with these sections running parallel and adjacent to each other as overhead lines between two line pylons 9, 10. The direct current line 3 is, for example, an HVDC line, and the alternating current line 5 is a line of an alternating current network.

[0022] The measuring arrangement 7 comprises an inductive voltage transformer 11 and a protective device 13 according to the invention. The voltage transformer 11 has a primary winding 15 and a secondary winding 17. A first primary winding end 15.1 of the primary winding 15 is electrically connected to the AC line 5. A second primary winding end 15.2 of the primary winding 15 is connected to a ground potential. A secondary voltage is tapped at the secondary winding 17, from which the AC voltage present on the AC line 5 relative to the ground potential is determined.

[0023] The protective device 13 comprises a current-discharge coil 19 and a magnetic core 21. The current-discharge coil 19 is connected in parallel to the primary winding 15 of the voltage converter 11 and has a significantly lower electrical resistance than the primary winding 15. For example, the resistance of the primary winding 15 is at least ten times greater than the resistance of the current-discharge coil 19.

[0024] The current-discharge coil 19 extends around a first magnetic core section 21.1 of the magnetic core 21, which has an air gap 23. In a second magnetic core section 21.2, which is not surrounded by the current-discharge coil 19, the magnetic core 21 has a further air gap 24. The air gaps 23, 24 are each filled, for example, with laminated paper or pressboard (not shown). Other embodiments of the protective device 13 can, in particular, have a magnetic core 21 with more than just two air gaps 23, 24.

[0025] Figure 2 (FIG 2) shows a broken-away perspective view of an embodiment of a protective device 13. The current discharge coil 19 and the magnetic core 21 are arranged in a housing 25. A shielding electrode 27 for shielding electric fields from the housing 25 is arranged around the current discharge coil 19. An electrical conductor 29 is led out of the housing 25, which is surrounded outside the housing 25 by a hollow insulator 31 and via which the current discharge coil 19 can be contacted from the outside.

[0026] 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 invention as claimed.

Claims

1. A power transmission system (1), comprising - a DC line (3), - an AC line (5) running adjacent to the DC line (3), and - a measuring arrangement (7) for measuring an AC voltage on the AC line (5), the measuring arrangement (7) comprising - an inductive voltage transformer (11) having a primary winding (15) having a first primary winding end (15.1), which is electrically connected to the AC line (5), and - at least one protection device (13), the protection device (13) comprising - at least one current drain coil (19) connected to the AC line (5) in parallel with the inductive voltage transformer (11), and - for each current drain coil (19) a magnetic core (21) having a first magnetic core section (21.1), around which the current drain coil (19) runs, wherein - each current drain coil (19) of the protection device (13) is connected in parallel with the primary winding (15) of the voltage transformer (11), and - the protection device (13) has a lower effective electrical resistance than the primary winding (15) of the voltage transformer (11).

2. The power transmission system (1) as claimed in claim 1, wherein the DC line (3) and the AC line (5) are suspended between the same line masts (9, 10) at least in sections.

3. The power transmission system (1) as claimed in any of the previous claims, wherein the DC line (3) and the AC line (5) are overhead lines.

4. The power transmission system (1) as claimed in any of the previous claims, wherein the protection device (13) comprises at least one magnetic core (21) that has at least one air gap (23, 24).

5. The power transmission system (1) as claimed in any of the previous claims, wherein the protection device (13) comprises at least one magnetic core (21), of which a first magnetic core section (21.1) has at least one air gap (23).

6. The power transmission system (1) as claimed in any of the previous claims, wherein the protection device (13) comprises at least one magnetic core (21), which has a second magnetic core section (21.2), around which the current drain coil (19) does not run and which has at least one air gap (24).

7. The power transmission system (1) as claimed in any of the previous claims, wherein the effective resistance of the primary winding (15) of the voltage transformer (11) has a magnitude at least double that of the effective resistance of the protection device (13).

8. The power transmission system (1) as claimed in any of the previous claims, wherein a second primary winding end (15.2) of the primary winding (15) of the voltage transformer (11) is connected to a ground potential.

9. A method for being carried out in an energy transmission system (1) according to one of the preceding claims for protecting an inductive voltage transformer (11) electrically connected to an AC line (5) against damage as a result of DC currents flowing in the AC line (5), wherein each current drain coil (19) of the protection device (13) is electrically connected to the AC line (5) in parallel with the voltage transformer (11).

10. The use of a power transmission system (1) as claimed in any of claims 1 to 8 for a high-voltage direct current transmission via the DC line (3).