Circuit arrangement for compensation of a DC component in a transformer

Abstract

A circuit arrangement for compensation of a DC component in a transformer, wherein the transformer includes a winding arrangement connected via connecting lines to a power system for transporting electrical energy, and includes a neutral point connected to earth, where the circuit arrangement includes a transductor circuit arranged in a current path that connects a connection point situated on a node-free portion of the connection line to earth, a control and regulation device that controls the transductor circuit via a control signal and to which is fed, on the input side, a signal provided by a detection device with respect to a size and direction of the DC component to be compensated.

Claims

1. A circuit arrangement for compensation of a DC component in a transformer including a winding arrangement connected via connecting lines to a power system for transporting electrical energy, and including a neutral point connected to earth, comprising: a transductor circuit arranged in a current path which connects a connection point situated on a node-free portion of the connection line to earth; a control and regulation device which controls the transductor circuit via a control signal; and a detection device, which feeds a signal with respect to a size and direction of the DC component to be compensated, on an input side of the control and regulation device.

2. The circuit arrangement as claimed in claim 1, further comprising: includes a load winding and an uncontrolled valve arranged in each respective branch of two parallel current branches of the transductor circuit; wherein each uncontrolled valve is connected antiparallel; wherein each load winding is magnetically coupled to an associated control winding via a transductor core; and wherein the control signal is fed to the control winding.

3. The circuit arrangement as claimed in claim 1, wherein the transductor circuit includes a single load winding which is arranged in series with a switching device for reverse-poling a current flow direction of a single valve; and wherein the single load winding is magnetically coupled to an associated control winding via a transductor core.

4. The circuit arrangement as claimed in claim 1, wherein the transductor core is configured as a slit strip core.

5. The circuit arrangement as claimed in claim 2, wherein the transductor core is configured as a slit strip core.

6. The circuit arrangement as claimed in claim 3, wherein the transductor core is configured as a slit strip core.

7. The circuit arrangement as claimed in claim 4, wherein the slit strip core is made from sheet metal lamellae of a soft magnetic material which has an essentially narrow rectangular hysteresis loop.

8. The circuit arrangement as claimed in claim 7, wherein the transductor core is arranged in a magnetic circuit which has at least one air gap, such that a magnetic flux density is limited to less than or equal to 20% of a saturation flux density.

9. The circuit arrangement as claimed in claim 1, wherein the detection device is a magnetic field measuring device which is arranged on a core of the transformer to measure a magnetic unidirectional flux portion caused in the core by the DC component.

10. The circuit arrangement as claimed in claim 2, wherein the detection device is a magnetic field measuring device which is arranged on a core of the transformer to measure a magnetic unidirectional flux portion caused in the core by the DC component.

11. The circuit arrangement as claimed in claim 3, wherein the detection device is a magnetic field measuring device which is arranged on a core of the transformer to measure a magnetic unidirectional flux portion caused in the core by the DC component.

12. The circuit arrangement as claimed in claim 9, wherein the detection device comprises a shunt component which diverts a magnetic partial flux from the core of the transformer, such that an electrical voltage is induced in a sensor coil provided at the shunt component, by which a measurement signal is formed.

13. The circuit arrangement as claimed in claim 2, wherein one of (i) each uncontrolled valve arranged in each respective branch of the two parallel current branches of the transductor circuit and (ii) the single valve is configured as a high-blocking power diode.

14. The circuit arrangement as claimed in claim 3, wherein one of (i) each uncontrolled valve arranged in each respective branch of the two parallel current branches of the transductor circuit and (ii) the single valve is configured as a high-blocking power diode.

15. The circuit arrangement as claimed in claim 2, further comprising: a current-limiting reactor arranged in a current path in series with the transductor circuit.

16. The circuit arrangement as claimed in claim 3, further comprising: a current-limiting reactor arranged in a current path in series with the transductor circuit.

17. The circuit arrangement as claimed in claim 2, wherein one of (i) each of the two parallel-connected load windings and (ii) a single load winding is configured for current limitation in a current path.

18. The circuit arrangement as claimed in claim 3, wherein one of (i) each of the two parallel-connected load windings and (ii) a single load winding is configured for current limitation in a current path.

19. A method for compensating for a DC component in a winding arrangement of a transformer, the winding arrangement being connected via connecting lines to a power system for transporting electrical energy, the winding arrangement having a neutral point connected to earth, the method comprising: arranging a transductor circuit in a current path which connects a connection point situated on a node-free portion of the connection line to earth; controlling, by a control and regulation device, the transductor circuit via a control signal; and feeding, by a detection device, a signal with respect to a size and direction of the DC component to be compensated, on an input side of the control and regulation device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For further explanation of the invention, reference will be made in the following section of the description to drawings which illustrate further advantageous embodiments, details and developments of the invention, using a non-limiting exemplary embodiment, in which:

(2) FIG. 1 shows a simplified circuit diagram of a circuit arrangement according to a first embodiment of the invention;

(3) FIG. 2 shows a simplified circuit diagram of a circuit arrangement according to a second embodiment of the invention; and

(4) FIG. 3 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(5) FIG. 1 shows a simplified circuit diagram of a first embodiment of the inventive circuit arrangement. The circuit consists essentially of a transductor circuit 1 arranged in a current path 20. The current path 20 connects a connection point 12, which lies on a feed line 3 to the transformer 4, to earth potential 11. For the sake of simplicity, in FIG. 1 only one of the feed lines 3 is shown, representing the three strands of the 3-phase system. Also for the sake of simplicity, only one winding 8 of the winding system of the transformer 4 is represented. The neutral point of the transformer 4 is earthed, i.e., connected to the earth point 11. Both the feed lines 3 and the current path 20 are also emphasized schematically by a bold line style (power path); in FIGS. 1 and 2, the conduction of the measurement signal 17 and the control signals 16 (measurement and control signal paths) are represented with a thin line style.

(6) In the example in FIG. 1, the transformer is a distribution transformer at the interface between a high voltage power system and a medium voltage system. Normally, such distribution transformers are implemented in the vector group Yy0, i.e., with earthed neutral point. Urban network distribution transformers also typically have an accessible neutral point, such as in the vector group Yz5.

(7) The connection point 12 lies on a feed line portion 31 between a connection node point 14 and a transformer connection 13. The node point 14 is part of a power system 15 for the generation, transmission and distribution of electrical energy that also comprises further node points 14, 14, 14. No further network nodes are arranged between the connection network node 14 and the transformer connection 13, i.e., the portion 31 of the three-phase conductor system 3 is node-free.

(8) It is assumed that a DC component (I.sub.DC) flows in the feed lines 3 (represented in FIG. 1 by a double arrow). The current flow direction of the DC component (I.sub.DC) is directed toward or away from the transformer. As already disclosed, this DC component is highly undesirable for the transformer 4. In accordance with the present invention, this DC component is already counteracted before entry into the transformer 4. Similarly to a set of points, the DC component is diverted to earth 11, so that it cannot develop its disruptive effect in the core of the transformer. In contrast to conventional DC compensation methodologies in which a compensation winding in the interior of the transformer housing is assumed, no separate compensation winding is herein required. Rather, the DC current is diverted at the feed line. This diversion is brought about essentially by a transductor circuit 1 that acts like a protective device for the transformer.

(9) The transductor circuit 1 functions as a magnetic switch or magnetic valve and is controlled by a control and regulation unit 6. In the conductive state, the current limitation occurs via a choke 2 that is arranged in a series connection with the transductor circuit 1. The control and regulation unit 6 comprises a computer unit with an algorithm able to execute thereon. This generates the control signal 16, where the measurement signal 17 fed in on the input side is used. The measurement signal 17 is a representation of the DC component to be compensated and is provided by a magnetic field sensor 5. This magnetic field sensor 5 is arranged in the interior of the transformer 4, where it measures a unidirectional flux portion flowing in the core of the transformer and originating from the DC component. PCT/EP2010/054857 describes one type of a magnetic field sensor.

(10) The transductor circuit 1 also enables the compensation of comparatively high GIC DC currents, which can amount to more than 50 A. In the embodiment shown in FIG. 1, the transductor circuit 1 consists of two parallel current paths in each of which a transductor load winding 9 and a diode 7 are arranged in series. The two diodes 7 in the parallel paths are arranged antiparallel (the conducting direction is opposed), which means that in the representation of FIG. 1, the diode 7 in the left branch points toward earth 11 and in the right branch, the diode 7 points toward the feed line 3. Each load winding 9 in the parallel branches is magnetically coupled via a saturation-capable transductor core 19 to an associated transductor control winding 10. The two control windings 10 are arranged in series behind one another in a control circuit. The control signal 16 is fed into the control circuit so that the saturation state of the transductor core 19 and thus the current flow in the current path 20 is pre-settable. Depending on the control signal 16, it can be achieved that a compensation current I.sub.K forms in the current path 20 (power path) in one or the other direction (either from the connection point 12 in the direction of earth 11 or vice versa). With this bidirectional compensation current I.sub.K (mixed current with harmonics) in the current path 20, the disruptive unidirectional flux portion in the core of the transformer is counteracted or fully compensated. In the representation of FIG. 1, the complete DC compensation is represented, in each case, through two equal-sized arrows, i.e., an equal-sized DC component I.sub.DC (dashed arrow) is directed contrary to each compensation current I.sub.K (continuous arrow).

(11) FIG. 2 shows a differently configured solution approach. In contrast to FIG. 1, the transductor circuit 1 does not consist herein of two transductor load windings, but consists of a single load winding 9 and a transductor control winding 10 associated therewith. The load winding 9 and the control winding 10 are again magnetically coupled via a saturation-capable transductor core 19. The control winding 10 is arranged in a control circuit into which the control signal 16 is fed. (The control circuit is illustrated in FIG. 2 with a thin line style). The control signal 16 is again provided by a control and regulation unit 6 on its output side. On the input side, the measurement signal 17 is fed to this control and regulation unit 6 so that in this embodiment of the invention, the information regarding the size and direction of the DC component to be compensated is present in the control and regulation unit 6. The control signal 16 renders the saturation state of the transductor core 19 such that the inductively operating switch 1 is made conductive in a suitable manner, by which the current flow in the current path 20 is pre-settable (harmonic-laden current, mirror-inverted relative to I.sub.DC).

(12) Arranged in series with the load winding 9 is a switching device 18 that includes a first switch contact 18 and a second switch contact 18. Arranged between these switch contacts 18, 18 is a single diode 7. In the switching position shown, the first switch contact 18 is connected to the anode of the diode 7, and the second switch contact 18 to the cathode. Depending on the switching position of these two switch contacts 18, 18, the polarity of the diode 7 can be reversed. Thus, also in this circuit embodiment, where only a single uncontrolled valve 7 is used, a bidirectional compensation of a DC component is possible. (See double arrow in FIG. 2).

(13) The actuation of the switching device 18 can occur in different ways, such as through an actuator or a motor, and manual operation is also conceivable.

(14) Again, for the sake of clarity, the reference numeral 3 in FIG. 2 represents just one line of the 3-phase system. The portion 31 of the lines 3 again lies between a network node 14 of an energy supply network 15 and a connection point 13 of the transformer 4. Between these two points, the feed line portion 31 to the transformer 4 is node-free. The circuit arrangement 1 is situated in proximity to the transformer 4, such as in a transformer station.

(15) In FIGS. 1 and 2, the same reference numerals denote identical or functionally similar elements. Both in the embodiment of FIG. 1 and also in the embodiment of FIG. 2, a current limiting choke 2 is shown in the current path 20. It is also possible, however, that the two load windings 9 or the one load winding 9 is/are configured such that in the conductive state of the magnetic valve, the electrical current in the current path 20 is limited.

(16) In the two embodiments, the DC protective effect occurs according to the principle of DC points directly at the feed line, i.e. the compensation current I.sub.K need only have the mirror-inverted size of the disruptive DC current on the line 31.

(17) It is herein particularly advantageous that with the present circuit arrangement, large currents of over 50 A, as can occur with GIC, can also be counteracted.

(18) Both embodiments have the essential advantage that the installation of a compensation winding is not necessary either subsequently in the context of a retrofit or during the production of the transformer.

(19) For a transformer already in operation, the substantial advantage results that for the first time, a DC protection/DC compensation is realizable at a reasonable cost.

(20) During the production of a transformer, the installation space that would otherwise be required for the compensation winding is dispensed with. This results in a compact design. This is particularly advantageous if large GIC currents are to be compensated because, in this case, the compensation winding is relatively voluminous and a correspondingly large installation space has to be provided.

(21) The circuit arrangement has no active power electronics, but only passively acting components. As a result, the circuit arrangement, can easily be dimensioned for large voltages. The inductive switch 1 is, in principle, a transformer in no-load operation, where the entire voltage (110 kV, 220 kV, 340 kV, etc.) drops to ground. It can be realized with relatively little cost. The other components are common in transformer design or are commercially available.

(22) Although the invention has been illustrated and described in detail based on the two preferred exemplary embodiments, the invention is not restricted by the examples given and other variations can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.

(23) FIG. 3 is a flowchart of a method for compensating for a DC component (I.sub.DC) in a winding arrangement (8) of a transformer (4), where the winding arrangement (8) is connected via connecting lines (3) to a power system (15) for transporting electrical energy, and where the winding arrangement (8) includes a neutral point connected to earth (11). The method comprises arranging a transductor circuit (1) in a current path (20) which connects a connection point (12) situated on a node-free portion (31) of the connection line (3) to earth (11), as indicated in step 310.

(24) Next, a control and regulation device (6) controls the transductor circuit (1) via a control signal (16), as indicated in step 320. Next, a signal (17) with respect to a size and direction of the DC component (I.sub.DC) to be compensated is fed on an input side of the control and regulation device (6) by a detection device (5), as indicate in step 330.

(25) While there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.