Equipment for connection to the high-voltage power grid

Abstract

To provide a device (1) for connection to a high-voltage network carrying an alternating voltage, the high-voltage network having a plurality of phases, the device comprising: an active part (7) having at least one phase connection (2) for connection to a phase of the high-voltage network; at least one step winding (8, 9, 25, 26, 27) connected downstream of one of the phase connections and having a plurality of taps; and a step switch having a selector (10, 11, 28, 29, 30) and a load changeover switch (12, 13, 31, 32) for each step winding. 2, 33), the selector is used to switch from the current tap of the graded winding to the desired tap when there is no current, the load switching switch is connected in series downstream of the selector, and is used to switch the current from the current tap to the desired tap, thereby avoiding a large short-circuit current in the graded winding or in the graded switch, and it is proposed that an impedance unit (15) is arranged between each selector (10, 11, 28, 29, 30) and each load switching switch (12, 13, 31, 32, 33), and the impedance of the impedance unit (15) can be switched between low impedance and high impedance.

Description

Technical Field

[0001] The present invention relates to a device for connection to a high-voltage power grid having multiple phases and carrying an AC voltage. The device comprises an active part having at least one phase connection terminal for connection to a phase of the high-voltage power grid; at least one step-down winding connected downstream of one of the phase connection terminals and having multiple taps; and a step-down switch having, for each step-down winding, a selector for switching from a current tap of the step-down winding to a desired tap in the absence of current, and a load changeover switch connected in series downstream of the selector for commutating the current from the current tap to the desired tap. Background Art

[0002] Such equipment is known in practice. For example, equipment used for power transmission and distribution is designed to be connected to a power supply grid operating at high voltage potential. The high voltage minimizes losses during transmission. For this reason, high-voltage grids operate at voltages between 50 kV and 1200 kV. Examples of power transmission equipment connected to high-voltage grids include switches, chokes, and transformers.

[0003] Transformers are used for voltage conversion. They typically have a pair of windings for each phase of a high-voltage power grid, often referred to as a primary and secondary winding. To adjust the voltage or impedance, transformers are equipped with so-called tap switches, which contact the taps of the tap windings. The tap windings are connected in series with the primary and / or secondary windings, with the tap windings being connected to the low-voltage side of the corresponding main winding, i.e., the primary or secondary winding. By selecting the taps of the tap windings using the tap switches, the number of series-connected windings on the primary or secondary side can be varied, thereby changing the ratio between the input and output voltages as needed.

[0004] In transformers with tap changers, particularly on-load tap changers (OLTC), faults or overvoltages in the tap changer or in the tap winding can lead to a short circuit between two taps or stages. This generally results in a very high short-circuit current through a portion of the tap winding, which significantly exceeds the current in the event of an external short circuit. In most cases, this leads to complete destruction of the tap changer, and in some cases, the transformer, with considerable risks, such as fire, flying parts, or oil spills.

[0005] In the field of power transformers, in particular, there is no known technology to prevent or at least minimize faults or their consequences. Conventional systems (e.g., differential protection devices) require at least 40 milliseconds or more before the associated circuit breaker disconnects the transformer, thereby isolating it from the high-voltage grid. However, during this time, the greatest damage has already occurred. Summary of the Invention

[0006] The object of the present invention is therefore to provide a device of the type mentioned at the outset, with which a short-circuit current in a tapping switch or in a part of a tapping winding can be limited.

[0007] The present invention solves the above technical problem in the following manner: an impedance unit is arranged between each selector and each load changeover switch, and the impedance of the impedance unit can be switched between low impedance and high impedance.

[0008] According to the present invention, a tap switch is equipped with an impedance unit, which is arranged in the current path between each selector and the load changeover switch connected in series with the selector. The tap switch according to the present invention preferably has at least two selectors and at least two load changeover switches, wherein each selector is connected in series with a load changeover switch. In other words, the tap switch is formed by multiple pairs of selectors and load changeover switches connected in series. Each tap winding has a pair of tap switches formed by a selector and a load changeover switch. A component of the impedance unit is arranged in each current path between a selector and a load changeover switch, and its impedance, or in other words, its AC resistance, can be changed between two states, or in other words, switched. During normal operation, the impedance unit has a low impedance, thereby providing a low-resistance current path between each selector and each load changeover switch. In the event of a fault, the impedance unit is actively set to a second state, for example, by an external control signal. In this second state, the impedance unit provides a high impedance, thereby limiting short-circuit currents in the tap switches and / or tap windings. This prevents damage to the transformer before an external circuit breaker, arranged between each phase connection of the device according to the present invention and the high-voltage power grid, disconnects the transformer from the grid.

[0009] Advantageously, the impedance unit can be changed passively. In other words, in this embodiment, the device according to the invention itself ensures that the impedance unit goes from its normal operating state with low impedance to a limiting state in which it ensures a high impedance in the current path between the selector and the load changeover switch of the step switch.

[0010] Advantageously, the active part has at least one main winding for each phase, which is connected to one of the tapping windings at its end remote from the phase connection. Each selector has a first selector contact portion for connection to the current tap and a second selector contact portion for connection to the desired tap. Each load changeover switch has a first load changeover switch contact A galvanically connected to the first selector contact portion and a second load changeover switch contact B galvanically connected to the second selector contact portion, and a movable portion that contacts the first load changeover switch contact A in a first switching position of the tapping switch and contacts the second load changeover switch contact B in a second switching position. The impedance unit comprises a first component and a second component, wherein the first component is connected to the first selector contact portion of each selector and the first load changeover switch contact A of each load changeover switch, and the second component is connected to the second selector contact portion of each selector and the second load changeover switch contact B of each load changeover switch, so that current can flow through one component or the other depending on the switching position of the tapping switch.

[0011] According to this embodiment, the active part has at least one main winding for each phase, which is connected to one of the grading windings at its end remote from the phase connection. Each grading winding is connected to a pair formed by a selector and a load changeover switch. Thus, each selector has a first and a second selector contact section, wherein each load changeover switch has a first and a second load changeover switch contact. When a pair formed by a selector and a load changeover switch is associated with a grading winding, the first selector contact section is galvanically connected to the first load changeover switch contact, and each second selector contact section is galvanically connected to the second load changeover switch contact. The impedance unit has a first and a second component, wherein each component of the impedance unit is connected to each selector and each load changeover switch.

[0012] It is important that one component of the impedance unit is connected to the contacts of all selectors and load changeover switches that carry the corresponding current. Therefore, within the scope of the present invention, current flows through this one component of the impedance unit in the first switching state of the step switches, while current is kept off in the corresponding other components. Thus, for example, the first component is connected to the first selector contact part and the first load changeover switch contact of a first pair of step switches, and to the first selector contact part and the first load changeover switch contact of a second pair. During operation of the device, the first selector contact part rests against the tap of the step winding that carries the current. The moving part of the step switch contacts each first load changeover switch contact. Therefore, during normal operation, the current flows through the first selector contact part and the first load changeover switch contact in each pair of selectors and load changeover switches. All current flows through the first component of the impedance unit.

[0013] To select another tap, the selector is operated so that the second selector contact section contacts the desired tap of the stepping winding. This occurs in a current-free manner because the second load changeover switch contacts connected in series are not in contact with the moving part of the stepping switch. If the moving part of each load changeover switch is brought into contact with the second load changeover switch contact, the current is commutated to each second selector contact section and each second load changeover switch contact. The second component of the impedance unit is connected to these contacts. In other words, the current now flows only through the second component of the impedance unit. Each component is designed so that the current flowing through it symmetrically ensures that the impedance of the component is very low and approximately zero. However, if one of the currents flowing through the component increases sharply, this will ensure a high impedance for the desired component.

[0014] Each component of the impedance unit has an impedance winding for each phase of the device, wherein the impedance windings of the components are inductively coupled to one another and connected to one another so that when a symmetrical current flows through the phases of the device, the reactances of the impedance windings of the components compensate one another, so that the corresponding component has a resulting low impedance value.

[0015] In this embodiment of the invention, each component of the impedance unit has a plurality of impedance windings that are inductively coupled to one another. The number of impedance windings corresponds to the number of phases of the system.

[0016] In a different variant of the device according to the invention, the device is designed to be single-phase and has two symmetrical current paths, wherein at least one main winding of the active part is arranged in each current path, the main winding having a high-voltage end connected to the phase connection terminal and a low-voltage end connected to the grading winding, wherein each component of the impedance unit has two impedance windings that are inductively coupled to each other, wherein one of the impedance windings is connected to the selector and the load changeover switch of the first grading winding and the other impedance winding is connected to the selector and the load changeover switch of the second grading winding, and the connection is such that when a symmetrical current flows through the two current paths, the reactances of the impedance windings of the components compensate for each other, so that the corresponding component has a low impedance.

[0017] In this embodiment of the present invention, the device is designed to be single-phase, but forms two symmetrical current paths. At least one main winding of the active part is arranged in each current path. Each main winding is connected in series with a step-down winding. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantageous embodiments and advantages of the present invention are the subject matter of the following description of exemplary embodiments of the present invention with reference to the accompanying drawings, in which identical reference numerals designate functionally identical components, and in which:

[0019] Figure 1 An embodiment of the device according to the invention is schematically shown, and

[0020] Figure 2 A further embodiment of the device according to the invention is schematically shown. DETAILED DESCRIPTION

[0021] Figure 1 An embodiment of a device 1 according to the invention is shown, having a phase connection 2 which can be connected to a phase of a high voltage network carrying an alternating voltage. The capital letter I denotes the phase current. Figure 1 In the exemplary embodiment shown, the phase current flows from the phase connection 2 to the ground connection shown further below.

[0022] The device 1 has two symmetrically designed current paths 3 and 4, wherein a main winding 5 or 6 of an active part 7 is arranged in each current path. Each main winding 5 or 6 has a high-voltage terminal 5a, 6a connected to the phase connection terminal 2. In addition, each main winding 5 or 6 has a low-voltage terminal 5b, 6b connected to a stepping winding 8 or 9. Each stepping winding 8 or 9 is equipped with a tap, which is indicated by a dashed line. Each stepping winding 8 or 9 is associated with a selector 10 or 11 of a stepping switch, wherein each selector 10 or 11 has a first selector contact part 10a, 11a for connecting to the current tap and a second selector contact part 10b, 11b, which can contact the desired next tap.

[0023] Each selector is associated with a load changeover switch 12 or 13, each of which has two load changeover switch contacts A and B. In the position shown, the moving part of the respective load changeover switch 12, 13, implemented as a switching blade 14, is connected to the first load changeover switch contact A. The same applies correspondingly to the switching blade 14 of the load changeover switch 13. An impedance unit 15 is arranged in the current path between each selector 10, 11 and the associated load changeover switch 12, 13. The impedance unit 15 comprises a first component 16 and a second component 17.

[0024] Component 16 of impedance unit 15 has a first impedance winding 18, which is connected to the first selector contact portion 10a of selector 10 and the first load-changing switch contact A of load-changing switch 12. On the other hand, the second impedance winding 19 of component 16 is connected to the first selector contact portion 11a of selector 11 and the first load-changing switch contact A of load-changing switch 13 of the second stepping winding 9. The same applies to second component 17, whose impedance windings 18 and 19 are connected to the second selector contact portion of selector 10 or 11. They are also connected to each of the second load-changing switch contacts B of load-changing switches 12 and 13. Thus, each component 16 and 17 is connected to all selectors and all load-changing switches. Therefore, depending on the switch position of the stepping switch, current flows through the impedance winding of component 16 or 17.

[0025] Thus, the first current path 3 includes the main winding 5, the grading winding 8, the first impedance winding 18 of the first component 16, the load changeover switch contact A of the first load changeover switch 12, and finally the ground connection 20. The second current path 4 passes through the main winding 6, the grading winding 9, the selector 11, the second impedance winding 19 of the first component 16, and the load changeover switch contact A of the second load changeover switch 13. Thus, the same current flows through the windings 18 and 19 of the first component. Here, the windings 18 and 19 are wound in opposite directions, as indicated by the opposite wiring and the points shown above the windings. The inductive coupling of the first and second windings 18 and 19 is achieved via the core 21, which is only shown schematically.

[0026] Due to the symmetrical current flow and inductive coupling, first component 16 has zero impedance during normal operation, resulting in no losses. In the event of a fault, such as a short circuit in a grading winding, the current flowing through first impedance winding 18 of first component 16 is greater than the current flowing through second impedance winding 19 thereof. Consequently, the impedance windings no longer compensate for each other. An impedance forms between grading winding 8 and load changeover switch 12, limiting the short-circuit current and allowing action to be taken before irreparable damage to device 1 occurs.

[0027] If the switching blade 14 of the load changeover switch is switched to the load changeover switch contact B, the current flows only through the component 17 of the impedance unit 15 which is designed like the component 16 . This component 17 plays the same role as described with respect to the first component 16 .

[0028] Figure 2 Another embodiment of the device 1 according to the invention is shown, with Figure 1Unlike the illustrated embodiment, the device 1 is designed as a three-phase device. It has three phase terminals 2, through which currents I1, I2, or I3 flow, respectively. The active part 7 has a main winding 22, 23, 24 for each phase, which is connected to the phase terminal 2 at its high-voltage terminal 22a and to a stepping winding 25, 26, 27 at its low-voltage terminal 5b. Each main winding 25, 26, 27 is inductively coupled to a secondary winding arranged concentrically with respect to the respective main winding. The secondary winding is arranged within the respective main winding and is therefore not shown in the figure. Each stepping winding 25, 26, 27 is in turn connected to a selector 28, 29, 30, wherein each selector 28, 29, 30 is connected in series with a load changeover switch 31, 32, 33. Load changeover switches 31, 32, and 33 switch synchronously, moving each switching blade 14 from a position in which the switching blade 14 contacts the first load changeover switch contact A to a second position in which the switching blade 14 abuts the second load changeover switch contact B. Furthermore, an impedance unit 15 having two components 16 and 17 can be seen. Each component 16, 17 of impedance unit 15 includes a first impedance winding 37, a second impedance winding 38, and a third impedance winding 39. Each first impedance winding is connected to selector 28 of the first phase and load changeover switch 31, each second winding is connected to selector 29 of the second phase and load changeover switch 32, and the third winding 39 is connected to selector 30 of the third phase and load changeover switch 33.

[0029] If Figure 2 Each of the load changeover switches 31, 32, and 33 shown is designed so that the moving contact of the switching blade 14 abuts the load changeover switch contact A. Currents for all phases flow through component 16 of impedance unit 15. The three inductively coupled impedance windings 37, 38, and 39 of component 16 are connected so that when current flows symmetrically through the phases, the impedances of the impedance windings cancel each other out. In other words, component 16 has a near-zero impedance when current flows symmetrically.

[0030] In the event of a short circuit in one of the grading windings 25, 26, 27, the current flowing through one of the windings 37, 38 or 39 is much greater than the current flowing through the other two impedance windings, so that the mutual compensation of the impedances ends, resulting in a very high impedance of the component 16 as a whole. Components 16, 17 of the impedance unit 15 thus ensure that the short-circuit current between the selectors 28, 29, 30 and the corresponding load changeover switches 31, 32, 33 is reduced, so that suitable measures can be taken to limit the fault, for example, disconnecting the device 1 from the grid.

Claims

1. A device (1) for connection to a high-voltage power grid carrying an alternating voltage, the high-voltage power grid having a plurality of phases, the device having - an active part (7) having, for each phase, at least one phase connection for connection to a phase of the high-voltage network, - a plurality of graded windings (8, 9, 25, 26, 27) connected to one of the phase connection terminals and the active part and having a plurality of taps, and - a step-down switch, said step-down switch comprising a selector (10, 11, 28, 29, 30) and a load changeover switch (12, 13, 31, 32, 33) for each step-down winding, said selector being used to switch from a current tap of the step-down winding to a desired tap in the absence of current, said load changeover switch being connected in series downstream of said selector for switching the current from the current tap to the desired tap, wherein - an impedance unit (15) is arranged between each selector (10, 11, 28, 29, 30) and each load changeover switch (12, 13, 31, 32, 33), the impedance of the impedance unit (15) being variable between low impedance and high impedance, - the active part (7) has for each phase at least one main winding (5, 6, 22, 23, 24) connected at its end remote from the phase connection end to one of the graded windings (8, 9, 25, 26, 27), - each selector (10, 11, 28, 29, 30) has a first selector contact portion (10a, 11a) for connection to the current tap and a second selector contact portion (10b, 11b) for connection to the desired tap, - each load changeover switch (12, 13, 31, 32, 33) has a first load changeover switch contact A galvanically connected to the first selector contact section and a second load changeover switch contact B galvanically connected to the second selector contact section, and has a moving part (14) which, in a first switching position of the step switch, contacts the first load changeover switch contact A and, in a second switching position, contacts the second load changeover switch contact B of the load changeover switch (12, 13, 31, 32, 33), and - the impedance unit (15) comprises a first component (16) and a second component (17), wherein the first component (16, 17) is connected to a first selector contact portion of each selector (10, 11, 28, 29, 30) and a first load changeover switch contact A of each load changeover switch (12, 13, 31, 32, 33), and the second component is connected to a second selector contact portion of each selector and a second load changeover switch contact B of each load changeover switch, so that current can flow through one component or the other component (16, 17) depending on the switch position of the step switch, It is characterized in that Each component (16, 17) of the impedance unit (15) has an impedance winding for each phase of the device (1), wherein the impedance windings of the components (16, 17) are inductively coupled to each other and connected to each other so that when a symmetrical current flows through the phases of the device (1), the reactances of the impedance windings of the components (16, 17) compensate each other, so that the corresponding components (16, 17) have a resulting low impedance value.

2. The device (1) according to claim 1, It is characterized in that The impedance unit (15) can be changed in a passive manner.

3. A device (1) for connection to a high-voltage network carrying an alternating voltage, the high-voltage network having a plurality of phases, the device having - an active part (7) having at least one phase connection for connection to a phase of the high-voltage network, - a plurality of graded windings (8, 9, 25, 26, 27) connected to one of the phase connection terminals and the active part and having a plurality of taps, and - a step-down switch, said step-down switch comprising a selector (10, 11, 28, 29, 30) and a load changeover switch (12, 13, 31, 32, 33) for each step-down winding, said selector being used to switch from a current tap of the step-down winding to a desired tap in the absence of current, said load changeover switch being connected in series downstream of said selector for switching the current from the current tap to the desired tap, wherein - an impedance unit (15) is arranged between each selector (10, 11, 28, 29, 30) and each load changeover switch (12, 13, 31, 32, 33), the impedance of the impedance unit (15) being variable between low impedance and high impedance, - the active part (7) has for each phase at least one main winding (5, 6, 22, 23, 24) connected at its end remote from the phase connection end to one of the graded windings (8, 9, 25, 26, 27), - each selector (10, 11, 28, 29, 30) has a first selector contact portion (10a, 11a) for connection to the current tap and a second selector contact portion (10b, 11b) for connection to the desired tap, - each load changeover switch (12, 13, 31, 32, 33) has a first load changeover switch contact A galvanically connected to the first selector contact section and a second load changeover switch contact B galvanically connected to the second selector contact section, and has a moving part (14) which, in a first switching position of the step switch, contacts the first load changeover switch contact A and, in a second switching position, contacts the second load changeover switch contact B of the load changeover switch (12, 13, 31, 32, 33), and - the impedance unit (15) comprises a first component (16) and a second component (17), wherein the first component (16, 17) is connected to a first selector contact portion of each selector (10, 11, 28, 29, 30) and a first load changeover switch contact A of each load changeover switch (12, 13, 31, 32, 33), and the second component is connected to a second selector contact portion of each selector and a second load changeover switch contact B of each load changeover switch, so that current can flow through one component or the other component (16, 17) depending on the switch position of the step switch, It is characterized in that The device (1) is constructed to be single-phase and has two symmetrical current paths (3, 4), wherein at least one main winding (5, 6) of the active part (7) is arranged in each current path (3, 4), the main winding having a high-voltage end (5a, 6a) connected to the phase connection end and a low-voltage end (5b, 6b) connected to the step winding (8, 9), wherein each component (16, 17) of the impedance unit has two impedance windings (18, 19) inductively coupled to each other. 9), wherein one impedance winding (18) of the impedance windings is connected to the selector (10) and the load changeover switch (12) of the first grading winding (8), and the other impedance winding (19) is connected to the selector (11) and the load changeover switch (13) of the second grading winding (9), and is connected so that when symmetrical currents flow through the two current paths (3, 4), the reactances of the impedance windings (18, 19) of the components (16, 17) compensate each other, so that the corresponding components (16, 17) have low impedance values.

4. The device (1) according to claim 3, It is characterized in that The impedance unit (15) can be changed in a passive manner.

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