On-load tap changer and method for operating an on-load tap changer

Abstract

The present invention relates to an on-load tap changer, comprising: a first fixed contact, a second fixed contact, a first movable contact capable of contacting each of the fixed contacts, a second movable contact capable of contacting each of the fixed contacts, a main branch having a switching element, the main branch being capable of connecting the first movable contact to a load lead, and an auxiliary branch having a varistor, the auxiliary branch being capable of connecting the second movable contact to the load lead, wherein the on-load tap changer is designed so that when switching from the first fixed contact to the second fixed contact, the first movable contact is only operated when the second movable contact has reached the second fixed contact.

Description

Technical Field

[0001] The invention relates to an on-load tap changer and a method for operating such an on-load tap changer. Background Art

[0002] On-load tap changer is used for non-interrupted switching between winding leads of transformer. In known on-load tap changer according to the principle of fast resistance switching, the circular current is limited by ohmic resistance and thus ensures the non-interrupted change of the transformer's transformation ratio, and the circular current flows through the tap contact connected in real time and the new tap contact selected in advance during the period of contact connection at the same time during the switching. The ohmic resistance must be designed accordingly according to the specific circuit topology, specific operating conditions, load current and tap voltage, especially the corresponding application of the on-load tap changer. Here, the voltage occurring between the tap contact connected in real time and the tap contact selected in advance of the on-load tap changer is called tap voltage. This resistor design is complex on the one hand and also has an impact on the entire structural structure of the tap changer on the other hand. Depending on the application, resistors of different numbers and sizes are required here. Therefore, the design of the resistance value has an impact on the structural space required for the resistor on the one hand and therefore has an impact on the structural design of the remaining tap changer components. Summary of the invention

[0003] The object of the present invention is therefore to provide an improvement for a tap changer which can be adapted more easily to different applications.

[0004] The development is based on the idea that a varistor is integrated as a current-limiting element into the auxiliary branch of the on-load tap changer. A varistor is a resistance structural element whose resistance value is dependent on the applied voltage.

[0005] According to the improved scheme, an on-load tap changer is proposed, which is used for interruption-free switching between winding taps of a regulating winding of a transformer. The interruption-free switching occurs in particular between adjacent winding taps of a regulating winding. The on-load tap changer includes a first fixed contact, a second fixed contact, a first movable contact and a second movable contact. The fixed contact can be connected to the winding tap of the regulating winding of the transformer. The two movable contacts are constructed so that they can contact each of the fixed contacts. In addition, the on-load tap changer includes a main branch with a switching element, an auxiliary branch with a varistor and a load lead. The main branch can connect the first movable contact to the load lead via the switching element, and the auxiliary branch can connect the second movable contact to the load lead via the varistor. Here, the on-load tap changer is designed so that when switching from the first fixed contact to the second fixed contact, the first movable contact is only operated when the second movable contact has reached, in particular, contacts the second fixed contact.

[0006] In the rest position, ie after the end of one on-load switching operation and before the start of the next on-load switching operation, the two movable contacts are located, for example, on the same fixed contact.

[0007] Furthermore, a movable contact in particular always contacts only one fixed contact, ie the movable contact does not occupy a bridging position between two adjacent fixed contacts.

[0008] The varistor is preferably dimensioned in such a way that when a voltage less than or equal to the tap voltage drops across the varistor, the varistor is in a locked state. The locked state is characterized in that no appreciable current flows through the varistor. In particular, the current flowing through the varistor during the locked state is so small that the movable selector contact can be separated from the fixed contact or connected to the fixed contact without being damaged by the fixed contact. Typically, this is the case when the current intensity is less than 100 mA, preferably less than 10 mA. This locked state of the varistor is obtained in particular even when the tap changer is in a rest position, in which the two movable contacts are on the same fixed contact and the auxiliary branch is thus short-circuited by the parallel main branch.

[0009] The varistor is preferably dimensioned such that in a phase during which a load current, for example in the order of magnitude of several tens of A, for example 30 A, flows through the varistor, the voltage drop across the varistor is a multiple of the tap voltage, for example approximately 1.2 to 1.5 times the tap voltage. Preferably, the voltage drop is less than a predetermined limit value, for example less than 2.0 times the tap voltage.

[0010] The varistor is preferably designed as a metal oxide varistor, for example based on zinc oxide, since the current-voltage characteristic curve of a metal oxide is closer to the ideal characteristic curve of a varistor.

[0011] Since the varistor is in a locked state, in which no significant current flows through it, or in an open state, in which a load current flows through it, no circulating current occurs during the switching process. Therefore, the duration of the losses occurring at the varistor is shorter than when an ohmic resistor is used as a switching resistor.

[0012] When an ohmic resistor is used as a switching resistor, in the time period when the load current flows through the resistor, the output voltage of the transformer reduces the voltage drop caused by the load current on the resistor. This voltage disturbance should not exceed a certain times, such as 5 times, preferably 2.0 times, of the tap voltage for the sake of voltage quality. As a result, when the tap voltage is the same, it is not necessary to use different resistors for different load currents. When using a varistor according to the improved scheme, the interference of the output voltage of the transformer is basically independent of the load current. This is confirmed by the typical current-voltage characteristic curve of the varistor according to the improved scheme and the sudden drop of its different resistances when transitioning from the locked state to the open state. Therefore, the selection of a suitable varistor is not obviously related to the load current, but only to the tap voltage. Thus, the complex design of the switching resistor and the structural design of the on-load tap changer related to it in different application situations can be cancelled in most cases, and thus the entire tap changer design and assembly can be greatly simplified. The tap changer can be prefabricated as stock for a certain tap voltage, for example, regardless of the actual load current.

[0013] According to at least one embodiment, the on-load tap changer is designed such that, when switching from the second fixed contact to the first fixed contact, the second movable contact is not actuated until the first movable contact has reached, in particular has made contact with, the first fixed contact.

[0014] According to at least one embodiment, the on-load tap changer is designed such that, when switching from the second fixed contact to the first fixed contact, the first movable contact is not actuated until the second movable contact has reached, in particular contacts the first fixed contact.

[0015] According to at least one embodiment, the switching element is designed as a disconnect switch, for example as a vacuum interrupter, ie the switching element can assume a closed position in which a load current can flow or an open position in which the load current is interrupted.

[0016] According to at least one embodiment, the first contact and the second contact each have a first contact surface and a second contact surface different from the first contact surface, wherein the first contact surface can be contacted by the first movable contact and the second contact surface can be contacted by the second movable contact. In addition, in particular, the second contact surface cannot be contacted by the first movable contact and the first contact surface cannot be contacted by the second movable contact.

[0017] According to the improved scheme, a method for operating an on-load tap changer is also provided, wherein the on-load tap changer comprises at least a first movable contact and a second movable contact and a load lead. According to the method, when switching from the first fixed contact to the second fixed contact, the load current is switched from the main branch to the auxiliary branch. The load current in the auxiliary branch is limited by means of a varistor, and the first movable contact is only operated when the second movable contact has reached the second fixed contact. Then the load current is switched from the auxiliary branch to the main branch again.

[0018] According to at least one embodiment, when switching from the second fixed contact to the first fixed contact, the load current is switched from the main branch to the auxiliary branch. The load current in the auxiliary branch is limited by means of a varistor, and the second movable contact is not actuated until the first movable contact has reached the first fixed contact.

[0019] According to at least one embodiment, when switching from the second fixed contact to the first fixed contact, the load current is switched from the main branch to the auxiliary branch. The load current in the auxiliary branch is limited by means of a varistor, and the first movable contact is not actuated until the second movable contact has reached the first fixed contact.

[0020] According to at least one embodiment, switching is performed along a first switching direction from a first stationary state to a second stationary state, in which the first stationary state both movable contacts make contact with the first fixed contact, and in the second stationary state both movable contacts make contact with the second fixed contact.

[0021] According to at least one embodiment, switching is performed along a second switching direction from a second stationary state to a first stationary state, in which the two movable contacts both make contact with the second fixed contact, and in the first stationary state, the two movable contacts both make contact with the first fixed contact.

[0022] According to at least one embodiment, the second movable contact is separated from the first fixed contact and connected to the second fixed contact in a first switching direction. The load current is then switched from the main branch to the auxiliary branch. The first movable contact is then separated from the first fixed contact and connected to the second fixed contact.

[0023] According to at least one embodiment, the load current is switched from the main branch to the auxiliary branch in a second switching direction. The first movable contact is then separated from the second fixed contact and contact-connected with the first fixed contact. The load current is then switched from the auxiliary branch to the main branch and the second movable contact is then separated from the second fixed contact and contact-connected with the first fixed contact.

[0024] According to at least one embodiment, the second movable contact is separated from the second fixed contact and connected to the first fixed contact in the second switching direction. The load current is then switched from the main branch to the auxiliary branch. The first movable contact is then separated from the second fixed contact and connected to the first fixed contact.

[0025] According to at least one embodiment, in step a, the switching element is closed or remains closed and the second movable contact is separated from the second fixed contact and is connected to the first fixed contact. Then, in step b, the switching element is opened and the first movable contact is thus separated from the load lead, and then in step c, the first movable contact is separated from the first fixed contact and is connected to the second fixed contact. Then, in step d, the switching element is closed and the first movable contact is thus connected to the load lead. The load current now flows again through the main branch. Preferably, step b is carried out after step a, step c after step b and step d after step c, wherein "after" in particular means "directly after".

[0026] According to at least one embodiment, in step a', the switching element is opened and the first movable contact is thereby separated from the load lead. Then, in step b', the first movable contact is separated from the second fixed contact and is contact-connected with the first fixed contact. Then, in step c', the switching element is closed again and the load current is thereby switched from the auxiliary branch to the main branch. Finally, in step d', the second movable contact is separated from the second fixed contact and is contact-connected with the first fixed contact. Preferably, step b' is implemented after step a', step c' after step b' and step d' after step c', wherein "after" in particular means "directly after".

[0027] According to at least one other embodiment, in step a", the second movable contact is separated from the second fixed contact and connected to the first fixed contact. In the following step b", the switching element is opened and the first movable contact is separated from the load lead, and then in step c", the first movable contact is separated from the second fixed contact and connected to the first fixed contact. Then, in step d", the switching element is closed and the first movable contact is connected to the load lead again. The load current now flows through the main branch again. Preferably, step b" is carried out after step a", step c" after step b", and step d" after step c", wherein "after" in particular means "directly after".

[0028] Further embodiments of the on-load tap changer result directly from different embodiments of the method or vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will be explained in detail below with reference to the accompanying drawings by means of exemplary embodiments. Components having the same function or having the same effect may be provided with the same reference numerals. Identical components or components having the same function may be explained only with respect to the drawing in which they first appear. The explanation does not necessarily have to be repeated in the following drawings.

[0030] In the attached figure:

[0031] Figure 1 A schematic diagram showing an exemplary embodiment of an on-load tap changer according to the development;

[0032] Figure 2a to Figure 2d An exemplary switching sequence and an exemplary method in an on-load tap changer according to the development are shown;

[0033] Figure 2e shows an exemplary current-voltage characteristic curve of a varistor according to the improvement;

[0034] Figures 3a to 3d A further exemplary switching sequence and a further exemplary method in an on-load tap changer according to the development are shown;

[0035] Figure 4a 1 to 2 show a further exemplary switching sequence and a further exemplary method of an on-load tap changer according to this development. DETAILED DESCRIPTION

[0036] Figure 1A schematic diagram of an exemplary embodiment of an on-load tap changer for non-interruption switching between winding taps of a regulating winding 11 of a transformer (not shown) is shown. According to the improved scheme, the on-load tap changer 1 includes at least a first fixed contact 2 and a second fixed contact 3, which can be connected to the winding taps of the regulating winding 11 of the transformer respectively. The total number of fixed contacts is related to the number of winding taps. Each fixed contact 2, 3 has a first contact surface 2.1, 3.1 and a second contact surface 2.2, 3.2. In addition, the on-load tap changer 1 includes a first movable contact 4 and a second movable contact 5, which can respectively contact and connect the respective fixed contacts of the regulating winding. Here, the first movable contact 4 can contact and connect the first contact surfaces 2.1, 3.1 of the fixed contacts 2, 3, but does not contact and connect the second contact surfaces 2.2, 3.2. Correspondingly, the second movable contact 5 can make contact with the second contact surfaces 2.2, 3.2 of the fixed contacts 2, 3, but does not make contact with the first contact surfaces 2.1, 3.1. Figure 1 The schematic diagram showing an exemplary embodiment of an on-load tap changer, in particular the arrangement of the contact surfaces 2.1, 1.2 and 3.1, 3.2 relative to one another, is not absolutely necessary.

[0037] Figure 1 The on-load tap changer 1 is shown in a rest state, in which the two movable contacts 4 , 5 are in contact with the same fixed contact 2 . L Here, current flows via the main branch 6 from the first movable contact 4 via the closed switching element 8 to the load shunt 10. The varistor 9 is in the blocking state, since the auxiliary branch 7 is short-circuited by the parallel-connected main branch 6.

[0038] The main branch 6 connects the first movable contact 4 to the load shunt 10 via the switching element 8. The switching element 8 is preferably designed as a vacuum switching tube. The auxiliary branch 7 connects the second movable contact 5 to the load shunt 10 via the varistor 8 as well.

[0039] exist Figure 2a to Figure 2d Detailed description of an exemplary switching sequence of an on-load tap changer 1 according to the novel concept is given in FIG. 1 , in which a switch is made from a first fixed contact 2 to a second fixed contact 3 or to a corresponding winding tap.

[0040] In step a (see Figure 2a ), the switch element 8 is closed or remains closed. As a result, the load current I LThe current flows through the main branch 6 and the second movable contact 5 can be separated from the first fixed contact 2 without current. After the movable contact 5 has been in contact with the second fixed contact 3, the tap voltage drops via the varistor 9. The current flowing here is so small that it does not damage the selector when the second fixed contact 3 is contacted. Here, the second movable contact 5 contacts the corresponding second contact surfaces 2.2, 2.3 of the fixed contacts 2, 3.

[0041] In step b (see Figure 2b ), the switch element 8 is opened. As a result, the first movable contact 4 is separated from the load lead 10 and the load current I L The main branch 6 is switched to the auxiliary branch 7. The voltage drop across the varistor 9 increases, for example, to approximately 1.2 to 1.5 times the tap voltage. Figure 2e The current-voltage characteristic curve of a varistor used according to the development, for example a metal oxide varistor based on zinc oxide, is schematically shown in . It can be seen from this that the voltage drop in the off state is not significantly dependent on the current.

[0042] In step c (see Figure 2c ), the first movable contact 4, which is no longer current-carrying, is separated from the first fixed contact 2 and is brought into contact with the second fixed contact 3. Here, the first movable contact 4 first contacts the first contact surface 2.1 of the first fixed contact 2 and then contacts the first contact surface 3.1 of the second fixed contact 3.

[0043] In step d (see Figure 2d ), the switching element 8 is closed again. The first movable contact 4 is now connected to the load lead 10 again and the load current I L The flow again flows through the main branch 6 . The varistor 9 is again in the blocking state and the tap changer is again in the rest position in which the two movable contacts 4 , 5 make contact with the second fixed contact 3 .

[0044] exist Figures 3a to 3d 2 shows a further exemplary switching sequence of the on-load tap changer 1 according to the novel concept, in which switching occurs from the second fixed contact 3 to the first fixed contact 2 .

[0045] In step a' (see Figure 3a ), the switch element 8 is opened. As a result, the first movable contact 4 is separated from the load lead 10 and the load current I L The switchover occurs from the main branch 6 to the auxiliary branch 7. The voltage drop across the varistor increases, for example, to approximately 1.2 to 1.5 times the tap voltage.

[0046] In step b' (see Figure 3b), the first movable contact 4, through which current no longer flows, is separated from the second fixed contact 3 and connected to the first fixed contact 2.

[0047] In step c' (see Figure 3c ), the switch element 8 is closed again, so that the first movable contact 4 is connected to the load lead 10 again and the load current I L The flow occurs via the main branch 6. The varistor 9 enters a blocking state, in which the tap voltage drops across the varistor.

[0048] In step d' (see Figure 3d ), the second movable contact 5 is separated from the second fixed contact 3 without current and is in contact with the first fixed contact 2. Because the varistor 9 is in the locked state, the current flowing through the auxiliary branch 7 is so small that it does not damage the selector when the first fixed contact 2 is contacted. The tap changer is now in the rest position again, in which both movable contacts B1, B2 are in contact with the first fixed contact 3. The varistor 9 is in the locked state because the auxiliary branch 7 is short-circuited by the parallel main branch 6.

[0049] exist Figures 4a to 4d A further exemplary switching sequence of the on-load tap changer 1 according to the novel concept is described in , in which switching likewise takes place from the second fixed contact 3 to the first fixed contact 2 .

[0050] In step a" (see Figure 4a ), the second movable contact 5 is separated from the second fixed contact 3 without current, because the switching element 8 is closed and the load current I L The current flows through the main branch 6. When the second movable contact 5 has contacted the first fixed contact 2, the tap voltage drops via the varistor 9. The current flowing here is so small that when the first fixed contact 2 is contacted, the current does not damage the selector.

[0051] In step b" (see Figure 4b ), the switch element 8 is opened. As a result, the first movable contact 4 is separated from the load lead 10 and the load current I L The switch is made from the main branch 6 to the auxiliary branch 7. The voltage drop across the varistor 9 increases to approximately 1.2 to 1.5 times the tap voltage.

[0052] In step c" (see Figure 4c ), the first movable contact 4, through which current no longer flows, is separated from the second fixed contact 3 and connected to the first fixed contact 2.

[0053] In step d" (see Figure 4d), the switch element 8 is closed again. The first movable contact 4 is now connected to the load lead 10 again and the load current I L The flow again flows through the main branch 6 . The varistor 9 is again in the blocking state and the tap changer is again in the rest position, in which both movable contacts B1 , B2 make contact with the first fixed contact 2 .

[0054] Reference numerals list

[0055] 1 tap switch

[0056] 2First fixed contact

[0057] 3 Second fixed contact

[0058] 4First movable contact

[0059] 5Second movable contact

[0060] 6 Main branch

[0061] 7 Auxiliary Road

[0062] 8 Switching elements

[0063] 9 Varistor

[0064] 10 Load leads

[0065] 11 Adjust the winding.

Claims

1. An on-load tap changer (1), comprising: - a first fixed contact (2), - a second fixed contact (3), - a first movable contact (4) capable of contacting each of said fixed contacts, - a second movable contact (5) capable of making contact with each of said fixed contacts, a main branch (6) having a switching element (8), which connects the first movable contact (4) to the load shunt (10), and the switching element (8) is designed as a disconnect switch, - an auxiliary branch (7) having a varistor (9), said auxiliary branch (7) connecting said second movable contact (5) to said load lead (10), in, The on-load tap changer (1) is designed so that when switching from the first fixed contact (2) to the second fixed contact (3), the first movable contact (4) is actuated only when the second movable contact (5) has reached the second fixed contact (3), and the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7), During switching, the load current in the auxiliary branch (7) is limited by means of the varistor (9) and no circulating current occurs during the switching process.

2. The on-load tap changer (1) according to claim 1, wherein: The on-load tap changer (1) is designed such that, when switching from the second fixed contact (3) to the first fixed contact (2), the second movable contact (5) is actuated only when the first movable contact (4) has reached the first fixed contact (2).

3. The on-load tap changer (1) according to claim 1, wherein: The on-load tap changer is designed such that, when switching from the second fixed contact (3) to the first fixed contact (2), the first movable contact (4) is actuated only when the second movable contact (5) has reached the first fixed contact (2).

4. The on-load tap changer (1) according to any one of claims 1 to 3, wherein: - each of the fixed contacts has a first contact surface, which can be contacted by the first movable contact (4), Each of the fixed contacts has a second contact surface, which can be contacted by the second movable contact (5).

5. Method for operating an on-load tap changer, the on-load tap changer having a first movable contact (4) and a second movable contact (5), a first fixed contact (2) and a second fixed contact (3) and a load lead (10), and the on-load tap changer being designed according to any one of claims 1 to 4, wherein: - when switching from the first fixed contact (2) to the second fixed contact (3), the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7); - limiting the load current in the auxiliary branch (7) by means of a varistor (9); - the first movable contact (4) is operated only when the second movable contact (5) has reached the second fixed contact (3); and - No circulating currents occur during the switching process.

6. The method according to claim 5, wherein: - when switching from the second fixed contact (3) to the first fixed contact (2), the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7); - limiting the load current in the auxiliary branch (7) by means of a varistor (9); and - the second movable contact (5) is actuated only when the first movable contact (4) has reached the first fixed contact (2).

7. The method according to claim 5, wherein: - when switching from the second fixed contact (3) to the first fixed contact (2), the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7); - limiting the load current in the auxiliary branch (7) by means of a varistor (9); and - The first movable contact (4) is actuated only when the second movable contact (5) has reached the first fixed contact (2).

8. The method according to any one of claims 5 to 7, wherein: - switching from a first stationary state to a second stationary state along a first switching direction, in which in the first stationary state, both the first movable contact (4) and the second movable contact (5) are in contact with the first fixed contact (2), and in the second stationary state, both the first movable contact (4) and the second movable contact (5) are in contact with the second fixed contact (3); -Switching from a second stationary state to a first stationary state along a second switching direction, in which the first movable contact (4) and the second movable contact (5) are both in contact with the second fixed contact (3), and in the first stationary state, the first movable contact (4) and the second movable contact (5) are both in contact with the first fixed contact (2).

9. The method according to claim 8, wherein: In the first switching direction, - separating the second movable contact (5) from the first fixed contact (2) and connecting the second movable contact (5) to the second fixed contact (3); - Then the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7); - Then the first movable contact (4) is separated from the first fixed contact (2) and is brought into contact with the second fixed contact (3).

10. The method according to claim 8, wherein: In the second switching direction, - The load current (I L ) is switched from the main branch (6) to the auxiliary branch (7), - then the first movable contact (4) is separated from the second fixed contact (3) and is connected to the first fixed contact (2); - Then the load current (I L ) is switched from the auxiliary branch (7) to the main branch (6); - Then the second movable contact (5) is separated from the second fixed contact (3) and is brought into contact with the first fixed contact (2).

11. The method according to claim 8, wherein: In the second switching direction, - separating the second movable contact (5) from the second fixed contact (3) and connecting the second movable contact (5) to the first fixed contact (2); - Then the load current (I L ) is switched from the main branch (6) to the auxiliary branch (7); - Then the first movable contact (4) is separated from the second fixed contact (3) and is brought into contact with the first fixed contact (2).

12. The method according to any one of claims 5 to 7, wherein: - In step a, the switching element (8) is closed or kept closed and the second movable contact (5) is separated from the first fixed contact (2) and is connected to the second fixed contact (3); - in step b, the switching element (8) is opened and thereby the first movable contact (4) is separated from the load lead (10); - In step c, the first movable contact (4) is separated from the first fixed contact (2) and is connected to the second fixed contact (3); In step d, the switching element (8) is closed and thereby the first movable contact (4) is connected to the load shunt (10).

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