AU2019286437A1

AU2019286437A1 - On-load tap-changer and method for actuating an on-load tap-changer

Info

Publication number: AU2019286437A1
Application number: AU2019286437A
Authority: AU
Inventors: Christian Hammer
Original assignee: Maschinenfabrik Reinhausen GmbH; Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen GmbH
Priority date: 2018-06-12
Filing date: 2019-06-11
Publication date: 2021-01-28
Also published as: EP3807916B1; EP3807916A1; CN112219251A; WO2019238669A1; DE102018113982B4; EP3807916C0; DE102018113982A1

Abstract

The invention relates to an on-load tap-changer, comprising – a first fixed contact, – a second fixed contact, – a first movable contact, which can contact each of the fixed contacts, – a second movable contact, which can contact each of the fixed contacts, – a main branch having a switch element, which can connect the first movable contact to a load discharge, – an auxiliary branch having a varistor, wherein the auxiliary branch connects the second movable contact to the load discharge, wherein the on-load tap-changer is designed such that, on a changeover from the first fixed contact to the second fixed contact, the first movable contact is not actuated until the second movable contact has reached the second fixed contact.

Description

ON-LOAD TAP CHANGER AND METHOD FOR ACTUATING AN ON-LOAD TAP CHANGER

The invention relates to an on-load tap changer and to a method for actuating an on-load tap changer.

On-load tap changers are used for uninterrupted switching over between winding taps of a transformer. In known on-load tap changers based on the principle of resistance rapid switching, the circular current which at the time of switching over flows during the interim simultaneous contacting of the currently connected tap contact and the preselected new tap contact is limited by ohmic resistances and thereby ensures uninterrupted change of the translation ratio of the transformer. The ohmic resistance has to be appropriately dimensioned in dependence on the actual circuit topology, the individual operating conditions, the load current and the tap voltage, thus specifically on the respective case of use of the on-load tap changer. In that regard, designated as tap voltage is every voltage which appears between the currently connected tap contact and the preselected tap contact of the on-load tap changer. This resistance format on the one hand is expensive and on the other hand also has an influence on the overall constructional form of the tap changer. A different number and dimensioning of resistances is required here depending on the respective case of use. The dimensioning of the resistance value therefore has an effect on the constructional space required for the resistances and thus on the constructional design of the remaining tap changer components.

It is therefore an object of the invention to indicate an improved concept for a tap changer, which can be more simply adapted to different cases of use.

This object is fulfilled by the subjects of the independent claims. Further forms of embodiment are described in the dependent claims.

The improved concept is based on the idea of integrating a varistor as current-limiting element in an auxiliary branch of the on-load tap changer. Varistors are resistive components having a resistance value dependent on the applied voltage.

According to the improved concept an on-load tap changer for uninterrupted switching over between winding taps of a regulating winding of a transformer is indicated. The uninterrupted switching over takes place, in particular, between adjacent winding taps of the regulating winding. The on-load tap changer comprises a first fixed contact, a second fixed contact, a first movable contact and a second movable contact. The fixed contacts are connectible with the winding taps of the regulating winding of a transformer. The two movable contacts are of such a configuration that they can each contact the fixed contacts. Moreover, the on-load tap changer comprises a main branch with a switching element, an auxiliary branch with a varistor, and a load diverter. The main branch in that case can connect the first movable contact with the load diverter by way of the switching element and the auxiliary branch can connect the second movable contact with the load diverter by way of the varistor. In that regard, the on-load tap changer has such a configuration that when switching over from the first fixed contact to the second fixed contact takes place the first movable contact is actuated only when the second movable contact has reached, in particular contacted, the second fixed contact.

In a stationary setting, i.e. after the conclusion of a load changeover process and prior to the start of the next load changeover, the two movable contacts both stand at, for example, the same fixed contact.

In addition, a movable contact makes contact with, specifically, always only one fixed contact, i.e. it does not adopt a bridging position between two adjacent fixed contacts.

The varistor is preferably dimensioned in such a way that it is in a blocking state when a voltage, which is smaller than or equal to the tap voltage, decays across it. The blocking state is distinguished by the fact that no significant current flows by way of the varistor. In particular, the current which flows via the varistor during the blocking state is so small that the movable selector contacts can be separated from a fixed contact or connected with a fixed contact without damage. This is typically the case for a current strength less than 100 mA, preferably smaller than 10 mA. This blocking state of the varistor applies particularly also when the tap changer is in a stationary setting in which both movable contacts stand at the same fixed contact and thus the auxiliary branch is short-circuited by the parallel main branch.

The varistor is preferably dimensioned in such a way that in a phase during which the load current flows across the varistor in, for example, the order of magnitude of several 10 A, for example 30 A, 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. The voltage drop is preferably less than a predetermined limit value, for example less than 2.0 times the tap voltage.

The varistor is preferably constructed as a metal oxide varistor, for example on the basis of zinc oxide, since the current/voltage plot of metal oxide varistors is closer to the ideal plot of a varistor.

Since the varistor is disposed either in a blocking state in which no significant current flows across it or in an open state in which the load current flows across it, no circular current arises during the switching-over process. Compared with use of an ohmic resistance as switching-over resistance, the time period in which losses at the varistor occur is therefore smaller.

In the case of use of an ohmic resistance as switching-over resistance the output voltage of the transformer is reduced in the time period, in which the load current flows via the resistance, by the voltage drop, which is produced by the load current, at the resistance. For reasons of voltage quality, this voltage decline should not exceed a specific multiple of the tap voltage, for example 5.0 times, preferably 2.0 times. As a consequence thereof, in a given case - with the same tap voltage - different resistances have to be used for different load currents. When a varistor according to the improved concept is used, the decline of the output voltage of the transformer is substantially independent of the load current. This is due to the typical current/voltage plot of a varistor according to the improved concept and the abrupt drop of its differential resistance at the time of transition from the blocking state to the open state. The selection of the suitable varistor therefore substantially depends not on the load current, but merely on the tap voltage. The expensive dimensioning of switch-over resistances and the constructional design, which is dependent thereon, of the on-load tap changer due to different cases of use can thus be eliminated for the most part and as a result the overall tap changer layout and assembly can be significantly simplified. For example, the tap changer can then be prefabricated as stock items for specific tap voltages regardless of the actual load current.

According to at least one form of embodiment the on-load tap changer is designed in such a way that when switching over from the second fixed contact to the first fixed contact takes place the second movable contact is actuated only when the first movable contact has reached, in particular contacted, the first fixed contact.

According to at least one form of embodiment the on-load tap changer has such a configuration that when switching over from the second fixed contact to the first fixed contact takes place the first movable contact is actuated only when the second movable contact has reached, in particular contacted, the first fixed contact.

According to at least one form of embodiment the switching element is configured as an 'off' switch, for example as a vacuum interrupter, i.e. the switching element can adopt either a closed setting in which the load current can flow or an open setting in which the load current is interrupted.

According to at least one form of embodiment the first and second fixed contacts respectively have a first contact surface and a second contact surface different from the first contact surface, wherein the respective first contact surface can be contacted by the first movable contact and the respective second contact surface can be contacted by the second movable contact. Moreover, in particular, the respective second contact surface cannot be contacted by the first movable contact and the respective first contact surface cannot be contacted by the second movable contact.

According to the improved concept, in addition a method for actuation of an on-load tap changer is indicated, wherein the on-load tap changer comprises at least one first movable contact and second movable contact and a load diverter. According to the method, when switching over from the first to the second fixed contact takes place a load current is switched over from a main branch to an auxiliary branch. The load current is limited in the auxiliary branch by means of a varistor and the first movable contact is actuated only when the second movable contact has reached the second fixed contact. The load current is thereafter switched back from the auxiliary branch to the main branch.

According to at least one form of embodiment, when switching over from the second to the first fixed contact takes place the load current is switched over from a main branch to an auxiliary branch. In that case, the load current in the auxiliary branch is limited by means of a varistor and the second movable contact is actuated only when the first movable contact has reached the first fixed contact.

According to at least one form of embodiment when switching over from the second to the first fixed contact takes place the load current is switched over from the main branch to an auxiliary branch. The load current in the auxiliary branch is in that case limited by means of a varistor and the first movable contact is actuated only when the second movable contact has reached the first fixed contact.

According to at least one form of embodiment in a first switching direction there is switching over from a first stationary state in which the movable contacts both contact the first fixed contact to a second stationary state in which the movable contacts both contact the second fixed contact.

According to at least one form of embodiment in a second switching direction there is switching over from a second stationary state in which the movable contacts both contact the second fixed contact to a second stationary state in which the movable contacts both contact the first fixed contact.

According to at least one form of embodiment in the first switching direction the second movable contact is separated from the first fixed contact and is contacted by the second fixed contact. A load current is thereafter switched over from a main branch to an auxiliary branch. The first movable contact is thereafter separated from the first fixed contact and is contacted by the second fixed contact.

According to at least one form of embodiment in the second switching direction the load current is switched over from the main branch to the auxiliary branch. The first movable contact is thereafter separated from the second fixed contact and is contacted by the first fixed contact. The load current is thereupon switched over from the auxiliary branch to the main branch and thereafter the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact.

According to at least one form of embodiment in the second switching direction the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact. The load current is thereafter switched over from the main branch to the auxiliary branch. The first movable contact is thereafter separated from the second fixed contact and contacted by the first fixed contact.

According to at least one form of embodiment in a step a the switching element is closed or remains closed and the second movable contact is separated from the second fixed contact and contacted by the first fixed contact. The switching element is thereupon opened in a step b and the first movable contact is thereby separated from the load diverter, whereupon in a step c the first movable contact is separated from the first fixed contact and contacted by the second fixed contact. The switching element is then closed in a step d and the first movable contact is thereby connected with the load diverter. The load current now flows again via the main branch. For preference, step b is performed after step a, step c is performed after step b and step d is performed after step c, in which case "after" means, in particular, "directly after".

According to at least one form of embodiment the switching element is opened in a step a' and the first movable contact is thereby separated from the load diverter. The first movable contact is thereafter separated from the second fixed contact in a step b' and is contacted by the first fixed contact. The switching element is thereupon closed again in a step c' and the load current thereby switched over from the auxiliary branch to the main branch. Finally, in a step d' the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact. For preference, step b' is performed after step a', step c' is performed after step b' and step d' is performed after step c', in which case "after" means, in particular, "directly after".

According to at least one further form of embodiment in a step a" the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact. In a step b" following thereupon the switching element is opened and the first movable contact separated from the load diverter, whereupon in a step c" the first movable contact is separated from the second fixed contact and is contacted by the first fixed contact. The switching element is then closed in a step d" and the first movable contact connected again with the load diverter. The load current now again flows via the main branch. For preference, step b" is performed after step a", step c" is performed after step b" and step d" is performed after step c", in which case "after" means, in particular, "directly after".

Further forms of embodiment of the on-load tap changer are evident directly from the different forms of embodiment of the method and conversely.

The invention is explained in detail in the following on the basis of exemplifying forms of embodiment with reference to the drawings. Components which are functionally identical or have an identical effect can be provided with identical reference numerals. Identical components or components with identical functions are in certain circumstances explained only with respect to the figure in which they first appear. The explanation is not necessarily repeated in the succeeding figures.

In the drawings:

Fig. 1 shows a schematic illustration of an exemplifying form of embodiment of an on-load tap changer according to the improved concept;

Figs. 2a - d show an exemplifying switching sequence in the on-load tap changer and an exemplifying method according to the improved concept;

Fig. 2e shows an exemplifying current/voltage plot of a varistor according to the improved concept;

Figs. 3a - d show a further exemplifying switching sequence in the on-load tap changer and a further exemplifying method according to the improved concept; and

Figs. 4a - d show a further exemplifying switching sequence in the on-load tap changer and a further exemplifying method according to the improved concept.

Figure 1 shows a schematic illustration of an exemplifying form of embodiment of an on load tap changer for uninterrupted switching over between winding taps of a regulating winding 11 of a transformer (not illustrated). According to the improved concept the on load tap changer 1 comprises at least one first fixed contact 2 and second fixed contact 3, which can each be connected with a winding tap of the regulating winding 11 of the transformer. The total number of fixed contacts is dependent on 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 comprises a first movable contact 4 and a second movable contact 5, which can each contact the individual fixed contacts of the regulating winding. In that case, the first movable contact 4 can contact the first contact surfaces 2.1, 3.1 of the fixed contacts 2, 3, but not the second contact surfaces 2.2, 3.2. Correspondingly, the second movable contact 5 can contact the second contact surfaces 2.2, 3.2 of the fixed contacts 2, 3, but not the first contact surfaces 2.1, 3.1. Figure 1 illustrates a schematic diagram of an exemplifying form of embodiment of the on load tap changer; in particular, the arrangement of the contact surfaces 2.1, 2.2 and 3.1, 3.2 opposite one another is not absolutely necessary.

Figure 1 shows the on-load tap changer 1 in a stationary state in which the two movable contacts 4, 5 contact the same fixed contact 2. The load current IL here flows via a main branch 6 from the first movable contact 4 to the load diverter 10 via the closed switching element 8. The varistor 9 is disposed in the blocking state, since the auxiliary branch 7 is short-circuited by the parallel main branch 6.

The main branch 6 connects the first movable contact 4 with a load diverter 10 via a switching element 8. The switching element 8 is preferably constructed as a vacuum interrupter. The auxiliary branch 7 similarly connects the second movable contact 5 with the load diverter 10 via a varistor 9.

An exemplifying switching sequence of the on-load tap changer 1 according to the new concept is described in Figures 2a to 2d, wherein switching over takes place from the first fixed contact 2 to the second fixed contact 3 or the corresponding winding taps.

In a step a (cf. Fig. 2a), the switching element 8 is closed or remains closed. The load current IL thus flows via the main branch 6, and the second movable contact 5 can be separated free of current from the first fixed contact 2. After the movable contact 5 has been contacted by the second fixed contact 3, the step voltage decays across the varistor 9. The current flowing is then so small that it does not damage the selector when contacting of the second fixed contact 3 takes place. In that case, the second movable contact 5 contacts the respective second contact surface 2.2, 2.3 of the fixed contacts 2, 3.

The switching element 8 is opened in a step b (cf. Fig. 2b). The first movable contact 4 is thereby separated from the load diverter 10 and the load current k is switched over from the main branch 6 to the auxiliary branch 7. The voltage drop via the varistor 9 increases, for example, to approximately 1.2 to 1.5 times the tap voltage. A typical current/voltage plot of a varistor, such as is used in accordance with the improved concept, for example a metal oxide varistor on the basis of zinc oxide, is schematically shown in Figure 2e. It can be seen therefrom that the voltage drop in the opened state is not significantly dependent on the current.

In a step c (cf. Fig. 2c), the first movable contact 4, which now no longer conducts current, is separated from the first fixed contact 2 and is contacted by the second fixed contact 3. In that case the first movable contact 4 initially contacts the first contact surface 2.1 of the first fixed contact 2 and thereafter the first contact surface 3.1 of the second fixed contact 3.

In a step d (cf. Fig. 2d), the switching element 8 is closed again. The first movable contact 4 is now connected again with the load diverter 10 and the load current IL again flows via the main branch 6. The varistor 9 is again in the blocking state and the tap changer again in a stationary setting in which both movable contacts 4, 5 contact the second fixed contact 3.

A further exemplifying switching sequence of the on-load tap changer 1 according to the new concept is described in Figures 3a to 3d, wherein switching over is from the second fixed contact 3 to the first fixed contact 2.

In a step a' (cf. Fig. 3a) the switching element 8 is opened. The first movable contact 4 is thereby separated from the load diverter 10 and the load current IL is switched over from the main branch 6 to the auxiliary branch 7. The voltage drop via the varistor increases, for example, to approximately 1.2 to 1.5 times the tap voltage.

In a step b' (cf. Fig. 3b) the first movable contact 4, which now no longer conducts current, is separated from the second fixed contact 3 and contacted by the first fixed contact 2.

In a step c' (cf. Fig. 3c) the switching element 8 is closed again so that the first movable contact 4 is connected again with the load diverter 10 and the load current IL flows via the main branch 6. The varistor 9 goes to the blocking state, in which the tap voltage drops across it.

In a step d' (cf. Fig. 3d) the second movable contact 5 is separated in current-free manner from the second fixed contact 3 and contacted by the first fixed contact 2. Since the varistor 9 is in the blocking state the current flowing via the auxiliary branch 7 is so small that it does not damage the selector when contacting the first fixed contact 2. The tap changer is now again in a stationary setting in which both movable contacts 4, 5 contact the first fixed contact 3. The varistor 9 is in the blocking state, since the auxiliary branch 7 is short-circuited by the parallel main branch 6.

A further exemplifying switching sequence of the on-load tap changer 1 according to the new concept is described in Figures 4a to 4d, wherein switching over from the second fixed contact 3 to the first fixed contact 2 similarly takes place.

In a step a" (cf. Fig. 4a) the second movable contact 5 is separated in current-free manner from the second fixed contact 3, since the switching element 8 is closed and thus the load current IL flows via the main branch 6. After the second movable contact 5 has been contacted by the first fixed contact 2, the tap voltage across the varistor 9 decays. The current flowing in that case is so small that it does not damage the selector when contacting the first fixed contact 2.

In a step b" (cf. Fig. 4b) the switching element 8 is opened. The first movable contact 4 is thereby separated from the load diverter 10 and the load current IL is switched over 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.

In a step c" (cf. Fig. 4c) the first movable contact 4, which now no longer conducts current, is separated from the second fixed contact 3 and is contacted by the first fixed contact 2.

In a step d" (cf. Fig. 4d) the switching element 8 is closed again. The first movable contact 4 is now again connected with the load diverter 10 and the load current IL again flows via the main branch 6. The varistor 9 is again disposed in the blocking state and the tap changer is again in a stationary setting in which the two movable contacts 4, 5 contact the first fixed contact 2.

REFERENCENUMERALS

1 tap changer 2 first fixed contact 3 second fixed contact 4 first movable contact second movable contact 6 main branch 7 auxiliary branch 8 switching element 9 varistor load diverter 11 regulating winding

Claims

1. On-load tap changer comprising - a first fixed contact, - a second fixed contact, - a first movable contact, which can contact each of the fixed contacts, - a second movable contact, which can contact each of the fixed contacts, - a main branch with a switching element, wherein the main branch can connect the first movable contact with a load diverter, and - an auxiliary branch with a varistor, wherein the auxiliary branch can connect the second movable contact with the load diverter, wherein - the on-load tap changer has such a configuration that when switching over from the first fixed contact to the second fixed contact takes place the first movable contact is actuated only when the second movable contact has reached the second fixed contact.

2. On-load tap changer according to the preceding claim, wherein - the on-load tap changer has such a configuration that when switching over from the second fixed contact to the first fixed contact takes place the second movable contact is actuated only when the first movable contact has reached the first fixed contact.

3. On-load tap changer according to claim 1, wherein - the on-load tap changer has such a configuration that when switching over from the second fixed contact to the first fixed contact takes place the first movable contact is actuated only when the second movable contact has reached the first fixed contact.

4. On-load tap changer according to any one of claims 1 to 3, wherein - the switching element is configured as an 'off' switch.

5. On-load tap changer 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,

- each of the fixed contacts has a second contact surface, which can be contacted by the second movable contact.

6. Method of actuating an on-load tap changer which comprises a first and second movable contact, a first and second fixed contact and a load diverter and which is, in particular, constructed in accordance with any one of the preceding claims, wherein - when switching over from the first to the second fixed contact takes place a load current IL is switched over from a main branch to an auxiliary branch; the load current in the auxiliary branch is limited by means of a varistor; and wherein the first movable contact is actuated only when the second movable contact has reached the second fixed contact.

7. Method according to the preceding claim, wherein - when switching over from the second to the first fixed contact takes place a load current IL is switched over from a main branch to an auxiliary branch; the load current in the auxiliary branch is limited by means of a varistor; and wherein the second movable contact is actuated only when the first movable contact has reached the first fixed contact.

8. Method according to claim 6, wherein - when switching over from the second to the first fixed contact takes place a load current IL is switched over from a main branch to an auxiliary branch; the load current in the auxiliary branch is limited by means of a varistor; and wherein - the first movable contact is actuated only when the second movable contact has reached the first fixed contact.

9. Method according to any one of claims 6 to 8, wherein in a first switching direction there is switching over from a first stationary state in which the movable contacts both contact the first fixed contact to a second stationary state in which the movable contacts both contact the second fixed contact, and in a second switching direction there is switching over from a second stationary state in which the movable contacts both contact the second fixed contact to a first stationary state in which the movable contacts both contact the first fixed contact.

10. Method according to claim 9, wherein in the first switching direction - the second movable contact is separated from the first fixed contact and is contacted by the second fixed contact; thereafter a load current IL is switched over from a main branch to an auxiliary branch; - thereafter the first movable contact is separated from the first fixed contact and is contacted by the second fixed contact.

11. Method according to claim 9 or 10, wherein in the second switching direction - a load current IL is switched over from a main branch to an auxiliary branch; - thereafter the first movable contact is separated from the second fixed contact and is contacted by the first fixed contact; - thereafter the load current IL is switched over from the auxiliary branch to a main branch; - thereafter the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact.

12. Method according to claim 9 or 10, wherein in the second switching direction - the second movable contact is separated from the second fixed contact and is contacted by the first fixed contact; - thereafter a load current IL is switched from a main branch to an auxiliary branch; - thereafter the first movable contact is separated from the second fixed contact and is contacted by the first fixed contact.

13. Method according to any one of claims 6 to 12, wherein - in a step a the switching element is or remains closed and the second movable contact is separated from the first fixed contact and is contacted by the second fixed contact; - in a step b the switching element is opened and the first movable contact is thereby separated from the load diverter; - in a step c the first movable contact is separated from the first fixed contact and is contacted by the second fixed contact;

- in a step d the switching element is closed and thereby the first movable contact is connected with the load diverter.