EP3007193A1

EP3007193A1 - A tap-changer for oil-filled electric transformers

Info

Publication number: EP3007193A1
Application number: EP15188801.3A
Authority: EP
Inventors: Marco De Peron
Original assignee: ELETTROMAULE COMPONENT Srl
Current assignee: ELETTROMAULE COMPONENT Srl
Priority date: 2014-10-10
Filing date: 2015-10-07
Publication date: 2016-04-13
Anticipated expiration: 2035-10-07
Also published as: TR201908022T4; EP3007193B1; MA39739A

Abstract

A tap-changer for oil-filled electric transformers comprising: a guide element (2) provided with a plurality of electric contacts (3) and a slide (4) slidable along the guide element (2) to change the electric connection between two or more of the electric contacts (3); moving means (5) of the slide (4) comprising a driving group (6) having at least one rotatable portion (8) and defining a plurality of discrete positions of the slide (4) with respect to the guide element (2), each one corresponding to a different electric connection between the electric contacts (3). The moving means (5) comprising: a ring-nut (20) susceptible to be put in rotation by the driving group (6) and whose side surface has two or more flat surfaces (21); a core (23) counter-moved with the side surface of the ring-nut (20), the portion (24) of the core (23) faced towards the ring-nut (20) having a flat surface (25) susceptible to be arranged one-to-one with the flat surfaces (21) of the side surface of the ring-nut (20) when the slide (4) and the guide element (2) are placed in correspondence of one of the discrete positions.

Description

Field of invention

The present invention is generally applicable to the technical field of electric transformers and it particularly relates to a tap-changer for transformers.
More in detail, the present invention is particularly applicable to a tap-changer for oil-filled electric transformers.

Background of the Invention

In the field of electric transformers the use of high voltage tap-changer is known. The manufacturing of the latter is particularly delicate in case of transformers for high electric potentials because the high potentials involved may cause electric shocks between the poles of the tap-changers or in the tap-changer group in general. The case of the oil-filled transformers is one of these. They are applied to power lines crossed by high electric potentials.
The tap-changers used in transformers that operate with high electric potentials typically have a plurality of rods of electric contact, usually made of copper or of a copper alloy, aligned on a support shaft made of insulating material. Such a shaft is a guide for one or more slides whereon short-circuit contacts are assembled. The arrangement of such slides with respect to the guide leads to short-circuit different rods therebetween thus changing the ratios of electric transformation of the transformer.
The reciprocal movement between slides and guide is accomplished by means of a rack associated with the slides and whereon a toothed gear engages that is rotated by means of a moving group available to a user.
Typically, such moving group comprises a rotating pivot associated with the toothed gear and provided, at one end, with a knob available to the user who, by driving on it, puts in rotation the toothed gear that acts upon the rack creating a translational movement of the slides along the guide.
However, such a movement is continuous, while it is clear that the positions wherein the aforementioned short-circuit connections are accomplished are defined by the position of the rods and of the contacts on the slide. In other words, the positions of the slides with respect to the guide bar to ensure certain electric contacts between the rods are very specific and they do not correspond to a continuous movement between the two elements, but to a discrete movement from a contact position to another contact position. The intermediate positions are to be avoided not only because they may not power supply the desired parameters, but also because they may cause electric shocks between contacts and rods such as to be potentially dangerous.
For such reasons, according to the prior art regarding the axis thereof of the toothed gear there is a second star-shaped gear, that is substantially a star-shaped multi-tipped ring-nut where the tips have a rounded concave shape while the fitting between the tips is rounded convex.
Such a ring-nut is counter-placed with a ball pushed towards the ring-nut thereof by a spring. By rotating such a ring-nut, in correspondence to the tips of the star the ball is moved away thus compressing the spring, while in correspondence to the fittings the spring, while running down, pushes the ball to be inserted therein. In such operating instants the moving group reaches a stable position that corresponds to a contact position. By imparting a rotary movement to the knob, the star-shaped gear rotates until reaching the next stable position where the ball is inserted in the adjacent fitting towards the direction of rotation.
If such an embodiment allows to make the movements of the slides discrete with respect to the guide with reduced costs of implementation, however, it has as first drawback the difficulty of rotating the knob.
In fact, the rotation of the knob requires a considerable effort because it is necessary a sufficient torque to overcome the opposition to the compression of the spring that pushes the ball to penetrate in the fittings. Since such connections are rounded convex, it is clear that such a shape is not advantageous to such a movement.
A further drawback is that the described implementation does not allow to fully overcome the above mentioned drawbacks, that is the possibility that the slides stop in an intermediate position between two contact positions. The involved friction between the guide and the slides, the internal friction of the moving group, the effect of the decompression force of the spring that acts upon the ball together with the rounded shape of the tips of the star contribute, all together, to ensure that the rotation of the star-shaped gear thereof may be stopped in correspondence to one of its tips and it reaches, in such a position, a stable configuration although not being in correspondence to a contact point. Therefore, the above described risks and problems occur again if the operator does not pay attention to have caused a complete rotary movement of the moving group.

Summary of the invention

Object of the present invention is to at least partially overcome the above mentioned drawbacks by providing a tap-changer for oil-filled transformers whose tap-changing between a contact position and the next one does not require excessive effort.
Another object of the invention is to provide a tap-changer for oil-filled transformers that ensures the exclusive tap-changing between contact positions avoiding the risk that the tap-changer reaches unwanted intermediate positions.
A further object is to provide a tap-changer for oil-filled transformers that is automatically arranged in correspondence to one of the contact points even in case of an incomplete movement by the user.
Another object of the invention is to provide a tap-changer for oil-filled transformers that has costs almost equivalent to the equivalent known tap-changers.
Such objects, and others that will appear more clear hereinafter, are fulfilled by a tap-changer for oil-filled transformers according to the appended claims that are an integral part of the present patent.
In particular, the tap-changer comprises, as known, at least one guide element provided with a plurality of electric contacts and at least one slide sliding along the guide element to change the electric connection between two or more contacts. Furthermore, the tap-changer thereof comprises moving means of the slide along the guide element, in their turn comprising a driving group having at least one rotatable portion available to a user and at least one mechanical transmission to transform the rotation of the rotatable portion in a sliding movement of the slide along the guide element.
More in detail, the driving group defines a plurality of discrete positions of the slide with respect to the guide element, each one of them corresponds to a different electric connection between the electric contacts.
According to an aspect of the invention, this occurs for a particular configuration of the moving means.
In fact, they comprise at least one ring-nut susceptible to be put in rotation by the rotatable portion of the driving group and whose side surface has two or more flat surfaces. Moreover, they comprise at least one core associated with the driving group and counter-moved by first elastic means with the side surface of the ring-nut. Furthermore, the portion of the core faced towards the side surface of the ring-nut has a flat surface susceptible to be arranged one-to-one with the flat surfaces of the side surface of the ring-nut when the slide and the guide element are placed in correspondence to one of the discrete positions.
In other words, the rotary movement of the rotatable portion of the driving group, that is responsible for the translation of the slide on the guide element, is not continuous, but it is subjected to a discretization due to the contrast between the side surface of the ring-nut and the core moved thereto by the first elastic means. More in detail, during such a rotary movement, the ring-nut pushes back the core until there is a one-to-one contact between the flat surface of the core faced towards the ring-nut and one of the flat surfaces of the side surface of the ring-nut.
Such a configuration of one-to-one contact is advantageously particularly stable and it allows to block the rotation with the exception of the application of a high torque to the rotatable portion. Whereas, during the rotation the necessary torque is advantageously less than the starting one since the starting one shall push away the core from the flat surface of the ring-nut compressing the first elastic means, while during the rotation the elastic means promote the rotary motion in their expansive thrust until a new position of one-to-one contact is reached between the core and one flat surface of the side surface of the ring-nut.
However, advantageously, the torque to be given to leave a discrete position and to move to the next one is, nevertheless, less than what occurs in the prior art due to the different shape of the elements that are in contrast. In fact, it is evident that a coupling one-to-one between two elements pushed against one another by elastic means offers less resistance with respect to a coupling of at least partial interpenetration as that one of the prior art.
Nevertheless, still advantageously, the coupling one-to-one is absolutely stable and, therefore, it fully accomplishes its object.
According to another aspect of the invention, the flat surfaces are adjacent to each other and functionally arranged in series along at least one portion of the side surface of the ring-nut. Moreover, each flat surface is divided from the adjacent ones by a corner.
Advantageously, such a detail with the action of the first elastic means that promote the rotation of the ring-nut with respect to the core when they are not arranged in one-to-one contact, allow to avoid that the contact position between a corner and the flat surface of the core is a stable position. In this way, the danger that the tap-changer reaches an intermediate position between a position of electric contact and the next one is avoided.

Brief description of the drawings

Further features and advantages of the invention will appear more evident upon reading the detailed description of a preferred but not exclusive embodiment of a tap-changer for oil-filled transformers according to the invention, shown as non-limiting example with the help of the annexed drawings wherein:

FIG. 1 shows a tap-changer for oil-filled transformers in an axonometric view;
FIG. 2 shows a detail of the tap-changers of FIG. 1;
FIG. 3 shows a tap-changer according to the invention in partially exploded view;
FIG. 4 shows a detail of the tap-changer of FIG. 3.

Detailed description of some preferred embodiments

With reference to the above mentioned figures, and particularly to fig. 1, it is described a tap-changer 1 for oil-filled transformers. It is used to change the electric parameters of such a type of transformer and, therefore, it has dimensions and physical features such as to bear high electric values.
As may be seen in the figures, the tap-changer 1 comprises a guide element 2 provided with a plurality of electric contacts 3 and a slide 4 sliding along such a guide element 2. The movement of the slide 4 with respect to the guide element 2 allows to change the electric connection between two or more electric contacts 3.
Typically, the latter consist of copper rods, while the guide element 2 and the slide 4 are made of plastic or bakelite material, but such details should not be considered as limitative for different embodiments of the invention where the materials and the conformation of such components is different.
Moreover, the number of guide elements and of slides should not be considered as limitative for different embodiments since a tap-changer with more guide elements and / or more slides is, nevertheless, falling within the protective scope of the present patent.
According to an aspect of the invention, the tap-changer 1 further comprises moving means 5 of the slide 4 on the guide element 2 comprising a driving group 6. The latter has a rotatable portion 8 available to a user and a mechanical transmission 9 to transform the rotation of the rotatable portion 8 in a sliding movement of the slide 4 along the guide element 2.
In particular, the rotatable portion 8 comprises a knob 10 suitably shaped for the handle of the user, while the mechanical transmission consists of a rack 12 integral with the slide 4 and engaged by a toothed gear 14. The latter and the knob 10 are mechanically connected by a shaft 15 so as a rotary movement impressed on the knob 10 is transformed in a rotary movement of the toothed gear 14.
Obviously, even the described embodiments of the rotatable portion and of the mechanical transmission are features to be considered as non-limitative for the present invention.
As aforementioned, a mechanical transmission such as the one just described leads, in view of a continuous rotation of the knob 10, to a continuous movement of the slide 4 along the guide element 2. This is not acceptable since not only there is a risk to arrange the transformer in a configuration having electric parameters not in conformity to its use, but also because the voltages and the electric currents involved may have values such as to create sparks or electric shocks dangerous not only for the integrity of the transformer thereof, but also of what surrounds it.
For such a reason, according to another aspect of the invention, the driving group 6 is shaped so as to define a plurality of discrete positions of the slide 4 with respect to the guide element 2, each one corresponding to a different electric connection between the electric contacts 3.
To achieve such a technical effect, according to another aspect of the invention the moving means 5 comprise, as it is also observed in fig. 2, a ring-nut 20 that is put in rotation by the rotatable portion 8 of the driving group 6 and whose side surface has two or more flat surfaces 21.
In particular, in the embodiment that is described the ring-nut 20 has a side surface that, in cross section, has a polygonal shape, however, such a detail should not be considered as limitative for different embodiments of the invention where, for example, only a part of the side surface of the ring-nut has flat surfaces, while the remaining part has a curved profile.
The profile of the ring-nut 20 that is observed in the figures has the flat surfaces 21 adjacent to each other, functionally arranged in succession on at least one portion of the side surface and divided from one another by a corner, however, this should not be considered as limitative for the invention.
Besides the ring-nut 20, according to a further aspect of the invention the moving means 5 comprise a core 23 placed laterally to the ring-nut 20, associated with the driving group 6 and counter-moved with the side surface of the ring-nut 20 by first elastic means not shown in the figures and typically, but not necessarily, consisting of a spring.
In particular, the portion 24 of the core 23 faced towards the perimeter of the ring-nut 20 has a flat surface 25 susceptible to be arranged in one-to-one contact with one of the flat surfaces 21 of the side surface of the ring-nut 20 when the slide 4 and the guide element 2 are placed in correspondence to one of the discrete positions.
In the figures it is observed that the toothed gear 14 and the ring-nut 20 are integral with the shaft 15 put in rotation by the rotatable portion 8 of the driving group 6. Evidently, even such an aspect should not be considered as limitative for the invention. Advantageously, in any case, a rotary movement of the rotatable portion 8, that is responsible for the translation of the slide 4 along the guide element 2, is not continuous, but it is subjected to a discretization due to the contrast between the side surface of the ring-nut 20 and the core 23 moved thereto by the first elastic means.
Even more in detail, during such a rotary movement, the ring-nut 20 pushes back the core 23 until there is a one-to-one contact between the flat surface 25 of the core 23 and one of the flat surfaces 21 on the side surface of the ring-nut 20.
Such a configuration of one-to-one contact is advantageously stable and it allows to block the rotation with the exception of the application of a high torque to the rotatable portion 8. However, it goes against the rotation of the tap-changer 1 in a less emphasised manner with respect to what occurs in the prior art, thus making the tap-changer 1 thereof more manageable.
Whereas, during the rotation the necessary torque is advantageously lower than the starting one. Moreover, during the rotation the first elastic means promote the rotary movement in their expansive thrust until a new one-to-one contact position is reached between the core 23 and one flat surface 21 of the side surface of the ring-nut 20.
Previously, it has been said that the flat surfaces 21 are adjacent to each other and divided by a corner. Such a detail, together with the above mentioned action of the first elastic means, advantageously allows to avoid that the contact position between a corner and the flat surface 25 of the core 23 is a stable position. In this way, the danger that the tap-changer 1 reaches an intermediate position between a position of electric contact and the next one is avoided.
With regards to the implementation of the core 25, in the embodiment that is described it has a substantially parallelepiped body, but such a detail should not be considered as limitative for different embodiments of the invention wherein the core has different shapes. In fact, what is important is that it has a flat surface faced towards the side surface of the ring-nut.
According to another aspect of the invention, the knob 10 comprises, as shown in fig. 3 and in the detail of fig. 4, a first body 30 shaped for the handle of the user and integral with the shaft 15 in rotation. However, the first body 30 thereof is movable with respect to the shaft 15 along the longitudinal axis of the latter. Moreover, the knob 10 comprises a second body 31 stably coupled to the fixed body of the driving group 6 and susceptible to receive as abutment the first body 30.
In particular, the reciprocally facing portions of the first body 30 and of the second body 31 have projections and recesses susceptible to reciprocally interpenetrate when the first body 30 is arranged as abutment on the second body 31 so as a rotary movement imposed on the first body 30 is prevented.
Therefore, operationally, when it is necessary to vary the configuration of the tap-changer 1, the first body 30 is pushed away by the second body 31 so as it is free to integrally rotate with the shaft 15. This action is allowed by the freedom of axial movement of the first body 30 with respect to the shaft 15. Therefore, the rotation of the first body 30 causes the rotation of the toothed gear 14 and of the ring-nut 20. Once the rotation is finished, the first body 30 is arranged again in contact with the second body 31 so as to prevent further involuntary rotation thereof. Such an action is promoted by the presence of second elastic means, even typically but not necessarily consisting of a spring, susceptible to be compressed when the first body 30 is pushed away by the second body 31. Therefore, after the rotation, the release of the first body 30 allows the return to the rest position of the second elastic means that bring the first body 30 in contact with the second body 31.
Even more in detail about the embodiment shown in the figures, the projections and the recesses comprise a pivot 32 protruding from the first body 30 and faced towards the second body 31 and a plurality of recesses 33 on the surface 34 of the latter faced towards the first body 30. Obviously, such recesses 33 are suitably shaped so as to be at least partially penetrated by the protruding pivot 32.
According to an aspect of the invention, the recesses 33 have smoothed edges 35 towards the bottom of the recesses 33 thereof so as to accompany the penetrating pivot 32. Jointly, the latter has a sharp shape at least at the end 36 faced towards the second body 31.
Advantageously, this allows to increase the automatic positioning of the tap-changer 1 on one of the discrete positions even when the rotation imposed to the knob 10 is not finished. In fact, in this case, the action of the first elastic means on the core 23 with the shape of the perimeter of the ring-nut 20 that has flat surfaces 21 connected by corners, already allows to avoid, as aforementioned, the intermediate positions of the tap-changer 1 by accompanying the rotary movement of the moving means 5 until the closest discrete position. However, the particular shape of the protruding pivot 32 and the smoothed edges 35 of the recesses 33 allow to better accompany such a conclusion of the rotary movement that ensures the impossibility that the tap-changer 1 reaches an intermediate configuration.
Therefore, in light of the foregoing, it is understood that the tap-changer for oil-filled transformers of the invention fulfils all the intended objects.
In particular, its tap-changing between a contact position and the next one does not require excessive effort as, instead, occurs in the prior art.
Furthermore, the tap-changer thereof ensures the exclusive tap-changing between contact positions avoiding the risk of reaching unwanted intermediate positions. Such a disposition is automatic in case of incomplete movement by the user.
Moreover, the tap-changer thus manufactured has costs almost equivalent to the equivalent known tap-changers.
The tap-changer of the invention is susceptible of numerous modifications and variations, all falling within the inventive concept expressed in the appended claims. All the details may be replaced with other technically equivalent elements, and the materials may be different according to requirements, without departing from the scope of the invention.
Although the tap-changer of the invention has been described with particular reference to the annexed figures, reference numbers used in the description and in the claims are used to improve the intelligence of the invention and are not limitative for the claimed object.

Claims

A tap-changer for oil-filled electric transformers comprising:
- at least one guide element (2) provided with a plurality of electric contacts (3) and at least one slide (4) slidable along said guide element (2) to change the electric connection between two or more of said electric contacts (3);

- moving means (5) of said slide (4) along said guide element (2) comprising a driving group (6) having at least one rotatable portion (8) available to a user and at least one mechanical transmission (9) to transform the rotation of said rotatable portion (8) in a sliding movement of said slide (4) along said guide element (2), said driving group (6) defining a plurality of discrete positions of said slide (4) with respect to said guide element (2), each one of said discrete positions corresponding to a different electric connection between said electric contacts (3),
said moving means (5) comprising:
- at least one ring-nut (20) susceptible to be put in rotation by said rotatable portion (8) of said driving group (6) and whose side surface has two or more flat surfaces (21);

- at least one core (23) associated with said driving group (6) and counter-moved with said side surface of said ring-nut (20) by first elastic means, the portion (24) of said core (23) faced towards said side surface of said ring-nut (20) having a flat surface (25) susceptible to be arranged one-to-one with the flat surfaces (21) of said side surface of said ring-nut (20) when said slide (4) and said guide element (2) are in correspondence to one of said discrete positions.
Tap-changer according to claim 1, wherein said flat surfaces (21) of said ring-nut (20) are adjacent to each other, functionally arranged in succession on at least one portion of said side surface and divided from one another by a corner.
Tap-changer according to claim 1 or 2, wherein said side surface of said ring-nut (20) has, in cross section, a polygonal shape.
Tap-changer according to one or more of the preceding claims, wherein said core (23) has a substantially parallelepiped body.
Tap-changer according to one or more of the preceding claims, wherein said driving group (6) comprises a knob (10) available to the user and associated with a shaft (15) integral with said ring-nut (20).
Tap-changer according to claim 5, wherein said knob (10) comprises a first shaped body (30) for the handle of the user, integral with said shaft (15) in rotation and movable with respect to said shaft (15) along the longitudinal axis of said shaft (15), and a second body (31) integral with said driving group (6) and susceptible to receive as abutment said first body (30), the reciprocally facing portions of said first and second body (30, 31) having projections and recesses suitable to reciprocally interpenetrate when said first body (30) is arranged as abutment on said second body (31) so as said second body (31) prevents rotary movements of said first body (30).
Tap-changer according to claim 6, comprising second elastic means susceptible to be compressed when said first body (30) is moved away from said second body (31).
Tap-changer according to claim 6 or 7, wherein said first body (30) comprises a pivot (32) protruding towards said second body (31) and said second body (31) comprises a plurality of recesses (33) on its surface (34) faced towards said first body (30) and shaped so as to be at least partially penetrated by said protruding pivot (32).
Tap-changer according to claim 8, wherein said recesses (33) have edges (35) smoothed towards the bottom of said recesses (33) so as to guide said pivot (32) in penetration into said recesses (33) when said pivot (32) comes in contrast with said edges (35).
Tap-changer according to claim 8 or 9, wherein said pivot (32) has a sharp shape at least at the end (36) faced towards said second body (31) of said knob (10).