EP4651165A1

EP4651165A1 - Static contact unit, contact system and tap changer

Info

Publication number: EP4651165A1
Application number: EP24175759.0A
Authority: EP
Inventors: Borislav VASILEV; Veselin NIKOLOV; Georgi MANEV; Georgi Dimitrov
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2024-05-14
Filing date: 2024-05-14
Publication date: 2025-11-19
Also published as: WO2025237684A1

Abstract

A static contact unit (20) for a tap changer comprises a contact body (4), a pair of contact elements (5) and a spring element (6). The contact body (4) is configured to be arranged statically with respect to a movable contact (3) that is arranged at a moving shaft (1) of the tap changer. The two contact elements (5) are coupled to the contact body (4) configured to establish an electrical contact to the movable contact (3) of the moving shaft (1). The spring element (6) is coupled to both contact elements (5) inbetween with respect to a longitudinal axis (L1) of the moving shaft (1) configured to bias the contact elements (5) so that, with respect to a state in which the tap changer is assembled, the contact elements (5) are biased simultaneously in direction towards each other in sections at least.

Description

The present disclosure is related to a static contact unit, a contact system and a tap changer.
Tap changers realize a mechanism in transformers which allows for variable turn ratios to be selected in distinct steps, for example. In view of movable and stationary electrically engaging contacts it is a challenge to provide a stable and reliable mechanism.
Thus, it is an objective to provide a static contact unit for a tap changer, a contact system for a tap changer and a tap changer that each allows for a stable and reliable mechanism of electrically engaging movable and stationary contacts.
According to an embodiment, a static contact unit for a tap changer comprises a contact body that is configured to be arranged statically with respect to a movable contact that is arranged at a moving shaft of the tap changer. The static contact unit further comprises two contact elements that are coupled to the contact body configured to establish an electrical contact to the movable contact of the moving shaft. The static contact unit further comprises a spring element that is coupled to both contact elements inbetween with respect to a longitudinal axis of the moving shaft configured to bias the contact elements so that, with respect to a state in which the tap changer is assembled, the contact elements are biased or pre-loaded simultaneously in direction towards each other in sections for making electrical contact at least.
By use of the described static contact unit a secure and reliable mechanism of electrically engaging movable and stationary contacts is feasible. The respective static contact unit can form an upper, lower or middle electrical static contact of a contact system realizing a pre-selector of an on-load tap changer. The aforementioned moving shaft and the one or more movable contacts realize components of such a pre-selector interacting with the one or more static contact units. Accordingly, the components of the static contact unit and the components of the pre-selector are configured preferably in coordination with each other.
According to an embodiment, the spring element is formed as a cylindrical coil torsion spring and comprises two spring arms at opposite ends which are coupled to a respective associated contact element. Each spring arm can comprise a respective hook at its end which is in contact with an associated outer surface of the respective contact element pulling or pushing the respective contact element towards the other one. Regardless of whether it is referred to as pulling or pushing, the spring force acts in the direction towards each other so that a reliable electrical contact with the movable contact can be established.
According to a further embodiment, the respective contact element comprises a spring arm recess at an outer surface configured in coordination with the associated spring arm or spring hook of the spring element so that the end portion of the respective spring arm is arranged inside the spring arm recess of the associated contact element. Due to such a configuration, the spring can be securely attached to the contact elements and is not bulky so that the outer surface of the contact elements is nearly flat.
According to a further embodiment, the contact body and/or the contact elements comprises one or more guiding and/or limiting elements which are configured to guide and/or limit a movement of the contact elements relative to the contact body. For example, the contact body can comprise two limiters one forming a front wall element and the other one forming a back wall element with respect a longitudinal axis of the contact unit. With respect to a state in which the tap changer is assembled, the front wall element is arranged closer to the moving shaft than the back wall element.
According to a further embodiment, the static contact unit comprises an axle configured to support the spring element, wherein the axle extends through the spring element and an axle recess of the contact body and is fixed to the contact body by a retaining element. In this way, a clear and space-saving design can be realized in which the interacting components are arranged particularly securely and work together reliably. The axle supports the spring element and holds it in a given axial position. Preferably, the axle is arranged closer to the aforementioned back wall element than to the front wall element. Such a configuration can contribute to a beneficial stability and force effect of the spring element and the contact elements.
According to a further embodiment of the static contact unit, the contact elements each comprise a front side contact and a rear side contact with respect a longitudinal axis of the contact unit so that, with respect to a state in which the tap changer is assembled, the respective rear side contact is in contact with the contact body and the front side contact is configured to establish a respective electrical contact to a contact element of the movable contact of the moving shaft. The contact elements can realize parallel contact plates that are statically coupled to the contact body. Each parallel contact element extends in a direction towards the moving shaft to establish a respective electrical contact to a contact surface of the movable contact of the moving shaft when the tap changer is assembled. The contact elements are designed to establish the operational contact and set up electrical switching.
According to a further embodiment, the static contact unit comprises four contact elements that are coupled to the contact body configured to establish an electrical contact to the movable contact of the moving shaft, and two spring elements that are coupled to a respective pair of two contact elements inbetween, preferably above each other supported by an axle. The spring elements are both configured to bias the associated contact elements so that, with respect to a state in which the tap changer is assembled, the respective pair of contact elements are biased or pre-loaded simultaneously in direction towards each other in sections at least.
According to an embodiment, a contact system for a tap changer comprises a linear moving shaft elongated predominantly along a longitudinal axis, and a knife contact unit that is configured axially movable along a longitudinal axis of the moving shaft. The contact system further comprises one or more embodiments of the static contact units described above, which are arranged statically relative to the knife contact unit in view of the contact body at least.
In particular, the contact system can realize a pre-selector of a tap changer and enables secure and reliable electrical switching. The contact system can be implemented in an on-load tap changer with a space-saving design due to the static contact units, in particular in combination with cylindrical coil torsion spring elements. As a result of that the contact comprises an embodiment of the static contact unit as described above, features and characteristics of the static contact unit are also disclosed with respect to the contact system and vice versa.
According to an embodiment, the contact system comprises three static contact units according to an embodiment as described above. A first static contact unit is configured to form an upper or positive contact, a second static contact unit is configured to form a lower or negative contact, and a third static contact unit is configured to form a middle or ground contact between the first and the second contact with respect to the longitudinal axis of the moving shaft. The knife contact unit comprises a plurality of movable contacts coupled to the moving shaft configured to establish electrical contact to one or more of the static contact units for electrical switching. Such a configuration of the static contact units and the contact system allows for a beneficial structure of a pre-selector that can securely and reliably enable electrical switching.
According to a further embodiment of the contact system, the knife contact unit comprises at least one movable contact with two contact wing elements, wherein the two wing elements forming a funnel-shaped movable contact and are geometrically formed in coordination with the contact elements of the static contact units. When an electrical contact is established, the associated wing element is arranged between and in contact with both contact elements of the respective contact unit. Due to such a configuration a very reliable and secure electrical contact between the static contact unit and the movable contact can be established for electrical switching. The contact elements of the respective contact units and the wing elements of the movable knife contact unit can comprise edges and/or corners with a chamfer or rounding configured to establish a respective secure electrical contact. Such a configuration enables low-resistance, low-wear contacting.
According to an embodiment, a tap changer comprises an embodiment of the contact system described above forming a pre-selector of the tap changer, and a selector with one or more contact devices for electrical switching coupled to the pre-selector. As a result of that the tap changer comprises an embodiment of the contact system and the static contact unit as described above, features and characteristics of the contact system and/or the static contact unit are also disclosed with respect to the tap changer and vice versa.
The described embodiments for the static contact unit, the contact system and the tap changer each allow for a compact electrical contact design providing contact force in an electrical contact pair by means of a spring element, preferably realized as a cylindrical coil torsion spring.
It is a recognition of the present disclosure that usual designs for a pre-selector for an on-load tap changer are based on complex set ups to provide contact force to a contact element. Such conventional configurations require more space to be situated in a contact system and may cause a larger distance between contact elements, which unwanted because of the larger unfavorable electrodynamic forces in the system.
The described static contact unit enables to counteract such unwanted effects. The static contact unit allows for a compact electrical contact system with tension and compression spring elements. It beneficially enables to keep required insolation distances and it needs little space in a corresponding transformer tank assembly and contributes to less production and assembling time and reduced costs.
A simple cylindrical coil spring element can provide a desired contact force in an electrical contact pair with preferably one or more of the following characteristics:

a cylindrical coil torsion spring element is mounted between the electrical contact pair as each of the two spring arms of the spring element simultaneously presses the corresponding contact element of the contact pair by means of a tail or hook formed at the end of each arm, transmitting the spring force to the associated contact element;
at least one electrical contact pair is mounted in a static contact holder forming the contact body, wherein a respective back stationary side of said contact pair conducts the current through the contact holder;
the cylindrical coil torsion spring element is kept in the correct position by means of a supporting fixed axis or axle, passing inside the coils of the spring element;
a movable knife contact element conducts the current between the front sides of the contact pairs like a contact bridge.

Exemplary embodiments are explained in the following with the aid of schematic drawings and reference numbers. The figures show:

Figures 1-3 an embodiment of a pre-selector for a tap changer in different views, and
Figures 4-5 an embodiment of a static contact unit for the pre-selector according to the figures 1 to 3 in perspective views.

The accompanying figures are included to provide a further understanding. Identical reference numbers designate elements or components with identical functions. In so far as elements or components correspond to one another in terms of their function in different figures, the description thereof is not repeated for each of the following figures. For the sake of clarity elements might not appear with corresponding reference symbols in all figures, possibly.
Figures 1 to 3 illustrate an embodiment of a contact system 30 realizing a pre-selector for a tap changer in different views. Figure 1 shows a perspective view. Figure 2 shows a side view with partial cross section. Figure 3 shows a top or bottom view along a longitudinal axis L1.
The contact system 30 comprises three static contact units 20 (see also Figs. 4 to 5). The contact system 30 comprises a linear moving shaft 1 elongated predominantly along a longitudinal axis L1 and a knife contact unit 2 that is configured axially movable along the longitudinal axis L1 of the moving shaft 1. The three static contact units 20 are arranged above each other and statically relative to the knife contact unit 2.
A first static contact unit 21 is configured to form an upper contact unit, a second static contact unit 22 is configured to form a lower contact unit, and a third static contact unit 23 is configured to form a middle contact unit between the first and the second contact unit 21, 22 with respect to the longitudinal axis L1 of the moving shaft 1 (see Fig. 2). The first contact unit 21 can realize a contact with positive potential, the second contact unit 22 a contact with negative potential and the third contact unit 23 can form a ground contact with zero potential.
The static contact units 21, 22, 23 each comprise four contact elements 5 forming two respective parallel contact pairs above each other with respect to the longitudinal axis L1. The contact elements 5 each are coupled to an associated contact body 4 of the corresponding static contact unit 20 configured to establish an electrical contact to a respective cam or movable contact 3 of a knife contact unit 2 arranged at the moving shaft 1.
The knife contact unit 2 comprises a movable contact 3 with two contact wing elements 11. The wing elements 11 comprise a respective inner and outer contact surfaces configured to make electrical contact to front portions of the contact elements 5 of the respective static contact unit 20 (see Fig. 3). The wing elements 11 form a funnel-shaped contact element 3 that is geometrically formed in coordination with parallel contact elements 5 of the static contact units 20.
The figures 4 and 5 show in a perspective illustration a respective disassembled view of the static contact unit 20. The figures 4 and 5 are equal with respect to their illustration but comprise different reference signs in part for sake of clarity.
The respective contact unit 20 further comprise two spring elements 6 formed as cylindrical coil tension springs which are coupled to an associated pair of contact elements 5 inbetween. The spring elements 6 are configured to bias the contact elements 5 so that the contact elements 5 are pre-loaded simultaneously in direction towards each other at the front portion at least to establish an electrical contact securely and reliably with an associated wing element 11 of the movable contact 3 (see Fig. 3). Each spring element 6 comprises two spring arms 7 at opposite ends which are coupled to a respective associated contact element 5. Each spring arm 7 comprises a spring hook 8 at its end which are in contact with an outer surface 19 of the respective associated contact element 5 pulling or pushing the respective contact element 5 towards the other one.
The contact body 4 can be formed from one-piece and may comprise a cross-shape with two levels for the two pair of contact elements 5. The contact body 4 comprises four guidance channels 18 for the four contact elements 5 (see Fig. 5). The contact body 4 further comprises limiting element which are configured to limit and/or guide a movement of the contact elements 5 relative to the contact body 4. With respect to a longitudinal axis L2 of the static contact unit 20 (see Fig. 3), the contact body 4 comprises a front wall element 9, a back wall element 10 and a limiter recess 16 acting as limiting and/or support or guiding elements. The front wall element 9 is arranged closer to the moving shaft 1 than the back wall element 10.
The contact elements 5 comprise a respective limiter 15 arranged inside the limiter recess 16 of the contact body 4. The front wall element 9 limits a movement of the contact element 5 in direction towards the moving shaft 1. The back wall element 10 limits a movement of the spring element 6 in direction away from the moving shaft 1.
The static contact unit 20 further comprises an axle 12 which supports the spring elements 6. The axle 12 extends through the spring elements and through an axle recess 17 of the contact body 4 (see Fig. 4). The axle 12 is fixed to the contact body 4 by retaining rings 13 arranged at opposite sides of the contact body 4 in a respective ring recess 14. For reasons of stability and force effect, the axle 12 is preferably arranged closer to the back wall element 10 than to the front wall element 9 (see Fig. 3).
The contact elements 5 each comprise a front side contact and a rear side contact with respect the longitudinal axis L2 of the contact unit 20 so that the respective rear side contact is in contact with the contact body 4 and the front side contact is configured to establish a respective electrical contact to the associated wing element 11 of the movable contact 3 of the moving shaft 1.
The described contact system 30 can realize a compact electrical contact system for an on-load tap changer with the three static contacts (e.g. +, 0, -) situated in vertical direction. The knife contact element unit 2 forms a contact bridge in a current-carrying chain, which is fixed to the movable or moving shaft 1. The moving shaft 1 can be moved along the longitudinal axis L1 in vertical direction from (+) to (-) position and back. The first, second and third static contact units 21-23 are mounted and situated in vertical direction. Alternatively, the design can be arranged horizontally as well.
Respective two pairs of parallel contact elements 5 are mounted in the guiding channels 18 in every static contact unit 20 and create a contact bridge between the contact bodies 4 and contact surfaces of the wing elements 11 on the movable knife contact 3. The respective limiter 15 can be formed in the middle of each of the contact elements 5 and is configured to prevent their movement in front direction to the front wall 9 of each contact body 4. The movement in back direction is prevented by the back wall 10 situated of the back side on the contact holders 4.
A respective cylindrical coil torsion spring element 6 is mounted between the parallel electrical contact pair 5. Each of the two arms 7 of the spring element 6 simultaneously presses the corresponding contact element 5 of the contact pair by means of its corresponding tail or hook 8 formed at the end of the spring arms 7. Hence, a contact force is transmitted from the spring arms 7 to the parallel contact elements 5. The hooks 8 of the spring arms 7 are situated on this way that is reduced the sliding between the hooks 8 and the parallel contact elements 5. Additionally, the outer surface 19 of the respective contact element 5 can comprise a groove or slot to avoid an unwanted sliding of the hook 8.
The supporting axle 12 passes inside the respective coils of the spring elements 6 and is fixed to the contact body 4 by means of the two retaining ring elements 13 which keep the spring elements 6 in the correct position. The two arms 7 of the corresponding spring element 6 are rotating around the supporting axle 12 during connecting and disconnecting of the pair of parallel contact elements 5 to the knife contact element 3. Preferably, in view of operation of the parallel contact elements 5 and to reduce sliding between the hooks 8 of the spring arms 7 and the parallel contact elements 5, the supporting axle 12 is situated closer to the back stationary contact points at the back wall 14 than to the front wall 9.
Alternatively, the axle 12 can be arranged in a middle between the front wall 9 and the back wall 10 or closer to the front wall 9 than to the back wall 10. Furthermore, the hook 8 is arranged in a middle of the outer surface 19 of the respective contact element 5 but can alternatively arranged closer to a back end in direction to the back wall 10 along the longitudinal axis L2 or closer to a front end in direction to the front wall 9 along the longitudinal axis L2. Such a modification can be considered by forming the spring arms 7 shorter or longer, respectively and depending on specifications regarding stability and force effect, for example.
The described embodiments of the static contact units 20-23 and the contact system 30 each allow for a smaller distance between the pair of contact elements 5, in particular at the same level, thus beneficially affecting electrodynamic forces. In addition, the torsion springs elements 6 are located inside the contact unit 20 and there are no protruding springs or parts at the outside, which leads to a better distribution of the electromagnetic field and allows reducing the dielectric distances and reducing the dimensions of the static contact unit 20. The torsion spring elements 6 can be advantageously formed symmetric and provide a relatively constant spring force over their operating range and allow for uniform contact force under geometric and manufacturing deviations.
The embodiments shown in the figures 1 to 9 as stated represent exemplary embodiments of improved static contact units 20, an improved contact system 30 and a corresponding tap changer; therefore, they do not constitute a complete list of all embodiments according to possible arrangements. Actual arrangements of the static contact unit 20, contact system 30 and/or the tap changer may vary from the embodiments shown in the figures.

Reference Signs

1: moving shaft
2: knife contact unit
3: movable contact / cam of the knife contact unit
4: contact body
5: contact element
6: spring element
7: spring arm
8: spring hook
9: front wall element
10: back wall element
11: wing element of the movable contact
12: axle
13: retaining ring
14: ring recess
15: limiter
16: limiter recess
17: axle recess
18: guiding channel
19: outer surface of the contact element
20: static contact unit
21: first, upper static contact unit
22: second, lower static contact unit
23: third, middle static contact unit
30: contact system / pre-selector

L1: longitudinal axis of the moving shaft / axle axis
L2: longitudinal axis of the contact unit

Claims

Static contact unit (20) for a tap changer, comprising:
- a contact body (4) that is configured to be arranged statically with respect to a movable contact (3) that is arranged at a moving shaft (1) of the tap changer,

- two contact elements (5) that are coupled to the contact body (4) configured to establish an electrical contact to the movable contact (3) of the moving shaft (1), and

- a spring element (6) that is coupled to both contact elements (5) inbetween with respect to a longitudinal axis (L1) of the moving shaft (1) configured to bias the contact elements (5) so that, with respect to a state in which the tap changer is assembled, the contact elements (5) are biased simultaneously in direction towards each other in sections at least.
Static contact unit (20) according to claim 1, wherein the spring element (6) is formed as a cylindrical coil torsion spring and comprises two spring arms (7) at opposite ends which are coupled to a respective associated contact element (5).
Static contact unit (20) according to claim 2, wherein each spring arm (7) comprises a spring hook (8) at its end which are in contact with an outer surface (19) of the respective associated contact element (5) pulling or pushing the respective contact element (5) towards the other one.
Static contact unit (20) according to claim 2 or 3, wherein the respective contact element (5) comprises a spring arm recess at an outer surface (19) configured in coordination with the associated spring arm (7) of the spring element (6) so that the end portion of the respective spring arm (7) is arranged inside the spring arm recess of the associated contact element (5).
Static contact unit (20) according to any of the preceding claims, wherein the contact body (4) and/or the contact elements (5) comprises one or more limiting elements (9, 10, 15, 16) which are configured to limit a movement of the contact elements (5) relative to the contact body (4).
Static contact unit (20) according to claim 5, wherein the contact body (4) comprises two limiters one forming a front wall element (9) and the other one forming a back wall element (10) with respect a longitudinal axis (L2) of the contact unit (20) so that, with respect to a state in which the tap changer is assembled, the front wall element (9) is arranged closer to the moving shaft (1) than the back wall element (10).
Static contact unit (20) according to any of the preceding claims, comprising:
an axle (12) configured to support the spring element (6), wherein the axle (12) extends through the spring element (6) and an axle recess (17) of the contact body (4) and is fixed to the contact body (4) by a retaining element (13).
Static contact unit (20) according to claim 7 in conjunction with claim 6, wherein the axle (12) is arranged closer to the back wall element (10) than to the front wall element (9).
Static contact unit (20) according to any of the preceding claims, wherein the contact elements (5) each comprise a front side contact and a rear side contact with respect a longitudinal axis (L2) of the contact unit (20) so that, with respect to a state in which the tap changer is assembled, the respective rear side contact is in contact with the contact body (4) and the front side contact is configured to establish a respective electrical contact to a contact element (11) of the movable contact (3) of the moving shaft (1).
Static contact unit (20) according to any of the preceding claims, comprising:
- four contact elements (5) that are coupled to the contact body (4) configured to establish an electrical contact to the movable contact (3) of the moving shaft (1), and

- two spring elements (6) that are coupled to a respective pair of two contact elements (5) inbetween with respect to a longitudinal axis (L1) of the moving shaft (1) configured to bias the associated contact elements (5) so that, with respect to a state in which the tap changer is assembled, the respective pair of contact elements (5) are biased simultaneously in direction towards each other in sections at least.
Contact system (30) for a tap changer, comprising:
- a linear moving shaft (1) elongated predominantly along a longitudinal axis (L),

- a knife contact unit (2) that is configured axially movable along a longitudinal axis (L) of the moving shaft (1), and

- one or more static contact units (20) according to any of the preceding claims, which are arranged statically relative to the knife contact unit (2).
Contact system (30) according to claim 11, comprising:
three static contact units (20), wherein a first static contact unit (21) is configured to form an upper contact unit, a second static contact unit (22) is configured to form a lower contact unit, and a third static contact unit (23) is configured to form a middle contact unit between the first and the second contact unit (21, 22) with respect to the longitudinal axis (L) of the moving shaft (1), and

wherein the knife contact unit (2) comprises a plurality of movable contacts (3) coupled to the moving shaft (1) configured to establish electrical contact to one or more of the static contact units (20) for electrical switching.
Contact system (30) according to claim 11 or 12, wherein the knife contact unit (2) comprises at least one movable contact (3) with two contact wing elements (11) forming a funnel-shaped movable contact (3), wherein the wing elements (11) are geometrically formed in coordination with a respective pair of contact elements (5) of the static contact units (20) so that, when an electrical contact is established, the associated wing element (11) is in contact with both contact elements (5) between them.
A tap changer, comprising:
- a contact system (30) according to any of the claims 11 to 13 forming a pre-selector of the tap changer, and

- a selector with one or more contact devices for electrical switching coupled to the pre-selector.