EP4664501A1

EP4664501A1 - Contact system for an on-load tap changer and on-load tap changer

Info

Publication number: EP4664501A1
Application number: EP24182240.2A
Authority: EP
Inventors: Georgi MANEV; Borislav VASILEV; Veselin NIKOLOV
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2024-06-14
Filing date: 2024-06-14
Publication date: 2025-12-17
Also published as: WO2025256881A1

Abstract

A contact system (1) for a tap changer comprises a first and a second fixed contact unit (20) each with at least one fixed electrical contact element (24), and a movable contact unit with at least one movable electrical contact element (10). The moveable contact unit comprises a two-level driving contact with contact portions (11, 12) which are arranged offset to each other with respect to a rotation axis (R2) of the moveable contact element (10). The contact system (1) further comprises a driving unit (3) to rotationally drive the movable contact element (10) towards the respective fixed contact element (24) of the associated fixed contact unit (20). The driving unit (3) comprises a two-level driving contact with protrusions (6, 7) which are arranged offset to each other with respect to a rotation axis (R1) of the driving unit (3). The movable contact unit and the driving unit (3) are configured so that a first state, in which the movable contact element (10) is in electrical contact with the contact element (24) of the first fixed contact unit (20), and a second state, in which the moveable contact element (10) is in electrical contact with the contact element (24) of the second fixed contact unit (20), are settable.

Description

The present disclosure is related to a contact system for an tap changer and a corresponding 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 with low wear and friction.
Thus, it is an object to provide a contact system for a tap changer that allows for a stable and reliable mechanism and contributes to low wear of interacting components.
According to an embodiment, a contact system for a tap changer, e.g. an on-load tap changer, comprises a first and a second fixed or stationary contact unit each with at least one fixed electrical contact element. The contact system further comprises a movable contact unit with at least one movable electrical contact element that is configured to make electric connection to the respective contact element of the associated fixed contact unit. The moveable contact unit comprises a two-level driving contact with contact portions which are arranged offset to each other with respect to a rotation axis of the moveable contact element. The contact system further comprises a driving unit that is configured to rotationally drive the movable contact element bidirectionally around the rotation axis of the moveable contact element towards the respective fixed contact element of the associated fixed contact unit. The driving unit also comprises a two-level driving contact with protrusions which are arranged offset to each other with respect to a rotation axis of the driving unit. The movable contact unit and the driving unit are configured in coordination with each other so that a respective protrusion is temporarily in contact with the associated contact portion to drive the movable contact element so that a first state and a second state can be set or adjusted. In the first state, the movable contact element is in electrical contact with the contact element of the first fixed contact unit. In the second state, the moveable contact element is in electrical contact with the contact element of the second fixed contact unit.
By use of the described contact system an electric connection mechanism for a tap changer is feasible that allows for a stable and reliable functioning and that contributes to low wear and low friction of interacting components and less precision requirements. The contact system enables fast motion for a tap changer acting independently of the positioning of a driving shaft of the driving unit. Such a motion resistor contact system is applicable for a vacuum-type on-load tap changer (OLTC), and can be controlled by a two-level cam and independent of an end positions of a driving shaft of the driving unit.
According to an embodiment of the contact system, the moveable contact element is formed with ramifications comprising a first and a second arm realizing the contact portions of the two-level driving contact of the moveable contact unit. The driving unit comprises a cam or control disc element with a first and a second protrusion realizing the two-level driving contact of the driving unit. The arms and the protrusions are configured in coordination with each other so that the first protrusion is temporarily in contact with the first arm and the second protrusion is temporarily in contact with the second arm to respectively drive the movable contact element and to set the first state or the second state of the contact system. Preferably, the control disc element and the first and second protrusions are formed integrally in one piece. Alternatively or additionally, the moveable contact element and the first and second arms are formed integrally in one piece.
According to a further embodiment of the contact system, the respective protrusion of the driving unit comprises a circumferentially tapering shape along a circular path around the rotation axis of the driving unit so that the respective protrusions each have a wider section and a narrower section. The respective wider sections are preferably facing each other circumferentially in relation to a top view of the control disc element, for example. The respective wider section is configured to contact the associated contact portion for driving the movable element so that the first state and the second state of the contact system are settable independent of a rotational end position of the driving unit.
According to a further embodiment of the contact system, the respective contact elements of the fixed contact units each comprise a chamfered or wedge-shaped contact section.
According to a further embodiment of the contact system, the movable contact element comprises a rod-shaped electrical contact portion with rounded contact tips at opposite ends of the rod-shaped contact portion. Preferably, the moveable contact element and the electrical contact portion are formed integrally in one piece. Preferably, the electrical contact portion comprises buffer protrusions at opposite sides which are configured in coordination with buffer elements of the fixed contact units to set a rotational end position of the movable contact element.
According to a further embodiment of the contact system, the fixed contact units each comprise two or more contact elements formed spaced apart from each other with a given distance in between that is formed in coordination with a thickness of a contact portion of the moveable contact element. Alternatively, the moveable contact unit and the fixed contact units can be configured in reverse so that the moveable contact unit comprises two or more contact elements formed spaced apart from each other with a given distance in between that is formed in coordination with a thickness of a contact portion of the respective fixed contact unit.
According to a further embodiment of the contact system, the fixed contact units each comprise two pivotable contact elements with respective contact sections which are configured to make electrical contact to the movable contact element in the first or the second state. The fixed contact units each further comprise a spring element that is arranged between and coupled to the respective contact arms so that the contact arms are pretensioned and the associated contact sections are pressed towards each other. Alternatively, the moveable contact unit and the fixed contact units can be configured in reverse so that the movable contact unit comprises two pivotable contact elements with respective contact sections which are configured to make electrical contact to a contact portion of the respective fixed contact unit in the first or the second state.
According to a further embodiment of the contact system, the contact portions of the movable element each comprise a rotatable roller element that is configured to get in contact with the associated protrusion of the driving unit when the movable contact element is to be rotated.
According to a further embodiment of the contact system, the protrusions of the driving unknit each comprise a curved contact surface facing and configured to get in contact with the associated contact portion of the movable contact unit when the movable contact element is to be rotated.
According to a further embodiment of the contact system, the protrusions of the driving unit are formed at a given radial distance from the rotation axis of the driving unit. The contact portions of the movable contact element are arranged in coordination with the radial distance of the associated protrusion so that, when the interacting contact portion and protrusion are free of contact and the driving unit rotates, the protrusion is moved towards the contact portion, contacts the contact portion and drives the moveable element towards one of the fixed contact units.
According to an embodiment, a tap changer, e.g. an on-load tap changer, for setting a gear ratio comprises an embodiment of the described contact system and a driving shaft that forms a drive for the contact system. The driving unit of the contact system is coupled to the shaft. As a result of that the tap changer comprises an embodiment of the contact system as described above, features and characteristics of the contact system are also disclosed with respect to the tap changer and vice versa.
It is a recognition of the present disclosure that some designs for contact concepts or switching schemes with diverter switches with vacuum interrupters include an acting main and resistor contact system. The main contact system is usually actuated in a middle of a stroke of a symmetrically rotating main shaft. The resistor contact system can be actuated at both ends of a set angle of rotation of the shaft. Such a set up requires a plurality of additional drive parts and it is difficult to perform or assemble. In particular, such a set up includes the adverse effect that a driving surface of the driving element mounted on the main shaft after pushing a driven contact continues its movement together with it until a final position of the shaft is reached. This means that a desired switching angle of a rotating contact of the resistor contact concept must be consistent with the angle at which the main shaft completes its movement. This is very difficult to design. At a greater difference between these angles, an additional idle travel has to be set after the desired point of engagement of the single contact with the fixed grip-shaped contacts. Such idling is undesirable due to an additional movement and friction in already closed pinch contacts and the need to provide greater insulation distances in the diverter switch.
By use of the described contact system, it is possible to counteract the aforementioned difficulties due to the specific set up of the movable contact unit and the fixed contact units and the implementation of the two-level driving contacts which are arranged offset vertically. Accordingly, the contact portions and the protrusions can also be referred to as upper and lower contact portion or protrusion, respectively. The contact system is feasible with a clear, compact and simple design of a rotatable fast-motion resistor contact system which acts near an end of the stroke of a main driving shaft, performing a switching operation. Due to the specific design, a single rotating contact can be driven by control surfaces located on the respective two-level driving contact of a specially profiled cam or control disc element and the one of the moveable contact unit, one for each of the two directions of rotation. The control disc element is mounted on the main driving shaft, which after performing the switching operation continues its movement as long as necessary until its final position is reached. In addition, the cam profile provides locking of the contact in the desired position when final position of the shaft is reached. When the shaft starts to perform the next switching operation and subsequently rotates in the opposite direction, the described operations are performed by corresponding control surfaces located at the other level of the control disc element.
The described configurations of the contact system and the corresponding tap changer each enable a simple fast motion contact system with acting independently of the positioning of the driving shaft. The contact system and the tap changer enable or provide at least some of the following features and/or advantageous:

1. The fast-acting resistor contact system comprises a rotating passive contact which, at both ends of its stroke, engages with corresponding fixed pairs of grip-shaped contacts. The movable contact element thus described is driven by a drive cam rotating symmetrically back and forth in two directions. This cam can form the control disc element and is positioned on a central main shaft of the diverter switch and has specially profiled control surfaces form the protrusions which are mirror-imaged but on two levels above each other. At a set angle, in its movement, each of these surfaces meets a roller element located at the same level of the rotating contact, causing it to move. As the contact rotates and reaches its operating position, the other roller element comes to rest in the operating area of the other operating surface of the cam, located on the second level, where it will be set in motion on the return stroke of the main driving shaft. In the manner described each of the two control profiles can precisely rotate the controlled movable contact element in one direction, and in the opposite movement the same profile does not touch the contact.
2. After executing one work stroke as described above, the cam has an additional functionality whereby it provides a lock to the rotating contact element. This can be done by transition of the working profile into a cylindrical surface. Once the cam operating profile with its protrusions has driven the associated roller element of the movable contact element and set it in its operating position, the cylindrical surface of the cam protrusions rests behind the roller element and prevents an unwanted backward rotation of the movable contact element.
3. According to the described configuration, at both ends of the rotating contact stroke described above, there are two pairs of fixed grip-shaped contact elements executed in the shape of clips with corresponding contact springs and inserted in an insulating carrier. Each clip in this carrier together with its spring is electrically isolated from the other and spaced at the specified isolation distance. When the passive movable contact element stands between the two spaced apart ad fixed contact elements, it makes an electrical connection between them.
4. The described configuration is also applicable to a main contact system and to a slow-motion contact system for an on-load tap changer, for example.

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

Figures 1-6 an embodiment of a contact system for a tap changer in different perspective views, and
Figures 7-8 an embodiment of a movable contact element of the contact system according to the figures 1-6.

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.
The figures 1-6 each illustrate a perspective view of components for a tap changer, e.g. an on-load tap changer, for a transformer which can allow for variable turn ratios to be selected in distinct steps without a supply interruption during a tap change. The on-load tap changer comprises a contact system 1 that enables a stable and reliable electrical connecting mechanism and contributes to low wear and low friction of interacting components.
The contact system 1 comprises a first and a second fixed contact unit 20 and a movable contact unit with a movable electrical contact element 10. The fixed contact units 20 each comprise two plate-shaped fixed electrical contact elements 24. The associated contact elements 24 are formed spaced apart from each other with a given distance in between that is formed in coordination with a thickness of a contact portion 14 of the moveable contact element 10.
The movable contact element 10 is configured to make electrical connection to the respective contact elements 24 of the associated fixed contact unit 20. The moveable contact element 10 comprises a two-level driving contact with contact portions 11 and 12 which are arranged offset to each other with respect to or along a rotation axis R2 of the moveable contact element 10.
The contact system 1 further comprises a driving unit 3 that is configured to rotationally drive the movable contact element 10 bidirectionally around the rotation axis R2 towards the respective fixed contact elements 24 of the associated fixed contact unit 20. The driving unit 3 comprises a two-level driving contact with protrusions 6, 7 which are arranged offset to each other with respect to or along a rotation axis R1 of the driving unit 3. The movable contact unit and the driving unit 3 are configured in coordination with each other so that a respective protrusion 6, 7 is temporarily in contact with the associated contact portion 11, 12 to drive the movable contact element 10 so that a first state and a second state can be set. In the first state, the movable contact element 10 is in electrical contact with the contact elements 24 of the first fixed contact unit 20 (e.g. see Figs. 1-3). In the second state, the moveable contact element 10 is in electrical contact with the contact elements 24 of the second fixed contact unit 20 (e.g. see Fig. 5). The Figs. 4 and 6 show a transition between the first and the second state, wherein the movable contact element 10 is not in contact with the contact elements 24 of the first and the second fixed contact unit 20.
The contact system 1 can be implemented in one of the phases of a diverter switch for an on-load tap changer. The contact system 1 is mounted on an insulating plate 2 and comprises the two fixed contact units 20 each including two opposite fixed insulating blocks 21 of insulating material which are associated to the respective pair of clip contact elements 24. The contact elements 24 are rotatable or pivotable around a corresponding rotation axis R3 (see Fig. 1). A contact pressure is set by an associated spring 26.
On the insulating plate 2 there is a fixed support that serves as a rotation axle 16 of the movable contact element 10 (see Fig. 2) defining the rotation axis R2. The axle 16 is arranged inside an axle recess 17 of the movable contact element 10 (see Figs. 7 and 8). The moveable contact element 10 is formed with ramifications comprising a first arm 11 and a second arm 12 realizing the contact portions of the two-level driving contact of the moveable contact unit. The driving unit 3 comprises a control disc 5 with the first protrusion 6 and the second protrusion 7 realizing the two-level driving contact of the driving unit 3. The arms 11, 12 and the protrusions 6, 7 are configured in coordination with each other so that the first protrusion 6 is temporarily in contact with the first arm 11 and the second protrusion 7 is temporarily in contact with the second arm 12 to respectively drive the movable contact element 10 and to set the first state or the second state of the contact system 1. With respect to the rotation axes R1 and R2, the first arm 11 can also be referred to as the upper arm and the second arm 12 can also be referred to as the lower arm. Accordingly, the first protrusion 6 can also be referred to as the upper protrusion and the second protrusion 7 can also be referred to as the lower protrusion.
When the contact element 10 is engaged between the clip contact elements 24 of one of the two fixed contact units 24, electrical contact is made between the respective lower contact element 24 and the respective upper contact element or vice versa. The movable contact element 10 comprises a rod-shaped electrical contact portion 14 with rounded contact tips 15 at opposite ends of the contact portion 14 (see Figs. 4 and 6-8). The respective contact elements 24 of the fixed contact units 20 each comprise a chamfered or wedge-shaped contact section 25 interacting with the rounded contact tips 15 of the movable contact element 10 proving a precise and reliable contact making. When the contact element 10 is engaged between the clip contact elements 24 of one of the two fixed contact units 24, the current flow to the contact elements 24 and is carried out by the flexible contact wires 27 (see Fig. 2).
The movable contact element 10 is arranged between the fixed contact units 20 and the driving unit 3. In a rear part of the contact element 10 there are two levels of rollers 13, the axes of which do not coincide, but are shifted at an appropriate predetermined angle. The drive of the movable contact 10 is carried out by the control disc 5, which has the two convex cam profiles or teeth forming the protrusions 6 and 7 located at two levels, which correspond to the levels on which the rollers 13 are located on the contact element 10. In each of the two operating positions, the contact makes the electrical connection between the corresponding contact elements 24. At the same time, the current transmitting contact element 10 is locked between an outer surface of the corresponding protrusion 6, 7 and a buffer 22 of the respective fixed contact unit 20 (see Fig. 2). The buffer 22 then contacts a respective buffer protrusion 18 of the movable contact element 10 (see Fig. 8).
When performing a switching operation, initially the control disc 5 passes a set idle travel, after which the corresponding protrusion 6, 7 hits the respective roller 13, which starts the movement of the movable contact element 10 (see Fig. 4). Arrows shown in Fig. 3 indicate a movement direction of the corresponding movable elements. In this movement, the other roller 13 moves freely, and preferably does not touch anything, and does not participate in the steering. Thus, there can be a gap between the roller 13 and the associated protrusion 6, 7 after the desired rotation of the moveable contact element 10. Upon completion of the switching operation, the contact element 10 engages between the two contact elements 24 making an electrical connection between them. At this time, the roller 13 has turned to such an angle that it can no longer be pushed by the associated protrusion 6, 7 but can roll against an outer cylindrical surface, whereupon the movement of the contact 10 stops to the buffer 22 (e.g. see Fig. 5). In this case, the movement of a diverter switch control shaft 4, on which the control disc 5 is mounted, can continue without restrictions, until reaching the angle set for it.
When performing the next switching operation, the shaft 4 with the control disc 5 is rotated in the opposite direction, using the other protrusion 7 and the roller 13, located at the upper level to drive the contact element 10, as shown in Figure 6, until reaching the other end position shown in the Figs. 1 and 2.
The embodiments shown in the figures 1 to 8 as stated represent exemplary embodiments of an improved contact system 1 and a corresponding tap changer; therefore, they do not constitute a complete list of all embodiments according to possible arrangements. Actual arrangements of the contact system 1 and/or the tap changer may vary from the embodiments shown in the figures.

Reference Signs

1: contact system
2: insulating plate
3: driving unit
4: shaft
5: control disc
6: first protrusion
7: second protrusion
10: movable contact element
11: first contact portion / first arm
12: second contact portion / second arm
13: roller
14: electrical contact portion
15: contact tip
16: axle
17: axle recess
18: buffer protrusion
20: stationary contact unit
21: insulating block
22: buffer
24: contact element
25: contact section
26: spring
27: contact wire

R1: rotation axis of the driving unit
R2: rotation axis of the moveable contact element
R3: rotation axis of a contact arm

Claims

Contact system (1) for a tap changer, comprising:
- a first and a second fixed contact unit (20) each with at least one fixed electrical contact element (24),

- a movable contact unit with at least one movable electrical contact element (10) that is configured to make electric connection to the respective contact element (24) of the associated fixed contact unit (20), wherein the moveable contact unit comprises a two level driving contact with contact portions (11, 12) which are arranged offset to each other with respect to a rotation axis (R2) of the moveable contact element (10), and

- a driving unit (3) that is configured to rotationally drive the movable contact element (10) bidirectionally around the rotation axis (R2) of the moveable contact element (10) towards the respective fixed contact element (24) of the associated fixed contact unit (20), wherein the driving unit (3) comprises a two level driving contact with protrusions (6, 7) which are arranged offset to each other with respect to a rotation axis (R1) of the driving unit (3), wherein the movable contact unit and the driving unit (3) are configured in coordination with each other so that a respective protrusion (6, 7) is temporarily in contact with the associated contact portion (11, 12) to drive the movable contact element (10) so that a first state, in which the movable contact element (10) is in electrical contact with the contact element (24) of the first fixed contact unit (20), and a second state, in which the moveable contact element (10) is in electrical contact with the contact element (24) of the second fixed contact unit (20), are settable.
Contact system (1) according to claim 1, wherein the moveable contact element (10) is formed with ramifications comprising a first arm (11) and a second arm (12) realizing the contact portions of the two level driving contact of the moveable contact unit, and wherein the driving unit (3) comprises a control disc element (5) with a first protrusion (6) and a second protrusion (7) realizing the two level driving contact of the driving unit (3), wherein the arms (11, 12) and the protrusions (6, 7) are configured in coordination with each other so that the first protrusion (6) is temporarily in contact with the first arm (11) and the second protrusion (7) is temporarily in contact with the second arm (12) to respectively drive the movable contact element (10) and to set the first state or the second state of the contact system (1).
Contact system (1) according to claim 2, wherein the control disc element (5) and the first and second protrusions (6, 7) are formed integrally in one piece.
Contact system (1) according to claim 2 or 3, wherein the moveable contact element (10) and the first and second arms (11, 12) are formed integrally in one piece.
Contact system (1) according to any of the preceding claims, wherein the respective protrusion (6, 7) of the driving unit (3) comprises a tapering shape along a circular path around the rotation axis (R1) of the driving unit (3) so that the respective protrusions (6, 7) each have a wider section and a narrower section, wherein the respective wider section is configured to contact the associated contact portion (11, 12) for driving the movable element (10) so that the first state and the second state of the contact system (1) are settable independent of a rotational end position of the driving unit (3).
Contact system (1) according to any of the preceding claims, wherein the respective contact elements (24) of the fixed contact units (20) each comprise a chamfered or wedge-shaped contact section.
Contact system (1) according to any of the preceding claims, wherein the movable contact element (10) comprises a rod-shaped electrical contact portion (14) with rounded contact tips (15) at opposite ends of the rod-shaped contact portion (14).
Contact system (1) according to claim 7, wherein the moveable contact element (10) and the electrical contact portion (14) are formed integrally in one piece.
Contact system (1) according to claim 7 or 8, wherein the electrical contact portion (14) comprises buffer protrusions (18) at opposite sides which are configured in coordination with buffer elements (22) of the fixed contact units (20) to set a rotational end position of the movable contact element (10).
Contact system (1) according to any of the preceding claims, wherein the fixed contact units (20) each comprise two or more contact elements (24) formed spaced apart from each other with a given distance in between that is formed in coordination with a thickness of a contact portion (14) of the moveable contact element (10).
Contact system (1) according to any of the preceding claims, wherein the fixed contact units (20) each comprise two pivotable contact elements (24) with respective contact sections which are configured to make electrical contact to the movable contact element (10) in the first or the second state, and wherein the fixed contact units (20) each further comprise a spring element (26) that is arranged between and coupled to the respective contact arms (24) so that the contact arms (24) are pretensioned and the associated contact sections are pressed towards each other.
Contact system (1) according to any of the preceding claims, wherein the contact portions (11, 12) of the movable element (10) each comprise a rotatable roller element (13) that is configured to get in contact with the associated protrusion (6, 7) of the driving unit (3) when the movable contact element (10) is to be rotated.
Contact system (1) according to any of the preceding claims, wherein the protrusions (6, 7) of the driving unknit (3) each comprise a curved contact surface facing and configured to get in contact with the associated contact portion (11, 12) of the movable contact unit when the movable contact element (10) is to be rotated.
Contact system (1) according to any of the preceding claims, wherein the protrusions (6, 7) of the driving unit (3) are formed at a given radial distance from the rotation axis (R1) of the driving unit (3), and wherein the contact portions (11, 12) of the movable contact element (10) are arranged in coordination with the radial distance of the associated protrusion (6, 7) so that, when the interacting contact portion (11, 12) and protrusion (6, 7) are free of contact and the driving unit (3) rotates, the protrusion (6, 7) is moved towards the contact portion (11, 12), contacts the contact portion (11, 12) and drives the moveable element (10) towards one of the fixed contact units (20).
Tap changer, comprising:
- a shaft (4) that is configured to provide a drive, and

- a contact system (1) according to any of the preceding claims, wherein the driving unit (3) of the contact system (1) is coupled to the shaft (4).