WO2014127995A1

WO2014127995A1 - Tap changer contact system

Info

Publication number: WO2014127995A1
Application number: PCT/EP2014/052227
Authority: WO
Inventors: Jean Mathae
Original assignee: Abb Technology Ltd
Priority date: 2013-02-20
Filing date: 2014-02-05
Publication date: 2014-08-28
Also published as: WO2014127995A9; EP2959493A1; CN105393323B; EP2959493B1; CN105393323A

Abstract

The invention relates to a contact system for a tap changer. The system includes a fixed contact part (1) having a first contact surface (4), and a movable contact part (2) having a second contact surface. The movable contact part (1) is movable from an electrical non-contact position to an electrical contact position and vice versa. The direction of movement is substantially parallel to the first contact surface (4). Force applying means (F) is arranged to urge said contact surfaces towards each other. According to the invention one of said contact parts includes a wheel means (3) arranged to roll against an abutment surface (6,) of the other contact part during an entering phase of the movement from the electrical non-contact position to the electrical contact position. The rolling contact is a sole and singular contact between the contact parts (1, 2,) during the entering phase

Description

TAP CHANGER CONTACT SYSTEM

Field of invention

The present invention relates to contact system for a tap changer, which system includes a fixed contact having a first contact surface and a movable contact having a second contact surface, the movable contact part being movable from a non-contact position to a contact position and vice versa, the direction of movement being substantially parallel to the first contact surface, and whereby force applying means is arranged to urge the contacts towards each other.

The invention also relates to a tap changer and to a transformer.

Background of invention

A tap changer is commonly used in connection with a transformer in order to vary the transformation rate thereof. In a transformer with a tap changer one of the windings in the transformer has a fixed amount of turns connected to the circuit. The other winding has one fixed connection point, whereas the other connection point can be selected among a number of fixed contacts to attain a required voltage. The selectable fixed contacts may be located after each other along a portion of the winding corresponding to 70% to 100% of its full extension.

Upon a change in the load connected to the transformer or due to other influences it might be required to change the connection point. The need of changing the tap point is often triggered automatically in response to sensed parameters. Tap changing includes a plurality of maneuvers including the opening and closing of switches e.g. via a spring loaded energy accumulator and moving a fine selector arm to a new fixed contact. These maneuvers have to be performed in a certain sequence and in a certain time relation.

In the tap changer there thus is a plurality of fixed contacts cooperating with a movable contact. A change of connection points the maneuvers include to move the movable contact out of contact with one fixed contact and then move the movable contact into contact with another fixed contact.

When bringing the movable contact into contact with the fixed contact there is an initial entering stage when the movable contacts one end of the fixed contact. Thereafter the movable contact moves a short distance along the fixed contact into its resting position where full contact is established. At the entering stage there is a tendency that wear occurs on the entering end of the fixed contact such that contact material is burned off. This might lead to damage en risk for fault function of the tap changer. A corresponding problem is present when the movable contact leaves the fixed contact in order to move to another fixed contact. Thereby wear will occur also at the other end of the fixed contact.

This problem is addressed by the device disclosed in GB 2049288. In this device the movable contact consist of a contact roller arranged to contact the fixed contact. At each end of the contact roller there is a lateral roller made of insulating material and coaxially arranged with the contact roller. At the fixed contact there is a cam surface arranged on each side thereof, which cam surfaces extend in the direction of movement of the movable contact at tap changing. The movable and the fixed contacts are urged toward each other by a transversally directed spring acting on the movable contact.

When the movable contact is to enter the fixed contact, the laterally rollers will initially roll on a raised portion of the respective cam surface, whereby the contact roller will be located a short distance above the contact surface of the fixed contact. After a certain travel distance the shape of the cam surface allows lowering the pack of rollers such that the contact roller comes into contact with the contact surface of the fixed contact. Each cam surfaces also has a raised portion at its other end such that a corresponding lifting of the contact roller will occur also when the movable contact moves out of contact from the fixed contact.

By the lifting of the contact rollers by the cam surfaces at the entering and leaving position, the intention is to avoid wear at the ends of the fixed contact.

Similar arrangements relating to the cooperation between movable and fixed contacts in a tap changer are disclosed in EP 88296, US 20090071806, JP 62213106 and JP 5821706.

The device of GB 2049288 is complicated and its construction may lead to performance problems. Since the contact surface of the movable contact is a roller, there is contact along a line. The construction thereby requires a reduced number of degrees of freedom. The line contact also makes it necessary that the spring force is transversally directed and as a consequence that a cam surface is required on each side of the contact surface of the fixed contact. Having a cam surface at each side leads to an over-determination of the system that might cause problems. Further, the device will be sensitive to inclination of the movable part, whereby the wear problem might be accentuated.

In the device of EP88296 the movable contact part has the periphery of a wheel as the contact surface contacting the fixed contact The fixed contact part has an oblique surface on which the wheel rolls before reaching the contact surface. This, however has nothing to do with the wear problem and does not solve this problem because the electrical contact starts at the very front edge of the circular contact surface on the fixed contact part and thus creates burning off of material. It is a disadvantage that the contact surface of the movable contact part is a wheel periphery since that means that the contact will occur along a line in stead of area contact. The line contact will probably worsen the burn off problem, in particular since the line contact initially will be very short, i.e. a dot.

Summary of invention

The object of the present invention is to reduce wear on the fixed and movable contacts of a tap changer and simultaneously avoid drawbacks related to previous known attempts in this respect.

This object is according to the present invention achieved in that a contact system of a tap changer as specified in the introduction of the present application includes the specific features specified in the characterizing portion of claim 1 . Thus one of said contact parts includes a wheel means separate from and rotatable relative to its contact surface and_arranged to roll against an abutment surface of the other contact part during an entering phase of the movement from the electrical non-contacting position to the electrical contacting position, which rolling contact is a sole and singular contact between the contact parts during the entering phase.

Thanks to the fact that there is no electrical contact during the entering phase the problem of wear of the edge portion of the first contact surface during that phase is eliminated or at least reduced. Electrical contact will occur first after the entering phase when the second contact surface is positioned well away from that edge portion. The reduced wear increases the life time of the contact system. The rolling contact between the wheel means and the abutment surface also assures that the mechanical wear of these components is minimized. Particularly advantageous is that the rolling contact is arranged to be singular. This simplifies the construction by avoiding over-determination of the system, that otherwise would require specific measures to cope with.

According to a preferred embodiment, the wheel means is arranged to roll correspondingly on the other contact part also during a leaving phase of the movement from the electrical contact position to an electrical non-contact position.

Thereby the wear problem when the movable contact leaves the fixed contact also is eliminated or reduced.

According to a further preferred embodiment, the movable contact part is arranged pivotally with respect to a pivot axis, and the force applying means is arranged to act in the pivoting direction.

The pivoting arrangement of the movable contact part simplifies the urging of the movable contact part towards the fixed one since the requirements for guiding the movable contact part into electric contact are reduced in comparison with a translator acting force.

According to a further preferred embodiment, the wheel means at a portion thereof arranged for said rolling contact has a circular profile in a plane through its axis.

Due to the circular profile the rolling contact between the wheel means and the abutment surface will substantially be a point contact. The point contact leads to a more precise and reliable cooperation than would be the case with a cylindrical wheel resulting in line contact.

According to a further preferred embodiment, the second contact surface is stationary in relation to the movable contact part.

This provides a distinct and predictable cooperation between the contact surfaces.

According to a further preferred embodiment, the fixed contact part includes said wheel means.

This is a very important embodiment of the invention, since the accuracy of the cooperation between the wheel means and the abutment surface can be easier optimized when the wheel means is on the fixed contact part.

According to a further preferred embodiment in the alternative when the wheel means is on the fixed contact part, the wheels means includes a first wheel located at one end of the fixed contact part and a second wheel at the other end of the fixed contact part, whereby ends are defined in relation to the movement direction of the movable contact part and which first and second wheels are aligned in said movement direction.

When the wheel means is on the fixed contact part, the arrangement of a wheel at each end is a suitable adaption for the wear reduction also at leaving.

According to a further preferred embodiment of the alternative when the wheel means is on the fixed contact part, the first contact surface is located at a level below the upper rolling point of the wheel means.

This arrangement contributes in an advantageous way to attain that the electrical contact does not occur until the wheel means leaves the abutment surface during the entering phase. The corresponding relates to the leaving phase.

According to a further preferred embodiment, the first contact surface is located at a level above a relief surface of the fixed contact part, which relief surface is a portion located in alignment with the first wheel in the direction of said movement.

Thereby it is attained that the abutment surface on the movable contact part does not contact the fixed contact part when the electrical contact is established such that the electrical contact is not disturbed or affected.

According to a further alternative preferred embodiment, the movable contact includes said wheel means.

Arranging the wheel means on the movable contact part may in some applications be more advantageous, since a reduced number of wheels thereby is sufficient. Only one single wheel is required for both the entering and the leaving phase, and the number of contact parts that has to be equipped with wheels is lower, since the number of fixed contacts in a tap changer is much larger than the number of movable contacts.

According to a further preferred embodiment, the first contact surface is located at a level below the rolling point of the wheel means.

According to a further preferred embodiment, the first contact surface is located at a level above a relief surface of the fixed contact part, which relief surface is a portion located in alignment with said abutment surface in the direction of said movement. The two embodiments next above have advantages similar to those of the corresponding embodiments related to the alternative where the wheel means are on the fixed contact part.

The terms "above" and "below" used in the embodiments above where the level of the first contact surface is specified in relation to cooperating components, is to be understood as related to the direction from the fixed contact part towards the movable contact part as being the upward direction. This might be contextually evident, but for the sake of clarity it is underlined regarding the interpretation of the corresponding claims.

The term "in alignment with" may relate to linear alignment or to alignment along a circular line.

The invented tap changer is provided with a contact system according to the present invention, and the invented transformer is provided with a tap changer according to the present invention.

The above described preferred embodiments of the invention are specified in the dependent claims. It is to be understood that further preferred embodiments of course can be constituted by any possible combination of the preferred

embodiments above and by any possible combination of these and features mentioned in the description of examples below.

The invention will be further explained through the following detailed description of examples thereof and with reference to the accompanying drawings.

Short description of the drawings

Fig. 1 is a perspective view of the contact parts according to a first example of the invention.

Fig. 2 is a side view of the contact parts of fig 1 , where the movable contact part is depicted in three different positions.

Fig. 3 is a view from above of the contacts parts in fig. 2 depicting the movable contact part in one of the positions.

Fig. 4 is a cross section along the line B-B in fig. 2

Fig. 5 is a cross section along the line C-C in fig. 2.

Fig. 6 is a perspective view of the contact parts according to a second example of the invention. Fig. 7 is a side view of the contact parts of fig 6, where the movable contact part is depicted in three different positions.

Fig. 8 is a view from above of the contacts parts in fig. 7 depicting the movable contact part in one of the positions.

Fig. 9 is a cross section along the line B-B in fig. 7

Fig. 10 is a cross section along the line C-C in fig. 7.

Description of examples

In fig. 1 the fixed contact part 1 and the movable contact part 2 are

illustrated. The fixed contact part 1 is one a plurality of similar fixed contact parts arranged in a tap changer. The movable contact part 2 is arranged to be in contact with one of the fixed contacts parts in the tap changer. By moving the movable contact part 2 from one fixed contact to another the connection point to the transformer provided with the tap changer is changed and thereby the

transformation rate of the transformer. The general arrangement of the fixed and movable contacts in the tap changer as well as the operation steps performed at tap changing may be of conventional kind, except for the inventive features related to the contact system. An explanation of the general construction and the general operation of a tap changer are thus supposed to be superfluous.

The change of connection point includes that the movable contact part 2 first leaves a first fixed contact part, travels to another fixed contact part and then enters the other fixed contact part. The figures illustrate the part of the operation when entering a fixed contact part.

Fig. 2 illustrates the process when the movable contact part 2 enters the fixed contact part 1 . In position A the movable contact part 2 is traveling from another (not shown) fixed contact part to the fixed contact part 1 . In position B the movable contact part 2 is in the entering phase, where the abutment surface 6 of the movable contact part 2 rolls on the wheel 3a of the fixed contact part 1 . The force F from force applying means urges the movable contact part 2 angularly with respect to the pivot axis O-O against the wheel 3a. The force applying means may for example be a mechanical pressure spring. As the movable contact part 2 continues to move in the rightward direction in the figure it leaves the rolling contact with the wheel 3a and reaches the position C, in which the contact parts 1 , 2 establish electric contact. Between the wheels 3a, 3b there is a relief surface 5 at a level below the upper periphery of the wheels and aligned with these. Behind the relief surface 5 is the contact surface 6 of the fixed contact part 1 . The contact surface is located at a level above the relief surface 5, but at a level below the upper periphery of the wheels 3a, 3b.

In fig. 3 being a view from above the relative location of the relief surface 5, the contact surface 4 and the wheels 3a, 3b can be seen. The position in fig. 3 relates to position C of fig.2.

Fig. 4 illustrates the B position when the abutment surface 6 rolls on the wheel 3a and fig. 5 illustrates the C position when electric contact is established.

The spring force F urges the movable contact part 2 towards the fixed contact part 1 . When the movable contact part 2 travels to position B from position A and reaches the wheel 3a it will initially be raised by the wheel 3a against the force F of the spring. When the abutment surface 6 of the movable contact part 2 rolls on the wheel, the contact surface 7 of the movable contact part 2 thereby will be in a lifted position in relation to the contact surface 4 of the fixed contact part 1 as illustrated in fig. 4.

When the movable contact part 2 travels further to the right in the figure from position B to position C, the abutment surface 6 will initially roll down on the wheel 3a such that the contact part 2 will be lowered. The contact surface 7 of the movable contact part thereby gradually will come closer to the contact surface 4 of the fixed contact part 1 and finally come into contact therewith as illustrated in fig. 5. This represent position C. The abutment surface 6 of the movable contact part 1 thereby is at a small distance from the relief surface 5 on the fixed contact part 1 . The spring force F presses the contact surfaces 4 and 7 against each other to provide a safe electric contact.

If tap changing is required from the fixed contact part 1 to another fixed contact part, the movable contact part is operated to move to the right in fig. 2 towards the wheel 3b, or, when applicable, to the left towards the wheel 3a. When reaching wheel 3b the abutment surface 6 will start to roll on the wheel 3b in a leaving phase. After a movement pattern mirroring what have been described above for the entering phase, the movable contact part 2 then travels to an adjacent fixed contact part and being brought into electric contact therewith. Fig. 6-10 illustrate a second example of a contact system according to the invention. The figures represent corresponding views as fig. 1 -5. In this case the movable contact part 102 is provided with a wheel 103 arranged to cooperate with a profiled part of the fixed contact part 101 . The profiled part has of an abutment surface 106, consisting of an abutment portion 106a, 106b at each end of the profiled part. Between the abutment portions 106a, 106b there is a relief surface 105. The fixed contact part 101 has a contact surface 104 along the side of the relief surface 105.

During the entering stage, position B, the wheel 103 rolls on the abutment portion 106a on the fixed contact part 101 , and the contact surfaces 104, 107 are maintained separated from each other. When the contact surfaces 104, 107 has come into contact with each other as shown in fig. 10 the wheel 103 no longer rolls against the fixed contact part 101 , but is located a short distance above the relief surface 105 thereof. The movement pattern is similar to that of the device illustrated in fig. 1 -5.

In both the examples the contact surfaces are located closer to the pivot axis of the movable contact part than the cooperating wheel/abutment is. It is to be understood that it comes within the scope of the present invention to have this relation inverted, i.e. to have contact surfaces more remote from the pivot axis than the cooperating wheel/abutment is.

In both examples the travelling of the movable contact part 2, 102 is illustrated as a linear movement. Alternatively, the movement of the movable contact part 2, 102 may be in the rotational direction such that the portions of the movable contact part that contact the fixed part 1 , 101 move along a circular movement path. In that case the fixed part 1 , 101 has a correspondingly slight circular extension in the plane of fig. 3 and fig. 8, respectively.

Claims

A contact system for a tap changer , which system includes a fixed contact part (1 , 101 ) having a first contact surface (4, 104), and a movable contact part (2, 102) having a second contact surface (7, 107), the movable contact part (1 , 101 ) being movable from an electrical non-contact position (A) to an electrical contact position (C) and vice versa, the direction of movement being substantially parallel to the first contact surface (4, 104), and whereby force applying means (F) is arranged to urge said contact surfaces (4, 7, 104, 107) towards each other, characterized in that one of said contact parts includes a wheel means (3, 103) separate from and rotatable relative to its contact surface and arranged to roll against an abutment surface (6, 106) of the other contact part during an entering phase of the movement from the electrical non-contact position (A) to the electrical contact position (C), which rolling contact is a sole and singular contact between the contact parts (1 , 2, 101 , 102) during the entering phase.

A contact system according to claim 1 , characterized in that said wheel means (3, 103) is arranged to roll correspondingly on the other contact part also during a leaving phase of the movement from the electrical contact position to an electrical non-contact position.

A contact system according to claim 1 or 2, characterized in that the movable contact part (2, 102) is arranged pivotally with respect to a pivot axis (O) and in that the force applying means (F) is arranged to act in the pivoting direction.

A contact system according to any one of claims 1 -3, characterized in that the wheel means (3, 103) at a portion thereof arranged for said rolling contact has a circular profile in a plane through its axis.

5. A contact system according to any one of claims 1 -4, characterized in that the second contact surface (7, 107) is stationary in relation to the movable contact part (2, 102). 6. A contact system according to any one of claims 1 -5, characterized in that the fixed contact part (1 ) includes said wheel means (3).

7. A contact system according to claim 6, characterized in that said wheels means (3) includes a first wheel (3a) located at one end of the fixed contact part (1 ) and a second wheel (3b) at the other end of the fixed contact part (1 ), whereby ends are defined in relation to the movement direction of the movable contact part and which first and second wheels (3a, 3b) are aligned in said movement direction. 8. A contact system according to claim 6 or 7, characterized in that the first contact surface (4) is located at a level below the rolling point of the wheel means (3).

A contact system according to any one of claims 6-8, characterized in that the first contact surface (4) is located at a level above a relief surface (5) of the fixed contact part (1 ), which relief surface (5) is a portion located in alignment with the first wheel (3a) in the direction of said movement.

A contact system according to any one of claims 1 -5, characterized in that the movable contact (102) includes said wheel means (103).

1 1 A contact system according to claim 10, characterized in that the first contact surface (104) is located at a level below the rolling point of the wheel means (103).

12. A contact system according to claim 10 or 1 1 , characterized in that the first contact surface (104) is located at a level above a relief surface (105) of the fixed contact part (101 ), which relief surface is a portion located in alignment with said abutment surface (106) in the direction of said movement.

A tap changer, characterized in that the tap changer is provided with at least one contact system according to any of claims 1 -12.

14. A transformer, characterized in that the transformer is provided with a tap changer according to claim 13.