-
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 of a moving shaft of the tap changer. The static contact unit further comprises at least one contact element that is pivotably coupled to the contact body configured to establish an electrical contact to a movable contact that is arranged at the moving shaft. The static contact unit further comprises a spring element that is coupled to the contact element configured to bias the contact element so that, with respect to a state in which the tap changer is assembled, the contact element is preloaded in direction of the moving shaft with respect to a longitudinal axis of the moving shaft.
-
According to an embodiment, the static contact unit comprises two contact elements that are pivotably coupled to the contact body configured to establish a respective electrical contact to the movable contact of the moving shaft. The spring element is coupled to both contact elements inbetween with respect to the 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, both contact elements are preloaded in direction of the moving shaft with respect to the longitudinal axis of the moving shaft.
-
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.
-
It is a recognition of the present disclosure that usual designs for a pre-selector of an on-load tap changer are based on the need of tie-in potential resistors which are mounted to the pre-selector structure. This requires additional space in a corresponding transformer tank assembly, and additional production time, which makes the product more complex and more expensive.
-
It is a further recognition of the present disclosure that the use of tie-in resistors can be avoided if the speed of breaking on the pre-selector contact system is increased during the transient process of switching the pre-selector, when a tap winding of the transformer remains at floating potential.
-
The static contact unit and a corresponding contact system or pre-selector arrangement allow for a high speed disconnecting with a disconnecting velocity of with a velocity of 4-6 m/s, for example. The one or more pivotable contact elements enable to achieve double breaking, because of the simultaneously disconnecting on both sides of an interacting movable contact.
-
According to a further embodiment of the static contact unit, the respective contact element and the associated contact body each comprise a contact surface facing each other configured to limit a pivot movement of the contact element relative to the contact body.
-
According to a further embodiment of static contact unit, the respective contact element comprises a first arm and a second arm, wherein the first arm is pivotably coupled to the associated contact body and the second arm is pivotably coupled to the first arm. Such a pivotable two-arm-contact-lever allows for beneficial movability in interaction with a movable contact that moves and passes the static contact unit.
-
According to a further embodiment of static contact unit, the first arm and second arm of the respective contact element each comprise a contact surface facing each other configured to limit a pivot movement of the second arm relative to the first arm. The two arms of the respective contact elements are configured in coordination with each other to allow and limit a predetermined pivot movement. For example, the static contact unit comprises one contact element and is configured to realize an upper static contact of a pre-selector of a tap changer. The spring element pulls the contact element upwards against a stopping or contact surface but the second arm is configured to be pivotable further upwards in interaction with a moving contact pushing it upwards. In the opposite direction of movement, the moving contact pushes the contacting second arm downwards until the contact surface of the second arm contacts the contact surface of the first arm and thus limits the pivot movement of the second arm relative to the first arm. A further pivot movement of both arms together can be still possible.
-
According to a further embodiment of static contact unit, the second arm of a respective contact element comprises a chamfered or rounded tip configured to establish a respective electrical contact to a contact surface of the movable contact of the moving shaft, with respect to a state in which the tap changer is assembled. Such a configuration of the contact element enables low-resistance, low-wear contacting and also guidance of the second arm movement during engaging with a corresponding contact surface of the movable contact.
-
According to a further embodiment, the static contact unit comprises parallel contact elements that are statically coupled to the contact body. Each parallel contact elements extend in direction towards the moving shaft to establish a respective electrical contact to a contact surface of the movable contact of the moving shaft, with respect to a state in which the tap changer is assembled. The contact elements are designed in particular as snap fingers and establish a temporary contact with the movable contact at the moving shaft until the parallel contacts establish the operational contact and set up electrical switching. The parallel contacts provide current in normal position of the pre-selector or the contact system. This realizes a static position before starting of electrical switching. The pre-selector provides current in the static position. During a switching process when the movable shaft is in the middle position before releasing of snapping fingers or the contact elements the parallel contacts are disengaged already. There may be a transition process without high current because the selector is disengaged before that.
-
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. The one or more contact elements are also fixed in relation to the longitudinal axis at a pivot point but are pivotable to a given extent.
-
In particular, the contact system can realize a pre-selector of a tap changer and enables secure and reliable electrical switching. 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, wherein a first static contact unit is configured to form an upper contact, a second static contact unit is configured to form a lower contact, and a third static contact unit is configured to form a middle contact between the first and the second contact with respect to the longitudinal axis of the moving shaft. The first and the second contact unit each comprise one contact element and one spring element biasing the associated contact element. The third contact unit comprises two contact elements and one spring element biasing the two contact elements. 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 rapidly and securely enable double braking and 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 limit a funnel-shaped contact notch inbetween that is geometrically formed in coordination with parallel contact elements of the static contact units. 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.
-
According to a further embodiment of the contact system, the two contact wing elements of the corresponding movable contact each include a respective groove and a contact wall which are geometrically formed in coordination with a respective pivotable contact element of the associated static contact unit. The contact notch described above is formed in coordination with the parallel contacts and the previously established provisional contact is set up by the groove and the contact element forming a snap finger, for example.
-
For example, the contact wall limits the groove to one side with respect to the longitudinal axis of the movable shaft so that a first state and a second state are adjustable when the electrical contact between the respective pivotable contact element of the associated static contact unit and the movable contact of the knife contact unit is formed. In the first state the contact element contacts the contact wall and in the second state the contact element is arranged inside the groove contact-free to the contact wall and the wing element, whereas the parallel contact elements now are in contact with a wing element and the movable contact.
-
According to a further embodiment of the contact system, the contact wall comprises a chamfer or rounding configured to establish a respective electrical contact to a pivotable contact element of the associated static contact unit. Such a configuration of the contact wall enables low-resistance, low-wear contacting, in particular in combination with a rounded or chamfered tip of the contact element.
-
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 of the static contact unit and the contact system allows for a speed up of pre-selector design in an on-load tap changer by means of snap contact fingers for double breaking of the electrical circuit of the tap changer. The static contact units interacting with the movable contacts enable accelerating a disengagement of the pre-selector contact system by means of the pivotable snap contact fingers controlled by a cam profile of the movable contacts for charging and releasing.
-
The pivotably mounted snap contact fingers of the respective static contact units can provide the following characteristics:
- a low-speed motion vertical pre-selector shaft actuates and charges a pair of snap contact fingers during its movement by means of spring elements;
- a cam profile of the movable contact of the pre-selector moving shaft holds and releases the snap contact fingers, as immediately disconnects the electrical chain with high speed;
- to perform the above-mentioned actions, the snap contact fingers comprise two arms or elements with hinges. Only one spring element can be used to achieve the movements of the contact finger element in a desired sequence.
-
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 perspective views, and
- Figures 4-9 embodiments of static contact units for the pre-selector according to the figures 1 to 3 in cross section 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 different states of an embodiment of contact system 30 realizing a pre-selector for a tap changer in perspective views. The contact system 30 comprises three static contact units 20 (see also Figs. 4 to 6). The contact system 30 comprises a linear moving shaft 1 elongated predominantly along a longitudinal axis L and a knife contact unit 2 that is configured axially movable along a longitudinal axis L of the moving shaft 1. The three static contact units 20 are arranged 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 L of the moving shaft 1 (see Figs. 2-3).
-
The first and the second static contact unit 21, 22 each comprise a contact element 5 and a spring element 6 biasing the associated contact element 5. The respective spring element 6 is coupled to the associated pivotable contact element 5 on one side forming a movable spring contact 15 and to a static spring contact element 14 on the other (see Figs. 4 and 7). The third contact unit 23 comprises two contact elements 5 and a spring element 6 biasing the two contact elements 5. The spring element 6 of the third static contact unit 23 is coupled to both pivotable contact elements 5 on opposite sides. The contact and spring elements 5, 6 form a respective snap finger contact.
-
The contact elements 5 each are pivotably 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 the knife contact unit 2 arranged at the moving shaft 1.
-
The knife contact unit 2 comprises two movable contacts 3, one upper and one lower contact 3, coupled movable up and down along the moving shaft 1. Each movable contact 3 comprises two contact wing elements 7, wherein the two wing elements 7 comprise a respective inner contact surface 9 which together limit a respective funnel-shaped contact notch 8 inbetween that is geometrically formed in coordination with parallel contact elements 18 of the static contact units 20. The two wing elements 7 further each include a respective groove 10 and a contact wall 31 which are geometrically formed in coordination with the respective pivotable contact element 5 of the associated static contact unit 20.
-
The contact wall 31 limits the corresponding groove 10 to one side with respect to the longitudinal axis L of the movable shaft 1 so that a first state and a second state are adjustable when the electrical contact between the respective pivotable contact element 5 of the associated static contact unit 20 and the movable contact 3 of the knife contact unit 2 is formed. In the first state the contact element 5 contacts the contact wall 31 (see Figs. 2, 3, 6 and 8) and in the second state the contact element 5 is arranged inside the groove 10 contact-free to the contact wall 31 (see Figs. 1, 4, 5, 7 and 9). The respective contact wall 31 comprises a chamfer or rounding configured to establish a respective electrical contact to the pivotable contact element 5 of the associated static contact unit 20 or 21-23, respectively (see Figs. 4-9).
-
Each contact element 5 comprises a first arm 5a and a second arm 5b. The first arm 5a is pivotably coupled to the associated contact body 4 around a first rotation axis R1. The second arm 5b is pivotably coupled to the first arm 5a around a second rotation axis R2 (see Figs. 4-9). Each second arm 5b comprises a chamfered or rounded tip 26 configured to establish a respective electrical contact to the contact wall 31 of the movable contact 3.
-
The first arm 5a and second arm 5b of each contact element 5 comprise a contact surface 25a, 25b facing each other configured to limit a pivot movement of the second arm 5b relative to the first arm 5a (see Figs. 8-9). Each second arm 5b further comprises a reinforcement portion in the area of its contact surface 25b to improve the operational stability of the respective interacting arms 5a, 5b.
-
The parallel contact elements 18 of each static contact unit 20 are statically coupled to the contact body 4 each extending in direction towards the moving shaft 1 to establish a respective electrical contact to the respective contact surface 9 of the wing element 7 of the movable contact 3.
-
Moreover, each contact element 5 or its first arm 5a and the associated contact body 4 comprise a respective contact surface 19, 24, 25 facing each other configured to limit a pivot movement of the contact element 5 or its first arm 5a relative to the contact body 4 (see Figs. 8-9). The contact surface of the contact body 4 can be formed as an upper or lower body surface (see Figs. 4 and 6-9) and/or as a protruding pin 19 (see Fig. 5). The protruding pins 19 of the third, middle static contact unit 23 support the contact elements 5 in normal position to avoid electrical connection with the cam or movable contact 3 of the knife contact unit 2 when it is inbetween the two contact elements 5.
-
In addition, each static contact unit 20 can comprise a locking element 13 to ensure a position of the first and the second arm 5a, 5b relative to each other on one side (see Fig. 4).
-
Figure 1 illustrates a state in which the parallel contact elements 18 of the first, upper contact unit 21 and the third, middle contact unit 23 are in contact with the movable contacts 3 of the knife contact unit 2. The contact element 5 of the first static contact unit 21 and the contact elements 5 of the third static contact unit 23 are arranged inside the groove contact-free to the respective wing element 7.
-
Figure 2 illustrates a state in which the knife unit 2 is moved downwards and the contact element 5 of the first static contact unit 21 is in contact with the wall 31 of one wing element 7 of the upper movable contact 3. The upper contact element 5 of the third static contact unit 23 is contact-free and the lower contact element 5 is in contact with the wall 31 of one wing element 7 of the lower movable contact 3. Figure 3 illustrates the state of figure 2 in a view from further down.
-
Figures 4 and 5 illustrate in a respective cross section view the first or the third static contact unit 21, 23 respectively in a state corresponding to figure 1, for example.
-
Figures 6 to 7 illustrate in a respective cross section view the second static contact unit 22 when the lower movable contact 3 is moved downwards to establish electrical contact to the corresponding parallel contact elements 18. Figures 8 and 9 are identical to the figures 6 and 7 but merely illustrate other reference signs in part.
-
The described contact system 30 can realize an accelerating drive system with the three contacts (e.g. +, 0, -) situated in vertical direction. The snapping fingers 5 or the contact elements 5 can be locked on one side by locking element 13 that allows the two arms 5a, 5b rotate together like one part on first direction and split their rotation on the second opposite direction.
-
The pairs of parallel contact elements 18 are mounted to every static contact unit 20 and create a contact bridge between the static contact bodies 4 and the contact surfaces 9 on the knife movable contacts 3. In a normal position, all snapping fingers 5 are disconnected from the cams 3 of the knife contact unit 2, thus avoiding the parallel electrical circuit and the current flows only through the pairs of parallel contact elements 18 (see Figs. 1, 4, 5, 7 and 9). During movement in vertical direction along the longitudinal axis L of the pre-selector moving shaft 1, the parallel contact elements 18 disengage from the contact surfaces 9 of the respective movable contact 3. At the same time the snapping fingers 5a, 5b are charging and keep potential between the static contact bodies 4 and the movable contact 3. The charging of the snapping fingers 5 becomes by means of the springs and contact wall 31 of the movable contacts 3.
-
When the knife contact unit 2 reaches a middle position, the pair of snapping fingers 5 immediately disconnect the electrical chain with high speed, e.g. with a velocity of more than 1 m/s, for example with 3-7 m/s, for example with 5 m/s. Such a high speed disconnecting is much faster than compared to conventional systems which may allow disconnecting with velocities of 50 mm/s or 100 mm/s. Thus, the described embodiments of the contact system 30 and its static contact units 20 allows to achieve double breaking, because of the simultaneously disconnecting on both sides of the knife movable contact 3.
-
Then there are two dielectric distances between the movable contact 3 and the disengaged static contact unit 23. Before reaching the end position of the pre-selector moving shaft 1 (see Figs.7 and 9) the contact walls 31 press the snapping fingers 5, rotate them (see Figs.6 and 8), and release them so they stay in a proper position at the end of the movement, ready for next operation. In the other direction, the sequence is the same. Combination of accelerating the switching speed and both dielectric distances can lead to very short arcing/sparking times, can increase the switching capacity of the pre-selector or the contact system 30, and can reduce a gas generation. The described embodiments further allows to avoid the need of tie-in resistors in a pre-selector design and enable a clear structure with secure and reliable functioning.
-
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 / snap finger
- 5a
- first arm of the contact element
- 5b
- second arm of the contact element
- 6
- spring element
- 7
- wing element
- 8
- contact notch
- 9
- contact surface
- 10
- groove
- 13
- locking element
- 14
- static spring contact element
- 15
- movable spring contact
- 18
- parallel contact element
- 19
- pin element
- 20
- static contact unit
- 21
- first, upper static contact unit
- 22
- second, lower static contact unit
- 23
- third, middle static contact unit
- 24
- contact surface
- 25
- contact surface
- 25a
- contact surface
- 25b
- contact surface
- 26
- tip of the second arm
- 27
- reinforcement portion
- 30
- contact system / pre-selector
- 31
- contact wall
- L
- longitudinal axis of the moving shaft / pre-selector
- R1
- first rotation axis
- R2
- second rotation axis