Patent Description:
Tap changers realize a mechanism in transformers which allows for variable turn ratios to be selected in distinct steps, for example. Document <CIT> discloses a rolling contact for the tapping switch of a transformer. An original sliding moving contact is changed into a rolling moving contact. A moving contact, a push rod, a core shaft and a spring are all arranged in a guide limiting groove. The documents <CIT>, <CIT>, <CIT>, <CIT> and <CIT> disclose further switching or contact arrangements for tap changers. In view of movable and stationary electrically engaging contacts it is a challenge to provide a stable and reliable mechanism with low wear and stress.

Thus, it is an object to provide a contact unit and contact system for an on-load tap changer that allows for a stable and reliable mechanism and contributes to low wear and stress of interacting components.

According to an embodiment, a contact unit for an on-load tap changer comprises a connector body and a contact holder coupled to each other, wherein the connector body is configured to connect the contact holder to a contact of the on-load tap changer. The contact unit further comprises a contact element coupled to the contact holder and configured to make electrical contact to a contact element of a contact device for the on-load tap changer. The contact unit further comprises drive and guiding means coupled to the contact holder such that the contact element is movable driven and linearly guided in a direction away from the connector body. The drive and guiding means comprise at least one linear bearing and an axis arranged inside the bearing which are configured to provide linearly guided movement of the contact element of the contact unit. The contact unit further comprises a further contact holder, a further contact element and further drive and guiding means assembled as the aforementioned ones to enable secure electrical engagement with the contact element of the contact device due to two or more contact elements of the contact unit. The contact holders, the contact elements and the corresponding drive and guiding means are coupled to the connector body such that the directions the corresponding contact elements are movable along enclose a predetermined angle.

By use of the described contact unit a linearly guided contact system for an on-load tap changer is feasible at low cost and allows for secure and reliable functioning. The contact unit may realize a movable contact which is configured to interact with a corresponding stationary contact to provide voltage transfer in a selector of a power diverter switch for an on-load tap changer. The described configuration may enable to provide electrical contact for voltage transfer at an upper and/or a lower position of the corresponding contact element of a contact device. Thus, a secure interaction between the contact elements can be set up which also allows for freedom of movement to a certain extent and which can further contribute to low wear and reduced mechanical stress during an engagement processes.

It is a recognition of the present disclosure that usual designs for contact systems of selector mechanisms in column type on-load tap changers consists of one or several sets of current carrying contacts placed on a static holder or joint adjacent one to each other in an angle corresponding to the placement of the respective odd and even tap positions. Such a static system is usually defined around a rotational axis concentric to a main axis of an on-load tap changer. The so formed rotating lever mechanism causes force concentrations at an end of the mechanism, i.e. the engaging contacts, that leads to wear and stresses which are functionally bound to an overall stiffens of such a system. Moreover, conventional mechanisms usually may cause complexity and difficulty during an installation phase where in order to assemble the system several steps for alignment has to be fulfilled so that correct and secure contact engagement can be provided.

The described contact unit enables to counteract the aforementioned difficulties due to an implementation of a linearly guidance of the contact element, which allows for both the reduction of contact stress via an implementation of interacting contacts as well as for contacts retraction when assembled and engaged to corresponding fixed contacts.

According to an embodiment of the contact unit the contact element comprises a rotatable roller to make electrical contact to a contact element of a contact device for the on-load tap changer. Using a rotatable and electrically conductive roller allows for reduced friction and contributes to low wear and stress with respect to engagement with corresponding contact elements of the contact device. Alternatively or additionally, the contact element of the contact unit comprises a slider to make electrical contact to a corresponding contact element of a contact device.

According to a further embodiment the drive and guiding means comprise a tensioned or biased spring configured to act a spring force driving the contact element of the contact unit away from the connector body. Such a spring element realizes a simple and low-cost component to reliably provide a force pushing the contact element in the desired direction, towards a corresponding stationary contact element of a contact device, for example. Moreover, alternative or additional force acting elements may be used as well to act on the contact element of the contact unit.

The drive and guiding means comprise at least one linear bearing and an axis arranged inside the bearing which are configured to provide linearly guided movement of the contact element of the contact unit. In combination with the aforementioned spring element, a spring-loaded and linearly guided contact unit is feasible which causes a relative low friction and thus contributes to low wear and stress while enabling a reliable electrical contact engagement and secure current conduction and/or power transfer.

According to a further embodiment the drive and guiding means comprise two or more linear bearings and corresponding axes arranged inside the associated bearing. The contact element of the contact unit is arranged between the bearings to provide a stable and reliably guided movement of the contact element towards a corresponding contact element of a contact device.

According to an embodiment a contact system for an on-load tap changer comprises an embodiment of the described contact unit and a contact device with a contact terminal and a contact element configured to provide power supply due to engagement and interaction of the contact elements of the contact unit and the contact device. As a result of that the contact system comprises an embodiment of the contact unit as described above, features and characteristics of the contact unit are also disclosed with respect to the contact system and vice versa.

The contact unit may realize a moving contact arranged at a movable contact element of the contact system whereas the contact device may realize a stationary contact assembled at a predetermined position. Thus, due to movement of the contact unit towards the stationary contact device electrical engagement can be set up to enable power transfer. Alternatively, the contact unit may realize a positionally fixed contact whereas the contact device may be movably arranged such that an electrical engagement can be set up by movement of the contact device towards the contact unit. In general, the contact unit and the contact device of the contact system are configured to be movable relative to each other.

The contact device is configured in coordination with the contact unit to provide low friction and reduced mechanical stresses and to contribute to reliability, ease of assembly and even self-alignment of the interacting contact elements. For instances, the contact element of the contact device comprises a curved shape and extends along a ring section. Such a configuration can be beneficial with respect to a movable contact unit moving along a respective a circular path.

According to a further embodiment the contact elements of the contact unit and the contact device comprise a respective contact surface configured to face each other along the direction the contact element of the contact unit is movable.

According to an embodiment an on-load tap changer for setting a gear ratio comprises a rotatable contact ring, and an embodiment of the aforementioned contact system including the contact unit and the contact device. The contact device is configured stationary and the contact unit is connected to the rotatable contact ring and thus configured movable. The contact element of the contact unit is driven and linearly guided in the direction away from the connector body and towards the stationary contact element of the contact device.

As a result of that the on-load tap changer comprises an embodiment of the contact system as described above, features and characteristics of the contact system and the contact unit as well as the contact device are also disclosed with respect to the on-load tap changer and vice versa.

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

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.

<FIG> illustrates a perspective view of components for an on-load tap changer for a transformer which allows for variable turn ratios to be selected in distinct steps without a supply interruption during a tap change. The on-load tap changer comprises one or more rotatable contact rings <NUM> movable with respect to a longitudinal axis L configured to enable tap change and power transfer. The on-load tap changer further comprises a plurality of contact units <NUM> and contact devices <NUM> configured and arranged in coordination with each other to enable power transfer due to engagement of corresponding electrical contact elements <NUM> and <NUM> (see also <FIG>).

One contact unit <NUM> and a corresponding contact device <NUM> realize a contact system <NUM> for the on-load tap changer. With respect to the embodiment shown in <FIG> there is a respective contact unit <NUM> arranged to a corresponding contact ring <NUM> via a contact body <NUM> of the contact unit <NUM>. Due to its arrangement at the rotatable ring <NUM> the contact unit <NUM> realizes a movable contact whereas the contact devices <NUM> realize stationary contacts fixed in position. Thus, due to rotation of one of the contact rings <NUM> the correspondingly arranged contact unit <NUM> is rotated as well towards one of the contact devices <NUM> to electrically engage the contact elements <NUM> and <NUM>.

<FIG> shows a perspective view of components of the contact unit <NUM> and its assembly options. The contact unit <NUM> comprises the connector body <NUM> and two contact holders <NUM> coupled to each other. The connector body <NUM> is configured to connect the contact holders <NUM> and to connect the contact unit <NUM> to the contact ring of the on-load tap changer. The contact unit <NUM> further comprises two contact elements <NUM> which are formed as electrical rollers belonging to the respective contact holder <NUM>. The contact element <NUM> are coupled to the contact holder <NUM> fixed but rotatable due to an axis <NUM>. The contact element <NUM> of the contact unit <NUM> is configured to make electrical contact to a corresponding contact element <NUM> of the contact device <NUM> which further comprises an electrical contact terminal <NUM> (see <FIG>).

The contact unit <NUM> further comprises drive and guiding means for each contact holder <NUM>. The respective drive and guiding means include two linear ball or sliding bearings <NUM>, two axes <NUM> and a spring <NUM> coupled to the contact holder <NUM> such that the respective contact element <NUM> is spring-loaded and movable driven and linearly guided in a corresponding direction T1 or T2 away from the connector body <NUM> and towards the contact element <NUM> of the stationary contact device <NUM>.

The contact body <NUM> realizes a main block which connects the two roller contact holders <NUM> by means of the axes <NUM> and locking elements <NUM> formed as locking screws, for example. The linear movement of the respective contact holder <NUM> along its associated direction T1 or T2 is provided by the linear ball bearings <NUM> and retaining motion/force is applied by the inserted spring <NUM>. The roller contact element <NUM> comprises a contact surface <NUM> configured to contact a corresponding contact surface <NUM> of the contact element <NUM> of the contact device <NUM>.

The electrical contact between the contact device <NUM> and a selector contact <NUM> of the contact unit <NUM> is provided due to contact of the contacting surfaces <NUM>, <NUM> between the fixed contact element <NUM> and the movable selector contact element <NUM>. This is achieved via the contact element <NUM> which is realized as a rotatable roller with respect to the embodiment as illustrated in <FIG>. Alternatively, according to an embodiment the contact element <NUM> can be realized as a nonrotatable slider as shown in <FIG>. Both, the roller or the slider comprise a curved shape configured in coordination with the curved shape of the contact element <NUM> of the contact device <NUM>. This enables a secure and reliable electrical engagement of the contact element <NUM> and <NUM> with low friction and low mechanical stress, respectively.

The contact element <NUM> is retained in its place due to the axis <NUM>. Current is evenly distributed via flexible connections <NUM> and connection terminals <NUM>. When force is applied to the roller or slider contact element <NUM> the contact holders <NUM> translate via their axes <NUM> and linear ball bearings <NUM> and the spring <NUM> deforms and the entire contact holder <NUM> retracts. This movement reduces overall wear on the roller or slider contact element <NUM>, friction is reduced between the fixed contact element <NUM> and the movable contact element <NUM> and linear guidance is applied due to the linear ball bearings <NUM>.

The described linearly guided roller/slider contact system <NUM> realizes a carrier of movable contacts in a selector of the on-load tap changer and allows for a stable and reliable mechanism of electrical engagement and power transfer and contributes to low wear and mechanical stress of the interacting components. The retractability of the contact system <NUM> enables an easier engagement and self-adjustment during assembly and operation as well.

Claim 1:
Contact unit (<NUM>) for an on-load tap changer, comprising:
- a connector body (<NUM>) and a contact holder (<NUM>) coupled to each other, wherein the connector body (<NUM>) is configured to connect the contact holder (<NUM>) to a contact of the on-load tap changer,
- a contact element (<NUM>) coupled to the contact holder (<NUM>) and configured to make electrical contact to a contact element (<NUM>) of a contact device (<NUM>) for the on-load tap changer, and
- drive and guiding means (<NUM>, <NUM>, <NUM>) coupled to the contact holder (<NUM>) such that the contact element (<NUM>) is movable driven and linearly guided in a direction (T1, T2) away from the connector body (<NUM>), characterized in that the drive and guiding means comprise at least one linear ball bearing (<NUM>) and an axis (<NUM>) arranged inside the bearing (<NUM>) configured to provide linearly guided movement of the contact element (<NUM>) of the contact unit (<NUM>), and in that the contact unit (<NUM>) comprises:
- a further contact holder (<NUM>) coupled to the connector body (<NUM>),
- a further contact element (<NUM>) coupled to the further contact holder (<NUM>) and configured to make electrical contact to a contact element (<NUM>) of a contact device (<NUM>) for the on-load tap changer, and
- further drive and guiding means (<NUM>, <NUM>, <NUM>) coupled to the further contact holder (<NUM>) such that the further contact element (<NUM>) is movable driven and linearly guided in a direction (T1, T2) away from the connector body (<NUM>), and
wherein the contact holders (<NUM>), the contact elements (<NUM>) and the corresponding drive and guiding means (<NUM>, <NUM>, <NUM>) are coupled to the connector body (<NUM>) such that the directions (T1, T2) the corresponding contact elements (<NUM>) are movable along enclose a predetermined angle.