Patent Description:
On-load tap changers, for example, are built into power transformers and regulate their voltage under-load, i.e. without interrupting the power supply to consumers.

<CIT> relates to a power tap changer which has a first Maltese-cross mechanism for opening the moving contacts from stationary contacts before the movement of the moving contacts in conjunction with control elements, and a second Maltese-cross mechanism for moving the moving contacts to adjacent, stationary contacts.

<CIT> relates to a selector for an on-load tap changer which contains an upper metal flange with a body and a lower metal flange with cage-like segments made of insulating material. On the segments there are mounted odd and even stationary contact elements.

It is desirable to provide a switching system for an on-load tap changer that is reliable and allows an easy switching as well as a corresponding on-load tap changer and a corresponding method for switching a tap connection of an on-load tap changer.

According to the invention a switching system for an on-load tap changer comprises:.

The switching system allows an application of a Geneva mechanism in an on-load tap changer. During operation, the rotatable driving wheel rotates about its longitudinal axis and thereby rotates the protrusion. When the protrusion is connected to the recess, the driving force of the driving wheel is transmitted to the rotatable ring. Thus, the connector is rotated and a connection with a specific tap of the tap changer is possible.

Only the rotatable ring needs to be moved to change the position of the connector. The rotatable ring rotates around a phase unit and other static elements of the on-load tap changer. For example the rotatable ring rotates relative to the holder and the diverter switch of the phase of the on-load tap changer. This allow a reduction of the complexity of the driving mechanism and makes an increase in reliability possible. Furthermore, a large number of individual positions for the connector is possible and thus more tap positions are possible. Since only the rotatable ring needs to be moved, the masses that need to be moved for a tap change are reduced. Thereby flywheel energy is reduced and the requirements for damping are reduced.

According to an embodiment the switching system comprises a drive shaft. The drive shaft is rotatable to rotate the driving wheel. The drive shaft is arranged eccentrically to the rotatable ring. The eccentric orientation of the drive shaft allows an efficient use of space inside the housing.

According to a further embodiment the switching system comprises a bearing arrangement. The bearing arrangement is configured to guide the rotation of the rotatable ring around the holder. Thus, the friction between the rotatable ring and the holder can be reduced and thereby the force needed to move the rotatable ring can be reduced.

According to a further embodiment the bearing arrangement comprises a plurality of bearings. The bearings are coupled to the holder. For example, the bearings comprise ball bearings that are arranged to support the rotatable ring with respect to the holder and to reduce a friction between the rotatable ring and the holder. Thus, the rotatable ring is fastened, attached and supported on the holder in a way that a reliable rotational movement and positioning relative to the housing is possible.

According to a further embodiment, the rotatable ring comprises a current carrier ring. The current carrier ring is electrically connected with the connector. For example, the current carrier ring is a copper ring or comprises copper or another electrically conductive material. The rotatable ring further comprises a drive ring. A drive ring is fixed relative to the current carrier ring and is rotatable by the driving wheel. For example, the drive ring is made out of an electrically insulating material. The drive ring is configured to transmit a rotational force of the driving wheel vent to electrically insulate the drive ring from the current carrier ring.

According to a further embodiment, the drive ring comprises an intermediate ring and a Geneva ring. The Geneva ring comprises the recess. For example, the Geneva ring comprises a multitude of recesses, for example three recesses, four recesses, five recesses, six recesses or more recesses. The intermediate ring is arranged between the Geneva ring and the current carrier ring to transmit a rotational force from the Geneva ring to the current carrier ring. Thus, the Geneva ring can be designed to beneficially interact with the driving wheel and the protrusion. The driving wheel and the Geneva wheel form an internal Geneva mechanism. The intermediate ring allows reliable support of the rotatable ring on the holder. Furthermore, the intermediate ring realizes the electrical insulation.

According to a further embodiment, the switching system comprises a further Geneva mechanism. For example, the further Geneva mechanism is configured and designed like the first Geneva mechanism described herein. The Geneva mechanism and the further Geneva mechanism correspond to each other in a way that they allow a rotation of the respective rotatable ring by a Geneva mechanism. For example, the Geneva mechanism is arranged to connect the respective connector to a tap at odd positions. The further Geneva mechanism, for example, is arranged to connect the respective connector to taps at even positions. For example, the respective rotatable rings of the Geneva mechanism and the further Geneva mechanism are turned alternately. The Geneva mechanism and the further Geneva mechanism, for example, are arranged axially offset from each other. For example, the drive shaft is arranged to rotate the driving wheels of both Geneva mechanisms and the Geneva mechanism and the further Geneva mechanism are arranged axially offset from each other along the longitudinal axis of the drive shaft.

According to the invention an on-load tap changer comprises a switching system according to at least one embodiment described herein. The on-load tap changer comprises the housing and the switching system is arranged inside the housing. The housing surrounds the rotatable ring coaxially. The on-load tap changer comprises the tap. The tap is fixed to the housing. For example, the on-load tap changer comprises a multitude of taps, in particular four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen or more taps.

According to a further embodiment the on-load tap changer comprises a number of taps. The rotatable ring comprises a number of recesses. The number of recesses corresponds to the number of taps. In case there are two Geneva mechanisms with two rotatable rings the number of recesses is equal to half the number of taps. The number of taps is divided equally between the rotatable ring of the Geneva mechanism and the further rotatable ring of the further Geneva mechanism. For example, the taps of the on-load tap changer are arranged into ring-shaped arrangements which are axially offset from each other. Each rotatable ring comprises the number of recesses such that it is able to contact the taps that are assigned to it.

According to the invention a method for switching a tap connection of the on-load tap changer comprises:.

Thereby only reduced masses have to be moved and thus the reliability of the positioning of the rotatable ring can be enhanced.

According to a further embodiment, the method comprises:.

Thus, switching operations between all odd and even positions are possible.

For example, the method for switching the tap connection is performed with the aid of a switching system described herein. Features and advantages described in connection with the switching system also apply to the method and the other way around.

The present invention will be further described with reference to the accompanying drawings, wherein:.

Throughout the drawings, identical components and components of the same type and effect may be represented by the same reference signs.

<FIG> shows an exemplary embodiment of an on-load tap changer <NUM> at least in parts.

The on-load tap changer is configured for regulation of the output voltage of a power transformer to required levels. With the aid of the on-load tap changer the turn ratios of the transformer can be altered. As cylindrical housing <NUM> surrounds a switching system <NUM>. Taps <NUM> to <NUM> (see also <FIG>) are arranged in circular forms at the housing. For example, the taps <NUM> to <NUM> are arranged in two circles that are offset from each other with respect to a longitudinal axis of the housing <NUM>.

A drive shaft <NUM> is arranged inside the housing <NUM>. The drive shaft <NUM> can be driven by a motor or another actuator to rotate around its longitudinal axis. The drive shaft <NUM> drives a first Geneva mechanism <NUM> and a further Geneva mechanism <NUM>. The further Geneva mechanism <NUM> may also be referred to as the second Geneva mechanism <NUM>. The first Geneva mechanism <NUM> and the further Geneva mechanism <NUM> are constructed in the same way. Therefore, features and advantages described in connection with one of the Geneva mechanisms <NUM>, <NUM> apply to the other one of the Geneva mechanisms <NUM>, <NUM>.

The Geneva mechanism <NUM> comprises a holder <NUM>. The holder <NUM> is immovable with respect to housing <NUM>. The holder is a ring-shaped element that is configured and designed to hold further elements of the Geneva mechanism <NUM> that may rotate to the housing <NUM> and the holder <NUM>.

The Geneva mechanism <NUM> comprises a rotatable ring <NUM>. The rotatable ring <NUM> is coupled to the holder <NUM>. The rotatable ring <NUM> is supported by the holder <NUM> such that the rotatable ring <NUM> is rotatable with respect to the holder <NUM>. Thereby, the rotatable ring <NUM> is rotatable relative to the housing <NUM> and the taps <NUM> to <NUM> as well. The housing <NUM>, the holder <NUM> and the rotatable ring <NUM> are arranged coaxially. The drive shaft <NUM> is arranged eccentrically inside the housing <NUM> offset to the longitudinal axis around which the rotatable ring <NUM> rotates.

The rotatable ring <NUM> comprises a current carrier ring <NUM>. The current carrier ring <NUM> is made out of an electrically conductive material and is configured to conduct electrical current.

The rotatable ring <NUM> comprises a drive ring <NUM>. The drive ring <NUM> comprises a plurality of recesses <NUM>. For example, the drive ring <NUM> comprises as many recesses <NUM> as taps <NUM> to <NUM> are arranged in the corresponding line at the housing <NUM>. For example, the drive ring <NUM> comprises five recesses <NUM> and five taps <NUM> to <NUM> are arranged at the circumference of the drive ring <NUM> at the housing <NUM> (see also <FIG>). For example, the recesses <NUM> are formed in a Geneva ring <NUM> that is part of the drive ring <NUM>. The Geneva ring <NUM> comprises the recesses and is connected to an intermediate ring <NUM> of the drive ring <NUM>. This allows a decoupling of the Geneva ring <NUM> from the current carrier ring <NUM> and an easy mounting.

The recesses <NUM> are open to an inner side of the rotatable ring <NUM>. The recesses <NUM> penetrate into the rotatable ring <NUM> from a central inner side. Thus, an internal Geneva mechanism <NUM> is realized.

The intermediate ring <NUM> is mechanically connected to the current carrier ring <NUM>. The Geneva ring <NUM> is mechanically connected to the intermediate ring <NUM>. The intermediate ring <NUM> is arranged between the current carrier ring <NUM> and the Geneva ring <NUM>.

A connector <NUM> is electrically and mechanically connected with the current carrier ring <NUM>. The connector <NUM> is configured and designed to couple with one of the respective taps <NUM> to <NUM> to conduct electrical current between the current carrier ring <NUM> and the respective tap <NUM> to <NUM>. By rotating the current carrier ring <NUM> together with the connector <NUM>, the connector <NUM> can be connected to a desired one of the respective taps <NUM> to <NUM>.

The rotation of the current carrier ring <NUM> is caused by a rotation of the drive shaft <NUM>. The rotation of the drive shaft <NUM> is transmitted to the rotatable ring <NUM> via a driving wheel <NUM>. The driving wheel <NUM> is connected to the drive shaft <NUM> and rotates together with the drive shaft <NUM>. The driving wheel <NUM> comprises a protrusion <NUM>. The protrusion protrudes radially with respect to the drive shaft <NUM>. The protrusion <NUM> is configured to interact and engage with the recess <NUM>. When the protrusion engages the recess <NUM>, the rotatable ring <NUM> rotates together with the driving wheel <NUM>. Thereby the connector <NUM> is moved from one tap, for example tap <NUM>, to the directly adjacent next tap, for example tap <NUM>. After the protrusion <NUM> leaves the recess <NUM>, the rotatable ring <NUM> stands still and the driving wheel <NUM> rotates relatively to the rotatable ring <NUM>. The rotation of the driving wheel <NUM> is not transmitted to the rotatable ring <NUM>. Thus, the driving wheel <NUM> rotates uniformly and the rotatable ring <NUM> rotates step-by-step between specific positions. These specific positions correspond to the positions of the taps <NUM> to <NUM>.

The second Geneva mechanism <NUM> is configured in a same way.

The second Geneva mechanism <NUM> comprises a second holder <NUM>. The holder second <NUM> is immovable with respect to housing <NUM>. The second holder is a ring-shaped element that is configured and designed to hold further elements of the second Geneva mechanism <NUM> that may rotate to the housing <NUM> and the second holder <NUM>.

The second Geneva mechanism <NUM> comprises a second rotatable ring <NUM>. The second rotatable ring <NUM> is coupled to the second holder <NUM>. The second rotatable ring <NUM> is supported by the second holder second <NUM> such that the second rotatable ring <NUM> is rotatable with respect to the second holder <NUM>. Thereby, the second rotatable ring <NUM> is rotatable relative to the housing <NUM> and the taps <NUM> to <NUM> as well. The housing <NUM>, the second holder <NUM> and second the rotatable ring <NUM> are arranged coaxially. The drive shaft <NUM> is arranged eccentrically inside the housing <NUM> offset to the longitudinal axis around which the second rotatable ring <NUM> rotates.

The second rotatable ring <NUM> comprises a second current carrier ring <NUM>. The second current carrier ring <NUM> is made out of an electrically conductive material and is configured to conduct electrical current.

The second rotatable ring <NUM> comprises a second drive ring <NUM>. The second drive ring <NUM> comprises a plurality of recesses <NUM>. For example, the second drive ring <NUM> comprises as many recesses <NUM> as taps <NUM>, <NUM> are arranged in the corresponding line at the housing <NUM>. For example, the second drive ring <NUM> comprises five recesses <NUM> and five taps <NUM>, <NUM> are arranged at the circumference of the second drive ring <NUM> at the housing <NUM>. For example, the recesses <NUM> are formed in a second Geneva ring <NUM> that is part of the second drive ring <NUM>. The second Geneva ring <NUM> comprises the recesses <NUM> and is connected to a second intermediate ring <NUM> of the second drive ring <NUM>. This allows a decoupling of the second Geneva ring <NUM> from the second current carrier ring <NUM> and an easy mounting.

The recesses <NUM> are open to an inner side of the second rotatable ring <NUM>. The recesses <NUM> penetrate into the second rotatable ring <NUM> from a central inner side. Thus, an internal Geneva mechanism <NUM> is realized.

The second intermediate ring <NUM> is mechanically connected to the second current carrier ring <NUM>. The second Geneva ring <NUM> is mechanically connected to the second intermediate ring <NUM>. The second intermediate ring <NUM> is arranged between the second current carrier ring <NUM> and the second Geneva ring <NUM>.

A second connector <NUM> is electrically and mechanically connected with the second current carrier ring <NUM>. The second connector <NUM> is configured and designed to couple with one of the respective taps <NUM>, <NUM> to conduct electrical current between the second current carrier ring <NUM> and the respective tap <NUM>, <NUM>. By rotating the current second carrier ring <NUM> together with the second connector <NUM>, the second connector <NUM> can be connected to a desired one of the respective taps <NUM>, <NUM>.

The rotation of the second current carrier ring <NUM> is caused by a rotation of the drive shaft <NUM>. The rotation of the drive shaft <NUM> is transmitted to the second rotatable ring <NUM> via a second driving wheel <NUM>. The second driving wheel <NUM> is connected to the drive shaft <NUM> and rotates together with the drive shaft <NUM>. The second driving wheel <NUM> comprises a second protrusion <NUM>. The second protrusion <NUM> protrudes radially with respect to the drive shaft <NUM>. The second protrusion <NUM> is configured to interact and engage with the recesses <NUM>. When the second protrusion <NUM> engages the recess <NUM>, the second rotatable ring <NUM> rotates together with the second driving wheel <NUM>. Thereby the second connector <NUM> is moved from one tap, for example tap <NUM>, to the directly adjacent next tap in the corresponding level. After the second protrusion <NUM> leaves the recess <NUM>, the second rotatable ring <NUM> stands still and the second driving wheel <NUM> rotates relatively to the second rotatable ring <NUM>. The rotation of the second driving wheel <NUM> is not transmitted to the second rotatable ring <NUM>. Thus, the second driving wheel <NUM> rotates uniformly and the second rotatable ring <NUM> rotates step-by-step between specific positions. These specific positions correspond to the positions of the corresponding taps <NUM>, <NUM>.

The further protrusion <NUM> of the second Geneva Mechanism <NUM> is offset to the protrusion <NUM> of the first Geneva mechanism <NUM>. Thus, the rotatable ring <NUM> of the first Geneva mechanism <NUM> and the further rotatable ring <NUM> of the further Geneva mechanism <NUM> can be moved successively one after another. When the protrusion <NUM> engages the recess <NUM> and moves the rotatable ring <NUM>, the further protrusion <NUM> runs at idle and does not move the further rotatable ring <NUM>. After disconnection of the protrusion <NUM> out of the recess <NUM>, the further protrusion <NUM> engages the further recess <NUM> and the further rotatable ring <NUM> moves. Thus, it is possible to drive the Geneva mechanism <NUM> and the further Geneva mechanism <NUM> with the same drive shaft <NUM>. The driving wheel <NUM> and the further driving wheel <NUM> are connected to the drive shaft <NUM> and move uniformly. For example, with the Geneva mechanism <NUM> the even numbers of the connections of the tap changer <NUM> are connectable and with the further Geneva mechanism <NUM> the odd numbers of the connections of the tap changer <NUM> are connectable.

More than two Geneva mechanisms with rotatable rings driven by driving wheels of the drive shaft <NUM> are possible, for example three, four or more Geneva mechanisms, like Geneva mechanism <NUM>.

<FIG> shows a bearing arrangement <NUM> that is arranged between the holder <NUM> and the rotatable ring <NUM>. For example, the intermediate ring <NUM> and the current carrier ring <NUM> are coupled together to the holder <NUM> to support the rotatable ring <NUM>. The bearing arrangement <NUM> is configured to reduce the friction between the holder <NUM> and the intermediate ring <NUM> and the current carrier ring <NUM> when the current carrier ring <NUM> together with the intermediate ring <NUM> rotates to the holder <NUM>. For example, the bearing arrangement <NUM> comprises a multitude of bearings <NUM>, for example four bearings or other amounts of bearings. The holder <NUM> and the rotatable ring <NUM> are coupled with each other by mountings <NUM>. For example, the mountings <NUM> are realized as bolts that provide a radial support for the rotatable ring <NUM> at the holder <NUM>. Alternatively or in addition, rolls or other mountings are provided to axially support the rotatable ring <NUM> at the holder <NUM>. The connection between the further holder <NUM> and the further rotatable ring <NUM> is realized correspondingly.

<FIG> shows a flowchart of a method for switching a tap connection of the on-load tap changer <NUM> according to an embodiment.

In step S1 the driving wheels <NUM>, <NUM> are rotated.

One of the protrusions <NUM>, <NUM>, for example the further protrusion <NUM>, couples to the corresponding recess <NUM>, <NUM>, for example to the further recess <NUM> (step S2). In this example, the protrusion <NUM> is not connected to the recess <NUM> and runs at idle.

The connection of the further protrusion <NUM> with the further recess <NUM> leads to a rotation of the further rotatable ring <NUM> (step S3). The rotatable ring <NUM> is not rotated and keeps its position.

In step S4 the further connector <NUM> rotates driven by the rotation of the further rotated ring <NUM> relative to the housing <NUM>. Thereby the further connector <NUM> decouples from one of the taps and connects with the next one of the corresponding taps, for example tap <NUM>.

When the driving wheels <NUM>, <NUM> rotate further, the further protrusion <NUM> rotates idle. The protrusion <NUM> of the driving wheel <NUM> engages the recess <NUM> of the rotatable ring <NUM> and thereby moves the connector <NUM> to another tap.

The on-load tap changer <NUM> with the Geneva mechanisms <NUM>, <NUM> reduces the complexity of the interconnected mechanisms and benefits the reliability of the overall system. The rotatable rings <NUM>, <NUM> rotate independently by means of the respective driving wheels <NUM>, <NUM> around the phase unit, for example the statically placed diverter switch of the phase of the on-load tap changer <NUM>. The tap changer <NUM> with the Geneva mechanisms <NUM>, <NUM> makes a large number of individual positions of the connectors <NUM>, <NUM> possible, for example six or more positions for each connector <NUM>, <NUM>. This also makes a more significant number of tap positions possible.

The holders <NUM>, <NUM> and the rotatable rings <NUM>, <NUM> are placed concentrically inside the insulation cylinder of the on-load tap changer <NUM>. The switching operations between all odd and even positions of the tap changer <NUM>, respectively the movement of the selector, are performed via the driving wheels <NUM>, <NUM>. The rotatable ring <NUM> of the first Geneva mechanism <NUM> and the protrusion <NUM> of the driving wheel <NUM> are angularly displaced in relation to the further rotatable ring <NUM> and the further protrusion <NUM> of the further driving wheel <NUM>. Thus, by performing a switching operation both rotatable rings <NUM>, <NUM> move in a subsequent motion and thereby select the relevant tap position.

The rotatable motion by the internal Geneva mechanisms <NUM>, <NUM> is implemented via the connection of the respective Geneva rings <NUM>, <NUM> to the respective intermediate rings <NUM>, <NUM> and the respective current carrier rings <NUM>, <NUM> which are embedded around the static fixed holders <NUM>, <NUM> via mountings <NUM> and the bearing arrangements <NUM>.

Claim 1:
A switching system for an on-load tap changer, comprising:
- a Geneva mechanism (<NUM>, <NUM>), wherein the Geneva mechanism (<NUM>, <NUM>) comprises:
- a holder (<NUM>, <NUM>), the holder (<NUM>, <NUM>) being fixed relative to a housing (<NUM>),
- a rotatable ring (<NUM>, <NUM>) with a recess (<NUM>, <NUM>), the rotatable ring (<NUM>, <NUM>) being supported by the holder (<NUM>, <NUM>) and being rotatable relative to the holder (<NUM>, <NUM>),
- a connector (<NUM>, <NUM>), the connector (<NUM>, <NUM>) being rotatable together with the rotatable ring (<NUM>, <NUM>) to electrically connect with a tap (<NUM>, <NUM>, <NUM>, <NUM>) of the tap changer (<NUM>),
- a rotatable driving wheel (<NUM>, <NUM>) with a protrusion (<NUM>, <NUM>), the protrusion (<NUM>, <NUM>) being coupleable with the recess (<NUM>, <NUM>) to rotate the rotatable ring (<NUM>, <NUM>), the driving wheel (<NUM>, <NUM>) being arranged inside the rotatable ring (<NUM>, <NUM>).