Title of Invention

TAP CHANGER

Abstract

The present invention relates to a tap changer for uninterrupted switching over between different winding taps of a tapped transformer, comprising a fine selector and optionallY a preselector for power-free selection of the winding tap to be switched over to subsequently, a load changeo'ver switch for subsequent rapid switching over from the previous winding tap to the selected winding tap with transient switching in of at least one switching-over resistance, and a drive for activating not only the fine selector and optional preselector, but also the loac changeover switch on each switching-over, characterized ir that the drive comprising at least one torque motor in the form of a three-phase brushless synchronous motor witt permanent excitation.

Full Text

Tap changer The invention relates to a tap changer for uninterrupted switching-over between different winding taps of a regulating transformer. Tap changers are devices, which have been known for decades, for voltage regulation and ensuring a high quality of electrical energy. According to their principle of operation they can be divided into resistance quick-action switches and reactor switches. The principle of all resistance quick-action switches goes back to German Reich Patent No. 474 613 which was granted in 1929 and which describes for the first time the principle of abrupt uninterrupted switching-over between different winding taps by means of transiently swrtched-in switch-over resistances. Tap changers based on this principle are known in numerous forms of embodiment. A typical representative is the type 'M' described in the company publication 'Stufenschalter Typ M - Inspektionsanweisung" of the applicant. This on-load tap changer comprises a tap selector for load-free preselection of that winding tap which is to be switched over to, and a load changeover switch, which is arranged spatially thereabove in a separate oil vessel, for the actual uninterrupted switching over. The actuation of this on-load tap changer is carried out by a motor drive with an electric motor which, if it is placed in operation for an intended switching over, on the one hand continuously actuates the fine selector and optionally a preselector and on the other hand draws up a force store of the load changeover switch. The motor drive is in that case seated, in spatial terms, laterally outside the transformer. The energy is conducted to the tap changer by way of linkage, angle drive, transmission stages and mechanical Maltese transmission. If the force store has reached its end setting, i.e. it is fully drawn up, the lock thereof, which was fixed until then, is released and it executes an abrupt movement by which rt actuates the load changeover switch. The drive trains of this known on-load tap changer are schematically illustrated in Figure 1, A modified such onload tap changer is shown in Figure 2, which has, instead of a usual preselector, a multiple coarse selector; this arrangement is similarly known to the expert, A further tap changer is described in the company publication 'Lastwahler Typ V -Inspektionsanweisung' of the applicant. In the case of this type V constructed as a load selector the preselection of the respective winding tap, which is to be switched over to, and the components for this subsequent switching over are constructionally combined. In this case as well there is provided a motor drive with the above-described spatial arrangement, which initially draws up the force store. After complete drawing-up thereof and subsequent triggering a rotatabie switching shaft is actuated which switches over rapidly and without interruption from one fixed contact to another, adjacent fixed contact, which are each electrically connected with a respective winding tap. A typical gear train of such a known load selector is schematically illustrated in Figure 3. A tap changer of the reactor switch type is known from, for example, DE-PS 40 11 019 and DE-PS 41 26 824 as well as the company publication 'Load Tap Changer Type RMV-r of Reinhausen Manufacturing Inc., Alamo, Tennessee, USA. It comprises two load branches which are preselectable by a tap selector and between which is arranged, in each phase to be switched, a switch, here a vacuum switching cell Each vacuum switching cell can be bridged over by a bypass contact which in turn connects at least one of the two load branches with the load shunt. Actuation of each of the vacuum switching cells takes place by way of a respective force store which is drawn up by the movement of the drive shaft. A double-sided cam disc, which is rotated through 180 degrees by the drive shaft in each switching step, is physically arranged, for each phase to be switched, between the bypass contact and the force store. Disposed on the side of the double-sided cam disc facing the bypass contact is a groove for controlling the bypass contact and on the other side a further groove for controlling the force store driving the vacuum switching cells. The control of the force store is in that case of such a kind that in each switching step it is stressed once and then released and in that case actuates the vacuum switching cells. The actuation of this tap changer takes place by a motor drive with an electric motor, which, if it is set in operation in the case of an intended switching over, on the one hand continuously actuates the selector contacts and on the other hand by way of the described contact disc not only similarly continuously actuates the bypass contact, but also draws up the described force store. If the force store has reached its end setting, i.e. it is completely drawn up, the locking thereof, which until then is fixed, is freed and it executes an abrupt movement by which it actuates the load changeover switch. The drive trains of this known tap changer are schematically illustrated in Figure 7. A further tap changer of the reactor switch type is already known from DE-PS 197 43 864, in which, moreover, the functional differences between reactor switches on the one hand and resistance fast-action switches are illustrated in explanatory manner. In the case of this known tap changer fixed selector contacts, which can be electrically contacted by two movable selector contacts, are provided for each phase andT in addition, preselector contacts are provided for each phase. Moreover, bypass contacts are again arranged for each phase and in each instance a vacuum switching cell is actuable by means of a force store. A single drive mechanism for actuation of all movable contacts and all vacuum switching cells in the appropriate switching sequence is arranged in a separate, lateral housing part, wherein this single drive acts on the individual components by means of insulating shafts extending through the housing. A typical drive train of this known tap changer is illustrated in Figure 8. In the known tap changers the drive takes place by an electric motor drive. Such a drive is described in, for example, WO 98/38661. All mechanical and electrical subassemblies required for drive of the tap changer are combined in such a known motor drive. Important mechanical subassemblies are, in that case, the load transmission and the control transmission. The load transmission directly actuates the tap changer; for that purpose it comprises an appropriately dimensioned electric motor The control transmission contains a cam disc which rotates through a complete rotation in each switching-over of the tap changer. The cam disc in turn comprises a plurality of switching cams for mechanical actuation of numerous cam switches or cam-actuated contacts. The control transmission moreover contains means for indication of the tap setting or the switching step. Different current circuits belong to the electrical subassemblies in the motor drive. Thus, there is present a motor power circuit by which the terminals of the electric drive motor are connected with the current supply by way of motor circuitbreakers, brake circuitbreakers and other switching means. Moreover, a control power circuit and various reporting circuits and trigger circuits for a motor circuitbreaker switch are present. The control of the motor drive itself is carried out according to the principle of step-switching, i,e. an adjusting process by one switching step is initiated by a single control signal and thereafter constrainedly taken to a conclusion; the driven shaft of the motor drive, which is coupled with the drive shaft of the tap changer, in that case executes a precisely predetermined number of revolutions. Moreover, the known motor drive also comprises, apart from other safety devices, a run-on protection device preventing the motor drive from running through to the end setting in the event of failure of the described step control. The described known motor drive has, in common with the downstream Maltese transmission in the tap changer of the resistance quick-action switch type, a number of functions to fulfil: generation of a rotational torque with subsequent conversion into a movement for the tap selector transmission as well as stepping-up/stepping-down of the torque drawing-up of a force store conversion of a continuous movement into a step movement fixing of the switching element after a completed switching step report of setting mechanical end abutment function. Overall, not only the conventional motor drive, but also the downstream transmission are complicated in construction and costly in production, since they are necessarily highly accurate, and in common with the force store they usually represent the most expensive part of the entire tap changer. In the case of a tap changer of the reactor switch type the described known motor drive in common with the downstream transmission, particularly the Maltese transmission as well as a lever reversing transmission has to fulfil the following functions in the tap changer generation of a rotational torque with subsequent conversion into a movement for the fine selector as well as, separately thereof, the preselector actuation of the bypass contacts drawing-up of a force store for subsequent actuation of the vacuum switching cells report of setting mechanical end abutment function. Overall, in this connection again not only the conventional motor drive, but also the downstream transmissions are complicated in construction and expensive in production, since they are necessarily highly precise, and together with the force store they usually • represent the most expensive part of the entire tap changer. The object of the invention is to drastically simplify the basic construction of tap changers such as they have been established for decades and become fixed in the state of the art. This object is fulfilled by a tap changer with the features of the accompanying patent claims 1, 6 and 11; the subclaims concern respectively advantageous possible developments and modifications of the invention. The invention is based on the broad inventive idea to employ at least one torque motor, which is known per ses as a constituent of the drive train or driveline of a tap changer. Such torque motors are known from, for example, the publication 'BQrstenlose Torque-Motoren' of the company ETEL Such a known torque motor functions on the same physical basis as a linear drive, only that the stator, which here lies flat, is wound to form a circle. A torque motor is therefore a servo-drive optimised for a high torque; modern realisations are, in electrical terms, three-phase brushless synchronous motors with permanent excitation. They are currently used in machine-tool construction. No attempt had previously been undertaken to implement them in tap changers or render them usable in principle for drive of a tap changer. There was, in fact, in the past already an attempt, described in DD Patent Specification 58 131 of 1967, to depart from the conventional drive concept of the tap changer as was described further above. This concerns a solution in which a tap selector is formed from as.many hydraulically actuated individual drive modules as taps are provided, so that it was possible to switch between any individual winding taps and not only between adjacent winding taps. However, due to the high functional risk, for example the risk of aging of feed lines and seals, this hydraulic solution has not been realised. In addition, various other drive mechanisms have in general been proposed for switching apparatus. Thus, for example, EP 996 135 relates to a magnetic travelling-wave drive for switchgear and WO 99/60591 and WO 00/05735 describe drives in the manner of a stacking motor for switchgear. These solutions are also not usable for tap changers without further measures, since they do not allow abrupt movements and are overall problematic for realisation of dynamic processes, as well as at low temperatures. Finally, a controlled drive for switchgear, which, however, is similarly unsuitable for a tap changer, has been proposed in WO 01/06528. References with respect to the use in accordance with the invention of at least one torque motor at a tap changer cannot, however, be inferred from any of these efforts for further development of the drive technology of switchgear. According to the invention such a torque motor as a constituent of a tap changer can be provided at different installation locations. It can be arranged outside the transformer space and, in particular, at the top on the transformer or also laterally at the transformer. Moreover, it can also be arranged within the transformer space and there replace the force store of the load changeover switch, the fine selector drive or also a preselector drive or even several of these subassemblies. The use in accordance with the invention of one or more torque motors, whereby newly structured positioning units are formed, has numerous advantages. At the outset, neither clutch nor separate transmission is required, which considerably reduces the number of parts. Moreover, a more compact construction is realised. Resulting through the low elasticities is a high degree of rigidity and through the low masses and the low moment of inertia a high level of dynamics, with the possibility of also being able to realise abrupt movements and thus of rendering a conventional force store redundant Finally, by way of a suitable control any desired switching step can be imposed independently of the specifically effective counter-moment, whereby, for example, temperature influences can be largely excluded. The invention will be explained in more detail by way of example in the following by reference to schematic illustration, wherein: Figures 1 to 3 show already explained drive trains of known tap changers of the resistance quick-action switch type, in schematic illustration; Figures 4a, 4b and 5a, 5b show schematic possibilities of the use according to the invention of at least one torque motor in an on-load tap changer of this type, Figures 6a, 6b show schematic possibilities of the use according to the invention of at least one torque motor in a load selector of this type, Figures 7 and 8 show already explained drive trains of known tap changers of the reactor switch type, in schematic illustration, Figures 9a, 9b, 10a, 10b and 11a, 11b show schematic possibilities of the use according to the invention of at least one torque motor in a first tap changer of this type and Figures 12a, 12b show schematic possibilities of the use according to the invention of at least one torque motor in a second tap changer of this type. In the following schematic illustrations the subassemblies according to the invention, which each contain a torque motor, are respectively termed "positioning unit" and shaded grey. Cursive mention is made in the respective field of the concrete function which the respective torque motor, Le. the respective positioning unit, executes. In Figure 4a there is shown - for the constructional location of a tap changer outside the transformer - that here in accordance with the invention a torque motor replaces the former motor drive and the downstream transmission and acts directly on the force store of the load changeover switch, the Maltese transmission of the fine selector and optionally also of the preselector. Below that there is schematically illustrated a further form of embodiment of the invention in which a torque motor additionally also replaces the former force store according to the state of the art and the associated transmission in such a manner that this new positioning unit with torque motor acts directly on the Maltese transmission of the fine selector and optionally also of the preselector as well as directly actuates the load changeover switch. This second form of embodiment can also be arranged entirely within the transformer, as is shown in Figure 4b. Further forms of embodiment of the invention are schematically illustrated in Figures 5a and 5b. In Figure 5a there is shown, for an installation location of the tap changer outside the transformer, that a first torque motor according to the invention directly actuates the load changeover switch in that it also makes redundant the former force store (lefthand positioning unit); a further torque motor (righthand positioning unit) directly actuates the Maltese transmission of the fine selector and optionally of the preselector. By contrast to the forms of embodiment of the invention in Figures 4a and 4b in which in each instance only a single torque motor is provided, several such positioning units with torque motors are thus shown here. Below that a further modified form of embodiment of the invention is illustrated, which provides in total three such torque motors: a first positioning unit according to the invention (lefthand) directly actuates - with avoidance of a former force store - the load changeover switch, a second positioning unit (centre) directly actuates the fine selector and a third positioning unit (righthand) directly actuates the preselector insofar as such is present In Figure 5b these forms of embodiment of the invention are shown in the case of an installation location of the tap changer within the transformer. It is also possible within the scope of the invention to physically separate the load changeover switch from the fine selector and optional preselector, i.e. to separately arrange the two subassemblies of the tap changer at different positions. Moreover, it is possible to also separately drive the fine selector and optional preselector by means of a stepping motor known per se. Since the selectors are actuated slowly and continuously, the disadvantage of the known stepping motors, namely the poor dynamic behaviour thereof, does not have a disturbing effect here. Possible forms of embodiment of the invention in the case of a tap changer of the on-load selector type are shown in Figures 6a and 6b in the same schematic form of illustration. Figure 6a again relates to the arrangement of the tap changer outside the transformer and Figure 6b to such within the transformer. The upper illustration respectively clarifies the form of embodiment in which a torque motor directly actuates the force store, which again in known manner abruptly rotates the switching column and in addition optionally actuates the preselector. The centre illustration respectively shows a form of embodiment of the invention in which the torque motor also takes over the function of the former force store and directly abruptly rotates the switch column. The lower illustration finally respectively shows a form of embodiment with two separate torque motors in such a way that the first of these novel positioning units directly abruptly rotates the switch column and the second positioning unit separately actuates a possibly present preselector. In Figure 9a there is shown, for an arrangement of the tap changer outside the transformer, in the upper half of the illustration that here in accordance with the invention a torque motor replaces the former motor drive and directly acts on the drive shaft and the reversing transmission. The drive shaft in turn then further actuates, in each phase, preselector, fine selector, bypass contact and - by way of the force store (not illustrated) -the vacuum switching cell. Below that there is schematically illustrated a further form of embodiment of the invention in which a torque motor in each phase respectively forms a new positioning unit which also embraces the former reversing transmission. Figure 9 shows the corresponding arrangements for a tap changer arranged in the transformer. Further forms of embodiment of the invention are again schematically illustrated in Figures 10a and 10b. In Figure 10a it is shown in the upper part that in each phase a first torque motor simultaneously actuates, by means of a transmission, preselector and fine selector and in each instance a second torque motor actuates the bypass contact as well as - again by the force store able to be drawn up - the vacuum switching cell. Below that there is illustrated a further form of embodiment of the invention which in each phase has, in total, three such torque motors which in common with the corresponding transmissions form independent positioning units and directly act in each instance on the preselector or the fine selector or not only the bypass switch, but also the force store of the vacuum switching cell Figure 10 again shows these forms of embodiment for an arrangement of the tap changer in the transformer. Modified forms of embodiment of the invention are again shown in Figures 11a and 11b. In these forms of embodiment the previously fundamental association of the individual components with respective phases to be switched is broken up. A first torque motor here actuates the preselectors of all three phases, a second torque motor actuates the fine selectors of all three phases and a third torque motor actuates not only the bypass contacts, but also the force stores and thus vacuum switching cells of all three phases. Possible forms of embodiment of the invention are shown in Figures 12a and 12b in the same schematic form of illustration in the case of a further known tap changer according to category, the known drive train of which according to the state of the art was illustrated in Figure 8 and already explained. The upper illustrations in each instance show an embodiment in which a single torque motor respectively actuates, by way of intermediate transmissions, the preselector, the fine selector and at the same time bypass contact and vacuum switching cell, again by way of a force store. The centre illustrations disposed thereunder each show a form of embodiment in which two such torque motors are provided in each phase. One of them actuates not only preselector, but also fine selector, and the other actuates not only bypass contact, but also force store of the vacuum switching cell. Finally, right at the bottom there is shown a respective further variant in which three torque motors for actuation are provided in each phase: one for the preselector, one for the fine selector and one for the bypass contact and the force store of the vacuum switching cell. It is also possible here to break up the arrangement by phase and to undertake, for all illustrated arrangements in Figures 12a and 12b, actuations of the individually described components simultaneously for all three phases by the respective positioning unit The explained Figure 12 further relates to the arrangement of the tap changer outside the transformer and Figure 12 to arrangement thereof in the transformer Patent Claims 1. Tap changer for uninterrupted switching over between different winding taps of a tapped transformer according to the principle of a resistance quick-action switch, consisting of a fine selector and optionally a preselector for power-free selection of the winding tap to be switched over to subsequently, further consisting of a load changeover switch for subsequent rapid switching over from the previous winding tap to the preselected winding tap with transient switching in of at least one switching-over resistance, wherein not only fine selector and optional preselector, but also load changeover switch are actuable by a drive on each switching-over, characterised in that at least one torque motor constructed as a three-phase brushless synchronous motor with permanent excitation is provided as drive. 2. Tap changer according to claim 1, characterised in that the at least one torque motor actuates not only a known force store of the load changeover switch, but also the fine selector and optional preselector. 3. Tap changer according to claim 1, characterised in that at least one torque motor directly actuates not only the load changeover switch, but also the fine selector and optional preselector. 4. Tap changer according to claim 1, characterised in that at least one first torque motor respectively directly actuates the known force store of the load changeover switch and at least one second torque motor respectively actuates the fine selector and optional preselector. 5. Tap changer according to claim 1, characterised in that at least one first torque motor respectively directly actuates the load changeover switch, at least one second torque motor respectively directly actuates the fine selector and optionally at least one third torque motor respectively actuates the preselector. 6. Tap changer for uninterrupted switching-over between different winding taps of a tapped transformer according to the principle of a resistance quick-action switch, consisting of a load selector for simultaneous selection of the winding tap which is to be switched over to, as well as for rapid switching-over from the previous winding tap to the preselected winding tap with transient switching in of at least one switching-over resistance, wherein an abruptly actuable switching element particularly a switch column, serves for the switching over, characterised in that at least one torque motor constructed as a three-phase brushless synchronous motor with permanent excitation is provided as drive. 7. Tap changer according to claim 6, characterised in that the at least one torque motor directly actuates a known force store which in turn abruptly moves the switching element in known manner and optionally actuates a preselector. 8. Tap changer according to claim 6, characterised in that the at least one torque motor directly abruptly moves the switching element and optionally actuates a preselector. 9. Tap changer according to claim 6, characterised in that at least a first torque motor directly abruptly moves the switching element and optionally at least a second torque motor directly actuates the preselector. 10. Tap changer according to one of claims 1 to 5, characterised in that the load changeover-switch on the one hand and the fine selector and optional preselector on the other hand are arranged to be physically separate and/or the fine selector and optional preselector is or are drivable separately by at least one stepping motor. 11. Tap changer for uninterrupted switching-over between different winding taps of a tapped transformer according to the principle of a reactor switch, consisting of a fine selector with two load branches, between which a vacuum switching cell is arranged in each phase to be switched, consisting of a preselector and of a bypass contact, which bridges over the vacuum switching cell each time and by which in turn at least one of the two load branches is connectible with the load shunt, as well as a force store which actuates the respective vacuum switching cell, wherein a single drive is provided which actuates all stated components by means of various transmissions and by drive shafts, characterised in that at least one torque motor constructed as a three-phase brushless synchronous motor with permanent excitation is provided as drive, 12. Tap changer according to claim 11, characterised in that the at least one torque motor actuates all drive shafts. 13. Tap changer according to claim 11, characterised in that three separate torque motors are arranged in such a manner that each of them actuates the components of one phase, namely preselector, fine selector, bypass contact and force store of the associated vacuum switching cell. 14. Tap changer according to claim 11, characterised in that two separate torque motors are provided for each phase, of which one actuates preselector and fine selector and the other actuates bypass contact and force store of the vacuum switching cell. 15. Tap changer according to claim 11, characterised in that three separate torque motors are provided for each phase, of which respectively one actuates the preselector, one actuates the fine selector and one actuates not only the bypass contact, but also the force store of the vacuum switching cell. 16. Tap changer according to claim 11/characterised in that in total three separate torque motors are provided, of which one actuates the preselectors of all three phases, another actuates the fine selectors of all three phases and the third actuates not only the bypass contacts, but also the force stores of the vacuum switching cells of all three phases.

Documents:

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