Abstract:
A switching device, for a wye-delta switch in a multiphase motor each phase having one motor winding having a connection pair and contact device (CD), has an electromagnetic drive for drive axle movement between three axial positions, the CD having first and second motor winding connection contacts (MWCC), phase connection contact (PCC), and movable contact bridge (MCB) coupled to the drive axle and movable thereby into the three positions. In position- 1,  axially between positions- 2/3,  the MCB is open—no CC is connected to another CC by the MCB; in position- 2,  the MCB is in ‘wye’ contact position—the MCB connects the PCC to the first MWCC, and the second MWCC is connected to the second MWCC of all other CDs using the ‘wye’ coupled to the drive axle; and in position- 3,  the MCB is in a ‘delta’ contact position—the MCB connects the FCC to the first and second MWCC.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application under 35 U.S.C. §371 of International Application No. PCT/EP2015/054154, filed on Feb. 27, 2015, and claims benefit to German Patent Application No. DE 10 2014 105 579.9, filed on Apr. 17, 2014. The International Application was published in German on Oct. 22, 2015, as WO 2015/158457 A2 under PCT Article 21(2). 
     
    
     FIELD 
       [0002]    The invention relates to a switching device for a star-delta changeover in a multiphase motor. 
       BACKGROUND 
       [0003]    A star-delta changeover is employed, for example, in order to start up three-phase (electric) motors. For purposes of limiting the high start-up current, the three motor windings are interconnected during the start-up phase of the motor to form a star connection in which the three phases L 1  to L 3  are connected to the power supply of the motor via the connectors U 1 , V 1  and W 1  of the motor windings, and the connectors U 2 , V 2  and W 2  are interconnected. Owing to this interconnection, the total output of the motor during start-up is reduced to one-third of the operating output. During operation, the motor windings are interconnected to form a delta connection in which the connectors U 1 , W 2  and V 1 , U 2  and W 1 , V 2  are interconnected and connected to the phase L 1  or L 2  or L 3 , respectively. 
         [0004]    In order to implement such a star-delta changeover, three contactors Q 11  (mains contactor), Q 12  (delta contactor) and Q 13  (star contactor) as shown in  FIG. 1  are used. In this context, the contactors Q 12  and Q 13  effectuate the star-delta changeover. For purposes of the star connection, the contactor Q 13  is closed and the contactor Q 12  is opened. The opposite is done for the delta connection. In order to prevent short circuits between the phases L 1 , L 2  and L 3  caused by the simultaneous switching of the contactors Q 12  and Q 13  during the changeover, these contactors are blocked with respect to each other, which is ensured by means of auxiliary contacts. 
         [0005]    East German patent application DD 268569 A1 discloses a switching device for a star-delta contactor in which three contact planes are provided so that the mains contactor, the delta contactor and the star contactor can be integrated together with a time relay in one module. The star-delta changeover takes place via a bimetal that releases a mechanical block and forces the contactor from the star operation to the delta operation when the contacts of the mains plane are closed. A bimetal, however, is not very precise, so that the point in time of the changeover from the star connection to the delta connection cannot be exactly determined. Moreover, this prior-art configuration makes use of many springs for generating the forces needed to hold the contacts in position or to put them in position. Since the elasticity of such springs can decline over the course of time, this can detrimentally affect the reliability of the switching device. 
         [0006]    International patent application WO 00/57444 A1 likewise describes an integrated star-delta changeover having two contactor drives in the form of coils by means of which contacts that are held with springs and that can be moved by a lever can be moved between two positions in order to change over from star to delta connection. This lever construction, however, is laborious and likewise requires many springs that entail the above-mentioned drawbacks. Moreover, two contactor drives are needed. 
       SUMMARY 
       [0007]    An aspect of the invention provides a switching device for a star-delta changeover in a multiphase motor including one motor winding per phase, each motor winding including a motor winding connector pair, the switching device comprising: an electromagnetic drive configured to move a drive shaft between first, second, and third defined axial positions; for each motor winding, a contact device including a first and a second motor winding connection contact, a phase connection contact, and a movable contact bridge, the movable contact bridge being coupled to the drive shaft and movable using the drive shaft into the three defined axial positions, wherein, when the movable contact bridge is in the first defined axial position, the first position arranged axially between the second and third defined axial positions, the movable contact bridge is in an open position in which none of the connection contacts is electrically connected to another one of the connection contacts via the movable contact bridge, wherein, when the movable contact bridge is in the second defined axial position, the movable contact bridge is in a star-contact position in which the movable contact bridge electrically connects the phase connection contact to the first motor winding connection contact, and the second motor winding connection contact is electrically connected to the second motor winding connection contacts of all other contact devices via a star contact coupled to the drive shaft, and wherein, when the movable contact bridge is in the third defined axial position, the movable contact bridge is in a delta-contact position in which the movable contact bridge electrically connects the phase connection contact to the first and second motor winding connection contacts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
           [0009]      FIG. 1 : a conventional star-delta changeover in a three-phase motor with three contactors; 
           [0010]      FIG. 2 : a sectional view of an embodiment of a contact device of a switching device according to the invention; 
           [0011]      FIG. 3 : a first embodiment of an electromagnetic drive with a movable permanent magnet of a switching device according to the invention; and 
           [0012]      FIG. 4 : a second embodiment of an electromagnetic drive with a movable electromagnet of a switching device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Before this Background, an aspect of the present invention provides an improved switching device for a star-delta changeover in a multiphase motor. 
         [0014]    An aspect of the present invention involves providing one contact device for each winding of a multiphase motor, said contact device being configured in such a way that it integrates the switching functions of the mains contactor, of the delta contactor and of the star contactor, and it has a contact bridge which is coupled to a drive shaft of an electromagnetic drive and which can be moved by means of the drive shaft between three defined axial positions. In this context, the contact device does not require any springs to generate the force or to hold the contact bridge since its placement or axial position can be controlled very precisely by means of the electromagnetic drive. Moreover, the process and timing of the changeover from the star connection to the delta connection and vice versa can be controlled exactly by means of the electromagnetic drive. 
         [0015]    One embodiment of the invention relates to a switching device for a star-delta changeover in a multiphase motor having one motor winding per phase, whereby each motor winding has a motor winding connector pair U 1 , U 2 , V 1 , V 2 , W 1 , W 2 , and whereby the switching device comprises the following: an electromagnetic drive to move a drive shaft between three defined axial positions and, for each motor winding, a contact device with a first and a second motor winding connection contact, a phase connection contact, and a movable contact bridge that is coupled to the drive shaft and that can be moved by the latter into the three defined positions. When the movable contact bridge is in a first and axial position between the two other positions, it is then in an open position in which none of the connection contacts is electrically connected to another one of the connection contacts via the contact bridge. When the movable contact bridge is in a second position of the three defined positions, it is then in a star-contact position in which the contact bridge electrically connects the phase connection contact to the first motor winding connection contact, and the second motor winding connection contact is electrically connected to the second motor winding connection contacts of all other contact devices via a star contact coupled to the drive shaft. When the movable contact bridge is in a third position of the three defined positions, it is then in a delta-contact position in which the contact bridge electrically connects the phase connection contact to the first and second motor winding connection contacts. 
         [0016]    In particular, the contact device can comprise the following: a conductive contact arm which starts from the first motor winding connection contact and leads to the plane of the star-contact position and which is contacted by the contact bridge in the star-contact position; a conductive contact arm which starts from the first motor winding connection contact and leads to the plane of the delta-contact position and which is contacted by the contact bridge in the delta-contact position; a conductive contact arm which starts from the phase connection contact and leads to the plane of the star-contact position and which is contacted by the contact bridge in the star-contact position; a conductive contact arm which starts from the phase connection contact and leads to the plane of the delta-contact position and which is contacted by the contact bridge in the delta-contact position; and a conductive contact arm which starts from the second motor winding connection contact and leads to the plane of the delta-contact position and which is contacted by the contact bridge in the delta-contact position as well as by the star contact in the star-contact position. The two conductive contact arms which start from the first motor winding connection contact as well as from the phase connection contact can form a U or V; other leg ends are each provided with contact points onto which corresponding contact points of the contact bridge are pressed in order to establish contact in the corresponding position of the contact bridge. 
         [0017]    The electromagnetic drive can have a movable permanent magnet coupled to the drive shaft as well as a stationary electromagnet. In this context, when the stationary electromagnet is in its de-energized state, the movable permanent magnet can be held by springs in a first position so that the drive shaft is in the first defined position and, when the stationary electromagnet is in its energized state, the movable permanent magnet can be pressed, as a function of the current direction, into a second or third position, counter to the force of the springs, against a stop or against poles of the stationary electromagnet, so that the drive shaft is in the second or third defined position. 
         [0018]    Alternatively, the electromagnetic drive can also have a movable electromagnet coupled to the drive shaft as well as a stationary electromagnet. In this context, when the movable or stationary electromagnet is in its de-energized state, the movable electromagnet can be held by springs in a first position so that the drive shaft is in the first defined position and, when both electromagnets are in their energized state, the movable electromagnet can be pressed, as a function of the current direction, into a second or third position, counter to the force of the springs, against a stop or against poles of the stationary electromagnet, so that the drive shaft is in the second or third defined position. The springs here can be provided in the form of electric feed lines that serve to energize the movable electromagnet. 
         [0019]    The contact device can also have semiconductor switches that are installed between the movable contact bridge and the first and second motor winding connection contacts and the phase connection contact. 
         [0020]    Additional advantages and application possibilities of the present invention ensue from the following description in conjunction with the embodiments shown in the drawings. 
         [0021]    The description, the claims, the abstract and the drawings make use of the terms and appertaining reference numerals as cited in the list of reference numerals presented at the end. 
         [0022]    Identical, functionally equivalent and functionally related elements can be provided with the same reference numerals in the description that follows. Absolute values are indicated below only by way of example and should not be construed as being of a limiting nature for the invention. 
         [0023]    The switching device for a star-delta changeover in a three-phase motor having one motor winding per phase according to the invention integrates the three contactors Q 11 , Q 12  and Q 13  of the conventional star-delta changeover shown in  FIG. 1  by means of a special contact device  20 , a sectional view of which is shown in  FIG. 2 . For this purpose, each motor winding is provided with its own contact device  20 , so that a three-phase motor requires three of the contact devices  20  shown in  FIG. 2 . 
         [0024]    The contact device  20  stands out especially for the fact that the axially (see the double-headed arrow in  FIG. 2 ) movable contact bridge  28  can be moved into three defined and different positions: an open position or open placement  14  (middle position of the contact bridge as shown in  FIG. 2 ), a star-contact position or star-contact placement  16 , and a delta-contact position or delta-contact placement  18 . The three positions or placements  14 ,  16 ,  18  correspond to three different planes. 
         [0025]    The contact bridge  28  is moved axially between the three axial positions  14 ,  16  and  18  by means of a drive shaft  12  which is connected to the contact bridge  28  and which is made of a material that is not electrically conductive, especially an insulator. The movement is brought about by an electromagnetic drive. As shown in  FIG. 2 , the contact device  20  does not need any springs to hold the contact bridge  28  in its three positions  14 ,  16 ,  18 . 
         [0026]    The contact device  20  shown in  FIG. 2  has a first motor winding connection contact  22 , a second motor winding connection contact  24  and a phase connection contact  26 . In the first of the three contact devices, the connection contact  22  is connected to U 1 , the connection contact  24  to V 2  and the connection contact  26  to L 1 . In the second of the three contact devices, the connection contact  22  is connected to V 1 , the connection contact  24  to W 2  and the connection contact  26  to L 2 . In the third of the three contact devices, the connection contact  22  is connected to W 1 , the connection contact  24  to U 2  and the connection contact  26  to L 3 . 
         [0027]    Two electrically conductive contact arms  44  and  46  lead from the connection contact  22  to the plane of the star-contact position  16  or to the delta-contact position  18 . As shown in  FIG. 2 , the contact arms  44  and  46  have a somewhat U-shaped cross section. Analogously, two electrically conductive contact arms  48  and  50  lead from the connection contact  26  to the plane of the star-contact position  16  or to the delta-contact position  18  and, as shown in  FIG. 2 , they likewise have a somewhat U-shaped cross section. In the space enclosed by the contact arms  44 ,  46 ,  48  and  50 , there is a contact bridge  28  which, in the star-contact position  16 , is pressed against the contact arms  44  and  48  while, in the delta-contact position  18 , it is pressed against the contact arms  46  and  50 . Another electrically conductive contact arm  52  leads from the connection contact  24  out of the plane of the delta-contact position  18 . As shown in  FIG. 2 , the end of this contact arm  52  is provided with a double contact, as a result of which, when the connection contact  24  is in the star-contact position  16 , it is contacted by a star contact  30  that is attached to the drive axis  12  and, when it is in the delta-contact position  18 , it is contacted by the contact bridge  28 . 
         [0028]    Therefore, if the contact bridge  28  is moved out of the open position  14  in which none of the connection contacts  22 ,  24  or  26  is connected to another contact into the star-contact position  16 , then the connection contacts  22  and  26  are electrically connected to each other (that is to say, U 1  and L 1 , V 1  and L 2 , W 1  and L 3 ), and the connection contact  24  is electrically connected to the star contact  30  which is electrically connected to the star contacts of the other contact devices (that is to say, V 2  to W 2  and U 2 ). In this manner, the star-contact position  16  corresponds to the closing of the contactors Q 11  and Q 13  in the circuit shown in  FIG. 1 . 
         [0029]    In the delta-contact position  18 , the contact bridge  28  short-circuits all three connection contacts  22 ,  24  and  26  (that is to say, U 1  to L 1  and V 2 , V 1  to L 2  and W 2 , W 1  to L 3  and U 2 ). In this manner, the delta-contact position  18  corresponds to the closing of the contactors Q 11  and Q 13  of the circuit shown in  FIG. 1 . 
         [0030]    Since the construction of the contact device  20  is such that the changeover from the star-contact position  16  to the delta-contact position  18  and vice versa always takes place via the open position  14 , no short-circuits can occur between the phases L 1 , L 2  and L 3 . 
         [0031]      FIG. 3  shows an electromagnetic drive  10  for the drive shaft  12  having a permanent magnet  32  which is movably mounted and attached to the drive shaft  12  and which is held by springs  36  in a first position between stops  38  and poles  40  of a stationary electromagnet  34 , as long as the electromagnet  34  is de-energized and is not exerting any magnetic force onto the permanent magnet  32 . 
         [0032]    In the first position of the permanent magnet  32 , the contact bridge  28  that is coupled to the drive shaft  12  is in the open position  14 . When the stationary electromagnet  34  is appropriately energized (voltage U 1  in  FIG. 3 ), the permanent magnet  32  can be attracted or repelled by the electromagnet  34 . In order to move the contact bridge  28  that is coupled to the drive shaft  12  into the star-contact position  16 , the electromagnet  34  is energized in such a way that the permanent magnet  32  is repelled and pressed against the stops  38 . In order to move the contact bridge  28  that is coupled to the drive shaft  12  into the delta-contact position  18 , the electromagnet  34  is energized in such a way that the permanent magnet  32  is attracted and pressed against the poles  40 . 
         [0033]    Instead of a permanent magnet  32 , it is also possible to use a movable electromagnet  42 , like the electromagnetic drive  11  shown in  FIG. 4 . In this context, the movable electromagnet  42  can be energized by means of the springs  36  (voltage U 2  in  FIG. 4 ) so that additional electric lines are not needed. 
         [0034]    If the transitions between the individual positions  14 ,  16  and  18  are problematic in terms of arc formation, then semiconductor switches can be installed between the movable contact bridges and the connection contacts  22 ,  24  and  26  that are then switched through in order to prevent arc formation when the connection contacts  22 ,  24  and  26  are opened. 
         [0035]    The switching device according to the invention could be actuated, for example, as follows: a time switch could prescribe a time after which the mode of operation is to be changed, for instance, changed over from a star connection to a delta connection. The changeover can also be carried out by a control unit that actuates the electromagnetic drive accordingly. Since there is no need to query any auxiliary switches as would be the case in the conventional star-delta changeover shown in  FIG. 1 , the programming resources needed to control the changeover can be considerably reduced by means of the invention. As another alternative, a prescribed electric voltage, for instance, with a ramp function, could be checked in order differentiate between the switching states. 
         [0036]    The switching device according to the invention is especially well-suited for use in motor starters. The switching device according to the invention merely requires the connection of the motor and of the phases of the source of alternating current. The electromagnetic drive of the switching device according to the invention can be controlled as desired either by means of a programmable logic controller (PLC) or by simply applying an electric voltage. Owing to its high functional density, the switching device according to the invention permits a compact design. Finally, the switching device according to the invention makes it possible to reduce the amount of material needed for its production since it requires only one electromagnetic drive, only one electronic unit for actuation, no pre-wiring of several contactors during production and only one housing. 
         [0037]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
         [0038]    The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C. 
       LIST OF REFERENCE NUMERALS 
       [0039]      10  electromagnetic drive with permanent magnets 
         [0040]      11  electromagnetic drive with electromagnets 
         [0041]      12  drive shaft made of non-conductive material 
         [0042]      14  open position 
         [0043]      16  star-contact position 
         [0044]      18  delta-contact position 
         [0045]      20  contact device 
         [0046]      22  first motor winding connection contact 
         [0047]      24  second motor winding connection contact 
         [0048]      26  phase connection contact 
         [0049]      28  movable contact bridge 
         [0050]      30  star contact 
         [0051]      32  movable permanent magnet 
         [0052]      34  stationary electromagnet 
         [0053]      36  springs 
         [0054]      38  stop 
         [0055]      40  poles of the stationary electromagnet 
         [0056]      42  movable electromagnet 
         [0057]      44  conductive contact arm 
         [0058]      46  conductive contact arm 
         [0059]      48  conductive contact arm 
         [0060]      50  conductive contact arm 
         [0061]      52  conductive contact arm