Abstract:
An earthing switch is disclosed that includes a base for mounting the earthing switch, a first contact element that is mounted on the base via a first insulating element, a shaft mounted in the base, a second contact element, mounted on the shaft, that can swivel relative to the first contact element, so that the second contact element can move between a closed and an open position, a locking and/or monitoring apparatus for locking the shaft and/or for monitoring the position of the shaft, wherein the locking and/or monitoring apparatus is fitted to the base next to the first contact element, wherein a second insulating element held between the base and the first insulating element has an insulating plate that protrudes from the base and that is arranged between the first contact element and the locking and/or monitoring apparatus.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of medium and high voltage technology. It is based on an earthing switch according to the preamble of the independent claim. 
     BACKGROUND OF THE INVENTION 
     Earthing switches are used for example in switch cabinets, where the electrical circuits that are under voltage must always be earthed before the door of the switch cabinet is opened. 
     Such switch cabinets may for example contain components of a converter for an electrical drive. Since the voltages used are ever increasing, it is necessary that the internal electrical insulation of the earthing switches is correspondingly improved with respect to flashovers and creeping currents. 
     Switches of the type in question are known for example from U.S. Pat. No. 2,331,632, from U.S. Pat. No. 2,009,815 and from U.S. Pat. No. 4,263,487. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide an earthing switch that has good electrical insulating properties. 
     This object is achieved by the subject matter of independent claim  1 . Further embodiments of the invention are provided by the dependent claims and the description that follows. 
     The invention relates an earthing switch that can be used for example for voltages of up to 15 kV (approximately 13.8 kV). The earthing switch may for example be arranged in a switch cabinet in such a way that the door of the switch cabinet can only be opened when the earthing switch has been moved into a closed position. 
     According to one embodiment of the invention, the earthing switch comprises a base for mounting the earthing switch, a first contact element, which is mounted on the base by way of a first insulating element, a shaft mounted in the base, a second contact element, which is mounted on the shaft and can swivel in relation to the first contact element by means of the shaft, so that the second contact element can move between a closed position and an open position, and a locking and/or monitoring device for locking the shaft and/or for monitoring the position of the shaft, which is attached to the base next to the first contact element, wherein a second insulating element is held between the base and the first insulating element and has an insulating plate that protrudes from the base and is arranged between the first contact element and the locking and/or monitoring device. 
     In other words, the electrical insulation between the first contact element, which is under high voltage, and the locking and/or monitoring device can be improved by the further insulating element, which provides an insulating plate between these two components, so that an already existing insulation by way of an air gap is further improved. 
     The base may comprise a metal plate, on which the first and/or second insulating element is mounted. The metal plate may comprise side walls, in which the shaft is held in bearings and/or on which the locking and/or monitoring device is mounted. The earthing switch can be connected to earth potential by way of the base. 
     It should be understood that the first insulating element and the second insulating element are generally two separate components. However, it is also possible that the first insulating element and the second insulating element are provided by one component, though the two insulating elements can be separately distinguished from one another. The first insulating element may for example comprise a body which on one side carries the first electrical contact and on the other side is connected to the second insulating element. 
     According to one embodiment of the invention, the second insulating element has an elongate portion, which is held between the first insulating element and the base and has first openings for mounting the second insulating element on the base and second openings for mounting the first insulating element on the second insulating element. In other words, the second insulating element may be mounted on the base, for example by means of screws, and the first insulating element may be mounted on the second insulating element, for example by means of screws. 
     According to one embodiment of the invention, the openings are separated from one another by webs on the elongate portion. The openings may be located on opposite sides of the elongate portion. The webs may extend substantially orthogonally in relation to the opposite sides. 
     According to one embodiment of the invention, a portion of the second insulating element that protrudes from the elongate portion is configured in the form of a spade, so that the insulating plate is delimited in a U-shaped manner by side walls. When considered from the side, the elongate portion and the insulating plate may run substantially parallel, the insulating plate being connected to the elongate portion for example by way of a sloping surface. The sides of the insulating plate extending away from the first contact element may be connected to side walls that provide stiffening and/or increase the insulation. 
     According to one embodiment of the invention, the first contact element comprises a contact shoe and the second contact element comprises a contact blade, which are inserted one into the other during the closing of the earthing switch. A contact shoe may in this case comprise one or more spring elements, between which a contact blade can be clamped. A contact blade may be an elongate, flat contact element. 
     According to one embodiment of the invention, the earthing switch comprises three first contact elements, which are for example arranged in a row on the base, and three second contact elements, which are for example arranged in a row on the shaft. The three first contact elements may for example be connected to a DC link of a converter, for example to its positive, negative and neutral potential. The three second contact elements may be connected in parallel (for example by way of the metallic shaft) and be connected to the earth potential (for example by way of the base). 
     According to one embodiment of the invention, one of the three second contact elements is provided by an L-shaped component mounted on the shaft and the remaining two second contact elements are provided by a U-shaped component mounted on the shaft. One leg of the L or the legs of the U may in this case provide a contact blade or contact blades. 
     According to one embodiment of the invention, the locking and/or monitoring device comprises an actuator with a locking pin, mounted on the base, and a locking disk, mounted on the shaft, the locking disk having for fixing the shaft at least one clearance in which the locking pin can engage. With this actuator it can be ensured that the earthing switch remains in a desired open position or closed position. 
     According to one embodiment of the invention, the actuator comprises a spring, which presses the locking pin in the direction of the locking disk, and/or the actuator of the locking device comprises an energizable coil, which when energized pulls the locking pin away from the locking disk. This coil may for example be activated by a controller when the earthing switch is to be opened or closed and/or is allowed to be opened or closed. 
     According to one embodiment of the invention, the locking disk has a clearance for fixing the shaft in an open position and/or a clearance for fixing the shaft in a closed position. The locking disk may be a circular disk, which has the clearances in its border. The aforementioned locking pin can engage in the clearances. 
     According to one embodiment of the invention, the locking and/or monitoring device comprises a plurality of switches, which are mounted on the base and mesh on a camshaft mounted on the shaft, in order to determine a position of the shaft. These switches may be activated and deactivated by a correspondingly formed camshaft (with elevations and/or depressions) when the shaft is at a specific rotational angle. 
     According to one embodiment of the invention, the switches and the camshaft are configured in such a way that an open position, an intermediate position and a closed position can be detected. It can be ensured in this way that at least these positions can be monitored by an external controller. 
     According to one embodiment of the invention, the shaft is mounted in the base by bearings (for example sliding bearings). A locking disk and/or a camshaft of the locking and/or monitoring device may be mounted on the shaft in such a way that, with respect to the bearings, it/they is/are arranged outside a portion of the shaft that carries the second contact element. For example, the locking disk and/or the camshaft may be held in a box which is mounted laterally on the base and which may for example also carry the switches. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Exemplary embodiments of the invention are described in detail below with reference to the accompanying figures. 
         FIG. 1  shows a perspective view of an earthing switch according to one embodiment of the invention. 
         FIG. 2  shows a perspective view of the underside of an insulating element for an earthing switch according to one embodiment of the invention. 
         FIG. 3  shows a diagram with switching states of monitoring switches for an earthing switch according to one embodiment of the invention. 
     
    
    
     The designations used in the figures and their meaning are presented in a summarizing form in the list of designations. In principle, parts that are identical or similar parts are provided with the same designations. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  shows an earthing switch  10 , which comprises a base  12 , in which three first contact elements  14   a ,  14   b ,  14   c  are mounted. Additionally mounted on the base  12  is a shaft  16 , in which three second contact elements  18   a ,  18   b ,  18   c  are mounted. Turning of the shaft  16  allows the second contact elements  18   a ,  18   b ,  18   c  to be moved between an open position (shown) and a closed position. 
     The base  12  and/or the shaft  16  may be produced from metal or a conductive material. 
     Each of the first contact elements  14   a ,  14   b ,  14   c  comprises a contact shoe  20  comprising two springs, which are connected to a contact block  22 , which is mounted on a first insulating element  24 . For this purpose, the insulating element  24  has for each contact element  14   a ,  14   b ,  14   c  a post  26 , which keeps the contact elements  14   a ,  14   b ,  14   c  at a distance from the base  12 . 
     Between the posts  26 , the first insulating element  24  may be connected directly to the base  12  and/or to a second insulating element  28 . 
     The second insulating element  28  has an elongate portion  30  and a spade-shaped portion  32 . The elongate portion  30  is in this case held between the first insulating element  24  and the base  12 . The elongate element extends under the three posts  26  of the first insulating element  24  and then goes over into the spade-shaped portion  32 , which extends away from the earthing switch substantially orthogonally in relation to the direction of extent of the posts  26 . 
     The first insulating element  24  and/or the second insulating element  28  are produced from a very poorly conducting material or insulating material, such as for instance plastic or ceramic. 
     The shaft  16  is mounted in two sliding bearings  34  in side walls  36   a ,  36   b  of the base  12 . Between the two bearings, the shaft  16  has a rectangular profile, on which the second contact elements  18   a ,  18   b ,  18   c  are mounted. The first contact element  18   a  is in this case formed as an L-shaped component, one leg providing a contact blade  38 . The contact elements  18   b  and  18   c  are provided by a U-shaped component, the legs of which provide two further contact blades  38 . 
     Mounted on the side wall  38   a  and on the base  12  is a securing spring  40 , with which the shaft  16  can be kept in the open position. The securing spring  40  thereby engages in a groove in the contact element  18   a.    
     Additionally mounted on the side wall  38   a  are a locking device and a monitoring device  44 . The spade-shaped portion  32  or its insulating plate  46  spatially separates the locking device  42  and the monitoring device  44  from the contact elements  14   a ,  14   b ,  14   c , so that an insulating gap is extended by the air between these components. 
     The locking device  42  comprises an actuator  48  in the form of an energizable coil, with which a locking disk  52 , which is located on the shaft  16 , can be prevented from rotation by means of a pin  50  (see  FIG. 3 ). 
     The monitoring device  44  comprises a plurality of switches  54 , which mesh on a camshaft  56  and can thus provide information concerning the position of the second contact elements  18   a ,  18   b ,  18   c.    
     At the end that protrudes through the side wall  36   a , through the locking device  42  and through the monitoring device  44 , the shaft  16  has a rectangular rod  58 , onto which a key for turning the shaft  16  can be fitted. 
     The earthing switch  10  can be connected to a ground potential or earthing potential by way of the base  12 . The contact elements  16   a ,  16   b ,  16   c  can also be connected to this potential by way of the shaft  16 . 
     The contact elements  14   a ,  14   b ,  14   c  may be understood as the high-voltage region of the earthing switch. The contact elements  14   a ,  14   b ,  14   c  may for example be connected to a power circuit in a switch cabinet, such as for instance the DC link of a converter, which during operation can be at a voltage of up to 15 kV (for example 6.9 kV or 13.8 kV). 
     For example, the contact element  14   a  may be connected to a negative potential, the contact element  14   b  may be connected to a neutral potential and the contact element  14   c  may be connected to a positive potential of the DC link. By connecting to the contact elements  18   a ,  18   b ,  18   c , the DC link can then be discharged and set to ground potential. 
     The contact elements  18   a ,  18   b ,  18   c , the base  12 , the shaft  16 , the locking device  42  and the monitoring device  44  may be understood as the low-voltage region of the earthing switch  10 . The contact elements  18   a ,  18   b ,  18   c , the base  12  and the shaft  16  are at ground potential. The locking device  42  and the monitoring device  44  are as a maximum at the potential of a control voltage (for example a maximum of 100 V). 
     The second insulating element  28  and the insulating plate  46  improve the electrical insulation between the high-voltage region and the low-voltage region. 
       FIG. 2  shows a perspective view of the second insulating element  28  obliquely from below. 
     The elongate portion  30  has a U-shaped side wall  60 , which provides a substantially cuboidal basic shape for the elongate portion  30 . On the side wall  60  there is a plate  62 , which protrudes beyond the side wall  60 , and consequently forms a peripheral border  64 . In the plate  62  are two openings  66 , which serve for mounting the first insulating element  24  on the second insulating element  28 . These openings are delimited by webs  68 , which (in the same way as the side wall  60 ) protrude orthogonally from the plate  62 . The webs  68  carry three flat portions (parallel to the plate  62 ), in which there are a further three openings  70 , by way of which the second insulating element  28  can be mounted on the base  12 . The openings  66 ,  70  are spaced equally apart and/or lie on one line. 
     The spade-shaped portion  32  comprises the insulating plate  46 , which is connected by way of the orthogonal side wall  72  to the plate  62 , which at its end is widened in a T-like manner. The side walls  72  surround the insulating plate  46  in a U-shaped manner. 
       FIG. 3  shows the earthing switch  10  schematically in an open position, a half-closed position, a contacting position and a closed position (from left to right). 
     In the closed position and in the open position, the earthing switch  10  is kept in this position by the locking device  42 , in that the locking pin  50  engages in a respective clearance  74  in the locking disk  52 . The actuator  48  may for example comprise a coil, which when energized pulls the locking pin  50  away from the locking disk  52 , and/or comprise a spring, which presses the locking pin in the direction of the locking disk. 
     With the locking device  42 , the earthing switch  10  can only be actuated when the actuator  48  (or its coil) has been energized. 
     In the diagram, the switching state of the earthing switch  10  and of the switches  54  of the monitoring device  44  can be read off under the various positions. The shaft  16  can move in an angular range from 0° to 90°. 
     Between 0° (completely open position) and 74° (contacting position), the earthing switch  10  is open (“off”) and after that closed up to 90° (completely closed position) (“on”). 
     The cam disk  56  is designed in such a way that one or more first switches  54  between 0° and a minimum of 82° are switched off (“no”) and after that are switched on (“yes”). One or more second switches  54  are switched on between 0° and a maximum of 8° (“yes”) and after that are switched off (“no”). 
     For example, the coil can only be energized by way of a controller when the controller detects that at least one of the switches  54  is switched on (“yes”). 
     It should additionally be pointed out that “comprising” does not exclude other elements or steps and “one” or “a(n)” does not exclude more than one. Furthermore, it should be pointed out that features or steps that have been described by reference to one of the exemplary embodiments above can also be used in combination with other features or steps of other exemplary embodiments described above. Designations in the claims should not be regarded as restrictive. 
     LIST OF DESIGNATIONS 
     
         
           10  Earthing switch 
           12  Base 
           14   a ,  14   b ,  14   c  First contact element 
           16  Shaft 
           18   a ,  18   b ,  18   c  Second contact element 
           20  Contact shoe 
           22  Contact block 
           24  First insulating element 
           26  Post 
           28  Second insulating element 
           30  Elongate portion 
           22  Spade-shaped portion 
           34  Sliding bearing 
           36   a ,  36   b  Side wall of the base 
           38  Contact blade 
           40  Securing spring 
           42  Locking device 
           44  Monitoring device 
           46  Insulating plate 
           28  Actuator 
           50  Locking pin 
           52  Locking disk 
           54  Switch 
           56  Camshaft 
           58  Rod for key 
           60  Side wall 
           62  Plate 
           64  Border 
           66  Opening 
           68  Web 
           70  Opening 
           72  Side wall 
           74  Clearance