Patent Publication Number: US-11043342-B2

Title: Change-over switch

Description:
FIELD OF THE INVENTION 
     The present invention relates to a change-over switch. 
     A change-over switch is a switching device comprising a first supply terminal, a second supply terminal and a load terminal, and adapted to selectively provide a first connection between the first supply terminal and the load terminal, and a second connection between the second supply terminal and the load terminal. When a current circuit of a change-over switch is opened, an electric arc whose temperature is thousands of degrees may occur in the change-over switch. An electric arc includes ionized gas, which contains a large number of free electrons. Such a gas plasma is electrically conductive. 
     In addition to the fact that electric arc is conductive, metal which has been vaporized from contact surfaces by the electric arc may, upon solidification, impair the insulation capacity of the surfaces of the switching device. Soot produced by the electric arc may also cause insulation problems. 
     It is known in the art to provide a change-over switch with a gas discharge arrangement for discharging gasses produced by switching events from a frame of the change-over switch, the gas discharge arrangement comprising gas flow openings formed in a side wall of the frame. The gas discharge arrangement enables expanded gas to discharge from the frame of the change-over switch, which prevents pressure inside the frame from becoming too high. 
     One of the problems associated with known change-over switches is that in connection with a switching event, gas discharging from the frame through the gas flow openings may cause a short circuit. Depending on the design of the change-over switch, and the environment of the change-over switch, said short circuit may occur between a terminal of the change-over switch and an adjacent earthed part, or between terminals of the change-over switch. Risk for the short circuit may increase gradually due to electrically conductive material that is deposited in the vicinity of the gas flow openings. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An object of the present invention is to provide a change-over switch so as to solve the above problem. The objects of the invention are achieved by a change-over switch which is characterized by what is stated in the independent claim  1 . The preferred embodiments of the invention are disclosed in the dependent claims. 
     The invention is based on the idea of locating a first supply terminal and a second supply terminal on a first side wall of a frame of a change-over switch while a load terminal is located on a second side wall facing substantially opposite direction relative to the first side wall, and providing the change-over switch with a gas discharge arrangement adapted to discharge gasses produced by switching events through gas flow opening(s) formed in the second side wall. 
     An advantage of the change-over switch of the invention is that a risk of a short circuit is reduced in connection with opening a current circuit of the change-over switch, because the gas flow opening(s) are on the same side wall as the load terminal which is at the same electric potential as the supply terminal whose current circuit is being opened in the switching event in question. Further, long gas discharge passages cool gasses produced by switching events, and remove at least part of metal particles vaporized from contact surfaces by the switching events. Lowering temperature of the exhaust gases lowers electrical conductivity of the exhaust gases. Reducing amount of metal particles in the gas flow exiting the frame reduces amount of electrically conductive material that is deposited outside the gas flow openings, in the vicinity of the gas flow openings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which 
         FIG. 1  shows a change-over switch according to an embodiment of the invention; 
         FIG. 2  is a side view of the change-over switch of  FIG. 1  with half of a frame of the switch removed so as to show an internal structure of the switch; 
         FIG. 3  shows the change-over switch of  FIG. 1  with half of the frame removed; and 
         FIG. 4  shows a cross section of the change-over switch of  FIG. 1  taken along a plane parallel to a first side wall of the switch, through which supply terminals of the switch extend. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a change-over switch comprising a frame  2 , a first supply terminal  41  adapted to be connected to a first power supply, a second supply terminal  42  adapted to be connected to a second power supply, and a load terminal  6  adapted to be connected to a load. The first supply terminal  41  and the second supply terminal  42  project from a first side wall  21 , and the load terminal  6  projects from a second side wall  22 . The second side wall  22  faces substantially opposite direction relative to the first side wall  21 . The first side wall  21  and the second side wall  22  are spaced apart in a longitudinal direction. The change-over switch of  FIG. 1  is a single-phase module adapted to be coupled to other modules in order to provide a multiphase change-over switch. 
       FIG. 2  is a side view of the change-over switch of  FIG. 1 . In  FIG. 2  a half of the frame  2  has been removed so as to show an internal structure of the change-over switch.  FIG. 3  shows the change-over switch of  FIG. 1  with half of the frame  2  removed.  FIGS. 2 and 3  show that the change-over switch comprises a selector contact  8 , a gas discharge arrangement, a plurality of first arc extinguisher plates  941  and a plurality of second arc extinguisher plates  942 . 
     The gas discharge arrangement comprises a first gas discharge passage  51 , a second gas discharge passage  52 , a first gas flow opening  31  and a second gas flow opening  32 . The first gas discharge passage  51  comprises a remote portion  514 , an outer portion  515  and a plate portion  519 . The second gas discharge passage  52  comprises a remote portion  524 , an outer portion  525  and a plate portion  529 . 
     The selector contact  8  is adapted to rotate relative to the frame  2  around a rotation axis  81  between a first position and a second position. The rotation axis  81  is perpendicular to the longitudinal direction. In the first position the selector contact  8  electrically conductively connects the first supply terminal  41  to the load terminal  6 , and electrically isolates the second supply terminal  42  from the load terminal  6 . In the second position the selector contact  8  electrically conductively connects the second supply terminal  42  to the load terminal  6 , and electrically isolates the first supply terminal  41  from the load terminal  6 . The frame  2  is made from material whose electrical conductivity is low. 
     The selector contact  8  comprises a first blade contact  851  for establishing electrically conductive connection with the first supply terminal  41 , and a second blade contact  852  for establishing electrically conductive connection with the second supply terminal  42 . Electrically conductive connection between the selector contact  8  and the first supply terminal  41  is adapted to be closed and opened in a first contact zone  91 . Electrically conductive connection between the selector contact  8  and the second supply terminal  42  is adapted to be closed and opened in a second contact zone  92 . The contact zones  91  and  92 , and the plurality of first arc extinguisher plates  941  and the plurality of second arc extinguisher plates  942  are located inside the frame  2 . 
     The selector contact  8  is in a fixed electrically conductive connection with the load terminal  6 . The fixed electrically conductive connection between the selector contact  8  and the load terminal  6  comprises two braided conductors  801  and  802 , which are adapted to allow rotation between the selector contact  8  and the load terminal  6  due to flexibility thereof. The braided conductors  801  and  802  are made from copper wire. 
     The gas discharge arrangement is adapted for discharging gasses produced by switching events from the frame  2 . The switching events comprise a first type switching event occurring between the selector contact  8  and the first supply terminal  41 , and a second type switching event occurring between the selector contact  8  and the second supply terminal  42 . The first type switching event takes place in the first contact zone  91 , and the second type switching event takes place in the second contact zone  92 . 
     The first gas flow opening  31  and the second gas flow opening  32  are formed in the second side wall  22 , and adapted to provide a flow path for the gasses from inside the frame  2  to outside the frame  2 . The first gas flow opening  31  is adapted for gasses produced in the first type switching event. The second gas flow opening  32  is adapted for gasses produced in the second type switching event. The first gas flow opening  31  and the second gas flow opening  32  are located on opposite sides of the load terminal  6  in a height direction. The height direction is perpendicular to the longitudinal direction and a width direction, the width direction being parallel to the rotation axis  81 . 
     The first gas discharge passage  51  originates from the first contact zone  91  and ends to the first gas flow opening  31 . The second gas discharge passage  52  originates from the second contact zone  92  and ends to the second gas flow opening  32 . In an alternative embodiment both the first gas discharge passage and the second gas discharge passage end to the same gas flow opening. In a further alternative embodiment both the first gas flow opening and the second gas flow opening comprise a plurality of sub-openings. 
       FIG. 4  shows a cross section of the change-over switch of  FIG. 1  taken along a plane parallel to the first side wall  21  of the switch, and passing through the selector contact  8 .  FIG. 4  shows that a width of each of the outer portions  515  and  525  is substantially equal to inner width of the frame  2 . Further, a cross-sectional area of each of the outer portions  515  and  525  is sufficient to provide a low resistance path for the gasses. Together  FIGS. 2, 3 and 4  show that the first gas discharge passage  51  provides a path of least resistance for a gas flow from the first contact zone  91  to the first gas flow opening  31 , and the second gas discharge passage  52  provides a path of least resistance for a gas flow from the second contact zone  92  to the second gas flow opening  32 . 
     The first contact zone  91  and the second side wall  22  are located on opposite sides of the rotation axis  81  in the longitudinal direction. The second contact zone  92  and the second side wall  22  are located on opposite sides of the rotation axis  81  in the longitudinal direction. Therefore both the first gas discharge passage  51  and the second gas discharge passage  52  are long passages allowing gasses produced by switching events to cool properly before discharging the gasses from the frame  2 . 
     The plurality of first arc extinguisher plates  941  is located adjacent the first contact zone  91  and adapted to extinguish electric arcs produced in the first type switching event. The plurality of first arc extinguisher plates  941  is located between the rotation axis  81  and the outer portion  515  of the first gas discharge passage  51  in a radial direction perpendicular to the rotation axis  81 . The plurality of second arc extinguisher plates  942  is located adjacent the second contact zone  92  and adapted to extinguish electric arcs produced in the second type switching event. The plurality of second arc extinguisher plates  942  is located between the rotation axis  81  and the outer portion  525  of the second gas discharge passage  52  in a radial direction perpendicular to the rotation axis  81 . Majority of both the first arc extinguisher plates  941  and the second arc extinguisher plates  942  are located on opposite side of the rotation axis  81  than the second side wall  22  in the longitudinal direction. 
     The remote portion  514  of the first gas discharge passage  51  is located further from the second side wall  22  in the longitudinal direction than the plurality of first arc extinguisher plates  941 . The remote portion  524  of the second gas discharge passage  52  is located further from the second side wall  22  in the longitudinal direction than the plurality of second arc extinguisher plates  942 . Gasses passing through the remote portions  514  and  524  travel substantially longer distance than a direct distance between the corresponding contact zone and gas flow opening. Further, when flowing from a contact zone to corresponding remote portion, gasses actually recede from corresponding gas flow opening, which makes the path of the gasses longer and allows the gasses to cool more. 
     Each of the plurality of first arc extinguisher plates  941  and each of the plurality of second arc extinguisher plates  942  is a substantially planar element which defines a corresponding extinguisher plate plane. The extinguisher plate plane of each first arc extinguisher plate  941  and each second arc extinguisher plate  942  is positioned such that a radial direction is substantially parallel to the extinguisher plate plane, the radial direction is a direction perpendicular to the rotation axis  81 . The shape of the arc extinguisher plates  941  and  942  can be best seen in  FIGS. 3 and 4 . 
     Each of the plurality of first arc extinguisher plates  941  and each of the plurality of second arc extinguisher plates  942  is made from zinc-plated steel. Each of the first arc extinguisher plates  941  and each of the plurality of second arc extinguisher plates  942  is electrically isolated from the other arc extinguisher plates  941  and  942 . In an alternative embodiment each of the plurality of first arc extinguisher plates and each of the plurality of second arc extinguisher plates is made from another material with high electrical and thermal conductivity. 
     The plate portion  519  of the first gas discharge passage  51  extends between the plurality of first arc extinguisher plates  941 . The plate portion  529  of the second gas discharge passage  52  extends between the plurality of second arc extinguisher plates  942 . The plate portion  519  of the first gas discharge passage  51  is in gas connection with the outer portion  515  of the first gas discharge passage  51 . The plate portion  529  of the second gas discharge passage  52  is in gas connection with the outer portion  525  of the second gas discharge passage  52 . 
     Plate portions  519  and  529  of the gas discharge passages  51  and  52  cool gasses passing through them effectively due to high thermal conductivity of the arc extinguisher plates  941  and  942 . The arc extinguisher plates  941  and  942  are adapted to absorb heat from gasses passing through the plate portions  519  and  529 . 
     It will be obvious to a person skilled in the art that the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.