Patent Publication Number: US-9425003-B2

Title: Electric current switching apparatus

Description:
RELATED APPLICATIONS 
     This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/FI2013/050383, which was filed as an International Application on Apr. 8, 2013 designating the U.S., and which claims priority to European Application 12163952.2 filed in Europe on Apr. 12, 2012. The entire contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     The present disclosure relates to an electric current switching apparatus. 
     BACKGROUND INFORMATION 
     A known issue associated with opening a DC current is that an arc builds between the contacts of the switch when the contacts are separated from each other. The arc is erosive and may thus damage nearby parts of the switch. 
     There have been attempts to use a magnetic field, produced by permanent magnets or a coil placed in proximity of the contacts, to blow the arc away to quenching plates. Often the case is that currents close to the nominal current are easier to switch than currents that are small compared to the nominal current. This is because an arc associated with a nominal current seeks to the quenching plates but an arc with low current more easily remains to burn between the contacts of the switch. 
     However, known techniques for quenching an arc in the switches are either complicated or do not fully meet the demand for durability of the switch. 
     SUMMARY 
     An exemplary embodiment of the present disclosure provides an arc quenching plate for an electric switch. The exemplary arc quenching plate includes a base portion, a first side portion, and a second side portion. The first and second side portions extend from the base portion and are substantially parallel to each other. The first and second side portions include a first mounting portion and a second mounting portion, respectively, for mounting of the quenching plate to respective recesses of the switch. A propagation channel for the arc is formed between the side portions of the plate, the propagation channel being asymmetric. The first mounting portion and the second mounting portion have a different form when compared to each other. 
     An exemplary embodiment of the present disclosure provides an electric switch module which includes a first switch module housing and a second switch module housing to be assembled together. The first and second switch module housings respectively include recesses for receiving quenching plates. The exemplary electric switch module also includes quenching plates arranged between the first and second switch module housings when assembled together. The quenching plates form a propagation channel for an electric arc. The propagation channel formed by the quenching plates is non-uniform. A recess for receiving one of the quenching plates in the first switch module housing has a different form than a recess in the second switch module housing for receiving the same quenching plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, disclosed features of the present disclosure will be described in greater detail by way of exemplary embodiments, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a view of an exemplary embodiment of a switch; 
         FIG. 2  shows another view of an exemplary embodiment of the switch of  FIG. 1 ; 
         FIG. 3  highlights an arc chamber according to an exemplary embodiment of the present disclosure; 
         FIG. 4A  shows a group of quenching plates according to an exemplary embodiment of the present disclosure; and 
         FIG. 4B  shows one quenching plate from the side, according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure provide a switch which can alleviate issues associated with known techniques. 
     Exemplary embodiments of the present disclosure provide an electric switch for switching electric current. The switch of the present disclosure may be applied in various areas, such as electric motors and solar systems, for example. 
     In accordance with an exemplary embodiment of the switch according to the present disclosure, there is provided an arc chamber for quenching an arc caused by separating the contacts of the switch. The arc chamber houses a plurality of quenching plates, and there is provided a permanent magnet for blowing the arc towards the plates. 
     In accordance with an exemplary embodiment, the quenching plates have a bottom portion and side portions extending from the bottom portion. The permanent magnet may be arranged such that the arc is directed towards one of the side portions of the plates. 
     The switch of the present disclosure is easy to mount and is effective in quenching the arc caused by the separation of switch contacts. 
       FIG. 1  shows an exemplary embodiment of a single-pole electric switch  100  without a top cover. The switch has an electrically insulating module housing  102 , and by stacking such modules together, multi-pole switches can be constructed. 
     At the ends of the switch, there are stationary contacts  104 ,  106  for connecting the switch to power terminals. A movable/rotary contact  108  may include contact arms  110 ,  112 , between which a contact portion of the stationary contact  106  fits when the contact is made. The contact arms of the rotary contact may have a form of a lengthy knife, for instance. 
       FIG. 1  shows the switch in the open position, where the contact arms  110 ,  112  of the movable contact are not in contact with the stationary contact but rest against a stoppage element  116 , according to an exemplary embodiment of the present disclosure. 
     The switch also includes an arc chamber  120  for quenching an arc caused by separating the contacts from each other. The arc chamber houses a plurality of quenching plates  122  via which the contact arms  110 ,  112  of the movable contact move when the switch is opened. As the figure shows, the quenching plates are arranged to the arc chamber next to each to each other such that they are arranged a distance away from the contact area of the rotary contact and the stationary contact. That is, the second quenching plate lies further away from the contact area than the first quenching plate. 
     There is also provided a permanent magnet  132 , which is placed into a housing  130  for the magnet. The housing residing in the first switch module housing  100  may include a wall portion that is provided between the magnet and the contact area and the plates. There also may be provided side portions extending perpendicularly from the wall portion. According to an exemplary embodiment, the purpose of the wall portion and the side portion is to keep the magnet in its place thereby resisting the traction between the magnet and the plates, and protecting the magnet from the erosive effects of the arc. A second switch module housing to be mounted to the first switch module housing  100  may include a support portion, which supports the magnet in housing  130  and further protects it from the arc. 
     The position of the housing is behind the quenching plates, and at the beginning of the arc chamber when seen from the stationary contact point of view. According to an exemplary embodiment, the permanent magnet is positioned such that it is behind one or more such plates that lie closest to the contact area. In the exemplary embodiment of  FIG. 1 , the magnet lies behind substantially the first half of the quenching plates. In this way, sufficient blowing effect can be caused to the arc immediately when the arc builds up to push it towards one of the side portions of the plates. In  FIG. 1 , the arc is thus blown towards the side of the plates that is arranged against the bottom of the housing, or towards the opposite side of the plates, depending on which way the current is arranged. 
       FIG. 2  shows the switch  100  of  FIG. 1  seen from the top, according to an exemplary embodiment of the present disclosure. 
     It can be seen that the stationary contact  106  has a plane-like contact portion  106 A to be contacted by the contact arm  110  of the movable contact. When the movable contact arm  110  is in contact with the stationary contact  106 A, the arm rests substantially against the stoppage element  118 . 
     In the exemplary embodiment of  FIG. 2 , there are six quenching plates placed to the arc chamber  120  such that there are small intervals between the plates. The first quenching plate  122 A is in immediate proximity, or even in contact, of the stationary contact  106 A, and the last plate  122 B may be arranged such that the arm  110  is not in the area of plates when the movable contact is in its open position. 
     According to an exemplary embodiment, the quenching plates have a base/bottom portion and two side portions extending from the base portion, that is, the base portion connects the side portions. The side portions may be arranged substantially parallel to each other. An example of such a form is a letter U form. In  FIG. 2 , the base of the quenching plates  122 A,  122 B points towards the end of the switch having the stationary contact  106 , that is, the base points substantially towards the magnet  132 . The plate is thus arranged such that the base resides thus between the magnet  132  and the quenching area of the plate, which is the area between the side portions of the plate. In the viewing angle of  FIG. 2 , mainly the top side portions of the plates are visible to the top. 
     According to an exemplary embodiment, the permanent magnet  132  may have a rectangular cross-section in the horizontal direction as shown in  FIG. 2 . In the vertical direction, the cross-section of the magnet may be a square or rectangle, for instance. The poles of the magnet are arranged such that magnetic field B of the magnet is directed in the horizontal plane, which is highlighted by the two-headed arrow. The direction of the magnetic field between the two alternatives depends on which way the permanent magnet is placed to the housing  130 . In either direction, the magnetic field is substantially parallel to the principal directions of the side portions, and perpendicular to the base portion of the plates. The magnetic field is thus substantially parallel to the longitudinal direction of the rotary contact at the point of rotation of the rotary contact when it separates from the stationary contact, which is the point where the arc builds up. 
     The square cross-section form of the permanent magnet and the housing is advantageous as the magnet can be mounted to the housing in any position and the magnetic field B is directed in one of the directions shown in  FIG. 2 . If the permanent magnet has a square form, there are eight available mounting positions for the magnet. The person doing the assembly can mount the magnet to the magnet housing in any of the eight positions, and the magnet field produced by the magnet is one of the alternatives shown in  FIG. 2 . 
     According to an exemplary embodiment, the permanent magnet according to embodiments may be a small-sized magnet. In an example, the dimensions of the magnet are 1 cm*1 cm*2 mm. With such a small-sized magnet, special advantages are achieved when quenching small currents compared to the nominal current. 
     If the cross-section of the magnet on the side that faces the quenching plates is rectangular, there are four available mounting positions. According to an exemplary embodiment, there are also other forms that could be used, such as square or triangular. In the case of a triangular magnet, there are six mounting positions, and in the case of a square, there are two alternative mounting positions. 
     The form of the magnet housing and the magnet are such that the magnet housing forces the person doing the assembly to place the magnet into the housing in a position that is acceptable and results the magnetic field to be created in a desired way. Thus, any mounting position the user chooses is acceptable and allowable. The mounting direction of the magnet thereby need not be indicated in any way. 
       FIG. 2  also shows alternatives for the direction of the current I in the arc when the switch is opened. The direction of the current can thus vary between the two alternatives depending on which way the stationary contacts are mounted to the power supply. 
     According to the Lorentz force law, the force F acting on a point charge is directed in vertical direction in the situation of  FIG. 2  depending on the direction of the magnetic field B and the current I. That is, the force F acting on the arc blows the arc towards one of the side portions of the quenching plates. 
       FIG. 3  further highlights the structure of the arc chamber  120 , according to an exemplary embodiment of the present disclosure. In the arc chamber, there are six slots/recesses  140 ,  142  for receiving respective quenching plates. The number of slots and plates is not limited to six but can vary depending on the size of the switch and other design factors. 
     In accordance with an exemplary embodiment, there are two types of slots. The odd numbered slots  140 A,  140 B, that is the first, third and fifth slots are similar. Correspondingly, the even numbered slots  142 A,  142 B, that is the second, fourth and sixth slots are mutually similar. The quenching plates are formed such that the outer edge of the first side portion, that is, the first mounting portion, of the plate is suitable to for mounting to the odd numbered slots, and the edge of the other side portion, that is the second mounting portion, is suitable for mounting to the even numbered slots. Thereby the form of the slots and the plates force that the plates are mounted to the slots in a correct way. If the plates are not mounted correctly to the slots, the plates may prevent mounting of the first and second switch module housings together. 
     The illustrated exemplary embodiment is not limited to there being only two different types of recesses in the switch, as there can be a greater number of different types of recesses. However, also in such a case, the form of the recess is such that it forces the quenching plate to be assembled in a correct position to the switch. 
       FIG. 3  shows the bottom housing module  120  of a switch module, according to an exemplary embodiment of the present disclosure. There is also provided a top housing module for the switch module. The top housing may have similar slots for receiving the quenching plates; however, they are in an inverse order compared to the slots in the bottom housing. That is, a slot of a first type in the bottom housing is opposite to a slot of second type in the top housing module. Thereby also the top housing ensures that the quenching plates are mounted to the switch in correct position. 
       FIG. 4A  further illustrates a group of quenching plates, and  FIG. 4B  shows one plate from the side, according to an exemplary embodiment of the present disclosure. 
     In  FIG. 4A , all the plates are similar but they are arranged alternately such that each other plate is flipped 180 degrees. However, the plates are asymmetric in view of a middle line of the plate. The asymmetry shows inside of the plate where a propagation channel  450  for the arc is formed. The asymmetry also shows on the outside of the plates, especially on the edges of the plates including a first mounting portion  468  and second mounting portion  470  for mounting the plate to respective recesses in the switch. When, in a group of plates, each other plate is flipped 180 degrees, the propagation channel  450  for the arc between the side portions of the plates becomes non-continuous or non-uniform. The form of the channel changes between adjacent plates in the group of plates. Thereby, the propagation path length can be increased, which effectively causes quenching of the arc. 
     As can be seen from  FIG. 4B , the quenching plate  122 B is substantially U-shaped, having a base/bottom portion  464  and two side portions  460 ,  462  extending from the base portion. In the exemplary embodiment of  FIG. 4B , the base portion  464  may include a vertical portion, and the side portions may include horizontal portions, that is, they are arranged at least substantially perpendicularly to each other. It can be seen that the two side portions  468 ,  470  are substantially parallel with respect to each other. Between the side portions, a propagation channel  450  is formed for the arc. 
     As the figure shows, the top and bottom halves of the plate are asymmetric in view of a horizontal middle line. The propagation channel of the plate is thus asymmetric in view of a horizontal middle line, which thus refers to a line, which is perpendicular to the longitudinal vertical direction of the base in the figure. The middle line is thus substantially parallel to the longitudinal direction of the side portions. 
     Within the propagation channel, a propagation bottom  466  may be provided in the lower half of the plate, which propagation bottom is closest to the base  464 . The propagation bottom thus lies aside from the middle of the plate thereby causing the propagation channel to become non-uniform when similar plates are mounted alternately to the switch. According to an exemplary embodiment of the present disclosure, the arc seeks the furthest point in the plate, and the purpose of the propagation bottom is to maximize the length and to give variety to the form of the arc propagation path. In the neighbouring plate, as the plate is 180 degrees flipped to plate  122 B, the propagation bottom would be in the higher half of the plate. 
     It can also be seen that the mounting portions, that is the upper edge  468  and lower edge  470  of the respective side portions  460 ,  462  are mutually different from each other. As  FIG. 4A  shows, the first mounting portion  468  comprises a first portion  468 A, which may be substantially parallel the first portion  470 A of the second mounting portion  470 . The two first portions  468 A,  470 A are the most distant edges of the side portions  460 ,  462 , and they may be parallel to the walls of the housing receiving the mounting portions. The first portions may be the most distant portions of the side portions when viewed from the base  464 . It can be seen that the first portions may have different lengths when compared to each other. In the illustrated exemplary embodiment, the first portion  468 A is longer than the first portion  470 A. There may be provided second portions  468 B,  470 B, which are arranged to an angle with respect to the first portions and the third portions  468 C,  470 C, which may be substantially parallel to the first portions  468 A,  470 A. As the figures show, the propagation space between the sides  460 ,  462  of each plate is asymmetric when seen from the middle of the side portions. 
     The recesses in the module housings are arranged respectively, such that one of the housings is capable of receiving the first mounting portion of a quenching plate, and the opposite housing is capable of receiving the second mounting portion of the same quenching plate. 
     In this manner, the plate  122 B can be mounted to either of the slots  140 A or  142 A depending on which mounting portion is used. 
     It will be obvious to a person skilled in the art that, as the technology advances, 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. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.