Patent Publication Number: US-11651916-B2

Title: Switching device or contactor with high arc extinguishing capabilities

Description:
CROSS REFERENCE AND PRIORITY CLAIM 
     This patent application is a U.S. National Phase of International Patent Application No. PCT/EP2019/072795 filed Aug. 27, 2019, which claims priority to European Patent Application No. 18194780.5, the disclosure of which being incorporated herein by reference in their entireties. 
     FIELD 
     The disclosed embodiments relate to an improved switching device or contactor with high arc extinguishing capabilities for industrial and railways applications. More specifically, but not exclusively, the disclosed embodiments relate to a contactor device for industrial and/or railways applications wherein, for instance, a high D.C. current must be switched on and off with high capacity of switching actions to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads. 
     BACKGROUND 
     As it is well known in this specific technical filed, contactors are remotely controlled switches including an electromagnetic actuator that may be used in many industrial or railways applications wherein a high A.C. or D.C. current must be switched on and off with relatively high frequencies switching actions. 
     Generally speaking, a contactor may be considered a switching device for high current and voltage applications, no matter which is the electric load to be driven. 
     Just to give an idea of the working conditions and the range of current values involved for these kind of contactors, it should be noted that these devices must be able to efficiently switch currents at least in the range between 400 A to 1800 A and under operating voltage ranges between 1000 V and 4000 V. 
     Those operating ranges may even be referred to a single pole of the contactor but in many applications, it is however necessary to provide a double or a three poles configuration. 
     A contactor of known structure normally include fixed contacts, movable contacts and at least a contactor coil. In normally open devices, when a sufficient starting current flows through the contactor coil, the contactor responds and turns on the loads connected in the load circuit. 
     To maintain the contactor in this state, a holding current must continuously flow through the contactor. After the holding current is switched off, the contactor drops out. The energy stored in the contactor coil is dissipated in a free-wheeling circuit or, better, in a quick and proper overvoltage protection, like a Varistor or a Transil. 
     Contactors of high quality and performance require an arc extinguishing portion, so-called arc chute portion, for properly extinction of the electric arc that may be generated in the high voltage portion of the switch where the movable contacts are provided. 
     One of the main problems encountered in the manufacturing of the switching devices for high current and voltage applications is=the correct dimensioning of the arc extinguishing portion. 
     SUMMARY 
     The disclosed embodiments provide an improved switching device or contactor for high current or high voltage switching applications having such structural and functional characteristics to allow a more efficient dissipation of the electric arc that may be generated during the opening or closure phase of the movable contacts thus conferring to the device higher arc extinguishing capabilities. 
     Disclosed embodiments provide a switching device having a higher reliability and a longer operating life due to a higher efficiency in the turn off phase of the possible electric arc. 
     Disclosed embodiments provide a switching device that may be constructed with materials having reasonable industrial costs. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows a schematic and perspective view of a switching device or contactor realized according to the disclosed embodiments; 
         FIG.  2    shows a schematic and front view of the switching or contactor device of  FIG.  1    with a lateral cover removed; 
         FIG.  3    shows a schematic and perspective view of the switching device of  FIG.  1    with a lateral cover removed; 
         FIG.  4    shows a schematic enlarged front view of a central upper portion of the contactor device of  FIGS.  2  and  3   ; 
         FIG.  5    shows a schematic and top view of a single pole contactor according the disclosed embodiments with the arc chute portion removed and a visible upper extinguishing arc portion; 
         FIG.  6    shows a schematic and lateral view of a movable contact of the contactor portion of  FIG.  5    seen from a central point of the contactor; and 
         FIG.  7    shows a perspective view of different arc chute portions according to the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The design phase is particularly critical since the arc chute portion requires sometimes to be enlarged and expanded according to the version of the switching device; in other words, according to the operating current or voltage that the switching device must manage. Moreover, the extinguishing phase of the electric arc is a real problem when the contactor is used for low current applications. 
     As a matter of fact, the contactors are generally designed to switch high currents and when the switched current is under a predetermined threshold, for instance of few Ampere only, the magnetic field generated in the blow-out coil is not sufficient to detour the electric arc toward the extinguishing chamber. Such a current which is not sufficient to detour the electric arc toward the extinguishing chamber is defined as a “low (switched) current”. Such a current is also known as “critical current”. 
     The technical problem underlying the present disclosed embodiments is that of providing an improved switching device or contactor for high current or high voltage switching applications having such structural and functional characteristics to allow a more efficient dissipation of the electric arc that may be generated during the opening or closure phase of the movable contacts thus conferring to the device higher arc extinguishing capabilities. 
     Another aim of the present disclosed embodiments is that of providing a switching device having a higher reliability and a longer operating life due to a higher efficiency in the turn off phase of the possible electric arc. 
     A further utility of the present disclosed embodiments is that of providing a switching device that may be constructed with materials having reasonable industrial costs. 
     Disclosed embodiments provide hardware means able to blow out the electric arc when low currents are switched by the contactor. 
     These hardware means preferably include magnetic elements positioned in the proximity of moving contacts of the contactor to generate a magnetic field sufficient to at least partially detour the electric arc and to extinguish the arc generated when low switched currents are involved. Advantageously, those magnetic elements are permanent magnets. 
     According to the disclosed embodiments and to one aspect of the disclosed embodiments, the technical problem is solved by an improved switching device or contactor having high arc extinguishing capabilities and comprising, in a protective casing: 
     a switch base portion including electrical switching means of a low voltage driving portion active on moving contacts; 
     a high voltage portion including the moving contacts driven towards and away from each other with respect to a mutual contact position, the moving contacts being mounted at respective contact ends of a toggle mechanism which is movable by a low voltage driving portion, and a top arc chute extinguishing portion covering the high voltage portion. 
     Hardware is provided in the proximity of the moving contacts to influence an electric arc occurring when currents are switched on and off by the moving contacts moving towards and away from each other. Advantageously, the hardware means include magnetic elements positioned close to the moving contacts to generate a magnetic field sufficient to at least partially detour the electric arc when low switched currents are involved. 
     Advantageously, the magnetic elements are permanent magnets. 
     Moreover, advantageously, the magnetic elements are positioned at each lateral side of each moving contact. 
     Each of the magnetic elements is structured as a disk supported laterally of a corresponding moving contact in a fixed position when the moving contacts are in the rest or open position. 
     Advantageously, the contactor of the disclosed embodiments includes at least four magnetic elements, two for each moving contact. 
     Advantageously, the hardware is active to detour the electric arc toward the top arc chute and they are mainly active when the low currents are not enough, when flowing through the blow out coil, to generate the proper electromagnetic force. 
     Arc runners are advantageously provided over each corresponding moving contact in their open or rest position and the hardware means including magnetic elements are positioned at both sides of each arc runner. 
     Each arc runner is advantageously formed by a flat metal plate extended over the corresponding moving contact and bent on both lateral sides with opposite flanges that partially and laterally protect the corresponding moving contact; the magnetic elements being positioned at both sides of the opposite flanges. 
     Further features and advantages of the switching or contactor device of the disclosed embodiments will appear from the following description given by way of not limiting example with reference to the disclosed Figures. 
     With reference to the Figures,  FIG.  1    is globally and schematically shown a switching or contactor device realized according to the disclosed embodiments. 
     In particular, but not exclusively, the contactor  1  is specifically provided for industrial or railways applications wherein, for instance, a high D.C. current must be switched on and off with high frequencies switching actions to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads. 
     Just to give an idea of the working conditions and the range of current values involved for these kind of contactors, it should be noted that these devices must be able to efficiently switch currents at least in the range between 400 A to 1800 A and under operating voltage ranges between 1000 V and 4000 V. For instance, a LTX family of line contactors is structured to operate under high voltage rating, high thermal current and when high breaking capacity (up to 4 kV) are required. 
     Those operating ranges may even be referred to a single pole of the contactor. In many applications it is however necessary to provide a double pole configuration and/or a three poles configuration that may be obtained by coupling single poles side by side thanks to a modular single pole structure, even if not shown in the drawings. 
     In the following lines just the structure of a single pole module is detailed, as the same principle is applied on each couple of moving contacts even installed in a bipolar or tripolar contactor. 
     The module presents an envelope or housing  10  protecting and covering all the moving portions of the contactor device  1 . The envelope  10  is made by a synthetic plastic material having a predetermined isolation coefficient and high coefficient of trace index CTI. Such an envelope  10  has a base flange  13  and includes an internal frame  20  supporting the various moving components of the contactor  1 . 
     It should be noted that fixed terminal power contacts  11  and  12  are provided for the contactor  1 . Those fixed contacts  11 ,  12  are projecting on opposite lateral sides of the envelope  10 ; however, other dispositions may be adopted. 
     Those terminal power contacts  11 ,  12  are each associated to a corresponding internal moving contact  21 ,  22  provided inside the contactor device  1 , as will be explained hereinafter. Advantageously, the creepage and clearance distances between the moving contacts  21  and  22  has been widely dimensioned for safe applications in polluted environments but the narrow outline of the envelope  10  is especially conceived for applications where space is a critical issue. 
     The contactor  1  of the disclosed embodiments is structured to be used on electrical equipment working in presence of severe shocks and vibrations that normally occurs on-board of traction vehicles. However, nothing refrains from employing this kind of contactors  1  in all the applications wherein a high A.C or D.C. current must be switched on and off, for instance: line contactors, power switches or converters, traction motors, electromagnetic brakes and heating/air conditioning systems. 
     The contactor  1  comprises a switch base portion  2  and an upper arc extinguishing portion  3 . The innovative design (of LTX line) of the disclosed embodiments combines the traditional technology of the arc chute (ceramic fins) with a new blow out system. Ceramic arc chute enables to withstand the highest current ratings and the new blowout system guarantees a high reliability with critical currents. 
     The switch base portion  2  is common for each different modular contactor  1  and corresponds to the main structure of the envelope  10  while the upper arc extinguishing portion  3  may be considered as a top coverage of the envelope  10  that may have a different size according to the different power category and voltage ranges that the contactor shall provide. The switch base portion  2  includes electrical switching means  35 . 
     The upper arc extinguishing portion  3  may be structurally different according to the different voltage ranges, as shown in  FIG.  7   , that must be treated and the corresponding arc chute type and energy capacity that shall be extinguished in total security. 
     An arc extinguishing portion  3  for a voltage value of 1000 V may have the structure shown in  FIG.  1 ,  2  or  3    while an arc extinguishing portion for a higher voltage value up to 3000 V may require a greater or thicker extinguishing portion and larger polar expansions. 
     According to the disclosed embodiments, hardware means  40  are provided in the switch base portion  2  of the contactor  1  for attracting the electric arc when relatively low currents are switched by the contactor  1 . Such an electric arc is schematically shown in  FIGS.  4 ,  5  and  6    with the number  29 . 
     These hardware means  40  include magnetic elements  41 ,  42  positioned in the proximity of the moving contacts  21 ,  22  of the contactor  1  to generate a magnetic field  18  sufficient to partially detour the electric arc  29  and to extinguish such an arc  29  generated in particular when low switched currents are involved. 
     Advantageously, those magnetic elements  41 ,  42  are permanent magnets. 
     Moreover, the magnetic elements  41 ,  42  are positioned at each lateral side of each moving contact  21 ,  22 . 
     Each of the magnetic elements  41 ,  42  is structured as a disk supported laterally of a corresponding moving contact  21 ,  22  in a fixed position when the moving contacts  21 ,  22  are in the rest at the open position. 
     The shown embodiment of the contactor  1  includes at least four magnetic elements  41 ,  42 , that is two for each moving contact  21 ,  22 . 
     The hardware means are active to detour the electric arc toward the top arc chute and they are mainly active when the low currents are flowing through the main contacts. 
     These magnetic elements  41 ,  42  are supported in the casing  10  in an inclined position substantially perpendicular to a corresponding moving contact  21 ,  22  and at predetermined distance of few millimeters from arc runners  23 ,  24 . 
     The internal schematic structure of this switch base portion  2  including the electrical switching means  35  is shown in  FIG.  2   . 
     The switch portion  2  may be separated in a low voltage portion  4  and a high voltage portion  5  located over the low voltage portion  4 . The low voltage portion  4  is provided for driving the switching of the internal moving contacts  21 ,  22  of the upper high voltage portion  5 . 
     The contactor  1  of the disclosed embodiments is a monostable element that is provided with normally open contacts according to the vast majority of customer requirements. 
     The internal moving contacts  21  and  22  of the upper high voltage portion  5  are put in abutment one against the other for allowing the passage or flow of the high DC current. Advantageously, the electrical contacts  21 ,  22  are symmetrically moving towards and away from each other. 
     The contactor  1  includes a couple of reciprocally symmetrically moving contacts  21 ,  22  driven towards and away from each other with respect to a central mutual contact position or abutting position. 
     Each moving contact  21  or  22  is positioned at the end of a corresponding elongated arm  25 ,  26  of a toggle mechanism  30 , as shown in  FIGS.  2  and  3   . The arms  25 ,  26  are manufactured by a conductive material, for instance a metal. 
     Over the contacts  21 ,  22 , but still part of the switch base portion  2 , respective arc runners  23 ,  24  are provided. 
     Those arc runners  23 ,  24  are normally provided to help in dissipating the electric arc  29  formed during the opening phase of the moving contacts  21 ,  22 . Depending on the application, arc running can be installed or not. 
     Each of the arc runner  23 ,  24  is electrically connected to a respective dissipation or blow coil  51 ,  52 . Each coil  51 ,  52  is provided at the shoulder of each moving contact  21 ,  22  of each arm  25 ,  26 . 
     Each arc runner  23  or  24  is formed by a flat metal plate extended over the corresponding moving contact  21  or  22  when they are in the open or rest position. The upper flat metal plate is bent on both lateral sides with opposite flanges  44 ,  45  that partially and laterally protect the corresponding moving contact  21  or  22 , as shown in  FIG.  6   . 
     The lateral metal flanges  44 ,  45  represent detouring elements that may attract the arc flow path as a function of the DC current direction, as shown by the arched curves  29  in  FIG.  6   . 
     Advantageously, each magnetic element  41  or  42  is located outside a corresponding flange  44  or  45  laterally from the moving contact  21  or  22 . 
     Moreover, a polar expansion  50 , that is to say a metal plate, is provided on both sides of the moving contacts  21 ,  22 . In  FIG.  5    only one plate  50  is shown since only half a shell of the housing  10  is shown but it should be considered also the presence of a corresponding plate situated in a parallel position on the other side of the envelope with respect to the contacts  21 ,  22 . 
     For completeness sake we will now disclose the other portions of the contactor  1  that are dedicated to the switching action. 
     The toggle mechanism  30  shown in  FIGS.  2  and  3    includes a couple of legs  31  and  32  that are joined at one end in a sliding hinge  33  that is movable along a vertical slot  19  of the frame  20 . The legs  31  and  32  are made by an insulating material, for instance a thermosetting material. 
     The opposite ends of each of the legs  31 ,  32  are hingedly linked to a corresponding end of the arms  25  and  26  supporting the moving contacts  21 ,  22 , respectively. More specifically, each end of the arms  25 ,  26 , opposite to the moving contacts  21 ,  22 , is linked to a corresponding end of the legs  31 ,  32 . 
     Each arm  25  or  26  is pivotally supported in the frame  20  by a corresponding pivot  27 ,  28  in a position that corresponds substantially to one third of the whole longitudinal length of the arm. 
     The legs  31 ,  32  and the arms  25 ,  26 , together with the corresponding hinge joint  33  form the toggle mechanism  30  that allows driving the moving electric contacts  21  and  22  one toward the other and vice versa. The rods  31 ,  32  as well as the arms  25 ,  26  are formed by a couple of identical parallel components that are linked together more or less like a truss beam. 
     Between each of the pivots  27 ,  28  and the corresponding fixed terminal power contact  11  or  12  there is a fork arm  47 ,  48  made by a conductive material, such as a metal. 
     Those fork arms  47 ,  48  are substantially linked to the fixed terminal power contacts  11  and  12  to provide electric continuity between the moving electric contacts  21 ,  22  and the fixed terminal contacts  11 ,  12 . 
     The toggle mechanism  30  is activated by the low voltage driving portion  4  that will be disclosed hereinafter. 
     The hinge joint  33  is provided with a central annular elastic element  39  that is contacted by an active end of the low voltage driving portion  4  and may be considered as a bumper between the active end and the whole toggle mechanism  30 . This hinge joint  33  is forced to slide along the vertical slot  19  by a sliding guide  39 , not visible in the drawings. 
     The low voltage driving portion  4  includes a coil  6  that is electrically supplied by a low voltage reference potential, not shown being of a conventional type and driven by a suitable switching actuator. 
     The coil  6  is active on a stem  7  that is extended horizontally and parallel to the base flange  13  of the contactor envelope  10  inside the switch base portion  2 . The stem  7  is moved against the contrast of an elastic element  8 , for instance an elongated spring to be compressed. 
     The free or distal end  14  of the stem  7  is linked to one end of a lever  15  which is pivotally mounted on a fulcrum  16  fixed or integral with the internal frame  20  of switch base portion  2  of the contactor  1 . 
     The lever  15  has a first arm linked to the free distal end  14  of the stem  7  and another or second arm free to move around the fulcrum  16  when the lever  15  is actuated by the coil  6  and the stem  7 . 
     The free end of this second arm is active on the hinge joint  33  of the toggle mechanism  30 . 
     An electric circuit  49  is provided for supplying the coil  6  related voltage values according to the different needs to drive the low voltage driving portion of the actuator. This circuit  49  is substantially a voltage level shifter suitable to receive a plurality of different voltage values. According to the present embodiment two types of electromagnets or coils  6  have been considered, that is to say: high and low voltage coils having a control card to control starting current and holding current. This electronic control of the main coil allows to combine a high closing power with a reduced power consumption during the holding phase. 
     In view of the previous description, the functioning of the contactor device  1  of the disclosed embodiments are evident. 
     According to the solution idea at the basis of the disclosed embodiments, in the contactor device  1  there is not a fixed contact but, on the contrary, a couple of movable contacts  21 ,  22  that are driven towards and away from each other with respect to a mutual contact position. 
     According to set initial conditions, the electromagnet  6  of the low voltage driving portion  4  is biased to move the stem  7  that is joined to one end of the two arms lever  15  pivotally hinged on the fulcrum  16 . 
     The movement of the stem  7  moves the free end of the lever  15  that acts on the sliding hinge  33  of the toggle mechanism  30 . That sliding hinge  33  is free to move up and down or axially along a slot of the frame  20  so to push up or down and this movement forces the whole toggle mechanism  30  to provide a closure or an aperture of the moving contacts  21 ,  22  accordingly. 
     The structure of the double symmetrically moving contacts  21 ,  22  of the disclosed embodiments allows obtaining a physical separation of the contacts of at least 73 mm that allows reducing the risk of electric arc and renders particularly reliable the switching of the contactor device of the disclosed embodiments with respect of the insulation characteristics. 
     Contacts  21  and  22  open with double speed and the toggle mechanism  30  guarantees also a higher distance between them. 
     The magnetic elements  41 ,  42  positioned at both sides of the opposite flanges  44 ,  45  of the arc runners  23 ,  24  allow detouring the electric arc toward the top arc chute  3  mainly when low switching currents are involved. 
     The contactor according to the disclosed embodiments may be used also for switching in high AC current applications. 
     In the previous lines the directional terms like: “forward”, “rearward”, “front”, “rear”, “up”, “down”, “above”, “below”, “upward”, “downward”, “top”, “bottom”, “side”, “vertical”, “horizontal”, “perpendicular” and “transverse” as well as any other similar directional terms refer just to the device as shown in the drawings and do not relate to a possible use of the same device. Accordingly, these directional terms, as utilized to describe the contactor in its upright vertical position on a horizontal surface have just the meaning to identify a portion of the device with respect to another portion as shown in the figures. 
     The term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. This concept also applies to words of similar meaning, for example, the terms “have”, “include” and their derivatives. 
     Moreover, the terms “member”, “section”, “portion”, “part” and “element” when used in the singular can have the dual meaning of a single part or a plurality of parts.