Patent Publication Number: US-8526159-B2

Title: Surge protector having a thermal separating device

Description:
The invention relates to an overvoltage protection device comprising a thermal disconnection device and a fault indicator as well as at least two first protection elements, specifically disc-shaped varistors, and at least one second protection element, specifically a gas arrester, wherein the first and the at least one second protection elements are interconnected in a Y-arrangement, further comprising a device housing or supporting part for receiving the protection elements and means for mechanically preloading the thermal disconnection device, wherein the thermal disconnection device comprises a low-melting solder and the first protection elements are arranged in the device housing such that one connection pin of one protection element is positioned opposite the connection pin of the other first protection element at a distance, and the thermal disconnection device is located mainly in the so formed distance space, according to the preamble of patent claim  1 . 
     BACKGROUND OF THE INVENTION 
     An overvoltage protection device comprising a thermal disconnection device is already known from the German Utility Model DE 295 19 313 U1. The surge arrester described in this document comprises a lower part which is electrically connected to ingoing and outgoing leads of the system to be protected or the device to be protected. In addition, a plug-in part is provided, which comprises at least one varistor. The plug-in part can be detachably, yet electrically connected to the lower part by a mechanical connector. A thermal release is provided on the plug-in part in the event of the varistor being inadmissibly heated. A supporting wall is located in the plug-in part, with the varistor being mounted on a side face of the supporting wall and the thermal disconnection device as well as corresponding connection means being provided on the other side face of the supporting wall. Thus, the thermal release is placed opposite the varistor. 
     The prior plug-in part is trough-shaped, with the bottom of the trough forming the aforementioned supporting wall and the edge of the trough surrounding the region next to the supporting wall in which the varistor provided on the supporting wall is located. The varistor itself is provided with two connecting lugs serving the electrical connection. One of the connecting lugs is connected to the thermal release element. 
     In the overvoltage protection device according to EP 0 727 091 B1 two or more varistors accommodated in a housing are provided as protection elements, whose earth electrodes are electrically interconnected by means of a strip with a contact piece. The mains electrodes are connected to contact pieces by means of disconnection devices connected in series to the protection elements. 
     According to EP 0 727 091 B1 the problem is to be overcome to simplify the disconnection device in structure, without disadvantageously affecting the protective properties. 
     To this end, all disconnection devices are arranged in the pivoting region of the web of an essentially U-shaped bail designed as a rocker and swivel-mounted in the housing. A displaceably mounted actuating bolt is bearing on the web, and an indicating device is further arranged on the bail. As a common rocker is allocated to all the disconnection devices, in turn allocated to protective elements installed in the overvoltage protection device, the construction is simplified. All the same it is ensured that when the disconnection device is opened (released), i.e. also when only one disconnection device is opened, the actuating bolt is displaced and the provided release indicating device reaches a position which indicates that an exchange of the overvoltage protection device is necessary. 
     In the device for protection against the occurrence of transient electrical overvoltages according to EP 0 716 493 B1 at least two varistors are provided. Moreover, separating means are provided which are sensitive with respect to the condition of the varistors, especially in thermal terms. Each of the varistors can and should be disconnected separately. 
     The generic document WO 2007/105066 A1 describes an overvoltage protection device comprising two disc-shaped varistors and a gas arrester, with the varistors and the gas arrester being interconnected in a Y-arrangement. 
     The varistors and the gas arrester are located on a circuit board. The two connection pins of the varistors are oriented to face each other, and a metallic electrical bridge is provided interconnecting the aforementioned connection pins by means of low-melting solder. 
     The bridge is held under a preload by means of a spring, with the spring being supported with one spring end on a bolt fixed on the circuit board. 
     The disconnecting bridge is connected to the gas arrester by means of a conductor section. In one practical embodiment the conductor section is realized as a flexible strand. 
     If the varistors are thermally overloaded the melting temperature of the low-melting solder is reached and the bridge is moved away from the connection pins of the varistors in the disconnecting direction. This solution, too, just like the other prior art, requires an additional separating means. Moreover, there is the risk of an undesired one-sided separation of the bridge. 
     SUMMARY OF THE INVENTION 
     Based on the foregoing it is the object of the invention to provide a further developed overvoltage protection device comprising a thermal disconnection device and the possibility of indicating a fault. The actual disconnection device is to be realized without additional technical means without function limitations resulting therefrom. 
     The solution to the object of the invention is achieved with an overvoltage protection device comprising a thermal disconnection device according to the combination of features defined in patent claim  1 . The dependent claims define at least useful embodiments and advancements. 
     The solution according to the invention permits the realization of an overvoltage protection device in a Y-connection, which is formed of a minimum number of components, which is equipped with commercially available wired protection components, and which does not require any additional disconnecting elements. Additionally, an unequivocal status indication is provided, which is also readable in a currentless state. 
     The commercially available protection elements may be disc varistors and gas arresters. 
     The protection elements and means for mechanically preloading the thermal disconnection device are located in the device housing of the overvoltage protection device. The thermal disconnection device comprises a low-melting solder or the like means, e.g. a wax. The first protection elements are arranged in the device housing such that one connection pin of one protection element is positioned opposite the connection pin of the other protection element at a distance. The thermal disconnection device is located mainly in the so formed distance space. 
     According to the invention one connection pin of the second protection element, especially of a gas arrester, directly bypasses the aforementioned connection pins of the first protection elements in the distance space. In the distance space the connection pin of the second protection element contacts the corresponding connection pins of the first protection elements, preferably by a solder. A finger of a mechanically preloaded disconnecting component acts on the bypass connection pin in such a way that, in the event of an overload, the bypass connection pin is physically placed away from the connection pins of the first protection elements, resulting in the desired reliable disconnection from the mains. 
     According to a preferred embodiment the connection pins of the first protection elements are positioned substantially parallel relative to each other and are disposed on one plane. 
     In one embodiment, the connection pin of the second protection element includes an offset, that is, it is bent correspondingly, wherein the offset or bent end forms the region of the bypass connection pin which is connected to the connection pins of the first protection elements. 
     The bent end is oriented substantially perpendicular to the parallel connection pins of the first protection elements. 
     The other connection pins of the first protection elements are connected in the usual manner to contact pins or other connection elements of the overvoltage protection device, which is preferably realized in the form of a plug-in part. 
     At least the free ends of the bypassed connection pins of the protection elements and/or the bent end of the bypass connection pin have a flat, nearly plane shape obtained by pressing or the like measure. 
     In one embodiment of the invention the disc-shaped first protection elements are located in the device housing parallel relative to each other and separated by a wall, wherein the disconnecting component is mounted in the partition wall plane in a pivotably movable manner. 
     Preferably, the bypass connection pin is in a position upstream of the connection pins of the first protection element, and the finger of the disconnecting component includes an oblique bearing surface for the bypass connection pin for preventing a one-sided disconnection. 
     The finger of the disconnecting component engages behind the bypass connection pin at least in a partial section of the distance space so as to ensure that it is reliably carried along in the event of a disconnection. 
     Below the distance space a free space is provided in the device housing, which receives the bypass connection pin and the part of the disconnecting component pivoting into the same in the event of a disconnection. 
     On the end opposite the finger of the disconnecting component the disconnecting component is provided with a display surface known per se for indicating the status. This surface may be a colored surface symbolizing a proper state and, when pivoted, exposing a differently colored surface provided underneath thereof which then indicates the present fault condition. 
     Summarizing, the point of separation is formed by a wire bypass consisting of the bent and flat, pressed connecting wire of the second protection element, specifically of the gas arrester, wherein the same is connected to a flat, pressed connection pin of the varistors of the first protection element by the low-melting solder. 
     As the point of separation is formed of the original connection pins of the protection elements, which connection pins are, for this purpose, merely shaped, no further disconnecting elements or separating means are needed. 
     By displacing the wire bypass to be in front of the varistor connection pins and due to the aforementioned obliqueness of the disconnecting component in the bearing surface a one-sided disconnection is effectively prevented. 
     The invention shall be explained in more detail below by means of an embodiment and with the aid of figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a detailed view of the disconnection device including the connection pins of the first protection elements and the bypass connection pin of the second protection element located in the distance space; 
         FIG. 2  shows a first lateral view of the overvoltage protection device with a preloaded disconnecting component; 
         FIG. 3  shows a second lateral view of the overvoltage protection device with a preloaded disconnecting component; 
         FIG. 4  shows the state after the reaction of the disconnection device in a lateral view similar to that of  FIG. 2 ; and 
         FIG. 5  shows the state after the reaction of the disconnection device in a view similar to that of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The overvoltage protection device shown in the figures is made of a base plastic molding  1  which is surrounded by a cap not illustrated in the figures. 
     In the bottom area  2  of the base plastic molding  1  through holes for plug contacts  3  are provided. Moreover, a recess  4  is provided so as to trigger a remote indicator contact depending on the position of the disconnecting component  5 . 
     The base plastic molding  1  comprises a partition wall  6 . 
     On the left and right sides of the partition wall  6  a disc-shaped varistor  7  is located comprising, in each case, two connection pins. 
     A first connection pin of the respective varistor  7  is connected to one of the plug contacts  3 . 
     A second connection pin extends into a free space  8  inside the base plastic molding  1 . 
     Moreover, a gas arrester  9  is provided. A connecting wire  10  of the gas arrester  9  leads to one of the plug contacts  3 . The varistors  7  and the gas arrester  9  are interconnected in a Y-connection. 
     The disconnecting component  5  is mounted in a pivotably movable manner on a pin-shaped prolongation which forms part of the base plastic molding  1 . Furthermore, the disconnecting component is held under a mechanical preload by means of a spring  11 . 
     To this end, one end of the spring  11  engages into a recess in the disconnecting component  5 , while the other end of the spring  11  is held on an upright prolongation in the base plastic molding  1 . 
     In order to simplify the illustration the spring  11  was omitted in  FIGS. 4 and 5 . 
     The varistors  7  are each located on either side of the partition wall  6 , in a position parallel next to each other in such a way that the varistor terminals  12  not leading to the plug contacts  3  are disposed substantially parallel next to each other and on one plane. 
     A distance space  13  is defined between the varistor terminals  12 . 
     The distance space  13  and thus the varistor terminals  12  are directly bypassed by another connecting wire  14  of the gas arrester  9 . 
     Thus, by means of an offset of the connecting wire  14 , a bypass connection pin  15  is formed, which acts as a disconnecting element without any other separate means. 
     The disconnecting component  5  leads into a finger  16  (see  FIG. 5 ). With a bearing surface the finger  16  presses against the bypass connection pin  15 . 
     The bypass connection pin  15  is connected to the varistor terminals  12  by a low-melting solder. 
     The varistor terminals  12  are very short so that the bypass connection pin  15  is located close to the varistor and is correspondingly thermosensitive. 
     By means of the disconnecting component  5  and the finger  16 , in cooperation with the spring  11 , a permanent force is acting on the bypass connection pin  15 . 
     An inadmissible heating of the varistor(s) leads to the heating of the solder which acts as connecting means. As a result, the spring-preloaded disconnecting component  5  including the finger  16  moves downwardly, as is shown in  FIGS. 4 and 5 , and presses the bypass connection pin  15  away from the point of connection between the varistor terminals  12 , namely into a safe disconnected position. 
     The bent end of the connecting wire  14  of the gas arrester, which is particularly easy to recognize in  FIG. 1 , extends substantially perpendicular to the parallel connection pins  12  of the varistors  7 . 
     The free ends of the varistor terminals  12  as well as the bypass connection pin  15  have a flat shape, wherein this desired flat shape may be obtained, for instance, by a pressing pressure. 
     Physically, the bypass connection pin  15  is located upstream of the varistor terminals  12 , which represent the first protection elements. 
     The finger  16  of the disconnecting component  5  additionally includes an oblique bearing surface  17 . The oblique bearing surface  17  permits, in combination with the shape of the finger  16  which engages behind the distance space at least in a partial section, to effectively prevent a one-sided disconnection. 
     In the event of a disconnection the free space  8  receives the bypass connection pin  15  and the part of the disconnecting component  5  pivoting into the same (see  FIGS. 4 and 5 ). 
     The end of the disconnecting component  5  opposite the finger  16  comprises a display surface  18 . 
     In the proper operating state (see  FIGS. 2 and 3 ) the display surface  18  covers a signal surface  19  provided underneath the former, which may be colored in red. In the fault state (see  FIGS. 4 and 5 ) the display surface  18  of the disconnecting component  5  moves away from the congruent position relative to the signal surface  19  so that the signal surface  19  is exposed. A corresponding view window in the non-illustrated housing cap then reveals the signal surface  19  and indicates the fault state. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  base plastic molding 
           2  bottom area 
           3  plug contact 
           4  recess 
           5  disconnecting component 
           6  partition wall 
           7  varistor 
           8  free space 
           9  gas arrester 
           10 ;  14  connecting wire 
           11  spring 
           12  varistor terminal 
           13  distance space 
           15  bypass connection pin 
           16  finger 
           17  oblique bearing surface 
           18  display surface 
           19  signal surface