Abstract:
The present invention teaches an overvoltage protection device that includes at least one non-linear resistance element and a single cut-off device coupled with the at least one non-linear resistance element to disable the at least one non-linear resistance element when the at least one non-linear resistance element reaches a pre-determined temperature. The single cut-off device may include stranded wire, a first solder having a first melting point connecting the stranded wire to the at least one non-linear resistance element, and a second solder having a second melting point, higher than the first melting point, connecting the stranded wire to the at least one non-linear resistance element. The single cut-off device may further include a shifting part that shifts when the at least one non-linear resistance element heats the first solder to the first melting point. In other particular embodiments, the overvoltage protection device may further include a status indicator configured to be moved by the single cut-off device to indicate one of at least two conditions of the at least one non-linear resistance element. The status indicator may include a lever, and the single cut-off device moves the lever to indicate the one of at least two conditions of the at least one non-linear resistance element.

Description:
FIELD OF THE INVENTION 
     The invention relates to an overvoltage protection device having at least one non-linear resistance element with a cut-off device coupled with a status indicator of overvoltage protection. 
     BACKGROUND 
     Overvoltage protection devices have a protective element which generally includes a non-linear element (varistor) which, due to its loading of electric current and by an impulse loading of a protected network, gradually decreases the value of its resistance. Due to this, the current running through the protective element increases, and its temperature increases as well. Therefore, the overvoltage protection includes a temperature cut-off device which serves to disable the protective element due to its temperature, preventing the protective element from properly fulfilling its function. Disabling the protective element from the network is indicated either visually directly on the overvoltage protection or remotely by transmission of a suitable signal. Once the protective element is cut off from the network, the network is no longer protected, so it is necessary to regain the protected status by replacing the protective element of overvoltage protection. 
     The visual indication of the status of overvoltage protection is required, especially for overvoltage protection of category II equipment according to the IEC 61643-11. This status indicator distinguishes between two modes of status, the “good one”—green color, and the “fault one”—red color. The status modes may be expressed even differently than through this colorful resolution. The disadvantage of such status indicators is that it does not identify when the overvoltage protection is already partially degraded but not yet disabled from the protected circuit by means of a built in cut-off device. Due to the fact that only the enabled or disabled status of the protected circuit is indicated, a situation may occur when the overvoltage protection is degraded due to deterioration t or disabled before the non-functioning or disabled overvoltage protection is replaced by a functioning one, causing the respective electrical circuit to be not protected, and thus increasing the hazard of damage of the non-protected electrical equipment due to an overvoltage condition. 
     There is a known solution in which between the phase and neutral or ground wire there are included two parallel connected varistors, with each varistor having its own cut-off device from the protected circuit. The first varistor is cut off due to melting of the temperature fuse which causes the pressure spring to move the shifting part to act upon the swiveling part to block about half of the overvoltage protection signal which provides optical information that the overvoltage protection device is partially deteriorated. The shifting part, changes its position to simultaneously activate the remote status indication of overvoltage protection. When the second varistor is cut off, the entire overvoltage protection signal is blocked through the same mechanism to create the visual indication that the entire overvoltage protection for the protected circuit is disabled. 
     Considerable complexity and coupling of several functional elements results in higher production costs which is disadvantageous for this solution. 
     There is another known solution which signals partial deterioration of overvoltage protection by means of a pair of parallel connected varistors equipped with cut-off mechanisms, each having its own spring. The function of both cut-off mechanisms always depends on the temperature of both varistors. One of the cut-off mechanisms disconnects at a lower temperature of the varistors than the second one. The status indicator shows a green light in case the overvoltage protection is in flawless status. As a result of the operation load and aging of the varistors, the varistors warm up until the cut-off device with the lower temperature setting actuates to screen the status indicator and produce a yellow color indication, creating a visual indication of partial deterioration of overvoltage protection which is, henceforth functioning. Simultaneously through movement of the cut-off mechanism, the remote status indication of overvoltage protection is activated. As a result of further increasing of varistor temperature, upon co-acting of the second spring, the second cut-off mechanism actuates to screen the status indicator and produce a red color to indicate that the overvoltage protection is totally deteriorated and disabled from the protected circuit. 
     Disadvantage of this solution is its considerable complexity of a pair of independent complete cut-off mechanisms which results in high costs for such overvoltage protection. 
     The objective of the invention is to eliminate or at least to minimize the disadvantages of the background art. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one embodiment of the present invention, an overvoltage protection device includes at least one non-linear resistance element and a single cut-off device coupled with the at least one non-linear resistance element to disable the at least one non-linear resistance element when the at least one non-linear resistance element reaches a pre-determined temperature. The single cut-off device includes stranded wire, a first solder having a first melting point connecting the stranded wire to the at least one non-linear resistance element, and a second solder having a second melting point, higher than the first melting point, connecting the stranded wire to the at least one non-linear resistance element. 
     In particular embodiments, the at least one non-linear resistance element may be a varistor. The single cut-off device may further include a shifting part that shifts when the at least one non-linear resistance element heats the first solder to the first melting point. In addition, the shifting part may shift to disable the at least one non-linear resistance element when the at least one non-linear resistance element heats the second solder to the second melting point. In other particular embodiments, the overvoltage protection device may further include a status indicator configured to be moved by the single cut-off device to indicate one of at least two conditions of the at least one non-linear resistance element. The status indicator may include a lever, and the single cut-off device moves the lever to indicate the one of at least two conditions of the at least one non-linear resistance element. 
     An alternate embodiment of the present invention is an overvoltage protection device that includes at least one non-linear resistance element and a single cut-off device coupled with the at least one non-linear resistance element to disable the at least one non-linear resistance element when the at least one non-linear resistance element reaches a pre-determined temperature. The single cut-off device includes a lever and a conductive connecting element. A spring connected to the lever biases the lever against the conductive connecting element, and an adaptor is coupled to the conductive connecting element. A first solder having a first melting point connects the adaptor to the conductive connecting element, and a second solder having a second melting point, higher than the first melting point, connects the adaptor to the at least one non-linear resistance element. 
     A still further embodiment of the present invention is an overvoltage protection device having at least one non-linear resistance element and a single cut-off device coupled with the at least one non-linear resistance element to disable the at least one non-linear resistance element when the at least one non-linear resistance element reaches a pre-determined temperature. The single cut-off device includes a lever, a conductive strip coupled to the at least one non-linear resistance element, and a spring connected to the lever to bias the lever against the conductive strip. A first solder having a first melting point connects the conductive strip adaptor to the at least one non-linear resistance element. A second solder having a second melting point, higher than the first melting point, connects the conductive strip adaptor to the at least one non-linear resistance element. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  shows a side plan view of a first embodiment of the overvoltage protection device; 
         FIG. 2  shows a perspective view of the first embodiment of the overvoltage protection device; 
         FIG. 3   a  shows a top plan view of the shifting element shown in  FIGS. 1 and 2 ; 
         FIG. 3   b  shows a side plan view of the shifting element from  FIGS. 1 and 2 ; 
         FIG. 4   a  shows a perspective view of a second embodiment of the overvoltage protection device; 
         FIG. 4   b  shows a perspective view of the second embodiment of the overvoltage protection device; 
         FIG. 5   a  shows a perspective view of a third embodiment of the overvoltage protection device; 
         FIG. 5   b  shows a perspective view of the third embodiment of the overvoltage protection device; 
         FIG. 6   a   1  shows a rear plan view of a fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   a   2  shows a side plan view of the fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   a   3  shows a front plan view of the fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection (position “everything OK”); 
         FIG. 6   b   1  shows a rear plan view of the fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   b   2  shows a side plan view of the fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   b   3  shows a front plan view of the fourth embodiment of the overvoltage protection indicating the temporary status of overvoltage protection (position “temporary status”); 
         FIG. 6   c   1  shows a rear plan view of a fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   c   2  shows a side plan view of the fourth embodiment of the overvoltage protection device indicating the temporary status of overvoltage protection; 
         FIG. 6   c   3  shows a front plan view of the fourth embodiment of the overvoltage protection indicating the temporary status of overvoltage protection (position “circuit not protected”); 
         FIG. 6   d  shows a cross section view of an embodiment of the shifting part, stranded wire, and stop; 
         FIG. 6   e  shows a cross section view of an alternate embodiment of the shifting part, stranded wire, and stop; 
         FIG. 7   a  shows a side plan view of an embodiment of the slide-in protective element with encoding device and with a device to enable turning of the slide-in protective element by 180° without affecting its function; 
         FIG. 7   b  shows a cross section view in B direction from  FIG. 7   a;    
         FIG. 7   c  a detail of the embodiment of encoding device to enable turning of the slide-in protective element by 180° without affecting its function; 
         FIG. 8  shows a side plan view of another alternative embodiment of overvoltage protection with temporary status indication of overvoltage protection; 
         FIG. 9  shows a side plan view of another alternative embodiment of overvoltage protection with temporary status indication of overvoltage protection; and 
         FIG. 10  shows a side plan view of another alternative embodiment of overvoltage with temporary status indication of overvoltage protection. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, an overvoltage protection device may include a holder  1 , in which in a replaceable manner a slide-in protective element  2  is mounted. In one holder  1  several slide-in protective elements  2  may be positioned side by side, e.g., for each phase of a three phase electrical line. Also several single pole holders  1  may be connected into one unit, e.g., using rivets. The holder  1  may include arms  1   a  and  1   b  that may include clamps (not shown) for connecting electric wires of a protected circuit. In the illustrated embodiment of the overvoltage protection device with remote indication of status change, the holder  1  also includes in its lower part a positioning member  3  of remote indication with a pressure spring (not shown). The holder  1  is provided with means for mechanical and electrical connection of the slide-in protective element  2 . For electrical connection between the slide-in protective element  2  and the holder  1 , the holder  1  is equipped with current lines and contacts, and the slide-in protective element  2  is provided with contacts  5  and  6 . 
     In the body  7  of the slide-in protective element  2  as a protective element, at least one non-linear resistance element is connected, for example, a varistor  8  or a group of parallel connected varistors. A lower electrode  9  of the varistor  8  connects with one end of stranded wire  10  by means of low-fusing solder. The stranded wire  10  may be modified to increase rigidity by welding individual strands to create the stranded wire, for example. The second end of the stranded wire  10  connects with contact  5  of the slide-in protective element  2 . An upper electrode  11  of the varistor  8  connects with contact  6  of the slide-in protective element  2 , e.g., by means of a connecting element  12 , which may be either a fixed part of the contact  6  or may be also an independent element connected to the upper electrode  11  and to the contact  6 . 
     In the body  7  there is also positioned an identifier  13 , provided with identification elements  13   a  which, in the engaged status of the slide-in protective element  2  in the holder  1 , engage with an identifier  14  on the holder  1  to confirm a correct arrangement of the holder  1  and the slide-in protective element  2  or that the slide-in protective element  2  includes required protective properties. 
     In the body  7  of the slide-in protective element  2  in a shifting manner there is positioned a shifting part  4 , which, by means of a pressure spring  15 , is spring-loaded directly against the stranded wire  10  and acting on the low-fusing link of the stranded wire  10  and against the lower electrode  9  of the varistor  8 . The pressure spring  15  in the illustrated embodiment is positioned in a cavity  4   a  of the shifting part  4  and rests against a wall  7   a  of the body  7  of the slide-in protective part  2 . The connection of the stranded wire  10  and the lower electrode  9  of the varistor  8  holds the shifting part  4  in its basic position when the pressure spring  15  is depressed. In the embodiment illustrated in  FIGS. 6   a  to  6   e , on the upper side of the stranded wire  10  in the area of its connection with lower electrode  9  of the varistor  8 , a stop  10   a  is fastened to provide a temperature suitable link between the stranded wire  10  and the lower electrode  9 . In this embodiment, the shifting part  4  rests against the stop  10   a  (is pressed to it by the spring  15 ) and primarily acts against the link of the stop  10   a  and the stranded wire  10  to hold it in its basic position when the pressure spring  15  is depressed. Implicitly through the stop  10   a , the shifting part  4  is also acting upon the link of lower electrode  9  and the stranded wire  10 . In the embodiment illustrated in  FIG. 6   d , the shifting part  4  in the initial position rests against a vertical portion  10   a   0  of the stop  10   a . In the embodiment illustrated in  FIG. 6   e , the shifting part  4  in its initial position rests against the vertical portion  10   a   0  of the stop  10   a  and also against a horizontal portion  10   a   1  of the stop  10   a . In the embodiments illustrated in  FIGS. 6   a  to  6   e , the shifting part  4  includes a pressure wall  40  to engage with one end of the stranded wire  10  when the shifting part  4  actuates. Also, the embodiments shown in  FIGS. 1 to 5   b  may be adapted to include the stop  10   a , the purpose and function of which will be described hereinafter. 
     In the embodiments shown in  FIGS. 1 to 4   b , the shifting part  4 , between its walls  4   b  and  4   c , has an inserted lower arm  16   a  extending from one end of a flat lever  16 . The flat lever  16  is rotatably mounted on the body  7  by a pin  7   b  located outside the perimeter of the varistor  8  or the varistors  8 . In the embodiment shown in  FIG. 5   a  and  5   b , the shifting part  4 , instead of the walls  4   b  and  4   c , includes a gradual wall  4   d  against which the lower arm  16   a  of the lever  16  rests, this being rotatably mounted on the body  7  by the pin  7   b . The lower arm  16   a  of the lever  16  permanently contacts the gradual wall  4   d  of the shifting part  4 , maintained by a tension spring  16   c  connected on one end to the body  7  and on a second end to the lever  16 . The tension spring  16   c  may be substituted with a pressure spring (not shown), arranged in a suitable manner. In the embodiment shown in  FIG. 6   a  to  6   c , the shifting part  4  includes the walls  4   b  and  4   c  that form the cranked groove in which the lower arm  16   a  is inserted. 
     The lever  16  on its other end is equipped with an indicator arm  16   b  provided with the colorful surface or colorful surfaces for visual indication of the status of overvoltage protection. For that purpose the body  7  is provided with a slot  7   c  of visual indication. In the slot  7   c  of visual indication is a surface or insert  17  with color corresponding to the visual indication of the status of overvoltage protection, in which the indicator arm is not attached to the slot  7   c  in the body  7 . 
     The lower wall  7   e  of the body  7  and the identifier  13  include oval slots  7   d  and  13   b  through which the above described positioning member  3  passes and rests against the shifting part  4 . The positioning member  3  at the slide-in protective element  2  is inserted in the holder  1  and contacts the shifting part  4  to transmit the status information of overvoltage protection for remote indication through respective functional elements in the holder  1 . In the displaced position of the shifting part  4  (it will be described hereinafter), the positioning member  3  moves into the body  7  of the slide-in protective element  2 . The identifier  13  is equipped with identifying protrusions  13   a  that engage with corresponding holes in the holder  1 . 
       FIGS. 7   a  to  7   c  show an embodiment that enables the slide-in protective element  2  to rotate in the holder  1  by 180° without influencing the protective and indication (remote as well as visual) functions of the slide-in protective element  2 . In this embodiment, the positioning member  3  in the holder  1  is situated outside the axis “a” of symmetry of the contacts  5 ,  6  or outside the centre of distance of contacts  5 ,  6 , and simultaneously it is situated also outside the longitudinal axis “b” of the slide-in protective element  2 . Oval slots  7   d  and  13   b  are situated askew to axes “a” and “b”. The shifting part  4  includes a supporting wall  41  with a gradual end  41   a . In each portion of the skewed oval slots  7   d  and  13   b  is a section  410 ,  411  of supporting wall  41  of the shifting part  4 . In basic position of the shifting element  4 , the end of the spring-loaded positioning member  3  in one position of the slide-in protective element  2  is touching the first section  410  of supporting wall  41  of the shifting part  4 , while in position of the slide-in protective element  2  turned by 180°, the end of the spring-loaded positioning member  3  is touching the second section  411  of the supporting wall  41  of the shifting part  4 . In displaced position of the shifting part  4 , both sections  410 ,  411  of supporting wall  41  are situated outside the track of the spring-loaded positioning member  3 , and it does not prevent it to be inserted into the skew oval slots  7   d  and  13   b  into the body  7  of the slide-in protective element  2  for the remote indication of the status of the overvoltage protection. In angle spacing on the circle around the crosswise arranged oval slots  7   d ,  13   b  there are positioned the identification protrusions  13   a  engaging in both positions of the slide-in protective element  2  (initial as well as the turned by 180°) into the corresponding holes in the holder  1 . In an embodiment not illustrated, the slide-in protective element  2  my not turn in the holder  1 . 
     In embodiments illustrated in  FIGS. 1 to 3   b , all of the elements of the device for cutting off the non-linear resistance element from network and all of the elements of status indication (visual as well as remote) of overvoltage protection inside the body  7  of the slide-in protective element  2  are located entirely outside the perimeter of the non-linear resistance (varistor  8 ) in the view in direction perpendicular to the side surface of the non-linear resistance element (varistor  8 ), i.e., in the direction of the body width  7 . In this arrangement, it is possible to position the required number of parallel connected non-linear resistance elements (varistors  8 ) side by side in the direction of width of the body  7  without modifying the device for indicating the status of overvoltage protection. When using a lower than maximum number of non-linear resistance elements (varistors  8 ), the remaining space of the body  7  between the side wall of non-linear resistance elements (varistors  8 ) and the side wall of the body  7  is free, and no part of the device for cutting off the non-linear resistance element from the network or of the indication (visual as ell as remote) of the status of overvoltage protection is in this space. 
     In the embodiments shown in  FIGS. 4   a  to  6   c , the pin  7   b , on which the lever  16  is rotatably mounted, is situated outside the perimeter of the non-linear resistance element (varistor  8 ) in the view in direction perpendicular to the side surface of the non-linear resistance element (varistor  8 ), i.e., in direction of width of the body  7 , while the lever  16  is flat in the direction parallel with the side wall of the non-linear resistance element (varistor  8 ). The lower arm  16   a  and the indicator arm  16   b  are situated outside the perimeter of the non-linear resistance element (varistor  8 ) in the view in direction perpendicular to side wall of the non-linear resistance element (varistor  8 ), i.e., in direction of width of the body  7 . Also, the tension spring  16   c  used in the embodiment shown in  FIGS. 5   a  and  5   b  is parallel with the side wall of the non-linear resistance element (varistor  8 ). As shown in the embodiments of  FIGS. 4   a  to  6   c , it is possible to arrange in the body  7  non-linear resistance elements (varistors  8 ) having larger dimensions (and also of performance) differently than shown in the embodiments of  FIGS. 1 to 3   b  so that the overvoltage protection has the same external dimensions and can use the unified holder  1 . 
     The overvoltage protection device in embodiments shown in  FIGS. 1 to 7   c  works in the following way. 
     Upon occurrence of overvoltage in a protected electrical circuit, the overvoltage protection fulfils its function, i.e., it decreases overvoltage in the protected circuit to the permissible value. Nevertheless, aging and overloading of the protective element (non-linear resistance element, varistor  8 , a group of varistors, etc.), change the properties of the protective element. For example, electrical current gradually flows through the protective element (varistor  8 ), which causes the protective element (varistor  8 ) to increase in temperature. Heat from the protective element (varistor  8 ) naturally flows to the outlets  9  and  11 , causing the lower electrode  9  of varistor  8  to gradually warm up. 
     In the embodiments according to  FIGS. 1 to 5   b , the increased temperature of the lower electrode  9  of varistor  8  causes melting of the solder connecting the outlet to the stranded wire  10 . As a result, the link loses its rigidity, and pressure from the spring  15  moves the shifting part  4  to the end of the stranded wire  10 ) towards the contact  5 . This disconnects the outlet of the lower electrode  9  from the stranded wire  10 , thus disconnecting the protective element (varistor  8 ) from the network. In the embodiments shown in  FIGS. 1 to 3   b , the movement of the shifting part  4  in the initial phase does not change the position of the lever  16 . Nevertheless, the wall of the shifting part  4   b  does not support the lever  16  any more in the position which is not screened. With further shift of the shifting part  4  upon the lower arm  16   a  of the lever  16 , the wall  4   c  of shifting part  4  starts its acting and turns the lever  16  on the pin  7   b , and the indicator arm  16   b  of the lever  16  screens the slot  7   c  of visual indication, which changes the visual indication of the status of overvoltage protection. In the embodiments shown in  FIGS. 4   a  and  4   b , the shifting of the shifting part  4  turns the lever  16  through the lower end  16   a  of the cranked groove between the walls  4   b  and  4   c  of the shifting part  4 , and the indicator arm  16   b  of the lever  16  screens the slot  7   c  of visual indication, changing the visual indication of the overvoltage protection. In the embodiment shown in  FIGS. 5   a  and  5   b , the shift of the shifting part  4  turns the lever  16  through the gradual wall  4   d  of the shifting part  4 , with which the lower end  16   a  of the lever  16  is maintained in contact by means of the spring  16   c . As a result, the indicator arm  16   b  of the lever  16  screens the slot  7   c  of visual indication, which causes a change of the visual indication of the status of overvoltage protection. Shift of the shifting part  4  in all of these embodiments also clears the space for pushing forward the positioning member  3  by the pressure spring (not shown). As the positioning member  3  pushes forward, it produces the remote indication of status change of overvoltage protection. The attending person then easily remotely or at the personal inspection of the overvoltage protection recognizes that the given slide-in protective part  2  must be replaced. 
     In the embodiments of  FIGS. 6   a  to  6   e , sufficient heating of the lower electrode  9  of the varistor  8  melts the solder by which the stranded wire  10  is connected with the stop  10   a . This causes the link between the stranded wire  10  and the stop  10   a  to lose rigidity. The shifting part  4  shifts from the pressure spring  15  to shift the stop  10   a  towards the contact  5  until it is stopped by the stranded wire  10 , which is all the time connected with the lower electrode  9  of varistor  8 , and at the same time the protective element (varistor  8 ) is all the time connected to the network. This limited movement of the shifting part  4  acts upon the lower end  16   a  of the lever  16 , which in a restricted way turns into the position so that the visual indicator arm  16   b  of the lever  16  adjusts on the colored surface indicating the “temporary status” of overvoltage protection (i.e. status when the non-linear resistance element (varistor  8 ) is getting warm due to various influences, still fulfilling its function). Already in this “temporary status,” it is recommended to replace the slide-in element  2  preventively as the moment of total disconnection of the overvoltage protection from the protected circuit is approaching. Simultaneously this limited movement of the shifting part  4  causes a change on the positioning member  3  of remote indication, which is then remotely indicated as a fault status “circuit is not protected”, by which the possibility of timely replacement of the slide-in protective element  2  is secured still before the total fallout of the overvoltage protection. With ongoing warming of the lower electrode  9  of varistor  8  consequently the solder is melted, (by which the lower electrode  9  of varistor  8  is connected with stranded wire  10 ), through which even this link loses its rigidity, and the shifting part  4  upon pressure of the pressure spring  15  shifts the end of stranded wire  10  also with the stop  10   a  towards the contact  5 , by which the lower electrode  9  of varistor  8  is disconnected from the stranded wire  10 , thus the non-linear resistance element (varistor  8 ) is disconnected from the network. This further shift of the shifting part  4  causes another turning of the lever  16 , whose indicator arm  16   b  positions on the colored surface indicating the status “circuit not protected”. 
     In the embodiment shown in  FIG. 8 , the overvoltage protection has a different mechanism than the embodiment shown in  FIGS. 1 to 7   c . Here, the respective cut-off mechanism includes a spring  18  which acts on a “T” lever  180 . One arm  1801  acts against a conductive connecting element  181 . A solder  185  with a lower melting temperature connects an end  1810  of the connecting element  181  with an adapter  184 . A solder  183  with a higher melting temperature connects the adapter  184  with an electrode  182  of a non-linear resistance element (varistor). Adapter  184  is electrically conductive with a contact  186  of overvoltage protection. A stop  187  restricts movement of the connecting element  181 . Through warming from the electrode  182 , the solder  185  with the lower melting temperature is molten first, after which the spring  18  acts to turn the lever  180 , and the connecting element  181  is shifted opposite the stop  187 , by which an indicator end  1802  of the lever  180  shifts and indicates partial deterioration of overvoltage protection, e.g., it changes the indicating window to yellow. The overvoltage protection is all the time functioning. Through further warming from the electrode  182 , the solder  183  with the higher melting temperature is molten. This causes further turning of the lever  180  by action of the spring  18 . The connecting element  181 , the adapter  184 , and the stop  187  are displaced from the electrode  182 , disconnecting the electrode  182  from contact  186 , and the indicator end  1802  of the lever  180  further shifts and indicates total impairment of overvoltage protection, e.g., it changes the indicating window to red. In this way the overvoltage protection is disconnected from the protected circuit. 
     In the embodiment illustrated in  FIG. 9 , the overvoltage protection includes a spring  19 , which applies a permanent pressure to a conductive connecting element  190 , through which an electrode  191  of non-linear resistance element (varistor) is electrically connected with the stranded wire  192 . Interlink  194  is connected electrically by means of solder  193  with a higher melting temperature with electrode  191 . The interlink  194  is connected electrically by means of solder  195  with a lower melting temperature with conductive connecting element  190 . The interlink  194  is equipped with a stop  196  of the conductive connecting element  190 . By warming from electrode  191 , the solder  195  with the lower melting temperature is molten, causing the conductive connecting element  190  through action of the spring  19  to shift by the distance Δ to the stop  196  on the interlink  194 . This shift of the conductive connecting element  190  produces the indication of partial deterioration of overvoltage protection, e.g., the conductive connecting element  190  changes the window of visual indication to yellow. By further warming, the solder  193  with the higher melting temperature is molten, releasing the interlink  194  entirely, and the conductive connecting element  190  through action of the spring  19  disconnects from contact  191 , disconnecting the overvoltage protection from the protected circuit and producing an indication of entire impairment of overvoltage protection, e.g., the conductive connecting element  190  changes a window of visual indication to red. 
     In the embodiment illustrated in  FIG. 10 , the overvoltage protection contains a spring  20  which constantly acts by tension upon a lever  21  that acts upon a conductive strip  22  passing through a hole in an electrode  23  of non-linear resistance element (varistor). The conductive strip  22 , in the initial status when the overvoltage protection is entirely intact, is connected by means of a solder  24  with a lower melting temperature to the electrode  23  of non-linear resistance element (varistor). At the end of conductive strip  22  behind the electrode  23 , the conductive strip  22  is provided with a stop being released by heat, e.g., the strip is coated with a layer or a ball or other suitable shape of solder  25  with a higher melting temperature which prevents the conductive strip  22  from slipping out from the hole in electrode  23  when the solder  25  is non-molten. By warming the electrode  23  of varistor, the solder  24  melts first, and the spring  20  turns the lever  21 , pulls the conductive strip  22  from the solder  24  to the electrode  23 . Through movement of the lever  21 , the indication of partial deterioration of overvoltage protection is established, e.g., the indicator arm  210  of the lever  21  changes a window of visual indication to yellow, and possibly the remote indication is established. By further warming of electrode  23 , the solder  25  with the higher melting temperature is molten, and the conductive strip is released from electrode  23 , the spring  20  turns the lever  21  further, thus establishing the indication of total impairment of overvoltage protection, e.g., indicator arm  210  of the lever  21  changes the window of visual indication to red, and possibly the remote indication is established. 
     The main principle of invention flows from the above mentioned description of various arrangements, which consists in that the gradually of individual steps of indicating partial and then total impairment of overvoltage protection is exercised always by a single cut-off mechanism, indicating partial impairment of overvoltage protection and consequently of total impairment of overvoltage protection. 
     The invention is not limited only to the expressly described or directly illustrated embodiments, but the modification of principle of gradual shifting of a single cut-off mechanism depending on temperature of varistor or varistors establishing gradually status indication of partial and total impairment of overvoltage protection lies in the scope of mere specialized skill of an average specialist in this technical field. The invention is not limited to the two-stage indication of partially impaired-totally impaired.