Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/12—Overvoltage protection resistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors

Definitions

• the invention relates to the device for overvoltage protection comprising terminals for connection to protected circuit, between which there is arranged the current path, in which the protective element is connected, and in the current path there is created a point of intentional cutting off the current path performed through connection of one end of a flexible electric conductor with one end of fixed electric conductor by means of first solder, and with flexible electric conductor the cut-out device is coupled, while the device further comprises the device for signalling the status of overvoltage protection and an additional thermal cut-out with adjustable parameters of melting.
• the overvoltage protection is provided with thermal cut-out device (hereinafter referred to as TCD) which once a certain temperature of varistor is achieved cuts-out the current path of the device for overvoltage protection, through which varistor is disconnected from the protected circuit or network (hereinafter referred to as network only), which secures that due to flowing current no further warming of varistor above the permissible limit may occur.
• TCD thermal cut-out device
• TCD In electric network also other effects occur when TCD is subject to action of considerably different conditions, which it must manage in a manner securing a safe operation of an instrument (device for overvoltage protection) even in situations when the protective elements (varistors) are overloaded and their voltage failure occurs. In such situation it is required, that even at a high short- circuit current, declared for the given instrument, the TCD is not disconnected, but the circuit in the overcurrent protection positioned in the circuit before the device for overvoltage protection is cut off. Disconnection of TCD could cause occurence of electric arc between the disconnected elements with danger of fire.
• 0SN EN 61643-11 states or international norms (standards), e.g. 0SN EN 61643-11 , which also specifies conditions for correct functioning of the device for overvoltage protection in situation of voltage failure of varistor, for maximum short-circuit current in the point of connection of the device for overvoltage protection.
• 0SN EN 61643-1 specifies these requirements including evaluation of results of tests in paragraph 7.7.3. of the above mentioned norm.
• This new testing in an expressive manner enlarges requirements as to parameters of TCD, especially at the devices for overvoltage protection on basis of varistor for higher energies (category I, type I).
• This testing requires a long-term (seconds in order) acting of low short-circuit current, which substantially changes thermal loading of the whole current path of the device for overvoltage protection.
• the current path including TCD is considerably warmed- up. This warming results in that, even during flowing the low short-circuit current, the TCD may be disconnected, which may cause occurrence of electric arc with possible fire.
• TCD there is by a norm prescribed maximum temperature, at which its disconnection must occur, with respect to this condition for connection of elements of current path such low-fusing solders are used, whose temperature of melting lies considerably lower, than the melting temperature of the remaining elements of the current path.
• the low-fusing solder connects elements of the current path, it is required that it features the best electrical conductivity which is of course lower than at other elements of current path, which usually are made of copper (of course with exception of varistor, that fulfils its strongly non-linear characteristic protective function of overvoltage protection).
• solder connecting elements of current path with respect to lower electric conductivity when compared with other elements of current path, also gets quicker warmer due to flowing electric current, which may to a certain level be compensated by a size of soldered area connecting the elements of current path.
• electrical conductivity at metals strongly correlates with temperature conductivity. This results into a fact, that if the soldered surface is sufficiently thin, during warming the solder also heat removal from the solder into elements of current path occurs simultaneously.
• This thermal mechanism ensures relatively low temperature of the solder only at the situation, when temperature of elements of the current path is relatively low. If, nevertheless this temperature raises to the level of temperature of solder melting, there occurs an undesirable disconnection of TCD instead of cutting off the circuit in overcurrent protection, which is positioned before the device for overvoltage protection.
• the device for overvoltage protection comprises terminals for connection to a protected circuit, while between the terminals there is arranged the current path, in which the protective element is connected.
• the current path In the current path there is created the point of intentional cutting off the current path, to which a device for signalling the protection status is assigned.
• an additional fusing thermal cut-out with preset parameters of melting In the point of intentional cutting off the current path there is further created an additional fusing thermal cut-out with preset parameters of melting.
• the elements of current path being intentionally disconnected are connected by means of first solder and additional fusing thermal cut-out with preset parameters of melting is formed by second solder.
• the second solder has the same or approximately the same temperature of melting as the first solder, but simultaneously the second solder has lower, or depending on structural embodiments and selected materials also the same value of thermal conductivity, than the first solder.
• This device functions so that it prevents the disconnection of TCD immediately after melting the first solder which connects the elements of the current path, so that temperature of this first solder, which is already in liquid status, may further raise up to the boiling point of the first solder, as melting of the second solder takes longer time with respect to the greater dimension of the second solder, that must be heated and molten.
• Another particular structural embodiment is described by a solution at which the additional fusing thermal cut-out with preset parameters of melting is formed of a fusing rivet, which is positioned in a through opening which is performed in current path elements being intentionally disconnected, while the heads of fusing rivet abut against the outer exterior surfaces of current path elements being intentionally disconnected.
• the goal of this invention is to further enhance the limit for applicability of the device for overvoltage protection on basis of varistor from the point of view of energetic loading.
• the goal of the invention has been achieved by a device for overvoltage protection, whose principle consists in that, the additional thermal cut-out is performed by a second solder arranged between the flexible electric conductor and the fixed electric conductor parallel to the point of intentional cutting off the current path and outside the joint of flexible electric conductor and fixed electric conductor by means of the first solder, while the second solder is at least thermally conductively connected with the flexible electric conductor and with the fixed electric conductor, and the first solder and the second solder feature the same or approximately same temperature of melting.
• the invention is schematically represented in the drawing where the Fig. 1 shows a cross-section of exemplary embodiment of the device according to the invention in functioning status, the Fig. 2 a cross-section of exemplary embodiment of the device according to the invention in disconnected status, the Fig. 3 the detail "P" from the Fig. 2.
• the invention will be described on particular examples of embodiment of the device for the overvoltage protection on basis of varistor.
• the device comprises the frame 0 in the form of lockable box, in which the current path of the device is arranged.
• the current path of the device for overvoltage protection is finished with not represented terminals for electric connection of the device for overvoltage protection to protected circuit.
• Individual parts of the device are dimensioned towards expected great energy, to meet those by the norms specified requirements, in compliance with declared parameters of the device.
• the device for overvoltage protection there is connected at least one not represented varistor or a group of parallel connected varistors, possibly the varistor or a group of varistors is besides connected in series with a discharge arrester (discharger).
• the point X of intentional cutting off the current path is situated in the point of contact of lower surface of one end of flexible, e.g. copper, electric conductor 1 and of upper surface of fixed electric conductor 2, while end of the flexible electric conductor 1_ and end of the fixed electric conductor 2 are connected by means of the first solder with required temperature of melting. End of the flexible electric conductor ⁇ connected with end of the fixed electric conductor 2 is strengthened through stiffening.
• Second end of the flexible electric conductor 1 is electrically conductively by means of auxiliary conductor 0 connected with one terminal for electric connection of the device for overvoltage protection to protected circuit.
• the fixed electric conductor 2 in the represented example of embodiment is directly created by electrode of varistor, which is in a not movable manner mounted in the frame 0 of the device and whose second, not represented electrode is directly or via other conductive elements in electric conductive manner connected with the second terminal for electric connection of the device for overvoltage protection to protected circuit.
• the flexible electric conductor on its upper surface is provided with the plate 3, e.g.
• the supporting surface 00 which in the represented example of embodiment is formed of surface of the flexible electric conductor i in area of connection of the flexible electric conductor 1 and the auxiliary conductor 01.
• the supporting surface 00 is performed on the wall of the frame 0.
• the second end 42 of the cut-out lever 4 is situated before the protrusion 50 on the face side of spring-loaded shifting part 5, which is slideably mounted in the frame 0.
• the spring-loaded shifting part 5 in the represented example of embodiment is spring loaded with the pressure spring 51 slipped on the stud 52 mounted on the frame 00 of the device.
• the spring-loaded shifting part 5 is spring loaded in another suitable manner, i.e. by means of another suitable structural solution.
• the spring-loaded shifting part 5 is provided with profiled groove for one end 9 of the lever of optical signalling of device status, i.e. overvoltage protection, possibly it is further provided with mating surface for functional element of the device for remote signalling of device status, i.e. overvoltage protection.
• auxiliary plate 6 bent in direction to the first end 40 of the cut-out lever 4 and provided with a groove in area of the first end 40 of the cut-out lever 4, the first end 40 of the cut-out lever 4 is passing through this groove as it is represented in the Fig. 1.
• This section of auxiliary plate 6 with groove is situated in distance from the face side of end of the flexible electric conductor and of the plate 3.
• the first end 40 of the cut-out lever 4 by means of the second solder is attached to the auxiliary plate 6.
• the second solder features the same or approximately the same melting temperature as the first solder, and simultaneously the second solder features the same or lower value of thermal conductivity when compared with value of thermal conductivity of the first solder, preferably at least by one order.
• thickness of layer of the first solder is in tens of millimeter, while dimension of the second solder, which must be totally heated and molten, is significantly greater.
• the second cutting off means 82 In represented examples of embodiment between the auxiliary plate 6 and the fixed electric conductor 2 there is positioned the second cutting off means 82 and between a portion of the auxiliary plate 6 with groove and the opposite walls of the flexible electric conductor and the plate 3 the first cutting off means 81 is positioned.
• the function of the cutting off means 81 and 82 first of all is to reduce passage of heat and passage of electric current between the neighbouring elements of the device, this specially for the reason of better setting of parameters of total melting of the second solder.
• the device is performed without cutting off means 81 , 82.
• the time of melting of the second solder in its entire volume is considerably longer than the period of melting of the first solder, because the second solder gets warmer slower than the first solder by gradual leading of warm through the auxiliary plate 6, through the plate 3 , the first end 40 of cut-out lever 4, which is possibly also modified, e.g. slowed down upon usage of the cutting off means 81 , 82.
• the period between initiating the short circuit in protected circuit and the moment of intentional cutting off the current path in the X point is longer than the period defined and necessary for cutting off the protected circuit in overcurrent protection, which is positioned before the device for overvoltage protection.
• the defined cutting off the whole protected circuit in the specified point i.e. in the front-end overcurrent protection, outside the device itself for overvoltage protection, which enables to involve device for overvoltage protection on basis of varistors also for high energies, and it also enables to increase dimensioning of the front-end overcurrent securing of the device for overvoltage protection in compliance with requirements specified by the norm cited in the background art.
• the invention is applicable in protection of electric circuits against overvoltage. List of referential markings

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Emergency Protection Circuit Devices (AREA)
• Fuses (AREA)
• Thermistors And Varistors (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=43836922

Family Applications (1)

Country Status (3)

Family Cites Families (7)

• 2009
  • 2009-10-19 CZ CZ2009683A patent/CZ308826B6/cs unknown
• 2010
  • 2010-09-17 WO PCT/IB2010/002345 patent/WO2011048450A2/en not_active Ceased
  • 2010-09-17 EP EP10803484A patent/EP2491564A2/en not_active Withdrawn

Non-Patent Citations (1)

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