Patent Publication Number: US-11025037-B2

Title: Arrester for protection against overvoltages

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a national phase filing under section 371 of PCT/EP2018/061833, filed May 8, 2018, which claims the priority of German patent application 10 2017 115 030.7, filed Jul. 5, 2017, each of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     An arrester for protection against overvoltages is described. 
     BACKGROUND 
     A surge arrester—arrester for short—serves for limiting dangerous or undesirable overvoltages in electrical lines and devices. By this means, damage to the lines and devices due to overvoltage can be avoided. Gas-filled arresters, which are also designated as gas-discharge arresters, are arresters in which the overvoltage in the gas-discharge arrester is reduced by the automatic igniting of a gas discharge. Such arresters operate by the gas-physics principle of arc discharge, whereby after an arrester response voltage—designated for short as response voltage or as ignition voltage—has been attained an arc forms in the gas-tight discharge chamber within nanoseconds. By virtue of the high current-carrying capacity of the arc, the overvoltage is effectively short-circuited. 
     In conventional gas-discharge arresters with two electrodes, a vapor deposition of conducting electrode material on the ceramic inner wall may occur. This leads to a reduction of the insulation resistance of the arrester. Furthermore, impermissibly high leakage currents can be brought about as a result in the course of operation at the rated AC voltage. 
     German Application No. DE 10 2008 029 094 A1 describes an arrester with an undercut ceramic. By this means, the ceramic inner wall is intended to be protected better. 
     SUMMARY 
     Embodiments provide an arrester for protection against overvoltages that exhibits improved properties. For instance, an arrester is to be specified that is particularly reliable, compact and/or durable. 
     According to one aspect, an arrester for protection against overvoltages is specified. The arrester exhibits a housing. The housing is designed to receive further components of the arrester in an inner region of the housing. The housing may, for instance, have been designed in the form of a hollow cylinder. The housing has further been designed to act as an external electrode. The housing features an electrically conductive material, for instance copper. 
     The arrester further exhibits a central electrode or internal electrode. The central electrode is arranged completely within an inner region of the housing. A discharge region is formed between the central electrode and the housing. In other words, an arc discharge takes place between the central electrode and the housing in the case of an overvoltage. The central electrode has, for instance, been designed in the form of a cylinder. The central electrode features an electrically conductive material, for instance tungsten and/or copper. 
     The arrester further includes a ceramic body. The ceramic body serves for insulation. In particular, the ceramic body is designed and arranged for the purpose of electrical separation of the housing and the central electrode. The ceramic body is preferentially in direct mechanical contact with the housing. Preferentially, a direct mechanical contact between the ceramic body and the central electrode is prevented, preferentially by the housing. The ceramic body is arranged in offset manner relative to the discharge chamber. 
     The electrical separation of the central electrode and the housing occurs in the coaxial direction, the ceramic body being arranged as insulator between the central electrode and the housing. As a result, the ceramic as spacer between the electrodes of the arrester is dispensed with. In particular, the external electrode becomes the body/housing of the arrester. By this means, the outside diameter of the arrester is reduced. Furthermore, an inner wall of the ceramic body is optimally protected against a vapor deposition of electrode material. Hence high leakage currents in the course of operation at the rated AC voltage can be avoided. 
     The arrester further includes a shielding element. The shielding element is designed and arranged to protect the housing against thermal loading. The shielding element is constituted by a cladding of at least one partial region of an inside of the housing. The shielding element is arranged on the inside of the housing. The shielding element has been firmly connected to the housing, for instance by means of brazing or press fit. The shielding element has an extent along a longitudinal axis of the arrester. Furthermore, the central electrode also has an extent along the longitudinal axis of the arrester—that is to say, a longitudinal extent. The shielding element extends over an entire longitudinal extent of the central electrode along the inside of the housing. In this way, the housing can be efficiently protected against thermal loading. In an alternative embodiment, the shielding element may also extend at least partly perpendicular to the longitudinal axis of the arrester. Hence a front side of the inner region of the housing can also be protected against thermal loading/fusion. 
     By virtue of the arrangement described above, an arrester is made available that is not only particularly efficient and durable but also has a small outside diameter. 
     According to one embodiment, the arrester exhibits a coupling element. The coupling element is designed and arranged to contact the central electrode electrically. The coupling element features copper, for instance. The ceramic body exhibits an aperture. The aperture penetrates the ceramic body preferentially completely in a central region of the ceramic body. The coupling element is designed and arranged to extend at least partly through the aperture into the inner region of the housing. 
     In particular, the coupling element exhibits a connection region. The connection region is elongated or pin-shaped. The connection region is designed to be connected to the central electrode. The connection region extends through the aperture. The coupling element, in particular the connection region, has been soldered to the central electrode. 
     The coupling element further exhibits an end region. The end region projects out of the housing and the ceramic body. In particular, the end region does not extend through the aperture. The end region is designed to be connected to a further electronic component or to an electronic device. The end region exhibits a screw thread, for instance an M8 screw. 
     The coupling element further exhibits a central region. The central region is formed between the end region and the connection region. The coupling element has preferentially been formed in one piece. In other words, the connection region, the central region and the end region merge directly with one another. 
     The coupling element has been connected—for instance, soldered—to the ceramic body via the central region. The central region is plate-shaped or disk-shaped. The central region has a larger diameter than the connection region. The central region has a larger diameter than the end region. The end region has a larger diameter than the connection region. 
     According to one embodiment, the arrester exhibits a ceramic element. The ceramic element serves as insulator. In particular, the ceramic element is designed and arranged to shield the ceramic body from the discharge chamber even better. Hence the efficiency and durability of the arrester are enhanced. 
     The ceramic element is of annular design, for instance. For instance, the ceramic element exhibits a ceramic disk with an aperture. The aperture serves for feeding the coupling element through. The ceramic element is formed between the ceramic body and the central electrode. The ceramic element is spaced from the central electrode. The ceramic element has been fastened—for example, soldered—to the shielding element. The ceramic element—for instance, a circumferential edge region of the ceramic element—preferentially rests directly on a partial region of the inside of the housing. 
     The ceramic element exhibits a step or elevation. The step has preferentially been formed circumferentially on a surface of the ceramic element. The step or elevation preferentially arises from an outer surface of the ceramic element facing toward the central electrode. By virtue of the step, surface-leakage currents after loading are reduced. 
     According to one embodiment, the arrester exhibits an ignition aid. By virtue of the ignition aid, the dynamic response voltage of the arrester is reduced. As a result, a very efficient arrester is made available. The ignition aid exhibits graphite strips, for instance. The ignition aid is preferentially arranged on the ceramic body. For instance, the ignition aid is formed on an inner wall of the aperture of the ceramic body. The ignition aid is arranged parallel to a longitudinal axis of the arrester. By virtue of the arrangement parallel to the longitudinal axis, a charge difference on the end regions of the ignition aid can be obtained. 
     According to one embodiment, the ceramic body exhibits an end region facing away from the central electrode. The end region is arranged outside the housing. A gradation is formed on the end region. The gradation is formed circumferentially around an edge region of the aperture. By virtue of the gradation, the insulation resistance of the arrester is improved. 
     What has been described above will be elucidated in more detail in the following with reference to embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described below are not to be interpreted as being true to scale; rather, in individual dimensions the representations may have been represented in enlarged, reduced or even distorted manner. 
         FIG. 1 a    shows a sectional representation of an arrester for protection against overvoltages, according to the state of the art; 
         FIG. 1 b    shows a perspectival view of the arrester according to  FIG. 1   a;    
         FIG. 2 a    shows a sectional representation of an arrester for protection against overvoltages, according to the state of the art; 
         FIG. 2 b    shows a perspectival view of the arrester according to  FIG. 2   a;    
         FIG. 3 a    shows a sectional representation of an arrester for protection against overvoltages; and 
         FIG. 3 b    shows a perspectival view of the arrester according to  FIG. 3   a.    
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIGS. 1 a , 1 b , 2 a  and 2 b    show arresters  1 ,  10  for protection against overvoltages, according to the state of the art. The arresters  1 ,  10  represented in  FIGS. 1 b  and 2 b    are to be regarded as being true to scale. 
     The conventional structural design of surge arresters includes two electrodes  2 ,  3  ( FIG. 1 a   ) or  11 ,  12  ( FIG. 2 a   ) which are positioned either coaxially or against one another. Furthermore, in each instance a ceramic body  4 ,  13  is provided as insulator or spacer between the electrodes. 
     At high current loads (for example, wave 10/350 μs, currents up to 100 kA), a vapor deposition of conducting electrode material occurs on an inner wall of the ceramic body  4 ,  13 . This leads to a reduction of the insulation resistance of the arrester  1 ,  10 . Under certain circumstances, impermissibly high leakage currents arise as a result in the course of operation at rated AC voltage. 
     The arrester  30  described in connection with  FIGS. 3 a  and 3 b    solves the problems described above by exhibiting a better protection of the ceramic inner wall and an improvement of the insulation resistance after loading. 
     The arrester  30  exhibits a housing  31 . The housing  31  serves for receiving further components of the arrester  30 . At the same time, the housing also acts as an external electrode. The housing  31  preferentially features copper. 
     In a first end region  43  the housing  31  exhibits a coupling element  42 , for instance a screw thread. The coupling element  42  has a length  52  of less than or equal to 8 mm, for instance 7 mm. 
     The housing  31  further exhibits a central region  45 . The central region  45  serves for receiving a central electrode  33  or internal electrode, as will be described in detail later. The housing  31  further exhibits a second end region  44 . The second end region  44  serves for connecting the housing  31  to an insulator or ceramic body  36 , as will be described in detail later. 
     The first and second end regions  43 ,  44  each directly adjoin the central region  45 . In particular, the housing  31  has preferentially been formed in one piece. The first end region  43  has a diameter that is smaller than a diameter of the central region  45  and of the second end region  44 . The diameter of the second end region  44  is furthermore smaller than the diameter of the central region  45 . The diameter of the central region  45  of the housing  31  is preferentially less than or equal to 20 mm, for instance 16.8 mm. 
     An outer surface of the central region  45  extends parallel to a longitudinal axis L of the arrester  30 . An outer surface of the second end region  44 , on the other hand, includes an angle with the longitudinal axis L. In other words, the second end region  44  is formed obliquely. 
     The housing  31  exhibits an inner region  31   a . The central electrode  33  is arranged in the inner region  31   a . The inner region  31   a  forms a discharge chamber between the housing or the external electrode  31  and the central electrode  33 . The inner region  31   a  has a diameter  57  that is preferentially less than or equal to 15 mm, for instance 12 mm or 13 mm. 
     The central electrode  33  preferentially features tungsten-copper. The central electrode  33  has a diameter  55  of less than or equal to 10 mm, for instance 7.5 mm. The central electrode  33  has for instance been designed to be cylindrical. 
     The central electrode  33  is spaced from an inside or inner longitudinal side  31   b  and from an inner front side  31   c  of the housing  31 . The inside  31   b  and front side  31   c  together constitute a wall of the inner region  31   a  of the housing  31 . 
     The spacing between the central electrode  33  and the inside  31   b  or front side  31   c  preferentially amounts to up to 6 mm. A spacing  51  between a front side of the central electrode  33  and front side  31   c  amounts, for instance, to 5.5 mm or less. 
     The arrester  30  further exhibits a shielding element  32 . The shielding element  32  serves to enhance the performance of the external electrode  31 . In particular, the shielding element  32  protects the housing or the external electrode  31  against thermal loading. The shielding element  32  preferentially features tungsten-copper. 
     The shielding element  32  is formed in the inner region  31   a  of the housing  31 . The shielding element  32  consequently reduces the diameter  57  of the inner region  31   a . A diameter  56  of the inner region  31   a  reduced by the shielding element  32  preferentially amounts to less than or equal to 12 mm, for instance 11 mm. A thickness or radial extent (extent at right angles to the longitudinal axis L) of the shielding element  32  amounts to less than or equal to 2 mm. The shielding element  32  has been firmly connected to the housing  31 , for instance by brazing or press fit. 
     The shielding element  32  extends on the inside  31   b  of the housing  31  along the longitudinal axis L of the arrester  30 . A length of the shielding element  32  is such that the shielding element  32  extends along a complete length of the central electrode  33 . In other words, a longitudinal extent of the shielding element  32  is greater than a longitudinal extent of the central electrode  33 . In particular, the shielding element  32  extends along the complete inside  31   b  of the housing  31 . For instance, the length of the shielding element  32  amounts to up to 20 mm, for instance 17 mm. An overall length  50  of the arrester  30  preferentially amounts to less than or equal to 50 mm, for instance 46 mm or 47 mm. In addition, the shielding element  32  may also extend at least partly on the inner front side  31   c  of the housing  31  (not represented explicitly). 
     The arrester  30  further exhibits the ceramic body or insulator  36 . The arrester  30  exhibits a coupling element  34 . 
     The ceramic body  36  serves for electrical insulation of the housing  31  and of the central electrode  33 . The ceramic body  36  is arranged in the second end region  44  of the housing  31 . The ceramic body  36  is consequently arranged in a manner offset from the discharge chamber which is formed between the housing  31  and the central electrode  33 . Hence an insulating body directly between the housing or external electrode  31  and the central electrode  33  is dispensed with. Hence an outside diameter of the arrester  30  is reduced. For instance, the outside diameter of the arrester  30  amounts to less than or equal to 20 mm, for instance 17 mm (see also  FIG. 3 b   , which is to be understood as a true-to-scale representation of an embodiment of the arrester  30 ). 
     The ceramic body  36  exhibits a central aperture  36   a . The aperture  36   a  has a diameter  54  of less than or equal to 10 mm, for instance 8.5 mm. The aperture  36   a  serves for feeding the coupling element  34  through into the inner region  31   a . The coupling element  34  will be described in detail later. 
     The ceramic body  36  is firmly connected to the housing  31 . For instance, the ceramic body  36  and the housing  31  have been soldered together. The ceramic body  36  has been soldered to the housing  31 , in particular in a soldering region  38  in the end region  44  of the housing  31 . 
     For this purpose, the ceramic body  36  exhibits a specially shaped first end region. The first end region faces toward the housing  31 . The first end region exhibits a step. The step is formed circumferentially. The step serves as stop surface for the end region  44 , and also as soldering region  38 . 
     The ceramic body  36  further exhibits a second end region  36   b . The second end region  36   b  faces away from the housing  31 . The second end region  36   b  exhibits a gradation or undercut  39 . The gradation  39  is formed circumferentially around the aperture  36 . In other words, the gradation  39  is constituted by a bulge of the ceramic body  36 , in particular of a front face of the ceramic body  36 , that is formed directly adjacent to the aperture  36 . The gradation  39  extends outward in the radial direction from lateral edges of the aperture  36   a . The gradation  39  has a diameter  53  of less than or equal to 13 mm, for instance 11 mm. The gradation  39  serves to reduce surface-leakage currents after loading of the arrester  30 . 
     The coupling element  34  is pin-shaped. The coupling element  34  has been firmly connected—for instance, soldered—to the central electrode  33 . In particular, the coupling element  34  has been soldered to the electrode  33  in a connection region or end region  34   c . In this way, the central electrode  33  becomes more resistant to the thermal loading arising during the discharge. The coupling element  34  features copper, for instance. The coupling element  34 , in particular the connection region  34   c , has a diameter  58  of less than or equal to 8 mm, for instance 6 mm. For the electrical contacting of the central electrode  33 , the coupling element  34 , in particular the connection region  34   c , has been passed through the aperture  36  and into the inner region  31   a.    
     The coupling element  34  exhibits an end region  34   a  which protrudes from the ceramic body  36 . On the end region  34   a  a screw thread  41 , for instance an M8 screw, is formed. A diameter of the end region  34   a  is larger than the diameter  58  of the connection region  34   c.    
     The coupling element  34  has been firmly connected to the ceramic body  36 , for instance by means of brazing. For this purpose, the coupling element  34  exhibits a widened central region  34   b . A diameter of the central region  34   b  is larger than the diameter  58  of the connection region  34   c  and larger than the diameter of the end region  34   a . The central region  34   b  is disk-shaped. The central region  34   b  directly adjoins the end region  34   a . In particular, the central region  34   b  is arranged between the end region  34   a  and the connection region  34   c . The central region  34   b  rests, at least in a partial region, directly on the ceramic body  36 , in particular on a front face of the ceramic body  36 . 
     Between the front face of the ceramic body  36  and an upper side of the central region  34   b , in particular an annular outer region of the upper side, a soldering region  47  is formed for soldering the coupling element  34  and the ceramic body  36  together. 
     In this embodiment, the arrester  30  further exhibits a ceramic element  35 , but embodiments without a ceramic element  35  are also conceivable. The ceramic element  35  is annular. In particular, the ceramic element  35  exhibits an aperture for feeding the coupling element  34  through. 
     The ceramic element  35  is arranged in the inner region  31   a . In particular, the ceramic element  35  seals or bounds the inner region  31   a  of the housing in the direction of the ceramic body  36 . The ceramic element  35  rests in a lateral region directly on the housing  31 , in particular on the inside  31   b  thereof. The ceramic element  35  is arranged in the longitudinal direction of the arrester  30  between the shielding element  32  and the ceramic body  36 . 
     The ceramic element  35  improves the shielding of the ceramic body  36  relative to the discharge chamber which is located between the housing  31  and the central electrode  33 . The ceramic element  35  preferentially exhibits a step or elevation  40 . The step  40  is formed circumferentially on an outer surface of the ceramic element  35 , for instance on a surface of the ceramic element  35  facing toward the shielding element  32 . The step  40  is designed to reduce surface-leakage currents after loading. 
     The ceramic element  35  has been soldered to the shielding element  32 , for instance by means of brazing. For this purpose, a soldering region  46  is formed between the shielding element  32  and the ceramic element  35 , in particular the step  40 . 
     The arrester  30  further exhibits an ignition aid  37 . The ignition aid  37  may exhibit a graphite strip or a plurality of graphite strips. The ignition aid  37  extends parallel to the longitudinal axis L of the arrester  30 . 
     The ignition aid is arranged on an inner wall of the ceramic body  36 . In particular, the ignition aid  37  is formed in the region of the aperture  36   a  and, in particular, in the region of the side walls of the aperture  36   a . The ignition aid  37  serves to reduce the response voltage of the arrester  30 . 
     The description of the subject-matters specified herein is not limited to the individual special practical forms. Rather, the features of the individual practical forms can—to the extent that this is technically meaningful—be combined arbitrarily with one another.