Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T1/00—Details of spark gaps
  • H01T1/14—Means structurally associated with spark gap for protecting it against overload or for disconnecting it in case of failure
• • 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
  • H01C7/126—Means for protecting against excessive pressure or for disconnecting in case of failure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T4/00—Overvoltage arresters using spark gaps
  • H01T4/10—Overvoltage arresters using spark gaps having a single gap or a plurality of gaps in parallel
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H37/00—Thermally-actuated switches
  • H01H37/74—Switches in which only the opening movement or only the closing movement of a contact is effected by heating or cooling
  • H01H37/76—Contact member actuated by melting of fusible material, actuated due to burning of combustible material or due to explosion of explosive material
  • H01H37/767—Normally open

Definitions

• the technical solution relates to a device which increases the operating reliability of voltage limiters containing a protection element.
• the voltage limiter is used to eliminate impermissible high contact voltages on non-live metal parts of railroad devices in both AC and DC traction systems by creating a temporary or permanent connection of conductive parts with a rail over the time the permissible value of the contact voltage is exceeded. It is also used in protection systems of photovoltaic sources.
• the excessive current melts the pellet via the secondary spark gap and the short- circuiting shell moves by spring force so that it connects the opposing conductors.
• the surge arrester subject to this document is loaded with a pulse current, the current will divide into two paths in the ratio of their impedance.
• One part of the current passes through the metal shell, movable connection and the short-circuiting shell into the ground.
• the other part of the pulse current passes through the spring and the short- circuiting shell also into the ground.
• the inductance of the spring negatively influences the division of the pulse current to both current paths.
• a considerable part of the pulse current also passes through the moving connection of both shells and can cause welding of one part to another, which results in a loss of protection in case of surge current overload states. Such a condition cannot be reasonably established or measured.
• Another disadvantage of this solution lies in tough requirements for production of both shells, which must necessarily have narrow tolerances.
• the invention according to documents DE102008027589A1 , resp. W02009049940A1 “SPARK GAP ARRANGEMENT WITH A SHORT-CIRCUITING DEVICE” deals with a spark gap arrangement with a short-circuiting device containing two opposing main electrodes arranged in a pressure-resistant housing, the said main electrodes being electrically connected to an external connection.
• a cavity which houses a movable, conductive short-circuiting element, is provided in at least one of the main electrodes, the short-circuiting element being loaded by a pre-stressed spring.
• the short-circuiting element is held in the cavity by means of a temperature-sensitive substance or a similar element.
• WO2016045982A1 OVERVOLTAGE PROTECTION ASSEMBLY HAVING A SHORT-CIRCUITING DEVICE
• an overvoltage protection assembly containing a two-part metal housing, a surge arrester and a short-circuiting device consisting of two opposing contact electrodes which are under mechanical spring force and are allowed to move relatively one towards the other by force of the spring in case of a short circuit.
• the contact electrodes are separated by means of a lost element which, if the surge arrester heats up, allows the contact electrodes to make a relative motion.
• the surge arrester contains a varistor or a varistor designed in series and a gas discharge tube. The disadvantage of this solution is that the short- circuit current passes through the spring, which limits its size.
• the non-patented documentation describes technical solutions of voltage limiters comprising an efficient gas discharge tube positioned in a metallic, or non-metallic, housing in the shape of a hollow cylinder with a terminal situated at the bottom and one electrode of the gas discharge tube touching the terminal, while the second terminal provided with a stud touches the second electrode.
• the housing is closed with a pressed-in cover, or both the housing and cover are provided with a thread.
• the above-stated disadvantages are eliminated by the voltage limiter with a short- circuiting device according to the submitted solution.
• the voltage limiter consists of a housing shaped as a cylinder with the inner cavity provided with terminals on the opposing sides, protruding from the housing and electrically connected to the protection element.
• the short-circuiting device comprises fixed and movable parts connected via a fusible element.
• the limiter features a pre-stressed spring.
• the principle of the new solution is that the fixed part of the short-circuiting device consists of a cylinder-shaped, electrically-conductive contact situated in the cavity of the housing. The contact touches one terminal with one of its surfaces, while its second surface touches one surface of the protection element. The other surface of the protection element contacts the second terminal.
• a movable part is slipped onto the contact, the part consisting of an electrically-conductive short-circuiting element which is connected via the fusible element to the contact.
• This short-circuiting element is provided with a stopper at the upper end loaded with the upper end of the pre-stressed spring.
• the spring slips onto the short-circuiting element with its bottom end leaning against the terminal.
• the short-circuiting element is geometrically adjusted to bridge the distance between the short-circuiting element and the terminal in case of thermal surge current overload.
• the short-circuiting element forms an electrically- conductive movable part of a short-circuiting device, and it partially embraces the protection element, i.e. , 50 % up to 90 % of its length.
• the housing is electrically conductive, at least one terminal is insulated from the housing by an insulating pad.
• Another embodiment is also possible, in which one of the terminals is insulated from the electrically-conductive housing by an insulating pad and the second terminal is connected to the housing to form one unit.
• the protruding terminals are not insulated.
• the fusible element is made of a tin alloy with a melting temperature of between 140 °C and 240 °C.
• the contact which forms the fixed part of the short-circuiting device can consist of a solid or hollow cylinder.
• the cavity inner diameter ranges from 50% to 75% of the external diameter of the contact and the protection element sits on the annulus surface.
• This embodiment can be modified in such a manner that the inner shell of the hollow cylinder is extended at its upper end with a recess to plug in the bottom end of the protection element.
• the protection element comprises any of the elements from the below-stated group - at least one varistor, at least one varistor connected in series with a gas discharge tube, at least one gas discharge tube.
• the spring can be a pre-stressed compressive spring or it can consist of a wire with shape memory, or it can contain at least one flat spring.
• Another embodiment is also possible with the terminal being connected to the contact to form one unit.
• the advantage of this new arrangement of the voltage limiter is that it is electrically and mechanically resistant to the influence of pulse overvoltage and short-circuit currents, as no electromagnetic forces which would load the parts specified to form the short circuit arise from the passage of the current.
• the solution does not generate any circuit loops which would worsen mechanical strength and increase the protection level.
• the behaviour of the voltage limiter can be optimized by the selection of a suitable spring and the melting temperature of the fusible element for the passage of ordinary and failure current and can ensure a reliable continuous short circuit after loading with excess failure current.
• Fig. 1 shows the arrangement of the voltage limiter with its fixed part consisting of a contact in the form of a solid cylinder and a short-circuiting device in the open condition.
• Fig. 2 shows the same arrangement; however, the contact consists of a hollow cylinder and, at the same time, the short-circuiting device is in the closed condition.
• Fig. 3 shows the same arrangement; however, the contact consists of a hollow cylinder and, at the same time, the short-circuiting device is in the closed condition.
• the voltage limiter with a short-circuiting device consists of the cylinder-shaped housing 1 which features an inner cavity, the housing is provided with terminals 2 on opposing sides, protruding from the housing 1 and electrically connected to the protection element 3.
• the short-circuiting device comprises a fixed and a movable part.
• the fixed part of the short-circuiting device features a cylinder- shaped electrically-conductive contact 4, situated in the cavity of the housing 1
• One surface of the contact 4 adjoins one terminal 2_and its second surface adjoins one surface of the protection element 3.
• the second surface of the protection element 3 is in contact with the second terminal 2.
• the protection element 3 can be implemented in various ways, for example, with at least one varistor, or at least one varistor designed in series with the gas discharge tube, or at least one gas discharge tube.
• a moving part is slipped over the contact 4 which comprises an electrically-conductive short-circuiting element 5, which is connected to the fusible element 7_at the connection 9, for example, with a solder consisting of a tin alloy with its melting temperature being between 140 °C and 240 °C, with the contact 4.
• the short-circuiting element 5 can partially embrace the protection element 3, i.e. , in the scope of 50 % to 90 % of its length.
• the short- circuiting element 5 comprises a stopper 5A at its upper end, loaded with the upper end of a pre-stressed spring 6. This spring 6 is slipped over the short-circuiting element 5 and fits against the terminal 2 at its bottom end.
• the short-circuiting element 5 is geometrically arranged in such a manner that in case of thermal or surge current overload it bridges the distance between the short-circuiting element 5 and the terminal 2.
• the housing 1 can be electrically conductive or non-conductive. If it is electrically conductive, then at least one terminal 2 is insulated from the housing 1. with an insulating pad 8. The second, non-insulated terminal can be connected to the housing 1 in one unit. If the housing 1 is electrically non-conductive, the terminals 2 are not insulated.
• the contact 4 can be formed in different manners.
• Fig. 1 shows a solution where the contact 4 is in the shape of a solid cylinder.
• Fig. 2 shows an example where the contact 4 consists of a hollow cylinder and, at the same time, the short-circuiting device is in the closed condition.
• the inner diameter of the cavity is from 50% to 75 % of the external diameter of the contact 4 and the protection element 3 sits on the annulus surface.
• This embodiment can be modified in such a manner that the inner shell of the hollow cylinder is at the upper end extended into a recess in order to tightly plug in the bottom end of the protection element 3, as shown in Fig. 3.
• the spring 6 can consist of a pre-stressed compressive spring, a spring made from a shape memory wire, or at least one flat spring.
• the terminal 2 and contact 4 are connected into one unit.
• the protection element 3 is activated to form a temporary conductive path featuring low impedance between the protected item and the earth. Dangerous voltage is eliminated and consequently, once the failure phenomenon disappears, the voltage limiter renews the state of high impedance.
• a prolonged current or a high amplitude current can overload and consequently damage the protection element 3, which would result in the loss of the protective function.
• the flowing current heats up the path of the current, especially the protection element 3, and the contact surface 9, contact 4 and the short- circuiting element 5.
• the fusible element 7 will soften on the contact surface 9, as a result of which the contact surface 9 loses its strength.
• the short-circuiting element 5 moves to create a continuous electrical connection with the terminal 2, as a result of which a parallel current path to the protection element 3 is formed.
• the short-circuiting element 5 is geometrically adjusted to bridge the distance between the short-circuiting element 5 and the terminal 2.
• the voltage limiter with the short-circuiting device is usually connected between a protected device and the earth via terminals 2, whereas the optimum possibility of the design can always be selected.
• the housing 1 is, in the advantageous embodiment, electrically conductive and can be connected into one unit with one terminal 2.
• the second terminal 2 in this arrangement is insulated from the housing 1_by an insulating pad 8.
• the housing 1 is electrically non-conductive, so the electrically conductive terminal 2 protrudes non-insulated, without using the insulating pad 8.
• the short-circuiting element 5 and the stopper 5A are well conductive electrically and thermally, and they are made as one unit for manufacturing reasons.
• the terminal 2 and the contact 4 are connected in one unit.
• the design of the voltage limiter with a short-circuiting device according to this solution can be used where the protection of persons, instruments, machinery and metal constructions from dangerous contact voltage, overvoltage and stray currents should be provided.
• the voltage limiter with a short-circuiting device creates a transient or continuous connection of non-live conductive parts with a return circuit, or with the earth over the time the permissible value of the contact voltage is exceeded. It also eliminates high impulse overvoltage induced into the traction line or electrical and electronic equipment by lightning strikes.

Applications Claiming Priority (1)

Publications (1)

Family

ID=62685007

Family Applications (1)

Country Status (3)

Family Cites Families (12)

• 2018
  • 2018-05-14 WO PCT/IB2018/053354 patent/WO2019220171A1/en unknown
  • 2018-05-14 EP EP18732880.2A patent/EP3782245A1/de not_active Withdrawn
• 2020
  • 2020-10-21 ZA ZA2020/06537A patent/ZA202006537B/en unknown

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