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
  • H01C7/126—Means for protecting against excessive pressure or for disconnecting in case of failure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H83/00—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current
  • H01H83/10—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by excess voltage, e.g. for lightning protection
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
  • H01H9/30—Means for extinguishing or preventing arc between current-carrying parts
  • H01H9/42—Impedances connected with contacts

Definitions

• the invention relates to the method of overvoltage protection of direct-current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current, at which in the device for overvoltage protection the current path is cut off in the place (X) of intentional cutting off the current path.
• the invention relates to the device for overvoltage protection of direct-current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current, which comprises the contacts (00) for connection of electric conductors of protected circuit, between the contacts (00) the current path is arranged with at least one varistor (1), between the varistor (1) and one contact (00) there is created a point (X) of intentional cutting off the current path with soldered joint of surface of fixed element of current path and surface of moving element of current path, to the point (X) of intentional cutting off the current path there is assigned thermal initiated cut-out mechanism (3) with spring-loaded moving action member, which applies a force (F) towards the moving element of the current path in direction parallel with plane of the soldered joint of surface of the fixed element of current path and surface of moving element of current path.
• the document DE 10 2007 015 933 discloses the device for overvoltage protection of photovoltaic sources of direct- current electrical circuits, which comprises between the terminals for connection to protected circuit an inserted switched discharger and cutting-off discharger. Parallel to both dischargers between the terminals for connection to protected circuit there is connected a non-linear resistance element, which in the represented example of embodiment is formed of a pair of varistors.
• the device further comprises a control circuit working as a co-ordinating and supervising unit and comprising a number of further parts.
• Contacts of varistor are flat, while one contact of varistor is electrically conductively coupled with one contact of the device for overvoltage protection, and the second contact of varistor is on its surface connected by means of a solder with opposite surface of the first end of flexible electrically conductive means, through which a point of intentional cutting off the current path is created.
• the flexible electrically conductive means is with its second end electrically conductively coupled with second contact of the device for overvoltage protection.
• the spring-loaded moving element is assigned, which to the first end of the electrically conductive means develops a force F in direction parallel with solder connected surfaces of the second contact of varistor and the first end of flexible electrically conductive means.
• Known is also device for overvoltage protection which comprises the current path with point of intentional cutting off, which is performed as a change-over switch of the current path between the branch with varistor and the short-circuit branch with a fuse cut-out, when in initial status the current path is lead through the branch with varistor.
• the goal of the invention is to remove or at least minimise shortcomings of the background art at direct-current electrical circuits, especially at photovoltaic sources of electric current, at which in case of a short circuit of varistor the flowing currents achieve the values of even tens of amperes.
• the goal of the invention has been achieved through the method of overvoltage protection of direct-current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current, whose principle consists in that during cutting off the current path in the point (X) between the current path elements being disconnected the value of electric current is limited, through which occurrence of uncontrolled electric arc between the current path parts being disconnected is suppressed.
• This invention enables in simple and price affordable means to realise a safe cutting off the current path in the device for overvoltage protection of direct-current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current, this both at values of current under 10 A even above 10 A, which meets the requirements of praxis and requirements of the draft (DRAFT) of the norm prEN 50539-11.
• Another advantage is that only for a short time of heating the current path in a point paintingX" the electric current flows through the device for overvoltage protection and the protected circuit e.g. the photovoltaic source of electric current after cutting off the current path is fully functional.
• Another advantage is, that it is not necessary to insert into the current path of the device for overvoltage protection a fuse for direct current as it is in the background art, because the fuse for direct current including the holder is relatively expensive, so that the invention enables besides also to reduce price of the device for overvoltage protection.
• Another advantage is that the capacitor for the whole service life of the device for overvoltage protection without voltage, through which its voltage loadability for the whole period of service life of the device for overvoltage protection is preserved. Voltage on the capacitor is acting only from the moment of cutting off the current path in the point X till the moment the varistor insertion is replaced.
• the invention is schematically represented in the drawing where the Fig. 1 shows a ground plan of one device for overvoltage protection, the Fig. 1a an example of another arrangement of the device for overvoltage protection, the Fig. 2 exemplary embodiment of the point X of intentional cutting off the current path of the device for overvoltage protection with parallel assigned capacitor, the Fig. 3a to 3d an exemplary embodiment of the point X with parallel assigned capacitor and a temporary serial resistance and the individual phases of concurrence of these elements and the Fig. 4 a time course of electric voltage and of electric current at the method according to the invention.
• the method of overvoltage protection of direct-current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current consists in that the current path is cut off in a place of intentional cutting off the current path, at the same time at this cutting off the conditions unfavourable for occurrence of uncontrolled electric arc are created, so that in the moment when between the current path elements being disconnected a nonzero interval is created, value of electric current in the point of cutting off is limited, by which occurrence of uncontrolled electric arc between the current path elements being disconnected is prevented.
• the value of electric current in the point of cutting off is limited due to increase of voltage through rerouting the flow of electric current to parallel current path formed of capacitor (condenser or a group of condensers).
• the capacitor at moment of creation of the nonzero interval between the current path elements being disconnected represents only a minor electric resistance, because the voltage on capacitor corresponds to the status before creation of the nonzero interval between the current path elements being disconnected and it is being increased in dependence on capacity of the capacitor and the value of current.
• Speed of mutual shifting away the current path elements being disconnected is so high, that the breakdown strength of air gap between the mutually shifting away elements of the current path being disconnected increases quicker than voltage on the capacitor, which increases due to charging the capacitor by a incoming electric charge from the rerouting flow of electric current, and this voltage grows up to the height of maximum voltage of the source of the direct-current electric current.
• Such behaviour of the device for overvoltage protection may be achieved by a suitable structure of the device for overvoltage protection with respective dimensioning of individual elements.
• Exemplary embodiment of the device for overvoltage protection of direct- current electrical circuits with currents even in tens of amperes, especially of photovoltaic sources of electric current comprises the box 0, in which individual functional elements of the device for overvoltage protection are built-in.
• the device for overvoltage protection comprises contacts 00 for connection of electric conductors of protected circuit. Between the contacts 00 there is in the box 0 arranged the current path, in which as a protective element at least one non-linear resistance element is integrated, for example varistor 1 or a group of parallel integrated varistors 1.
• the point X of intentional cutting off the current path is arranged.
• the point X in the represented example of embodiment is performed in the contact place of the upper surface of the lower electrode 10 of varistor 1_ and of the lower surface of the first end of flexible electric conductor 11.. Both these contact surfaces are connected by means of solder 12.
• Function of cutting off the current path in the point X is realised by means of thermal initiated cut-out mechanism 3, which is assigned to the point X, and which in the represented example of embodiment is formed of a spring loaded moving action member, which on the flexible electric conductor 11.
• the force F is either developed directly in direction parallel with upper surface of the lower electrode 10 of varistor and with lower surface of the first end of flexible electric conductor IjL
• the force F is either developed directly in direction parallel with upper surface of the lower electrode 10 of varistor and with lower surface of the first end of flexible electric conductor ⁇ or it acts in this direction, e.g. thanks to production deviations etc., as a component of totally acting force.
• the force F after melting the solder 12 as a result of increased temperature of varistor pushes off the first end of flexible electric conductor 11. from the lower electrode 10 of varistor 1 by a shearing action on the molten solder 12, i.e. by sliding motion of the first end of flexible electric conductor 11.
• Solder 12 is molten and the thermal initiated cut-out mechanism 3 is initiated by means of a heat, which is partly developed by a non-linear resistance element (varistor 1) integrated in the current path, and which is also developed by passage of electric current through the current path.
• a non-linear resistance element variablestor 1
• Thermal initiated cut-out mechanism 3 is coupled with means for optical and/or remote signalling of status of the device for overvoltage protection.
• the device is provided with swing lever 4, which is coupled with thermal initiated cut-out mechanism 3
• the auxiliary electric conductor 13 which has distinctly higher electric resistance, than the lower electrode 10 of varistor 1 and a flexible electric conductor 1_1 have, e.g. it is formed of a strip made of stainless steel of a small thickness.
• the auxiliary electric conductor 13 runs along the lower surface of the lower electrode 10 of varistor 1 up to a free space in distance A from the edge of the lower electrode 10 of varistor 1_ , where it finishes with a contact edge 130 situated in a free space behind the first end of flexible electric conductor H outside the contact with flexible electric conductor 11.
• the distance A is smaller than the length of the first end of flexible electric conductor 11.
• the auxiliary electric conductor 13 and the lower electrode 10 of varistor 1 there is, with exception of the place of connection of the auxiliary electric conductor 13 to the lower electrode 10 of varistor 1 , situated electric insulation 14, e.g. insulation foil.
• Capacitor 16 is parallel to the current path through the point X connected between the lower electrode 10 of varistor and the non-moving section of the flexible electric conductor H still after the first end of flexible electric conductor 11
• the Fig. 3a represents full functioning status of the device for overvoltage protection without occurrence of a failure status.
• Solder 12 is in a solid status and holds the first end of flexible electric conductor H and the lower electrode 10 of varistor 1 together.
• the capacitor 16 shows voltage Uo.
• the Fig. 3b represents the status when solder 12 has already been molten and the spring-loaded moving action member of thermal initiated cut-out mechanism 3 has already begun to push off the first end of flexible electric conductor V_ in direction of actioning the force F parallel with surface of the lower electrode 10 of varistor ⁇ .
• the first end of the flexible electric conductor H moves in gradually increasing speed, at the same time it is still in electric contact with the lower electrode 10 of varistor 1 and it newly has entered into electric contact with contact edge 130 of auxiliary electric conductor 13.
• the capacitor 16 shows voltage Uoi.
• the Fig. 3c represents status when the spring-loaded moving action member of thermal initiated cut-out mechanism 3 has already pushed off the first end of the flexible electric conductor H in a still increasing speed parallel with surface of the lower electrode 10 of varistor 1 totally outside electric contact with lower electrode 10 of varistor 1, nevertheless the first end of flexible electric conductor 1_1 remains in electric contact with contact edge 130 of auxiliary electric conductor 13.
• the capacitor 16 shows voltage U2.
• the Fig. 3d represents status of total cutting off the current path of the device for overvoltage protection in the point X, when the spring- loaded moving action member of thermal initiated cut-out mechanism 3 has pushed off the first end of the flexible electric conductor V ⁇ totally outside electric contact with contact edge 30 of the auxiliary electric conductor 13.
• the capacitor 16 shows voltage U 3 .
• the spring-loaded moving action member starts gradually with increasing speed in sliding manner to shift the first end of the flexible electric conductor 11_ on surface of the lower electrode 10 of varistor 1 , while thanks to molten solder 12 , electric current still passes between the first end of flexible electric conductor V ⁇ _ and the lower electrode 10 of varistor 1. Once the nonzero interval occurs between the first end of the flexible electric conductor 1 and the lower electrode 10 of varistor ⁇ , voltage between the first end of flexible electric conductor 11.
• this first end of flexible electric conductor 11 Thanks to sliding motion of the first end of the flexible electric conductor H on surface of the lower electrode 10 of varistor ⁇ , this first end of flexible electric conductor 11 , at the moment of creation of the mentioned nonzero interval reaches still a sufficient speed of its motion, so that at its further shifting away from the lower electrode 10 of varistor 1 the interval being created increases, and with it also its breakdown strength quicker than the voltage is increased on capacitor 16, which (voltage on the capacitor 16) increases due to charging the capacitor 16 by the incoming electric charge from the re-routed flow of electric current. This voltage on capacitor 16 increases till the value of maximum voltage of the source of electric direct-current.
• the invention is applicable at overvoltage protection of direct current electric circuits with currents even in tens of amperes, especially of photovoltaic sources of direct current.

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

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Citations (7)

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• 2010
  • 2010-06-03 EP EP10164827.7A patent/EP2393088B1/en active Active
  • 2010-06-03 CZ CZ20100440A patent/CZ2010440A3/cs unknown
  • 2010-08-02 WO PCT/IB2010/001951 patent/WO2011151668A1/en not_active Ceased

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