Arrangement for overload protection for overvoltage protection equipment

Abstract

The invention relates to an arrangement for overload protection of overvoltage protection devices, consisting of at least one type II surge arrester with or without a thermal disconnecting device that responds in the event of an of overload. According to the invention, a switching unit free of movable contacts is connected in series with the at least one surge arrester and structurally combined therewith, which switching unit has at least two fixed narrow spaced switching contacts, wherein the spacing of the switching contacts is specified in such a way that in the event of every surge current or discharge process, the switching device changes into a quasi-closed state because of the arc formed; whereas in the idle state, the voltage of the connected mains drops at the switching device, with the surge arrester arranged in series remaining free of leakage current.

Claims

1. Arrangement for overload protection of overvoltage protection devices, consisting of at least one surge arrester (2), in particular of type II with or without thermal disconnecting device (3) which responds in an event of an overload, wherein the at least one surge arrester (2), which is structurally connected thereto, is connected in series with a switching unit (6) which is free of movable contacts and which comprises at least two fixed narrow spaced switching contacts (7; 8), a spacing of the respective at least two fixed narrow spaced switching contacts (7; 8) being specified in such a way that in the event of every surge current or discharge process, the switching unit (6) changes into a quasi-closed state as a result of an arc formed; whereas in an idle state, a voltage of a connected mains drops at the switching unit (6), with the at least one surge arrester (2) arranged in series remaining free of leakage current, wherein the switching unit (6) is formed as a miniaturized, open spark gap.

2. The arrangement according to claim 1, wherein the at least two fixed narrow spaced switching contacts (7; 8) are designed in such a way that the arc generated in the event of a discharge remains in place and an increase of the arc drop voltage is omitted.

3. The arrangement according to claim 1, wherein the switching unit (6) is designed as a switch which changes into an open state in an event of zero current passage of a line follow current.

4. The arrangement according to claim 1, wherein the surge arrester is embodied as a varistor, in particular as a metal oxide varistor (MOV).

5. The arrangement according to claim 1, wherein the switching unit (6) and the at least two fixed narrow spaced switching contacts (7; 8) are designed in such a way that in the event of surge currents, a quasi-switching process with current flow can be triggered via the at least one surge arrester (2).

6. The arrangement according to claim 1, wherein a power conversion in the switching unit (6) can be limited for each surge current operation by limiting an arc voltage between the at least two fixed narrow switching contacts (7; 8).

7. The arrangement according to claim 1, wherein an overload indicator is activated when the switching unit (6) is overloaded and triggered for the first time in order to deactivate or replace the surge arrester.

8. The arrangement according to claim 1, wherein the surge arrester is deactivated or destroyed on initial overload and activation of the switching unit (6).

9. The arrangement according to claim 1, arranged in a housing comprising a series connection of the at least one surge arrester and the switching unit, wherein two external terminals (4; 5) of the series connection are provided.

Description

(1) In the following the invention is explained in more detail based on exemplary embodiments and with reference to the attached Figures.

(2) These show:

(3) FIG. 1 a schematic illustration of the overload protection unit, comprising a series connection consisting of a switching unit and surge arrester with thermal disconnecting device and

(4) FIG. 2 an illustration similar to the one in accordance with FIG. 1, however with a type II surge arrester without additional thermal disconnecting device that responds in the event of an overload.

(5) For the Figures, a unit 1 is first assumed.

(6) This unit 1, which is characterized by a common housing, comprises in its interior a type II surge arrester 2.

(7) This type II surge arrester 2 has, in case of the embodiment in accordance with FIG. 1, a thermal disconnecting device 3 that responds in case of overload, which is known per se.

(8) Furthermore, unit 1 comprises external terminals 4 and 5.

(9) The type two surge arrester is internally connected in series with a switching unit 6.

(10) The switching unit comprises two fixed, non-movable contacts 7; 8.

(11) The contacts 7; 8 are located closely spaced and can be part of the connections of the surge arrester 2.

(12) The spacing is selected in such a way that in the event of every surge current or discharge process, the switching unit 6 changes into a quasi-closed state as a result of the arc formed.

(13) Whereas in the idle state, the voltage of the mains connected to the terminals 4 and 5 drops at the switching unit 6, with the surge arrester 2 arranged in series remaining without leakage current and therefore without stress.

(14) The switching unit 6 can be compared as to its function with a miniaturized spark gap, which is integrated as an additional component in unit 1 or in the surge arrester 2.

(15) The response characteristic of the switching unit 6 is selected in such a way that it is also activated during each discharge process and is therefore closed on the current side in the event of overload or malfunction; whereas normally it remains passive.

(16) The switching unit is embodied in such a way that surge current loads do not lead to unacceptable aging or similar effects.

(17) This can be achieved by the emerging arc remaining at an ignition contact point during surge current operation.

(18) According to an exemplary embodiment, the spacing of the switching contacts 7 and 8 is chosen to be very small. This avoids an increase in the arc drop voltage. Also in case of a surge current load, there only occur arc voltages within the range of 20 V to 30 V. Such a small arc voltage is only accompanied by a small power conversion in the emerging arc, which reduces burn-off or wear at the switching contacts.

(19) The illustration in FIG. 2 is an alternative version to the embodiment due to the fact that no leakage current flows through the arrester 2 during normal operation due to the disconnection of surge arrester 2 from the mains through the open switching unit. This eliminates the need for a thermally activated disconnecting device. Due to the fact that the switching unit is active during each discharge operation, any emerging mains-frequency line follow currents may be limited and interrupted without time delays. In this case, the arc generated by the surge current is quickly moved away from the region between the switching contacts and is thereby extended and cooled, so that the arc voltage of the arc increases, thereby achieving the desired residual current limitation.

(20) Since, unlike mechanical switchgears, the switching unit does not first have to disconnect the contacts on the basis of a spark gap as a backup protection device, there are no typical surge current problems as with contact-type switching devices. The switching unit may be quasi-triggered by a third contact which is located at a distance between the contacts 7 and 8.

(21) Thus, an overload indicator is for example realizable.