EP2502251B1 - Switching unit for switching high dc voltages - Google Patents

Description

The invention relates to a switching unit for switching high DC voltages, in particular for DC interruption between a DC power source and an electrical device, having two terminals protruding from a housing, which are electrically conductively coupled via a conductor path, and arranged with one between the first and the second terminal mechanical contact system with two contacts which are movable relative to each other and can be transferred from a closed position to an open position, as well as with a triggered by a thermal fuse disconnecting device for extinguishing an arc resulting when opening the contacts. In this case, a direct current source is understood to mean, in particular, a photovoltaic (PV) generator (solar system) and an electrical device, in particular an inverter.

When switching from higher direct voltages to 1500 V (DC) arise in such switching units between the contact zones due to the high field strengths (by gas ionization) conductive channels, which are known as electric arcs or arc plasmas. The arc that occurs when disconnecting the switch contacts must be extinguished as quickly as possible, because the arc releases a large amount of heat (gas temperature of a few thousand degrees Kelvin), which leads to a strong heating of the switch contacts and the environment. This strong heating can cause damage to the switching unit, such as a burning of the switching unit, and also the parent installation unit.

From the DE 20 2008 010 312 U1 is a PV system or solar system with a so-called PV generator known, which in turn consists of grouped, combined into sub-generators solar modules. The solar modules are connected in series or in parallel strands. While a sub-generator outputs its DC power through two terminals, the DC power of the entire PV generator via an inverter fed into an AC power grid. In order to keep the cabling and power losses between the sub-generators and the central inverter low, so-called generator junction boxes are placed close to the sub-generators. The thus-accumulated DC power is usually fed via a common cable to the central inverter.

Depending on the system, PV systems permanently supply an operating current and an operating voltage in the range between 180V (DC) and 1500V (DC). A reliable separation of the electrical components or devices from the effective as a DC power source PV system is desirable, for example, for installation, assembly or service purposes and in particular for general personal protection. A corresponding disconnecting device must be capable of interrupting under load, that is, without first switching off the DC power source.

For load separation mechanical switches (switching contact) can be used. These have the advantage that when the contact opening is made as well as a galvanic isolation of the electrical device (inverter) from the DC power source (PV system) is made.

Such switching units are generally known in the art. The arcs that occur when the contacts are opened under load are quickly moved to designated extinguishing devices where the corresponding arc extinction takes place. The force required for this is done by magnetic fields, so-called Blasfelder, which are typically generated by one or more permanent magnets. By special design of the contact zones and the Lichtbogenleitstücks the arc is passed into appropriate extinguishing combs, where the arc extinction takes place according to known principles.

Such extinguishing combs consist, for example, of arc splitter stacks. The material used for the quenching plates usually ferromagnetic materials are used, since the magnetic field that accompanies the arc, in the vicinity of a ferromagnetic material tends to pass through the magnetic better conducting quenching plates. This creates a suction effect in the direction of the quenching plates, which causes the arc to move to the arrangement of the quenching plates and is divided between them.

In simple mechanical switching units occur in practice numerous sources of error that adversely affect safe switching or even impossible. One possible error is the lack of an arc-extinguishing component, such as a quenching plate or the blowing magnet. In addition, incorrectly mounted components can also lead to the failure of the switching unit, for example due to a polar reversed insertion of the blowing magnet. Especially with hybrid switch systems, there are further possibilities for errors due to missing or faulty electronic components.

In order to bring the PV system into a safe state for man and plant in the event of such errors, the circuit must be permanently disconnected so that the operator can detect the error and replace the switching unit. When transferring to this state, do not damage or destroy the switch housing of the device so that the live parts remain isolated. The transfer in such an error case is done by a so-called fail-safe element of the switching unit, without having to take advance activation measures, such as a manual intervention or the like must be made.

Typical fail-safe elements are triggered by an exceeding of a permissible material-dependent current density (current per area). An electrical conductor is melted through and the circuit is interrupted. This is a common way to detect and turn off overcurrents, such as those used in fuses. However, this method can not be used in PV systems, since it can not be assumed that there is a specific current density or current level. The triggering or error detection should rather be independent of current heights.

From the DE 10 2008 049 472 A1 is a surge arrester with at least one diverting element, as well as with a separating device, in which on the one hand, a thermally realizable separation of the at least one diverting element can be made. On the other hand, it is possible to bring about the case of short circuit with further energetic, in particular thermal load. Here, in the path of movement of a conductor section moved by the separating device between a melting point and a conductive element forming a mating contact, there is a thermally releasable stop device. When triggered and in case of overload, the movement of the conductor section is interrupted by the stop device before reaching the end position. If there is an error case in which the separating device can not interrupt the power safely and an arc between the fixed terminal of the diverter and the conductor portion arises or persists, which corresponds to an additional heat input, the stopping action is released and moves the movable conductor portion in the end position , The shutdown of the short circuit and thus the separation of the surge arrester from the network takes over in a conventional manner an upstream overcurrent protection device, in particular a fuse.

Such a fail-safe element is also not suitable for the above-described application, since here too the error detection takes place only from a certain overcurrent. A pending arc would occur in the event of a fault at higher voltages in the current working range of the switching unit. EP1953788A discloses a switching unit according to the preamble of claim 1.

The invention has for its object to provide a switching unit of the type mentioned, which can reliably and safely switch a high DC voltage. In particular, the switching unit should be suitable for carrying out a DC interruption between a DC power source, in particular a PV generator, and an electrical device, in particular an inverter. Furthermore, the switching unit should be set up to extinguish an arcing fault that does not automatically extinguish within the switching unit without the need for activation measures beforehand, for example a manual intervention or the like.

The object is achieved by the features of claim 1. Advantageous embodiments and further developments are the subject of the dependent claims.

For this purpose, the switching unit comprises two terminals protruding from a housing, which are electrically conductively coupled via a conductor path. Between the first and the second connection, a mechanical contact system with two contacts is arranged, which are movable relative to each other and can be transferred from a closed position to an open position. A releasable by means of a thermal fuse separator is used to extinguish an arc resulting from the opening of the contacts. The thermal fuse comprises a melting point arranged in the conductor path, which is connected on the one hand to the contact system and on the other hand via a movable conductor section to the first connection.

Under load, in the event of a fault - due to the high voltage applied between the contact surfaces - a non-self-extinguishing arc can form when the contact system is opened. The separation device is triggered and the connection between the conductor section and the contact system at the melting point is separated when the melting point of the melting point is reached or exceeded as a result of the arc.

The occurring in case of failure arc is very energy rich. In contrast to the prior art is not the current density in an overcurrent, but the heat energy generated by the arc, which increases disproportionately in the event of a fault, used to trigger the thermal fuse or to melt the melting point. As a result, a fail-safe of the switching unit is given, the triggering or fault detection is independent of current level.

The thermal fuse of the switching unit thus serves as a fail-safe element, which is particularly suitable for use in PV systems. Furthermore, the failure protection the switching unit cost-effectively and thus meets the requirements of economic manufacturability.

In an expedient embodiment, the melting point is in particular a solder joint, which is separated when the response temperature is reached or exceeded. As the solder material between the contact system and the conductor portion, a fused alloy such as an aluminum-silicon-tin alloy or other well-known low-melting alloys may be used. The melting point of such alloys is usually in the range of 150 ° C to 250 ° C. As a result, the current is safely conducted in rated operation, without the thermal fuse is triggered. However, it is also conceivable to use other temperature-sensitive and electrically conductive materials as melt material, such as an electrically conductive plastic.

Depending on the field of application, by selecting the conductive and / or insulating materials of the switching unit a corresponding variation in the response temperature and / or the triggering time can be achieved. Furthermore, it is conceivable that with a suitable dimensioning and composition of the materials used, such a switching unit can also be used for lower voltages.

In an advantageous development, the separating device comprises a prestressed spring element. The spring restoring force acts along a direction of separation directly or indirectly on the movable conductor section. If, in the event of a fault, the melting point is heated inadmissibly, it is melted and as a result the switching unit causes a power interruption due to the spring restoring force. In particular, the preloaded spring element thus allows an automatic power interruption without an activation measure must be made by a person in case of failure.

When the melting point separates, an arc also forms between the contact system on the one hand and the movable conductor section on the other hand. Due to the spring restoring force, the conductor portion of the contact system moved away and thus the arc or the arc plasma artificially extended. If this arc is extinguished in this way, the arc between the contact surfaces of the contact system also goes out. As a result, the DC power source is galvanically isolated from the electrical device.

In a suitable embodiment, the spring element deflects the conductor section when the separation device is triggered by a pivot point which is at a distance from the melting point. The covered swing angle is in particular greater than or equal to 90 °. By pivoting the conductor portion of the second arc is artificially extended and thus further cooled. This additional lengthening or cooling ensures that the distance between the contact system and the conductor section is opened as quickly and widely as possible in order to extinguish the (second) arc arising when the conductor section is detached and the (first) arc present at the contact system. The spring restoring force is chosen to be large enough to pivot the conductor section as quickly as possible, so that damage to the switching housing is advantageously avoided by the arcs.

In a suitable embodiment, the housing of the switching unit has an insulating chamber adjacent to the melting point. In a successful release of the separator, the conductor portion is pressed as a result of the spring restoring force in this isolation chamber. The insulating chamber is used for the spatial and thus insulating separation of the conductor portion of the contact system, whereby the extinction of the arc is advantageously supported.

In an equally suitable embodiment, the separating device has a separating element which is movably held in the housing and which is guided against the conductor section. The melting point is naturally sensitive to external forces acting on it. Due to the aforementioned spring restoring force of the separating device on the conductor section, the melting point is relatively heavily loaded. By the separating element, the restoring force on a larger contact surface on Start ladder section effectively. In other words, this means that the resulting torque acting at the melting point is advantageously reduced. As a result, less mechanical stress is applied to the melting point.

In a suitable embodiment of the invention, the separating element also sets close to the melting point on the conductor section, so that the force arm and thus the acting torque at the melting point is further reduced. This torque, or the Kraftarmlänge and / or the Trennelementbemessung can be used as an additional parameter for dimensioning the response temperature and / or the trip time of the fail-safe of the switching unit or the separation device.

In an expedient continuation of the conductor portion is covered after triggering the separation device relative to the melting point by the separator at least partially insulating, whereby the arc is advantageously suppressed.

In an expedient embodiment of the switching unit, the separating element in the housing is guided slidingly movable and is moved when triggering the separator, by the spring restoring force, together with the conductor portion in the insulating chamber. As a result, the conductor section is completely covered in the tripped state. When the disconnecting device is triggered, the further arc, due to the pivoting of the conductor section, is squeezed between the separating element and the insulating chamber. The crushing ensures a particularly quick and safe extinguishing of the arc.

In a preferred embodiment, the spring element is in this case a helical compression spring which presses the separating element along the separation direction in the insulating chamber. The separating element and the insulating chamber are geometrically complementary designed for this purpose, so that the arc in the chamber can be squeezed and the conductor portion of the separating element relative to the contact system is completely concealed. The Einquetschlänge is expedient adaptable to the performance parameters of the DC power source.

In an alternative, equally advantageous embodiment of the switching unit, the separating element is rotatably held in the housing. When the separation device is triggered, the conductor section is pivoted by the separation element about the pivot point spaced from the fusion point. In an expedient embodiment, the spring element is a leg spring, by means of which a pivot lever pivots the conductor section in the event of a fault.

In a simple embodiment of the invention, the contact system comprises a moving and a fixed contact. Between the fixed contact and the melting point, an electrically conductive contact carrier is arranged, which couples the fixed contact and the melting point thermally conductive. Instead of a moving and a fixed contact and two movable contacts can be provided. The heat capacity or the melting point of the contact carrier is higher than that or of the melting point. In an expedient embodiment, the contact carrier is made of a thermally and electrically highly conductive material, such as copper, so that a fast and reliable release of the separator is ensured. In order to support the thermal conductivity (heat flow per cross-sectional area and temperature gradient), the contact carrier can be designed and dimensioned accordingly, for example by a taper on the carrier.

In a suitable development of the moving contact is coupled via a trigger mechanism with a rocker arm for manually actuating the contact system. In a typical embodiment, the triggering mechanism, the moving contact and the fixed contact form a (mechanical) jump contact system. In such a jump contact - as a result of actuation - the contacts are typically removed from each other as quickly as possible by a prestressed leg spring, typically in a few milliseconds. As a result, a (first) emerging arc is normally erasable, so that the separation device is not triggered.

In a typical embodiment of the switching unit, the movable conductor section is a flexible connecting element, in particular a stranded conductor, whose fixed end is unsolvable with the first connection and whose loose end is soldered to the melting point, preferably to the contact carrier.

In a likewise typical embodiment, the housing of the switching unit accommodates the conductor path, the mechanical contact system, the disconnecting device and the thermal fuse. As a result, the current-carrying parts of the switching unit are isolated from the environment. In particular, this advantageously protects a person operating the switching unit against the high voltages and currents applied.

In an advantageous embodiment, the housing and the separating element made of a thermally stable plastic material, in particular made of a thermosetting plastic material. This ensures that the high heat development due to the arc, the switch housing is not damaged or destroyed. As a result, the current-carrying parts continue to be isolated in the event of a fault in a touch-proof manner. Furthermore, it is ensured that the separating element is not damaged or destroyed by the second arc in the region of the melting point. As a result, the separating element reliably disconnect the switching unit from the mains in the event of a fault.

In a suitable embodiment, the separating element and / or the insulating chamber are made of a plastic material outgassing in the event of fire, in particular of polyamide. Likewise suitable are, for example, polycarbonate or polyoxymethylene. The plastic outgassing contribute advantageously to a fast extinction of the (second) arc. In particular, the gases hinder ionization of the air gap in the region of the dissolved melting point or allow it to decay faster.

The interaction with the choice of suitable plastics for housing, insulating chamber and separating element, the shape and the material of the contact carrier and the dimensioning of the squeezing and the acting torque The melting allow exact triggering of the separator in case of failure and a reliable extinction of the arc.

With respect to a disconnecting device for DC interruption between a DC power source and an electrical device, in particular between a PV generator and an inverter, said object is achieved by the features of claim 16. Thereafter, the device comprises a current-carrying switching unit according to the invention.

In an expedient embodiment of the switching unit, the terminals and the housing are suitable and arranged for a circuit board assembly for this purpose. In the preferred use of the switching unit, the separating device is therefore particularly suitable for reliable and touch-safe galvanic DC interruption both between a PV system and one of these associated inverter as well as in connection with, for example, a fuel cell system or an accumulator (battery).

Fig. 1

in einem Blockschaltbild die erfindungsgemäße Schalteinheit mit einem Fail-Safe-System zwischen einem PV-Generator und einem Wechselrichter,

Fig. 2

in einer Schnittdarstellung die Schalteinheit in einem geschlossenen Schaltzustand,

Fig. 3

in einer Schnittdarstellung die Schalteinheit gemäß Fig. 1 beim Öffnen des mechanischen Kontaktsystems und bei Bildung eines Lichtbogens,

Fig. 4

in einer Schnittdarstellung die Schalteinheit gemäß Fig. 1 und Fig. 2 nach einer Auslösung des Fail-Safe-Systems,

Fig. 5

in einer Explosionsdarstellung die Schalteinheit,

Fig. 6

in einer Ausschnittsdarstellung die Trennvorrichtung,

Fig. 7

in einer Schnittdarstellung ausschnittsweise die Schalteinheit mit einer alternativen Trennvorrichtung, und

Fig. 8

in einer Schnittdarstellung ausschnittsweise die Schalteinheit gemäß Fig.6 im ausgelösten Fail-Safe-Zustand.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1

1 is a block diagram of the switching unit according to the invention with a fail-safe system between a PV generator and an inverter;

Fig. 2

in a sectional view of the switching unit in a closed switching state,

Fig. 3

in a sectional view of the switching unit according to Fig. 1 when opening the mechanical contact system and when forming an arc,

Fig. 4

in a sectional view of the switching unit according to Fig. 1 and Fig. 2 after triggering the fail-safe system,

Fig. 5

in an exploded view of the switching unit,

Fig. 6

in a sectional view of the separation device,

Fig. 7

in a sectional view of a detail of the switching unit with an alternative separation device, and

Fig. 8

in a sectional view of the switching unit according to detail Figure 6 in the triggered fail-safe state.

Corresponding parts and sizes are always provided with the same reference numerals in all figures.

Fig. 1 schematically shows a switching unit 1, which is connected in the embodiment between a PV generator 2 and an inverter 3. The PV generator 2 comprises a number of solar modules 4, which are guided parallel to each other on a common generator junction box 5, which effectively serves as a collection point.

In the main current path 6 representing the positive pole, the switching unit 1 comprises essentially two subsystems for the galvanic direct current separation of the PV generator 2 from the inverter 3. The first subsystem is a manually operable mechanical contact system 7, the second subsystem is a fail-safe triggering in the event of a fault independently. System 8. In the negative pole representing return line 9 of the switching unit 1 - and thus the entire system - can be connected in a manner not shown further contact and fail-safe systems 7, 8.

The Fig. 2 to 6 show a variant of the switching unit 1 according to the invention in a detailed representation. The switching unit 1 comprises a housing 10 from which two terminals (external terminals) 11 and 12 protrude. The switching unit 1 is connected via the terminals 11 and 12 in the main current path 6 between the PV generator 2 and the inverter 3.

The contact system 7 further comprises a via a rocker arm 13 and a coupling lever 14 manually operable contact bracket 15 is formed as a moving contact and a contact carrier 16 as a fixed contact. The contacts or contact surfaces 17a and 17b between the contact clip 15 and the contact carrier 16 are designed as plate-like contact elements.

The contact clip 15 is electrically conductively coupled to the terminal 11 via a fixed stranded conductor 18, wherein both the connection between the contact clip 15 and the stranded conductor 18 and the connection between the stranded conductor 18 and the terminal 11 are designed as a welded connection. The contact clip 15 is substantially hammer-shaped and made of an electrically conductive metal, wherein the contact surface 17a is arranged at the hammer head end and in the closed position of the switching unit 1 (FIG. Fig. 2 ) rests on the contact surface 17b.

The contact carrier 16 is made of copper, so that it has a high electrical and thermal conductivity. The contact carrier 16 has substantially the shape of a step, wherein at the upper step edge, the contact surface 17b is arranged. The step body of the contact carrier 15 has a tapered cross section to increase its thermal conductivity. At the lower step edge, a movable stranded conductor 20 is electrically conductively coupled via a solder 19.

The stranded conductor 20 may have an electrically insulating shield 21, which is removed at its two ends. One of the conductor ends (fixed end) of the stranded conductor 20 is permanently connected to the terminal 12 by welding, while the other end of the conductor (loose end) is soldered to the solder 19 on the contact carrier 15.

In the closed position of the switching unit 1, the circuit is thus closed via the two terminals 11 and 12 and the main current path 6. The current flows through a thus formed conductor path 22 comprising the terminal 11, the stranded conductor 18, the contact clip 15, the contact surfaces 17a and 17b, the contact carrier 16, the solder 19, the stranded conductor 20 and the terminal 12. The conductor path 22 extends approximately U-shaped within the housing 10th

The housing 10 is made of an electrically insulating and heat-resistant plastic and is - as in Fig. 5 visible - formed from two complementary housing halves 10a and 10b. The half-shells 10a and 10b can be connected by four holes 23 by means of screws or rivets, not shown. The holes 23 are arranged distributed approximately at the vertices of an imaginary quadrilateral evenly on the housing 10.

The housing 10 has an approximately rectangular cross-section, so that a simple assembly of several juxtaposed switching units 1 on a common circuit board is possible. The housing 10 has an approximately U-shaped circumference, wherein the two U-legs are interconnected by a horizontal part. For this horizontal part protrude the two terminals 11 and 12 and at the U-base at least partially the rocker arm 13 out. Furthermore, the half-shells 10a and 10b are designed with corresponding inner-profile structures, in which the individual components of the switching unit 1 can be used in a form-fitting manner or with play.

The rocker arm 13 serves not only to open and close the contact system 7, but also as an external optical indication of the switching state of the switching unit 1, as in Fig. 4 can be seen, in which the rocker arm 13 is in the open position. In a manual actuation of the rocker arm 13, an external force for tilting the switch is converted by a hinge system 24 in a pivoting movement of the contact clip 15.

The fail-safe system 8 ensures permanent galvanic isolation between the PV generator 2 and the inverter 3. The fail-safe system 8 comprises the contact carrier 16, the solder 19, the stranded conductor 20, a separating device 27 with a helical compression coil spring 28 and a slide 29 and an insulating chamber 30. This embodiment of the separation device 27 is in Fig. 6 shown in more detail.

The helical compression spring 28 is located in a guide chamber 31 of the housing 10, wherein a pin-like extension 32 of the guide chamber 31 is at least partially enclosed by the helical compression spring 28. The helical compression spring 28 presses against the slide 29 due to a spring restoring force F. the stranded conductor 20. The slider 29 has a projection 33 formed as a finger, which presses directly against the stranded conductor 20. The finger 33 begins near the solder 19, so that the torque acting on the soldering due to the spring restoring force F is as low as possible.

The guide chamber 31 and the insulating chamber 30 are at a height along a separation direction A and are separated from each other by the perpendicular thereto stranded conductor 20. The guide chamber 31 and the insulating chamber 30 further have the same (slider-shaped) cross-section.

In the event of a fault, a resulting arc 26 heats the contact surfaces 17a and 17b and thus also the contact carrier 16 due to the disproportionately increasing heat development. Due to its high heat capacity, the solder 19 is heated to a comparable extent and ultimately melted. As a result, the slider 29 is displaced along the separation direction A in the insulating chamber 30 by the spring restoring force F of the helical compression spring 28. The slide 29 and the insulating chamber 30 are geometrically complementary, so that they are easily slidable. The Einquetschlänge the isolation chamber 30 is suitably adapted to the performance parameters of the PV generator 2.

During the displacement of the slide 29 in the insulating chamber 30 of the stranded conductor 20 is pivoted about a pivot point 34, and finally bent by about 90 ° ( Fig. 4 ). When melting and separating the solder 19, a second arc (not shown) forms between the contact carrier 16 and the loose end of the stranded conductor 20, which runs approximately along the connecting line in the separated state. This second arc is on the one hand extended by the displacement of the slide 29, and thereby cooled, and on the other hand squeezed between the same and thus deleted due to the fit between the slide 29 and the insulating chamber 30 between the same. As soon as the second arc is extinguished, the contact carrier 16 and the stranded conductor 20 are galvanically separated, whereby at the same time the arc 26 is extinguished. The finger 33 favors the separation of the soldering and encapsulates the second arc when stop at the bottom of the insulating chamber 30 completely on or off.

Both the slider 29 and the inner walls of the insulating chamber 30 may be made of an outgassing and electrically insulating plastic material. Due to the evolution of heat in the vicinity of the second arc, in particular in the region of the separation device 27, gases are released from these plastic materials. The gases hinder ionization of the air gap in the region of the dissolved solder 19 or let the ionization decay faster. As a result, the second arc is more easily erased by the separation device 27.

The conductor path 22 of the switching unit 1 in the tripped state ( Fig. 4 ) Therefore, two galvanic separation points, namely on the one hand between the contact surfaces 17a and 17b and on the other hand between the contact carrier 16 and the loose end of the stranded conductor 20. The materials and dimensions of the switching unit 1 and its separator 27 are dimensioned accordingly, even in case of failure within a few Milliseconds to ensure a DC galvanic interruption between the PV generator 2 and the inverter 3.

Based on Fig. 7 and Fig. 8 Below is a second embodiment of the switching unit 1 with a separator 27 'explained, for the sake of clarity, only relevant for the fail-safe system 8 second half of the conductor path 22 (the contact carrier 16, the solder 19, the stranded conductor 20 and the Terminal 12) is shown. The separating device 27 'comprises a prestressed leg spring 35, an approximately hook-like pivoting head or lever 36 and an insulating chamber 30'. The inner profile of the housing 2 is set up and designed in accordance with the separating device 27 '.

The insulating chamber 30 'in this embodiment is substantially the lower half (of the top rail 12 of) of the housing 10. The pivoting head (pivot lever) 36 is approximately L-shaped, wherein both the pivoting head 36 and the Insulating chamber 30 'are made of an outgassing electrically insulating plastic material. The upper corner 36a of the horizontal L-leg of the swivel head 36 abuts the strand 20 in a similar manner as the finger 33 in the previously described variant. At the lower end of the vertical L-leg of the swivel head 36, the prestressed leg spring 35 is arranged. By the leg spring 35 of the swivel head 36 is pivotally or rotatably held.

When melting the solder 19 as a result of the evolution of heat of the arc 26, the leg spring 35 pivots the pivoting head 36 due to a spring restoring force F '. In this case, the strand 19 is pivoted about the pivot 34 'at an angle of about 90 ° in the direction of the lower right corner of the housing 10 and the insulating chamber 30'.

In contrast to the first embodiment, the arc is not crushed, but only artificially extended, so that the arc plasma can be erased due to the resulting cooling. The arc is much more prolonged compared to the first embodiment, since the stranded conductor 20 is not pressed in the direction of the right side wall, but is pivoted into the lower corner. The switching unit 1 is equipped with the separation device 27 'and adapted to ensure within a few milliseconds a galvanic DC interruption between the PV generator 2 and the inverter, both in normal and in case of failure.

In a suitable dimensioning of the housing dimension, the horizontal rail side bearing surface of the housing 10 is about 4 cm wide, the side edges of the housing about 6 cm long and the housing 10 about 2 cm deep. The distance of the contact surfaces 17a and 17b is in the open position about 1 cm and the distance between the contact carrier 15 and the loose end of the stranded conductor 20 after triggering of the separator 27 and 27 'at least 1.5 cm. The plastics for housing 10, insulating chamber 30/30 'and slide 29 or swivel head 35, the shape and the material of the contact carrier 16 and the torque acting on Lot 19 are selected so that the switching unit 1 has a nominal voltage of about 1500 V (DC).

The invention is not limited to the embodiments described above. On the contrary, other variants of the invention can be derived therefrom by the person skilled in the art without departing from the subject matter of the invention. In particular, furthermore, all the individual features described in connection with the various exemplary embodiments can also be combined with one another in other ways, without forgetting the subject matter of the invention.

LIST OF REFERENCE NUMBERS

1

switching unit

2

PV generator

3

inverter

4

solar module

5

junction box

6

Main current path

7

Contact system

8th

Fail-safe system

9

Return line

10

switch housing

10a, 10b

half shell

11, 12

connection

13

rocker arm

14

coupling lever

15

contact bow

16

contact support

17a, 17b

contact area

18

Stranded conductor

19

solder

20

Stranded conductor

21

shielding

22

conduction path

23

drilling

24

joint system

26

Electric arc

27, 27 '

separating device

28

Helical compression spring

29

pusher

30, 30 '

isolation

31

guide chamber

32

Guide extension

33

Finger tab

34

pivot point

35

Leg spring

36

Swivel head / lever

36a

Swivel head tip

A

Auftrennrichtung

F, F '

spring force

Claims (16)

1. Switching unit (1) for switching high direct current voltages, having two connections (11, 12) projecting from a housing (10), which are electrically conductively coupled via a conductor path (22), and having a mechanical contact system (7) arranged between the first and second connection (11, 12), having two contacts (15, 16) which are moveable relative to one another and can be transferred from a closed position to an open position, and having an isolating device (27, 27') which can be released by means of a thermal fuse (8) for extinguishing a light arc (26) which is produced when the contacts (15, 16) are opened,
   characterised in that,
   the thermal fuse (8) comprises a melting location (19) arranged in the conductor path (22), which is firstly connected to the contact system (7) and secondly to the first connection (12) via a mobile conductor section (20), wherein the isolating device (27, 27') is released and the connection between the conductor section (20) and the contact system (7) is broken at the melting location (19), when the melting temperature or melting location (19) has been reached or exceeded due to the light arc (26).
2. Switching unit (1) according to claim 1,
   characterised in that,
   the isolating device (27, 27') comprises a pre-stressed spring element (28, 35), the spring force (F, F') of which acts indirectly or directly on the conductor section (20) in a breaking direction (A).
3. Switching unit (1) according to claim 1 or 2,
   characterised in that,
   the spring element (28, 35) deflects the conductor section (20) around a pivot point (34) at a distance from the melting location (19) when the isolating device (27, 27') is released.
4. Switching unit (1) according to claim 3,
   characterised in that,
   the isolating device (27, 27') deflects the conductor section (20) at a pivot angle of greater than or equal to 90°.
5. Switching unit (1) according to one of claims 1 to 4,
   characterised in that,
   the housing (10) has an insulating chamber (30, 30') adjoining the melting location (19), in which the conductor section (20) is situated after a release of the isolating device (27, 27') has been carried out.
6. Switching unit (1) according to one of claims 1 to 5,
   characterised in that,
   the isolating device (27, 27') has an isolating element (29, 36) held moveably in the housing (10), which is directed against the conductor section (20).
7. Switching unit (1) according to claim 6,
   characterised in that,
   the isolating element (29, 36), after having been released, covers the conductor section (20) for provision of at least partial insulation from the melting location (19).
8. Switching unit (1) according to claim 6 or 7,
   characterised in that,
   the isolating element (29) is directed in the housing (10) in a slidingly-moveable fashion and, when the isolating device (27) is released, enters the insulating chamber (30) together with the conductor section (20).
9. Switching unit (1) according to claim 6 or 7,
   characterised in that,
   the isolating element (36) is held for rotatable movement in the housing (10) and, when the isolating device (27') is released, pivots the conductor section (20) around the pivot point (34) at a distance from the melting location (19).
10. Switching unit (1) according to one of claims 1 to 9,
    Characterised in that,
    the contact system (7) has a moving contact (17a) and a fixed contact (17b) or two mobile contacts (17a, 17b), wherein the melting location (19) is coupled to the fixed contact (17b) or to one of the moving contacts (17b) via an electrically conductive contact carrier (16) for heat conduction.
11. Switching unit (1) according to claim 10,
    Characterised in that,
    the moving contact (15) is coupled to a rocking lever (13) for operating the contact system (7) via a release mechanism (24, 25).
12. Switching unit (1) according to one of claims 1 to 11,
    Characterised in that,
    the movable conductor section (20) is a flexible connecting element, particularly in the form of a stranded conductor (20), the fixed end of which is soldered non-detachably to the first connection (12), and the loose end of which is soldered at the melting location (19), preferably to the contact carrier (16).
13. Switching unit (1) according to one of claims 1 to 12,
    Characterised in that,
    the housing (10) contains the conductor path (22), the mechanical contact system (7), the isolating device (27, 27') and the thermal fuse (8).
14. Switching unit (1) according to one of claims 1 to 13,
    Characterised in that,
    the housing (10) and the isolating element (29, 36) are made from a thermally stable plastic material, in particular from a thermoset material.
15. Switching unit (1) according to one of claims 1 to 14,
    Characterised in that,
    the isolating element (29, 36) and/or the insulating chamber (30, 30') are made from a plastic material which degases in case of fire, particularly from polyamide.
16. Isolating device (27, 27') for interrupting direct current between a direct current source and an electrical device, particularly between a photovoltaic generator (2) and an inverter (3), having a live switching unit (1) according to one of claims 1 to 15.

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