EP3053179B1 - Device and method for switching a direct current - Google Patents

Description

The invention relates to a device for switching a direct current. The device comprises an operating current branch, in which a mechanical switch is arranged, a circuit breaker connected to the operating current branch for interrupting the flow of current in the operating current branch, a capacitor branch arranged in a parallel circuit to the operating current branch, in which a capacitor is arranged, and a damping device, which is a resistance element includes.

Switching devices of this type are usually connected to an electrical DC voltage line or a DC voltage network and serve to interrupt the direct current carrying line in case of error. In a normal operation of the device, the mechanical switch and the circuit breaker are closed, so that the operating current flows through the operating current branch. In the event of a short circuit, the short-circuit current is commutated to the capacitor branch, whereby the capacitor is charged. In this case, a reverse voltage is built, whereby the device is de-energized.

Thus, the device mentioned above, for example, in the WO 2013/093066 A1 disclosed. The damping device according to the WO 2013/093066 A1 is arranged in parallel to the operating current branch and intended to enable reclosing of the device after a shutdown in case of failure within a short time.

In the known device is in a series circuit to the damping device, a further switching element. After a fault, the switching element can be closed with the circuit breaker open and the mechanical switch open, so that the capacitor can discharge via the damping device. This way is a fast one Restart the device allows. However, the same voltage dimensioning is necessary in the known device for the additional switching element, as for the circuit breaker, which should switch the current in the operating current branch. This leads to increased costs of the additional switching element.

The document WO2013 / 092873 discloses an apparatus according to the preamble of claim 1. The object of the present invention is therefore to propose a device of the type mentioned, which is inexpensive.

The object is achieved in that the damping device is arranged in the capacitor branch in a series circuit to the capacitor or in the operating current branch in a series circuit to the mechanical switch, wherein the damping device can be bridged by means arranged in a parallel circuit to the damping device bridging switch.

The bypass switch is closed in normal operation. If an error occurs, the capacitor in the capacitor branch can be charged until the current drops to zero due to the counter-voltage built up. With the circuit breaker open and the mechanical switch open, the bypass switch can be opened so that the capacitor can discharge via the damping device as soon as the mechanical switch is closed again.

The device according to the invention has the advantage that the dimensioning of the dielectric strength of the bypass switch can be reduced. Because after charging the capacitor and opening the circuit breaker, the entire capacitor voltage drops only transiently at the bypass switch alone. In this way, the overall cost of the device can be reduced, since the bypass switch does not have to be designed for a continuous voltage higher than the maximum capacitor voltage, but only for an impulse load during the discharging process.

In order to ensure the function of restarting the device after a short interruption, the resistance element of the damping device must be configured according to the energy optionally stored in the capacitor. Since an inductance can be assigned to each resistance element in addition to a resistance value, these two values must fulfill predetermined requirements for the desired time interval between the disconnection and the reclosing. Preferably, the resistance element has an electrical resistance and an inductance whose values allow a discharge of the fully charged capacitor via the damping device within a period of 50 ms to 500 ms, particularly preferably 100 ms to 250 ms.

For example, it can prove to be advantageous if the damping device comprises a separate coil element. The coil element forms a parallel circuit with the resistance element. The damping device formed in this way limits the peak value of the discharge current and absorbs the energy stored in the capacitor particularly effectively.

According to one embodiment of the invention, the device further comprises a varistor, for example a metal oxide varistor, which is connected in a parallel circuit to the capacitor and to the operating current branch. By means of the varistor, a limiting voltage can be defined, which can be built up maximum during charging of the capacitor. The varistor must be designed such that the limiting voltage is greater than a mains voltage of the DC voltage network to which the device is connected.

According to a further embodiment of the invention, the device further comprises a power semiconductor switch, which in a series circuit to the mechanical switch in the operating current branch is arranged. In the event of a short circuit, the current in the operating current branch initially rises approximately linearly. The power semiconductor switch is adapted to switch off in such a case with the smallest possible time delay, preferably in the microsecond range, whereby the further increasing current is commutated into the capacitor branch. At the same time, the opening of the mechanical switch is set in motion. The mechanical switch is then opened, so that the power semiconductor switch is not damaged by the high voltage applied (up to several hundred kilovolts). Depending on the design of the power semiconductor switch, the device may be designed as a unidirectional or bidirectional switch. The use of the power electronic switch also results in advantageous that the mechanical switch can be opened without current (whereby arcing can be avoided), and that the mechanical switch does not have to provide the necessary commutation voltage.

The capacitor arranged in the capacitor branch preferably has a capacitance value which lies between 25 μF and 200 μF.

According to one embodiment of the invention, the bypass switch is a mechanical circuit breaker. The mechanical disconnector uses, for example, an electromagnetic force to open and close its contacts. However, it is also conceivable that the bypass switch is a circuit breaker, for example, a common AC voltage switch. The bypass switch can always be switched in a de-energized state of the device. The requirements for the switching time of the bypass switch are therefore in the usual range of AC technology, preferably in the range of less than 100 ms.

Beyond the function described above, it is possible if the bypass switch is arranged in the operating current branch is to pre-charge by means of the device, for example, a cable, for example, a cable on the device, via the damping device. For this purpose, the bypass switch is opened before connecting the line by means of the circuit breaker. Any charge current thus flows through the attenuator, thereby reducing a peak and load on all components in the network. Once the current is reduced to a predetermined value, the bypass switch can be closed and normal operation can be started.

If the bypass switch is arranged in the operating current branch, then a further advantage of the device can be seen in the fact that, in the event of a fault, a residual current is to be commutated from the operating current branch to the capacitor branch, if necessary immediately the mechanical switch and the bypass switch can be opened immediately. As a result, an arc voltage of the two switches from the beginning as a commutation voltage available. Both switches are suitably very fast switches, which have a Lichtbogentragfähigkeit.

Furthermore, the invention relates to a method for switching the direct current by means of the device according to the species.

Starting from the prior art, the object of the invention is to propose an alternative method for switching the direct current by means of the device according to the species.

The object is achieved by the method in which the bypass switch is opened in the event of a fault after opening the circuit breaker and the capacitor is discharged via the operating current branch and the damping device.

According to an advantageous embodiment of the method, the bypass switch is closed only after discharging the capacitor and after closing the circuit breaker. If the bypass switch is arranged in the operating current branch, the current flows after the device has been switched on by closing the circuit breaker first for a limited time via the damping device. As a result, the current peak value and thus the load of a downstream component of the device can be reduced. For the normal operation, the bypass switch is closed again after a predetermined time.

Figur 1

zeigt ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung in einer schematischen Darstellung;

Figur 2

zeigt ein zweites Ausführungsbeispiel der erfindungsgemäßen Vorrichtung in einer schematischen Darstellung.

In the following, embodiments of the invention will be described with reference to FIG Figures 1 and 2 explained in more detail.

FIG. 1

shows a first embodiment of a device according to the invention in a schematic representation;

FIG. 2

shows a second embodiment of the device according to the invention in a schematic representation.

In detail shows FIG. 1 a first embodiment of the device 1 according to the invention for switching a DC current. The device 1 has two terminals 141, 142, by means of which the device 1 is connected to a DC voltage network. The current direction is indicated by the arrow 13. The device 1 comprises an operating current branch 2 and a capacitor branch 5, wherein the capacitor branch 5 is connected in parallel to the operating current branch 2. Furthermore, the device 1 has a varistor branch 15, wherein the varistor branch 15 is arranged in a parallel connection to the capacitor branch 5 and to the operating current branch 2. In the operating current branch 2, a mechanical switch 3 and a power semiconductor switch 12 are arranged, wherein the mechanical switch 3 and the power semiconductor switch 12 are connected in a series circuit. In the capacitor branch 5, a capacitor 6 is arranged. In the varistor branch 15, a metal oxide varistor 11 is arranged. The device 1 further comprises a damping device 7, which is arranged in a series circuit to the mechanical switch 3. In a parallel circuit to the damping device 7, a bypass switch 9 is arranged, by means of which the damping device can be bridged. The damping device 7 comprises a coil element 10 and a resistance element 8, wherein the coil element 10 and the resistance element 8 are arranged in a parallel circuit to each other.

In the present embodiment, the mechanical switch 3 and the bypass switch 9 are designed as mechanical disconnectors. The power semiconductor switch 12 is designed such that the device 1 can be used as a bidirectional switch.

The device 1 further comprises a circuit breaker 4, which is adapted to interrupt the flow of current in the operating current branch 2.

In a normal operation of the device 1, a load current flows through the circuit breaker 4, the mechanical switch 3, the half-circuit breaker 12 and the bypass switch 9 in the operating current branch 2. In an error occurs in the operating current branch 2 to a corresponding increase in current. In such an error case, an in FIG. 1 not shown control unit, the mechanical switch 3 and the power semiconductor switch 12 to turn off. The power semiconductor switch 12 is therefore locked and the mechanical switch 3 is opened. The current from the operating current branch is commutated to the capacitor branch 5. In addition, the circuit breaker 4 is also opened, initially the current continues to flow through the capacitor branch. The capacitor 6 is charged until a voltage across the capacitor 6 drops, which is greater than the mains voltage. At this time, the maximum voltage to which the capacitor 6 is charged is defined by the dissipating varistor 11. The current flowing through the device 1 is thereby forced to zero, thus extinguishing a possible arc in the circuit breaker 4. After such a shutdown of the device 1, the capacitor 6 is charged to about twice the nominal voltage. If now the device 1 is switched on again within a short time, the energy stored in the capacitor must first be released.

As soon as the current in the mechanical switch 3 and thus in the entire operating current branch is zero, the bypass switch 9 can be opened. If the shutdown of the device 1 is completed by the extinction of the arc in the circuit breaker 4, the switches 3, 12 can be closed again. About the mechanical switch 3, which is now closed, the power semiconductor switch 12, the damping device 7, the capacitor 6 now closes a circuit through which the capacitor 6 can be discharged. The coil element 10 and the resistance element 8 of the damping device 7 thereby ensure a limitation of the peak value of the discharge current and for absorption of the stored energy of the capacitor 6. As soon as the capacitor 6 is discharged, the bypass switch 9 can be closed again. The circuit is thus ready for the renewed connection of the device 1. The connection of the device 1 via the closing of the circuit breaker. 4

In FIG. 2 a second embodiment of the device 1 according to the invention is shown schematically. Similar elements in the Figures 1 and 2 are each provided with the same reference numerals. To avoid repetition is therefore in the following description of the FIG. 2 only on those elements, which the embodiment of the FIG. 2 from the embodiment of FIG. 1 differ.

In the in FIG. 2 illustrated embodiment of the device 1, the damping device 7 in a series circuit arranged to the capacitor 6 in the capacitor branch 5. The bypass switch 9 is connected in a parallel circuit to the damping device 7, wherein the damping device 7 can be bridged by means of the lock-up switch 9.

The operation of the device 1 according to the FIG. 2 corresponds substantially to the operation of the device 1 of FIG. 1 ,

In normal operation, a load current flows through the circuit breaker 4, the mechanical switch 3 and the half-circuit breaker 12 in the operating current branch 2. In an error occurs in the operating current branch 2 to a corresponding increase in current. In such an error case, an in FIG. 1 not shown control unit, the mechanical switch 3 and the power semiconductor switch 12 to turn off. The power semiconductor switch 12 is therefore locked and the mechanical switch 3 is opened. In addition, the circuit breaker 4 is also opened. In this way, the current from the operating current branch is commutated to the capacitor branch. In this case, the capacitor 6 is charged until a voltage across the capacitor drops, which is greater than the mains voltage. At this time, the maximum voltage to which the capacitor 6 is charged is defined by the dissipating varistor 11. The current flowing through the device 1 is thereby forced to zero, thus extinguishing a possible arc in the circuit breaker 4. After such a shutdown of the device 1, the capacitor 6 is charged to about twice the nominal voltage. If now the device 1 is switched on again within a short time, the energy stored in the capacitor must first be released.

Once the current in the mechanical switch 3 is zero, and the shutdown of the device 1 is completed by the extinction of the arc in the circuit breaker 4, the bypass switch 9 can be opened. Furthermore, the switches 3, 12 can be closed again. About the mechanical Switch 3, the power semiconductor switch 12, the damping device 7 and the capacitor 6 now closes a circuit through which the capacitor 6 can be discharged. The coil element 10 and the resistance element 8 of the damping device 7 thereby ensure a limitation of the peak value of the discharge current and for absorption of the stored energy of the capacitor 6. As soon as the capacitor 6 is discharged, the bypass switch 9 can be closed again. The circuit is thus ready for the renewed connection of the device 1. The connection of the device 1 via the closing of the circuit breaker. 4

LIST OF REFERENCE NUMBERS

1

Device for switching a direct current

2

Operating current branch

3

mechanical switch

4

breaker

5

capacitor branch

6

capacitor

7

attenuator

8th

resistive element

9

bypass switch

10

coil element

11

varistor

12

Power semiconductor switch

13

arrow

141

clamp

142

clamp

15

Varistorzweig

Claims (10)

1. Device (1) for switching a direct current, comprising

   - an operating current branch (2) in which a mechanical switch (3) is arranged,

   - a protective switch (4) connected to the operating current branch (2) for interrupting the current flow in the operating current branch (2),

   - a capacitor branch (5) arranged in parallel with the operating current branch (2), in which a capacitor (6) is arranged, and

   - an attenuator (7) which includes a resistance element (8), wherein the attenuator (7) in the capacitor branch (5) is arranged in series with the capacitor (6), or in the operating current branch (2) in series with the mechanical switch (3), characterized in that the attenuator (7) is bridgeable by means of a bridging switch (9) arranged in parallel with the attenuator (7).
2. Device (1) according to the preceding claim,
   characterized in that
   the resistance element (8) has an electric resistance and an inductance whose values are measured in such a way that the discharge time of a discharge of the capacitor (6) via the attenuator (7) is between 50 ms and 500 ms, preferably between 100 ms and 250 ms.
3. Device (1) according to either of the preceding claims,
   characterized in that
   the attenuator (7) includes a parallel circuit made up of the resistance element (8) and an inductor element (10).
4. Device (1) according to one of the preceding claims,
   characterized in that
   a varistor (11) is provided which is arranged in parallel with the operating current branch (2) and the capacitor branch (5).
5. Device (1) according to one of the preceding claims,
   characterized in that
   the device (1) furthermore includes a power semiconductor switch (12) which is arranged in series with the mechanical switch in the operating current branch (2).
6. Device (1) according to one of the preceding claims,
   characterized in that
   the capacitor (6) has a capacitance value between 25 µF and 200 µF.
7. Device (1) according to one of the preceding claims,
   characterized in that
   the bridging switch (9) is a mechanical circuit breaker.
8. Device (1) according to one of the preceding claims,
   characterized in that
   the bridging switch (9) is an electronic power switch.
9. Method for switching a direct current by means of the device (1) according to one of the preceding claims, in which, in the event of a fault, after opening the protective switch (4), the bridging switch (9) is opened and the capacitor (6) is discharged via the operating current branch (2) and the attenuator (7).
10. Method according to Claim 9, in which the bridging switch (9) is closed after discharging the capacitor (6) and after closing the protective switch (4).

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