DE102012005357A1 - Direct-current switch device for use in electric line of direct-current network to switch-off load currents if necessary, has PTC resistor enabling current flow in cold operating mode and interrupting current flow in heated operating state - Google Patents

Abstract

The device (10) has a switching current path (12) extending between two connection points (15) of an electric line (11). A switching contact (20) is provided with two contact elements in the switching current path. A PTC resistor (24) is arranged in a deletion current path (14) and enables a current flow through the deletion current path in a cold operating mode, and interrupts the current flow through the deletion current path in a heated operating state. The PTC resistor generates a sufficient offset voltage for extinguishing an arc between the contact elements. An independent claim is also included for a method for shutting down of a direct-current (DC).

Description

The present invention relates to a DC switching device having a switching current path which extends between two connection points of an electrical line and in which a first switching contact is provided with two contact elements which provide an electrically conductive connection between the connection points in mutual contact and which for switching off a through the electrical line guided direct current can be moved apart to form an arc, and with a running parallel to the switching current path between the connection points deletion current path.

Such switching devices are basically known and serve to switch on and off the power safely in DC networks. By DC is meant a zero-crossing current. Due to the lack of zero crossings, when switching off such currents, the current flow need not only be interrupted, but also reduced to zero within a certain period of time, with overvoltages in the network to be avoided. Furthermore, the stored energy in the network must be dissipated. For this purpose, a reverse voltage is generated in the erase current path, which extinguishes the arc and ultimately brings the current to a standstill. To achieve this, a power electronics unit may be provided in the cancellation current path. Switching devices of this type are also referred to as "DC hybrid switches".

It may be difficult in devices of the aforementioned type to move the contact elements apart sufficiently quickly. In addition, there is a risk of failure of the power electronics unit.

In this respect, the object of the invention is to provide a means for reliable shutdown of currents in DC networks with simple means.

To solve this problem, a DC switching device with the features of claim 1 is provided.

According to the invention, at least one PTC thermistor is arranged in the erase current path, which is designed to allow a current flow through the erase current path in a first cold operating state, which generates a countervoltage sufficient to extinguish the arc between the contact elements, and in a second, heated operating state to interrupt the erase current path.

In the case of contacting contact elements, the switching current path has a comparatively low electrical resistance, so that only a very small current flows through the parallel-connected PTC thermistor and thus the PTC thermistor assumes the first, cold operating state. As soon as the switching contact is opened, the current in the erasing current path increases sharply and generates a countervoltage which extinguishes the arc within a short time. However, this current in the cancellation current path comes to a standstill because the PTC thermistor heats up due to the increase in current and assumes the second operating state. If, at this time, the contact elements are sufficiently spaced apart that a dielectric strength or dielectric strength is produced, no new arc can be formed. The direct current is thus switched off safely.

According to the invention, it has been recognized that a suitably designed PTC thermistor in the quenching current path is sufficient to accomplish both arc quenching and current limiting. Thus, a complex and failure-prone power electronics unit can be dispensed with.

The PTC thermistor preferably has a dependence of the electrical resistance on the temperature, which is given by a non-linear characteristic. The characteristic curve may, for example, run in an S-shape, that is to say have a passband corresponding to the first operating state, a stopper region corresponding to the second operating state, and a transitional region therebetween, the transition region having a greater slope than the passband and the stopband. When the switch contact is opened, the PTC thermistor in the erase current path then switches from "pass" to "lock" within a relatively short period of time. Preferably, the pass band is narrow compared to the stop band to ensure a fast response time.

The PTC thermistor is preferably resettable and / or reusable to allow multiple switching operations.

According to one embodiment of the invention, the PTC thermistor comprises an amorphous metal, in particular an amorphous steel. Alternatively or additionally, the PTC thermistor may comprise a conductive ceramic material. To further tailor the properties of the PTC thermistor, it may also include one or more coatings based on a MAX phase material.

According to a further embodiment, the PTC thermistor has superconducting properties. This allows a particularly effective arc extinguishing.

An embodiment of the invention provides that the switching current path comprises a main current path and a secondary current path extending parallel thereto, wherein the first switching contact is provided in the secondary current path and a second switching contact with two associated contact elements is arranged in the main current path, wherein the contact elements of the second switching contact for interrupting a current flow through the main current path while avoiding an arc are moved apart. The main current path is used to continuously direct the load current when the network is in operation and is specially designed for this purpose. For example, the material of the contact elements and their shape and size are chosen such that the lowest possible contact resistance is achieved. In particular, the second switching contact does not have to have any special features for arc generation. In particular, with closed switch contacts, the electrical resistance of the main path may be lower than the electrical resistance of the secondary path.

To suppress an arc, the contact elements of the second switching contact can be arranged in a vacuum chamber. In principle, the contact elements of the second switching contact can also be arranged in a chamber filled with a dielectric gas or a dielectric liquid.

Furthermore, parallel to the switching current path and to the cancellation current path, a fuse current path can run between the connection points of the electrical line in which at least one further PTC thermistor is arranged. Such an additional PTC thermistor provides protection of the switching device against failure of one of the other components.

The contact elements can be shaped in such a way that, when they move apart, an arc which is subdivided into a plurality of partial arcs is formed. As a result, the arc voltage can be increased. For generating a plurality of partial arcs z. B. corresponding ribs, chambers or teeth may be provided on the contact elements. The switching device may further comprise an actuator for controlled movement of the contact elements and an associated control device.

Preferably, no further current-limiting element is provided in the deletion current path except the PTC thermistor. In other words, only the PTC thermistor is used to first generate a sufficient reverse voltage and to limit the current in the erase current path after erasing the arc and reaching the dielectric strength at the first switching contact.

The invention also relates to a method for switching off a direct current conducted through an electrical line, in particular by means of a switching device according to one of the preceding claims, comprising the steps:
Moving apart two contact elements of a first switching contact provided in a switching current path extending between two connection points of the electrical line, forming an arc,
Commutating the current flow to an erase current path extending parallel to the switching current path between the connection points,
Allowing sufficient current flow in the cancellation current path to extinguish the arc, and
Interrupting the flow of current in the erase current path as soon as the arc is extinguished and the contact elements are moved apart until the dielectric strength is reached.

According to the invention, the current flow is allowed to pass and the subsequent interruption of the current flow in the erase current path is effected by a PTC thermistor provided in the erase current path.

As mentioned above, the switching current path may comprise a main current path and a secondary current path extending parallel thereto, the first switching contact being provided in the secondary current path and a second switching contact having two associated contact elements being arranged in the main current path. According to one embodiment of the invention, prior to moving the contact elements of the first switch contact apart, the contact elements of the second switch contact are moved apart while avoiding an arc until the dielectric strength is reached.

Further developments of the invention are set forth in the dependent claims, the description and the accompanying drawings.

The invention will now be described by way of example with reference to the drawings.

1 is a circuit diagram of a DC switching device according to the invention.

2 is a sectional view of a specific embodiment of the DC switching device according to 1 ,

3 FIG. 12 illustrates a time course of the disengagement of respective contact elements for a first and a second switching contact of the DC switching device according to FIG 1 ,

According to 1 is a switching device 10 in an electric line 11 a DC power supply provided to switch off load currents and / or short-circuit currents if necessary. The switching device 10 includes a switching current path 12 and an erase current path 14 which are parallel to each other between two connection points 15 the electric wire 11 run. The switching current path 12 is in a main current path 16 and a parallel to this running Nebenstrompfad 18 divided. A first switching contact 20 is in the sidestream path 18 provided while a second switching contact 22 in the main stream path 16 is provided. In the deletion current path 14 is a PTC thermistor 24 intended. Furthermore, in the electrical line 11 a circuit breaker 26 intended.

How out 2 shows, the first switching contact 20 two contact elements 28a . 28b on, which in mutual contact an electrically conductive connection between the connection points 15 ( 1 ) and which for opening the first switch contact 20 be moved apart, as illustrated by arrows. The contact elements 28a . 28b of the first switch contact 20 are formed in the form of double-walled, interlocking sleeves. They surround a vacuum chamber 38 in which two stamp-like contact elements 32a . 32b of the second switch contact 22 are arranged. Also the contact elements 32a . 32b of the second switch contact 22 when in contact, make an electrically conductive connection between the connection points 15 ( 1 ) ready to open the second switch contact 22 apart, as indicated by arrows.

With additional reference to 3 will the functioning of the switching device 10 explained. In the upper diagram of 3 is the distance S1 of the contact elements 28a . 28b of the first switch contact 20 shown as a function of time, while in the lower diagram of 3 the distance S2 of the contact elements 32a . 32b of the second switch contact 22 is shown as a function of time.

During normal operation of the underlying DC network, both switching contacts 20 . 22 closed and the load current flows for the most part through the main current path 16 because it has the lowest electrical resistance. Due to the negligible current flow through the PTC thermistor 24 this is in a first, cold operating condition.

Once a shutdown of the electricity in the electrical line 11 is required, for. B. in case of failure, a control device, not shown, ensures that initially the contact elements 32a . 32b of the second switch contact 22 be moved apart. The moving apart begins according to the lower diagram in FIG 3 at time t1 and continues until the dielectric strength is reached at the distance S1. The formation of an arc is thereby through the vacuum chamber 38 avoided. Once at time t2, the dielectric strength of the second switch contact 22 is made, the control device ensures that the contact elements 28a . 28b of the first switch contact 20 be moved apart to form an arc. Due to the shape of the contact elements 28a . 28b of the first switch contact 20 the arc is divided into a plurality of parallel partial arcs, so that a relatively high arc voltage at the first switching contact 20 is generated, which is opposite to the working voltage. The associated voltage drop provides for commutation of the current flow to the cancellation current path 14 ,

The one in the deletion current path 14 provided PTC thermistor 24 is configured, in the first operating state, a current flow through the erasing current path 14 to enable which one to extinguish the arc between the contact elements 28a . 28b of the first switch contact 20 generates sufficient reverse voltage. Thus the arc is extinguished. At the same time, the PTC thermistor heats up 24 due to the current flow and transitions to the second operating state in which it is able to control the current flow through the erase current path 14 to interrupt. The electrical resistance of the PTC thermistor 24 rises rapidly to a high value and ensures that the current flow through the erase current path 14 comes to a halt. The reverse voltage drops again, but at this time t3 are the contact elements 28a . 28b of the first switch contact 20 already moved apart up to the distance S2, in which the dielectric strength is reached and no new arc can form. The electricity in the electric line 11 is thus safely switched off. Finally, the circuit breaker 26 open.

A switching device of the type described above is able to reliably and safely switch not only load currents, but also short-circuit currents in the range of 100 kA to 120 kA. A power electronics unit is not necessary.

LIST OF REFERENCE NUMBERS

10

switching device

11

electrical line

12

Switching current path

14

Extinction current path

15

junction

16

Main current path

18

In addition to current path

20

first switching contact

22

second switching contact

24

PTC

26

disconnectors

28a, 28b

Contact elements of the first switch contact

32a, 32b

Contact elements of the second switching contact

38

Vacuum chamber

S1, S2

Distance between the contact elements

t1, t2, t3

time

Claims (9)

DC switching device ( 10 ), with a switching current path ( 12 ) between two connection points ( 15 ) an electrical line ( 11 ) and in which a first switching contact ( 20 ) with two contact elements ( 28a . 28b ) is provided, which in mutual contact an electrically conductive connection between the connection points ( 15 ) and which for switching off by the electrical line ( 11 ) are guided apart under the formation of an arc, and one parallel to the switching current path ( 12 ) between the connection points ( 15 ), the erase current path ( 14 ), characterized in that in the deletion current path ( 14 ) at least one PTC thermistor ( 24 ), which is designed, in a first cold operating state, a current flow through the erasing current path (FIG. 14 ), which one for extinguishing the arc between the contact elements ( 28a . 28b ) generates sufficient countervoltage, and in a second heated operating state, the current flow through the erasing current path ( 14 ) to interrupt. DC switching device according to claim 1, characterized in that the PTC thermistor ( 24 ) comprises an amorphous metal, in particular an amorphous steel. DC switching device according to claim 1 or 2, characterized in that the PTC thermistor ( 24 ) has superconducting properties. DC switching device according to at least one of the preceding claims, characterized in that the switching current path ( 12 ) a main current path ( 16 ) and a secondary flow path running parallel thereto ( 18 ), wherein the first switching contact ( 20 ) in the secondary flow path ( 18 ) is provided and a second switching contact ( 22 ) with two associated contact elements ( 32a . 32b ) in the main current path ( 16 ) is arranged, wherein the contact elements ( 32a . 32b ) of the second switch contact ( 22 ) for interrupting a current flow through the main current path ( 16 ) are moved apart while avoiding an arc. DC switching device according to claim 4, characterized in that the contact elements ( 32a . 32b ) of the second switch contact ( 22 ) in a vacuum chamber ( 38 ) are arranged. DC switching device according to at least one of the preceding claims, characterized in that parallel to the switching current path ( 12 ) and to the cancellation current path ( 14 ) a fuse current path between the connection points ( 15 ) of the electrical line ( 11 ), in which at least one further PTC thermistor is arranged. DC switching device according to at least one of the preceding claims, characterized in that except the PTC thermistor ( 24 ) no further current-limiting element in the cancellation current path ( 14 ) is provided. Method for switching off an electrical line ( 11 ) guided direct current, in particular by means of a switching device ( 10 ) according to one of the preceding claims, comprising the steps of: moving apart two contact elements ( 28a . 28b ) one in one between two connection points ( 15 ) of the electrical line ( 11 ) switching current path ( 12 ) provided first switching contact ( 20 ) forming an arc, commutating the current flow to a parallel to the switching current path ( 12 ) between the connection points ( 15 ), the erase current path ( 14 Permitting sufficient current flow in the cancellation current path to extinguish the arc (US Pat. 14 ), and interrupting the flow of current in the cancellation current path ( 14 ), as soon as the arc is extinguished and the contact elements ( 28a . 28b ) of the first switch contact ( 20 ) are moved apart until the dielectric strength is reached, characterized in that the enabling of the current flow and the subsequent interruption of the current flow in the cancellation current path ( 14 ) by one in the cancellation current path ( 14 ) PTC thermistors ( 24 ) he follows. Method according to Claim 8, characterized in that the switching current path ( 12 ) a main current path ( 16 ) and a secondary flow path running parallel thereto ( 18 ), wherein the first switching contact ( 20 ) in the secondary flow path ( 18 ) is provided and a second switching contact ( 22 ) with two associated contact elements ( 32a . 32b ) in the main current path ( 16 ), wherein before moving apart of the contact elements ( 28a . 28b ) of the first switch contact ( 20 ) the Kontektelemente ( 32a . 32b ) of the second switch contact ( 22 ) while avoiding an arc until the dielectric strength is reached.

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