Electrical DC switching system

Abstract

An electrical DC switching system for extinguishing an electric arc, wherein the electrical DC switching system includes: a main contact arrangement having a first contact and a second contact, the main contact arrangement being operable between a closed position and an open position, a plurality of serial contacts connected in series with each other and connected in parallel with the main contact arrangement, each serial contact being operable between a closed position and an open position, wherein in a current breaking operation the main contact arrangement is configured to be set in the open position before the plurality of serial contacts are configured to be set in their open positions, and a current injection circuit including a resonance circuit configured to be connected across the serial contacts, and a first switch configured to be switched between an open state and a closed state and configured to be connected to the resonance circuit and to the serial contacts, wherein the first switch is configured to be set in the closed state when the serial contacts are in their open positions to enable an injection current to flow through the resonance circuit and into the serial contacts in a first flow direction which is opposite to a flow direction of an arc current flowing through the serial contacts.

Claims

1. An electrical DC switching system for extinguishing an electric arc, wherein the electrical DC switching system comprises: a main contact arrangement having a first contact and a second contact, the main contact arrangement being operable between a closed position and an open position, a plurality of serial contacts connected in series with each other and connected in parallel with the main contact arrangement, each serial contact being operable between a closed position and an open position, wherein in a current breaking operation the main contact arrangement is configured to be set in the open position before the plurality of serial contacts are configured to be set in their open positions, and a current injection circuit including a resonance circuit configured to be connected across the serial contacts, and a first switch configured to be switched between an open state and a closed state and configured to be connected to the resonance circuit and to the serial contacts, wherein the first switch is configured to be set in the closed state when the serial contacts are in their open positions to enable an injection current to flow through the resonance circuit and into the serial contacts in a first flow direction which is opposite to a flow direction of an arc current flowing through the serial contacts, wherein each serial contact, consists of a non-magnetic material.

2. The electrical DC switching system as claimed in claim 1, wherein the main contact arrangement consists of a silver or a silver alloy.

3. The electrical DC switching system as claimed in claim 1, wherein the non-magnetic material is brass or zinc.

4. The electrical DC switching system as claimed in claim 1, wherein the resonance circuit includes a capacitor and an inductor.

5. The electrical DC switching system as claimed in claim 4, wherein the current injection circuit includes a DC power source configured to charge the capacitor when the first switch is in the open position.

6. The electrical DC switching system as claimed in claim 1, comprising: a control system, wherein the current injection circuit includes a second switch connected to the resonance circuit and to the serial contacts, wherein the second switches is configured to be switched between an open state and a closed state, wherein in the closed state the second switch is configured to enable current to flow through the resonance circuit in a second flow direction opposite to the first flow direction, and wherein the control system is configured to alternatingly first set the first switch, and then the second switch, first in the closed state and then in the open state upon a current breaking operation, until a current pulse, emanating from energy supplied by the arc current, flowing through the resonance circuit and into the serial contacts reaches an amplitude which is equal to or greater than a magnitude of the arc current.

7. The electrical DC switching system as claimed in claim 6, wherein in each iteration of alternatingly first setting the first switch, and then the second switch, first in the closed state and then in the open state, the control system is configured to: set the first switch in the closed position, enabling a first current pulse to flow through the resonance circuit in the first flow direction, set first the first switch in the open state and then the second switch in the closed state when the first current pulse has become zero to enable a second current pulse to flow through the resonance circuit in the second flow direction, and to set the second switch in the open state when the second current pulse first has become zero.

8. The electrical DC switching systems as claimed in claim 6, wherein the second switch is connected across the resonance circuit.

9. The electrical DC switching system as claimed in claim 1, comprising a varistor connected in parallel with the main contact arrangement.

10. The electrical DC switching system as claimed in claim 2, wherein the non-magnetic material is brass or zinc.

11. The electrical DC switching system as claimed in claim 2, wherein the resonance circuit includes a capacitor and an inductor.

12. The electrical DC switching system as claimed in claim 2, comprising: a control system, wherein the current injection circuit includes a second switch connected to the resonance circuit and to the serial contacts, wherein the second switch is configured to be switched between an open state and a closed state, wherein in the closed state the second switch is configured to enable current to flow through the resonance circuit in a second flow direction opposite to the first flow direction, and wherein the control system is configured to alternatingly first set the first switch, and then the second switch, first in the closed state and then in the open state upon a current breaking operation, until a current pulse, emanating from energy supplied by the arc current, flowing through the resonance circuit and into the serial contacts reaches an amplitude which is equal to or greater than a magnitude of the arc current.

13. The electrical DC switching system as claimed in claim 7, wherein the second switch is connected across the resonance circuit.

14. The electrical DC switching system as claimed in claim 2, comprising a varistor connected in parallel with the main contact arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows an example of an electrical DC switching system for breaking a current;

(3) FIG. 2 shows the electrical DC switching system in FIG. 1 with a first implementation of a current injection circuit;

(4) FIG. 3 shows the electrical DC switching system in FIG. 1 with a second example of a current injection circuit; and

(5) FIGS. 4a-4c schematically show a current breaking operation by means of an example of the electrical DC switching system.

DETAILED DESCRIPTION

(6) The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

(7) A number of variations of an electrical DC switching system for breaking a current will be described herein. The electrical DC switching system comprises a main contact arrangement having a movable breaker contact and a fixed contact. The breaker contact can be actuated between a closed position in which it is in mechanical contact with the fixed contact and an open position in which the breaker contact is mechanically separated from the fixed contact. The movable breaker contact defines a first contact of the contact arrangement and the fixed contact defines a second contact of the contact arrangement. The main contact arrangement may for example comprise or consist of silver or a silver alloy. The movable breaker contact and the fixed contact may hence comprise or consist of silver or a silver alloy.

(8) The electrical DC switching system comprises a plurality of serial contacts connected in series with each other and connected in parallel with the main contact arrangement. Each serial contact is configured to be operated between a closed position and an open position. Each serial contact may comprise a fixed contact and a breaker contact which is arranged movably with respect to the fixed contact. In the closed position of a serial contact the corresponding fixed contact and breaker contact are in mechanical contact. In the open position the breaker contact is mechanically separated from the fixed contact.

(9) The serial contacts consist of a non-magnetic material. Examples of non-magnetic material are brass, zinc, copper, silver, gold, magnesium or various alloys of the aforementioned materials.

(10) The serial contacts may be constructed in a plurality of different ways. It is in general advantageous to make the package formed by the serial contacts as small as possible to ensure a small footprint of the electrical DC switching system. The serial contacts may for example be arranged mechanically in parallel with each other, side by side and adjacent to each other with an electrically insulating partitioning wall arranged between each adjacent serial contact. A compact serial contact package can be provided in this manner. A plurality of other serial contact configurations is also envisaged.

(11) The main contact arrangement and the serial contacts are normally set in their closed positions. Thus, when the electrical system in which the electrical DC switching system is connected operates normally without any fault, the main contact arrangement and the serial contacts are set in their closed positions. In a current breaking operation, the main contact arrangement is first configured to be set in the open position. The current is thereby commutated to the serial contacts. The serial contacts are thereafter configured to be set in their open positions. The serial contacts are configured to be set in their respective open position simultaneously.

(12) The electrical DC switching system comprises a current injection circuit including a resonance circuit, which is an LC-circuit comprising a capacitor and an inductor, and a first switch. The inductor may either be an inductor component or the inherent inductance of the conductors to which the capacitor is connected.

(13) The resonance circuit is configured to be connected across the serial contacts. The first switch is configured to be switched between a closed state and an open state. The first switch is configured to be set in the closed state when the serial contacts are set in their open positions. When in the closed state, an injection current is able to flow through the resonance circuit and into the serial contacts in a direction opposite to a flow direction of an arc current flowing through the serial contacts. The current injection circuit is, via the resonance circuit, configured to inject an injection current with an amplitude which is equal to or greater than a magnitude of the arc current. In this manner arc extinction may be provided.

(14) A plurality of examples of an electrical DC switching system will now be explained with reference to FIGS. 1-3.

(15) FIG. 1 shows a general example of an electrical DC switching system 1 for breaking a current and to extinguish an electric arc. DC switching system 1 comprises a main contact arrangement 3 having a first contact 3a and a second contact 3b. The first contact 3a may be a movable breaker contact and the second contact 3b may be a fixed contact. The main contact arrangement 3 may be set in an open position by moving the breaker contact away from the fixed contact, and in a closed position in which the breaker contact is in mechanical contact with the fixed contact.

(16) The electrical DC switching system 1 comprises a plurality of serial contacts 4 connected in series with each other. The serial contacts 4 are connected in parallel with the main contact arrangement 3. Although four serial contacts 4 are shown in the example, it is to be noted that there may be fewer than four serial contacts or more than four serial contacts provided. The number of serial contacts typically depends on the voltage rating of the electrical DC switching system 1.

(17) In normal operation, when no arc is to be extinguished, the main contact arrangement 3 and the serial contacts 4 are in the closed position. DC current will in this case flow mainly through the main contact arrangement 3 due to for example lower contact resistance. When the main contact arrangement 3 is set in the open position the DC current will be commutated to the serial contacts 4.

(18) The electrical DC switching system 1 also includes a current injection circuit 5 including a resonance circuit 6 connected across the serial contacts 4, and a first switch S1. The resonance circuit 6 includes a capacitor and an inductor. Alternatively the inductor comprises the inductance of the circuit path of the injection current, forming an LC-circuit.

(19) FIG. 2 shows an example of an electrical DC switching system 1-1 including a control system 11 configured to control the first switch S1. The resonance circuit 6 includes a capacitor C and an inductor L, alternatively the circuit inductance. The exemplified current injection circuit 5-1 further includes a DC power source 9 configured to charge the capacitor C to obtain a voltage with reverse polarity relative to that of the power source (not shown) feeding the main contact arrangement 3. The DC power source 9 is configured to maintain the capacitor C in a charged state when the first switch S1 is in the open state.

(20) In the event of a circuit breaking or arc extinguishing operation the first contact 3a is first moved away from the second contact 3b and the main contact arrangement 3 is thus set in the open position. Current is thereby commutated from the main contact arrangement 3 to the serial contacts 4 which are still in their closed positions. When the current has been commutated to the serial contacts 4, the serial contacts 4 are set in their open positions. Next, the control system 11 is configured to set the first switch S1 in the closed state, whereby a reverse current is injected into the serial contacts 4.

(21) Another example of an electrical DC switching system is shown in FIG. 3. According to the example in FIG. 3, electrical DC switching system 1-2 comprises a control system 11 and a current injection circuit 5-2 comprising the resonance circuit 6, including the capacitor C and the inductor L, or alternatively the circuit inductance, the first switch S1 and a second switch S2. The current injection circuit 5-2 is a pumping circuit, as will be elaborated upon in more detail in the following.

(22) The resonance circuit 6 is configured to be connected across the serial contacts 4. The resonance circuit 6 is in particular configured to be connected across the serial contacts 4 by means of the first switch S1 and by means of the second switch S2. The first switch S1 is configured to be switched between an open state and a closed state. The first switch S1 is connected to a first serial contact 4, at a first end of the serial contacts 4, and to the resonance circuit 6. The first switch S1 is connected in such a way that in the closed state it enables a current pulse emanating from energy supplied by the arc current to flow in a first flow direction through the resonance circuit 6. It furthermore enables the current to flow into the serial contacts 4 in a direction opposite to the arc current flow direction which flows through the serial contacts 4 via the arc.

(23) The second switch S2 is configured to be switched between an open state and a closed state. The second switch S2 is connected to a second serial contact 4, at a second end of the serial contacts 4, and to the resonance circuit 6. In particular, the second switch S2 is connected across the resonance circuit 6.

(24) As has been previously been described, in the event of a circuit breaking or arc extinguishing operation, the main contact arrangement 3 is set in the open position so that the current commutates into the serial contacts 4 which are still in their closed positions. The serial contacts 4 are subsequently set in their open position. The control system 11 is configured to, when the serial contacts 4 have been set in their open position, alternatingly switch first the first switch S1 between its open state and closed state and then to switch the second switch S2 between its open state and closed state. An injection current pumping functionality is thereby obtained. The control system 11 is configured to be triggered to control the first switch S1 and the second switch S2 by energy supplied by the arc current flowing through the serial contacts 4 now in their open positions. The control system 11 is configured to alternatingly switch first the first switch S1 between its open state and closed state and then to switch the second switch S2 between its open state and closed state until a current pulse, emanating from energy supplied by the arc current, flowing through the resonance circuit 6 and into the serial contacts 4 via the first switch S1 has an amplitude which is equal to or preferably larger than the arc current flowing through the serial contacts 4. At the time when the current pulse has an amplitude that equals the magnitude of the arc current, an artificial zero-crossing is created at the serial contacts 4, facilitating the extinguishing of the arcs over the serial contacts.

(25) The first switch S1, the second switch S2 and the resonance circuit 6 form a pumping circuit, which is configured to inject a current pulse with higher and higher amplitude for each repetition, i.e. for each iteration of alternatingly first set the first switch, and then the second switch, first in the closed state and then in the open state. Depending on the number of switches, and their connection to the resonance circuit, a half-wave pumping circuit, as exemplified above, or a full-wave pumping circuit, as disclosed in WO 2016/131949 A1 may be obtained.

(26) The first switch S1 and the second switch S2 may for example be semiconductor switches such as thyristors or transistors. The control system 11 according to any example provided herein may for example comprise gate drive units for semiconductor switches.

(27) According to any example presented herein, the electrical DC switching system may comprise a varistor, for example a MOV, connected in parallel with the main contact arrangement.

(28) FIGS. 4a-4c show the electrical DC switching system 1 in operation. In FIG. 4a, the electrical DC switching system 1 is shown when the main contact arrangement 3 and the serial contacts 4 are all in their closed position. A DC current I.sub.DC flows through the main contact arrangement 3. There will be essentially no current flowing through the serial contacts 4 at this point.

(29) FIG. 4b shows a situation where the main contact arrangement 3 has been set in the open position in a current breaking operation. The mechanical contact between the first contact 3a and the second contact 3b has thus been broken. An arc will thus be ignited between the first contact 3a and the second contact 3b. The serial contacts 4 are still for a short while in their closed positions. The current I.sub.DC will therefore be commutated to the serial contacts 4 and the arc across the main contact arrangement 3 will be extinguished.

(30) In the next stage, shown in FIG. 4c, the serial contacts 4 have also been set in their open position and a serial connected arc voltage U is created across the serial contacts 4. This arc voltage U may trigger the current injection circuit 5 to provide an injection current I.sub.inj into the serial contacts 4. In the examples shown in FIGS. 2 and 3 the control system 11 may be configured to be triggered by the arc voltage U to provide switching of the first switch S1. When the injection current I.sub.inj is equal in magnitude to the current I.sub.DC an artificial zero-crossing is created in the serial contacts 4. In this manner, the arcs over the serial contacts 4 may be extinguished and a current breaking operation may be obtained.

(31) The electrical DC switching systems presented herein may for example be a circuit breaker, a contactor, or a current limiter, and may be utilized in DC applications, for example in low voltage (LV) applications or medium voltage (MV) applications.

(32) The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.