JP7377105B2 - CO2 switch for high voltage DC grid - Google Patents

Description

The present invention relates generally to the technical field of high voltage direct current (HVDC) or medium voltage direct current (MVDC) transmission networks.

More specifically, the invention relates to an HVDC or MVDC gas-insulated switch for interrupting direct current (DC) in the lines of a high-voltage or intermediate-voltage DC transmission network.

A particularly advantageous application of the invention is the routing of power from one path in the network to another, for example in the event of a failure in a pole of the network or during long-term maintenance operations on the pole. (aiguiller) is the technical field of high-voltage or intermediate-voltage direct current networks.

In DC networks, it is known to use switches comprising a branch path with a DC circuit interrupter having an active circuit interrupter contained in a closed container containing a gaseous fluid. The state of the art has proposed many technical solutions for making gas-insulated DC circuit breaker devices.

For example, one known circuit breaker device is described in "Journal of power-energy division conference 1994 of Institute of Electrical Engineers", No. 621, pp. 824-825. A gas insulated DC circuit interrupter is provided at a branch of the line of the DC network. In parallel with this branch containing the circuit breaker device, firstly, a branch with an energy absorber for absorbing voltage surges is connected, and secondly, a resonant circuit with a predetermined capacitance and a predetermined inductance is connected. It is connected.

DC circuit interrupters are of the gas blow type and include an active circuit interrupter enclosed in a closed container containing a gaseous fluid. The circuit breaker has fixed contacts that allow DC to flow and movable contacts within the blast cylinder, the blast cylinder having an insulating nozzle fixed to the blast cylinder. In the state of the art, an electric arc is generated between the contacts when a piston rod incorporated in a movable contact is moved relative to a blast piston fixed in a fixed contact. As the piston rod moves, arc extinguishing gas, typically SF ₆ , contained inside the container is compressed so that it is blown onto the arc.

In the case of direct current, simply spraying the DC arc with SF ₆ may not be sufficient to interrupt the arc and successfully extinguish the arc. This is because, unlike alternating current (AC), direct current does not have periodic points where it crosses zero current.

For the purpose of extinguishing the arc, a resonant circuit comprising an inductance and a capacitance is coupled in parallel to the circuit breaker in order to superimpose an oscillating current (courant oscillant) on the direct current to provide a zero crossing to the circuit breaker. This allows the blasting system to spray compressed SF ₆ gas against the arc, forcing it to extinguish.

Considering that DC networks require higher voltages, the associated switches need to have improved switching performance with current values, which can be as high as 6000 amperes (A). . Furthermore, the switching performance based on the current value needs to be achieved over a wide range of operating temperatures of the switch. Typically, such switches must maintain current value switching performance even when operating temperatures drop to -50°C.

Patent US 5,737,162 proposes to maintain a plurality of DC circuit breaker devices in a standard closed enclosure, with the circuit breaker devices connected in series. This solution has the disadvantage of a large ground footprint and high cost.

Patent EP0740320 proposes optimizing the impedance and capacitance values of the resonant circuit depending on the DC cutoff value.

Furthermore, it has been proposed to use various types of arc-extinguishing gases, as described for example in patent application US 2016/261095. Patent application US 2016/261095 proposes the use of carbon dioxide as an alternative to SF ₆ for extinguishing electrical arcs in electrical equipment for use in the generation, transport, supply and/or utilization of electrical energy. . However, this document does not teach how the conditions for extinguishing an electric arc, which vary depending on the type of gas used, can be implemented in a DC circuit interrupter that includes a resonant circuit. do not have.

Similarly, patent application US 2011/0175460 describes a switch for a DC network with a resonant circuit and an active circuit interrupting member in a container containing SF ₆ . For such SF ₆ gaseous media, this document suggests adopting a capacitance value large enough to switch DC, regardless of the value chosen for the inductance. This solution does not allow optimization of the overall size of the resonant circuit, considering the electric arc stability criterion, which effectively limits the possible range of the inductance L of the LC circuit.

It is also known in the state of the art, for example from patent application FR 2975819, to use carbon dioxide-containing media as media for providing electrical insulation and/or arc extinction in medium- or high-voltage electrical equipment. This patent application does not give any information on how it can be implemented in a resonant circuit.

The present invention is a switch for high-voltage or intermediate-voltage direct current networks utilizing a mechanical circuit interrupting device associated with a circuit for injecting an oscillating current, the switch having a wide operating temperature range. It is an object of the present invention to alleviate the above-mentioned drawbacks by proposing a switch that is simple and compact while exhibiting high switching performance depending on the DC value over a wide range.

To achieve such an objective, a switch for a high-voltage or intermediate-voltage direct current transmission network is a DC circuit comprising an active circuit-breaking member in at least one closed container containing a gaseous fluid. A branch with a disconnection device is inserted into the network line, and in parallel with this branch, firstly a branch with an energy absorber is connected, secondly a predetermined capacitance and A resonant circuit having a predetermined inductance is connected.

According to the invention, the closed vessel of the DC circuit breaker device comprises at least 70% by volume of carbon dioxide and has a filling pressure in the range of 0.65 megapascals (MPa) to 1.1 MPa when measured at 20°C. It accommodates a gaseous fluid (un fluide gazeux comportant au moins 70% en volume de dioxyde de de carbone a une compression de remplissage comprising entre 0.65 MPa et 1.1 MPa mesuree a une temperature de 20°C) and has a capacitance in microfarads (μF). For the value of C, the inductance L in microhenries (μH) is less than 2700×C ^−0.84 .

Furthermore, the switches of the present invention may also include at least one and/or more of the following additional features:
・For the value of capacitance C in μF, inductance L in μH is in the range of 400×C ^-0.84 to 2700×C ^-0.84 ;
- the gaseous fluid is composed solely of carbon dioxide with a filling pressure in the range of 0.65 MPa to 1.1 MPa when measured at 20 °C;
- The gaseous fluid is composed of a mixture of carbon dioxide and sulfur hexafluoride;
- 20% to 30% by volume of sulfur hexafluoride;
- The gaseous fluid is composed of a mixture of carbon dioxide and carbon tetrafluoride;
・20% to 30% by volume of carbon tetrafluoride;
- the gaseous fluid is constituted by a mixture of carbon dioxide and fluoronitrile;
- 4% to 10% by volume of fluoronitrile;
- The gaseous fluid is composed of a mixture of carbon dioxide and oxygen;
- 5% to 15% oxygen by volume;
- The gaseous fluid is constituted by a ternary mixture of carbon dioxide, oxygen and fluoroketone; and - 5% to 15% by volume of oxygen and 4% to 10% by volume of fluoroketone.

The invention also provides a high-voltage or intermediate-voltage direct current network comprising at least one switch according to the invention.

Various other features will become apparent from the following description, which refers to the accompanying drawings, which illustrate, by way of non-limiting example, embodiments of the invention.

FIG. 1 is a diagram of an embodiment of a high voltage or intermediate voltage DC transmission network using at least one HVDC gas insulated switch according to the invention. FIG. 2 is a functional block diagram showing an HVDC gas insulated switch according to the present invention. FIG. 3 is a graph in which the value of the inductance L in μH is plotted as a function of the value of the capacitance C in μF, the selection of values for the resonant circuit of the circuit interrupting device of the HVDC gas-insulated switch according to the invention. shows. FIG. 4 is a graph plotting the value of capacitance C in μF as a function of the value of inductance L in μH for various values of the current at which the switch is made, illustrating the limits of current performance in the LC plane. . FIG. 5 is a diagram illustrating the shape of a closed container of a DC circuit breaker for implementing the present invention. Figure 6 shows the ratio of capacitance C (μF) divided by inductance L (μH) to obtain a normalized direct current (plotted in per unit) for the use of SF ₆ medium or for the use of CO ₂ medium. This is a graph plotted accordingly.

For example, FIG. 1 shows a high-voltage or intermediate-voltage direct current transmission network 1 comprising at least one, generally a plurality of HVDC or MVDC channels according to the invention for interrupting DC in network lines. A network 1 using gas insulated switches 2i is shown. Conventionally, the DC transmission network 1 includes an AC/DC converter 3 at at least one end and a DC/AC converter 4 at the other end. The converters 3, 4 do not constitute a part specific to the invention and are well known to those skilled in the art, so they will not be described in detail.

The switch according to the invention is designated by the reference numeral 2i. Here, i changes as a, b, . . . , n. These switches 2i according to the invention are connected between the converters 3, 4 between points of the network 1 so as to conduct power from one point of the network to another. For example, the switch 2i makes it possible to maintain a reduced power flow in the event of a failure in a utility pole of the network or in the event of long-term maintenance work on a utility pole. For example, the network 1 includes switches 2a, 2b adapted to the invention and a shorting switch 10 for transferring power from the ground conductor Ct to the overhead metal conductor Ca. Note that the short-circuit switch 10 only has the function of short-circuiting an unavailable utility pole of the converter, and in this respect is different from the switch 2i according to the present invention, which has a switching function for opening the circuit. I want to be

In order to transfer this power, the current is transferred from the grounding line Ct to the switch 2b according to the invention, which is connected in series between the grounding line Ct and the overhead metal line Ca and has been turned on in advance, and the shorting switch 10. The switch 2a, which is provided in the grounding electrical circuit Ct and is initially in the ON state, is opened so as to switch to the overhead metal electrical circuit Ca via and.

As can be seen more precisely in FIG. 2, the switch 2i is provided on the line of the network 1 carrying the direct current IDC, for example between points A and A' as shown. Between points A and A', each switch 2i is a DC circuit breaker device 5 of any known type, constituted by a sealed enclosure or a plurality of sealed enclosures connected in series, A branch is provided with a DC circuit interrupter 5 on which the current Iarc and the arc voltage Uarc appear.

The term "DC circuit breaker 5" refers to a mechanical device having an active circuit interrupting member in a closed container containing a gaseous fluid and a system for blowing the arc with the gaseous fluid. Used to mean equipment. As explained in more detail below, the gaseous fluid is selected for its insulating properties, specifically chosen to have a dielectric strength greater than that of dry air at an equivalent pressure, and its current It is selected for its ability to interrupt the arc, and is further selected for its ability to supply high arc voltage.

For example, a DC circuit breaker device 5 is shown in FIG. Conventionally, the DC circuit interrupter 5 includes a pair of arcing contacts 5b and 5c, and a pair of "permanents" in a closed enclosure 5a, which conduct current when the circuit interrupter is in the closing position. Contact points 5d and 5e are provided. In the opening operation, both the arc contacts 5b and 5c and the irreversible contacts separate. When the arc contacts 5b and 5c are separated, an electric arc is generated between them and the electric arc is confined to the inside of the spray nozzle 5f. The arc continues until a zero crossing of the current occurs, at which time gas is blown through the blowing nozzle 5f, so that the plasma can be replaced by cooling gas. This blowing action at the zero crossing of the current makes it possible to extinguish the arc and, moreover, makes it possible for the gaseous medium compressed between the arc contacts 5b and 5c to withstand the transient recovery voltage applied by the network, There is no re-arc or current recovery (reamorcer et retablir le courant).

Connected in parallel with this branch AA′ are firstly a non-precharged resonant circuit 6 and secondly a branch with an energy absorber 7 . The pre-charged resonant circuit 6 has a predetermined capacitance C, a resistance R and a predetermined inductance L in series. The resonant circuit 6 interacts with the arc voltage Uarc so as to generate an oscillating current that increases exponentially. This oscillating current is superimposed on the DC current IDC to produce a zero crossing of the current, at which point a gaseous fluid is blown to extinguish the arc.

The branch with energy absorber 7 includes any known type of surge protection device, such as a surge arrester (parafoudre). The energy absorber 7 is arranged so that the maximum surge voltage across the end of the capacitance C and the end of the circuit breaker 5 can be fixed and to absorb the energy of the network after interruption by the circuit breaker 5. It is set up in .

The switching performance of this type of switch is due to the close interaction between the electric arc growing between the arc contacts 5b and 5c of switch 2i and the LC resonant circuit connected in parallel to switch 2i, as shown in Figure 4. It originates from the action. The characteristics of an electric arc basically depend on the medium in which it appears. If the LC resonant circuit parallel to the switch 2i is the same, the limit of the DC switching performance of the switch is strongly influenced by the gaseous medium in which the electric arc appears. In other words, if the DC current through which the switching is made remains the same (pour un meme courant continu DC commute vise), the LC resonant circuit parallel to switch 2i is modified if the gaseous medium in which the electric arc appears changes. There is a need. In the prior art, a commonly used fluid for this application is sulfur hexafluoride (SF ₆ ).

According to the invention, the closed container 5a of the DC circuit breaker 5 is provided with a gaseous fluid containing at least 70% by volume of carbon dioxide and having a filling pressure in the range of 0.65 MPa to 1.1 MPa when measured at 20°C. It accommodates. Therefore, relative to the total volume of gaseous fluid contained in the closed container 5a of the DC circuit breaker 5, the container contains at least 70% by volume of _CO2 . As described in the embodiments below, the gaseous fluid is chosen for a gaseous mixture containing only CO ₂ or containing a mixture of CO ₂ and other components. The components involved depend, among other things, on the operating temperature of the switch. The pressure is measured at 20° C. when the closed container 5a is filled with gaseous fluid.

FIG. 6 advantageously shows the difference in performance between using a conventional SF ₆ medium and a gaseous medium according to the invention containing CO ₂ as gaseous medium in a closed container of a circuit breaker device. . Also plotted in FIG. 6 are measured values from a comparative test between an SF ₆ medium and a medium according to the invention containing CO ₂ . Figure 6 shows the effect of changing the gaseous medium of the switch 2i on the DC switching performance without changing the shape of the switch 2i, and shows that it is advantageous to use a medium mainly composed of _CO2 . It shows. Measurements from this test show that varying C/L in the LC resonant circuit from approximately 0.05 μF/μH to approximately 1.1 μF/μH does not substantially improve switching performance in SF ₆ media; This shows that it remains constant at 1 pu. On the other hand, it has been shown that the use of gaseous CO ₂ -containing media according to the invention consistently results in improved performance compared to SF ₆ media. This performance is further improved by modifying the LC resonant circuit, unlike in the case of SF ₆ media.

In a preferred embodiment, the closed vessel 5a of the DC circuit breaker 5 contains a gaseous fluid composed solely of carbon dioxide with a filling pressure in the range of 0.65 MPa to 1.1 MPa when measured at 20°C. ing. For example, in a switch with operating conditions where the temperature can drop to -40°C, the gaseous fluid may consist solely of carbon dioxide at 20°C and a filling pressure of 1.1 MPa. If the operating conditions of the switch are such that the temperature can drop to −50° C., the gaseous fluid may consist solely of carbon dioxide at 20° C. and a filling pressure of 0.08 MPa.

In another embodiment, the closed vessel 5a of the DC circuit breaker 5 contains a gaseous fluid constituted by a mixture of carbon dioxide and sulfur hexafluoride ( _SF6 ). The closed container 5a of the DC circuit breaker 5 contains 20% to 30% by volume of sulfur hexafluoride, and the balance is carbon dioxide. According to this embodiment, it is possible to realize a switch operating condition that allows the temperature to drop down to -50°C.

In another embodiment, the closed vessel 5a of the DC circuit breaker 5 contains a gaseous fluid constituted by a mixture of carbon dioxide and carbon tetrafluoride ( _CF4 ). The closed container of the DC circuit breaker 5 contains 20% to 30% by volume of carbon tetrafluoride and the balance carbon dioxide. According to this embodiment, it is possible to realize a switch operating condition that allows the temperature to drop down to -50°C.

In another embodiment, the closed container 5a of the DC circuit breaker 5 is constituted by a mixture of carbon dioxide and fluoronitrile (2,3,3,3-tetrafluoro-2-(trifluoromethyl)-propanenitrile). It contains a gaseous fluid. In this example, the closed vessel of the DC circuit breaker contains 4% to 10% fluoronitrile by volume, with the balance being carbon dioxide.

In another embodiment, the closed vessel 5a of the DC circuit breaker contains a gaseous fluid made up of a mixture of carbon dioxide and oxygen. In this example, the closed vessel of the DC circuit breaker contains 5% to 15% oxygen by volume, with the balance being carbon dioxide.

In another embodiment, the closed vessel 5a of the DC circuit breaker contains a gaseous fluid composed of a ternary mixture of carbon dioxide, oxygen and fluoroketone (C _n FK). In this example, the closed vessel of the DC circuit breaker contains 5% to 15% oxygen by volume, 4% to 10% fluoroketone, and the balance carbon dioxide.

Another feature of the invention is that the optimum values for the capacitance C and the inductance L of the resonant circuit 6 of the DC circuit interrupter 5 are adjusted according to the invention to the value of the switching current and to accommodate at least 70% by volume of _CO2 . This is to be determined depending on the performance of the circuit breaker device 5. FIG. 4 shows how the capacitance C required by the resonant circuit 6 varies depending on the value of DC at which it is switched. As the switching current I increases, it becomes necessary to increase the value of the capacitance C of the capacitor, so that current instability can occur. On the other hand, only when the inductance of the resonant circuit 6 (including the stray inductance in the loop) is lower than the limit value, such an instability can be maintained and lead to an oscillating current that increases exponentially.

According to the present invention, while the capacitance value C in the resonance circuit 6 is in μF, the inductance L in μH in the resonance circuit 6 remains at a value smaller than 2700×C ^−0.84 . According to a feature of an advantageous embodiment, for a capacitance value C in μF, the inductance L in μH lies in the range from 400×C ^−0.84 to 2700×C ^−0.84 .

This relationship is shown in FIG. For example, if the required capacitance is 30 μF, the inductance L of the resonant circuit 6 in order to effectively interact with the electric arc of the circuit interrupting device 5 according to the invention needs to be in the range 23 μH to 155 μH. .

Continuing the above discussion, the features relating to the resonant circuit and the features relating to the gaseous fluid interact in such a way that a combined technical effect is achieved.

Specifically, the LC resonant circuit of the switch generates an oscillating current when the electric arc is in its instability region. The boundary between the stable and unstable regions of the electric arc results from the interaction between the amplitude of the resonances of the LC circuit and the inherent characteristics of the electric arc. However, since the inherent characteristics of the electric arc depend on the gaseous medium in which the electric arc grows, the characteristics related to the resonant circuit interact with the characteristics related to the gaseous fluid.

An advantage of the present invention is that the DC circuit breaker includes a resonant circuit configured as described above, thereby making full use of the performance of the DC circuit breaker, so that the breaker performance is exhibited. Considering that the characteristics of the resonant circuit can be controlled, the cost of such a switch is reduced and the current switching performance of the switch is improved.

The invention is not limited to the examples described and illustrated. This is because various modifications can be made without exceeding the scope of the invention.

Claims (13)

Switch for a high-voltage or intermediate-voltage direct current network (1), said switch comprising at least one enclosure containing a gaseous fluid and a system for blowing an arc with said gaseous fluid. comprising a branch with a DC circuit interrupting device (5) comprising an active circuit interrupting member contained in a container (5a), said branch being inserted into a network line and parallel to said branch; , a branch path having an energy absorber (7) is connected, and secondly, a resonant circuit (6) having a predetermined capacitance (C) and a predetermined inductance (L) is connected, and said DC circuit breaker device The sealed container of (5) contains a gaseous fluid containing at least 70% by volume of carbon dioxide and having a filling pressure in the range of 0.65 MPa to 1.1 MPa when measured at 20° C., and has a capacitance in μF. A switch, characterized in that, for the value of (C), said inductance (L) in μH is in the range of 400×C ^−0.84 to 2700×C ^−0.84 . The closed container of the DC circuit breaker (5) contains a gaseous fluid composed only of carbon dioxide with a filling pressure in the range of 0.65 MPa to 1.1 MPa when measured at 20°C. Switch according to claim 1, characterized in that: Switch according to claim 1, characterized in that the closed container of the DC circuit breaker (5) contains a gaseous fluid constituted by a mixture of carbon dioxide and sulfur hexafluoride. Switch according to claim 3, characterized in that the closed container of the DC circuit breaker (5) contains between 20% and 30% by volume of sulfur hexafluoride. Switch according to claim 1, characterized in that the closed container of the DC circuit breaker (5) contains a gaseous fluid constituted by a mixture of carbon dioxide and carbon tetrafluoride. Switch according to claim 5, characterized in that the closed container of the DC circuit breaker (5) contains between 20% and 30% by volume of carbon tetrafluoride. Switch according to claim 1, characterized in that the closed container of the DC circuit breaker (5) contains a gaseous fluid constituted by a mixture of carbon dioxide and fluoronitrile. Switch according to claim 7, characterized in that the closed container of the DC circuit breaker (5) contains between 4% and 10% by volume of fluoronitrile. Switch according to claim 1, characterized in that the closed container of the DC circuit breaker (5) contains a gaseous fluid constituted by a mixture of carbon dioxide and oxygen. Switch according to claim 9, characterized in that the closed container of the DC circuit breaker (5) contains between 5% and 15% by volume of oxygen. Switch according to claim 1, characterized in that the closed container of the DC circuit breaker (5) contains a gaseous fluid constituted by a ternary mixture of carbon dioxide, oxygen and fluoroketone. . Claim 11, characterized in that the closed container of the DC circuit breaker (5) contains 5% to 15% by volume of oxygen and 4% to 10% by volume of fluoroketone. The switch described in High-voltage or intermediate-voltage direct current network, characterized in that it comprises at least one switch (2i) according to any one of claims 1 to 12.

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