WO2018069627A1

WO2018069627A1 - Co2 switch for a high voltage dc grid

Info

Publication number: WO2018069627A1
Application number: PCT/FR2017/052772
Authority: WO
Inventors: Christophe Creusot
Original assignee: Supergrid Institute
Priority date: 2016-10-10
Filing date: 2017-10-10
Publication date: 2018-04-19
Also published as: JP2019534535A; KR20190065285A; FR3057388A1; EP3523817B1; JP7377105B2; CN109891544A; CN109891544B; EP3523817A1; FR3057388B1

Abstract

The invention concerns a switch for a high or medium voltage DC grid, comprising a DC circuit breaker (5) the sealed chamber of which contains a gaseous fluid comprising at least 70% by volume carbon dioxide at a pressure of between 0.65 MPa and 1.1 MPa measured at a temperature of 20°C and a resonant circuit having a capacitance value (C) in μF and an inductance (L) in μΗ less than 2700*C^-0.84.

Description

C02 SWITCH

FOR HIGH VOLTAGE CONTINUOUS CURRENT NETWORK

The present invention relates to the general technical field of high-voltage direct current (HVDC) transmission networks or medium-voltage direct current (VDC), which is an acronym for Medium Voltage Direct Current.

More particularly, the invention relates to HVDC or MVDC gas switches interrupting a direct current in a line of a high or medium voltage DC transmission network.

The object of the invention finds a particularly advantageous application in the technical field of high or medium voltage DC networks in order to be able to direct the power of a path to another of the network in the event of, for example, failure on a pole or extended maintenance operations on a network hub.

In DC networks, it is known to use switches having a branch with a DC circuit breaker having active cut-off members enclosed in a sealed chamber containing a gaseous fluid. The state of the art has proposed numerous technical solutions for producing a gas continuous current circuit breaker.

For example, a known circuit breaker has been described in "Journal of Power-Energy Conference Division 1994 of the Institute of Electrical Engeeners", No. 621, pp. 824-825. The gas-fired circuit breaker is placed in a branch of a line of the continuous network In parallel with this branch containing this circuit breaker are mounted on the one hand, a branch with an energy absorbing element to absorb any overvoltage, and on the other hand, a resonant circuit having a given capacitance. and a given inductance.

The DC circuit breaker is of the blowing type and comprises active cut-off members enclosed in a sealed chamber containing a gaseous fluid. The circuit breaker has a fixed contact to allow the flow of direct current and a movable contact in a blow cylinder with a dielectric nozzle fixed on it. In the open state, an electric arc is generated between the contacts when a piston rod integrated in the movable contact is moved relative to the blower piston fixed on the fixed contact. As the piston rod moves, an arc extinguishing gas, typically SF6, contained within the enclosure is compressed to be sprayed onto the arc.

In the case of direct current, simply spraying the DC arc with the SF6 gas may not be sufficient to interrupt and extinguish it successfully due to the fact that, unlike AC current, the DC current does not cross not periodically the current zero point.

To extinguish the arc, the resonant circuit which includes an inductor and a capacitor is thus coupled in parallel with the circuit breaker to superimpose an oscillating current to the DC current, to provide a zero crossing at the circuit breaker. This allows the SF6 gas compressed by the blowing piston to be blown and sprayed against the arc forcing its extinguishing.

Since DC networks require higher and higher voltages, the associated switches have to increase the switching performance by up to 6000 A current value. This switching performance in current value must also be implemented. for a large operating temperature range of the switches. Typically, such switches must maintain their switching performance in current value while the operating temperature can reach -50 ° C.

US Patent 5,737,162 proposes to keep DC circuit breakers with a standard sealed enclosure but to put in series these circuit breakers. This solution has the disadvantage of a large footprint and a high cost.

EP 0 740 320 proposes to optimize the values of the impedance and the capacitance of the resonant circuit as a function of the interruption value of the direct current. It has also been proposed to use different types of extinguishing gas as indicated for example in the patent application US 2016/261095 which proposes to use carbon dioxide instead of SF6 for the extinction of the electric arc in an electrical apparatus for the production, transportation, distribution and / or use of electrical energy. However, as each type of gas used modifies the extinction conditions of the electric arc, this document does not teach for its implementation in a DC circuit breaker comprising a resonant circuit.

Similarly, US patent application 2011/0175460 discloses a switch for a DC network comprising a resonant circuit and active breaking members enclosed in an enclosure containing SF6. For such a SF6 gaseous medium, this document proposes to take a value of the capacity large enough to switch the direct current, whatever the choice of the value of the inductance. This solution does not make it possible to optimize the sizing of the resonant circuit by taking into account the criterion of stability of the electric arc which in practice restricts the range of use of the inductance L of the LC circuit.

In the state of the art, it is also known for example from the patent application FR 2 975 819 to use a medium containing carbon dioxide, as a medium for electrical insulation and / or extinction of electric arcs in a medium or high voltage electrical appliance. This patent application does not provide information on its implementation in relation to a resonant circuit.

The present invention aims to remedy the drawbacks stated above by proposing a switch for a high or medium voltage DC network, implementing a mechanical circuit breaker associated with an oscillating current injection circuit, such a switch being simple and compact while having high DC switching performance for a large operating temperature range of the switches. To achieve such an objective, the switch for a high or medium voltage DC network comprises a branch with a DC circuit breaker comprising active breaking members enclosed in at least one sealed chamber containing a gaseous fluid, this branch being inserted. in the line of the network and in parallel of which are mounted on the one hand, a branch with an energy absorbing element, and on the other hand, a resonant circuit having a given capacitance and a given inductance.

According to the invention, the sealed enclosure of the DC circuit breaker contains a gaseous fluid comprising at least 70% by volume of carbon dioxide at a filling pressure of between 0.65 MPa and 1.1 MPa measured at a temperature of 20 ° C and for a capacitance value C in pF, the inductance L in μΗ is less than 2700 * C ^0.84 .

In addition, the switch according to the invention may furthermore contain in combination at least one and / or the other of the following additional characteristics:

for a capacitance value C in pF, the inductance L in μΗ is between 400 * C ^{0 84} and 2700 * C ^{0 84} ;

a gaseous fluid composed exclusively of carbon dioxide at a filling pressure of between 0.65 and 1.1 MPa, measured at a temperature of 20 ° C .;

a gaseous fluid consisting of a mixture of carbon dioxide and sulfur hexafluoride;

between 20% and 30% by volume of sulfur hexafluoride;

a gaseous fluid consisting of a mixture of carbon dioxide and carbon tetrafluoride;

between 20% and 30% by volume of carbon tetrafluoride;

a gaseous fluid consisting of a mixture of carbon dioxide and fluoronitrile;

between 4% and 10% by volume of fluoronitrile;

a gaseous fluid consisting of a mixture of carbon dioxide and oxygen; between 5% and 15% by volume of oxygen;

a gaseous fluid consisting of a ternary mixture of carbon dioxide, dioxygen and fluoroketone;

between 5% and 15% by volume of oxygen and between 4% and 10% by volume of fluoroketone.

Another object of the invention is to propose a high or medium voltage DC network comprising at least one switch according to the invention.

Various other characteristics appear from the description given below with reference to the accompanying drawings which show, by way of non-limiting examples, embodiments of the subject of the invention.

Figure 1 is a diagram of an exemplary embodiment of a high or medium voltage DC transmission network implementing at least one HVDC gas switch according to the invention.

Figure 2 is a block diagram illustrating an HVDC gas switch according to the invention.

FIG. 3 is a diagram giving the values of the inductance L in μΗ as a function of the values of the capacitance C in pF, making it possible to illustrate the dimensioning of the resonant circuit of a circuit breaker of a HVDC gas switch conforming to FIG. 'invention.

FIG. 4 is a diagram giving the values of the capacitance C in pF as a function of the values of the inductance L in μΗ for various current values to be switched, making it possible to illustrate the current performance limit in the LC plane.

Figure 5 is a diagram illustrating by way of example the geometry of a sealed enclosure of a DC circuit breaker for the implementation of the invention.

Figure 6 is a diagram giving the ratio of the capacitance C (in pF) on the inductance L (in μΗ) for a standard DC continuous current (per unit), as a function of the use of an SF6 medium and of a medium C0 ₂ .

FIG. 1 illustrates by way of example a high or medium voltage DC transmission network 1 (HVDC or MVDC) implementing at least one, and in general, several switches 2i gas HVDC or MVDC according to the invention, interrupting a direct current in a line of the network. Conventionally, such a DC transmission network 1 comprises at least one side, AC / DC converters 3 and, on the other hand, converters 4 DC / AC. Current converters 3, 4 are not described in detail because they are not specifically part of the invention and are well known to those skilled in the art.

The switches according to the invention are designated by the reference 2 i with i varying from a, b, ... to n. These switches 2i according to the invention are mounted between the converters 3, 4 and points of the network 1 to allow to direct the power from one point of the network to another. These switches 2i allow for example to maintain a reduced power flow in case of failure on a pole or extended maintenance operations on a network pole. For example, a network 1 comprises adapted switches 2a, 2b according to the invention and short-circuit switches 10 for transferring the power from the earth conductor Ct to the aerial metallic conductor Ca. It should be noted that the switches Short circuit circuit 10 comprises only one function for short-circuiting an unavailable pole of the converter, unlike switches 2i according to the invention which have an opening switching capability.

To transfer this power, the switch 2a disposed on the ground conductor Ct which is initially closed, opens and switches the current of the earth conductor Ct to the overhead metal conductor Ca through the switches 2b according to the invention and the switches of short circuit 10, placed in series between the earth conductor Ct and the aerial metal conductor Ca and which have been previously closed.

As it appears more specifically from the Fíg. 2, a switch 2i is placed on a line of the network 1 traversed by a DC current ÏDC, for example between points AA 'as illustrated. Each switch 2i has between, points A-A ', a branch with a circuit breaker 5 of dc current of all types known per se consisting of one or more sealed enclosures arranged in series, having arc current arc and arc voltage Uarc.

By DC circuit breaker 5, there is included a mechanical device comprising active cutting members enclosed in a sealed enclosure containing a gaseous fluid and a system for blowing the arc by the gaseous fluid. As will be described more precisely in the description that follows, the gaseous fluid is chosen for its insulating nature, in particular so as to have a dielectric strength greater than that of dry air at equivalent pressure, for its capacity of power failure. and its ability to provide high arc voltage.

A DC circuit breaker 5 is for example described by Fíg. 5. Conventionally, the DC circuit breaker 5 comprises in a sealed enclosure Sa, a pair of arc contacts 5b and 5c and a pair of so-called "permanent" contacts 5d and 5e which ensure the passage of the current when the circuit breaker is in closed position. The arcing contacts 5b and 5c as well as the permanent contacts separate during the opening maneuver. When the arcing contacts 5b and 5c separate, the electric arc is established between them and is confined inside the blowing nozzle 5f. The arc continues until a zero crossing of the current occurs in which case the gas blown by the blowing nozzle 5f can replace the plasma with a cooler gas. This blowing action at zero crossing of the current makes it possible to extinguish the arc and allows the gaseous medium comprised between the arc contacts 5b and 5c to hold the transient recovery voltage imposed by the network without restarting and restoring the current.

In parallel with this branch AA 'is mounted on the one hand, a resonant circuit 6 not pre-charged and on the other hand, a branch with an energy absorbing element 7. The resonant circuit 6 not pre-charged present in series , a given capacitance C, a resistance and a given inductance L. This resonant circuit 6 interacts with the arc voltage Uarc to produce an exponentially increasing oscillating current. This oscillating current comes superimpose on the IDC direct current to provide a zero crossing of the current during which the gaseous fluid is blown to extinguish the arc.

The branch with the energy absorbing element 7 comprises an overvoltage device of all types known per se, such as a surge arrester. This energy absorbing element 7 is implanted to enable the maximum overvoltage to be fixed across the capacitor C and the circuit breaker 5 and to absorb the energy of the network after the cut-off by the circuit-breaker 5.

The switching performance of this type of switch as shown in FIG. 4 results from the intimate interaction between the electric arc developed between the arc contacts 5b and 5c of a switch 2 1 and the resonant circuit LC connected thereto in parallel. The characteristics of the electric arc depend essentially on the environment in which it is bathed. Thus, for the same LC resonant circuit parallel to a switch 2i, the DC switching performance limit DC of this switch is strongly influenced by the gaseous medium in which the electric arc bathes. Expressed in another way, for the same DC switched direct current, if one changes the gaseous medium in which the electric arc bathes, the LC resonant circuit parallel to a switch 2 i must be modified. The fluid commonly used for this application in the prior art is sulfur hexafluoride (SF6).

According to the invention, the sealed enclosure 5a of the DC circuit breaker 5 contains a gaseous fluid comprising at least 70% by volume of carbon dioxide and having a filling pressure of between 0.65 MPa and 1.1 MPa measured. at a temperature of 20 ° C. Thus, with respect to the total volume of the gaseous fluid contained in the sealed enclosure 5a of the DC circuit breaker 5, this enclosure contains in volume at least 70% by volume of CO 2. As will be described in the exemplary embodiments described hereinafter, the gaseous fluid contains exclusively CO 2 or a mixture of CO 2 with other components, the choice of the composition of the gaseous mixture depending in particular on the operating temperatures of the switches. The pressure is measured at a temperature of 20 ° C during the gaseous fluid filling of the sealed enclosure 5a.

FIG. 6 advantageously illustrates the differences in performance between the use as a gaseous medium in the sealed chamber of the circuit breaker, of a conventional SF6 medium and of a gaseous medium according to the invention comprising CO 2. Fig. 6 thus provides comparative test records between an SF6 medium and a medium according to the invention containing CO 2. This FIG. 6 makes it possible to illustrate the impact of the change of gaseous medium in the same switch geometry 2i on the DC switching performance DC and puts forward the advantage of the use of a medium consisting mainly of C02. The test records show that a variation of the resonant LC circuit over a range of C / L from ~ 0.05 to ~ 1.1 μΡ / μΗ almost did not bring any gain on the switching performance in the medium. SF6, the latter being fixed with reference to 1 pu. On the other hand, the use of the gaseous medium according to the invention containing CO 2 systematically shows a performance gain with respect to the SF6 medium. This performance is further improved by modifying the LC resonant circuit while this is not the case with the SF6 medium.

According to a preferred embodiment, the sealed enclosure 5a of the DC circuit breaker 5 contains a gaseous fluid consisting exclusively of carbon dioxide at a filling pressure of between 0.65 and 1.1 MPa, measured at a temperature of 20 ° C. ° C. For example, for operating conditions of the switch at a temperature of up to -40 ° C, the gaseous fluid may consist exclusively of carbon dioxide at a filling pressure of 1.1 MPa at 20 ° C For operating conditions of the switch at a temperature of up to -50 ° C, the gaseous fluid may consist exclusively of carbon dioxide at a filling pressure of 0.8 MPa at 20 ° C.

According to another exemplary embodiment, the sealed enclosure 5a of the DC circuit breaker 5 contains a gaseous fluid consisting of a mixture of carbon dioxide and sulfur hexafluoride (SF6). The sealed enclosure 5a of the DC circuit breaker 5 thus contains between 20% and 30% by volume of sulfur hexafluoride and in addition, carbon dioxide. This exemplary embodiment allows operating conditions of the switch at a temperature of up to -50 ° C.

According to another exemplary embodiment, the sealed enclosure 5a of the DC circuit breaker 5 contains a gaseous fluid consisting of a mixture of carbon dioxide and carbon tetrafluoride (CF4). The sealed enclosure of the DC circuit breaker 5 contains between 20% and 30% by volume of carbon tetrafluoride and in addition, carbon dioxide. This exemplary embodiment allows operating conditions of the switch at a temperature of up to -50 ° C.

According to another exemplary embodiment, the sealed enclosure 5a of the DC circuit breaker 5 contains a gaseous fluid consisting of a mixture of carbon dioxide and fluoronitrile (2,3,3,3-tetrafluoro-2- (trifluoromethyl) -propanenitrile). According to this example, the sealed enclosure of the DC circuit breaker contains between 4% and 10% by volume of fluoronitrile and in addition, carbon dioxide.

According to another exemplary embodiment, the sealed enclosure 5a of the DC circuit breaker contains a gaseous fluid consisting of a mixture of carbon dioxide and oxygen. According to this example, the sealed enclosure of the DC circuit breaker contains between 5% and 15% by volume of oxygen and in addition, carbon dioxide.

According to another exemplary embodiment, the sealed enclosure 5a of the DC circuit breaker contains a gaseous fluid consisting of a ternary mixture of carbon dioxide, oxygen and fluoroketone (C _n FK). According to this example, the sealed enclosure of the DC circuit breaker contains between 5% and 15% by volume of oxygen and between 4% and 10% by volume of fluoroketone and in addition, a ternary mixture of carbon dioxide. Another characteristic of the object of the invention is to determine the optimal values of capacitance C and of inductance L for the resonant circuit 6 of the DC circuit breaker 5 as a function of the value of the switching current and the performance of the circuit breaker according to the invention containing at least 70% by volume of CO 2. Fig. 4, illustrates the evolution of the capacitance C required for the resonant circuit 6 as a function of the value of the direct current to be switched. When the current to be switched I increases, it is necessary to increase the value of the capacitor C of the capacitor in order to be able to generate the instability of current. On the other hand, this instability can only be maintained and produce the oscillating current exponentially increasing if the inductance of the resonant circuit 6 (including the parasitic inductance of the loop) is lower than a limit value.

According to the invention, for a capacitance value C in the resonant circuit 6, the inductance L in μΗ of the resonant circuit 6 remains less than 2700 ° C. ^"0.84 According to an advantageous characteristic of embodiment, for a value of capacitance C in μΡ, the inductance L μΗ is between 400 * C ^{0 84} and 2700 * C ^{0 84} .

This relationship is illustrated in FIG. 3. For example, for a required capacity of 30 F, to be effective, the inductance L of the resonant circuit 6 interacting with the electric arc of the circuit breaker 5 according to the invention must be between 23 μΗ and 155 μΗ.

It follows from the foregoing description that the characteristics relating to the resonant circuit and those relating to the gaseous fluid interact to produce a combined technical effect.

Indeed, the resonant circuit LC of the switch produces an oscillating current if the electric arc is in its field of instability. The boundary between the field of stability of the electric arc and its field of instability results from the interaction between the magnitudes of the resonant LC circuit on the one hand and the intrinsic characteristics of the electric arc on the other hand. Since the intrinsic characteristics of the electric arc depend on the gaseous medium in which the electric arc develops, the characteristics relating to the resonant circuit interact with those relating to the gaseous medium.

An advantage of the invention is that the interruption performance is achieved because the DC circuit breaker comprises a resonant circuit sized as described above, to take full advantage of the performance of the DC circuit breaker. Since the capacity of the resonant circuit can be controlled, the cost of such a switch is reduced, the current switching performance is also increased.

The invention is not limited to the examples described and shown because various modifications can be made without departing from its scope.

Claims

1 - Switch for a high or medium voltage direct current network (1), comprising a branch with a DC circuit breaker (5) comprising active cut-off members enclosed in at least one sealed enclosure (5a) containing a gaseous fluid, this branch being inserted in the line of the network and in parallel of which are mounted on the one hand, a branch with an energy absorbing element (7), and on the other hand, a resonant circuit (6) having a given capacitance (C) and a given inductance (L), characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid comprising at least 70% by volume of carbon dioxide at a filling pressure of between 0.65 MPa and 1.1 MPa measured at a temperature of 20 ° C and that for a capacitance value (C) at F, the inductance (L) in μΗ is less than 2700 * C ° ^'84 .

2 - Switch according to claim 1, characterized in that for a capacitance value (C) in pF, the inductance (L) in μΗ is between 400 * C ^{0 84} and 2700 * C ^{"0 84} .

3 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid consisting exclusively of carbon dioxide at a filling pressure of between 0.65 and 1.1 MPa, measured at a temperature of 20 ° C

4 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid consisting of a mixture of carbon dioxide and sulfur hexafluoride.

5 - Switch according to claim 4, characterized in that the sealed enclosure of the DC circuit breaker (5) contains between 20% and 30% by volume of sulfur hexafluoride.

6 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a fluid gas consisting of a mixture of carbon dioxide and carbon tetrafluoride.

7 - Switch according to claim 6, characterized in that the sealed enclosure of the DC circuit breaker (5) contains between 20% and 30% by volume of carbon tetrafluoride.

8 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid consisting of a mixture of carbon dioxide and fluoronitrile.

9 - Switch according to claim 8, characterized in that the sealed enclosure of the DC circuit breaker (5) contains between 4% and 10% by volume of fluoronitrile.

10 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid consisting of a mixture of carbon dioxide and oxygen.

11 - Switch according to claim 10, characterized in that the sealed enclosure of the DC circuit breaker (5) contains between 5% and 15% by volume of oxygen.

12 - Switch according to claim 1, characterized in that the sealed enclosure of the DC circuit breaker (5) contains a gaseous fluid consisting of a ternary mixture of carbon dioxide, oxygen and fluoroketone.

13 - Switch according to claim 12, characterized in that the sealed enclosure of the DC circuit breaker (5) contains between 5% and 15% by volume of oxygen and between 4% and 10% by volume of fluoroketone.

14 - high or medium voltage DC network, characterized in that it comprises at least one switch (2i) according to one of claims 1 to 13.