Patent Application
20120228264
The present invention relates to composite materials comprising a polymeric matrix that may be a fluorinated polymer matrix and a specific metal fluoride filler used as electric arc extinction materials.
Such materials may be of application in electrical equipment where electric arcs may appear, such as switchgear, for example, in medium voltage or high voltage switches or medium voltage or high voltage switch disconnectors.
Thus, the general field of the invention is that of electric arcs and means for extinguishing them.
An electric arc is a visible electric current in a generally insulating medium, that is created between two conductive surfaces that are close to each other, providing the potential difference between said two surfaces is sufficient.
That electric current is manifested by ionization of a generally insulating medium through which it passes, thereby constituting neither more nor less than a plasma that may reach temperatures that are high, for example a temperature of 2000 (K) to 10,000 K.
When it strikes, an electric arc may cause degradation of the surrounding elements as well as large electromagnetic disturbances, which may prove to be a problem in electrical equipment and in particular in electrical equipment intended to interrupt a current, such as circuit breakers, switches, or switch disconnectors.
That type of equipment that is intended to interrupt current functions on the principle of separating contacts. After said contacts have separated, the current continues to flow in the circuit via an electric arc that is established between the ends of said separated contacts. In order to interrupt the current and also to prevent the electric arc that is produced thereby from degrading the equipment, various electric arc extinction means have been developed; examples that may be mentioned are:
extinction by the presence of an electric arc extinction gas in the zone in which the electric arc is produced;
extinction by the presence of an electric arc extinction liquid in the zone in which the electric arc is produced; and
extinction by placing the zone in which the electric arc is produced under vacuum.
The principle of electric arc extinction using extinction gases lies in the intrinsic qualities of the gases used; preferably, they must have the following qualities:
the capacity to transport the heat energy produced by the arc in order to allow rapid outward exchanges of heat from the core of the arc;
the capacity to capture the principal electrons responsible for electrical conduction in the gas;
reversible decomposition of its molecules, so that the quantity of operational gas in the equipment remains constant, thereby avoiding any need to re-fill the equipment with the gas throughout its service life.
An effective candidate for an electric arc extinction gas is sulfur hexafluoride SF6, which has a high thermal conductivity and constitutes a genuine electron trap. Those qualities mean that the gas is used in many types of switchgear, in particular in equipment of the switch disconnector type, where the gas surrounding the electric arcing contacts is stored in cells that are narrow (for example 375 mm for a cutoff voltage of 24 kV. However, that gas suffers from an environmental drawback, since it generates a recognized greenhouse effect. In order to comply with regulations that are in force, its use must therefore be managed very rigorously from its manufacture to the end of its life and also during recycling thereof.
In order to overcome this problem, several gases have been used to replace sulfur hexafluoride SF6; they include ambient air, nitrogen N2, and carbon dioxide. However, because of their poorer extinction capacities compared with sulfur hexafluoride SF6, cells including such gases, and in particular ambient air, must be bulkier (for example, cells with a width of 600 mm to 700 mm for a cutoff voltage of 24 kV).
As mentioned above, electric arc extinction may be ensured by liquids, in particular by oils. From a structural viewpoint, the arcing contacts between which the electric arc is formed during separation thereof are contained in oil placed in a metal tank or, in another mode, they may be sprayed by blowing vaporized oil. Under the action of the electric arc, the oil decomposes into a gas (essentially hydrogen and acetylene), and so the energy of the arc used for such decomposition brings about cooling of the medium.
However, that interruption technique suffers from the major disadvantage of requiring regular operations for replacing the spent oil, since decomposition thereof by the electric arcs is irreversible. Further, the formation of hydrogen must be very carefully monitored since an explosive mixture may be formed when hydrogen comes into contact with oxygen.
Finally, extinction of the electric arc established between two arcing contacts may be ensured by creating a vacuum atmosphere between the contacts; a vacuum is a very good insulator. However, that extinction technique is complex in implementation since it requires placing a vacuum bottle in series with the cell including said arcing contacts.
The inventors thus aimed to develop novel electric arc extinction means that, in addition to gas type electric arc extinction means, can improve the extinction performances of switchgear, in particular medium voltage switchgear.
One of the aims of the invention is to develop novel electric arc extinction means that mean that the use of sulfur hexafluoride SF6 as an extinction gas can be dispensed with.
The inventors thus surprisingly discovered that, by using the composite materials comprising specific inorganic fillers, it is possible to obtain better results in terms of electric arc extinction than the use of composite materials comprising inorganic fillers, such as magnesium fluoride or barium fluoride.
Thus, the invention provides the use of a composite material comprising a polymeric matrix and at least one metal fluoride filler selected from the cerium fluorides CeF3 and/or CeF4, lanthanum fluoride LaF3 and mixtures thereof, as an electric arc extinction material in electrical equipment.
These materials provide excellent results as regards electric arc extinction in switchgear, in particular medium voltage switchgear (namely equipment that conventionally functions at voltages in the range 1 kV to several tens of kilovolts, for example voltages in the range 1 kV to 52 kV).
The materials used in accordance with the invention advantageously include a fluorinated polymeric matrix, i.e. a polymer including fluorine atoms.
Fluorinated polymers that are suitable for the present invention may be polytetrafluoroethylene (abbreviated to PTFE), a tetrafluoroethylene-tetrafluoropropylene copolymer (abbreviated to FEP), or a tetrafluoroethylene-perfluorinated vinyl ether copolymer (abbreviated to PFA).
As mentioned above, metal fluoride type fillers selected from the cerium fluorides CeF3 and/or CeF4, lanthanum fluoride LaF3 and mixtures thereof may be dispersed in the polymeric matrix as defined above, in an amount that may be from 2% to 35% by weight relative to the total weight of the composite material, for example 5% by weight relative to the total weight of the composite material.
From a functional viewpoint, in contact with an electric arc, the materials as defined above release insulating electronegative atoms, in this example fluorine atoms, which atoms absorb a portion of the electric arc energy equal to the energy required for their liberation and thus contribute to extinction of the arc.
Because of their efficiency, these materials can be used in gaseous environments that include extinction gases that are less efficient than sulfur hexafluoride SF6 but that are less environmentally damaging, as with carbon dioxide, CO2.
Specific materials that may be used in accordance with the invention are:
a composite material comprising a PTFE matrix and 5% by weight of CeF3 relative to the total weight of the material;
a composite material comprising a PTFE matrix and 5% by weight of CeF4 relative to the total weight of the material; and
a composite material comprising a PTFE matrix and 5% by weight of LaF3 relative to the total weight of the material.
A particularly advantageous material in accordance with the invention is a material comprising cerium trifluoride CeF3 or cerium tetrafluoride CeF4 as the metal fluoride filler, said fillers also having the capacity to absorb ultraviolet radiation emanating from the electric arc, said cerium trifluoride or said cerium tetrafluoride CeF4 possibly being used in association with PTFE, FEP or PFA.
In addition to the fillers mentioned above, in a first variation, the material may include one or more fillers that absorb ultraviolet radiation (which is abbreviated to UV below) such as boron nitride BN, silicon dioxide SiO2, alumina Al2O3, CoOAl2O3, titanium dioxide TiO2, molybdenum sulfide MoS2, cerium trifluoride CeF3, cerium tetrafluoride CeF4 (which is capable of being transformed into CeF3 and of liberating fluorine F2), and mixtures thereof.
In accordance with a second variation, the composite material defined above may be used in association with another composite material comprising a polymeric matrix, for example a polymer matrix formed from a fluorinated polymer and at least one filler that absorbs ultraviolet radiation, such as a filler comprising boron nitride BN, silicon dioxide SiO2, alumina Al2O3, CoOAl2O3, titanium dioxide TiO2, molybdenum sulfide MoS2, cerium trifluoride CeF3, cerium tetrafluoride CeF4, and mixtures thereof.
Thus, in this second variation, in the electrical equipment in which they are used, the two materials may be in the form of distinct parts, for example:
a part formed from composite material comprising a polymeric matrix, for example a fluorinated polymer matrix, and at least one metal fluoride filler selected from the fluorides of cerium CeF3 and/or CeF4, lanthanum fluoride LaF3 and mixtures thereof located, for example, at the foot of the electric arc in the form, for example, of a washer surrounding one of the arcing contacts of the equipment;
a part formed from composite material comprising a polymeric matrix, for example a fluorinated polymer matrix, and at least one filler that absorbs ultraviolet radiation located, for example, on the path of the electric arc.
The advantage of also using a filler that absorbs UV is that it can absorb the ultraviolet radiation emanating from the electric arc and can thus contribute to facilitating extinction thereof.
The materials mentioned above may be used in medium voltage or high voltage electrical equipment, in particular in switchgear such as circuit breakers, switches, or switch disconnectors.
In particular, the materials mentioned above are adapted for use in switchgear units that also include an extinction gas other than sulfur hexafluoride SF6, such as switchgear including carbon dioxide CO2, nitrogen N2, or mixtures thereof.
Thus, in a second aspect, the invention provides electrical equipment comprising at least one first arcing contact and at least one second arcing contact between which an electric arc is established during their separation and including, as electric arc extinction means, at least one material as defined above, said material further optionally including one or more fillers that absorb ultraviolet radiation as defined below or being optionally in association with another composite material comprising a polymer matrix, for example, a matrix in a fluorinated polymer, and at least one filler that absorbs ultraviolet radiation as defined above.
Said composite material including a metal fluoride type filler may be disposed at the foot of the arc, i.e. around at least one of said arcing contacts, for example in the form of a washer around at least one of the electric arcing contacts of the equipment mentioned above or in the form of a strip located on the path of the electric arc.
The equipment mentioned above may be switchgear such as a circuit breaker, a switch or a switch disconnector, said equipment possibly being medium voltage equipment.
The equipment may include an extinction gas, for example an extinction gas selected from carbon dioxide, nitrogen, and mixtures thereof. Advantageously, the extinction gas is free of sulfur hexafluoride, SF6.
The invention is described below with reference to the implementations presented below, given by way of non-limiting illustration.
The movable contact 7 is in the form of a rod of length that is very slightly shorter than the inside diameter of the insulating chamber 1, with ends that can come into contact simultaneously with the ends 11 of the stationary contacts 3, 5 penetrating into the inside of the insulating chamber 1.
The current supply is symbolized by a first arrow 13 at a first stationary contact 3; the outgoing current is symbolized by a second arrow 15 leaving the other stationary contact 5 diametrically opposite to the first.
A washer (not shown in
It should be understood that the other end 9 may also be provided with a washer.
The empty space between the insulating chamber and the movable contact is occupied by a gas such as carbon dioxide, CO2.
As the movable contact starts to rotate (resulting in mechanical separation of the ends of the movable contact and the stationary contacts), an electric arc is generated between the ends 11 of the stationary contacts 3, 5 and the ends 9 of the movable contact 7. Because of the electric arc, each washer, located at the foot of the arc, is partially sublimated, thereby releasing highly electronegative insulating elements (in particular, fluorine atoms), that absorb the ions present in the plasma constituting the electric arc (such as ions from the contact materials and the surrounding gas), which contributes to cooling the plasma and thus to decay of the electric arc.
Because of their constitution, the above-mentioned strips can absorb a portion of the ultraviolet radiation emanating from the plasma (and thus a portion of its energy) and thereby contribute to extinction of the electric arc in collaboration with the material of the washer.
Tests in the presence of a carbon dioxide gas CO2 have revealed manifest effectiveness with regard to the amperage of the current.
Thus, by way of example, with a Fluokit switch type electric device comprising a PTFE protection strip filled with 5% by weight of cerium trifluoride CeF3, it is possible to interrupt electric currents of 630 A at 12 kV with a CO2 pressure of 1.3 bar relative, the mean arc time being 7.6 ms, whereas the same assay with a PTFE protection strip filled with 5% by weight of magnesium fluoride MgF2 led to a particularly higher mean arc time (being 13.6 ms), proving the higher efficiency of CeF3 over MgF2.
On the other hand, with a Fluokit switch type electric device comprising a PTFE protection strip filled with 5% by weight of cerium trifluoride CeF3, it is possible to interrupt electric currents of 645 A at 24 kV with a CO2/fluoroketone pressure of 1 bar relative, the mean arc time being 8.9 ms, whereas an assay with a PTFE protection strip filled with 5% by weight of magnesium fluoride MgF2 with electric currents of 320 A at 24 kV led to a higher mean arc time (being 9.7 ms), proving once again the higher efficiency of CeF3 over MgF2.
Referring now to
When the movable contact 33 separates from the stationary contact 25, an electric arc is created between one end of the movable contact and one end of the stationary contact 25, the foot of the electric arc being in contact with the washer 29 and running around said strip 31, with the washer 29 and the strip 31 contributing to reducing the extinction time of said electric arc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09 57767 | Nov 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/66740 | 11/3/2010 | WO | 00 | 5/2/2012 |
