EP3327744A1 - Device for detecting loss of vacuum in a vacuum bulb and vacuum-based cutoff apparatus comprising such a device - Google Patents

Abstract

The present invention relates to a device for detecting the loss of vacuum in a vacuum interrupter A, by the method of measuring electric discharges between the electrodes (3,4) and at least one conductive screen (16) with floating potential surrounding respectively at least one electrode and electrically connected to the ground M. This device is characterized in that it comprises in combination, so-called first means for increasing the electric field between the electrodes (3, 4) and the screen (16). ), and so-called second means for increasing the capacitive coupling between the aforementioned screen (16) and the mass M, these two means cooperating so that the ionization threshold of the air is exceeded at atmospheric pressure so that the electric discharges continue even after the rise of the pressure at atmospheric pressure.

Description

TECHNICAL AREA

The present invention thus relates to a device for detecting the loss of vacuum in a vacuum interrupter of a vacuum interrupter, said switchgear being located in a powered primary electrical network and the contacts of the bulb being housed in an envelope, said envelope housing a fixed electrode integral with one of the aforementioned bottoms and supporting a fixed contact, and a movable electrode supporting a movable contact, said movable electrode being slidably mounted through the other of the two bottoms, between a position closed of the apparatus in which the movable contact is in contact with the fixed contact and an open position of the apparatus in which the movable contact is separated from the fixed contact, this detection being carried out by the method of the measurement of electric discharges between the contacts and at least one floating potential conductive screen respectively surrounding at least one electrode and electrically connected t to the mass.

STATE OF THE PRIOR ART

The problem of detecting the loss of vacuum in a bulb in use can be solved by a deformable bellows system, which provides a late indication from the moment the pressure is raised to a significant fraction (for example 10% or 100mbar). ) atmospheric pressure, as described in the patent WO2007070700 .

Another way of detecting the decrease of the dielectric properties of the vacuum when the pressure exceeds 10 ^-2 mbar is to detect the discharges which occur between on the one hand, the electrodes (fixed and mobile contacts) brought to the service voltage and another, a potential screen floating around them, by measuring the potential difference between these electrodes and this screen when a bulb is in use.

This detection of discharges can be done either by measuring the electromagnetic wave signals generated when the pressure increases inside the bulb, or by capacitive coupling between the floating screen and the mass via the capacitance of the capacitor. discharge detection circuit, by measuring the increase of the potential difference between the floating screen and the mass, as described in the patents, US 4553139 , WO 02/49057 (Meidensha ) EP 1 763 049 and EP 2 463 883 .

However, according to this second method, the discharges cease when the bulb is raised to atmospheric pressure (Patm), because of the insulating properties of the air at 1 bar and the design rules of the ampoules to ensure a satisfactory dielectric strength during the vacuum type tests between the electrodes and the screen.

In the usual configurations of air-insulated vacuum switchgears, the voltage difference between the electrodes (contacts) and the floating screen is relatively small, due to the weak capacitive coupling between the floating screen and the ground surrounding. Discharges may therefore occur transiently during the passage through the hollow of the Paschen curve under the effect of a leak, and stop when the air pressure is sufficiently raised in the bulb. In the case of a sudden rise to atmospheric pressure (rapid leak due for example to sudden cracking of a ceramic, bellows, etc ...), the indication given by the indicator of loss of vacuum risk of being only transient and brief, which leads to a difficulty of interpretation and the need to memorize reliably the passage through the hollow of the Paschen curve in order to warn the operator that bulb whose pressure is raised to atmospheric pressure is in default.

It is therefore preferable that the detector continues to indicate a permanent defect of the bulb when it is raised to atmospheric pressure.

The document EP 1763049 describes the fact that the capacitive coupling between the floating potential screen and the ground is greatly increased when the bulb is coated with solid insulation covered with a conductive layer grounded. This increases the voltage difference applied between the electrodes under the operating voltage and the screen. This principle makes it possible to simplify the detection of discharges but the discharges are not maintained at Patm.

The document is also known US 5 399973 Describing a principle for increasing the pressure range in which vacuum loss detection is possible (by lowering the minimum pressure value at which discharges occur) via a protruding element provided on the outer surface screens, either on the inner surface of the envelope. However, this principle does not greatly increase the sensitivity of the detection towards high pressures, in particular up to atmospheric pressure.

The present invention solves these problems and proposes a device for detecting the loss of vacuum in a vacuum interrupter to obtain a reliable indication and maintained over the entire pressure range from about 10 ^-2 mbar to Patm, by the method of measuring electric discharges, without removing the vacuum cut-off device from the electrical network, as well as a vacuum breaking device comprising such a device.

SUMMARY OF THE INVENTION

For this purpose, the subject of the present invention is a device for detecting the loss of vacuum in a vacuum interrupter of the kind mentioned above, this device being characterized in that it comprises in combination so-called first means for increasing the field between the electrodes and the aforementioned floating potential screen, and so-called second means for increasing the capacitive coupling between the aforementioned screen and the mass, these two means cooperating so that the ionization threshold of the air is exceeded at atmospheric pressure so that the electric discharges continue even after the rise of the pressure at atmospheric pressure.

According to a particular embodiment, the so-called first means for increasing the electric field between the floating potential screen and the electrodes are supported at least partially by said screen.

According to one particular characteristic, the so-called first means comprise specific shapes provided on the floating potential screen and / or on an additional conductive screen located opposite said floating potential screen, said additional conductive screen being mounted around one of the electrodes to which it is electrically connected so as to be at the same electrical potential.

According to a particular characteristic, this additional conductive screen is a bellow protector screen or an insulating shield of the bulb, brought to the mains voltage.

According to another characteristic, the distance between the above-mentioned additional conductive screen and the floating potential screen is a few millimeters and / or aggressive forms are provided on the additional conductive screen and / or on the floating potential screen.

According to another characteristic, the so-called first means are positioned in the bulb on the side of the bulb remaining energized when the bulb is open or on both sides.

According to another feature, this floating potential screen comprises a cylindrical conductive strip pressed against the inner face of the insulating portion of the envelope, an elastic split metal ring or a layer of conductive material deposited on this inner face.

According to another characteristic, the so-called second means for increasing the capacitive coupling between the aforementioned screen and the mass, consist in that the bulb is of the type embedded in a shielded or screened solid insulation covered with a conductive layer connected to the potential of the mass.

According to another characteristic, the aforementioned floating potential screen has a T shape with a tip oriented towards the additional conductive screen, and a bar oriented towards the ground in order to increase the surface and therefore the capacity of that side. .

According to another characteristic, the value of the aforementioned electric field is increased so as to reach a value of 3kV / mm under the effect of the operating voltage, this value being greater than the threshold of ionization of the air at Patm.

According to another characteristic, these means said first are located in an electrically closed area of the bulb so that the discharges that occur there are not likely to propagate to the inter-contact space or along the insulator of the bulb during dielectric tests.

According to another characteristic, these so-called first means are located in an additional volume of the bulb dedicated to the detection of discharges, this volume being added to one of the ends of the bulb, and communicating with the main volume of the bulb by at least one orifice provided in the partition wall of the two volumes of the bulb.

According to another characteristic, the bulb comprises an additional insulator dedicated to this additional volume or a single insulator extended to cover the aforementioned additional zone of the bulb.

According to another characteristic, the detection of discharges is carried out by capacitive detection of discharges or by detection of the electromagnetic waves produced by means of a radio antenna.

The subject of the present invention is also a medium-voltage electrical breaking device comprising a device for detecting discharges. having the above mentioned features taken alone or in combination.

• La figure 1 est une courbe illustrant la loi de Paschen, et représentant en ordonnée la tension critique appliquée entre deux électrodes distantes de 1 cm, à partir de laquelle le courant électrique se décharge dans le gaz en fonction de la pression en abscisse dans un interrupteur à vide.
• Les figures 2,3 et 4 sont des vues en coupe longitudinale, illustrant respectivement trois réalisations différentes d'un pôle d'appareil de coupure dans le vide selon l'invention.

But other advantages and features of the invention will become more apparent in the detailed description which follows and refers to the accompanying drawings given solely by way of example and in which:

• The figure 1 is a curve illustrating Paschen's law, and representing on the ordinate the critical voltage applied between two electrodes 1 cm apart, from which the electric current discharges into the gas as a function of the abscissa pressure in a vacuum interrupter.
• The figures 2 , 3 and 4 are views in longitudinal section, respectively illustrating three different embodiments of a vacuum breaking apparatus pole according to the invention.

On the figures 2 , 3 and 4 , a pole I of vacuum interrupter comprising a vacuum interrupter and its coating, said bulb commonly comprising for the three embodiments, and in a manner known per se, an envelope E of substantially cylindrical form closed by two funds 1,2. The envelope encloses a fixed electrode 3 with respect to said envelope, and a movable electrode 4 with respect to said envelope, the two electrodes each supporting at their free end respectively a fixed contact 5 and a movable contact 6, said mobile electrode being mobile between a contact position of the two contacts and a position separated from the two contacts. The casing comprises a cylindrical portion 7 made of ceramic closed by two end covers 8,9 crossed respectively by the two aforementioned electrodes 3,4. The bulb also comprises two additional conductive screens 12, 13 electrically connected for one, to the mobile electrode 4, and for the other, to the fixed electrode 3.

The ceramic portion of the envelope E is embedded in a solid insulation 14 (typically epoxy resin) screened, covered with a conductive layer 15 connected to the potential of the mass.

The metallized outer surface of this pole is connected to the mass M by means of a so-called measuring capacitance, not shown, belonging to a circuit for measuring the potential difference between the aforementioned electrodes and a so-called floating screen placed between the one of the electrodes and the mass.

Thus, when a loss of vacuum occurs inside the bulb A, the dielectric strength between the moving electrode 4 and the ceramic part E is reduced, and it is possible to measure a decrease in the difference in potential between the electrodes 3,4 and the floating screen 16. For example, this reduction can be measured by increasing the capacitive current passing through the above-mentioned measurement capacitance.

On the figure 1 , the curve represents the so-called critical electrical voltage as a function of the pressure in the switch. This curve describes the principle that there is always a critical electrical voltage for a certain distance between the electrodes at a given pressure, allowing the electric current to discharge into the gas.

This electrical voltage for a certain distance corresponds to the minimum disruptive field, (valid only for the right branch of the Paschen curve), which is a voltage per unit length (V / m), which in this case is typically expressed in kV. / mm).

On the curve represented on the figure 1 this voltage corresponds to Ds. And it is seen that for a pressure of between 10 Pa and about 10 ⁴ Pa, that is to say between 10 ^-4 bar and 10 ^-1 bar, the electric current is discharged into the gas from a potential difference equal to Up between the electrodes and the floating potential screen, the value of Ds less than Up being degressive and progressive between these two values.

It can thus be seen that at a pressure value corresponding to the atmospheric pressure (10 ⁵ Pa = 1 bar), electric discharges do not occur more for the voltage Up, and that because of this, the information of the existence of the defect is transient.

According to the invention, this problem is solved by increasing (widening) the pressure range within which the electric discharges are likely to occur, so that this interval reaches the value of the atmospheric pressure. This is done by increasing the value of the electric field between the electrodes (contacts) 3,4 and the floating potential screen 16, when these electrodes are at the mains voltage. So, the figure 1 shows that when moving from the field corresponding to the voltage Up to a field corresponding to the voltage UHP, the pressure interval allowing the detection of discharges increases, and reaches the value of the atmospheric pressure, so as to allow the detection of discharges to this value of atmospheric pressure.

For this purpose, the present invention uses specific forms of conductive screens of the electrode 4 or floating screen to increase the electric field between the conductors and the floating screen under the influence of a potential of the mass close to the screen, the switch being covered with shielded solid insulation.

These electrodes and screens are thus intended solely for the detection of the loss of vacuum and make it possible to obtain a sufficient electric field between the electrodes and the screen so that the ionization threshold of the air is exceeded at atmospheric pressure and that discharges occur even after a rise in pressure to atmospheric pressure.

According to the particular embodiment of the invention illustrated on the figure 2 , this vacuum switch comprises, on the mobile contact 6 side, a floating screen 16, this screen being formed by a cylindrical conductive strip pressed against the inner face of the insulating portion of the envelope E and located opposite this strip , a tip 17 projecting from the outer surface of an additional conductive screen 13 surrounding the movable electrode 4 and at the same potential as this electrode.

Thus, the floating potential screen 16 faces an assembly comprising a central electrode 4 and an additional conductive screen 13 brought to the mains voltage.

In order for the electric field between the two electrodes 4, 16 to reach the sufficiently high value of 3 kV / mm below the operating voltage, the distance between the conductive screen 13 and the floating potential screen 16 must be relatively small, advantageously a few millimeters, or aggressive forms may be provided on the screen 16 or the additional screen 13, such as the tip 17 illustrated on this figure 2 .

In another embodiment, this aggressive form could consist of the edge of one or more thin disks provided on the conductive screen or the floating screen.

Thus, it is necessary between the additional conductive screen 13 and the floating potential screen 16 that the electric field must be strong for this to continue to discharge at atmospheric pressure.

According to another embodiment of the invention illustrated on the figure 3 , the switch comprises a floating screen 16a in the form of a conductive strip as in the previous embodiment, this strip being placed this time opposite the other electrode 3 associated with the fixed contact 5. The risk associated with the presence of this additional electrode and the local reinforcement of the electric field in the bulb A which is associated with it is a decrease in the performance of holding of the bulb during dielectric tests.

This risk is zero if the tests are carried out with the bulb in the closed position, because even in the event of a partial breakdown between the central electrode and the band plated on the ceramic, the combined thickness of ceramic and solid outer insulation is sufficient to prevent perforation between the sensor electrode 16a and the mass 15.

When the bulb is tested in the open position, in the event of a partial breakdown between the live central electrode and the floating potential electrode, the risk that the electrode acts as a relay and that the breakdown evolves crossing the input-output of the bulb should be considered.

To minimize it, one can consider either to have the floating screens (16, 16a, 16b) sufficiently far from the median ends of the screens interior of the bulb, either to accommodate the metal strip set back in the thickness of the ceramic, or to work the shapes of the ends of the strips in a manner similar to those of the additional conductive screen12.

If these provisions (possibly combined) allow to preserve the dielectric strength of the bulbs, we can add additional electrodes without questioning the normal architecture of the bulbs, as shown on the figures 2 and 3 .

It should be noted that the position of the sensor will advantageously correspond to the side of the bulb remaining energized when the bulb is open (most often the side of the busbar). When the bulb is closed, which corresponds to the most frequent situation in service, the position of the sensor is of course indifferent.

If it proves difficult to maintain the dielectric strength of a shielded coated bulb of conventional architecture after incorporating additional electrodes for the sensor function, a fallback solution is to add an additional portion to the bulb to accommodate the sensor function in an electric field configuration corresponding to that of the closed bulb, presenting no risk of propagation of a partial breakdown between the central electrode and the electrode of the sensor (or floating screen), the potential being the even on both sides of the conductive strip 16.

Such a solution is illustrated by the figure 4 , illustrating the position of the sensor 16b in an additional volume 18 communicating with the volume of the main vacuum 19 of the bulb A by an orifice provided in the metal wall separating the two volumes, this additional volume having been provided around the fixed contact. In this embodiment, an additional ceramic insulator 20 dedicated to the sensor function is used in addition to the main insulator 21, on which the sensor was placed in the two positions illustrated respectively on the figures 2 and 3 . It can be seen that the same principle can be applied by using only one extended insulator to cover the area of the additional volume 18.

In this case, the wall separating the "sensor" and "cutoff" zones would not extend to the ceramic, but would support the screen 22 protecting the interrupting chamber, leaving a small gap between the ceramic and the screen. In the latter case, even if the volume appears less "closed", the field configuration is equivalent, and the risk of propagation of a partial breakdown is discarded.

The principle of this fallback solution is therefore to provide an additional slice of the bulb, dedicated to the vacuum loss sensor function, in which the configuration of the central electrode 23 (or conductive screen) facing the screen 16b of the sensor is U-shaped. This screen consists of all the live conductors of the network facing the sensor 16b in the volume 18, that is to say the old end cap 8, the electrode 3 and the new end cap 8a, the surface of these three parts having a U-shaped configuration. This U-shaped configuration therefore creates an electric field of substantially radial orientation with respect to the cylindrical mass which surrounds, and the floating electrode of the sensor, said floating screen interposed between the conductive screen and the cylindrical mass. It will be noted that this U-shaped compartment can be provided both on the fixed contact side (shown on the figure 4 ) that mobile contact side of the bulb.

This increase in length of the envelope of the bulb does not necessarily require an extension of the main circuit but results in an increase in the bulb due to the elongation of the ceramic insulator and the addition of the electrodes. U specific. This solution should therefore be considered only if it is not possible to operate satisfactorily the sensor in one or the other of the two positions illustrated in FIGS. figures 2 and 3 .

Finally, the detection of partial discharges occurring between the floating screen 16 of the sensor and the live operating conductors (if the vacuum is degraded) can be done either by the emitted electromagnetic disturbances, as described in the patent mentioned at the beginning, or more simply by capacitive coupling with the electrode of the sensor. This capacitive coupling is easily achievable in the case of a bulb embedded in a solid insulation screened using a dedicated area of the screen 15, facing the internal electrode of the sensor and connected to the rest of the screen and to ground by the measurement capability of the discharge detection circuit.

A device has thus been achieved thanks to the invention making it possible to obtain a reliable fault indication maintained over an entire pressure range ranging from 10 ^-2 mbar to atmospheric pressure by the discharge method.

For this, it is used that the capacitive coupling between a floating potential screen and the mass is greatly increased when the bulb is coated with solid insulation covered with a conductive layer grounded, allowing increase the voltage difference applied between the electrodes under the operating voltage and the screen. In addition, specific screens are therefore used solely for the detection of loss of vacuum, which make it possible to obtain a sufficient electric field between the electrodes (contacts) and these screens so that the ionization threshold of the air is exceeded at the atmospheric pressure and the discharges continue even after a rise in pressure at atmospheric pressure.

As the existence of these high electric fields in the bulb, could affect the dielectric strength between the entry and the exit of the bulb, various provisions are envisaged to avoid this loss of performance, of which one presenting a great It is efficient to locate these screens in an electrically closed area of the bulb, so that the discharges that will occur there are not likely to propagate to the inter-contact space or along the ceramic insulator.

Of course, the invention is not limited to the embodiments described and illustrated which have been given by way of example.

On the contrary, the invention comprises all the technical equivalents of the means described and their combinations if they are carried out according to its spirit.

Claims (15)

Device for detecting the loss of vacuum in a vacuum interrupter of a vacuum interrupter, said switching device being located in a powered primary electrical network and the contacts of said bulb being housed in a closed envelope by two bottoms housing a fixed electrode integral with one of the aforementioned bottoms and supporting a fixed contact, and a movable electrode supporting a movable contact, said movable electrode being slidably mounted through the other of the two bottoms, between a closed position of the apparatus in which the movable contact is in contact with the fixed contact and an open position of the apparatus in which the movable contact is separated from the fixed contact, this detection being carried out by the method of measuring the electric discharges between the contacts and at least a floating potential conductive screen respectively surrounding at least one electrode and electrically connected to the ground,
characterized in that it comprises in combination, so-called first means, for increasing the electric field between the electrodes (3,4) and the above-mentioned floating potential screen (16,16a, 16b), and so-called second means, to increase the capacitive coupling between the aforementioned screen (16, 16a, 16b) and the mass M, these two means cooperating so that the threshold of ionization of the air is exceeded at atmospheric pressure so that the electric discharges are continue even after the rise of pressure to atmospheric pressure. Detection device according to claim 1, characterized in that the means said first to increase the electric field between the floating potential screen (16,16a, 16b) and the electrodes (3,4) are supported at least partially by said screen (16). Detection device according to claim 1 or 2, characterized in that said means comprise the first aggressive forms provided on the floating potential screen (16,16a, 16b) and / or on an additional screen conductor (12,13) located opposite said floating potential screen, said additional screen being mounted around one of the electrodes to which it is electrically connected so as to be at the same electrical potential. Detection device according to claim 3, characterized in that said additional conductive screen is a bellows shield (13) or an insulating shield of the bulb (12), brought to the mains voltage. Detection device according to claim 3 or 4, characterized in that the distance between said additional conductive screen (12,13) and the floating potential screen (16,16a, 16b) is a few millimeters and / or Aggressive forms (17) are provided on the additional screen (12,13) and / or on the floating potential screen (16, 16a, 16b). Detection device according to any one of claims 1 to 5, characterized in that said first means are positioned in the bulb A on the side of the bulb remaining energized when the bulb is open, or on both sides . Detection device according to any one of claims 1 to 6, characterized in that said floating potential screen (16, 16a, 16b) comprises a cylindrical conductive strip pressed against the internal face of an insulating part of the envelope, an elastic split metal ring or a layer of conductive material deposited on this inner face. Detection device according to any one of the preceding claims, characterized in that the means said second for increasing the capacitive coupling between the aforementioned screen (16,16a, 16b) and the mass M, consist in that the bulb is of the type embedded in a shielded or screened solid insulation (14) covered with a conductive layer (15) connected to the potential of the ground M. Detection device according to one of Claims 3 to 8, characterized in that the aforementioned floating potential screen (16, 16a, 16b) has a T-shape with a tip directed towards the additional conductive screen (12, 13), and a bar oriented towards the mass M in order to increase the surface and thus the capacity on that side. Detection device according to any one of the preceding claims, characterized in that the value of the aforementioned electric field is 3kV / mm under the effect of the operating voltage. Detection device according to any one of the preceding claims, characterized in that said means said first are located in an electrically closed area (18) of the bulb A so that the discharges that occur there are not likely to spread in an inter-contact space or along an insulator of the bulb during dielectric tests. Detection device according to claim 11, characterized in that said means said first are located in an additional volume (18) of the bulb dedicated to the detection of discharges, this volume being added to one end of the bulb , and communicating with the main volume (19) of the bulb by at least one orifice provided in the partition wall of the two volumes of the bulb. Detection device according to claim 12, characterized in that the bulb comprises an additional insulator (20) dedicated to this additional volume (18) or a single insulator extended to cover the aforementioned additional zone of the bulb A. Detection device according to any one of the preceding claims, characterized in that the detection of discharges is carried out by capacitive detection of discharges or by detection of the electromagnetic waves produced by means of a radio antenna. A medium-voltage vacuum electrical breaking apparatus having a discharge detection device according to any one of the preceding claims.

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