EP3327744B1 - Device for detecting loss of vacuum in a vacuum bulb and vacuum-based cutoff apparatus comprising such a device - Google Patents

Description

TECHNICAL AREA

The present invention thus relates to a device for detecting the loss of vacuum in a vacuum interrupter of a vacuum interrupting device, said interrupting device being located in a powered primary electrical network and the contacts of the interrupter being housed in an envelope, said envelope housing a fixed electrode secured to one of the aforementioned funds and supporting a fixed contact, and a mobile electrode supporting a mobile contact, said mobile electrode being slidably mounted across the other of the two funds, between a position closed position of the device in which the moving contact is in contact with the fixed contact and an open position of the device in which the moving contact is separated from the fixed contact, this detection being carried out by the method of measuring the electrical discharges between the contacts and at least one conductive screen with floating potential respectively surrounding at least one electrode and electrically connected to ground.

STATE OF PRIOR ART

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

Another way of detecting the reduction in the dielectric properties of the vacuum when the pressure exceeds 10 ^-2 mbar consists of detecting the discharges which occur between, on the one hand, the electrodes (fixed and mobile contacts) brought to the operating voltage and 'on the other hand, a potential screen floating which surrounds them, by measuring the potential difference existing 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 ground via the capacitance of the discharge detection circuit, by measuring the increase in the potential difference between the floating screen and the ground, 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 stop when the bulb is raised to atmospheric pressure (Patm), due to the insulating properties of air at 1 bar and the design rules for bulbs to guarantee satisfactory dielectric strength during vacuum type tests between the electrodes and the screen.

In typical configurations of air-insulated vacuum switchgear, 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 ground surrounding. The discharges are therefore likely to occur transiently, during the passage through the trough of the Paschen curve under the effect of a leak, and to be interrupted when the air pressure has risen sufficiently in the bulb. In the case of a sudden rise to atmospheric pressure (rapid leak due for example to sudden cracking of a ceramic, a bellows, etc.), the indication given by the loss of vacuum indicator therefore risks being only transitory and brief, which leads to a difficulty of interpretation and the need to reliably memorize the passage through the trough of the Paschen curve in order to warn the operator of the fact that a bulb whose pressure has risen to atmospheric pressure is in a fault situation.

It is therefore preferable that the detector continues to indicate a permanent fault in the bulb when it has risen to atmospheric pressure.

The document EP 1763049 describes the fact that the capacitive coupling between the floating potential screen and ground is greatly increased when the bulb is coated with solid insulation covered with a grounded conductive layer. 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.

We also know the document US 5 399973 describing a principle for increasing the pressure interval within which detection of loss of vacuum is possible (by lowering the minimum pressure value at which discharges appear) via a projecting member provided either on the outer surface screens, or on the interior surface of the envelope. However, this principle does not make it possible to greatly increase the sensitivity of 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 making it possible to obtain a reliable and maintained indication over the entire pressure range going from approximately 10 ^-2 mbar to Patm, by method of measuring electric discharges, without removing the vacuum breaking device from the electrical network, as well as a vacuum breaking device comprising such a device.

STATEMENT OF THE INVENTION

To this end, the subject of the present invention is a device for detecting the loss of vacuum in a vacuum interrupter according to claim 1.

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 a 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 electric potential.

According to a particular characteristic, this additional conductive screen is a bellows protection screen or a bulb insulating protection screen, brought to the network voltage.

According to another characteristic, the distance between the aforementioned additional conductive screen and the floating potential screen is a few millimeters and/or aggressive shapes 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 characteristic, this floating potential screen comprising a cylindrical conductive strip pressed against the internal face of the insulating part of the envelope can be an elastic split metal ring or a layer of conductive material deposited on this internal face.

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

According to another characteristic, the aforementioned floating potential screen has a T shape comprising a point oriented towards the additional conductive screen, and a bar oriented towards the mass in order to increase the surface and therefore the capacity on 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 ionization threshold of the air at Patm.

According to another characteristic, these so-called primary means are located in an electrically closed zone of the bulb so that the discharges which occur there do not risk propagating to the inter-contact space or along the insulator of the bulb during dielectric tests.

According to another characteristic, these so-called primary 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. bulb through at least one orifice provided in the wall separating the two volumes of the bulb.

According to another characteristic, the bulb includes 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 electromagnetic waves produced by means of a radio antenna.

The present invention also relates to a medium voltage vacuum electrical cut-off device comprising a discharge detection device comprising the previously mentioned characteristics 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 characteristics of the invention will appear better in the detailed description which follows and refers to the appended drawings given solely by way of example and in which:

• There 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 pressure on the abscissa in a vacuum switch.
• THE figure 2 , 3 And 4 are views in longitudinal section, respectively illustrating three different embodiments of a pole of a vacuum breaking device according to the invention.

On the figure 2 , 3 And 4 , we see a pole I of a 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 shape closed by two funds 1,2. The envelope contains a fixed electrode 3 relative to said envelope, and a movable electrode 4 relative to said envelope, the two electrodes each supporting at their free end respectively a fixed contact 5 and a movable contact 6, said movable electrode being movable between a contact position of the two contacts and a separate position of the two contacts. The envelope comprises a cylindrical part 7 made of ceramic closed by two end covers 8.9 crossed respectively by the two aforementioned electrodes 3.4. The bulb also includes two additional conductive screens 12,13 electrically connected, one to the mobile electrode 4, and the other to the fixed electrode 3.

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

The metallized exterior surface of this pole is connected to the mass M via a so-called measuring capacitor 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 ground.

Thus, when a loss of vacuum occurs inside the bulb A, the dielectric strength between the mobile electrode 4 and the ceramic part E is reduced, and a reduction in the difference in temperature can be measured. potential between the electrodes 3,4 and the floating screen 16. For example, this reduction can be measured by the increase in the capacitive current passing through the aforementioned measuring 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 electrical 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 an electrical voltage per unit of length (V/m) expressed in this case classically in kV /mm).

On the curve shown on the figure 1 , this voltage corresponds to Ds. And we see that for a pressure between 10 Pa and approximately 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 decreasing then progressive between these two values.

We thus see that at a pressure value corresponding to atmospheric pressure (10 ⁵ Pa = 1 bar), electric discharges do not occur. more for the Up voltage, and as a result, the information of the existence of the fault is transient.

According to the invention, this problem is solved by increasing (widening) the pressure interval within which electrical discharges are likely to occur, so that this interval reaches the value of atmospheric pressure. This is achieved 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 network voltage. Thus, the figure 1 shows that when we go from the field corresponding to the Up voltage to a field corresponding to the UHP voltage, the pressure interval allowing the detection of discharges increases, and reaches the value of atmospheric pressure, so as to allow the detection of discharges. discharges up to this atmospheric pressure value.

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

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

According to the particular embodiment of the invention illustrated on the figure 2 , this vacuum switch comprises, on the side of the movable contact 6, a floating screen 16, this screen being formed by a cylindrical conductive strip pressed against the internal face of the insulating part of the envelope E and, located opposite this strip , a tip 17 projecting from the exterior surface of an additional conductive screen 13 surrounding the mobile 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 network voltage.

For the electric field between the two electrodes 4.16 to reach the sufficiently high value of 3 kV/mm under the operating voltage, the distance between the conductive screen 13 and the floating potential screen 16 must be relatively reduced, advantageously of a few millimeters, or else aggressive shapes can be provided on the screen 16 or the additional screen 13, such as the tip 17 illustrated on this figure 2 .

According to another embodiment, this aggressive shape could consist of the edge of one or more thin discs provided on the conductive screen or the floating screen.

Thus, it is between the additional conductive screen 13 and the floating potential screen 16 that the electric field must be strong so that it continues 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 such as in the previous embodiment, this strip being placed this time opposite the other electrode 3 associated with the fixed contact 5. The risk linked to the presence of this additional electrode and the local strengthening of the electric field in the bulb A which is associated with it is a reduction in the resistance performance 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 strip plated on the ceramic, the combined thickness of ceramic and solid external insulation is sufficient to prevent perforation between the electrode 16a of the sensor 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 plays a relay role and that the breakdown progresses crossing the entrance-exit of the bulb must be considered.

To minimize it, we can consider either arranging the floating screens (16,16a,16b) sufficiently far from the middle ends of the screens interiors of the bulb, either to accommodate the metal strip recessed in the thickness of the ceramic, or to work the end shapes of the strips in a manner similar to those of the additional conductive screen12.

If these arrangements (possibly combined) make it possible to preserve the dielectric strength of the bulbs, additional electrodes can therefore be added without calling into question the normal architecture of the bulbs, as illustrated on the figure 2 And 3 .

Note 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 irrelevant.

If it proves difficult to maintain the dielectric strength of a screened coated bulb of conventional architecture after incorporating additional electrodes for the sensor function, a fallback solution is to add an additional part 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 sensor electrode (or floating screen), the potential being the even on either side 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 through 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 figure 2 And 3 . We see 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 as far as the ceramic, but would support the screen 22 protecting the cutoff chamber, leaving a reduced interval 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 avoided.

The principle of this fallback solution is therefore to provide an additional section 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 floating 16b of the sensor is U-shaped. This screen is constituted by all the live conductors of the network facing the sensor 16b in the volume 18, that is to say the old end cover 8, the electrode 3 and the new end cover 8a, the surface of these three parts having a U-shaped configuration. This U-shaped configuration therefore creates an electric field of essentially radial orientation relative to the cylindrical mass which surrounds, and to the floating electrode of the sensor, called floating screen, interposed between the conductive screen and this cylindrical mass. Note that this U-shaped compartment can be provided both on the fixed contact side (shown on the figure 4 ) than the moving 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 cost of the bulb due to the lengthening of the ceramic insulator and the addition of the electrodes in U specific. This solution should therefore only be considered if it is not possible to operate the sensor satisfactorily in either of the two positions illustrated on the figure 2 And 3 .

Finally, the detection of partial discharges occurring between the floating screen 16 of the sensor and the conductors under operating voltage (if the vacuum is degraded) can be done either by the electromagnetic disturbances emitted, as described in the patent mentioned at the beginning, or more simply by capacitive coupling with the sensor electrode. This capacitive coupling is easily achievable in the case of a bulb coated in screened solid insulation 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 measuring capacitance of the discharge detection circuit. We have therefore produced, thanks to the invention, a device making it possible to obtain a reliable fault indication and maintained over an entire pressure range going from 10 ^-2 mbar to atmospheric pressure by the discharge method.

For this, we use the fact that the capacitive coupling between a floating potential screen and the ground is greatly increased when the bulb is coated with solid insulation covered with a grounded conductive layer, which allows 'increase the difference in voltage applied between, on the one hand, the electrodes under the operating voltage and on the other hand, the screen. We therefore also use specific screens intended only 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 air ionization threshold is exceeded at atmospheric pressure and that the discharges continue even after the pressure rises to atmospheric pressure.

As the existence of these high electric fields in the bulb could harm the dielectric strength between the input and output of the bulb, various arrangements are considered to avoid this loss of performance, one of which presents a large effectiveness is to locate these screens in an electrically closed zone of the bulb, so that the discharges which 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 only been given by way of example.

Claims (15)

1. Device for detecting the loss of vacuum in a vacuum interrupter A of a vacuum switching device, said switching device being situated in a powered electrical primary network and the contacts (5, 6) of said interrupter A being housed in a jacket E closed by two end plates housing a fixed electrode (3) secured to one of the abovementioned end plates and supporting a fixed contact (5), and a movable electrode (4) supporting a movable contact (6), said movable electrode (4) being slidingly mounted through the other of the two end plates, between a closed position of the device in which the movable contact (6) is in contact with the fixed contact (5) and an open position of the device in which the movable contact (6) is separated from the fixed contact (5), this detection being made by the method of measuring electrical discharges between the contacts and at least one floating-potential conductive screen (16) respectively surrounding at least one electrode (3, 4),

   this device comprising in combination, so-called first means, for increasing the electrical field between the electrodes (3, 4) and the abovementioned floating-potential screen (16, 16a, 16b), and so-called second means, for increasing the capacitive coupling between the abovementioned screen (16, 16a, 16b) and the ground M,

   characterized in that the floating-potential screen (16, 16a, 16b) comprises a cylindrical conductive strip pressed against the inner face of an insulating part of the jacket, separating said screen from the ground,

   and in that the first means and the second means cooperate so that the ionization threshold of the air is exceeded at atmospheric pressure in order for the electrical discharges to continue even after the pressure has risen back to atmospheric pressure.
2. Detection device according to Claim 1, characterized in that the so-called first means for increasing the electrical field between the floating-potential screen (16, 16a, 16b) and the electrodes (3, 4) are supported at least partially by said screen (16).
3. Detection device according to Claim 1 or 2, characterized in that the so-called first means comprise aggressive forms provided on the floating-potential screen (16, 16a, 16b) and/or on a conductive additional screen (12, 13) situated opposite said floating-potential screen, said additional screen being mounted around the one of the electrodes to which it is electrically linked so as to be at the same electrical potential.
4. Detection device according to Claim 3, characterized in that the so-called first means comprise aggressive forms provided on a conductive additional screen (12, 13), and in that this conductive additional screen is a bellows protection screen (13) or an interrupter insulation protection screen (12), brought to the voltage of the network.
5. Detection device according to Claim 3 or 4, characterized in that the so-called first means comprise aggressive forms provided on a conductive additional screen (12, 13), and in that the distance between the abovementioned conductive additional screen (12, 13) and the floating-potential screen (16, 16a, 16b) is a few millimetres and/or aggressive forms (17) are provided on the additional screen (12, 13) and/or on the floating-potential screen (16, 16a, 16b).
6. Detection device according to any one of Claims 1 to 5, characterized in that the so-called first means are positioned in the interrupter A on the side of the interrupter that is still live when the interrupter is opened, or else on both sides.
7. Detection device according to any one of Claims 1 to 6, characterized in that this floating-potential screen (16, 16a, 16b) comprising a cylindrical conductive strip pressed against the inner face of an insulating part of the jacket can be an elastic slit metal ring or else a layer of conductive material deposited on this inner face.
8. Detection device according to any one of the preceding claims, characterized in that the so-called second means for increasing the capacitive coupling between the abovementioned screen (16, 16a, 16b) and the ground M, consist in that the interrupter is of the type coated in a shielded or screened solid insulation (14) covered with a conductive layer (15) linked to the potential of the ground M.
9. Detection device according to any one of Claims 3 to 8, characterized in that the abovementioned floating-potential screen (16, 16a, 16b) has a T-shape comprising a point oriented towards the additional conductive screen (12, 13), and a bar oriented towards the ground M in order to increase the surface area and therefore the capacitance on that side.
10. Detection device according to any one of the preceding claims, characterized in that the value of the abovementioned electrical field is 3kV/mm under the effect of the service voltage.
11. Detection device according to any one of the preceding claims, characterized in that these so-called first means are located in a closed zone of the interrupter A in order that the discharges which occur therein do not risk being propagated in an inter-contact space or along an insulator of the interrupter in dielectric tests.
12. Detection device according to Claim 11, characterized in that these so-called first means are located in an additional volume (18) of the interrupter dedicated to the detection of the discharges, this volume being added to one of the ends of the interrupter, and communicating with the main volume (19) of the interrupter by at least one orifice provided in the wall separating the two volumes of the interrupter.
13. Detection device according to Claim 12, characterized in that the interrupter comprises an additional insulator (20) dedicated to this additional volume (18) or else a single insulator extended to cover the abovementioned additional zone of the interrupter A.
14. Detection device according to any one of the preceding claims, characterized in that the detection of the discharges is made by capacitive detection of the discharges or else by detection of the electromagnetic waves produced by means of a radio antenna.
15. Medium-voltage vacuum electrical switching device comprising a device for detecting discharges according to any one of the preceding claims.

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