WO2009130290A1

WO2009130290A1 - Device and method for quick defect detection using a quick pressure sensor-recorder

Info

Publication number: WO2009130290A1
Application number: PCT/EP2009/054915
Authority: WO
Inventors: Patrice Juge; Claude Fournet
Original assignee: Areva T&D Sa
Priority date: 2008-04-25
Filing date: 2009-04-23
Publication date: 2009-10-29

Abstract

The invention relates to a pressure probe that can be positioned on the metal casing of an HV device and that comprises a probe body (150, 152) containing: pressure or pressure-variation detecting means (110) of the capacitive type; means (113) for contacting said pressure or pressure-variation detecting means with an external atmosphere (P); digital data processing means (130) for processing data from the pressure or pressure-variation detecting means; electric insulation means (154, 156, 140) for insulating the pressure or pressure-variation detecting means and the data processing means from the probe body or casing (150, 152).

Description

DEVICE AND METHOD FOR QUICK DETECTION OF QUICK PRESSURE RECORDER SENSOR FAULT

DESCRIPTION

TECHNICAL FIELD AND PRIOR ART

The invention relates to the field of medium or high voltage equipment. In this type of equipment, faults can occur.

It relates more particularly to a method and a device for the detection of an electrical fault, and more specifically of an internal arc, in an electrical connection or in an electrical station, at medium or high voltage, in a metal envelope (also called PSEM or GIS) or in a gas-insulated line (also called LIG or GIL).

The detection of the internal fault arc (unlike a cut-off arc) inside high voltage equipment is necessary for safety, maintenance and operation.

Other types of defects may require characterization, for example an external shock on the envelope of the high-voltage equipment, or a large leakage of insulating gas under pressure, or an expansion of the envelope.

A detection method based on pressure waves is known from document FR 2 773 420.

In practical terms, the known solutions use analog pressure sensors or optical sensors individually connected to acquisition units able to process simultaneously the information of all sensors. This leads to the use of overpowering acquisition units of a very high cost.

Various disadvantages are inherent in the implementation of the optical method: the defects are fugitive, there is no signal memory and this method also requires additional sensors and judiciously placed in the installation to monitor, it therefore results in a very high cost. More specifically, the principle of optical detection has limitations. A considerable part of HV equipment defects occur during the operation of the devices. On the basis of light, detection can be fast. But, this information is fleeting. Since the HV devices generate light during the maneuvers because of the cut arcs (which are not fault arcs), the arc detection system must be hidden.

The detection time of such a system is generally short (less than 20 ms), except when operating devices where it is blind. Another disadvantage is the difficulty of crossing insulators or active parts or elbows HT material that can lead to shadows. Since it is not easy to lay optical fibers (which are usually used to bring back the light emitted by the arc at the acquisition unit) over long distances and under difficult environmental conditions. To be exact the GIS are most often in building, by cons the GIL are outside. However, even in building, placing optical fibers between GIS equipment and cabinets containing the acquisition system is not easy because the journey is tortuous. This technique is also unsuitable for measurements on busbars or LIGs of several tens of meters to several hundred meters.

The parallel architecture of the light sensors leads to a multiplication of the number of optical cables and acquisition units with many inputs and therefore at low costs.

On the other hand, the optical sensors being inert (it is a simple optical conductor 5 to 10mm in section, extending the fiber inside the compartment and ending in a light collector), the light does not can be amplified. This is problematic because of the attenuation of the light signal inside the optical fibers. In addition, such a system is particularly exposed to fiber failures because of their number, their limited radius of curvature, and their exposure in the HV equipment maintenance areas. This is problematic because of the impossibility for the system to test itself. Therefore, close and complicated maintenance campaigns should be planned because of the need to manually generate a light at the end of each fiber and to test the reaction of the acquisition unit, this having an impact on the continuity of operation of the line. In addition, this system is also expensive.

The internal arc recognition based on the use of analog sensors is, in turn, not satisfactory, because the analog measurements are sensitive to the electromagnetic disturbances generated by the HV devices, and in particular those emitted by the internal arc itself. -even. The electromagnetic disturbances emitted during an internal arc result in the circulation of currents flowing in the envelopes of the high-voltage devices and in the earth circuits, but also in the screens of the sensor cables. These currents transmit by coupling disturbances on the wires of the cable. In the case of analog communication sensors, the measurement is disturbed.

There is therefore the problem of finding a new method and a new device making it possible to carry out fault identifications more effectively than by currently known techniques. In particular, faster identification of a defect and faster intervention following this identification is desirable. Preferably such a novel method or device is adaptable to the identification of various types of defects.

Another problem is the parasitic currents that occur in a metal casing of a device of the type indicated above.

(eg PSEM or GIS or LIG or GIL) especially the problem of so-called return currents that disturb any measure that would identify a defect. SUMMARY OF THE INVENTION

The invention relates to a method for detecting a defect in a high voltage device, comprising a metal casing, at least one central conductor, a pressurized gas acting as a dielectric insulator, and a plurality of compartments through which this conductor passes, this process comprising the following steps:

- Have, in each compartment, a digital pressure sensor provided with means for sampling pressure data, and to identify pressure data characteristic of said defect,

transmitting the digital pressure data characteristic of said fault to data processing means.

These data processing means are preferably common to all the sensors.

According to the invention, the acquisition of measurement data, and their processing to identify the occurrence of a defect, are performed by own, associated and dedicated means for each sensor.

A pressure sensor according to the invention, provided with its processing means and storage means, can therefore permanently perform an analysis of the evolution of the pressure. This can be measured according to a fast observation cycle.

Due to the existence of several sensors, a parallel processing architecture is used, taking advantage of the processing or calculation means available in each sensor. The synthesis of the data thus obtained can be transmitted to an acquisition unit in a single communication frame, for example of a duration of the order of a few milliseconds, which will mainly depend on the communication speed of the sensor. Thus, a duration of less than 1 msec per sensor could be obtained in the context of the present invention.

The storage by each sensor of the pressure disturbance over a sliding time window makes it possible to carry out an analysis leading to a very reliable diagnosis of the presence of a defect, for example an internal arc.

The processing means of each sensor are able to self-diagnose the presence of a defect, and spontaneously warn the acquisition unit, which has to deal with only the alarm message of a single sensor. For this purpose, the processing means may comprise one or more algorithms embedded in each sensor. This results in a shorter diagnostic period than that obtained with the existing devices. The diagnostic time can be divided by a factor of about 50 to 15.

Digital pressure data in a sliding time window can be stored. According to one embodiment, a trace of the evolution of the pressure, over a certain time window, is stored in a memory, such as a rotating memory, which precedes the measurement instant. An analysis, using the data processing means associated locally with each sensor, enables it to detect almost instantaneously, or very quickly, the presence of an anomaly, for example an overpressure anomaly, such as that generated. by an internal arc.

The sensor is therefore capable of transmitting, in a single frame, an alarm message containing a summary of the recent evolution of the pressure values.

The sensor also has the capacity to transmit, for a detailed analysis by the acquisition unit, the measured unit values within a time window which is determined either by the acquisition unit. either by the sensor according to its own analysis.

The response time of each sensor is preferably less than 1.5 msec.

Each pressure sensor is preferably of capacity variation type or piezo-resistive cell type.

Pressure variation data characteristic of a defect can be identified by means of a calculation of pressure variation ΔP for a certain duration ΔT, (ΔP / ΔT), and / or with the aid of a frequency of pressure oscillations and / or measurement of peak to peak pressure amplitude and / or identification of a damped pressure wave and / or a persistent pressure gradient . The ratio ΔP / ΔT and / or the oscillation frequency of the pressure and / or the peak-to-peak amplitude and / or the shape of the pressure wave can be measured or identified at regular intervals. In the case of the detection of an arc, pressure variation data, characteristic of an arc, can be identified by means of a calculation of pressure variation ΔP for a certain duration

ΔT, ΔP / ΔT, which can be performed at regular intervals.

It may be interesting to measure in addition a temperature representative of the temperature of the metal casing.

The sensors and the processing unit can operate in autonomous mode, which enables the sensor to inform, in an immediate manner, the processing unit of the detection of a phenomenon.

But the sensor and the processing unit are preferably in a master-slave relationship, each sensor being able to transmit data or information only if it has received processing means a request for data or information transmission.

Preferably, each sensor can transmit data or information, after receiving a request for data transmission or information, for a predefined and limited time.

A method according to the invention may comprise, between step a) and step b), a step a ') of transmitting, to the data processing means, a fault appearance information. After step a '), an abnormality signal may be produced, for example by the data processing means.

This anomaly signal can be produced before step b).

Preferably, step b) is performed on request of the data processing means to the sensor having identified a defect.

The defect is for example the appearance of an internal arc, or an external shock on the envelope, or an insulating gas leak, or an expansion of the envelope.

It is also possible to reconfigure a sensor, programmed for example to identify arcs, to identify another type of defect, for example a dilation.

The invention also makes it possible to solve the problem related to the influence of electromagnetic disturbances on the measurements.

Thus, it may happen that information, for example transmitted in the form of a frame, is affected by a disturbance (for example a byte becomes unreadable), and in this case the information, for example the frame in the example. chosen, can be reissued.

This is especially the case for digital communication sensors, for which there are at least two pairs of wires. One of the two pairs is dedicated to the supply of the sensor (for example: 24VDC nominal supply voltage), the other being dedicated to the communication, for example in the form of frame exchange. A transmission control can be realized (often called CRC). In addition, thanks to the memory of the sensor, the data transmission can be delayed, especially after the electromagnetic disturbances have disappeared (so after the fault that caused the disturbances). This can be particularly applied in the case where all the measurement points are downloaded for a posterior human analysis, after the sensor has detected and reported a defect in near real time. The sensor supply leads can also restore disturbances to the sensor, which operates during the fault. This is why filters, preferably EMC, can be provided at the sensor input. Other characteristics can be implemented for this type of situation: for example, a sufficient reserve of energy can be provided in the event of a voltage dip and / or an extended voltage operating range.

The invention also relates to a device for detecting a fault in a high voltage device, comprising a metal casing, a central conductor and a plurality of compartments traversed by this conductor. This detection device comprises: a plurality of digital pressure sensors, each sensor being provided with means for sampling pressure data, and for identifying pressure data characteristic of a defect, means for transmitting pressure variation data characteristic of a fault to data processing means.

The invention also relates to a high voltage device, comprising a metal casing, at least one central conductor and a plurality of compartments traversed by this conductor, and a device according to the invention, in particular as explained above. The invention also relates to a high-voltage device, comprising a metal casing, at least one central conductor and a plurality of compartments traversed by this conductor, and digital pressure measuring sensors for implementing a method according to the invention, in particular as explained above.

In a device according to the invention, the data processing means may comprise a switching power regulator. A device according to the invention may further comprise means capable of measuring a temperature representative of the temperature of the metal casing.

Each pressure sensor may be of capacity variation type.

The sensors and the processing unit preferably operate in autonomous mode or are in a master-slave relationship, the sensors being able to transmit only if they have been invited by the processing unit. Each sensor can be positioned inside an envelope, in which the insulating gas under pressure enters through a conduit.

The invention also relates to a high-voltage device, comprising a metal casing, at least one central conductor and a plurality of compartments traversed by this conductor, and a device according to the invention, each sensor of the plurality of digital sensors being positioned in a compartments and connected to the data processing means.

In a device according to the invention, each sensor and the corresponding data processing means may be contained in a probe body to be positioned on the metal casing of an HT device.

The invention therefore also relates to a sensor or a probe, comprising a probe body, able to be positioned on the metal casing of an HT device, this body containing:

pressure-sensing or pressure-variation means, of the capacitive type,

means, for example an opening, for bringing these pressure detection or pressure variation means into contact with an external atmosphere,

data processing means, for processing data of the pressure detection or pressure variation means, electrical insulation means for isolating, with respect to the body or the envelope of the probe, the means for detecting pressure or pressure variation and the data processing means.

Such a probe structure makes it possible to avoid nuisances due to parasitic currents flowing in an envelope on which or against which the probe is installed or disposed, in particular the return currents.

Connector-type means may be provided for connecting the data processing means to, for example, a connection cable. Such a cable preferably comprises a set of son surrounded by a metal screen, the assembly being surrounded by an insulating sheath. Preferably, the connector-type means form an extension of the metallic screen of the cable.

The connector type means may be extended by at least one inner envelope which contains at least the pressure detection or pressure variation means and / or the data processing means.

Each of the pressure detection or pressure variation means and data processing means is preferably contained in a material or envelope of insulating material, for example ceramic. It is also possible to use a material of silicone or polyurethane type.

According to a preferred embodiment, such a device is of elongate shape, substantially axial symmetry. In a device according to the invention, the data processing means of a sensor can be made in the form of a printed circuit housed in the probe body.

The invention also relates to a high voltage device, comprising a metal casing, at least one central conductor and a plurality of compartments traversed by this conductor, and digital pressure measuring sensors for implementing a method according to the invention, according to the invention. any of the embodiments described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an embodiment, according to the invention, of a metallic envelope HT line provided with sensors.

FIG. 2 represents the time evolution of pressure data measured by a sensor according to the invention.

FIG. 3 represents an embodiment of a method according to the invention.

FIG. 4 represents a sensor that can be used in the context of the invention.

FIGS. 5A and 5B are diagrammatic representations, on the one hand of a sensor that can be used in the context of the invention and, on the other hand, of its equivalent circuit.

FIG. 6 is a schematic representation of a temperature probe that can be used in a sensor according to the invention. Figure 7 is a schematic representation of an electronic card that can be used in a sensor according to the invention.

FIGS. 8A to 8C and 9-11 show temporal evolutions of pressure data measured by a sensor according to the invention.

Figures 12A-12C show measurements made according to the invention.

- Figure 13 shows the structure of a cable implemented in the present invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

An exemplary implementation of the invention is illustrated in FIG.

The invention can be implemented in GIS or GIL architectures. Cutoff or isolation devices, such as one or more circuit breakers or disconnectors, can be integrated in this type of architecture.

The invention can also be implemented in an interrupting chamber, for example at SF6, an unshielded circuit breaker or in an unshielded disconnector.

FIG. 1 shows a GIS comprising a compartmentalized metal envelope 2 and a central conductor 4, isolated by a gas under pressure, for example nitrogen and / or sulfur hexafluoride SF.sub.6. The compartments are delimited by insulating supports 6, which, in addition, maintain the electrical conductor 4. The invention also applies to high voltage equipment three-phase, having three conductors 4 in the same envelope.

On each compartment is mounted a pressure sensor 10 (the individual sensors are designated Sl, S2, S3, ... S8 etc. ..).

The different sensors are connected to an acquisition unit 12 by a digital communication bus 14.

Such acquisition means 12 are for example microcomputer-type and comprise for example a central unit or a microprocessor, which will make it possible to carry out processing on the data received from the sensors, and to store said data as well as calculations made from of these data. A display unit makes it possible to display data, for example in the form of graphs such as those of FIGS. 12A-12C, or calculated data.

The means 12 may be programmed to implement the method steps described in the present application.

According to the invention, it is not process by successive requests on each sensor and sending all the data to the unit 12, which would introduce a cycle time incompatible with a fast sampling on each sensor. On the contrary, each sensor 10 comprises means for sampling, preferably at high speed, the signal.

Each sensor 10 further comprises storage means, for example a rotating memory, which can temporarily store at least a certain number of data which have been taken during a time interval ΔT, elapsed, preceding the time tO measurement (this is the interval [tO-ΔT, tO]). Such an interval is represented for example in FIG. 2, which gives the evolution of the pressure as a function of time, as measured by a sensor 10. The mean of the pressure in FIG. evolution phase. On the curve of Figure 2 is further shown a pressure jump ΔP, which corresponds to the variation between the initial pressure and the final pressure, as detected by the sensor.

Each sensor 10 further comprises, locally, data processing means for processing the data stored in the storage means.

From this sampling and processing, an anomaly can be qualified.

For example, an internal arc can be detected from a high frequency of the movements of the pressure generated in the gas, or from a significant peak-to-peak pressure difference. Pressure measurements during an electric arc in SF6 made it possible to characterize frequencies and amplitudes as well as attenuations during propagation in the gas. The frequencies are greater than those of a mechanical noise, thus making it possible to distinguish with the case of a mechanical noise. The measurement of a peak-to-peak pressure difference is particularly well suited in "busbar or LIG" type compartments, where it is difficult to detect small energy-saving arcs, and where, therefore, ΔP pressure variations are often low due to a particularly large volume of compartments .

For example again, the pressure rise over a certain time interval, such as the interval ΔT above, is calculated. The data processing means associated with the sensor can therefore calculate an average value of the ratio ΔP / ΔT, where ΔT is a time window that immediately precedes the measurement instant. This value can be compared to a threshold value, below which there is no anomaly, and beyond which the anomaly is characterized, that is to say corresponds to an arc.

Other types of anomalies can be detected: for example an external shock on the envelope 2 can be detected, thanks to the non-persistent nature of the pressure disturbances, quickly damped in the gas. For example again, a "catastrophic" leak of gas, which can be caused for example by the opening or accidental bursting of a rupture disc, results in a shape of the pressure wave in "plunging wave" . Yet another type of anomaly consists of the expansion of the envelope: the efforts related to such an expansion cause a release of energy, and this results in a very short waveform or which can be correlated with variations in temperature, the temperature variations being at the origin of the phenomena of dilation. Information about these events is available in the sensor.

With a device and a method according to the invention, such events can be detected very quickly, and allow the establishment of a security measure of the installation, to prevent the situation, which results from the event in question, take on a very serious character.

Such events, or the corresponding information, can be stored or archived in a database, which can then be analyzed, for example in terms of aging and material wear.

Figures 8A-12C provide examples of pressure waveforms for various situations and types of events.

If the anomaly is characterized, then there may be backup of at least all or part of the sensor data identifying the anomaly. The presence of the anomaly is reported to the acquisition unit 12.

The latter can then immediately decide on an action (for example triggering a signaling or an alarm), then download all of these saved data, for example by querying the sensor that reported the anomaly.

As soon as the reception of the data by the acquisition unit 12 is good, the sensor 10 can resume the normal fast interrogation cycle.

The acquisition unit 12 therefore firstly has information relating to the occurrence of an incident (production of an arc or other anomaly), which saves time to trigger an alarm, rather than waiting for all the data to be received, those that identify the anomaly and possibly other data. The transfer of the measuring points, which justify the triggering of the alarm, can then be realized.

In other words, according to the invention, each sensor and the means which are locally associated with it, has the ability to detect an anomaly in a very short time, to report this anomaly to the unit 12, which will first act for that the situation resulting from the appearance of this anomaly is controlled.

An example of operation of a sensor according to the invention will be given in connection with FIG.

In this figure, process steps are referred to as SO - S5.

In a first step SO, the sensor is powered up.

Then, a fast sampling, for example at a frequency of 1000 Hertz, of the sensor signal is carried out. The sampled data is stored in a rotating memory, for example 512 points.

This is followed by a sliding analysis, that is to say the implementation of an algorithm for measuring pressure variations over a sliding time window as already explained above. The signal noise can be filtered at this point. The presence or absence of an abnormal pressure change is then confirmed or reversed (step S2).

In the second case (no abnormal pressure), the method loops back to the previous step S1. On the contrary, if the presence of an abnormal pressure change is confirmed, the data is stored permanently, and an alarm message can be sent to the acquisition unit 12 (step S3).

The pressure variation data can then be transmitted to this same acquisition unit 12 (step S4).

As long as this transmission is not completed, there is loopback on this step S4 (step S5). Only after the end of the transmission of the values can rapid sampling be carried out again (step S1).

FIG. 4 represents a probe comprising a sensor, which can be used within the scope of the invention.

In the illustrated embodiment, this probe is of substantially cylindrical shape about an axis AA '. It comprises a body, constituted for example in two parts 150, 152, fixed on a base 153. The outer portion 153 'of the base 153 bears on the metal casing 2 (see Figure 1). In addition, the last base 153 is traversed by a cylindrical passage 113, connecting the atmosphere of the compartment to the sensor. At the end of this passage, inside the body of the probe, is disposed the sensor 110. The latter is isolated from the body of the probe; it is for example maintained in a ceramic part 140, itself held by the base 153, and in the base of which an orifice 115 leaves the free passage to the ambient atmosphere from the conduit 113 and whose pressure is at measure.

The diameter of this orifice 115, as well as the diameter of the portion of the duct 113 located between the outer portion 153 'of the base 153 and the sensor 110 can be adjusted to form a low-pass mechanical filter, which makes it possible to filter the noises.

The outer tube 152, which forms the lower part of the body of the device, is preferably made of stainless steel and is fixed on the base 153. During operation, the temperature of this tube 152 is substantially that of the casing 2.

The cover 150 which closes the device may be a molded part, for example of treated polyurethane, and which holds the temperature over a range substantially between -40 ° C and + 110 ° C.

In the extension of the sensor 110, and substantially along the axis AA 'of the device, is a printed circuit 130, comprising processing means and data storage means measured from the sensor 110, as well as communication means with an acquisition unit 12 outside (see Figure 1). The sensor 110 is connected, from its rear face, to the circuit 130 by connections 111. The circuit 130 is held in a first tube 155, or inner tube, by a material of filling 156, electrically insulating

(It is for example based on silicone). A filler 154 forms an outer filling, between the inner tube 155 and the outer tube 152. This material is also electrically insulating, it is for example polyurethane foam and / or silicone. The two tubes 155 and

152 may be cylindrical symmetry, and arranged along the same axis of symmetry as in Figure 4. The circuit 130 is itself connected to a connector 170, on which connecting means 175 can be fixed. These means 175 are extended by a cable 180. The connector 170 comprises a peripheral cylindrical ring 171. The assembly comprising the sensor 110, the circuit 130 and the connector 170 can be held by the metal tube 155, itself maintained in the tube 152 by the filling material 154.

More specifically, the cable 180 comprises the structure shown in FIG. 13. It therefore comprises a set of wires 181, which are surrounded by a metal screen 183. This includes, for example, a tinned copper braid provided with a aluminum foil. The assembly is surrounded by a sheath 185. The sensor communication and supply means are represented here by a single wire, but there are actually several (2x2).

When the entire device of FIG. 4 is positioned on the envelope 2 (FIG. 1), the existence of so-called return currents is observed, in particular when a defect such as an internal arc product. Indeed, there are then currents between the conductor 4 (see Figure 1) and the envelope 2. The operation of the sensor, directly positioned on the envelope, is disturbed by these return currents.

By coupling, a portion of these parasitic currents can be distributed inside the cable 180. Leakage currents occurring in the cable screen can lead to the conclusion that there is a defect in the system that is under surveillance. , when in fact this is not the case.

In addition, when the sensor is in digital communication, these parasitic currents can cause loss of information frame. The structure of a sensor according to the invention provides insulation with respect to these parasitic currents. Indeed, the insulating material 156,154 and the insulating support means 140, electrically isolate the electronic means 130 and the sensor 110 of the outer casing 152 which may possibly lead parasitic currents. Similarly, we see in Figure 4, that the ring 171, and therefore the connector 170, is separated from the casing 152 by a layer of insulating material 154. During operation, the base 153 is at the potential of the metal casing 2, and the insulation achieved avoids the flow of a current on the casing 171 and the screen 183 of the cable 180. A sensor according to the invention therefore comprises an outer casing which contains a circuit 130 and a sensor 110, but these are isolated from the outer casing by means of electrical insulation, which take the form, in the example shown, the material layers 154, 156, and the insulating base 140.

These means of electrical insulation make it possible to give the device resistance to voltages of several kilovolts, for example at least 5 or 10 kV. These isolation means also make it possible to achieve a continuity of the screen 183 of the cable which, consequently, is extended towards the inside of the sensor, and envelops the electronics 130 and the sensor 110 itself while being separated from the casing 152 by means of insulation. Specifically, in the structure that has been described above, an electrical contact is established between the screen of the cable, the part or means 175 connection, and the connector 170,171. In turn, the latter is in contact with the tube 155.

Preferably, a starting distance d, calculated for a certain voltage value, for example 30 kV, separates the ring 171 from the connector 170 of the outer tube 152. FIG. 5A schematically represents the sensor 110 itself, of capacitive type. .

This pressure sensor 110 operates on the principle of a capacity variation caused by the bending of a ceramic membrane 112 (Al2O3) metallized on its internal face. This membrane is sealed on a base 114 itself ceramic and on which three electrodes 115, 117 and 119 have also been previously screen printed. This seal is made by serigraphy of a thin glass thickness 116 in the pasty state around the periphery of the membrane 112 and on the base 114.

Under the influence of pressure, the center of the diaphragm 112 approaches the base 114 and causes the increase of the measuring capacitance Cm constituted by the electrode 113 located in the center of the base and the membrane. The peripheral electrode serves as reference capacitor Cr.

In one embodiment, the equivalent circuit of this device is shown in FIG. 5B, in which the capacities, respectively of measurement and of reference are represented.

The measurement capacities Cm and reference Cr are of the order of 30pF each. The variation of the measurement capacitance (central capacitance) is of the order of 1 pF to 2 pF for the full scale of measurement.

The conditioning of the signal is carried out on the principle of charge transfer from a capacitor to both capacitors of the sensor. The voltage obtained across the two capacitors is then filtered to give an analog signal.

In order to determine the temperature of the casing 2 of the disconnector, temperature sensor means may be arranged in the measuring device, preferably with the electronic circuit 130. For example, two sensors of Temperature RTH1 and RTH2, arranged as shown in Figure 6, are used.

Each of these two sensors can be made of platinum, in the form of a resistive chip. The nominal resistance of each sensor, at 0 ⁰ C, is 1000 Ohm.

The two sensors are arranged in series, with a common terminal. Tcap near designates the temperature of the pressurized capsule, and Telectronique designates the temperature of the electronic circuit 130.

A calculation method for determining the temperature of the envelope is, for example, the following: Tandem = Tcap_pres - ((Telectronic -

Tcap_pres) / RTH2) * (RTHI + RTH2).

This type of calculation gives a very correct result insofar as the power (energy) dissipated by the electronic means is constant and where the insulation of the heart of the transmitter is correctly ensured (from the thermal point of view) with respect to the outside. . In this case, the flow of calories dissipated by the electronic card will be essentially to the envelope 2 of the device. This temperature-related information can then be exploited to determine the density of the isolation gas or the evolution of this density as a function of time. The information concerning the density, and / or the pressure and temperature information, can be sent to the acquisition unit, either spontaneously, in the case of a mode of operation "Autonomous", or on request of the acquisition unit, in the case of a master-slave operating mode.

According to a preferred embodiment, this sensor is precisely supplied and regulated under a DC voltage of 24 V. Its operation is permanent, so the heat flow is constant.

With such a sensor it is possible to precisely measure the temperature of the end (screwed tip 153) of the sensor 10, which is fairly representative of the temperature of the casing 2. The measurement accuracy is 1 ° C. or even lower.

The validity of the measuring principle is in particular ensured by the good thermal conductivity of the ceramic electrical insulation 140, which is about twice as good as that of the stainless steel used for the construction of the end 153 of the sensor.

FIG. 7 represents an electronic card of a pressure sensor according to the invention.

The transmitter electronics is structured around a microcontroller 132 which incorporates features such as signal acquisition and communication. In fact, this electronics comprises means or a card, for example in the form of printed circuits, central processor 132 with its power supply 134 and an interface 136, for example of the RS485 type. The means 132 comprise means for conditioning the signal of the capacitive pressure sensor.

The means 130 may comprise means, or a filtering card, in particular to provide EMI and EMC protection. In the structure of Figure 4 these means can be placed on the circuit 130, immediately behind the base 171.

Preferably, the microcontroller means 132 make it possible to perform analog signal acquisition (ADC) with a multiplexer with 4 inputs and 12 bits of minimum resolution. The acquisition time is preferably less than 10 μs.

These means 132 make it possible to calculate the effective value of the pressure and of the temperature in a computation time lower than 0.5 ms (including thermal compensation, linearity, scaling, etc.).

The RS485 serial link is of UART type with FIFO type buffers. These means are equipped with a memory

"FLASH" programmable in situ (minimum lβKbyte).

They also include a RAM sufficient to contain all the working variables as well as communication buffers and measurement records. Preferably this memory has a capacity of 2Kbyte, or more.

These means also include a memory

EEPROM, for storage of various information such as for example calibration parameters and / or references and / or serial number of the sensor. These microcontroller means 132 furthermore comprise an integrated clock system or real-time clock signal generation means. These clock means will also allow management of the synchronization of the chosen protocol.

Finally, the microcontroller will enable the management of interrupts with a table of programmable vectors.

For the specific use that is made of it, this microcontroller preferably has a low consumption, for example about 22 mA at 5 volts in 8 Mips. It operates over a wide operating voltage range, for example from 2.5V to 5.5V, and over a temperature range of -40 ^° C to 85 ° C (the latter corresponds to a functional guarantee for the measurement ). But, it is desirable that the component resistance to temperature is in fact about 140 ⁰ C, that is, for any temperature below 140 ⁰ C there is no destruction or irreversible damage.

An example of a microcontroller that can be used is dsPIC30F3012 or dsPIC30F3013 from MICROCHIP.

The device 130 includes means 134 for feeding.

Preferably, and in order to maintain a constant temperature gradient in the electronic card relative to its environment, and regardless of the supply voltage, this power supply implements switching energy conversion technology. On the microcontroller side, the consumption is almost constant, as long as it operates at a constant frequency. Whatever the power supply voltage, the power consumed by the electronic card is approximately constant, only the current varies.

Given the operating conditions of the entire system, the power supply can be one of the elements that can suffer the most directly from any disturbances generated by the environment. Therefore, it is preferred to choose a robust power supply, which can provide protection for the microcontroller; it is for example of the type qualified for embedded applications in the automotive field.

Preferably, the main characteristics of a switching power regulator 134 for this application are as follows:

- low consumption (operating current <1 mA),

a high switching frequency (for example of the order of 600 kHz) in order to minimize the value of the energy transfer choke,

- MOS technology with high voltage integrated power, to allow a wide range of input,

an integrated voltage reference,

- protection against current spikes and short circuits. A suitable switching regulator is the National Semiconductor LM5008 controller. His Built-in 100V MOS supports a power supply voltage range of 10 to 90Vdc (for a nominal 24Vdc supply voltage). The switching frequency varies, depending on the current delivered by the controller, between 100 kHz and 600 KHz. The value of the self is between 100 μH and 220 μH.

If the previously selected microcontroller (dsPlC30F3012) is programmed to provide a computing power of 4 MIPS, its theoretical power consumption at 5Vdc is 22 mA, which gives an overall consumption of (5V / 24V x 22mA) + ImA < 6 mA for a board powered by 24 Vdc, considering that the microcontroller is the main consumer of power. The stall level of this power supply is 8 volts, and a consumption of only 6 mA is satisfactory, far from the imposed limits.

The RS485 communication interface 136 transmits the data at 115 kbps in half duplex mode over a twisted pair.

Since the RS485 interface driver is one of the components that may be the most exposed to the disturbances generated by the environment (in particular the driven voltage peaks), it is preferably selected according to its performance vis-à-vis screw surges and short circuits. An ESD protection, for example of +/- 15 KV, is therefore integrated into the component. In order not to generate conducted or radiated disturbances itself, the RS485 driver is selected in the speed range between 500 Kbaud and 2.5 Mbaud. The choice of a component fast allows to limit current calls during switching. Since the current is drawn from the sensor supply, this may result in noise on the measurements. The current calls also depend on the load represented by the communication bus between the sensor and the acquisition unit.

Preferably, the consumption of the driver in operation does not exceed 1 to 2 mA.

Several drivers have been tested. The first is the LTCI785CS8 of

LinearTechnology. This driver is efficient in terms of protection against external disturbances: it allows protection against overvoltages up to 60V, against short circuits, and it supports ESD up to + _ 15KV without damage or Latchup (IEC-61000-4-2, level 4, which identifies electrostatic discharges) and transient, fast, burst discharges of + 4 KV (IEC-61000-4-4 level 4, which identifies type of landfill). Another component, Texas SN65176B, gave equally satisfactory results during the same tests.

An operation of a data processing and exploitation software implemented in means 132 of an individual sensor 10 is as follows.

Such software makes it possible to implement all or part of the functions or operations already described above. At power up, the microcontroller

132 manages itself, depending on the configuration programmed (specific memory area of the means 132)), its Reset phase as well as the activation of its oscillator.

All inputs / outputs (I / O) are preferably configured as input: in a first step, the software configures the inputs / outputs of the microcontroller 132 as well as the various associated functions (for example: the analog inputs for the sensor signals , UART (universal asynchronous transceiver) for the serial link that drives the RS485 driver, ....).

The interruptions (IT) in real time make it possible to ensure a good time flow, perfectly clocked. In a first phase, the real-time ITs are generated at a frequency that can be adjusted, for example every 200 μs. We seek a compromise between processing capacity in IT in real time and background tasks. In general, IT processing should not exceed 30% of the overall capacity.

The tasks performed in the processing of the IT in real time are essentially the acquisition of signals from the sensors and the incrementation of various counters such as those relating to the management of the temporal progress of the communication protocol between the sensors 10 and the unit 12.

One or more acquisitions of each of the sensor signals are performed at each interruption in real time. Each signal value thus obtained is added to the previous ones in a buffer register. All 8 ITs in real time, the buffer is transferred to initiate the pressure and temperature calculations, then reset for the next acquisition sequence. Calculations are supported by a background task manager (excluding

IT). Thus, it is possible to obtain an updated pressure and temperature value every 1 ms.

The treatment on each sample packet, for example 16 samples, leads to an average after elimination of the atypical values and the extreme values, by the use of an absolute and relative coherence filter.

The transmission and reception of information is done under IT. The microcontroller 132 is provided with buffers (in transmission and reception) which ensure a good transmission, without risk of loss of characters, and without risk of breaks in the rate of transmission of the characters of the frame (maximum time between 2 characters = 1 , 5 characters).

The main basic tasks activated in "measurement" mode are as follows:

- measurement management: pressure and temperature values are calculated according to acquisition values and calibration parameters (thermal compensation, linearity, scaling ...).

- Frames management: received frames are analyzed. There is no action if the frame is destined for another sensor or treatment of the command otherwise, with in this case loading the response buffer to the request of the master. When the command is processed and the buffer loaded, a flag is set to initiate the transmission of characters under IT UART. - Monitoring of the functioning of the transmitter: this function is ensured thanks to mechanisms of validity of the accesses in memories for the program and the data.

Secondary tasks include, for example, ancillary procedures that the main program occasionally uses to perform particular and exceptional functions, such as:

- a function that allows you to program or load or download a new version of the software without physically opening the product. This function is used to receive the new version of the program via the RS485 serial link. For this purpose a specific function of the protocol is reserved, and ensures the implementation in memory "FLASH". Possibly, this function makes it possible to implement another version of the data processing if one changes the type of fault to be characterized.

Calibration, which is a specific function that the main program uses only during the calibrator phase of the transmitter, in production or during subsequent calibrations. The transmitter is fully assembled prior to calibration, which is performed via the RS485 serial link and a specific control of the reserved protocol. This function includes the recording of traceability and identification data, which data are stored in a memory (eg EEPROM type) of the transmitter.

The offset and gain parameters can be adjusted beforehand, the calibration on site then being limited to a comparison with a standard.

The data of the sensors 10 are transmitted to the calculation unit 12. To do this, a dialogue protocol between these different elements has been developed. These elements are in master-slave relationship: the sensors (slaves) can only transmit if they have been invited by the unit 12 (the master). Each exchange of data is initiated by it. When it interrogates a sensor, it has a maximum duration (for example 1 ms or even 500 μs), to process the command and respond; a message sent out of this time window is considered invalid. Likewise after the execution of a command, or after reception of a frame of which it is not addressed, the transmitter 10 has a maximum duration of time, for example 500 μs, in order to get back into tune. unit 12.

The physical link is provided by an interface RS485 which transmits a differential signal in half-duplex (the different devices successively access the bus 14 (FIG. 1) This link uses a twisted pair for the data transmission, and a pair for the transmission of the data. power supply (24Vdc nominal) The format of the data transmitted on the bus is as follows: 1 bit Start.

8 bits of data (least significant bit first).

1 bit Stop. If the transmission speed is 115200

Baud, the duration of transmission of a character is therefore of the order of 100 microseconds.

When transmitting a frame, the characters are transmitted successively, without interruption. The transmission protocol can specify that the maximum duration between 2 characters is less than 1.5 characters, so less than 150 μs.

An interruption in the transmission of characters, for a duration greater than 3 characters, (thus greater than 300 μs) is interpreted as a frame end.

The format of a frame sent by the master is as follows:

The "station" address is that of the sensor concerned.

An address, for example 250, can be reserved for "BROADCAST" commands, that is to say commands addressed to all the sensors 10 simultaneously. These commands do not require any response from the sensors.

The other addresses, for example 1 to 249, can be used for the transmitters present on the bus 14. The function code determines the command to be executed by the station (slave). The function code is for example coded on 7 bits, the eighth bit (MSB) always being equal to 0. The parameters or data are the information allowing the execution of the function.

The 2 bytes CRC16 constitute a key of control of the whole frame and make it possible to guarantee the integrity of the received data. The calculation of CRC16 is subject to a standard described in the standard

Modbus (modbus.org).

A response sent by a transmitter responds to a specific format:

At the top of its answer, the transmitter returns its own address to confirm that it is he who performed the function.

If the transmitter has correctly executed the function, it returns the same function code as that sent by the master. If any error has occurred, it returns the function code by forcing the eighth bit (MSB) to 1. In this case, the following data is an exceptional error code. "Data" data is present if the function requires feedback.

For the bytes CRC16, one will refer to the explanations above.

In general, the length of a reply sent by a station comprises between 5 and 10 characters. Finally, exceptional errors can be programmed, such as transmission errors.

Each transmitter can implement the following functions:

- Reading of the calibration parameters and technical specifications.

- Writing of the calibration parameters and technical specifications. - Initialization of the devices; device identification given back.

- Programming the bus address.

- Reading the serial number.

- Reading of real pressure and temperature values in floating point format.

- Reading actual pressure and temperature values in whole format.

For each of these functions, is defined: a request from the master, according to a predefined format, for example that indicated above,

a response from the transmitter, according to a predefined format, for example that indicated above,

- one or more exceptional errors A function of reading the values measured in "cascade", also called "fast BUS", can be implemented. It consists of successively obtaining the response of several transmitters following a single request from the master, it is specific and contrary to the principle of the protocol "Modbus", but allows to improve the efficiency of a method according to the invention.

If several devices are connected to the bus, only the first is interrogated by the master; the others answer each in turn, provided that the addresses are in ascending and consecutive order.

Otherwise, the acquisition unit polls the sensors one by one.

Each pressure value measured, for example every millisecond, is stored in a rotating stack of 512 values.

This value is expressed in millibar. 2 bytes are used per value, a stack of 1024 bytes. This stack can be stored in a RAM of the DSP, using half of the RAM. The

1024 bytes remaining are sufficient for the purposes of the application.

The application has a pressure event detection algorithm, based on a threshold of

ΔP / ΔT (configurable). The calculation is done at regular intervals, for example each msec, by calculating the pressure rise over a certain time interval, for example an interval of 10 msec. If the threshold is exceeded, a confirmation based on the slope obtained by linear regression can be performed on, for example, 10 values.

In addition, if exceeded, the stack is frozen with a certain value taken as the original value of the record, for example the value N-

20. The following values (for example: 512 values) are recorded and kept at the disposal of the master during, for example, one minute.

The trigger triggers a millisecond counter for time marking of the event, when read by the master.

In case of an event, during the answer

(Regardless of the question, pressure or temperature), a specific code is returned to the master. The latter having been informed of an event, a function code makes it possible to load ("dump") the stack of these values as well as the time counter. The master returns an acknowledgment of receipt, or reiterates his request. On receipt of this acknowledgment, or at the latest after a predefined period, for example 64 seconds, the operation of the rotating battery is re-initialized, and the operation of the counter is stopped.

Preferably, the response time of a sensor is less than 1.5 msec. This makes it possible to ensure a duration of a Question / Answer (Q / R) cycle, during an exchange of data or information with the unit 12, less than 2.5 msec.

More preferably, the time between the end of a master's question and the beginning of the sensor's response is less than 500 microseconds.

The initialization time of the sensor is preferably less than 10 msec, and preferably less than 3 complete cycles of Q / R under pressure, ie at most 7 msec. In an exemplary embodiment, the dimensions of the electronic card are: 1 = 16 (+ 0.1) mm, L = 30 + _ 10mm. Optionally, the use of latest-generation CMS components makes it possible to ensure miniaturization and resistance to certain electromagnetic disturbances. The SMD resistors and capacitors are not subject to power requirements or voltage withstand, are in a 0402 package

(which is a miniature package, better except in case of heating of the component).

Non-limiting examples of embodiment details are as follows.

The operational amplifiers for the conditioning of the signals coming from the pressure or temperature sensors are in an MSOP8 package.

The printed circuit is of 4-layer class-5B or class-6B technology. The 2 central layers will be reserved mainly for the grounding of the microcontroller and the positive supply voltage of the microcontroller (for example +5 Volt).

The material is FR4 with a thickness of about 1.6 mm.

The thickness of the conductors (copper) is standard: +/- 35 microns, the protective coatings of drivers are in LPI - 2 x green. Given the extreme level of miniaturization, there is no silkscreen for the identification of components, it has more disadvantages for the good welding of components that real interest in the development or testing of cards .

The minimum width of the conductors (tracks) is 0.2mm, and the diameter of the holes is 0.35mm minimum. FIGS. 8A-8C and 9-11 show the evolutions of pressure signals as a function of time in the context of measurements made with a device according to the invention. In the 3 cases of FIGS. 8A-8C, an event occurs in the casing 2 of a high-voltage device for a duration Tare. Pressure variations are observed during this time interval, and the question arises whether these pressure variations effectively characterize the presence or absence of an electric arc. The pressure data are obtained, in all three cases, according to one of the methods according to the invention which have been described above. The first case (Figure 8A) is that of a small volume compartment, or that of a major defect, which releases a lot of energy. In this case, the amplitude ΔP, that is to say the difference between the pressure after defect and the pressure before defect is significant, that is to say greater than the measurement error of the pressure sensor. .

The second case (Figure 8B) is that of a large volume compartment, or a small defect, which releases little energy. In this case, it is preferable to identify the frequency of the pressure variations. If this frequency is high, and if the oscillations occur over a sufficient period of time, a fault can be characterized.

The third case (Figure 8C) is that of a large volume compartment, or a small defect, with a sensor located relatively close of the defect. In this case, it is preferable to identify the peak-to-peak amplitude ΔcP; a high peak to peak peak amplitude confirms the presence of an arc.

The cases of FIGS. 9 to 11 represent other situations that can be identified by means of a pressure variation detected by a method according to the invention.

The first case (Figure 9) represents the evolution of the pressure as a function of time, following an external shock. From the point of view of the evolution of the pressure, this shock is characterized by a quasi-absence of pressure variation between the initial pressure and the final pressure, as well as by the presence of a rapidly damped wave. The second case (Figure 10) represents the evolution of the pressure as a function of time, following a dilation. From the point of view of the evolution of the pressure, this expansion is characterized by a quasi-absence of pressure variation between the initial pressure and the final pressure, as well as by the presence of a high frequency wave and rapidly damped.

The third case (Figure 11) represents the evolution of the pressure as a function of time, following a catastrophic gas leak. From the point of view of the evolution of the pressure, this leak is characterized by the significant negative slope of the pressure curve as a function of time, this slope being preceded by a normal situation, during which the pressure is stable. FIGS. 12A-12C represent measurements, of the type shown diagrammatically in FIG. 8A or 2, for a 990 A arc (duration of 210 ms), performed with a self-triggering recording sensor from Bourdon. Pressure values can be identified for every millisecond.

On these 3 graphs, the abscissa axis is in ms and the ordinate axis in mbar.

The sensor is located in line with the arc for FIG. 12A and at 3.45 m from the arc for FIG. 12B. For Figure 12C two curves are shown, one (curve I) with the sensor located at the arc and the other (curve II) with the sensor located at 3.45 m from the arc. The ΔP measured is 24.5 mbar. The insulating gas is SF6 in all 3 cases.

Claims

A pressure probe, adapted to be positioned on the metal casing of an HT device, having a probe body (150, 152) containing:

means (110) for pressure sensing or pressure variation, of the capacitive type,

means (113) for bringing these pressure detection or pressure variation means into contact with an external atmosphere (P),

digital data processing means (130) for processing data of the pressure detection or pressure variation means,

means (154, 156, 140) of electrical insulation for isolating, relative to the body or the casing (150, 152) of the probe, the means for detecting pressure or pressure variation and the means for data processing.

The probe of claim 1, further comprising connector-type means (175, 170, 171) for connecting the data processing means to a connection cable (180);

3. Probe according to claim 2, the cable

(180) having a set of son (181) surrounded by a metal screen (183), the assembly being surrounded by an insulating sheath (185).

4. Probe according to claim 3, the connector-type means forming an extension of the metal screen of the cable.

5. Probe according to one of claims 2 to

4, the connector-type means being extended by at least one inner envelope (155) which at least partially contains the means (110) for detecting pressure or pressure variation and / or the data processing means (130) .

6. Probe according to one of claims 1 to

5, each of the pressure detection or pressure variation means and data processing means being at least partly surrounded by a material (152, 154, 140) of insulating material.

7. A method for detecting a fault in a high voltage device, comprising a metal envelope (2), at least one central conductor (4) and a plurality of compartments traversed by this conductor, this method comprising the following steps: a) arranging, in communication with each compartment, a pressure probe according to one of claims 1 to 6, for sampling pressure data, and for identifying pressure data characteristic of said fault, b) transmitting digital pressure data characteristic of the defect to data processing means (12).

The method of claim 7, wherein digital pressure data in a sliding time window is stored.

9. Method according to one of the claims

7 or 8, wherein a temperature representative of the temperature of the metal casing is furthermore measured.

10. Method according to one of the claims

7 to 9, in which the probes and the processing unit operate in autonomous mode or the probes and the processing unit are in master-slave relationship, each probe (10) being able to transmit data or information only if it has received processing means (12) a request for transmission of data or information.

11. Method according to one of claims 7 to 10, wherein the probes and the processing unit are in master-slave relationship, each probe (10) can not issue data or information after receiving a request. transmission of data or information from the processing means (12), only for a predefined and limited time.

12. Method according to one of claims 7 to 11, the pressure sensing means being of capacity variation type or piezo-resistive cell.

13. Method according to one of claims 7 to 12, comprising, between step a) and step b), a transmission step a '), to the data processing means, an information of appearance of failure.

The method of claim 13, wherein after step a '), an abnormality signal is generated.

The method of claim 14, wherein said abnormality signal is produced before step b).

16. Method according to one of claims 7 to 15, wherein step b) is performed on request of the data processing means to the probe having identified a defect.

17. Method according to one of claims 7 to 16, wherein the defect is the appearance of an internal arc, or an external shock on the envelope, or an insulating gas leak, or an expansion of the envelope .

18. Method according to one of claims 7 to 17, wherein pressure variation data characteristic of a defect are identified using a calculation of pressure variation ΔP for a certain duration ΔT, (ΔP / ΔT), and / or with the aid of a frequency of oscillations of the pressure and / or the measurement of the peak-peak amplitude of the pressure and / or with the aid of the identification of a wave of damped pressure and / or a persistent pressure slope.

19. The method of claim 18, ΔP / ΔT and / or the frequency of oscillations of the pressure and / or the peak-peak amplitude and / or the shape of the pressure wave being measured or identified at regular intervals.

20. Device for detecting a fault in a high-voltage device, comprising a metal envelope (2), at least one central conductor (4) and a plurality of compartments traversed by this conductor, this device comprising: a plurality of probes digital pressure sensor (10) according to one of claims 1 to 6 for sampling pressure data, and for identifying pressure data characteristic of said defect; means (136) for transmitting pressure data characteristic of said defect; data processing means (12) common to all the probes.

21. Device according to claim 20, the probes and the processing unit operating in autonomous mode or being in master-slave relationship, the probes (10) being able to transmit only if they have been invited by the processing unit ( 12).

22. Device according to one of claims 20 or 21, each probe (110) being positioned inside a casing (150, 152), wherein the insulating gas under pressure enters through a conduit (113).

23. High voltage device, comprising a metal casing (2), at least one central conductor (4) and a plurality of compartments through which this conductor passes, and a device according to one of claims 20 to 22, each probe of the plurality digital probe (10) being positioned in one of the compartments and connected to the data processing means.