DEVICE AND METHOD FOR PROTECTION AND / OR MONITORING OF AN ELECTRICAL TRANSFORMER OF THE TYPE CONTAINING DILEKRIFLUE ENSURE IN A HERMETICALLY SEALED TANK

Description

FIELD OF INVENTION

[0001] The present invention relates to a protection and monitoring device for an electrical transformer of the liquid dielectric type enclosed in a hermetically sealed tank. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Oil-immersed, hermetically sealed electrical distribution transformers are generally equipped with safety relays that control circuit breaker tripping via electromechanical contacts. These contacts switch in case of overpressure, excessive temperature, or when the oil level falls below a minimum value. These safety features prevent extreme situations that could lead to explosion, fire, and / or significant damage to the transformer.

[0003] Beyond these essential functions, the optimal operation of distribution transformers involves many other requirements. Regular monitoring of the transformer's condition is necessary. As document EP3032553 points out, this monitoring can be carried out by analyzing the oil, taken by sampling, generally once a year, on-site. This measurement is very important, but, by its very nature, it does not provide a precise picture of the conditions to which the transformer has been subjected in real time: overloads, abnormal temperature rises, or sudden pressure increases without reaching switching thresholds, traceability of events such as the switching of safety contacts, and lightning strikes on the primary side. These events can significantly impact the consumed / remaining service life and influence decisions regarding preventive maintenance or replacement.The energy efficiency of these devices is becoming increasingly important, and is often directly linked to the transformer load and its age. Quantifying losses and optimizing performance are crucial for achieving maximum efficiency.

[0004] On the other hand, when the electromechanical safety contacts trip, significant damage may already have occurred to the powered equipment, especially if the power outage lasts for a certain period. Unplanned power outages can also lead to substantial operational losses. Therefore, it would be advisable to be able to anticipate such tripping.

[0005] For the reasons mentioned above, it is therefore advantageous to monitor, in real time, the actual operating conditions of the transformer and the events occurring during its operation. Documents ES2253979, US4654806, and WO2014135015 describe instrumented electrical transformers designed to monitor their operation. In these established approaches, the transformer tank and its other components are equipped with distributed sensors to determine its main operating parameters: temperature, pressure and fluid level, secondary winding electrical load, etc.

[0006] In some cases, the collected measurements are used both to monitor transformer operation and to ensure essential safety functions. This approach requires prior instrumentation of the tank and, more generally, of the electrical transformer. Implementing such instrumentation across the installed base of transformers is difficult and costly.

[0007] Finally, we also know from document EP2682972 of a transformer protection relay monitoring device that includes a switch open / close state detection device. The detection circuit can operate (i.e., detect the open or closed state of the switch) even in the absence of an external voltage (Vext), by attempting to establish a voltage across one of the switch terminals when this external voltage is zero. The detection circuit is permanently connected in parallel and galvanically linked to the safety contact. In the event of a failure of all or part of the detection circuit, it may short-circuit, thus shorting the safety contact. This failure can lead to the transformer being de-energized and the inability to re-engage it if the short circuit persists. SUBJECT OF THE INVENTION

[0008] One aim of the invention is therefore to provide a device for monitoring distribution transformers that is easy to implement, without adding extra instrumentation or disrupting installers' habits, and whose failure is unlikely to cause the transformer to be switched off. BRIEF DESCRIPTION OF THE INVENTION

[0009] To achieve this goal, the object of the invention proposes a protection and monitoring device for an electrical transformer of the type with liquid dielectric enclosed in a hermetically sealed tank, the device comprising at least one electromechanical safety contactor whose switching is intended to cause the instantaneous opening of a circuit breaker of the transformer according to claim 1.

[0010] According to the invention, the device comprises: an electromechanical contactor switching detection circuit; an electronic measuring unit, connected to the detection circuit and configured to trace the occurrence of a switching event;

[0011] The detection circuit includes an indirect current measurement device for the current flowing in the contactor, which is not part of the invention.

[0012] In this way, we can monitor at least the switching events of the electromechanical safety contactor(s) without modifying the protection function of the transformer provided by this or these contactor(s) and without interfering with these contactors.

[0013] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: The electromechanical contactor is included in an electromechanical detector with a temperature, pressure, or liquid dielectric level threshold; the detection circuit includes a current transformer; the detection circuit includes components for conditioning a raw detection signal; the electronic measuring unit includes an energy storage means; the electronic measuring unit includes a communication interface; the device includes at least one circuit for measuring transformer monitoring information, the measuring circuit being electrically connected to the electronic measuring unit; the measuring circuit is a circuit for measuring the level, temperature, or pressure of the liquid dielectric, a circuit for measuring the magnetic field emitted by transformer windings, or a vibration measuring circuit;

[0014] Finally, according to yet another aspect, the object of the invention proposes a method for protecting and monitoring a liquid dielectric transformer enclosed in a hermetically sealed tank, the method comprising: the detection by a detection circuit of a switching event of an electromechanical safety contactor intended to cause the instantaneous opening of a transformer circuit breaker; the tracing, by an electronic measuring unit, of the switching event.

[0015] According to other advantageous and non-limiting features of this aspect of the invention, taken alone or in any technically feasible combination: The method includes the repetitive measurement and recording in the electronic measuring unit of at least one characteristic of the liquid dielectric or the transformer windings; the method includes a step of processing the switching event and measurements to establish and trace a significant event; the processing step includes the erasure, in the electronic measuring unit, of data that are not located in a temporal neighborhood of the significant event. BRIEF DESCRIPTION OF THE FIGURES

[0016] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which: [ Fig. 1 ] There figure 1 represents an electrical transformer equipped with a protection and monitoring device according to the present invention; [ Fig. 2a ] ] Fig. 2b ] ] Fig. 2c ] THE figures 2a to 2crepresent an architecture of the protection and monitoring device conforming to the invention; [ Fig. 3 ] There figure 3 represents a protection and monitoring device equipped with a temperature, pressure and level threshold detector; Fig. 4a ] ] Fig. 4b ] ] Fig. 4c ] THE figures 4a to 4c represent three possible configurations of a detection circuit; [ Fig. 5 ] There figure 5 represents a device architecture implementing advanced monitoring functions. DETAILED DESCRIPTION OF THE INVENTION

[0017] There figure 1This represents a schematic overview of an electrical transformer 2 equipped with a protection and monitoring device 1 conforming to this description. The transformer 2 comprises a hermetically sealed tank 3 containing a liquid or dielectric fluid in which primary windings 4a and secondary windings wound on a magnetic circuit 4b are immersed, ensuring electrical transformation.

[0018] The tank 3 has a top opening, the periphery of which can accommodate the protection and monitoring device 1 so that it can be partially immersed in the dielectric fluid, as will be described in detail later in this document. The top opening of the tank 3 is generally designed to allow the tank to be filled and topped up with dielectric fluid. The device 1 is configured to occupy the unused space of a leak-proof closure for this opening, such as a plug.

[0019] The transformer 2 also includes an electrical control cabinet 5, containing in particular the means to electrically isolate the primary and / or secondary windings 4a, 4b from the electrical network when a safety event is detected by the device 1. The cabinet 5 may thus include a circuit breaker comprising a detection coil connected to a connection terminal of the device 1, on which is reported an electrical signal whose switching indicates the occurrence of a safety event. General description of the protection and monitoring system

[0020] With reference to figures 2a to 2c We now describe the protection and monitoring device 1 which incorporates the structural principles of the safety device described in document FR2737357.

[0021] Device 1 comprises a dip tube 6 with a closed distal end 6a. When device 1 is correctly positioned on the transformer tank 3, the distal end 6a of the dip tube 6 is immersed in the dielectric fluid. The dip tube 6 also has an open proximal end 6b that terminates in an upper housing 7, to which the tube 6 is sealed by means of a base plate 6d. The upper housing 7 is designed to house the electromechanical safety devices and the wiring for connecting them to the terminals of device 1. All the terminals of device 1 collectively form a terminal block that can be arranged within the upper housing 7.

[0022] Device 1 shown on the figures 2a to 2cIt also includes a base 8 for fixing the device 1 to the contour of the tank opening 3. The base 8 is cylindrical and is traversed by the dip tube 6. An intermediate section 9, also traversed by the dip tube 6, is fixed to the base 8 in a watertight manner. The intermediate section 9 supports the upper housing 7. The upper housing 7 and the intermediate section 9 are, however, hermetically sealed from each other. In the example shown, the upper housing 7 consists of a cover and a lower section, the lower section forming a single unit with the intermediate section 9.

[0023] The intermediate section 9 includes a filling tube 9a sealed by a removable plug 10, here equipped with a drain valve. The dielectric fluid poured into the filling tube 9a can circulate within the internal space of the intermediate section 9 and through the internal space of the base 8 to fill the tank 3 of the electrical transformer 2.

[0024] In normal operating conditions, the transformer and device 1 are completely filled with dielectric fluid, including the tank 3, the internal space of the base 8, and at least part of the intermediate section 9. Advantageously, this section is made of a transparent material, such as plastic, to allow visual inspection of the fluid level. As will be described in detail later, the intermediate section 9 may include a primary float 13a to trip the electrical transformer 2 when the level falls below a critical threshold. A secondary float 15 may also be provided in the filling tube to detect small variations in the dielectric fluid level (the tube having a smaller cross-section than the intermediate section).In this case, it is necessary that the level of this fluid, in a normal operating state of transformer 2, be positioned in the filling tube 9a in an upper area of ​​this tube.

[0025] Device 1 shown on the figures 2a to 2c It also includes a peripheral housing 14 intended to house active electronic components, as will be shown later. The peripheral housing 14 comprises a first portion 14a arranged along and against the filling tube 9a and a second portion 14b arranged partly under the upper housing 7. The two portions 14a and 14b are connected by an intermediate portion 14c enclosing one side of the intermediate portion 9. To electrically connect the components arranged in the peripheral housing 14 to those arranged in the upper housing 7, the two housings can respectively carry complementary portions 16a (visible on the figure 2c), 16b of a 16 connector that can be fitted together.

[0026] In general, the device 1 consists of a first internal space defined by the intermediate part 9 and the base 8, which are in fluidic communication with the tank 3. The device 1 also consists of a second internal space defined by the internal volume of the dip tube 6 and the upper housing 7. This second internal space is not in fluidic communication with the interior of the tank 3 or with the first internal space. It is intended to house passive or active, electromechanical or electronic components, as will be presented later in this description. The device also consists of a third internal space defined by the peripheral housing 14, intended to house the active electronics of the device 1, such as an electronic measuring unit 17 visible on the figure 3electrically connected to the elements of the second internal space. The three internal spaces are distinct from one another, that is to say, separated from each other by walls and in a sealed manner, to form a modular device 1. This modular nature of the protection and monitoring device 1 constitutes a very advantageous aspect of the invention which ensures the safety of the assembly, its reliability, and the ease of its assembly and maintenance. Protective functions

[0027] To ensure its protection functions for transformer 2, the device includes at least one electromechanical safety threshold contactor, the switching of which is intended to cause the instantaneous opening of the transformer 2 circuit breaker. This may, for example, involve detecting an insufficient level of dielectric in tank 3, an excessive temperature or pressure of this dielectric.

[0028] An "electromechanical contactor" is a switching device that makes a dry electrical contact between two of its terminals. The device can switch between an open or closed position when a quantity measured by a transducer (for example, pressure, temperature, or level) crosses a predetermined threshold. It can also be a normally open contactor (which switches to the open position when the threshold is crossed), a normally closed contactor (which switches to the closed position when the threshold is crossed), or even a reversing contactor that can be configured for either of these operating modes. The transducer and the contactor together form an electromechanical threshold sensor.

[0029] Regardless of the type of contactor chosen, it has at least two switching terminals electrically connected to a terminal block of the protection and monitoring device 1. An alternating or direct voltage (typically between 24V and 240V) is applied to the switching terminals of the contactor, for example from a source located in the cabinet 5 and electrically connected to the terminals of the device 1. The presence or absence of voltage in this circuit can be detected by the detection coil of the transformer circuit breaker 2.

[0030] In the example shown on the figure 3 , device 1 is thus equipped with an electromechanical detector with temperature, pressure and level thresholds, each comprising an electromechanical contactor 11c, 12c, 13b whose switching is triggered by crossing a predetermined threshold in temperature, pressure or level of the dielectric fluid of the tank 3.

[0031] The temperature detector consists of a bulb 11a, i.e., a cavity filled with a material that expands according to the temperature to which it is subjected, and a capillary 11b that transmits the force produced by the expansion of the material in the bulb 11a. The bulb is positioned in the immersion tube 6 at its distal end 6a so that it is exposed to the temperature of the dielectric fluid. The capillary 11b runs inside the tube 6 and opens into the upper housing 7, where it is connected to a first electromechanical switch 11c configured to switch when the temperature to which the bulb 11a is exposed rises above a predetermined threshold. The device 1 can be equipped with several detectors, calibrated to switch when two distinct temperature thresholds are crossed.

[0032] The pressure sensor can take the form of a pressure switch located in the upper housing 7. A connecting tube from the pressure switch is inserted into an opening 7a in the upper housing 7, which leads into the intermediate section 9. The connecting tube is immersed in the dielectric fluid filling the internal space of the intermediate section 9 in order to detect the pressure. This pressure is transmitted to a diaphragm in the pressure switch, the deformation of which triggers a second contactor when the diaphragm exceeds a predetermined threshold.

[0033] The level detector may include the main float 13a housed in the intermediate section 9, here slidably mounted around the dip tube 6. The float 13a is supported by the dielectric liquid filling at least part of the internal space of the intermediate section 9. When the level of the dielectric liquid is within the specified range, the main float 13a is pressed against or near the upper wall of the intermediate section 9. The main float 13a carries at least one magnet. The level detector also includes a third electromechanical contactor 13b, sensitive to the magnetic field produced by the magnet, which causes it to switch. This contactor 13b is arranged in the dip tube 6 at the level of the intermediate section 9 so that falling below a level threshold in the dielectric liquid causes it to switch.

[0034] The detectors just described are specific examples of implementing detectors integrated into device 1. This device 1 can, of course, be equipped with other types of detectors or the detection functions described can be implemented in other ways, without departing from the scope of the present invention. In all cases, however, device 1 is equipped with at least one electromechanical contactor that performs a detection function for a safety parameter of the transformer 2. As already mentioned, each contactor is electrically connected via wires running through the upper housing 7 to terminals of a terminal block, in order to connect device 1 to the other components of the transformer 2, and in particular to the circuit breaker in the electrical cabinet 5. Monitoring functions

[0035] To perform its monitoring functions, the protection and monitoring device 1 also includes one or more circuits for detecting the switching of the contactor(s). It should be noted that the components ensuring the dry contact of the contactors or the components that trigger the switching of these contactors are not directly accessible, as they are enclosed within the pressure switch, the thermostat, the dip tube 6, or, more generally, embedded within the detector of which they are a part. However, several approaches are possible to achieve switching detection.

[0036] According to a first approach represented on the figure 4aThe detection circuit D includes a device for measuring the voltage or absence of voltage available at the terminals of the contactor C. To enable this, additional wiring is provided in parallel with that connecting the switching terminals of the contactor C to the terminals of device 1. This approach is advantageous because it ensures the effective connection of the contactor to the rest of the installation when a voltage is detected. However, a failure of the detection circuit D, such as a short circuit, can compromise the proper operation of the contactor and cause the circuit breaker to trip unnecessarily.

[0037] According to a second approach represented on the figure 4bThe detection circuit D includes a shunt device in the electrical wiring connecting the contactor C to the terminals of device 1. When the contactor switches, a current flows through this device, enabling its detection. However, inserting the detection circuit D into the electrical circuit containing the contactor poses the same safety problems as those discussed in the first approach, notably by rendering the safety circuit inactive in the event of a shunt failure.

[0038] Also, and according to a third approach represented on the figure 4cIt is preferable to detect the switching of contactor C by indirect current measurement. In this preferred approach, the detection circuit D can take the form of a current transformer. This current transformer can include a primary winding consisting of one or more turns wound around the contactor C wiring. It exploits the magnetic field produced when the inrush current flows through contactor C during contact switching. To increase the amplitude of this inrush current and facilitate its detection, contactor C should be connected to an inductive load, such as the circuit breaker trip coil, rather than a resistive load.

[0039] In practice, the detection circuit D can implement a current transformer on a solid ferrite toroid, as shown in the figure 4c, the ferrite toroid being arranged around a conductor connecting the contactor to a terminal of device 1. Alternatively, the current transformer may implement a cut ferrite toroid or a Hall effect sensor introduced into the air gap of a toroid, or a Rogoswski coil, or any other form of current transformer.

[0040] Regardless of the approach chosen, the detection circuit provides a raw detection signal on which the occurrence of a contactor switching event can be identified. The detection circuit can also perform, at least partially, conditioning of the raw signal to facilitate event detection and / or its digital processing. This is especially true when the detection circuit implements indirect current measurement. In such a case, the contactor switching generates a transient raw signal with an amplitude of several volts that can be easily recognized, but which has a very short duration (the rise time can be as short as 25 ns) and therefore requires extremely high-frequency sampling, which is best avoided.

[0041] For example, signal conditioning can involve clipping and thresholding the raw signal to identify its main peaks. These peaks can be stored using a flip-flop circuit, and this stored signal can be sampled at a reduced frequency via an on / off circuit, such as a digital input on the electronic measuring unit. Optionally, in parallel with this initial processing, the raw signal, or the clipped and thresholded raw signal, can be digitized at very high rates, for example, every 20 ns. A limited number of samples can then be stored in a temporary memory circuit (e.g., an FPGA) to maintain a window of approximately 10 ms of the raw signal.The electronic measuring unit 17 can implement a processing mechanism that, upon receiving a positive detection value in the sampled binary signal, verifies more precisely in the samples of the temporary memory circuit the actual occurrence of a switching event. This avoids false detections that could occur from simple binary signal analysis by more finely discriminating the raw signal.

[0042] In an alternative form of conditioning that can be integrated into the detection circuit, the raw signal can be conditioned by a tuned resonant circuit (of the RLC type) to induce free oscillations over an extended period when a transient corresponding to a switch occurs. The signal output of the resonant circuit can be filtered to recover its envelope. The signal envelope can then be sampled at a reasonable frequency, for example, using a dedicated input of the electronic measuring unit 17. This reasonable frequency could be on the order of 1 kHz to effectively detect an actual switch operation.

[0043] Whether the raw measurement signal has been conditioned or not, the protection and monitoring device 1 always includes an electronic measuring unit 17. This unit 17 is connected to the detection circuit via a digital input or an analog-to-digital converter as described above, to receive the signal provided by the detection circuit and detect the occurrence of a switching event. This event is logged, i.e., time-stamped and stored by the electronic measuring unit 17 so that it can be analyzed later.

[0044] The electronic measuring unit 17 is typically implemented by a microcontroller or a microcontroller board. This unit is electrically powered from a power source, for example, a source located in the electrical cabinet 5. To compensate for an interruption in power supply, for example, as a result of a transformer failure causing it to trip, the electronic measuring unit 17 is equipped with an energy storage means, such as a battery or a very high-capacity battery. The unit 17 also includes means for storing switching events and other data collected by the device 1. These means can consist of non-volatile memory integrated into the microcontroller or additional non-volatile memory located on the microcontroller board. This can be removable memory, allowing an operator to easily retrieve all the recorded data.Advantageously, the electronic measuring unit 17 includes a communication interface for sending recorded data to an external control device. In addition to data exchange, the communication interface allows the external control device to diagnose, configure, or otherwise interact with the electronic measuring unit. Specifically, the communication interface can connect the electronic measuring unit 17 to an external control device located in the electrical cabinet 5 or to a connector on such a device. The connection between the communication interface and the external control device can be of any type, wired or wireless, and can use any suitable protocol.It will also be possible to provide several communication channels allowing remote control, recording of measurements and recorded events or receipt of alarms issued by the protection and monitoring device 1, for example from a control center managing a whole fleet of transformers, and concurrently, to control or record this device 1 from a control device integrated into the electrical cabinet 5 or temporarily connected to this cabinet by a maintenance operator.

[0045] Thus, a device according to the invention can be used for the protection and monitoring of a liquid-dielectric transformer enclosed in a hermetically sealed tank. During this operation, a switching event of an electromechanical safety contactor is detected by the detection circuit and recorded by the electronic measuring unit. Measurement circuit

[0046] Device 1 can naturally be equipped with other circuits or components to collect a richer set of monitoring information via the electronic measuring unit 17. For example, the device could be equipped with a circuit for measuring at least one characteristic of the liquid dielectric or a characteristic quantity related to the transformer's operating regime, in order to record this information in the electronic measuring unit. This could involve repeatedly measuring and collecting monitoring data using a fluid level measurement circuit, a circuit for measuring its temperature and pressure, a circuit for measuring the magnetic field emitted by the transformer windings, or a vibration measurement circuit.In this way, by using the collected data, it is possible to monitor the proper functioning of transformer 2, its load, and even estimate its lifespan and plan preventive maintenance interventions. All these measurement circuits are located in device 1 and are electrically connected to the electronic measuring unit 17. Therefore, it is not necessary to equip the other elements of transformer 2, and in particular its tank 3, with sensors. The ability to collect monitoring data on the transformer's operating regime without directly equipping these windings is a very advantageous aspect of a protection and / or monitoring device conforming to one aspect of the invention, as will be illustrated in a later section of this description.

[0047] In its use, a device 1 according to the invention therefore makes it possible to repeatedly measure and record in the electronic measuring unit 17 at least one characteristic of the liquid dielectric and / or a quantity characteristic of the operating regime of the transformer 2.

[0048] The modular configuration of device 1 allows all passive or active components—protection or monitoring components, such as electromechanical threshold detectors and at least some of the detection circuits—to be placed in the second internal space formed by the upper housing 7 and the internal volume of the dip tube 6. Similarly, the electronic measuring unit 17 and other non-passive elements can be placed in the third internal space formed by the peripheral housing 14.

[0049] As an example, we have represented on the figure 5an architecture implementing advanced monitoring functions. Schematically represented in this figure is the upper housing 7, the filling tube 9a of the intermediate part 9 equipped with the secondary float 15, and the peripheral part 14 comprising the two portions 14a, 14b shown in the assembly figure 2a.

[0050] For example, the figure 5The electronic measuring unit 17 consists of a microcontroller board 17a located in the second portion 14b of the peripheral part 14. This board 17a is electrically connected to the connector 16 via a portion 16b, which is inserted into the complementary portion 16a attached to the upper housing 7. The connector 16 thus allows the components located in the upper housing 7 to be electrically connected to the electronic measuring unit 17 and to any other components located in the upper housing 7. The microcontroller board 17a has a power supply and connection box 17b, which allows the electronic measuring unit 17 to be connected to an external power source and to the external control device. For this purpose, the power supply and connection box 17b is associated with power and communication cables 17c, which can be connected to the electrical cabinet 5.The microcontroller board 17a may also include energy storage means, non-volatile memory, and any other component contributing to form, in combination, the unit of measurement 17. This board 17a may also include the raw signal conditioning components supplied in the sensing circuit or a part thereof.

[0051] In the example of the figure 5The electronic measuring unit 17 is connected to a set of measuring circuits for monitoring the operation of the transformer 2. An electronic board 18 is placed in the first portion 14a of the peripheral housing, which is arranged along the filling tube. This board carries a plurality of magnetic sensors 18a, for example, Hall effect sensors with analog outputs, arranged at regular intervals along the filling tube 9a. The secondary float 15 is equipped with at least one permanent magnet that generates a radial magnetic field, the intensity of which is measured by the magnetic sensors 18a according to the relative position of the secondary float 15 with respect to these sensors 18a. The signals provided by the sensors 18a are transmitted, for example via an electrical connection ribbon cable 19a, to the microcontroller board 17a for processing by the electronic measuring unit 17.

[0052] The electronic measuring unit 17 is thus configured to digitally process the signals provided by the magnetic sensors 18a and establish a measurement of the dielectric fluid level. This measurement can be plotted, i.e., time-stamped and stored in the memory of the electronic measuring unit 17. Measuring the dielectric fluid level allows for the early detection of a significant variation in this level and makes it possible to proactively anticipate the switching of the safety contact associated with this level. This prevents the circuit breaker from tripping. The oil level measurement can be taken approximately every 30 seconds, or at least every minute. It can also be taken more frequently, for example, once or twice per second.

[0053] Continuing the description of the example shown on the figure 5The upper housing 7 also includes a circuit for measuring the pressure and temperature of the dielectric fluid. This circuit includes a sensor located in the upper housing 7, on the base 6d of the dip tube 6. For this purpose, the lower wall of the housing 7 and the base 6d are provided with a second opening leading into the intermediate section 9, allowing the sensor's measuring head to be exposed to the dielectric fluid. The analog pressure and temperature values ​​of the fluid measured by the sensor are transferred to a routing board 19, to which all the circuits located in the upper housing 7 and in the tube 6 are electrically connected. The routing board 19 ensures the routing of the signals and their connection to the connector 16 for transmission to the electronic measuring unit 17.

[0054] An acquisition port on the electronic measuring unit 17 samples the pressure signal from the sensor at a frequency of approximately 1 kHz. This allows for the identification of sudden pressure increases which, while not triggering the pressure switch, provide important information that can affect the transformer's lifespan and performance. The electrical fluid temperature signal from the sensor can be recorded at a lower frequency, for example, once per minute or up to once every 5 minutes.

[0055] Advantageously, the device 1 can also be equipped with sensors for the magnetic field and / or vibrations generated by the windings or other active parts of the transformer 2, which are indicative of the transformer 2's operating regime. The corresponding measurements can be obtained from a single sensor providing this data along three axes or from a plurality of sensors. They can be supplied to the measuring unit 17 directly (if the sensors are located in the peripheral section) or via the routing card 19 and the connector 16 (if they are positioned in the upper housing 7). The ability to provide information relating to the operation of the windings is a significant advantage of the invention in its monitoring function.

[0056] In general, the electronic measuring unit 17 can include any other type of sensor and collect data at the appropriate frequency, depending on the dynamics of the phenomena being measured, and on the order of 10 Hertz for the measurement of fields and acceleration / vibration.

[0057] To conclude the description of the figure 5 We have also shown an additional card 20 to carry the detection circuit(s).

[0058] Equipped in this way, it is quite apparent that the protection and monitoring device 1 forms a complete and compact solution for the protection and monitoring of transformer 2.

[0059] Of course the invention is not limited to the implementation methods described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

[0060] Thus, the electronic measuring unit 17 can implement functions other than those just described in detail. In particular, it can process acquired data or measurements to detect threshold crossings, sudden variations, and contact activation to establish and track significant events. These events can trigger alarm messages, for example, via the communication interface or a dedicated interface, to an external control device that may be located in a remote monitoring center. The unit can also process data to limit the amount of memory required for recording. This could involve, for example, recording averages, minimums, and maximums over predetermined time windows rather than all recorded measurements.As a further example, this could involve storing or transmitting only measurements that occurred within a few minutes or hours before or after identified significant events. In other words, measurements not occurring within the time frame of a significant event can be erased from the electronic measuring unit's memory.

[0061] In certain cases, a device conforming to the invention can be configured to limit itself to its protection function or its monitoring function.

[0062] Based on this latter aspect, a protection and / or monitoring device for a liquid dielectric transformer enclosed in a hermetically sealed tank is proposed, comprising: a measurement circuit for at least one characteristic quantity of the transformer's operating regime; an electronic measuring unit, connected to the measurement circuit and configured to record a measurement provided by the measurement circuit.

[0063] The measuring circuit may be a circuit for measuring the magnetic field emitted by the transformer windings or a vibration measuring circuit. The device may include at least one electromechanical safety contactor whose switching is intended to cause the instantaneous opening of a transformer circuit breaker.

Claims

1. Protection and monitoring device (1) for a liquid dielectric transformer (2) enclosed in an airtight tank (3), the device (1) comprising at least one electromechanical safety contactor (11c, 12c, 13b), the switching of which is intended to cause the instantaneous opening of a circuit breaker of the transformer (2), the device (1) comprising: - a circuit (D) for detecting the switching of the electromechanical contactor (11c, 12c, 13b); - an electronic measurement unit (17) which is connected to the detection circuit (D) and configured to trace the occurrence of a switching event; the device being characterized in that the detection circuit comprises a device for measuring voltage across the terminals of the electromechanical contactor (11c, 12c, 13b), in that said device further comprises three mutually distinct internal spaces separated from one another in a sealed manner, the three internal spaces being referred to respectively as the first internal space (8, 9), the second internal space (6, 7) and the third internal space (14), the first internal space (9, 8) being in fluidic communication with the liquid dielectric of the tank (3), the electromechanical safety contactor (11c, 12c, 13b) and at least part of the detection circuit (D) being arranged in the second internal space, while the electronic measurement unit (17) is arranged in a third internal space (14) of the device (1).

2. Device (1) according to the preceding claim, wherein the electromechanical contactor (11c, 12c, 13b) is included in an electromechanical detector with a temperature threshold, a pressure threshold or a liquid dielectric level threshold.

3. Device (1) according to either of the preceding claims, wherein the detection circuit (D) comprises components for conditioning a raw detection signal.

4. Device (1) according to any of the preceding claims, wherein the electronic measurement unit (17) comprises an energy storage means.

5. Device (1) according to any of the preceding claims, wherein the electronic measurement unit (17) comprises a communication interface.

6. Device (1) according to any of the preceding claims, comprising at least one circuit for measuring a piece of information for monitoring the transformer, the measurement circuit being electrically connected to the electronic measurement unit (17).

7. Device according to the preceding claim, wherein the measurement circuit is a circuit (18, 18a) for measuring the level, the temperature or the pressure of the liquid dielectric, a circuit for measuring the magnetic field emitted by windings (4a, 4b) of the transformer (2) or a vibration measurement circuit.

8. Method for protecting and monitoring a liquid dielectric transformer (2) enclosed in an airtight tank (3) and implementing the protection and monitoring device (1) according to any of claims 1 to 7, the method comprising: - a detection circuit (D) detecting a switching event of an electromechanical safety contactor (11c, 12c, 13b) intended to cause the instantaneous opening of a circuit breaker of the transformer (2); - an electronic measurement unit (17) tracing the switching event.

9. Method according to the preceding claim, comprising the repetitive measurement and the recording in the electronic measurement unit (17) of at least one characteristic of the liquid dielectric or of the windings (4a, 4b) of the transformer (2).

10. Method according to the preceding claim, comprising a step of processing the switching event and measurements in order to establish and trace a significant event.

11. Method according to the preceding claim, wherein the processing step comprises erasing, in the electronic measurement unit (17), the data which are not situated in a temporal vicinity of the significant event.