WO2012107816A1

WO2012107816A1 - Device for preventing the exploding of an electric transformer fitted with a liquid indicator

Info

Publication number: WO2012107816A1
Application number: PCT/IB2012/000175
Authority: WO
Inventors: Philippe Magnier
Original assignee: Philippe Magnier Llc
Priority date: 2011-02-08
Filing date: 2012-02-01
Publication date: 2012-08-16
Also published as: FR2971357B1; TW201237896A; UY33900A; AR085328A1; FR2971357A1

Abstract

Device for preventing the explosion of an electric transformer (1) provided with a tank containing cooling liquid (7). The device comprises a rupture element (15) provided with zones that tear and with zones that crumple upon rupture. The rupture element (15) is able to rupture when the pressure inside the tank exceeds a predetermined upper threshold. A retaining bracket for the rupture element is positioned on the opposite side of the rupture element to the tank. A liquid detector (24) is positioned on the side of the rupture element (15) opposite to the tank.

Description

Device for preventing the explosion of an electric transformer provided with a liquid indicator.

The present invention relates to the field of prevention against the explosion of electrical transformers cooled by a volume of combustible fluid.

The Applicant has realized that the number of transformer explosions is increasing faster than the installed fleet and with a decorrelation with respect to the age of the transformers. Returning to heavily armored transformers does not seem realistic under today's very flexible regulatory conditions on build quality. But the explosions of transformers cause more than a hundred deaths a year in the world and many atmospheric pollutions and soils.

Electrical transformers suffer losses both in the windings and in the iron part, which require the dissipation of the heat produced. Thus, the high-power transformers are generally cooled by a fluid such as oil. The oils used are dielectric and are likely to catch fire beyond a temperature of the order of 140 ° C. Transformers are very expensive items, their protection requires special attention. An insulation fault causes, firstly, a large electric arc that causes an action of electrical protection systems that trigger the transformer power cell (circuit breaker). The electric arc also causes a consequent diffusion of energy which generates a release of gas by decomposition of the dielectric oil, in particular hydrogen and acetylene.

Following the release of gas, the pressure inside the tank of the transformer increases very rapidly, resulting in a blast often very violent. Deflagration results in a major tear of the mechanical connections of the tank (bolts, welds) of the transformer which puts said gas in contact with the oxygen of the ambient air. Since acetylene is self-igniting in the presence of oxygen, a fire starts immediately and spreads fire to other equipment on the site that may also contain large quantities of combustible products. Explosions are due to insulation failures due to short circuits caused by overloads, overvoltages, gradual deterioration of insulation, insufficient oil level, water or mold occurrence or failure. an insulating component.

In the prior art, fire suppression systems for electrical transformers are operated by fire or fire detectors. But these systems were implemented with significant inertia, when the transformer oil was already in flames. The fire was limited to try not to spread the fire to neighboring facilities.

The document WO 9712379 introduced for the first time the prevention against explosion and fire in an electric transformer equipped with a tank filled with combustible cooling fluid, by detecting a break in the electrical insulation of the transformer by a pressure sensor, depressurizing the cooling fluid contained in the tank, by means of a valve, and cooling the hot parts of the cooling fluid by injecting an inert gas under pressure into the bottom of the tank in order to stir said fluid and prevent oxygen from entering the transformer tank. This process is satisfactory and avoids the explosion of the transformer tank.

WO 0057438 discloses a quick-opening rupture element for a device for preventing the explosion of an electrical transformer.

WO 2007/003736 discloses an improved device for extremely rapid decompression of the tank to further increase the probability of safeguarding the integrity of the transformer, load tap-changers and bushings while implementing shaped parts simple. This type of installation has been proven to preserve many lives.

The invention improves the situation. During her research, the Applicant found the presence of liquid downstream of the rupture element without the device being triggered or damaged. The Applicant, in order to prevent a possible reduction in the effectiveness of the protective device due to this presence of liquid, has sought to avoid the presence of liquid. The accumulation of liquid at this point could, in extreme cases, modify the triggering threshold of the device, by increasing the pressure drops after tripping and / or by accelerating corrosion phenomena. The electrical transformer is provided with a tank containing combustible coolant, for example oil. The device comprises a rupture element provided with tearing zones and bending zones at break. The rupture element is capable of breaking when the pressure inside the tank exceeds a predetermined ceiling. The device comprises at least one retaining flange of said rupture element disposed on the side of the rupture element opposite to the tank. The device comprises a liquid detector disposed on the side of the rupture element opposite the tank. The detector may include a liquid sensor.

The liquid detector can be mounted in a bore in the holding flange. This provides the liquid detector as close as possible to the rupture element so as to detect as soon as possible a leakage of said rupture element.

The liquid sensor may comprise an externally threaded tubular body. Disassembly is simple and fast for maintenance operations. The liquid detector may also be provided with a liquid presence display window enabling an operator to see for the first time the presence of detected liquid, for example to quickly assess the extent of the leak. The liquid detector may comprise an upper branch supporting said liquid sensor, and a lower leg provided with a purge valve. The upper branch and the lower branch may be perpendicular to each other. We thus has a device whose features and parts are structurally independent to facilitate maintenance.

The purge valve can be closed in the rest position, that is to say in normal operation, and open in the purge position. This makes it possible to maintain the seal between the outlet of the rupture element and the external environment in the event of the triggering of said rupture element.

The rupture element can be bulged away from the tank. This structure is adapted to the selected mechanical reaction of the rupture element when it is triggered and in the single direction of rupture.

The holding flange may include a liquid collecting groove in the vicinity of the breaker member. The groove makes it possible to channel a flow of liquid towards the active part of the liquid detector so as to detect any leak as soon as possible.

The explosion prevention system of an electrical transformer provided with at least one tank containing coolant comprises a device as described above in communication with the tank. The tank contains main windings, a tap changer or a bushing.

The system may further include a preservative (or tank) connected to the vessel through a first conduit. A gas detector may be mounted on said first conduit. The system may comprise a passive degassing member of an upstream zone of the rupture element. Said degassing member may be in communication with the gas detector. Said gas detector may be sensitive to degassing gas. This makes it possible to ensure degassing upstream of the rupture element, to detect the presence of gas which may be a sign of a malfunction and to dispense with a second gas detector by fluidly linking the first pipe and the space located upstream of the rupture element. The passive degassing member may be permanent. This makes it possible to dispense with human intervention subject to error. The gas detector may be located at an altitude greater than the rupture element. The degassing gases displaced by buoyancy are detected. An automatic valve may be mounted on said first conduit between the conservator and the gas detector. This makes it possible to control the flow of coolant towards the tank and / or the fluid isolation of the preservative from the rest of the device.

The passive degassing member may comprise an end disposed in an upstream zone of the rupture element and close to the rupture element at a distance from the latter less than seventy millimeters. This allows the degassing gases accumulated near the rupture element to be degassed as soon as a small volume of said gases is present. The passive degassing member may comprise an end, fixed near the rupture element. We thus join the two elements.

The passive degassing member may include an end attached to the first conduit. The passive degassing member may comprise a sloping tube. This makes it possible to produce the degassing member quickly, inexpensively and easily adaptable to existing devices.

The liquid detector may further comprise a T-shaped tube or an X tube itself comprising an upper branch supporting said liquid sensor and a lower branch provided with a purge valve. This allows an operator to easily reset the liquid detector after detection.

The space upstream of the depressurization chamber and the first pipe may comprise a common section in the vicinity of the tank. This reduces the overall size of the system by minimizing the elements, this is particularly advantageous for devices essentially located above the tank. The passive degassing member may comprise a connection with a partial evacuation member. This connection makes it possible to create a partial vacuum in the tank and limit the consequences of a pressure gradient. It also limits the presence of oxygen, flammable gas. The purge of the passive degassing member is authorized for any dangerous gases during maintenance.

The first conduit may include a second degassing member fluidly bonding said first conduit to the first discharge line or the collection reservoir. It is thus possible to evacuate a volume of fluid situated above the tank directly downstream of the tank in the event of overpressure.

The inert gas injection pipe from the bottom of the tank can be equipped, in the vicinity of the tank, with a non-return valve. This makes it possible to prevent the liquid contained in the tank from being drained by the gas injection pipe, particularly in the event of improper handling of the pipe.

The depressurization chamber may be based on at least one damper supported by a console secured to the tank or soil. The vibrations of the transformer are then at least partially absorbed by the damper instead of being transmitted to the depressurization chamber.

Thanks to the invention, the reliability of the prevention is further increased. This is all the more important as the life of the transformers tends to be reduced, the occurrence of short circuits increasing.

The device also makes it possible to detect and treat leaks.

The device reduces the risk of factors interfering with the rupture element.

The device prevents the explosion of an electrical transformer by means of a rupture element capable of breaking when an internal pressure threshold is exceeded. transformer tank. The device prevents the consequences of a leak in the vicinity of the rupture element by the detection of liquid.

The explosion prevention device is particularly well suited for electrical transformers located in confined areas, for example tunnels, mines or underground in urban areas.

The present invention will be better understood on studying the detailed description of some embodiments taken as non-limiting examples and illustrated by the appended drawings, in which:

- Figure 1 is a schematic view of a fire prevention device;

FIG. 2 is a diagram of the thickness of a rupture element;

FIG. 3 is a cross-sectional view of a rupture element;

- Figure 4 is a top view from the downstream of a rupture element; FIG. 5 is a view from below, from the upstream side of a rupture element;

FIG. 6 is a partial schematic representation of the interior of a section of tubes located downstream of the rupture element; FIG. 7 is an exploded view of a liquid detector;

FIG. 8 is a schematic representation of a part of the device;

FIG. 9 is a detailed view of a protection device;

FIG. 10 is a variant of FIG. 9; - Figure 11 is a vertical variant of Figure 9;

- Figure 12 is a variant of Figure 11; FIG. 13 is a variant of the embodiment of FIG.

The accompanying drawings may not only serve to complete the invention but also contribute to its definition, if any. By normal operation is meant here the transformation of energy by the transformer. The terms "upstream" and "downstream" are to be understood in a direction of movement of the oil from the tank to the outside.

As illustrated in FIG. 1, the electrical transformer 1 comprises main windings 90 placed in a tank 2. The tank 2 rests on the ground 3 by means of feet 4. The main windings 90 are supplied with electrical energy via crossings 91 surrounded by insulators. The electrical bushings 91 protrude from the tank 2. The electrical bushings 91 are fed by electric lines 5. The electrical lines 5 are fed via a supply cell 38, which comprises means of power supply interruptions. such as circuit breakers and trip sensors. Circuit breakers can be tripped by differential relays, cf. US 4,441,134.

The tank 2 comprises a body 2a and a lid 2b. The tank 2 is filled with cooling dielectric liquid 7, for example oil. In order to guarantee a constant level of coolant 7, for example a full filling, in the tank 2, the electric transformer 1 can be provided with a conservator 8 also called auxiliary tank, in communication with the tank 2 by a first conduct 9. The conservator 8 is located above the tank 2. The supply of coolant 7 is useful in particular because of the thermal expansion of the tank 2 and the coolant 7 in use. The first pipe 9 may be provided with an automatic valve 10 which closes the first pipe 9 during a rapid movement of coolant 7. In operation or filling the tank 2, the automatic valve 10 is open. The automatic valve 10 is autonomous. The automatic valve 10 is mechanically operated. The automatic valve 10 can be linked to sensors. The automatic valve 10 can be locked in the open position for filling the tank 2. During a rapid movement of fluid in the first pipe 9, the closing of the automatic valve 10 occurs. This prevents the coolant 7 contained in the conservator 8 from draining. If the rupture element is triggered, this prevents an additional volume of combustible liquid to be evacuated. This type of valve has been sold by Sergi since the 1960s.

By way of example, it is possible to use a valve according to IT 1 226 525. The valve comprises an inlet duct and an outlet duct connected by a rectangular compartment. A movable flap is mounted in the compartment, movable about an axis and lockable by a lever during maintenance. The valve is provided with a seal and subjected to the flow of liquid passing through the compartment. The movable valve is able to stop or reduce the flow between the two ducts. A handle outside the compartment can be rotated counterclockwise to open the valve during maintenance operations. In use, when said flow increases sharply, the valve is moved by the flow to a closed position. The position of the lever indicates the state "active" or "in maintenance" of the device. Actuation of the lever may be indirect, for example by means of a switch connected to a centralized control box. An air purge valve is disposed at the top of the compartment.

The first pipe 9 may be provided with a gas detector 55. The gas detector 55 is capable of detecting the gases in the first pipe 9. The gas detector 55 is located between said automatic valve 10 and the tank 2. The gas detector 55 can be a Buchholz. The slowness of reaction of Buchholz relays has been known since at least 1964 (see FR 1 415 293). Buchholz are sensitive to slow degassing bubbles of oil by a float. The Buchholz comprise a pallet which can be actuated by a displacement of liquid in the first pipe 9. Nevertheless, many transformers equipped with Buchholz have exploded, the Buchholz being unsuited to rapid phenomena.

The tank 2 may also be provided with one or more fire detectors 1 1. As represented in FIG. 1, a fire detector 11 is mounted above the tank 2 and is supported by studs 12 resting on the lid 2b. A distance of a few centimeters separates the fire detector 11 from the cover 2b. The fire detector 11 may comprise two wires separated by a synthetic membrane with a low melting point, the two wires coming into contact after melting of the membrane. The fire detectors 1 1 may be arranged along a rectangular path near the edges of the tank 2.

The tank 2 may comprise a cooling system of the coolant 7 by injection and stirring of an inert gas, such as nitrogen, in the bottom of the tank 2, cf. Figure 1. The inert gas is stored in a pressure tank provided with a valve, a pressure reducer or a pressure reducer and a pipe 21 bringing the gas from the bottom of the tank 2. The tank under The injection pipe 21 comprises, in the vicinity of the tank 2, a non-return valve 103. The non-return valve 103 allows the inert gas to flow in the direction directed towards the tank. 2. The check valve 103 blocks the passage of the liquid in the direction directed towards the outside of the tank 2. The check valve 103 prevents the accidental emptying of the tank 2 in case of rupture of the injection pipe 21 or accidental opening of its opposite end to the tank 2. The check valve 103 can be linked and controlled by a control box 23. The prevention device comprises a maintenance valve 13, cf. figure

1. The prevention device comprises a first elastic sleeve 14. The prevention device comprises a rupture element 15. The prevention device comprises a liquid detector 24. The prevention device comprises a depressurization chamber 16 (or decompression chamber). The prevention device comprises a second elastic sleeve 14. The prevention device comprises a drain line 17. The prevention device comprises a collection reservoir 18. The prevention device may comprise the aforementioned elements in this order starting from the tank 2, in other words, from upstream to downstream.

The maintenance valve 13 is mounted on an outlet of the tank 2, here disposed at a high point of the body 2a. Closing the maintenance valve 13, during maintenance operations and in particular when filling the tank 2, isolates the elements located downstream of said valve. Said insulation of the elements situated downstream of the maintenance valve 13 also makes it possible to intervene on said elements without having to empty the tank 2 of its cooling liquid 7. Among said elements, the breaking element 15 is particularly isolated. normal operation, the maintenance valve 13 is open.

The first elastic sleeve 14 vibration absorber is disposed downstream of the maintenance valve 13. The first elastic sleeve 14 is disposed upstream of the rupture element 15. The first elastic sleeve 14 take the general shape of a pleated section . The first elastic sleeve 14 takes the general shape of an accordion section. The first elastic sleeve 14 is of structure and sealed material. The first elastic sleeve is configured to ensure the continuity of the seal with the outside between the maintenance valve 13 located upstream and the breaking element 15 located downstream. The first elastic sleeve 14 is of structure and / or of material capable of undergoing significant elastic deformation. The first elastic sleeve is configured to reduce vibration between the upstream maintenance valve 13 and the downstream breaker 15. The elastic sleeves may comprise materials chemically resistant to the coolant 7 and fire-resistant properties, for example polytetrafluoroethylene (PTFE). The rupture element 15 is located downstream of the first sleeve 14. The rupture element 15 is located upstream of the liquid detector 24 and the depressurization chamber 16. The rupture element 15 is designed to be mounted on an outlet orifice, not shown, of the tank 2. In the embodiment shown in FIG. 1, the first elastic sleeve 14 is inserted between said tank outlet 2 and the rupture element 15.

As can be seen in FIGS. 3 to 5, one embodiment of the rupture element 15 is of convex curved circular shape. The breaking element 15 is held tight between two retaining flanges 33, 34 in the form of disks, cf. FIG. 3. Each of the holding flanges 33, 34 is, in the mounted state, integral with the element element located immediately upstream respectively downstream of the rupture element 15. The rupture element 15 comprises a part retainer 35, cf. Figures 2 and 4, in the form of a metal thin film, for example stainless steel, aluminum, or aluminum alloy. The thickness of the retaining portion 35 may be between 0.05 and 0.25 mm. The retaining portion 35 is provided with radial striations 36 dividing it into several portions, cf. Figure 4. The radial striations 36 are tearing zones. The radial striations 36 are formed recessed in the thickness of the retaining portion 35 so that a break is made by tearing the retaining portion 35 at its center and without fragmentation to prevent fragments of the element. rupture 15 are torn off and displaced by the fluid passing through the rupture element 15 and may deteriorate a pipe located downstream.

The retaining portion 35 is provided with through holes 37 of very small diameter distributed one by radial striation 36 near the center of the retaining portion 35. In other words, several through holes 37 are arranged, for example in hexagon if the radial striations 36 are six in number, as shown in FIG. 4. The through holes 37 form low strength tear primers and ensure that the tear begins at the center of the retaining portion 35. The formation of at least one through hole 37 By radial striation 36 ensures that the radial striations 36 will separate simultaneously offering the cross section as strong as possible. Alternatively, the number of radial striations 36 may be different from six. Several through holes 37 per radial striations 36 may be provided. An additional sealing portion 49 comprising a thin film 50 is capable of closing through holes 37.

The bursting pressure of the rupture element 15 is determined, in particular, by the diameter and the position of the through holes 37, the depth of the radial grooves 36, the thickness and the composition of the material forming the retaining part 35. Preferably, the radial grooves 36 are formed over the entire thickness of the retaining portion 35. The remainder of the retaining portion 35 may have a constant thickness. Two adjacent radial striations 36 form a disk portion 39. The disk portion 39 comprises a side oriented along a radial strip 36, a second side oriented along another radial strip 36 and a third side having an arc shape. The disk portions 39 are connected, via said third arcuate side, inside a ring 35a included in the retaining portion 35. The ring 35a is disposed between the holding flanges 33 , 34. The ring 35a is devoid of radial striation 36. The disc portion 39, upon rupture, will separate from the neighboring disk portions 39 by tearing the material between the through holes 37 and deform downstream by folding. The disk portions 39 fold, in the vicinity of their third arc-shaped side, without tearing to prevent tearing of said disk portion 39 from the ring 35a and likely to damage a downstream pipe or to interfere with it. flow in the downstream pipe thus increasing the pressure drop and slowing the depressurization upstream side. In other words, after breaking of the rupture element 15, the disk portions39 open to the image of flower petals. The disk portions 39 remain in one piece with the ring 35a. The breaking of the rupture element 15 can be seen as a bursting of its central part. Said burst must be understood as not being the origin of the creation of splinters separating from the ring 35a. The retaining portion 35 remains in one piece. The number of radial grooves 36 also depends on the diameter of the rupture element 15.

The annular holding flange 34 disposed downstream of the annular holding flange 33 is pierced with a radial hole in which a protective tube 41 is arranged, cf. FIG. 3. The holding flange 34 disposed downstream of the holding flange 33 is pierced with a radial hole in which a liquid detector 24 is arranged. A rupture detector comprises an electrical wire 42 (see FIG. 4) fixed on the retaining part 35 on the downstream side and arranged in a loop. The electrical wire 42 is extended in the protection tube 41 to a connection box 43. The electrical wire 42 extends over almost the entire diameter of the breaking element 15, with a portion of wire 42a arranged in one side of a radial groove 36 parallel to said radial groove 36 and the other wire portion 42b disposed radially on the other side of the same radial groove 36 parallel to said radial groove 36. The distance between the two wire 42a, 42b is weak. This distance may be less than the maximum distance separating two through holes 37 so that the electric wire 42 passes between the through holes 37.

The electrical wire 42 is covered by a protective film which serves both to prevent its corrosion and to stick it on the downstream face of the retaining portion 35. The composition of this film will also be chosen to avoid changing the pressure of the rupture of the rupture element 15. The film may be made of weakened polyamide. The bursting of the rupture element 15 inevitably causes the electric wire 42 to be cut. This break can be detected extremely simply and reliably by interrupting the flow of a current passing through the electrical wire 42 or else by a gap of voltage between the two ends of the electric wire 42.

The rupture element 15 also comprises a reinforcing portion 44 disposed between the holding flanges 33 and 34 in the form of a metal veil, for example made of stainless steel, aluminum, or aluminum alloy (see FIGS. 2 and 5). The thickness of the reinforcing portion 44 may be between 0.2 and 1 mm. The reinforcing portion 44 comprises a plurality of petals, for example five, separated by radial slots 45, which can be formed throughout its thickness. The radial slots 45 may be tear zones. The petals connect to an annular outer edge. A folding zone 46, for example a streak, in an arc of a circle may be formed over the entire thickness of each petal except near the neighboring petals, thus giving the petals an ability to deform axially. Folding areas 46 may be torn on part of their thickness located on the upstream side to facilitate the folding of the petals to the downstream side. One of the petals is connected to a polygon central 47, for example by welding. The central polygon 47 closes the center of the petals and comes to rest on hooks 48 fixed on the other petals and offset axially with respect to the petals so that the central polygon 47 is arranged axially between the petals and the corresponding hooks 48. The central polygon 47 can come into contact with the bottom of the hooks 48 to support it axially. The reinforcing portion 44 provides good axial resistance in one direction and a very low axial resistance in the other direction, the direction of bursting of the rupture member 15. The reinforcing portion 44 is particularly useful when the pressure in the tank 2 of the electrical transformer 1 is lower than that of the depressurization chamber 16 which can occur if a partial vacuum is made in the tank 2 for the filling of the electrical transformer 1. Between the holding portion 35 and the part reinforcement 44, may be arranged a sealing portion 49 comprising a thin film 50 of tight synthetic material for example based on polytetrafluoroethylene surrounded on each side by a thick film 51 of pre-cut synthetic material avoiding a perforation of the thin film 50 by the retaining portion 35 and the reinforcing portion 44. Each thick film 51 may comprise a synthetic material, for example based on polytetrafluoroethylene thickness of the order of 0.1 to 0.3 mm. The precut of the thick films 51 can be performed in a circular arc of about 330 °. The thin film 50 may have a thickness of the order of 0.005 to 0.1 mm.

The rupture element 15 offers good resistance to pressure in one direction (here from downstream to upstream), a calibrated resistance to pressure in the other direction (here from upstream to downstream) , excellent sealing and low burst inertia. The rupture element 15 must be understood as a rapid rupture because the time between the creation of an overpressure in the tank 2 and the bursting of the rupture element 15 is of the order of milliseconds and directly related to the velocity of propagation of the waves in the coolant 7.

To improve the seal, the rupture element 15 may comprise a washer 52 disposed between the holding flange 33 and the reinforcing portion 44 and another washer 53 disposed between the holding flange 34 and the retaining portion 35. washers 52, 53 may be made from polytetrafluoroethylene. In other words, one of the functions of the rupture element 15 is that of a mechanical circuit breaker designed to yield, in case of abnormal pressure, instead of other mechanical elements more difficult to replace. A function of the rupture element 15 is to release said abnormal pressure in the tank 2, the pressure gradient resulting from an electrical insulation fault is reversed. The rupture element 15 bursts in a controlled manner preventing the tank 2 and other part of the transformer 1 from undergoing irreversible deformations as a consequence of a large pressure gradient.

The liquid detected by the liquid detector 24 may originate from leakage of the rupture element 15, cf. FIG. 3. The liquid detected by the liquid detector 24 may be caused by condensation in the vicinity of the rupture element 15. The liquid detector 24 is placed downstream of the rupture element 15. The liquid detector 24 is placed upstream of the depressurization chamber 16, cf. Figure 1. The liquid detector 24 is here fixed on the holding flange 34 of the rupture element 15, cf. FIG. 6. The liquid detector 24 comprises an active part 71. The active part 71 is in fluid communication with the inside of the device, that is to say here the internal part of the holding flange 34. Said fluid communication can be achieved by means of a substantially radial bore 80 of the holding flange 34. The bore 80 is radially traversed from an inner surface to an outer surface of the holding flange 34. The liquid detector 24 is here mounted in said bore 80 formed in the holding flange 34. The space 40 located downstream of the rupture element 15, upstream of the depressurization chamber 16 and inside the holding flange 34 is therefore in fluid communication with the active part 71 of the liquid detector 24, cf. Figures 1 and 6. The holding flange 34 here comprises a groove 81 for collecting liquid. The groove 81 is disposed in the vicinity of the downstream end of the rupture element 15. The collecting groove 81 is configured to guide, by gravity, the flow of a possible liquid towards the bore 80. The active part 71 of the liquid detector 24 will detect all the faster leakage of the rupture element 15, it is placed in the vicinity of the rupture element 15. The distance between the rupture element 15 and the detector of rupture liquid 24 may be less than 80 mm. The liquid detector 24 may comprise connecting elements 79, for example a flexible tube, a nut and a sleeve, cf. FIG. 7. The connecting elements 79 are located downstream of the space 40. The connecting elements 79 put in fluid communication the space 40 situated downstream of the rupture element 15 and an active part 71 of the liquid detector. 24.

The liquid detector 24 here comprises a tube 74 Té. The T-tube 74 is located downstream of the connecting elements 79. The T-tube 74 serves to fluidly bond together the connecting elements 79 and the active part 71 of the liquid detector 24. The T-tube 74 comprises a branch upper 75 supporting the active portion 71. The tube 74 Tee comprises a lower branch 76 provided with a purge valve 78.

The active part 71 of the liquid detector 24 is, here, a liquid sensor 71. The liquid sensor 71 here comprises a tubular body provided with external threads 72 adapted to ensure the screw-fastening of the liquid sensor 71. threads of the tubular body 72 of the liquid sensor 71 may be assembled at an interface 77. The liquid sensor 71 may for example be of the ultrasonic level sensor type.

The interface 77 serves to electronically link the liquid sensor 71 to the control box 23 or to any other information collection instrument. The purge valve 78 is located at a lower altitude than the remainder of the liquid detector 24, here on the lower branch 76 of the tube 74 Té. The purge valve 78 makes it possible to extract the liquid without dismantling the liquid detector 24. The purge valve 78 is closed in the rest position, that is to say in normal operation of the transformer 1 and open in a transient position. purge.

The liquid detector 24 here comprises a viewing window 73 for the presence of liquid. The viewing window 73 is a substantially transparent element that allows an operator to see firsthand the presence of liquid. In the embodiment shown in FIG. 7, the viewing window 73 and the purge valve 78 form a single piece.

In other embodiments, shown in FIGS. 6, 9, 10 and 11, the tube 74 is not in Tee but in X. The additional branch of the tube 74 in X supports a viewing window 73 distinct from the valve of FIG. purge 78.

The tube 74 Tee or X may be configured to adapt to a pre-existing configuration of a transformer to provide a liquid detector 24. The extrinsic configuration of the elements constituting the liquid detector 24 respects the constraints fluids subjected to gravity. In other words, the liquid sensor 71 is located in a space filled with priority, if necessary, by the liquid, so as to detect the lowest possible liquid volume.

The configuration of the liquid detector 24 and in particular the configuration of the connecting elements 79 can be adapted to many existing configurations of electrical transformers 1, cf. Figures 9 to 12.

The depressurization chamber 16 is of greater diameter than that of the rupture element 15. The depressurization chamber 16 is mounted downstream of the rupture element 15. The depressurization chamber 16 is mounted upstream of the second elastic sleeve 14 The depressurizing chamber 16 is disposed with its main axis substantially aligned with the output direction of a flow passing through the breaking member 15 at the moment of release. As represented in FIG. 1, the elements of the prevention device situated upstream of the depressurization chamber 16 and downstream of the tank 2, release a straight and short passage to the depressurization chamber 16 at the moment of triggering of the breaking element 15. Said passage straight and short ensures a low pressure drop of the outgoing flow. The depressurization chamber 16 may rest on dampers 28 supported by a bracket 29 fixed to the body 2a of the tank 2. Mechanical insulation is thus created between the vibrations from the electrical transformer 1 in service and the depressurization chamber 16. The mechanical insulation is also improved thanks to the elastic sleeves 14. The depressurization chamber 16 may be under the shape of a tube portion of diameter significantly higher than the diameter of the drain line 17 downstream. The depressurization chamber 16 may advantageously be designed to withstand higher pressures and mechanical forces than those for which the collection reservoir 18, located downstream of the drain line 17, is dimensioned. The depressurization chamber 16 makes it possible to reduce the speed of the outgoing flow by the rupture element 15 and to absorb the kinetic energy of said flow.

The second elastic sleeve 14 is similar to the first dimensioned. The second elastic sleeve 14 is mounted downstream of the depressurization chamber 16. The second elastic sleeve 14 is mounted upstream of the drain line 17. The second elastic sleeve 14 ensures the continuity of the seal between the depressurization chamber 16 located upstream and the drain line 17 downstream. The second elastic sleeve 14 is configured to reduce vibrations between the depressurization chamber 16 and the downstream discharge line 17.

The drain line 17 is disposed downstream of the depressurization chamber 16, cf. 1. The drain line 17 is arranged upstream of the collection tank 18. The drain line 17 is configured so as to guide a flow of liquid and gas at the outlet of the depressurization chamber 16 until 18. The size of the drain line 17 is designed to allow rapid evacuation of the flows after rupture of the rupture element 15.

The collection tank 18 is located downstream of the drain line 17, cf. 1. The collection reservoir 18 is a storage volume of liquid and gas from the tank 2 after rupture of the rupture element 15. The collection reservoir allows, after receiving the flow from the tank 2, to separate the liquid fraction of the gaseous fraction, for example by decantation. The collection tank 18 is here equipped with cooling fins 18a. The cooling fins 18a accelerate the cooling of the fluids from the tank 2 and reduce the risk of fire. The collection tank 18 is here The evacuation pipe 19 can be connected temporarily to a mobile tank to drain the collection tank 18. The tank 2 is thus depressurized immediately and subsequently. partially discharged into the collection tank 18. The discharge pipe 19 is here provided with an outlet valve 20. The outlet valve 20 prevents the entry of oxygen from the air reducing the risk of combustion of the gases. and that of the combustible liquid in the collection tank 18 and in the tank 2. The outlet valve 20 and prevents the uncontrolled exit of gas or liquid. The outlet valve 20 is constantly closed in normal operation to maintain the collection reservoir 18 hermetic. The outlet valve 20 can be opened when the collection reservoir 18 of the fluids therein is emptied, or a purge is performed.

The collection reservoir 18 may comprise a means of cooling the liquid stored by injection and mixing an inert gas, such as nitrogen, in the bottom of the collection reservoir 18, cf. Figure 1. The inert gas is stored in a pressure tank equipped with a valve, a pressure reducer or a pressure reducer and a pipe bringing the gas to the bottom of the collection tank 18. The reservoir This cooling means can be largely common with a cooling means of the tank 2 already described.

The fire detector 11, the rupture element 15, the automatic valve 10, the trip sensors, the outlet valve 20 and / or the cabinet 22 can be connected to the control box 23 intended to control the operation of the device, cf. FIG. 1. The control unit 23 may be equipped with information processing means receiving signals from the different sensors and capable of transmitting control signals.

Several electrical transformers 1 or neighbors may be connected to a collection tank 18, cf. In other words, several prevention devices of several different transformers may comprise a collection tank 18 and / or parts of the first discharge line 17 common. This is particularly advantageous in confined spaces where the available space is limited. As represented in FIG. 1, the electrical transformer 1 can be equipped with a tap changer 25 serving as an electrical interface between said electric transformer 1 and the electrical network to which it is connected to ensure a constant voltage despite variations in the network. .

The on-load tap changer 25 is here located in the main tub 2. The tap changer 25 has its own tub. The tank of the on-load tap changer 25 is used to fluidically isolate the on-load tap changer 25 from the coolant 7 present in the tank 2. The tank of the on-load tap-changer 25 is inserted into the tank 2. The tank The on-load tap-changer 25 is also cooled by a coolant, generally oil, similar or different to that of the tank 2, in the coolant 7 of the tank 2. The on-load tap changer 25 may have a conservator 8. Each preservative may be independently provided with a Buchholz, cf. EP 0 957 496, paragraph 30. Because of its high mechanical strength, the explosion of an on-load tap changer 25 is extremely violent and may be accompanied by splashes of ignited coolant jets. The on-load tap changer 25 is connected by a second drain line 26 to the first drain line 17. The second drain line 26 is provided with a rupture member 30. The rupture member 30 may be similar to the rupture element 15 of the tank 2 described above, adapted in size to the on-load tap-changer 25. The rupture element 30 may comprise a liquid detector 24. The rupture element 30 is capable of tearing itself apart. case of overpressure inside the on-load tap changer 25, especially in the event of a short-circuit. This reduces the probability of the explosion of the tank of said on-load tap changer 25. The operation of the on-load tap-changer protection device is relatively similar to the operation of the transformer 1. The second drain line 26 also serves depressurization chamber, the fluid volume at the outlet of the tap changer 25 being much lower than that of the tank 2, cf. figure 1. The electrical bushings 91 serve to isolate the main tank 2 of an electrical transformer 1 from the high and low voltage lines to which main windings 90 of the electrical transformer 1 are connected by means of electrical lines 5. Each bushing 91 can be surrounded by a tank 70 containing a certain amount of isolation fluid. The isolation fluid of the bushings 91 is separated from the main tank 2. The explosion prevention device is adapted for the main tank 2 of an electrical transformer 1, for the tank of the on-load tap changer 25, and for the tanks 70 of the electric bushings 91, also known as "oil boxes". .

The maintenance valve 13 can be closed for maintenance operations, the electrical transformer 1 being stopped. In use of the transformer 1, the maintenance valve 13 is open and the rupture elements 15, 30 intact, that is to say closed. The outlet valve 20 is also closed. The elastic sleeves 14 are capable of absorbing vibrations of the electrical transformer 1 that occur during its operation and during a short-circuit, to avoid transmitting vibrations to other elements, in particular to the rupture element 15.

The rupture element 15 may be provided to open at a given pressure of less than 1 bar, for example between 0.6 and 1 bar, preferably between 0.8 and 1 bar. During the bursting of the rupture element 15, following an electrical fault in the electric transformer 1, the pressure in the tank 2 decreases. A jet of gas and / or liquid passes through the open rupture element and spreads in the depressurization chamber 16, then flows into the drain line 17 to the collection tank 18. The role of the chamber depressurization 16 may be particularly important in the first milliseconds after bursting of the rupture element 15. The depressurization chamber 16 allows a strong flow during the bursting of the rupture element 15 through losses of extremely reduced loads.

Subsequently, an injection of inert gas, for example nitrogen, can be carried out in the bottom of the tank 2 to drive off the combustible gases that may be stay in the tank 2 and cool by stirring the hot parts of the liquid of the electric transformer 1 to stop the production of gas. The injection of inert gas can be triggered from a few minutes to a few hours after bursting of the rupture element 15.

Preferably a settling time in the collection tank 18 sufficient for gases and liquids to separate properly is provided. In addition, it is possible to wait for the cooling of the collection tank 18 and its contents. A portable tank can be brought into connection with the discharge pipe 19 to receive the fluids present in the collection tank 18 after opening the outlet valve 20. The collection tank 18 can be purged with an inert gas. Said combustible gases are evacuated from the collection tank 18 to a suitable mobile container. The rupture element 15 can then be replaced. For safety reasons, the tank of the inert gas is provided to inject inert gas for a period of about 45 minutes, which can be useful for cooling the coolant 7 and the hot parts by stirring of the liquid, and thus stop the production of gas by decomposition of the coolant 7.

In the event of an incident in the tank 2 or the tank of the tap changer 25, for example a short-circuit, the pressure increases suddenly. If the predetermined pressure threshold is reached, the rupture element 15, respectively 30, passive yields and opens abruptly in a planned course. The opening creates allows to evacuate a volume of liquid and / or gas quickly making quickly lower the internal pressure of the tank concerned. The detection of the triggering of the rupture element 15, respectively 30, causes the initiation of the stirring by inert gas after a chosen delay. The volume of fluid passing through the rupture element 15, respectively 30, is discharged to the collection tank 18 through the depressurization chamber 16. The transformer 1 is stopped, for example by triggering the circuit breaker of the cell d 38. The repairs, in particular the replacement of the rupture element 15, respectively 30, can take place. The probability of preserving the integrity of the tanks is increased. The inert gas injection from below, rather than from above, of the on-load tap changer tank 25 allows for better mixing, by means of an additional tube portion disposed in the tap changer tub. 25. Mixing from the top of the tank of the tap changer 25 has a lower interest in terms of stirring. Mixing from the top of the on-load tap changer tank 25 could, on the other hand, facilitate the circulation of air and stoke flames in the event of a fire. This solution is to be avoided.

Existing devices do not passively detect or evacuate gas accumulation upstream of said fast-opening rupture member. However, this accumulation may be indicative of an anomaly of varying importance and may present a risk of accumulation of harmful and / or explosive gases. The proposed device improves the device by detecting and evacuating the accumulation of gas.

The device, cf. FIGS. 8 and 12 are here provided with a passive degassing member 97 and a gas detector 55. The passive degassing member 97 here provides fluid communication between the space upstream of the rupture element. 15 and the interior of the first line 9 linking the conservator 8 to the tank 2. In the case, represented in FIG. 8, of a single gas detector 55, the said gas detector 55 must be placed at the altitude more suited to the possible presence of gas.

The passive degassing member 97 allows degassing of the space upstream of the rupture element 15, the side of the tank 2. Said space is filled with coolant 7 of the tank 2 in normal operation.

The passive degassing member 97 here comprises an end 98a disposed in the space upstream of the rupture element 15. Said end 98a of the passive degassing member 97 is fixed near the rupture element 15 The distance separating said end 98a and the breaking element 15 is preferably less than 70 millimeters. The passive degassing member 97 here comprises an end 98b opening into the first conduit 9. The passive degassing member 97 comprises here an end 98b attached to the first pipe 9. The passive degassing member 97 here comprises a monotonous slope tube 99. The monotonic slope of the tube 99 may, for example, be between 0 and 10%, preferably between 3 and 5%. As shown in FIG. 8, the passive degassing member 97 here comprises a maintenance valve 95. The maintenance valve 95 is constantly open in normal operating mode and can be closed for maintenance operations. The passive degassing member 97 may be permanent. The passive degassing member here comprises a connection 101 which can be closed during normal operation. The connection 101 can be fast coupling. The connection 101 makes it possible to connect a partial evacuation device to the passive degassing member 97. This partial evacuation can be carried out in the maintenance phase. This partial evacuation creates a slight depression inside the system limiting the consequences of a pressure gradient. This partial evacuation limits the amount of oxygen present in the system.

As shown in FIG. 1, a second degassing member 102 can be connected to the first duct 9. The second degassing member 102 fluidly links the first duct 9 to the collection tank 18. In a variant, the second degassing member 102 can bind fluidically the first pipe 9 to the first discharge pipe 17. In the event of overpressure in the conservator 8 and the first pipe 9, a volume of fluid (liquid and / or gas) can be directly removed from the vessel 2. In an alternative embodiment, the first pipe 9 and said space upstream of the rupture element 15 may comprise a common section in the vicinity of the tank 2. This variant is particularly interesting for installations whose horizontal surface is limited. A substantial part of the entire device can be disposed above the tank 2. Conversely, if the available height is limited, for example in the basement, a substantial portion of the entire device can be disposed at an altitude comparable to that of the tank 2. The passive degassing member provides fluid communication between the space immediately upstream of the rupture element 15 and the gas detector 55 for the detection of gas accumulated upstream of the rupture element 15. The organ Degassing passive 97 can be adapted to many configurations of existing electrical transformers 1, cf. figure 12.

In the embodiment of Figures 8, 11 and 12, the prevention device is disposed substantially vertically, for example on the lid 2b of the tank 2. The depressurization chamber 16 is oriented along a vertical axis. The depressurization chamber 16 may comprise a tube closed at the upper end and open at the lower end connected to the rupture element 15. The depressurization chamber 16 also forms the collection reservoir 18. As represented in FIG. the pipe 19a is connected to an upper zone of the cylinder of the depressurization chamber 16 for sampling the gas. A pipe 19b connects to a lower zone of the cylinder of the depressurization chamber 16 for the withdrawal of liquid. This embodiment is particularly compact, the prevention device being located largely above the tank 2. The collection tank 18 may have a phase separator function. The collection tank 18 may have a settling function.

The protection and detection device is economical, autonomous compared to neighboring installations, of small footprint and requires little or no maintenance.

Mounting the explosion prevention device in a transformer requires little modification of the transformer elements. The device responds to insulation failures in an extremely fast manner limiting the resulting consequences, including in confined spaces. The production of gas in minute amounts in normal operation is thus evacuated outside the tank. The accumulation and pocket formation of gases that can be dangerous is reduced. These gases are detected to better control them. The invention allows very early detection of minimal liquid leakage through the rupture element. This liquid can be purged. The downstream face of the rupture element remains substantially dry. There is little or no additional pressure drop in case of breakage of the rupture element. It reduces the risk of explosion of the tank and in particular the lid. We reduce the damage of a deformation. The detection of minimal leaks makes it possible to prepare a minor maintenance intervention, for example by replacing the rupture element during an already programmed stoppage, avoiding the reduction of the availability rate of the transformer in service. The device is adaptable to existing installations. The invention proposes an improved system and device for detecting leaks and accumulations of liquid (oil or water) before the phenomena in question pose a serious risk. The invention makes it possible to control a presence of liquid, for example condensation, and improves the detection of a possible operating anomaly of the rupture element.

A device in a normal operating condition includes an intact and fluid impervious rupture element. In this state, a first face defining the upstream side of the rupture element is oriented on the side of the vessel. The first face is in contact with the coolant contained in the tank. The first face is concave. The first face is wet in the sense that it is in contact with the coolant. In the normal operating state, a second face of the breaker member, opposite the first, defines the downstream side of said breaker member. The second face is oriented on the opposite side to the tank. The second face is not in contact with the coolant. The second face is in contact with the gas contained in the drain line and in the decompression chamber. The second face is convex. The second face is dry in the sense that it is in contact with the gas. The liquid detector is disposed on the side of the second face of the rupture element. The liquid detector is arranged to detect a presence of liquid on the second face of the rupture element or in its immediate vicinity. The position of the liquid detector is chosen to be closer to the second face of the rupture element without interfering with the operation in case of overpressure in the tank and bursting of the rupture element. The presence of liquid on the downstream side of the rupture element may be due, for example, to a deficiency in the hermeticity of the rupture element or to the presence of condensation on its surface. This undesired presence of liquid, in otherwise normal operation, is potentially detrimental to the good efficiency of the device in case of subsequent bursting. The detection of this liquid makes it possible to generate monitoring information for a maintenance intervention to eliminate the undesired presence of liquid on this side of the rupture element.

In the safety operating state, that is to say the bursting of the rupture element resulting from an overpressure in the tank, the liquid detector detects the presence of coolant discharged through the breaking element. In this case, the detection of the coolant coming from the tank by the liquid detector is a consequence of the triggering of the rupture element. The liquid detector acts as an additional trigger detector in relation to other specific failure detectors. The trigger detection of the safety device by the liquid sensor improves the reliability of the device. For example, in the event of a malfunction of a specific break detector, the triggering of the device will still be detected by the liquid detector. The liquid detector has an additional function of triggering detection of the safety device.

Claims

claims

1. Device for preventing the explosion of an electric transformer (1) provided with a tank (2) containing coolant (7), the device comprising a rupture element (15) provided with tear zones ( 36, 45) and breaking zones (46) at break, said breaking element (15) being capable of breaking when the pressure inside the tank (2) exceeds a predetermined ceiling, and at least one flange (34) for holding said rupture element (15) arranged on the side of the rupture element (15) opposite the tank (2), characterized in that it comprises a liquid detector (24) arranged on the side the rupture element (15) opposite the tank (2).

2. Device according to claim 1, wherein the liquid detector (24) is mounted in a bore (80) formed in the flange (34).

The device of claim 1 or 2, wherein the liquid sensor (24) comprises an externally threaded tubular body (72).

4. Device according to one of claims 1 to 3, wherein the liquid detector (24) comprises a viewing window (73) of presence of liquid.

5. Device according to one of claims 1 to 4, wherein the liquid sensor (24) comprises an upper branch (75) supporting a liquid sensor (71), and a lower branch (76) provided with a valve purge (78).

6. Device according to one of claims 1 to 5, wherein the rupture element (15) is curved opposite the tank (2).

7. Device according to one of claims 1 to 6, wherein the flange (34) comprises a groove (81) for collecting liquid in the vicinity of the rupture element (15).

8. Prevention system against the explosion of an electrical transformer provided with at least one tank containing coolant (7), the system comprising a device according to one of the preceding claims mounted in communication with said tank, said vessel containing main windings (90), a load changer (25) or a bushing (91).

9. System according to claim 8, comprising a conservator (8) connected to said tank by a first pipe (9), a gas detector (55) mounted on the first pipe (9) and a passive degassing member (97). an upstream zone of the element of rupture (15) in communication with the gas detector (55), the gas detector (55) being responsive to the degassing gas.

10. Device according to claim 9, wherein the passive degassing member (97) is permanent and the gas detector (55) is mounted at an altitude greater than the altitude of the rupture element (15).

1 1. Device according to one of claims 9 and 10, wherein the passive degassing member (97) comprises an end (98a) disposed in an upstream zone of the rupture element (15), near the breaking element (15), said end (98a) being at a distance from the breaking element (15) of less than seventy millimeters.

12. Device according to one of claims 9 to 1 1, wherein the passive degassing member (97) comprises an end (98a) fixed near the rupture element (15).

13. Device according to one of claims 9 to 12, wherein the passive degassing member (97) comprises an end (98b) fixed to the first pipe (9) and a tube (99) monotonous slope.

14. Device according to one of claims 9 to 13, wherein the passive degassing member (97) comprises a connection (101) with a partial vacuum member.

15. Device according to one of claims 9 to 14, wherein the first conduit (9) comprises a second degassing member (102) fluidly bonding said first conduit (9) to a first drain line (17) or a collection tank (18).

16. Device according to one of claims 1 to 15 comprising a pipe (21) for injecting inert gas from the bottom of the tank (2), the pipe (21) being equipped in the vicinity of the tank (2). , a non-return valve (103).

17. Device according to one of claims 1 to 16 wherein a depressurization chamber (16) rests on at least one damper (28) supported by a bracket (29) integral with the vessel (2) or soil (3) .