EP0883222A1 - Self-protected trip device for immersed electrical transformer - Google Patents

Abstract

The arrangement comprises a light lever (6) made from, e.g. polypropylene. The lever is asymmetrically arranged about a pivot (7). When the lever is horizontal, its shorter arm (8) just fails to contact, with its finger (11), an actuator (2) of a trip-switch (5) that controls a primary side circuit-breaker. An open-topped (20) cup (10), terminates a longer arm (9) of the lever and is filled with oil. Initially, at the end of the tank filling process the arm swings up vertically as the oil rises in the tank; its movement being halted by a tank lid stop (12). If the tank leaks (17,13), the finger rises against the actuator to apply a force (Fd) mainly due to the weight of oil in the cup, which, at a preset value, overcomes the actuator resistance and trips the circuit-breaker, optionally, after a time delay.

Description

The invention relates to the field of electrical power transformers or distribution of electrical energy, and more precisely that of submerged transformers self-protected.

Remember that an immersed transformer is a transformer whose windings and the magnetic circuit are cooled by immersion in a liquid dielectric, such as mineral oil, contained in an airtight container. It says "self-protected" when it includes on-board equipment allowing, without energy input outdoor, to automatically disconnect its primary windings from the network of electrical supply in the event of internal damage likely to lead to bursting of the tank. As examples of such damage, one can cite a too strong rise in pressure of the dielectric liquid, or an abnormal drop in its level following a leak out of the tank. A detailed example of a complete adapted self-protection equipment to multi-phase transformers is described in European Patent Application EP-A-0 653 765 in the name of the Claimant, or in other published documents, such as EP 0 093 076, or USP 4,223,364.

Such self-protection equipment usually consists of a disconnector solicited by an actuator, itself activated by a trigger consisting of a device of detection sensitive to variations in a quantity of the dielectric liquid capable of expressing the appearance of any risky anomalies within the tank, such as temperature, pressure or the level of the surface of the dielectric liquid in the tank.

The invention applies to self-protection equipment of the type comprising a trigger sensitive at least to level variations in order to prevent risks due to loss of dielectric coolant, for example due to leakage from the tank, enabling protection to be triggered when this level reaches a value abnormally low.

Such a trigger can be of the float type made of a material of lower density than the dielectric liquid (in polystyrene for example) and which therefore follows, in principle, faithfully the fluid level. However, the durability of a float device cannot be satisfactorily ensured. However, taking into account the lifetime of a transformer considered type, around thirty years or even beyond, it is inevitable that the float, especially if it has a large porosity, eventually soak up oil, because it is continuously subjected to pressure-vacuum cycles.

Under these conditions, it gradually loses its flotation capacity, which can lead to inadvertent trips of the protective device, always very penalizing because it requires manual intervention to disassemble the upper part of the transformer to reset it.

We could consider replacing conventional floats with hollow containers air-tight. However, this type of container would involve a delicate adjustment of the sensitivity of the protective device and would also be difficult to achieve because, despite its lightness, it should be able to resist throughout the life of the transformer both under vacuum (filling of the transformer takes place under vacuum) and at pressures high (in operation, the overpressure in the transformer can reach 0.2 mbar), as well as at temperatures systematically exceeding 100 ° C.

The object of the invention is to provide manufacturers of electrical transformers submerged self-protected a simple and economical device sensitive to the liquid level dielectric cooling in the tank and able to ensure, in the event of an anomaly of this level, triggering the self-protection device effectively and reliably throughout the life of the transformer.

With this objective in view, the invention relates to a trigger for a device on-board self-protection of an electric transformer immersed in a filled tank dielectric liquid cooling by disconnecting the primary from the supply network electric in the event of an abnormal drop in the level of the dielectric liquid, device comprising a disconnect activated by an actuator, itself being activated by said trigger, which is characterized by the fact that it is, on the one hand, by a lever first species rotating around a pivot dividing it into a short arm representing the "Resistance" and in a long arm representing the "Power" of the lever, the end of the long ras being provided with a container having a free entry opening, and, on the other hand, by means allowing the automatic filling of said container with the dielectric liquid by passing through said opening during filling of the tank; means being provided at the end of the short arm to exert a force on the actuator, said disconnection occurring when said force exceeds a predetermined resistance threshold opposite by the actuator, the relative dimensions of the lever arms and those of the container being such that, as long as the transformer tank is filled with dielectric liquid, the container is completely immersed in this liquid and the force exerted on the actuator is below said predetermined threshold, and if the surface of said liquid drops to a level considered dangerously low, said container, which remains filled with liquid, reaches a degree of emergence such that, under its weight, the force exerted on the actuator surpasses said predetermined trigger threshold.

The invention also relates to an underwater power or electricity distribution equipped with a self-protection device incorporating such a trigger.

As will be understood, the idea underlying the invention lies in the design of a lever type trigger that is sensitive to variations in liquid level dielectric in the tank, not as a level follower, but as a volume weighing at the end of the longest lever arm (lever called "advantageous") and subject to Archimedes' push from this liquid. This volume, originally empty, is then occupied by dielectric liquid coming from the tank itself in order to be able perform this filling automatically, when filling the tank, in a container provided open for this purpose at the end of the lever arm. Once filled, this container remains definitively and then has a high overall weight counterbalanced by force of Archimedes until, following an accidental drop in level in the tank, its degree of emergence at the surface of the tank liquid results in a force differential such as its apparent overall weight, transmitted to the disconnector by the report of transformation of the lever, then causes the desired protection to be achieved.

A decisive advantage of the trigger according to the invention lies in the fact that it simply manages to satisfy the seemingly contradictory constraints specific to lever floats intended to be installed in a cramped place where they must occupy the less space possible (here the very crowded part located under the cover of a transformer). Indeed, or one uses a heavy float in order to be able to shorten the lever arm that carries it, but in this case the float becomes bulky, because necessarily large to be able to float. Or we use a little float bulky, but in this case it must be mounted on a lever arm which then becomes itself bulky, because necessarily elongated to keep the moment of the lever. It is useful to emphasize that this problem is particularly posed in the case of transformer self-protection equipment by disconnection of the primary, because it suitable that the tripping force to be applied to the actuator by the end of the arm resistance of the lever is fairly high (around kg) to avoid excessive sensitivity of the protective device which would lead to untimely disconnections unjustified.

• la figure 1 représente schématiquement, vue en coupe, la cuve d'un transformateur immergé et le dispositif selon l'invention, avant le remplissage de la cuve par du liquide diélectrique de refroidissement;
• la figure 2 représente la même cuve et le même dispositif pendant le remplissage de la cuve;
• la figure 3 représente la même cuve et le même dispositif, mais au terme du remplissage de la cuve;
• la figure 4 représente la même cuve et le même dispositif après l'apparition d'une fuite de liquide diélectrique ayant provoqué une baisse dangereuse du niveau dudit fluide dans la cuve.

The invention will be well understood and other aspects and advantages will appear more clearly in the light of the description which follows, given with reference to the accompanying drawing plates in which:

• Figure 1 schematically shows, in section, the tank of an immersed transformer and the device according to the invention, before filling the tank with dielectric coolant;
• FIG. 2 shows the same tank and the same device during filling of the tank;
• Figure 3 shows the same tank and the same device, but after filling the tank;
• FIG. 4 represents the same tank and the same device after the appearance of a leak of dielectric liquid having caused a dangerous drop in the level of said fluid in the tank.

In the various figures, there is shown, and this with a size voluntarily exaggerated for the sake of clarity, that the elements that are helpful in understanding the invention. In particular, the essential electrical organs, which can be of any type known to those skilled in the art, do not appear there. Likewise, were not represented in the detail the organs of the self-protection device other than the trigger, and of which can if necessary find a complete description for example in the document cited above EP 0653765, the content of which is incorporated by reference in the present specification.

In the figures, the same elements have been designated by identical references.

In Figure 1, only some of the classic organs of a self-protected submerged transformer, namely tank 1, the part active 19 of the transformer shown in broken lines (where we distinguish the three parts juxtaposed constituting the phases of a three-phase transformer) and the disconnection from network 5 which must be triggered in the event of an anomaly which may cause explosion of the transformer, such as an abnormal drop in the liquid level dielectric. The tank 1 is sealed off by a cover 3, provided with a filling orifice 4 allowing, before the transformer is put into service for the first time, complete filling of the tank 1 under vacuum with a dielectric liquid such as oil mineral. This filling opening is also normally closed by a plug. watertight 18. The tank 1, in this figure 1 is shown before this initial filling.

• un levier de première espèce 6;
• un pivot horizontal 7, placé de telle manière qu'il divise ce levier 6 en deux bras de longueurs respectives "d" pour le plus court 8 constituant la "Résistance", et "D" pour le bras le plus long 9 constituant la "Puissance" du levier;
• un récipient 10 à l'extrémité du bras long 9, comportant une ouverture 20 de libre entrée, et dont le poids contribue, via le rapport de transformation D/d du levier, à l'établissement d'une force "F" dirigée vers le haut à l'extrémité du bras court 8. Ici, l'ouverture 20 est obtenue à la partie supérieure du récipient simplement par absence de cloison supérieure;
• un poussoir 11 à l'extrémité du bras court 8 et chargé d'appliquer en fonctionnement l'effort "F" à un actionneur 2 qui lui résiste en opposant une résistance "Fd" correspondant au seuil de déclenchement choisi pour solliciter l'organe de déconnexion 5 du réseau d'alimentation électrique des enroulements du primaire du transformateur.

According to the invention, inside the tank 1 is placed a self-protection device with lever release, comprising the following elements:

• a first-kind lever 6;
• a horizontal pivot 7, placed in such a way that it divides this lever 6 into two arms of respective lengths "d" for the shortest 8 constituting the "Resistance", and "D" for the longest arm 9 constituting the " Power "of the lever;
• a container 10 at the end of the long arm 9, comprising an opening 20 for free entry, and whose weight contributes, via the transformation ratio D / d of the lever, to the establishment of a force "F" directed towards the top at the end of the short arm 8. Here, the opening 20 is obtained at the upper part of the container simply by the absence of an upper partition;
• a pusher 11 at the end of the short arm 8 and responsible for applying in operation the force "F" to an actuator 2 which resists it by opposing a resistance "Fd" corresponding to the triggering threshold chosen to urge the disconnection 5 of the power supply network of the transformer primary windings.

The assembly formed by the trigger lever 6, the actuator 2 and the disconnector 5 constitutes the on-board self-protection device to which the invention refers.

With regard to the trigger 6, specific object of the invention, its characteristics dimensions and the positions of its constituent elements are determined according to criteria already expressed, which will be explained again below.

All the constituent parts of the self-protection device are made of dense materials (metallic or plastic) which may not be altered by their contact with the dielectric liquid during the entire period of use planned for the transformer. The trigger lever 6 with its container at the end 10 are in addition chosen from a less dense material than the dielectric liquid in order to take naturally a stable "high" position in normal transformer operation visible in figure 3.

When mounting a new transformer, in the absence of dielectric liquid in the tank 1, the lever 6 leans frankly on the side of the long arm 9, but the pusher 11 exercises then on the disconnection device 2 an empty force "Fo" image of the empty weight of the container 10 by the transformation ratio of the lever 6, and below a threshold "Fd" beyond from which the disconnection device 2 should be triggered.

The device also includes a stop 12, the function of which will be explained more far.

Figure 2 shows the transformer tank 1 during filling with dielectric liquid 13. This liquid is drawn from a reservoir 14 and transferred to the tank 1 by a pipe 15 connected to the orifice 4 of the cover 3. As shown in the figure 2, after the surface of the liquid 13 has reached the container 10 at the end of the long arm 9 lever 6, this empty container, under the effect of Archimedes' force, will rise gradually by floating on the surface until it comes to a stop on the stop plate 12 in "high" position.

In FIG. 3, an sees the tank 1 of the transformer when the dielectric liquid 13 is at its nominal volume within the tank, which will be assumed to be "full filling or almost total "in this case. Its surface 16 is, in any case, at a final level such as the container 10 is completely submerged. As mentioned above, the top edge of the container 10 first comes into contact with the stop 12, which prevents the container from rising more and therefore causes, by the upper inlet opening 20, the filling automatic of the latter by dielectric liquid as soon as the level of the surface 16 reaches the edge of the container. Once the container 10 is completely filled, its position completely immersed in the same liquid as the one it contains drives the pusher 11 preferably stay slightly behind the actuator 2, and in any case to exercise on him an effort below the trigger threshold "Fd".

Figure 4 shows the transformer tank 1 when it has a accidental perforation 17 and that dielectric liquid has spilled out of the tank. That resulted in a gradual drop in the level of the surface 16 of the liquid 13 within the tank, and therefore a corresponding reduction in the Archimedes' thrust exerted on the container 10 as soon as the latter, moderately retained by the resistance "Fd" exerted by the actuator on the pusher 11 at the end of the short arm, begins its emergence.

As the container remains filled with liquid 13, there is a degree of emergence from the container to the surface of the dielectric liquid in the tank which, once reached, corresponds to the point of equilibrium between the buoyancy and the apparent weight of the container 10. Beyond, the force "F" exerted by the pusher 11 on the actuator 2 begins to grow. When it reaches and exceeds the chosen value of the Resistance threshold "Fd" of the actuator, the protection device is triggered. This event can intervene immediately, or after a validation delay of the alert at the end a short movement authorized for this purpose of the actuator trigger (not shown) 2. The position of the pivot 7, the relative dimensions of the lever arms 6 (defining its transformation ratio) and the capacity of the container 10 are calculated so that the intensity the force "F" may become significantly greater than the trigger threshold "Fd", and that this threshold "Fd" is exceeded when the level of the surface 16 of the dielectric liquid has lowered to a point where there is a risk of explosion of the transformer. This level must of course be predetermined when designing the transformer.

As a simple non-limiting example, one can choose a lever 6 in polypropylene with a density of 0.9, with a total length of 330 mm, distributed in one arm long 9 (the Power of the lever) of length "D" = 300 mm and a short arm 8 (the resistance) of length "d" = 30 mm (ie a transformation ratio D / d = 10). The container 10 has a weight of 20g and a useful volume of 100 cm3 allowing it to contain 90g of oil mineral.

Under these conditions, the pusher 11 exerts on the actuator 2 a force "Fo" 'of 200g unladen, i.e. when there is no oil in the container 10 or in the tank in contact with this last. In addition, we will set trigger 6 so that the disconnection of the transformer only occurs when the force exerted by the pusher 11 exceeds a threshold 800 g "Fd" release button.

When the transformer is filled with oil, the container 10 is in situation total immersion. The force exerted by the pusher 11 on the trigger 2 is zero if it there is an absence of mutual contact, and in any case less than 200 g due to a differential Archimedes thrust in favor of the long arm 9 of the lever 6 because of its density lower than that of the dielectric liquid in which it is immersed.

However, when the oil level has dropped to the point that you end up in the situation of FIG. 4 where the filled container 10 is partially emerged, at 200g exerted normally by the pusher 11 on the actuator with a container is added a force equal to 90 x 10 = 900g due to the apparent weight of the volume of liquid 13 occupying the container 10. The effort "F" is then 200 + 900 = 1100 g, therefore clearly greater than the threshold of 800 g "Fd" trip: the transformer disconnection is therefore activated. The effect lowering due to the still submerged part of the long arm of the lever is of the second order of greatness compared to the other active forces involved at that time.

As we realized, this device for detecting the level of liquid dielectric, extremely simple in its design, construction and operation, is therefore very reliable. Its performance is not likely to deteriorate in the time. Another advantage, compared to a conventional float device, is that before or during filling of the transformer, a float device causes the tripping of the disconnection device. It must therefore be rearmed after filling, provided however that such a possibility has been retained from construction, unless provision has been made for blocking the float in the high position during the filling, which further complicates the construction of the triggering device.

It goes without saying that the invention is not limited to the example described with reference to figures, but extends to multiple variants or equivalents to the extent that the definition of the invention given by the claims below is observed.

For example, the stop 12 may very well be constituted by the bottom of the cover 3 himself. In this case, one or more notches formed on the edge of the container 10, of preferably on the inside of the lever, may advantageously constitute passages of entry of the dielectric liquid 13 into the container when the latter comes into abutment against the cover 3. Likewise, openings made through the wall of the container at the vicinity of the upper edge could also fulfill such a function.

Similarly, the automatic filling of the container 10 can be carried out other than from above. It is quite possible indeed to provide an orifice in its bottom through which the dielectric liquid will enter when filling the tank, this orifice being however provided with a non-return valve resting on the bottom to prevent then place the interior of the container in communication with the surrounding liquid medium.

More generally therefore, these means allowing the automatic filling of said container with dielectric liquid through its inlet opening during filling of the tank must be designed to prevent subsequent release of this liquid from the container by the same route.

Claims (6)

Trigger for an on-board transformer self-protection device electric (19) immersed in a tank (1) filled with dielectric liquid cooling by disconnection of the primary from the power supply network in the event of an abnormal drop in dielectric liquid level, device comprising a disconnector (5) urged by a actuator (2), itself activated by said trigger, which is characterized by the fact that it consists, on the one hand, of a lever (6) of the first kind rotating around a pivot (7) which divides it into a short arm (8) representing "Resistance" and into a long arm (9) representing the "Power" of the lever, the end of the long arm being provided with a container (10) having an inlet opening (20), and, on the other hand, by means allowing the automatic filling of said container with dielectric liquid through said opening (20) during filling of the tank; means being provided at the end of the short arm (8) for exerting a force on the actuator (2), said disconnection occurring when said effort exceeds a predetermined trigger threshold opposed by the actuator, the relative dimensions of the lever arms (8, 9) and those of the container (10) being such that, as long as the tank is filled with dielectric liquid (13), the container is completely immersed in this liquid and the force exerted on the actuator is less than said predetermined threshold, and if the surface (16) of said liquid drops to a level considered as dangerously low, said container, which remains filled with liquid (13), reaches a degree of emergence such that, under its weight, the force exerted on the actuator surpasses said predetermined trigger threshold. Trigger according to claim 1 characterized in that the container (10) to the end of the long lever arm (9) is open at its upper part (20). Trigger according to claims 1 and 2, characterized in that the means allowing the automatic filling of the container (10) with passing dielectric liquid through said opening (20) during filling of the tank are constituted by a stopper (12) cooperating with the edge of said container. Trigger according to claims 1 and 2, characterized in that the means allowing the automatic filling of the container (10) with passing dielectric liquid through said opening (20) during filling of the tank are constituted by notches formed on the edge of said container. Trigger according to claim 1, characterized in that the container (10) is provided with an entrance opening formed in its bottom and in that the means allowing automatic filling of said container with dielectric liquid passing through said opening are constituted by a non-return valve cooperating with the latter. Electric submersed power or energy transformer electrical of the type comprising on-board self-protection equipment (6,2,5) by disconnection from the electrical network in the event of a drop in the level (16) of the dielectric liquid (13) in the tank (2) which contains it, said equipment including a trigger sensitive to variations of said level, characterized in that said trigger (6) conforms to that of claim 1.

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