EP0003925A1 - Hydropneumatic piston accumulator provided with a gas shortage detector - Google Patents

Abstract

The invention relates to hydropneumatic piston accumulators provided with a gas shortage detection device, a movable member 14 of which is actuated in thrust by the piston 8 when the latter approaches too close to the bottom 4, gas side, of the 'accumulator. Connection means 28, 32, with movement reversal and acting in traction are interposed between the piston 8 and the movable member 14, these connection means having a dead travel of predetermined length. The invention makes it possible to verify the proper functioning of the detector device, by emptying part of the liquid contained in the compartment 12, the piston 8, when it approaches the bottom 6, actuating the detector device.

Description

The present invention relates to hydro-pneumatic piston accumulators and in particular those provided with a gas shortage warning device which are used in oleo-pneumatic controls of electric circuit breakers.

The first oil-pneumatic orders for high-voltage circuit breakers date from 1952, 25 years ago.

The reserve of hydraulic energy, immediately usable is stored in one (or more) hydro-pneumatic accumulator, in the form of a mattress of compressed gas, confined permanently in the gas chamber of the accumulator and pre-inflated to a pressure predetermined.

The success of such a technique required the realization of a type of accumulator whose reliability is high, inflated in the factory and capable of retaining its gas charge without losses for several years.

It is known that hydro-pneumatic piston accumulators are essentially constituted by a cylinder which is closed by two bottoms and which is divided, by a free piston, into two compartments, one containing a gas under pressure and the other a liquid , usually oil. These devices are used as a reserve of pressurized oil to actuate engine members, such as jacks, the accumulator being recharged with oil by a pump according to its consumption.

First, the metals constituting these three basic elements must be perfectly waterproof: 7h, which is not as obvious as it appears at first.

Then the sliding seal between the piston and the cylinder must be perfect, as well as the fixed seal between the cover and the cylinder. Both of these issues have been resolved.

With regard to said movable seal, the solution was to subject this seal, made of elastomer, permanently to an axial elastic force, giving it a radial deformation, applying it permanently against the wall of the cylinder under a pressure greater than the pressure to be sealed (French patent No. 1,024,868 of September 23, 1950, from the same inventor), making it possible to avoid the drawbacks resulting from the characteristic common to all elastomers, to take, as a function of time, a permanent deformation when they are subjected to a permanent effort, and also to compensate when the temperatures vary, the fact that their coefficient of expansion is greater than that of metals.

With regard to the very constitution of said sliding joint, several patents from the same inventor have given very valid solutions.

The problem of the fixed seal between the cylinder and the fixed bottom has been perfectly solved by the solution of the autoclave seal (French patent number 1.042.201, of September 14, 1951, by the same inventor), subjecting said fixed seal to a pressure several times greater than the gas pressure to be sealed, whatever the deformations, no improvement has since been made to this technique which has proved perfect from its first applications, an exceptional case in the technology.

At present, all the oleo-pneumatic accumulators used in circuit breaker control derive from this initial data. Several variations of detail have been claimed, more for commercial reasons than for real technological reasons.

When these devices are built or put into service, the gas compartment is filled with an inert gas under a determined pressure, called "pre-inflation pressure", and it is this elastic gas cushion which then ensures maintaining the liquid under pressure and which constitutes the elastic reserve of energy which the device can supply.

The components likely to cause a gas leak were thus reduced to the minimum possible, three metal elements (the cylinder, the piston and the cover) and two seals (a sliding piston seal and an autoclave cover seal) and l initial filling hole for which an adequate solution could be found.

To date, more than 100,000 oleo-pneumatic circuit breaker control accumulators meeting these characteristics have been put into service worldwide to the great satisfaction of users.

Users, however, are gradually increasing their requirements. In particular the current development of high voltage circuit breakers so-called "maintenance-free" leads to asking for accumulators guaranteed without gas leakage for five years, ten years, then now twenty years.

This result turns out to be possible, using in the accumulator as gas a neutral gas (nitrogen, nitrogen) for pressures up to 400 bars (kg / cm ² ) and helium for higher pressures (patent French No. 2,076,812 of January 20, 1970, from the same inventor), which prevents any corrosion of the metal parts and prevents aging of the elastomers constituting the seals, and the oils which are suitably filtered.

Any opening or closing operation of a high voltage electric circuit breaker when it is started must imperatively be carried out until its complete execution, under penalty of a serious incident leading at least to the destruction of the circuit breaker.

The operating energy being supplied by the accumulator, it is necessary that its reserve of gas is sufficient.

Any technique is never absolutely perfect, users have been led to request the establishment of a warning system for a disease in an oleopneumatic accumulator, causing a loss of gas, a disease which manifests itself in an abnormal position. piston for a given pressure.

In practice, it is especially important to know the position of the free piston when it approaches one or other of its normal limit switches, that is to say that if the piston approaches beyond a determined limit of the bottom of the gas compartment this means that there has been a loss of pre-inflation (and that it is therefore necessary either to repair a leak or "re-inflate" the accumulator), while if the piston comes too close to the bottom of the oil compartment, this means that there is a lack of oil (by leakage or by abnormal consumption).

Control systems have already been proposed triggering a warning signal when the piston comes too close to one of the bottoms of the cylinder and, in particular when the piston comes too close to the bottom of the gas compartment. For certain applications of hydro-pneumatic accumulators, for example the supply of these hydraulic controls for electric circuit breakers, the user even requires that such a safety system, by controlling the lack of gas, be incorporated in the accumulator.

Among the control systems known up to now, the simplest include an outgoing sliding rod, crossing the bottom of the cylinder on the gas side and projecting inside the gas compartment. When the piston approaches the bottom closer than a predetermined distance, the piston acts in pushing on the rod and the external end of this rod activates a warning system, for example activates an electric switch which closes a warning circuit.

This outgoing rod solution requires additional sealing, which can be a source of gas leakage.

It was desirable to produce such a system, not by itself risking weakening the accumulator from the sealing point of view. The best solution was to have inside the accumulator a permanent magnet actuated by the movable piston and acting magnetically on an electrical contact located outside the accumulator when the piston for normal oil pressure abnormally approaches the cover of the cylinder (French patent number 2,236,098, of July 4, 1973, of the same inventor).

Thanks to the facts that according to this device the bottom of the cylinder, gas side, is made of non-magnetic metal; that the permanent magnet is movable in a blind hole in this bottom opening out only in the gas compartment; and that the switch is housed in a second blind hole, adjacent to the first, but opening only to the outside, any additional sealing is avoided and, consequently, any risk of gas leakage caused by the control device itself even.

There are therefore various known solutions making it possible to warn the user of a lack of gas in an accumulator, these solutions consisting for the most part in causing the piston, or a member integral with the piston, to act by pushing against a movable member, which activates when it is moved by the push of the piston, a gas shortage warning system.

Although these various solutions, in particular that described in the aforementioned patent, provide the desired security, they nevertheless all have certain drawbacks.

• 1°) du fait de la fragilité des organes électriques de contrôle et de leur circuit, pouvoir contrôler le bon fonctionnement du système avertisseur ;
• 2°) les disjoncteurs de grande puissance à haute tension comprenant une pluralité d'accumulateurs oléo-pneumatiques, pouvoir contrôler, périodiquement, sans aucun démontage la pression de prégonflage individuelle de chaque accumulateur.

Two new problems have arisen:

• 1) due to the fragility of the electrical control members and their circuit, being able to control the proper functioning of the warning system;
• 2) high power high voltage circuit breakers comprising a plurality of oleo-pneumatic accumulators, being able to control, periodically, without any disassembly, the individual pre-inflation pressure of each accumulator.

Current hydro-pneumatic accumulators of good construction have, as we have seen, excellent gas tightness and can remain for several years (in storage or in service) without requiring "re-inflation" of the gas compartment. This means that the gas shortage monitoring devices discussed above only have to operate very rarely, and, in fact, very exceptionally, although their safety function is paramount.

This is why the user would be eager to be able to periodically check the correct functioning of the recording equipment and, above all, to be able to carry out this check when putting an installation into service, for example an installation of hydraulic circuit breaker control.

A simple means of verification would be to charge the accumulator with oil under sufficient pressure to bring the free piston closer to the bottom on the gas side, until the control device is triggered. But, in practice, this would cause the pressure in the accumulator to rise to a value higher than the normal operating pressure and which would approach the limit safety test pressures of the accumulator, which is strictly prohibited and dangerous. .

Of course, to avoid this drawback, we could first of all partially deflate the gas compartment so that the free piston, repelled by the oil, comes to actuate the control device without requiring excessively high pressures.

However, in this case, after checking, the gas accumulator should be re-inflated to normal pressure, an operation which must be carried out by specialists and which, preferably, is made in the factory, by the manufacturer of the accumulator.

The object of the present invention is to remedy these drawbacks and to allow the user to check, upon commissioning and even periodically thereafter, the proper functioning of the detector and gas shortage warning device.

The subject of the invention is a hydro-pneumatic accumulator of the aforementioned type, comprising a gas shortage warning system controlled by a mobile member actuated in thrust by the piston, when the latter approaches closer to the bottom on the gas side than first predetermined distance, said accumulator being characterized in that connection means, with movement reversal, acting in traction, are interposed between the piston and the movable member, and in that said connection means have a dead stroke of length predetermined, whereby said movable member is also moved in the same direction as when it is actuated directly in thrust by the piston and, therefore in the direction of actuation of the warning system, when the piston moves away from the bottom of the cylinder gas side, further than a second predetermined distance.

To check the correct functioning of the lack of gas control system, it is sufficient to lower the oil pressure in the accumulator until the free piston approaches the bottom of the oil compartment enough for the aforementioned connecting means move the movable member, which actuates the warning system.

The device according to the invention also has the advantage that, during the verification, all the elements of the control system function in the same way and in the same direction as when this control system actually works to report a loss of gas.

Once the verification has been carried out, it is sufficient to recharge the accumulator with oil at normal pressure, an operation which is extremely simple, since there is always an oil refill pump on the hydraulic control installation.

Finally, it should be noted that, without any additional complication, the device according to the invention makes it possible to signal, in addition to the lack of gas, any abnormal approximation of the piston relative to the bottom on the oil compartment side, approximation which would mean that there has a lack of oil (or abnormal oil consumption).

This makes it possible to carry out a control of the respective pre-inflation state of several individual accumulators mounted in parallel in the same installation. In fact, by lowering the oil pressure in the installation, the pistons of all the accumulators will come into contact with their bottom on the oil side and the warning systems of all the accumulators must function, if they are in good working order , which answers the first problem.

By gradually raising the oil pressure in the installation, the warning system of each accumulator will be extinguished when the oil pressure exceeds the pre-inflation pressure in gas of said accumulator.

By doing the two successive operations described above, we will have found that the. warning system for each accumulator and measures its precharge pressure, without dismantling and without introducing overpressure oil in the installation.

According to a preferred embodiment, the aforementioned connecting means comprise a lever movement reversing system of the first kind as well as a dead travel connecting member working in traction interposed between the piston and a first end of said lever, the second end of said lever cooperating with said movable member, whereby a tensile force exerted by the connecting member on the lever is transformed into a pushing force on the movable member.

Preferably, the connecting means acting in traction and having a dead stroke comprise a flexible link interposed between the piston and the first end of the aforementioned lever.

• La figure 1 est une vue partielle en coupe d'un accumulateur hydro-pneumatique équipé d'un dispositif simple de détection de manque de gaz du type dit "à tige sortante" et comportant, suivant l'invention, un système de vérification du bon fonctionnement dudit dispositif et de vérification de l'état de gonflage de l'accumulateur.
• La figure 2 est une vue partielle en coupe d'un accumulateur montrant une variante du système suivant l'invention.
• La figure 3 est une vue partielle en coupe d'un accumulateur équipé d'un dispositif de détection de manque de gaz tel que celui décrit dans le brevet précité et comportant un système de vérification du bon fonctionnement de ce dispositif.

The invention will be better understood on reading the detailed description which follows and on examining the appended drawings which represent, by way of nonlimiting examples, various embodiments of the invention.

• Figure 1 is a partial sectional view of a hydro-pneumatic accumulator equipped with a simple device for detecting a lack of gas of the type known as "with outgoing rod" and comprising, according to the invention, a system for checking the correct operation of said device and verification of the inflation state of the accumulator.
• Figure 2 is a partial sectional view of an accumulator showing a variant of the system according to the invention.
• Figure 3 is a partial sectional view of an accumulator equipped with a gas shortage detection device such as that described in the aforementioned patent and comprising a system for checking the proper functioning of this device.

The hydro-pneumatic accumulator shown in FIG. 1 comprises, as is conventional, a cylinder 2, two cylinder bottoms 4 and 6 and a free piston 8 which separates the volume of the cylinder into a gas compartment 10 and a liquid compartment 12. In the figures, the conventional gas inflation system of the gas compartment has not been shown.

The accumulator is provided with a simple device for detecting a lack of gas. This device comprises a movable member constituted by a rod 14 which passes through the bottom 4, on the side of the gas compartment, by a bore 15 provided with a seal 18. The end of the rod 14 protrudes from the inside the gas compartment so that, when the piston 8 approaches the bottom 4 closer than a predetermined distance D, as a result of a lack of gas, said piston acts in thrust on the rod whose outgoing end activates a gas shortage warning system, for example an electric switch 16, mounted in a housing 19. The switch 16 is mounted in an electric warning circuit (not shown) such that the closing of the switch 16 causes the supply an optical or sound control device or a device that automatically triggers the intervention of a safety device.

A spring 20, surrounding the rod 14 and bearing on a flange 22 integral with this rod, prevents the rod 14 from being pushed outwards by the pressure prevailing in the gas compartment, while stops 24 and 26 limit displacements of the rod.

This type of gas shortage detector is effective although it has the drawback of requiring ter an additional seal at the passage of the rod 14, a disadvantage that does not have other types of detectors.

However, as with all other types of detector, it is practically not possible, as indicated above, to check that the detector is in good working order. The device according to the invention makes it possible to carry out this verification and it also makes it possible to carry out certain other controls which will be described later.

According to the invention, there is interposed between the piston 8 and the movable rod 14 of the movement reversal connection means, acting in traction. In the embodiment shown in FIG. 1, these connecting means comprise a flexible link, such as an inextensible bead 28, one end of which is fixed, by hooking means 30, to the piston 8, and whose other end is fixed on a return lever 32. The lever 32, which constitutes a movement reversal member, is pivotally mounted at 34 on a yoke 36 secured to the bottom 4. The end of the lever 32 opposite the point of attachment the cord 28 is preferably fork-shaped and embraces the rod 14 between the flange 22 and a stop 38.

The cord 28 is given a length such that this connection system has a dead stroke of predetermined length before acting on the rod 14. As a result, when the piston moves away from the bottom 4 further than a predetermined distance D ', the rod 14 is also moved, in the same direction as if the piston 8 were to act in push against it, which makes the gas shortage warning system work and makes it possible to check its good working order.

To perform this verification, simply therefore allow the oil contained in the oil compartment 12 to be discharged until the pressurized gas from the gas compartment pushes the piston 8 to the distance D ′ for which the cord 28 is tensioned and actuates the rod 14. After this check, it is sufficient to recharge the accumulator with oil using the pump normally found in the installation.

It can therefore be seen that, thanks to the invention, it is possible to carry out the verification without having to intervene on the gas cushion of the gas compartment, that is to say without having to deflate it or over-compress it to excessive pressure.

It should be noted that, during the verification, all the components of the detector device operate in the same direction and under the same conditions as in the case of real operation due to lack of gas, which gives any assurance as to to the operation of the device, all the more so since, in the latter case, the displacement takes place under the effect of a simple push and that this displacement therefore has no reason not to occur in the event of a lack gas.

It should also be noted that the device according to the invention also gives an indication of the position of the free piston in the accumulator and signals an excessive approach of the piston relative to the bottom 6 on the oil side, an approach which would mean that the oil filling is insufficient. , for example due to leakage, abnormal consumption or insufficient flow from the recharge pump.

Finally, in the case of high power hydraulic installations, such as hydraulic circuit breaker controls, often used as a hydraulic power reserve, several accumulators mounted in parallel. Until now, it has been very difficult to know the individual inflation state of each accumulator. The device according to the invention also makes it possible to carry out such an individual check. Indeed, it suffices to gradually drain the oil from the installation and note the pressure each time one of the gas shortage detectors triggers. This determines the individual inflation state of each of the accumulators.

In the embodiment of FIG. 2, the gas shortage detector comprises a movable rod 14 'which slides in a blind hole 15' dug in the bottom 4 ', gas side, of the accumulator and which can be actuated by pushed by piston 8 in the event of lack of gas. The rod 14 'carries a spout 40 which can close a switch 16' arranged inside the gas compartment and which controls the electric circuit warning of lack of gas. The conductors 42-44 connected to the switch 16 pass through the bottom 4 'through fittings tightened by insulating cable glands 46.

This arrangement has the advantage that there is no mobile seal through the bottom 4 '. A switch 16 ′ or a micro-switch can without disadvantage be placed in the gas compartment which is filled with an inert gas such as nitrogen for example, but of course, this switch could be of the type with magnetic control of nearby, the rod 14 'then carrying a permanent magnet.

In the variant shown, the connection device for reversing the direction of travel is simply constituted by a flexible link 28 which is fixed to the piston 8, which passes through a return guide 48 fixed to the bottom 4 ', and which is hooked by a collar 50 to the rod 14'. The operation of this embodiment, for verifying the good condition of the gas shortage detector device, is identical to that which has been described in connection with FIG. 1.

In the preferred embodiment shown in FIG. 3, the invention is applied to an accumulator provided with a gas shortage detection system of the type described in the aforementioned French patent.

It suffices to recall that in this detection system, the mobile member against which the free piston 8 comes to act in thrust consists of a rod 14 "which slides in a blind hole 16 'and which carries a permanent magnet 52. In a second blind hole 54, adjacent to hole 16 ′, but opening to the outside is mounted a proximity switch with magnetic control 56, of the type with flexible blades in sealed bulb (switch known as "reed switch" or "ILS"). bottom 4 "being made of non-magnetic material, the magnet 52, when it sinks into the hole 16 ', actuates the switch 54. In this embodiment, to avoid having to give the length too long part of the rod 14 "which projects into the gas compartment 10, the piston is acted in thrust on the mobile rod not directly but by means of a part integral with this piston. In the example, this part is constituted by a perforated plate 58 which slides freely in the cylinder 2 and q ui is carried by a rod 60 fixed on the piston 8.

According to the present invention, the traction connection interposed between the piston 8 (and more precisely between the plate 58) and the movable rod 14 " comprises a cord 62 which actuates, when stretched, a lever 32 similar to the lever 32 shown in FIG. 1. This lever 32 pivots at 34 in a housing 64 which is fixed to the bottom 4 "and which houses the spring 20 of 14 "rod reminder. At the same time, the bottom of this housing serves as a stop for the lever 32 and the rod 14 ".

The operation is identical to what has been described in connection with FIG. 1, but it should be noted that the variant of FIG. 3 has the advantage of not requiring any additional sealing (movable as in the case of FIG. ₁ or fixed as in the case of FIG. 2) through the bottom 4 "of the accumulator.

Of course, the simple lever reversal system which has been shown in FIGS. 1 and 3 could be replaced by a double lever system or by any other more complex system.

Likewise, a flexible link such as an inextensible cord has above all been described as a connecting member working in traction, but it is understood that a telescopic link or a foldable link or even a rollable link could also be used.

Claims (7)

1. Hydro-pneumatic piston accumulator which comprises a cylinder, two cylinder bases and a free piston separating the cylinder into a liquid compartment and a gas compartment, of the type comprising a device for detecting gas shortage comprising a movable member , arranged inside the gas compartment and against which the piston acts, or a member secured to the piston, when said piston approaches the bottom of the cylinder on the gas side closer than a first predetermined distance, said member mobile actuating, when it is moved in thrust by the piston, a gas shortage warning system, said accumulator being characterized in that connection means, with movement reversal, acting in traction are interposed between said piston and said member mobile, and in that said connecting means have a dead travel of predetermined length, whereby said mobile member is also moved in the same direction as when it is st actuated directly in thrust by the piston and, therefore, in the direction of actuation of the warning system, when the piston moves away from the bottom of the cylinder on the gas side, farther than a second predetermined distance. 2. Accumulator according to claim 1, characterized in that the aforementioned connecting means comprise a lever reversal system of the first kind and a dead travel connecting member working in traction interposed between the piston and a first end of said lever, the second end of said lever cooperating with said movable member, whereby a tensile force exerted by the connecting member on the lever is transformed into a pushing force on the movable member. 3. Accumulator according to one of claims 1 or 2, characterized in that the connecting means acting in traction and having a dead travel comprise a flexible link. 4. Accumulator according to any one of claims 1, 2 or 3, characterized in that the aforementioned warning system comprises an electrical switch capable of closing an electrical warning circuit and in that said movable member is mounted in relation to actuation of said switch. 5. Accumulator according to claim 4, characterized in that said movable member and said switch are arranged inside the gas compartment. 6. Accumulator according to one of claims 4 or 5, characterized in that the switch aforementioned is a switch with magnetic actuation and in that the aforementioned movable member carries a magnet disposed in actuation relation of said switch. 7. hydro-pneumatic accumulator according to claim 6, characterized in that the aforementioned magnetic actuation switch is a proximity switch with blades, in sealed bulb; and in that said switch is housed in a blind hole which opens outwards and which is hollowed out in the bottom of the cylinder on the gas side; and in that said bottom is made of non-magnetic material; and in that the aforementioned magnet slides in a second blind hole, close to the first, dug in said bottom but opening inwards.

Images