Title of Invention

DECOMPRESSION VALVE

Abstract

A pressure relief valve for oil-filled transformers and tap changers with a covering, wherein a housing flange with a continuous opening, which in the rest state is sealed off by a spring-loaded valve cover and at least one seal, is provided, wherein a stationary spring cover is arranged above the valve cover, wherein at least one biased spring is arranged between spring cover and valve cover in such a manner that it is supported by its upper end at the lower side of the spring cover and by its lower end at the upper side of the valve cover, wherein the covering is constructed as a pot-shaped housing which enloses the entire pressure relief valve and which has at least one outlet opening and wherein the housing is fastened directly to the housing flange, characterised in that the housing is constructed to be separately mountable, that the housing has a lateral cut-out, that a vertically upwardly extending duct plate having at least one cable duct and filling out the lateral cut-out is provided laterally at the housing flange and that the housi~g is additionally screw-connected with the duct plate.

Full Text

Pressure relief valve The invention relates to a pressure relief valve for oil-filled transformers and tap changers. If a predetermined limit value is exceeded due to faulty functions or disturbances of the pressure in the transformer vessel of the transformer or in the tap changer then the pressure relief valve which is closed during normal operation opens and produces a pressure relief with the atmosphere surrounding the transformer or the tap changer. Such a pressure relief valve, which is mounted on an opening at the upper side of the transformer vessel, is known from US 3 914 528. It consists of a circular housing flange which is screwed onto the described opening of the transformer vessel. On the underside, which faces the upper side of the transformer vessel, of the housing flange an annular seal is inserted into this for oil-tight sealing. The opening of the housing flange is sealed at the top by a spring-loaded valve cover in the normal state, which is further discussed in more detail. A round, downwardly open, beaker-shaped housing cover is mounted on the housing flange by means of bolts and screws. The upper, approximately horizontal side of the housing cover in that case has concentric steps in its interior. One or more biased compression springs are arranged between the housing cover and the already described valve cover, i.e. these compression springs are supported by their upper spring ends on the inner side of the housing cover and by their lower spring ends on the upper side of the valve cover and thus press this against the housing flange in such a manner that the opening thereof is oil-tightly closed. For that purpose an encircling annular seal is additionally provided at the upper side, which faces the valve cover, of the housing flange. If the pressure in the transformer vessel exceeds the response pressure of the springs, the valve cover lifts and enables pressure equalisation; subsequently, it is pressed by the force of the spring back again against the annular seal at the upper side of the housing flange. In addition, it is possible with this known pressure relief valve to provide at the upper side, outside the housing cover, optical indicators which remotely signal to personnel whether the pressure relief valve has responded. Finally, electrical reporting contacts or switches for remote monitoring or remote indication as well as for switching off the transformer are also provided outside the housing cover. A further, quite similarly constructed pressure relief valve is known from US 4 843 187. It relates to a special cross-section and a special fastening of the already described encircling annular seal between the upper side of the housing flange and the underside of the valve cover. A further pressure relief valve is known from US 4 676 266. In that case the valve cover is of beaker-shaped construction; the downwardly open side walls correspond with a further seal, which is inserted into the encircling end face of the housing flange. This additional seal has a flat cross-section; in the closed state of the pressure relief valve it is pivoted out - comparable to a windscreen wiper blade - and seals off the valve cover at its side walls additionally against the housing flange. In the case of fault, when the valve cover rises due to excess pressure in the transformer vessel, the pressure on the entire valve cover area expands; the force acting on the cover increases and the valve jumps up particularly quickly, within a few milliseconds. However, all these known pressure relief valves have a number of disadvantages. Particularly serious is that in the fault case with impermissibly high pressure in the transformer vessel, when the valve cover is opened the medium disposed under high pressure sprays uncontrollably out of the pressure relief valve. Since this medium spraying out abruptly and 'without prior warning' is still extremely hot a significant risk of injury exists for personnel in the vicinity, quite apart from the quite substantial contamination of the surroundings. A further disadvantage with the known pressure relief valve consists in that the switch contacts are provided unprotected outside the actual apparatus; there is no kick protection and they are also not protected against ultraviolet rays, ozone, rain and other influences. Moreover, just like the electrical connecting cable they are similarly exposed in the case of triggering to the torrent of hot oil. A cover hood for pressure relief valves is already known from WO 98/54498, which is to be subsequently quasi 'inverted over1 such valves and which has an outlet opening ensuring a defined guidance and conducting away of the oil torrent in the case of triggering. This solution also cannot satisfy in technical terms. In the first instance it concerns a pure retrofit solution. Fastening of the cover hood is carried out at the vertical bolts and nuts already present at the pressure relief valve, by means of which the housing cover is mounted on the housing flange, wherein, as already explained, the springs disposed under high bias are disposed therebetween. For mounting the known cover hood it is thus necessary to loosen the nuts by which the housing cover similarly standing under bias is fastened. In that case the risk exists that due to the spring force the entire cover hood jumps upwardly and injures the mounting personnel. According to a further variant the known cover hood shall be connected with the transformer vessel by means of an additional flange connection according to the form of an adapter. This is an expensive variant which not only requires additional components, but also creates additional sealing problems able to be solved only by further seals, which additionally complicates the entire arrangement The object of the invention is to state a pressure relief valve of the kind mentioned in the introduction, which does not have the described disadvantages, is of particularly compact construction and ensures a defined discharge of the hot oil torrent in the case of fault as well as an additional protection of the components and the surroundings against contamination. This object is completely fulfilled by the invention. In the case of the pressure relief valve according to the invention a cover hood which is known per se is an integral component of the apparatus, i.e. there is provided, instead of a separate cover hood, a pot-shaped, upwardly closed housing completely enclosing the individual components. This housing no longer has to be fastened in complicated manner to the actual pressure relief valve like a separate cover hood according to the state of the art. In particular, it is not necessary to release the housing cover, which in the case of the invention is termed spring cover, disposed under spring stress. The described risk of accident is thus eliminated; similarly, possible overlooking the retightening of the cover hood or possible tightening of the cover hood at one side is avoided, the cover hood being mounted at the outset at the factory; the corresponding screws do not need to be later released again. In the case of the construction according to the invention an adapter, as is known from the state of the art, is also not necessary; thus, no additional sealing problems can arise. Overall, there is created by the pressure relief valve according to the invention a compact, closed apparatus with integrated housing enclosing all components, which can be mounted directly on the transformer cover without further measures. Outlet openings allowing a defined discharge of the oil torrent arising in the case of fault are provided in the substantially vertical, cylindrical side wall of the housing. These outlet openings can be dimensioned in the most diverse ways; through a suitable flow cross-section it is possible to avoid on the one hand an undesired throttle action, and on the other hand the oil torrent can be controlled and fractionated in its issue. In addition, through the arrangement of numerous small outlet openings instead of a single large outlet opening it is possible in simple manner to ensure that a finger cannot be inserted into in the interior of the apparatus and foreign bodies cannot penetrate into the apparatus. Equally, it is possible to provide horizontal ventilating slits and to furnish these with outlet scoops covering from above. Good protection against rain and dripping water is provided in all cases by the arrangement of the outlet openings in the substantially vertical wall. The pot-shaped housing moreover also protects optional, additionally mounted switch contacts. Due to the arrangement of cable passages at the duct plate, according to a particularly advantageous development of the invention the cable is, moreover, protected from high tension loads; these additional cable passages absorb a large part of the tension forces at the cable and thus very substantially relieve the cable screw connections at the electrical switch contacts. Moreover, the described cable is protected against the hot oil torrent, since the pressure relief valve according to the invention has a defined oil discharge region which in particularly advantageous manner is arranged spatially opposite the cable passages. The cable is thus prevented from being directly caught and damaged by the hot oil torrent. The invention will be explained in still more detail in the following by way of example with reference to drawings, in which: Fig. 1 shows a first pressure relief valve according to the invention in the closed (rest) state, in schematic side sectional illustration, Fig. 2 shows this pressure relief valve in the open state, triggered after excess pressure, in the same sectional illustration, but horizontally rotated through 90 degrees, Fig. 3 shows this pressure relief valve from outside in perspective illustration, Fig. 4 shows a second pressure relief valve according to the invention in closed (rest) state in schematic side sectional illustration, Fig. 5 shows this pressure relief valve in open state, triggered after excess pressure, in the same sectional illustration, but horizontally rotated through 90°, Fig. 6 shows this pressure relief valve from outside in perspective illustration, Fig. 7 shows a seal of this pressure relief valve by itself, Fig. 8 shows an enlarged detail cross-section of this seal, Fig. 9 shows a third pressure relief valve according to the invention, partly in side sectional illustration, and Fig. 10 shows a fourth pressure relief valve according to the invention, again in the manner of a detail in side sectional illustration. The basic construction of a first pressure relief valve according to the invention will initially be described by reference to Figure 1. It comprises a housing flange 1 which is preferably made by casting and has a duct opening 2. This housing flange 1 is screw-connected in a manner, which is known per se, with the transformer cover (not illustrated) by fastening screws 3, which are preferably arranged circularly. The opening 2 of the housing flange 1 is closed at the top in known manner by a valve cover 4. In order to ensure oil-tight sealing, there is provided an encircling seal 5 with an L-shaped cross-section which is fastened to the housing flange 1 by means of a clamping ring 6 and circularly arranged screws 7. For this purpose threads 8, into which the screws 7 are screwed, are formed at reinforcing ribs 9 of the housing flange 1 so that the clamping ring 6 reliably fixes the seal 5. Moreover, bolts 10, which extend vertically upwardly, with internal threads are screwed into the housing flange 1. A spring cover 11, which corresponds with the housing cover according to the state of the art, is fastened to this by means of screws 12 which are screwed from above into the internal threads of the bolts 10. Two biased springs, namely an inner spring 13 and an outer spring 14, are disposed in a manner known per se between spring cover 11 and valve cover 4. Not only the inner spring 13, but also the outer spring 14 are supported by their respective upper ends against concentric offsets at the underside of the spring cover 11; they are supported by their respective upper ends against the upper side of the valve cover 4, which similarly has a corresponding concentric profiling. A signal pin 15 extending vertically upwardly is additionally provided centrally at the valve cover 4. A vertical duct plate 16, which will be discussed in more detail later, is in addition laterally fastened to the housing flange 1 by means of fastening screws 17. The entire apparatus is enclosed by a pot-shaped housing 18 fastened to the housing flange 1 by means of screws 19 and to the duct plate 16 by means of further screws 20. One or more cable passages 21 are provided at the duct plate 16; so that the housing 18 can be mounted, it has a lateral cut-out 22 in such a manner that it can be pushed by this cut-out 22 from above over the cable passages 21 during mounting. The signal pin 15 has in its upper region in the interior of the apparatus a switching profile 23 by which one or more switches 24, roller switches or limit detectors, for example, can be actuated. Cables 25 lead from the switches 24 through the cable duct 21 to the outside. Outlet openings 26 are provided on the side of the housing 18 opposite the cable ducts 21 and are arranged in the pot-shaped side region 27 which extends vertically downwardly. In the illustrated example of embodiment these openings are a plurality of small bores, for example with a diameter less than or equal to 12 millimetres; however, as already explained further above, numerous other forms or sizes of these outlet openings are also conceivable within the scope of the invention. Finally, there is also shown a further seal 28 which is constructed as a sealing lip and already known US 4 676 266 and which is deflectable in the manner of a windscreen wiper blade and corresponds with the downwardly curved, pot-shaped edge region of the valve cover 4. However, this additional seal 28 is not an essential component of the pressure relief valve, but merely serves the purpose of, in specific operating conditions, increasing the opening speed as well as avoiding 'flutter1. Finally, it is additionally shown that the signal pin 15 penetrates the housing at the top in a passage 30, i.e. extends to the outside. The same apparatus, horizontally turned through 90 degrees, but now in opened state, is shown in Figure 2. It can be seen that due to the excess pressure in the transformer vessel (not illustrated) the valve cover 4 is now deflected upwardly against the force of the springs 13, 14. In this setting the valve cover 4 no longer lies on the seal 5; the seal 28 is similarly disposed out of engagement with the edge region 29 of the valve cover 4. The excess, hot fluid and gases thus pass into the interior of the pressure relief valve and through the outlet openings 26 to the outside in defined manner. The signal pin 15 also lifts upwardly together with the valve cover 4. The electrical switch 24 is actuated by the switch contour 23 of the pin. It is also possible to use the now further projecting end of the signal pin 15 for actuation of known optical indicating means, which are not illustrated in more detail here. The space which the oil can fill is closed upwardly by the spring cover 11 and the hot oil torrent thus cannot detrimentally affect either switch 24 or cable 25. As soon as the impermissible excess pressure has decayed, the valve cover 4 is pressed back into its rest position by the forces of the springs 13,14; the seals 5 and 28 again seal the valve cover 4 against the opening 2. The entire apparatus is shown once more in perspective illustration in Figure 3. It can be readily seen that the housing 18 completely encloses all components. It can be additionally seen that no additional adapter arrangement is necessary for fastening to the transformer vessel, even less that on some occasion during the period of use of the apparatus the spring cover disposed under spring stress has to be released. Finally, it can be readily seen from this illustration that no electrical switching or connecting means, which could possibly be damaged, are located outside the housing. The basic construction of a second, modified pressure relief valve according to the invention is shown in Figures 4 to 6. Like components are provided with the same reference numerals; the basic construction corresponds with that of the first example of embodiment. In departure from the first form of embodiment illustrated in Figures 1 to 3 and explained above there is indicated here a transformer cover 31 having an opening 32 on which the pressure relief valve is mounted by its housing flange 1 and its central opening 2. In this form of embodiment the signal pin 15 has at its upper, free end, which projects out of the housing 18, a mushroom 33 for covering. This mushroom 33 reliably protects the entire pressure relief valve and also the switch 24 against penetration of rainwater. Additional seals, which are not illustrated here, can also be provided. The mushroom 33 is, for example, fastened to the signal pin 15 from above by means of a fastening screw 34. Moreover in the case of this form of embodiment there are provided, instead of circular outlet openings, ventilation slots 35, 36, 37 which extend in different horizontal planes radially in the pot-shaped side region 27 of the housing 18. A respective outlet scoop 38, 39, 40 is integrally formed from the outside and offers a particularly good protection against rain in that it additionally protects the ventilation slots 35, 36, 37 from above in the form of a roof. It is also ensured in the case of this form of embodiment that it is not possible for fingers to access the interior or for foreign bodies to enter therein. The outlet scoops 38, 39, 40 can obviously also be respectively externally fastened to the housing 18 as separate shaped parts. Finally, in the case of this form of embodiment stiffening ribs 41, which guarantee a particularly high mechanical stability of the housing 18, can be provided in the upper, substantially horizontal region of this housing 18. The fastening of the switch 24 can take place in particularly advantageous manner by upwardly directed threaded pins 42, 43 which are pressed into the spring cover 11 and which are indicated in Figure 4. In this manner a simple, also subsequent, fastening of one or also more switches 24 is possible from above without further components having to be removed from the housing 18. Advantageously, such a number of threaded pins 42,43 is provided in defined position relative to one another that the maximum possible number of switches 24 can be mounted. If only a few, or even no, switches are mounted the unused threaded pins simply remain free. In fact, it would also be possible - this is known from the state of the art - to screw the switches 24 from above in each instance by means of a thread cut into the spring cover 11. However, in that case it is disadvantageous that, due to the small material thickness of the spring cover 11, tearing-out of the thread can occur. This disadvantage is securely avoided by the fastening, which is proposed here, by means of pressed-in threaded pins 42,43. Figures 7 and 8 show an already described seal 5 with an L-shaped cross-section. The limb 5.1, which is directed upwardly against the valve cover 4, of this seal 5 seals the opening 2. In a particularly advantageous embodiment the sealing surface 5.2, which in the rest state bears against the valve cover 4, is chamfered, for example by 15°. A reduction in the effective sealing area and an increase in the specific pressing pressure thereby results, which is particularly important in the case of small response pressures, for example 8 psi. Moreover, adaptation of the sealing surface 5.2 to the inevitable unevennesses of the valve cover 4 is facilitated by this chamfering. Figure 9 shows a detail of a further pressure relief valve according to the invention with a particularly advantageous development of the fastening of the housing 18 directly to the housing flange 1. Whereas in the case of the forms of embodiment explained further above the fastening took place by a horizontal screw connection, here press knobs 44 are provided for the fastening, the knobs being arranged in bores 45 of the housing 1 with their free ends resiliency urged outwardly, and aligning with corresponding openings in the pot-shaped side region 27 of the housing 18. In order to achieve this resilient action of the press knobs 44, these each have in the interior a respective spring 46 which is supported on the one hand against the inner end of the press knob 44 and on the other hand against the end face of the bore 44. Each press knob 44 has, for locking, a radial offset 47 at its cylindrical outer profile, which in turn is supported against a locking sleeve 48 screwed into the housing flange 1. The outwardly directed profile of the press knob 44 is formed to be spherical so as to facilitate sliding thereover of the side region 27 of the housing 18. This spherical end of the press knob 44 projects, in the mounted state of the housing 18, outwardly through the corresponding openings; for demounting it can be respectively pressed inwardly against the force of the spring 46 and the housing 18 removed upwardly. This form of embodiment allows an easy and simple mounting and demounting of the housing 18 without special tools and yet a reliable fastening of this housing 18 directly to the housing flange 1. Finally, a further detail of a particularly advantageous, further developed pressure relief valve according to the invention, with a possibility for ventilation, is shown in Figure 10. In the case of horizontal installation of the pressure relief valve it can happen that gas collects in the interior, for which purpose a separate possibility for ventilation in the case of specific constructions can be useful. For this purpose there is provided a ventilation bore 49 which leads through the housing flange 1 to a sealing cone 50 at the base of a horizontal threaded bore 51 leading to the outside. A ventilation screw 52, which similarly has at its lower end a sealing cone, is screwed into this threaded bore 51 from the outside. The sealing cone 50 of the threaded bore 51, as also the sealing cone of the ventilation screw 52, are dimensioned in their relationship to one another in such a manner that on screwing-in and tightening of the ventilation screw 52 there is effected a secure sealing of the ventilation bore 49 without the sealing rings required in the state of the art being necessary. The construction of the ventilation screw 52 as a hollow form with a central ventilation bore 53, which in the screwed-in, i.e. sealed-off, state of the ventilating screw 52 is closed, is particularly advantageous. Through this mode of construction the ventilation screw 52 does not have to be completely unscrewed for ventilating the pressure relief valve, but only somewhat loosened and, after ventilation has taken place, screwed tight again. Patent Claims 1. Pressure relief valve for oil-filled transformers and tap changers with a covering, wherein a housing flange (1) with a continuous opening (2), which in the rest state is sealed off by a spring-loaded valve cover (4) and at least one seal (5), is provided, wherein a stationary spring cover (11) is arranged above the valve cover (4), wherein at least one biased spring (13, 14) is arranged between spring cover (11) and valve cover (4) in such a manner that it is supported by its upper end at the lower side of the spring cover (11) and by its lower end at the upper side of the valve cover (4), wherein the covering is constructed as a pot-shaped housing (18) which encloses the entire pressure relief valve and which has at least one outlet opening (26) and wherein the housing (18) is fastened directly to the housing flange (1), characterised in that the housing (18) is constructed to be separately mountable, that the housing (18) has a lateral cut-out (22), that a vertically upwardly extending duct plate (16) having at least one cable duct (21) and filling out the lateral cut-out (22) is provided laterally at the housing flange (1) and that the housing (18) is additionally screw-connected with the duct plate (16). 2. Pressure relief valve according to claim 1, characterised in that the housing (18) is fastened by at least one press knob (44) which is arranged in the housing flange (1) to be resilienTLy urged outwardly and which corresponds with a respective opening in the pot-shaped side region (27) of the housing (18). 3. Pressure relief valve according to one of claims 1 and 2, characterised in that a ventilation bore (49) is provided in the housing flange (1) to penetrate this and is connected with a horizontal threaded bore (51), wherein the base of the threaded bore (51) has a sealing cone (50) and wherein a ventilation screw (52) can be screwed into the threaded bore (51) and has at the inner end thereof a further sealing cone which corresponds with the sealing cone (50) of the threaded bore (51). 4. Pressure relief valve according to any one of claims 1 to 3, characterised in that at least one ventilation slot (35, 36, 37) is provided as outlet opening and is closed off by a respective outwardly arranged outlet scoop (38, 39, 40), which is downwardly open. 5. Pressure relief valve according to any one of claims 1 to 4, characterised in that an electrical switch (24) known per se is provided within the housing (18) and is actuable by the deflection of the valve cover (4) via a signal pin (15) and that the cable (25) of this at least one switch (24) is led outwardly through the cable passages (21). 6. Pressure relief valve according to claim 5, characterised in that the fastening of the at least one switch (23) is effected by upwardly extending threaded pins (42, 43) pressed into the spring cover (11). 7. Pressure relief valve according to one of claims 5 and 6, characterised in that a mushroom (33) for covering is arranged at the signal pin (15) at the upper end thereof projecting out of the housing (18). 8. Pressure relief valve according to any one of claims 5 to 7, characterised in that the region in which the at least one electrical switch (24) and the cable (25) are disposed forms a separate, protected space separated off by the spring cover (11). 9. Pressure relief valve according to any one of claims 1 to 8, characterised in that the at least one outlet opening (26) is formed in such a manner that it fits into the contour of the pot-shaped side region (27) of the housing (18).

Documents:

2454-chenp-2005 abstract duplicate.pdf

2454-chenp-2005 claims duplicate.pdf

2454-chenp-2005 description (complete) duplicate.pdf

2454-chenp-2005 drawings duplicate.pdf

2454-chenp-2005-abstract.pdf

2454-chenp-2005-claims.pdf

2454-chenp-2005-correspondnece-others.pdf

2454-chenp-2005-correspondnece-po.pdf

2454-chenp-2005-description(complete).pdf

2454-chenp-2005-drawings.pdf

2454-chenp-2005-form 18.pdf

2454-chenp-2005-form 3.pdf

2454-chenp-2005-form 5.pdf

2454-chenp-2005-pct.pdf