Title of Invention

AIR-HUMIDIFIER FOR OIL-INSULATED TRANSFORERS, CHOKE COILS AND TAP CHANGERS

Abstract

An air dehumidifier for oil-filled transformers, choke coils and tap changers, for ehumidification of air inducted into oil expansion vessels, comprising a cylinder closed at the top by a lid and at the bottom by a base part, an air-permeable housing arranged within the cylinder and filled with a moisture-absorbing granulate, wherein a space which is filled by the inducted air after flowing through the granulate in the housing is present between an outer wall of the housing and an inner wall of the cylinder, an electrical heating device in the interior of the housing and a moisture sensor which is disposed in the space between the outer wall of the housing and the inner wall of the cylinder said moisture sensor activating the heating means is activatable when a limit value of the measured air humidity is exceeded, characterized in that the base part being made of metal or another material with a good specific thermal conductivity and having an inner contour formed to be funnel-shaped, the fwmel-shaped inner contour having a lower rounding-off.

Full Text

Air dehumidifier for oil-insulated transformers, choke coils and tap changers The invention relates to an air dehumidifier such as is used as an accessory in oil-insulated transformers, choke coils or tap changers for dehumidification of the air sucked into the oil expansion vessels. Such an air dehumidifier is already known from JP 60198710 A1. It has two identically formed filter chambers each filled with moisture-absorbing material. The inducted airflows from below, in each instance via a bell arrangement with a oil sump, to at least one of the two filter chambers, there runs through the moisture-absorbing material, is in that case dried and leaves the air dehumidifier in upward direction. In addition, an electrical heating device is provided in each of the two filter chambers. When the moisture absorbing capacity of the moisture-absorbing material in the respective filter chamber is exhausted, the corresponding heating device is switched on and thus the moisture-absorbing material is dried and regenerated. An outlet opening for exit of the heated-up moisture is provided each time in the upper region of each filter chamber. A further developed air dehumidifier has been proposed in European Patent Application EP 1313112 A1. In that case a moisture sensor, which actuates the heating in the interior of the filter insert in dependence on state, is arranged in the flow of the dried air after this has run through the actual filter insert filled with moisture-absorbing material. The moisture sensor then detects the moisture state of the air which flows around it and which should have already been dried. If the moisture sensor signals that the moisture in this inducted air exceeds a limit value, thus is too high, this means that moisture-absorbing material is saturated, can absorb no further moisture and has to be dried out. The electrical circuit of the heating device, preferably a resistance heater, in the filter insert is then closed by switching means. As a consequence, the moisture-absorbing material is heated and thus dried; the previously incorporated water shall drip downwardly into the free area. However, it has now proved that in the case of the known air dehumidifiers in practical operation the heated-up liquid neither leaves through exit openings arranged above the heating device nor drips off completely in downward direction. Rather, a part of this heated-up liquid precipitates on the cylindrical inner wall of the filter chamber or housing wall of the air dehumidifier in the form of fine droplets. These fine water droplets remain - due to the surface tension thereof - hanging there and cannot be removed. This is undesirable since in the course of time the moisture concentration in the region of the inner wall thereby constantly increases. Due to that, in addition also the value ascertained by the described moisture sensor as actual value of the moisture of the air, which surrounds the drying medium, for determination of the state of this medium is falsified. It is accordingly the task of the invention to eliminate the described disadvantages of the state of the art and to indicate an air dehumidifier of the stated kind which ensures by special measures that the liquid heated up from moisture-absorbing, regeneratable filter material by actuation of the heating device does also in fact leave the filter arrangement. This task is solved by an air dehumidifier with the features of the first patent claim. The subclaims concern particularly advantageous developments of the invention. The main advantage of the invention consists in that through the special construction in accordance with the invention of the base part there is achieved a defined, locally limited falling below of the dew point in the interior of the filter arrangement. Thus, there then takes place a selective condensation of the heated-up liquid at this base part and the liquid defined there and condensed in locally limited manner reliably runs off from there. The invention shall be explained in still more detail by way of example in the following on the basis of drawings, in which: Figure 1 shows a complete air dehumidifier according to the invention in lateral, schematic sectional illustration, Figure 2 shows, in the manner of a detail, the lower region by itself of a base part according to the invention, Figure 3 shows the view of a base part by itself of a further developed further air dehumidifier according to the invention, from below, and Figure 4 to 6 show different side sectional illustrations of the base part shown in Figure 3. Initially, for better understanding the entire construction of the air dehumidifier shall be described in more detail on the basis of Figure 1. The air dehumidifier comprises a base Dart 1 into which an annular seal 2 is placed, on which in turn a cylinder 3 rests. The cylinder 3 is closed upwardly by a lid 4; here, too, an annular seal 5 is again provided for sealing. Vertical stud bolts 6 with lower knurled nuts 6.1 screwed on outside the base part 1 are provided for fastening. Screws 7 are provided at the top as fastening means. An air-Dermeable housing 8 is disposed centrally in the cylinder 3. The housing 8 contains a -egeneratable granulate 9 as moisture-absorbing material as well as a heating means 10, [he heating elements of which are disposed between the granulate 9, i.e. are surrounded By this. The granulate 9 is, for the sake of clarity, not illustrated in more detail here, Above the lid 4 there is provided a magnet valve 12, and above the magnet valve 12 is disposed a lower flange 13 at which an upper flange 14 is fastened. A further housing 16 is arranged between upper flange 14 and a lid 15. Lower flange 13 and upper flange 14 are connected together by eye bolts 17 and wingnuts 18. The upper housing 16 has a specially shaped inner wall 19, which forms together with a downwardly open bell 20, which is fastened in the interior of the housing 16, an oil reservoir 21 which is known per se. The volume of the oil reservoir 21 is bounded by the inner wall 19 formed to be of tulip shape. A further annular seal 22 is disposed between lower flange 13 and upper flange 14, an annular seal 23 is disposed between upper flange 14 and housing 16 and finally an annular seal 24 is disposed between housing 16 and lid 15. A pipe flange 25 is arranged above the lid 15; fastening is again effected by eye bolts 26 and wingnuts 27. A switch housing 28 receiving the electrical connections and connecting lines is provided laterally. Moreover, a moisture sensor 29 is provided laterally within the cylinder 3 in the region of the flow of the air. This moisture sensor 29 detects, as already explained further above, the moisture state of the air flowing around it. If the detected moisture value exceeds a previously set limit value this means that the granulate 9 is at least substantially saturated, absorbs no further moisture and has to be dried out. In such a case the electrical circuit of the heating means 10 is closed in the switch housing 28 by switching means (not illustrated). At the same time the magnet valve 12 is similarly closed. The granulate 9 is now heated by the heating means 10 and thus dried out. For the sake of clarity the electrical connecting lines not only of the heating means 10, but also of the moisture sensor 29, which lead through a screw connection 30 to the switch housing 28, are not illustrated here. Finally, the switch housing 28 has further screw connections 31 for connection of electrical connecting lines, which are similarly not illustrated, and a current supply. Figure 2 shows in the manner of a detail the lower part of the air dehumidifier so as to be able to better explain the base part 1 according to the invention. The base part 1 consists of metal, is relatively thick and has a good specific thermal conductivity. The inner contour 1.1 is formed to be funnel-shaped; an opening 1.2 is provided at the deepest point of the funnel in the centre. The inducted air, which is still to be dried, passes into the cylinder 3 via this opening 1.2 and subsequently into the air-permeable housing 8, in which it runs through the granulate 9 and is dried. The heated-up liquid, which is heated at the inner contour 1.1, issues downwardly through the same opening 1.2. A defined, locally limited condensation of the heated-up liquid is achieved by this construction of the base part 1 with its good specific thermal conductivity and the explained funnel-shaped inner contour 1.1 and thus the task of the invention is solved. In order to assist the described effect it is particularly advantageous to produce the cylinder 3 from a material with a worse specific thermal conductivity. According to a further feature of the invention a lower radiusing 1.4 is provided at the inner contour 1.1, so that sharp transitions are avoided in the entire inner contour 1.1. This promotes the desired complete running off of the liquid condensed there. Finally, there is additionally shown in Figure 2 a screw connection 32 which is arranged in the opening 1.2 to be downwardly directed and which is explained in more detail in the following. A further base part 1 according to the invention is illustrated by itself in Figures 3 to 6. This base part 1 has special details, which are described in more detail in the following. The screw connection 32 here has a filter insert 33. It is ensured by such a filter insert 33 that no dirt particles or other foreign bodies can pass together with the inducted air or in another manner into the interior of the air dehumidifier. The filter insert 33 can be made from, for example, sintered bronze, whereby apart from the described filter action an additional noise damping is achieved. In general, dripping-off of the heated-up liquid in downward direction is not hindered by such a filter insert 33. However, under specific climatic conditions at low temperatures there can be risk of icing of this region. It can therefore be advantageous in many cases to provide an additional heating of the base part 1 of the air dehumidifier according to the invention. For this purpose an annular cut-out 34 from which a radial threaded bore 35 leads outwardly is provided in the base part 1. An electrical heater 36 is arranged in the cut-out 34. An electrical resistance heater is particularly advantageously usable for this purpose. The electrical connecting lines 37 of the heater 36 are led outwardly through the threaded bore 35 and a cable screw connection 38 screwed therein. The recess 34 which, as described, receives the heater 36 is closed downwardly by a base flange 39. The outer connection forms at the bottom a cover flange 40 having a central, flange-shaped dust protector 41 which encloses and protects the screw connection 32. Fastening of the cover flange 40 is effected by screws 42, 43, which are screwed into threads 44, 45 in the base part 1. Moreover, the base part 1 has passage bores 46, 47 serving for reception of the stud bolts, which are not illustrated here. These stud bolts were described in more detail further above in conjunction with Figure 1 and there carry the reference numeral 6. Finally, in many cases a thermal decoupling of the heating of the base part 1 by the electrical heater 36 is useful in order to ensure that effectively only, as desired, the environment of the screw connection 32 is heated. In other words, the electrical heater 36 should be effective only where a risk of icing actually exists. In order to achieve this thermal decoupling a first insulating washer 48 is provided between base part 1, electrical heater 36 and base flange 39 and a second insulating washer 49 between base part 1 and base flange 39. The insulating washers 48, 49 consist of, for example, Teflon' and thus prevent heating up of the remaining parts of the air dehumidifier according to the invention. Patent Claims 1. Air dehumidifier for oil-filled transformers, choke coils and tap changers, for dehumidification of air sucked into oil expansion vessels, comprising a cylinder (3) which is closed at the top by a lid (4) and at the bottom by a base part (1), an air-permeable housing (8) arranged within the cylinder (3) and filled with a moisture-absorbing granulate (9), wherein a space which is filled by the inducted air after this has flowed through the granulate (9) in the housing (8) is present between outer wall of the housing (8) and inner wall of the cylinder (3), an electrical heating device (10) in the interior of the housing (8) and a moisture sensor (29) which is arranged in the space between outer wall of the housing (8) and inner wall of the cylinder (3) and by which the heating means (10) is activatable when the limit value of the measured air humidity is exceeded, characterised in that a base part (1) of metal or another material with a good specific thermal conductivity is provided, the inner contour (1.1) is formed to be funnel-shaped, and that the funnel-shaped inner contour (1.1) has a lower radiusing (1.4). 2. Air dehumidifier according to claim 1, characterised in that the cylinder (3) consists of a material with a worse specific thermal conductivity than that of the base part (1). 3. Air dehumidifier according to claim 1 or 2, characterised in that a screw connection (32) with a water-permeable filter insert (33) is provided centrally at the deepest position in the base part (1). 4. Air dehumidifier according to claim 3, characterised in that the filter insert (33) consists of sintered bronze. 5. Air dehumidifier according to claim 3 or 4, characterised in that a further heating means (36) is provided in a circular cut-out (34) accessible from below and surrounding the screw connection (32). 6. Air dehumidifier according to claim 5, characterised in that the further heating means (36) is an electrical resistance heater, the electrical connecting lines (37) of which are led through a cable screw connection (38) radially screwed into the base part (1). 7. Air dehumidifier according to claim 5 or 6, characterised in that the heating means (36) is thermally decoupled from the base part (1) by at least one insulating washer (48, 49). 8. Air dehumidifier according to claim 5, 6 or 7, characterised in that the cut-out (34) is closed downwardly by a base flange (39) and/or a cover flange (40), which is fastened to the base part (1) by means of screws (42, 43).

Documents:

2452-chenp-2005-abstract.pdf

2452-chenp-2005-claims.pdf

2452-chenp-2005-correspondnece-others.pdf

2452-chenp-2005-correspondnece-po.pdf

2452-chenp-2005-description(complete).pdf

2452-chenp-2005-drawings.pdf

2452-chenp-2005-form 1.pdf

2452-chenp-2005-form 18.pdf

2452-chenp-2005-form 26.pdf

2452-chenp-2005-form 3.pdf

2452-chenp-2005-form 5.pdf

2452-chenp-2005-pct.pdf