DE29502038U1 - Kerosene drain device on an oil-filled tap changer - Google Patents

Description

Kerosene drain device on an oil-filled tap changer

The innovation relates to a kerosene discharge device according to the generic term of the first protection claim.

Such kerosene discharge devices are known, for example, from the company brochure "Step switch type G - operating instructions", imprint: BA 24/83de - 0685/500 of the applicant.

As a prerequisite for achieving the required dielectric values, the tap changer, as well as the oil-filled transformer itself, in whose tank it is installed and with whose winding tap it is electrically connected, must be dried before being filled with transformer oil. Vacuum drying and kerosene drying are known as suitable drying methods for this. With vacuum drying, the actual drying process takes place at a residual pressure of no more than 10"3 bar. If you want to avoid this complex evacuation, kerosene drying is preferable. The tap changer is dried with kerosene vapor heated to approx. 90 to 125° C. During this kerosene drying, a kerosene condensate forms in the oil vessel of the tap changer's load switch, which is why oil-filled tap changes usually have a kerosene drain device in the oil vessel base or on the tap selector bell, which must be opened before the actual drying process, but is closed during normal operation.

The known kerosene drain devices consist of a drain screw in a thread in the bottom of the oil container, as well as a sealing bell or a sealing plate, which seals the drain opening by means of one or more discarded seals when the drain screw is tightened. To operate the drain screw, the load switch insert must be pulled upwards out of its oil container, after which the drain screw is accessible from above through the opening. Due to the very limited accessibility, the drain screw in known kerosene drain devices is designed to be captive. From the company publication mentioned at the beginning, it is known that the drain screw is not provided with a thread over its entire shaft length, but rather that part of the shaft is undercut so that it has a smaller, smooth diameter, thus ensuring that it cannot be damaged.

It has also already been proposed that the drain screw be fitted with a cross bolt penetrating it or a spring washer or similar guided in a groove on the side of its threaded shaft facing away from the load diverter switch insert in order to ensure that it cannot be lost. A separate additional drain hole is provided which runs close to the thread and parallel to it and can be closed off by the sealing plate already mentioned.

It is guaranteed that the drain screw cannot be lost with all of these drain devices. However, if one of the seals has to be replaced, it is necessary to completely unscrew the drain screw in order to be able to remove the seal plate or the seal bell and insert the new seals. In order to be able to completely unscrew the screws, which are deliberately designed to be captive, they must be accessible from their lower side, facing away from the load diverter switch insert, due to the locking devices arranged there. This either requires the complete removal of the tap changer from the transformer tank, which is very complex, or the transformer must be emptied of fuel and it must be climbed in through the manhole of the transformer on the side facing away from the load diverter switch insert, which is no less complicated.

The aim of the innovation is therefore to provide a kerosene drain device which, on the one hand, is captive in the sense that when the drain device is opened, the drain screw cannot be completely unscrewed by accident and thus neither the drain screw nor the sealing plate can be lost or moved from the installation position, but which, on the other hand, allows a completely deliberate unscrewing in order to change the seal, with access only possible from above.

This task is solved by the innovation.

The main advantage of the new kerosene drain device is that when turning the drain screw, two different torques occur which are perceptible to the operator.

Loosening the drain screw by a certain number of turns to drain the kerosene condensate is done with low torque.

If the drain plug is to be completely unscrewed to change the seal, this must be done deliberately against increased resistance with a higher torque, but is under no circumstances possible unintentionally.

It is also particularly advantageous to fix the sealing plate axially to the shaft of the drain screw so that when the screw is loosened it automatically moves vertically upwards and the actual drain hole is exposed.

The innovation will be explained in more detail below using examples. Fig. 1 shows a kerosene discharge device according to the innovation in a side view.

Sectional view
Fig. 2 shows a drain plug as part of this device alone.

In an oil tank base 1 of the oil tank of a load changeover switch of a tap changer, a threaded bushing 2 is provided which penetrates vertically through the oil tank and is fastened here with a screw 3. Such a threaded bushing 2 is particularly advantageous in an oil tank base 1 which cannot bear particularly high mechanical loads in order to prevent the thread from tearing out; however, it is also possible to provide the thread directly in the material of the oil tank base 1 without a separate bushing.

In addition to the threaded bushing 2, the oil tank bottom 1 is also penetrated by a drain opening 4, which is closed when the entire device is closed, i.e. when the drain screw 5 is tightened, by a sealing plate 6 pressed against the oil tank bottom 1 by the latter. Ring seals 7 and 8 are inserted into the sealing plate 6.

The drain screw 5 has a clamping coating 5.1 over an area a in the lower area of its threaded shaft facing away from the load diverter switch insert. The clamping coating is particularly advantageously made of polyamide, such a coating is known from self-locking Tuflok screws. However, these known self-locking screws only have a point or spot-like coating in contrast to the all-round coating described here over a certain area. It is advisable not to coat the beginning of the thread so as not to make it more difficult to screw it back in.

The partial coating described ensures that the drain screw 5 can be unscrewed from the threaded bushing 2 by a certain amount without any particular effort, but that a considerably higher torque is required to completely unscrew it in the area in which the clamping coating 5.1 runs in the threaded bushing; the two different torques can be precisely distinguished by the operator, so that an erroneous complete unscrewing, which is not expressly intended, is practically impossible.

In any case, it is no longer necessary to have access to the lower side of the drain plug facing away from the load switch, so that the

Technically required complete dismantling of the tap changer from the transformer tank during the described seal change.

Fig. 2 shows the drain plugs 5 alone. It is particularly advantageous to provide two grooves 5.2 and 5.3 on the upper area of the shaft. The first groove 5.2 accommodates the first ring seal 7. A spring ring 9 or similar is clamped into the second groove 5.3 in such a way that the sealing plate 6 is axially fixed between the head 5.4 of the drain plug and the spring ring 9. This has the great advantage that it is ensured in a simple manner that when the drain plugs 5 are unscrewed, the sealing plate 6 is positively guided and reliably releases the drain opening 4 and cannot stick to the bottom of the oil container 1.

Reference number ascending

1 oil-filled bottom

2 threaded bushing

3 Screw for fastening the threaded bushing

4 Drain opening

5 Drain plug

5.1 clamping coating

5.2 first groove

5.3 second groove

5.4 Head

a Area of coating

6 Sealing plates

7 first ring seal

8 second ring seal

9 Spring ring

Claims (6)

Claims for compensation: 1. Kerosene drain device on an oil-filled tap changer, consisting of a drain screw which is arranged in a thread in the oil vessel base of the load changer switch of the tap changer, further comprising a sealing plate provided with one or more inserted seals, whereby the sealing plate can be pressed against the oil vessel base by means of the drain screw when it is tightened in such a way that a drain opening penetrating it can be closed, characterized in that the drain screw (5) has a clamping coating (5.1) on the lower area of its threaded shaft facing away from the load changer insert over a limited area (a) in the axial direction. 2. Kerosene discharge device according to claim 1, characterized in that the clamping coating (5.1) consists of polyamide. 3. Kerosene discharge device according to claim 1 or 2, characterized in that the threaded end has no clamping coating (5.1). 4. Kerosene drain device according to one of the preceding claims, characterized in that the drain screw (5) has a groove (5.2) on the upper region of its shaft facing the load diverter switch insert in the installed state, into which an annular seal (7) can be inserted. 5. Kerosene drain device according to one of the preceding claims, characterized in that the sealing plate (6) is axially fixed to the drain screw (5). 6. Kerosene drain device according to claim 5, characterized in that the drain screw (5) has a further groove (5.3) on the upper part of the shaft facing the load switch insert in the installed state, into which a spring ring 2· (9) such that the sealing plate (6) is axially fixed between the head (5.4) of the drain screw (5) and the spring ring (9).