DEVICE

DESCRIPTION

The present invention relates to a filtering device for self-regenerating breathers.

Self-regenerating breathers are devices for dehumidifying air intended for oil expansion vessels used in electrical power equipment, particularly oil- insulated equipment such as power electrical transformers, on-load tap changers and so on. It is well known that a power equipment containing insulating oil usually includes an oil expansion tank whose function is to compensate for the inevitable volume changes of the oil inside the transformer caused by temperature changes.

This oil expansion vessel is supplied with air that has been previously treated in a special breather to remove or drastically reduce its moisture. This is because air supplied to an oil expansion tank even with a minimal amount of residual moisture would have the negative side effect of reducing the breakdown tension of the insulating oil.

In their essential and main features, examples of breather of the known type include an outer casing, an electronic board and a regeneration system with a desiccant tank.

The reservoir, which has at least one inlet opening for the air to be dehumidified and at least one outlet opening for the dehumidified air, contains within it a desiccant element (such as Silica Gel) and/or desiccant media (consisting of a plurality of thermally regenerable granules or salts), capable of dehumidifying the air coming in from outside, a breathing system and means for detecting the humidity level of the dehumidified air, operatively connected to the heating element.

For example, the regeneration system may be a heating resistor, which is responsible for the thermal regeneration of the absorption media.

Typically, the means of activation of the regeneration procedure include humidity sensors, placed outside the tank and preferably near the outlet opening of the dehumidified air, or load cells or timers. 2

For example, the humidity sensor detects the residual moisture value in the dry air and triggers the activation of the heating resistor if this value exceeds a maximum permissible value; this means, in fact, that the desiccant media have lost or are losing their absorbing capacity and must be regenerated. However, it is possible for dust and/or pollutants to enter the desiccant, e.g. salts, resulting in malfunctions of the dryer and the connected electrical equipment.

The present invention intends to solve this problem of the prior art.

In particular, the primary object of the invention is to realise a filtering device for self-regenerating breathers, which makes it possible to prevent dust and/or pollutants from entering the desssicant salts and thus causing malfunctions of the dryer and the connected equipment.

A further object of the present invention is to realise a filtering device for self-regenerating breathers, which enables this filtering operation to be carried out in a simple, fast, effective and reliable manner.

These and other purposes are achieved by means of a filtering device for self-regenerating breathers according to claim 1 appended hereto; other detailed technical characteristics of said device are set forth in the related dependent claims.

The above-mentioned purposes and advantages will become more evident below, thanks to the description of a preferred form of embodiment of the invention, provided by way of example, but not limitation, and the accompanying drawings, in which

- Figure 1 is a perspective view of a filter device applied to a self regenerating breather;

- Figures 2 and 3 schematically show the phases of exhalation or exhaust and intake of air during operation of a self-regenerating breather operating with the filter device, according to the present invention;

- Figure 4 is an exploded view of a valve or diaphragm installed at the bottom of the self-regenerating breather and used for operating the filter device, according to the invention. 3

With reference to the above-mentioned figures, a self-regenerating breather for power electrical apparatus, such as electrical transformers, according to the invention, comprises an external housing 10, an electronic board 11 , at least one internal tank 12. Optionally, in the case of more than one tank, there is a three-way solenoid valve 13, two inlet ways and one outlet way, which determines in which of the tanks the air is circulating.

Each tank 12 has inlet openings 14 for the air to be dehumidified and outlet openings for the dehumidified air, and contains within it a desiccant element (Silica Gel) and/or other absorption means (granules or thermally regenerable salts), which are suitable for dehumidifying the air coming from outside, as well as a heating resistor (not illustrated in the accompanying figures) and means for detecting the degree of humidity of the dehumidified air operatively connected to the heating resistor. According to the present invention, in order to prevent dust and/or other contaminants from entering the salts placed inside the tank 12, an oil filter 15 communicating with the tanks 12 of the breather is placed on the side of the breather device.

Also placed on the bottom of the breather device is a one-way valve or membrane 16, advantageously provided with a gasket 17, a flexible blade 18 and a closing flange 19 secured by closing means 20.

Valve 16 opens or closes the openings at the bottom of the tanks 12 of the dryer device, depending on whether the device is exhaling or discharging air. In particular, when exhaling or exhausting air from the dryer device (fig. 2), valve 16 opens to evacuate condensate water (according to the path of arrows F of fig. 2), during the regeneration of salts inside the tanks 12, and to allow air to escape from the tanks 12 (according to the path of arrows G of fig. 2), during the heating phase of the electrical equipment connected to the breather.

When air is drawn in (fig. 3), during the cooling phase of the electrical apparatus connected to the breather, valve 16 is closed and the air from outside (according to the path of arrows H in fig. 3) is made to flow through 4 openings 20 of the oil filter 15 into the oil 21 contained in the oil filter 15, so as to be free of pollutants; at this point, the filtered air, free of pollutants, is sucked into the reservoirs 12 of the dryer device through the duct 22, which connects the oil filter 15 to the dryer (according to the path of arrows J of fig. 3); then, the suction air is forced to pass through oil 21 and thus be free of pollutants, thanks to the presence of valve 16, which closes and prevents air from entering the breather device except through oil filter 15, during the cooling phase of the electrical equipment connected to the breather.

By virtue of the foregoing, it is therefore understood how the filtering device for self-regenerating breathers, according to the invention, achieves the objectives and realises the above-mentioned advantages.

In particular, the advantages obtained are as follows

- it is possible to evacuate water during regeneration of salts inside the breather; - it is possible to evacuate air during the heating phase of the electrical apparatus connected to the breather;

- air is prevented from entering the breather, except through the oil filter, during the cooling phase of the electrical equipment apparatus to the breather; - in this way, the suction air is forced to pass through the oil and thus rid itself of pollutants before entering the breather's salt tanks.

Finally, it is clear that numerous other variants of the filtering device in question may be realised, without departing from the principles of novelty inherent in the inventive idea expressed in the appended claims, just as it is clear that, in the practical implementation of the invention, the materials, shapes and sizes of the illustrated details may be any, depending on requirements, and may be replaced with others that are technically equivalent.