Electric heating – Metal heating – Of cylinders
Patent
1991-07-08
1993-11-02
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1057, 219 1077, 296021, 148567, 427543, H05B 610
Patent
active
052585948
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The useful life of a transformer largely depends on the drying process, both of the dielectric liquid wherein the windings are immersed and of its solid insulating materials, which, furthermore, must not have been damaged by the heating to which they have been subjected to be dried. In the same way, no air bubble can be permitted to subsist, or to be trapped during the filling-impregnation-polymerization process.
For immersed transformers, a two stage process is performed: firstly, a drying treatment in an oven, air or kerosen heated, whose duration depends on the importance of the transformer, but always exceeds several hours, and can reach several days.
With the increase of the production all over the world, the vacuum drying devices have been left, because they were too expensive, compared with the hot air drying ones. Only the oil filling stage is performed under vacuum, in small autoclaves that just contain a few transformers. However, the quality and swiftness of the vacuum drying treatment are admitted and missed. There are some low frequency heating techniques, performed under vacuum, but, as with the previous systems, their cost has prevented them from spreading.
For the power transformers that have tanks able to withstand vacuum, the two stages are directly performed in the shut or welded tank. The drying is performed through a succession of heatings followed by settings under vacuum. This process lasts several days. The oil filling under vacuum follows the drying stage.
Numerous small repairers or manufacturers do not possess vacuum filling devices because of their cost, which is very high regarding their capacity. None of the methods or devices commonly used can really be automatically driven or controlled. The manufacturers still take into account a high safety coefficient, empirically determined, that brings about production costs that are higher than one could except, especially in the developing countries, where needs are more important.
SUMMARY OF THE INVENTION
The invention relates to a process that brings a reliable and economical solution whatever the type or importance of the production may be.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of a false tank wherein the core and coils are placed. The false-tank is connected by a three-way oil gate to a vacuum pump, an oil reserve, a generator and a driving and control cabinet.
FIG. 2 is a perspective view of an autoclave which is connected to a generator, a driving and control cabinet, an oil reserve, an oil drying device and a result recording set.
FIG. 3 is perspective view of a transformer with its own tank. The tank is connected to a generator, a driving and control cabinet, an oil reserve, a vacuum pump and a result recording set.
FIG. 4 is a perspective view of a cast resin transformer wherein windings are placed in their mould and suspended by isolating straps. The winding is connected to a generator and a vacuum pump.
FIG. 5 is a perspective view of an autoclave which comprises a spout, a panel, and a gutter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a process that consists in drying the core and coils (2) by supplying the LV windings with a HF current provided by a generator (9) in order to induce losses by Eddy currents. Both frequency and intensity of the current are determined for each type of transformer either by a diagram or by an automation.
Heating starts then within the windings (8) and propagates by contact both towards the periphery (HV windings) (8a) and the inner part (magnetic core) (10). Heating being performed under vacuum, all the losses by thermal radiation are practically suppressed, hence noticeable savings in energy; The three windings being connected to control devices, such as a thermostat (11) and a megohmeter (12), it is possible to control the temperature, so that it could never exceed the limit temperature of the solid insulating materials (class B 105.degree. C. for instance) result recording sets can also be added.
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REFERENCES:
patent: 3233311 (1966-02-01), Giegerich et al.
patent: 4249068 (1981-02-01), Mangan et al.
patent: 4355221 (1982-10-01), Lin
patent: 4649248 (1987-03-01), Yamaguchi et al.
patent: 4812608 (1989-03-01), Alexandrov et al.
Cahulau, heir by Colette
Pioch, deceased Rene
Pioch, heir by Evelyne
Pioch, heir by Isabelle
Pioch, heir by Olivier
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