Patent Application
20090212897
The disclosure relates to a low voltage coil for a transformer as well as a dry type transformer comprising such low voltage coil, as used for power distribution in a range of 50 kVA to 25'000 kVA.
WO 03/107 364 A1 discloses a coil resin-encapsulated and having spacer means based on a plurality of tubes made from a thermoplastic material and distributed over the entire cross section of the coil.
Exemplary embodiments disclosed herein can improve the known coil of generic type with respect to its fire resistance without impairing its mechanical properties.
A low voltage coil for a transformer is disclosed, with a winding made from a conductive foil and an insulating foil forming a plurality of turns where two subsequent turns of conductive foil are in each case separated by at least one turn of insulating foil, wherein the circumferential surface of the winding is at least partially covered by a fire resistant protective layer.
In another aspect, a dry type transformer is disclosed, comprising: a low voltage coil having a winding made from a conductive foil and an insulating foil forming a plurality of turns where two subsequent turns of conductive foil are in each case separated by at least one turn of insulating foil; a core with at least one leg surrounded by the said low voltage coil; and a high voltage coil surrounding the said at least one leg and said low voltage coil.
The disclosure is explained with reference to the following figures which show an exemplary embodiment.
It has been found that the exemplary embodiments according to the disclosure can significantly improve the fire resistance of a dry type transformer. Temperatures reached during a standard test were significantly lower and the time to self-extinguish was shortened by more than half. Mechanical properties were essentially equal to those of known generic type low voltage coils.
The continuous winding comprises an inner part winding 3 and a coaxial outer part winding 4 separated by a gap 5 which completely surrounds the inner part winding 3. The gap 5 is established by spacer means which comprises twelve individual spacers 6 in the shape of straight aluminium tubes of rectangular cross section which are distributed over the circumferential surface of the inner part winding 3, each of them being arranged parallel to the axis of the winding. In an exemplary embodiment, the spacers extend over the whole length of the coil. Of course, there can be more or less spacers than indicated, e.g., between ten and thirty and they may differ in cross section and other properties from the ones described. For instance, they can be profiles, in particular, U-profiles or T-profiles. Any material with adequate mechanical properties can be used, however, inorganic materials which are fire resistant are preferred, in particular aluminium, steel and/or some other metal and/or alloy and/or even ceramic and/or glass as the use of such materials has been found to have a positive effect on the fire resistance properties of the low voltage coil. Instead of individual spacers other spacer means may be employed, e.g., a corrugated metal sheet, in particular, an aluminium sheet with creases parallel to the axis. There may also be several gaps, subdividing the low voltage coils into three or more coaxial part windings. On the other hand, there may also be no gap at all. At the upper end of the low voltage coil the inner part winding 3 and the outer part winding 4 are filled with DMD saturated laminate.
The circumferential surface of outer part winding 4 is surrounded by several turns of the insulating foil 2 and at least partially by a fire resistant layer, in particular a wrap 7 which comprises several, in particular, four, turns of an insulating non-combustible protective foil 8. The protective foil 8 preferably comprises a layer of woven glass fibers impregnated with silicon resin, preferably with an admixture of mica. Such foils are also known as mica paper and are available from various sources. Cablosam® foils, e.g., Cablosam® 366.21-10, DURAPOL FR-HA 2, RAL 7001 and S 2000 E available from VonRoll Isola and CABLEFLEX 1/2A and 2/2 from jsi have been found to be suitable. However, other materials may be used as well as long as they have the required fire resistance and mechanical properties. In particular, the material has to be non-combustible and electrically insulating and be suitable for partially or completely covering the circumferential surface of the winding.
The low voltage coil is produced in the manner described below:
A winding machine is loaded with rolls of conductive foil 1 and insulating foil 2 and a narrower roll of DMD saturated laminate. The first lead-out is attached to the conductive foil by tungsten inert gas welding. Then the inner part winding 3 of the low voltage coil is wound and its upper part filled with the DMD saturated laminate wound up together with the conductive foil 1 and the insulating foil 2. After that the spacers 6 are put into place. The winding process is then continued and the outer part winding 4 applied in the same way as the inner part winding 3 before. The second lead-out is then attached to the conductive foil, again by tungsten inert gas welding. Now, the wrap 7 is applied to the circumferential surface of the outer part winding 4 by winding four turns of protective foil 8 on it. Finally, to apply the protective cover 9 the lower part of the low voltage coil is sealed with a liquid mass comprising epoxy resin and, finally, the low voltage coil is cured in an oven for 2 h at 120° C.
The low voltage coil as described and a reference coil without a wrap and a protective layer and with polyester-filled glass fiber spacers were subjected to fire tests according to the IEC 60076-11 standard. In each case, a fire was lighted with 7.7 I of alcohol and the temperature above the fire was measured as prescribed by the said standard.
The results were as follows:
Obviously, the fire resistance properties of the low voltage coil according to the above-described exemplary embodiment of the disclosure shows a very significant improvement over the respective properties of the conventional reference coil.
The disclosure also relates to a transformer comprising at least one inventive low voltage coil. The transformer may otherwise be of known construction, e.g., as shown in WO 00/31 761 A1, with a core with three legs connected by an upper yoke and a lower yoke, each leg being surrounded by a low voltage coil and a high voltage coil surrounding the leg and the low voltage coil. Such dry type transformers are employed in particular as distribution transformers for a power range of between 50 kVA and 25'000 kVA.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/CH2006/000582 filed as an International Application on Oct. 19, 2006 designating the U.S., the entire content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CH2006/000582 | Oct 2006 | US |
| Child | 12421659 | US |
