WO1987005412A1

WO1987005412A1 - Improvements in ferroresonant constant-voltage transformers

Info

Publication number: WO1987005412A1
Application number: PCT/EP1987/000101
Authority: WO
Inventors: Lorenzo Petrogalli
Original assignee: Elektrene S.R.L.
Priority date: 1986-02-28
Filing date: 1987-02-24
Publication date: 1987-09-11
Also published as: IT8619600A0; EP0302856A1; EP0302856B1; IT8619600A1; AU7125387A; IT1190079B

Abstract

A constant-voltage transformer is foreseen comprising two separate ring-shaped cores (10, 20) both made up of two facing "C" portions. One of them has opposed facing surfaces lapped in a mirror-like way that are drawn together in order to obtain a saturated magneted field, whilst the other is provided with a gap and thus operates in a linear magnetic field. Both cores (10, 20) have a part (11, 21) adjacent to the corresponding part of the other core being the primary winding (P) wound around these two adjoining parts (11, 12), whilst the secondary winding (S) is wound around another part (22) of the saturated core (20), the length of the magnetic circuit of the two cores being substantially different. Particularly the extension of the saturated magnetic circuit is greater by 10 % than of the other core. It is moreover foreseen that the two cores are spiral-wound using a continuous strip of core sheet.

Description

"IMPROVEMENTS IN FERRORESONANT CONSTANT-VOLTAGE

TRANSFORMERS"

The present invention relates to ferroresonant constant-voltage transformers. These are now widely used in order to obtain a stabilized voltage. These transformers are enjoying an increased sale on the market owing to the fact that many electronic products now in common use need a constant imput voltage in order to work properly.

Many transformers of this kind are already known. However, they are relatively inefficient and thus they easily heat up if the voltage increase is very high.

It is moreover known that the magnetic permeability of a core sheet is greater is the direction of the lamination. On the contrary, magnetic losses are smaller in this direction. The known ferroresonant transformers use blank superimposed core sheets having anisotropy in a single direction, in the direction of E's legs, whilst the other sides do not enjoy this privilege and thus suffer high magnetic losses.

GB-A-1-020.093 foresees a transformer having two cores: one with and the other without gap, both being provided with two adjacent portions on which the secondary winding is wound while the primary winding is wound only on the core's portion without gap, thus with a saturated magnetic circuit. This arrangement is quite inefficient because an input voltage increment causes the current to rise while the magnetic permeability of the material is reduced tending to saturation. At this point the primary winding, subjected to a very high current, produces an anomalous heating and thus excessive heat losses.

FR-A-2.140.038 shows two continuous cores (without gap) also having two adjacent portions on which a primary winding is wound. However for obtaining a constant voltage besides the main secondary winding a feed back secondary winding is also necessary. This complicates the construction and makes it more expensive and less reliable.

Aim of this invention is to carry out an improved ferroresonant transformer having a good efficiency, better than that of the present transformers, thus enabling considerable variations comprised between -50% and + 30% obtaining output variations comprised within±2%.

The above mentioned aim has been attained as better explained in the enclosed claims.

The invention will now be better clarified by an exemplary embodiment that has been illustrated in the enclosed drawings, in which:

Fig. 1 is a frontal view of the proposed transformer; and Fig 2 is a side view of the same transformer.

Reference being made to the drawings it will be noted that the proposed transformer is made up of two cores 10 and 20 each one comprising a single spiral wound core sheet strip that is cut in half to form two C-shaped portions respectively 15 and 16; 25 and 26. Both cores have a portion, respectively 11 and 21, that is adjacent to the other portion 11 or 21. Around both adjacent portions the transformer's primary P is wound. Around another section 22 of the saturated magnetic core 20 (without gap) the secondary S is wound.

Core 10 is made so as to work always in a linear magnetic field, whilst core 20 is made so as to work always with a saturated magnetic field. To do so, the facing surfaces of portions 25 and 26 of core 20 are lapped in a mirror-like way on their facing surfaces 27, then they are drawn together so that in between portions 25 and 26 the gap is practically "zero". Core 10, on which only the primary winding P is wound is instead provided with two gaps 18 between the two facing surfaces 17. The total value of the two gaps is preferably comprised between 000,2 and 2 per thousand of the core's magnetic circuit, i.e. for a 20 W power the circuit is about 130 mm. and the two gaps' total value is 0,05 mm. equal to the 0,4 per thousand, for a 250 W power the magnetic circuit is about 260 mm. and the total value of the two gaps is 0,4 mm. equal to the 1,5 per thousand.

As will be noticed from the drawings the extension of the magnetic field of core 10 is solely that strictly necessary for accomodating winding P. The extension of core 20's magnetic circuit is on the contrary much greater, particularly it is at least a 10% bigger than the magnetic field extension of core 10.

The two cores are preferably obtained by winding a magnetic core shaped as a continuous strip whose grains, as known, are positioned in the direction of lamination. This continuous strip is spiral wound starting from the inner winding's surface indicated with 13 and respectively with 23, and continuing until the outside surface, indicated respectively with 14 and 24 is reached. Each annular core is then cut in half thus forming two portions having opposed facing surfaces 17 and 27. With the proposed winding there is therefore a greater efficiency because the anisotropy created by the sheet is profitably exploited. On operation, when the input voltage increases, the permeability of core 10 linear magnetic circuit remains practically constant. Therefore in the primary winding the current will increase in a linear way when the input voltage increases. Therefore a phenomenon of anomalous heating will not occur.

Claims

C L A I M S

1. Ferroresonant constant-voltage transformer comprising two separate ring-shaped cores (10, 20) each one comprising two C-shaped portions having opposed facing surfaces (17, 27), one (10) of the cores being provided with a gap (18) that makes it work with a linear magnetic field while the other core (20) is without gap thus its magnetic circuit is saturated; the two cores being provided with a portion (11, 12) adjacent to the corresponding portion of the other core on which a winding is wound surrounding both these adjacent portions (11, 21) while another winding is wound on another portion of one of the two cores, said two cores (10, 20) having different magnetic circuit extension, characterized in that the primary winding (P) is wound on both cores (10, 20) while the secondary winding (S) is wound only on the core (20) that is without gap thus with a saturated magnetic circuit, and in that the core (20) which operates in a linear magnetic field has facing frontal surfaces (27) which are lapped in a mirror-like way so that its gap is practically reduced to nil.

2. Transformer according to claim 1, characterized in that the length of core (20) (without gap) is at least 10% bigger than that of core with gap (10).

3. Transformer as in any of the previous claims characterized in that the cores (10, 20) are obtained by spiral winding a strip of core sheet obtained by lamination in form of a continuous tape, i.e. they are made up of core sheets having lamination direction that is, all over, the same as that of the magnetic circuit.

4. Transformer as in any of the previous claims characterized in that the whole gap (17 + 17) between the half cores (15, 16) is comprised between 1 and 5 per thousand of the magnetic circuit's extension.