WO1981002648A1

WO1981002648A1 - Low-loss reactor

Info

Publication number: WO1981002648A1
Application number: PCT/SE1981/000056
Authority: WO
Inventors: A Sikander; A Bjoerkman
Original assignee: Lumalampan Ab
Priority date: 1980-03-04
Filing date: 1981-03-02
Publication date: 1981-09-17
Also published as: GB2083290B; GB2083290A; JPS57500222A; NO813702L; EP0047266A1; SE421844B; SE8001690L; IT8120101A0; FI813245L

Abstract

A low-loss reactor (1) is made up of a core having a coil (5), said core comprising an upper and a lower yoke (2, 3) and intermediary legs (4a, 4b, 4c). The two yokes and the legs are made up of laminations of plates, said laminations in at least one of the yokes consisting of non-directionally oriented plates. The laminations in the remaining yoke and legs consist of rolled plates of ferro-magnetic material having a magnetic preference direction.

Description

Low-loss reactor

Reactors are used in discharge lamps such as e.g. fluorescent tubes, in which the reactors limit the lamp current through their inductive resistance.

Th e present invention relates to a reactor for the above mentioned purpose, said reactor comprising a core provided with a coil. The core is made up of yokes and legs in such a manner that at least two openings are formed in the core. The yokes and the legs of the core are made up of laminations of plates. One air gap is arranged between one of the legs and a yoke.

Reactors (reactive coils) of this kind are previously known per se. There are two important factors that have to be borne in mind when designing reactors for fluorescent tubes. The reactor must be inexpensive to manufacture and it must have a good operating economy, which means that its loss of power should be as small as possible. In the normally used reactors for 4 0Y fluorescent tubes the loss of power amounts to about9-12 %

Irι order to optimize the above mentioned factors it is essential to bring about that the total length of iron in the reactor is as short as possible and that the necessary plates for making up the iron core are cut with is little waste as possible. To this end it should be seen to that the starting material is used in the best way. It should furthermore be seen to that the space for taking up the coil has proper dimensions in relation to the iron cross section, so that the amount of copper in the coil and iron in the co re results in the best possible optimal effect. It should be observed that the area of the iron is inversely proportional to the number of turna of winding of tlie copper thread.

A further factor that influences the design of a reactor for fluorescent tubs is to see to that gaps in the construction do not create a leak flux. Such a leak flux might excite adjacent iron parts and put these parts in t o vibrations, which would cause a non-desirable noise. In order to reduce the loss of power in a reactor, the core can be up of laminations of plates of ferro-magnetic material having a magnetic preference direction. This entails an essentially improved flux density, by what means the utilization factor of the reactor is improved.

One kind of a low-losa reactor has been suggested, which comprises a core made up of standardized elements, that are cut from bands of rolled, directionally oriented plates (fig. 1). This reactor comprises two coils and the air. gap is divided into four gaps. In this way the leak flux is minimised and a low level of noise is obtained. Such a reactor entails a low loss of power, but the relatively large area of copper makes it expensive to manufacture, due to the high costs of copper. In order to reduce the cost of material it has therefore been suggested to make a reactor with a reduced copper area and an increased iron area (fig. 2). The core of this reactor is alsomade up of standardized elements of directionally oriented plates. There ia no waste when cutting the plates, since they are cut at an angle of49° in relationto the rolling direction for the plates. This reactor entails a low loss of power but. its composition is so complicated that the manufacture of it, becomes too expensive.

In the reactor according to the present invention at least one of the yokes is made up of laminations of plates of a non-directionally oriented kind, whereas the remaining yoke and legs in the core consist of lam ina tions of plates having a magnetic preference direction. The core of one embodiment of the invention comprises an upper and a lower yoke having intermediary legs wherein the two yokes are made up of laminations of non-directionally oriented plates. The preferred embodiment of the invention is described further in detail below and with reference to the appended drawings wherein:

figs. 1-2 show examples of reactors having directionally oriented plates,

fig. 5 shows - partly in section - a perspective view of a preferred reactor, fig. A shows a schematic cross section of the preferred reactor.

As has already been mentioned above, there are known reactors (figs. 1-2) having cores made up of directionally oriented plates. The embodiment according to fig. 1 comprises two coils b and four air gaps c. a reactor having the coil enclosed by directionally oriented plates a with air gaps c according to fig. 2 entails a reduced copper area and an increased iron area.

The reactor 1 according to the invention (figs. 3-4) comprises an iron core, which is composed of an upper yoke 2 and a lower yoke 3 having three intermediary legs 4a,4b,4c. The coil 5 of the reactor 1 is carried by the middle leg 4b. The air gap 6 is situated between the upper yoke 2 and said middle leg 4b. Each of the yokes 2,3 and the legs is made up of laminations of plates. The laminations in the legs 4a, 4b, 4c consist of plates of ferro-magnetic material having a magnetic preference direction. The yokes and the legs are connected in a not described mariner to a closed unit 1.

In the above described reactor theloss of power in the operating condition is about 4.5 W. In comparison with the normal loss of power of 9-12 W this new reactor results in a 50% reduction of the loss of power. In view of the fact that every single fluorescent tube is equipped with a reactor, the save of energy is quite considerable.

The following is an example showing the loss of power in a low-loss reactor according to fig. 4. It is assumed that: the iron area A = 2 x 6 = 12 cm² the flux = 13700 Gauss at 168 V the frequency f = 50 Hz tiie diameter of the thread = 0.40 mm The turns of winding of the coil can now be calculated from the formula : t - ^~i χ \ - ^Veff '^ ' °^S • N - ^• V _ _ j _{= 46} > ^{■' x Λ} - U . 2 7T£ ' ^{W _} A ^{~ ~}2_ ^{~ D}

!i = 465 turns

The area of the copp er thread = 0.4 x 0.4 x 465 = 74-4 mm².

Under the assumption that the filling factor is 0.7, the space of the Thread =106mm² (total coil space) .

The length of the coil = 20 mm

The resistance of the coil can now be calculated:

R_15º = 465 x 2 (0.02 + 0.06 + 0.01) x 0.142 = 12Ω

The corresponding loss of power at a current intensity of 0.44 is then:

P_15º = 12 x 0.43² = 2.22 W.

The resistance and loss of power at 90ºC is also calculated below:

R_90° 12 + 12 x 0.004 x 75 15.6Ω

= 1 5 .6 x 0 2.89 W

R_90° .43² =

The copper weight =

he copper cost = 0.088 x 16.32 = 1.44 Sw. crowns.

The laminations in the legs 4a, 4c have the dimensions 20 x 10 mm.

The laminations in the middle leg 4b have the dimensions 19 x 10 mm.

The laminations in the yokes 2,3 have the dimensions 50 x 10. mm.

Vol ume of non-oriented iron = =

= 55.680 mm³ The weight of non-oriented iron = 0.056 x 7.4 = 0.41 kg

Volume of oriented iron = 10 x 20 x 60 x 2 + 20 x 19 x 60 = 46.800 mm³ The weight of oriented iron = 0.0468 x 7.4 = 0.35 kg

Total weight of iron = 0.41 + 0.35 = 0.76 kg Total loss of power in iron = 0.41 x 2.2 + 0.35 x 0.8 = 1.18 W The iron cost = 0.41 x 2.05 + 0.35 x 6.02 = 2.95 Sw. crowns 'i'υtal copper and iron cost = 1.44 + 2.95 = 4.39 Sw. crowns. Total loss of power in copper and iron = 2.89 + 1.18 = 4.07 W.

These calculations thus verify the above mentioned loss of power in a reactor according to the invention. The calculations also show that the cost of a reactor according to the invention is not higher than that of an ordinary one.

Claims

Patent claims

1. A low-loss reactor, particularly for discharge lamps, having a core comprising at least one coil (5), said core comprising an upper and a lower yoke (2,3) and intermediary legs (4a, 4b, 4c), that are perpendicular to said yokes, said legs and yokes defining at least two rectangular openings and consisting of laminations of plates, the core also comprising one air gap (6), c h a r a c t e r i z e d i n that at least one of said yokes (2,3) is made up of laminations of nondiroctionally oriented plates, whereas the remaining yoke and legs (4a , 4b ,4c ) are made up of laminations of rolled plates of ferro-magnetic material having a magnetic preference direction.

2. A low-loss reactor according to claim 1, c h a r a c t e r i z e d i n that it comprises three legs (4a , 4b ,4c ) , the middle one of which carries the coil (5).

3. A low-loss reactor according to claim 1 or 2, c h a r a c t e r i ¬z e d i n that the legs (4a, 4b, 4c) consist of laminations of plates having a magnetic preference direction, whereas the upper and the lower yoke (2,3) consist of laminations of non-directionally oriented plates.

4. A low-loss reactor according to one of the preceeding claims, c h a r a c t e r i z e d i n that the air gap (6) is arranged between an interior leg (4b) and the upper yoke (2).