EP0368712A1 - Adjustable electrical power generator and its use in the production of a hot fluid - Google Patents

Abstract

This generator, usable in a hot water induction boiler, of the "transformer" type having primary 3 and secondary concentric windings surrounding a magnetic core 4 and whose secondary winding, preferably disposed externally, is constituted by a short-circuited 8 tubular coil 2, comprises means of adjusting the power available to the secondary which are constituted by an auxiliary magnetic core 10 disposed in the space 11 separating the primary and secondary windings, without connection with the main core 4 and provided with an electrical control winding 12 and by a unit 13, 14 with adjustable direct -or rectified- current Ic supplying the control winding. Preferably, the auxiliary core is divided into two parts 10a and 10b each provided with its own control winding 12a and 12b in which the adjustable direct currents circulate together in opposite senses. The invention allows direct linear adjustment of the power, and, by comparison with the known generators of the same type, it is such as to procure appreciable advantages in size, simplicity and reliability. <IMAGE>

Description

The present invention relates, in general, to the supply of an adjustable electrical power to a circuit of use. It relates more particularly to the production of a hot fluid, in particular a liquid, such as water, within an electric induction boiler with adjustable heating power.

Boilers of the type under consideration are designed as transformers, the secondary winding of which, short-circuited, consists of a metal tube wound in a coil and traversed by the fluid to be heated. This is heated in contact with the wall of the coil, itself brought to temperature by the Joule effect, due to the induced currents which the variable magnetic flux produced therein produced in the magnetic circuit by the electric current of the primary

Thermo-inductive boilers of this type are already known, for example documents: FR-B-527687, GB-B-2178254 GB-A-2105159, USP 2,856,488, or even EP-A-0193843.

Unlike conventional electric boilers, these devices have the particularity of completely dissociating the electrical supply circuit (the primary) from the "heating" part. User safety is thus reinforced. In addition, the transformation ratio specific to transformers can be used to place the coil at low voltage while ensuring high power transmitted by the primary.

An essential aspect which has not yet been fully resolved, it seems, remains the adjustment of the power which must allow the heating of the fluid to be adjusted as required.

The first of the aforementioned documents (FR-B-527697) suggests, for this purpose, using a simple rheostat placed in series with the primary winding of a transformer with concentric windings.

The document EP-A-0193843 also cited above, proposes a solution more concerned with the energy efficiency of the device. The regulation of the heating power is obtained by means of thyristors connected in cascade on the coil at secondary. For this purpose, it consists of a battery of hydraulic mini-circuits in parallel. The regulation can only be done by discrete jumps. In addition, the apparatus seems complex, costly and its reliability depends on the holding in use of electronic components.

In its French patent application no. 87.04925 of 07-04-87, the Applicant has already proposed a solution for regulating the power "continuously", consisting in using a saturable inductor in series in the primary circuit. The magnetic core of the inductor is provided with a control winding in which a direct current - or rectified current - modifying the magnetic state of the core.

The present invention, applicable to boilers provided with co-axial windings, aims at a solution of "continuous" adjustment of the heating power, reliable just as much, but more economical and of even smaller footprint than the solution mentioned. above.

To this end, the invention relates to an adjustable electric power generator, in particular for the production of a hot fluid in an electric induction boiler, comprising a magnetic transducer, of the “transformer” type with coaxial primary and secondary windings. surrounding a magnetic core and means for adjusting the electric power available at the secondary, generator characterized in that said power adjusting means are constituted by an auxiliary magnetic core, separated from the main magnetic core, provided with an electric winding control and disposed between the primary and secondary windings, and by a direct current generator - or rectified - supplying said control winding and associated with means for adjusting the intensity of said direct current.

In the use of the generator as a boiler, the secondary winding is constituted by a tubular coil in short circuit, intended to be traversed by a fluid to be heated.

Preferably, the heating coil is arranged outside the primary winding.

According to a preferred embodiment, the outer winding is of oblong conformation to be able to accommodate the auxiliary magnetic core arranged at side of the interior winding.

According to another preferred alternative embodiment, the auxiliary magnetic core is formed by two similar parts each provided with a control winding, in which the direct or rectified currents flow in opposite directions. These two parts are advantageously arranged on either side of the interior winding.

For practical reasons, reference will be made in the following only to the boiler, it being understood that everything that will be said on this subject concerns the invention just as much in its more general sense as an adjustable electric power generator.

As will no doubt have already been understood, the idea underlying the invention is to vary the specific inductance of the heating coil using an additional (or auxiliary) magnetic core placed in the space separating the two windings and the permeability of which is controlled by application of a stationary magnetic field produced by a control winding with direct current - or redesigned - wound around the auxiliary core and the intensity of which is regulated.

This winding is of sufficient size to produce a magnetic field capable of saturating the auxiliary magnetic core when the control current is set to its maximum intensity, Ic max.

The auxiliary magnetic core is advantageously formed from two similar independent parts to take into account the fact that the excitation current at the primary is an alternating current. If it is a pure alternative with symmetrical alternations, the two constituent parts of the core may be strictly identical. Otherwise, they may have a difference between them, for example in the number of ampere-turns of the control windings, or of their mass of magnetic material.

The control windings are traversed by direct currents (or repressed) flowing in opposite directions to take account of the alternating nature of the magnetic field created by the primary. At any moment, this field is magnetizing for one of the parts of the auxiliary core and demagnetizing for the other, and "vice versa" at the next alternation Overall, we balance the effect of alternations over a period. The auxiliary core therefore operates completely independently of the direction of current flow in the primary winding.

• - la figure 1 représente schématiquement un transducteur monophasé élémentaire constitutif d'une chaudière triphasée selon l'invention, dans sa version de base la plus simple, vue en coupe longitudinale selon le plan B -B de la figure 2, et comportant un noyau magnétique auxiliaire unique à enroule­ment de commande unique;
• - la figure 2 montre en coupe transversale selon le plan A-A de la figure 1 les trois transducteurs élémentaires mono­phasés formant ensemble la chaudière;
• - la figure 3 est un schéma de montage électrique illus­trant le regroupement des trois transducteurs de la figure 2 pour former le générateur triphasé unique constituant la chaudière;
• - la figure 4 représente,vue en coupe longitudinale selon le plan C-C de la figure 5, une réalisation de la chau­dière à noyau magnétique auxiliaire dédoublé en deux parties dotées chacune d'un enroulement de commande;
• - la figure 5 représente la chaudière de la figure 4 vue en coupe transversale selon le plan D-D de la figure 4;
• - la figure 6 est un diagramme montrant,dans le cas d'une installation expérimentale de taille industrielle,l'évolution de la fraction de puissance de chauffage disponible"capturée" par le noyau magnétique auxiliaire en fonction de la section relative de ce noyau par rapport à celle du noyau principal;
• - la figure 7 est une vue analogue à la figure 5, mais montrant une autre forme de réalisation du circuit magnétique auxiliaire.

The invention will be well understood and other aspects and advantages will emerge more clearly in the light of the description which follows, given by way of example, with reference to the plates of attached drawings in which:

• - Figure 1 schematically shows an elementary single-phase transducer constituting a three-phase boiler according to the invention, in its simplest basic version, seen in longitudinal section along the plane B -B of Figure 2, and comprising a magnetic core single auxiliary with single control winding;
• - Figure 2 shows in cross section along the plane AA of Figure 1 the three single-phase elementary transducers together forming the boiler;
• - Figure 3 is an electrical circuit diagram illustrating the grouping of the three transducers of Figure 2 to form the single three-phase generator constituting the boiler;
• - Figure 4 shows, in longitudinal section along the plane CC of Figure 5, an embodiment of the auxiliary magnetic core boiler split into two parts each with a control winding;
• - Figure 5 shows the boiler of Figure 4 seen in cross section along the plane DD of Figure 4;
• - Figure 6 is a diagram showing, in the case of an experimental installation of industrial size, the evolution of the fraction of available heating power "captured" by the auxiliary magnetic core as a function of the relative section of this core by compared to that of the main nucleus;
• - Figure 7 is a view similar to Figure 5, but showing another embodiment of the auxiliary magnetic circuit.

In all these figures, the same elements are designated by identical references.

We recognize, in the elementary transducer 1 of FIG. 1, the usual structure of a transformer with coaxial windings outside 2 and inside 3 , surrounding a central magnetic core 4 . In the example considered, the coil forms the outer winding 2 . The inner winding 3 , supplied by the electricity distribution network symbolized by the unit 5 , therefore constitutes the primary winding here.

The coil 2 is advantageously a stainless steel tube. It is traversed by a heat transfer fluid to be heated, which one will admit to be water. Cold water enters through the inlet tubing 6 at the base of the coil. It emerges from it via the outlet pipe 7 at the upper end, after having heated up in contact with the internal wall.

The coil is short-circuited on itself by an electrical connection 8 which interconnects the inlet 6 and outlet 7 pipes. For safety, an earthing 9 of the secondary winding 2 is provided beyond the short-circuit bridging 8 .

As can be seen, an auxiliary magnetic core 10 is placed in the interior space 11 , between the interior primary winding 3 and the coil 2 . This core, formed by stacking magnetic sheets like the main core 4, has a control winding 12 surrounding it over part of its height. This winding is supplied with direct current (or rectified) by a unit 13 equipped with a variator, symbolized at 14 at its output, for adjusting the intensity I _c of this direct control current.

A switch 15 has also been provided on the primary circuit to allow rapid opening if necessary.

Figure 2 shows the complete boiler formed by three identical transducers 1 , 1 ′ and 1˝ arranged side by side. We are better aware, in view of this figure, of the oblong shape advantageously imparted to the outer winding 2 . This conformation makes it possible to accommodate, in space 11 , within the coil 2 , the primary winding 3 and the auxiliary magnetic core 10 , by placing them one next to the other while minimizing space 11 .

It is also very clear, in view of this figure and of FIG. 3, that the boiler according to the invention can perfectly be built on the basis of a transformer three phase. Each of the identical operational elements 1 , 1 ′ or 1˝ constitutes an autonomous transducer. Each transducer is connected to a different phase (U, V or W) of a three-phase power supply. The three primary windings 3 , 3 ′ and 3˝ are mounted here in a star shape . Each of them induces, via a magnetic circuit, in a coil 2 , 2 ′ or 2 ˝. Each coil is mounted on a branch of a hydraulic heating circuit, which contains three in parallel.

Each elementary transducer shown in FIG. 1 works as follows:

Because the coil 2 is short-circuited on itself, an electric current flows there when the switch 15 is in the closed position. This induced current causes heat generation by the Joule effect, which is transferred to the water at heat when it passes in contact with the internal surface of the coil.

This heat generation depends on the intensity of the current in the secondary 2 , which is determined by the voltage induced at the terminals of the latter. This voltage is linked to the voltage across the primary 3 , by the magnetic coupling between the two windings.

In order to regulate the heating power developed by the coil, the invention modifies this coupling by virtue of the auxiliary core 10 placed in the space separating the coil from the internal primary winding.

In fact, this auxiliary magnetic core, where it is between the two windings of the transducer, acts with respect to the coil like an iron core in an induction coil. We modify the coefficient of self induction of the coil by varying the magnetic state of the auxiliary core by means of direct current (or recursed) I _c flowing in the control winding 12 mounted for this purpose around the core:

When I _c = 0, the self effect is maximum ("self in the iron"). The active power, that is to say the heating power of the secondary, is therefore minimal.

When I _c is maximum (I _c = I _max ), the self effect is the weakest. The heating power is then maximum.

If, according to the invention, I _max manages to saturate the auxiliary nucleus (I _max = I _sat ), then we are in a situation of the "self in air" type. The magnetic substance constituting the nucleus no longer has any influence on the inductance of the secondary. The heating power delivered by the coil is then the same as that which the primary would provide to it in the absence of an auxiliary core.

Between these two extreme operating points, the choice of the value of I _c allows the heating power to be adjusted to the desired level.

Furthermore, in accordance with an advantageous embodiment of the invention, the magnetic substance of the auxiliary core is in sufficient quantity to prevent, when I _c = 0, that the core saturates before being at its maximum magnetization under the effect of the field. magnetic created by the coil. The pure self effect is then very large and the heating power is, in return, almost zero. Experience has shown that this "sufficient" quantity of magnetic substance is produced with a mass equal to approximately once that of the main magnetic core 4 . In the most frequent embodiments, the magnetic cores all having the same height, this condition is reduced to a ratio of straight sections close to unity. This is shown by the curves in FIG. 6, to which we will refer in more detail later.

We have in fact understood that the auxiliary core is always working at saturation. The control current I _c serves to regulate the initial magnetic state, or, which amounts to the same thing, to regulate the speed with which the magnetization at saturation will be reached during alternation of the primary current.

In fact, this saturating magnetization is carried out, in principle, only by one of the two half-waves, namely that creating in the auxiliary core a magnetic induction which is added to that already present, generated by the control current. .

To achieve that each alternation is saturating it is possible, as shown in the alternative embodiment shown in Figures 4 and 5, to divide the auxiliary magnetic core into two identical parts 10a and 10b . These parts are arranged symmetrically on both sides of the primary winding 3 in the space 11 within the coil. Each part is provided with its own control winding 12a or 12b for the circulation of the control current I _c (or I _c ′) produced by the unit 13 . The winding directions of the windings (or their mode of connection to the terminals of the source 13 ) are such that the control currents flow simultaneously in opposite directions in their respective windings.

The explanation of such provisions has already been explained before. It is due to the "alternating" character of the primary current, as opposed to the "continuous" character of the control current. Having control currents flowing in opposite directions in their respective windings 12a and 12b makes the magnetic field produced by the heating coil 2 more quickly saturating in one of the parts of the auxiliary core during alternation. , and more quickly saturating, symmetrically, in the other at the next alternation. Overall, this amounts to rendering variations in the alternating current of the primary without any effect on the behavior of the auxiliary core.

It is recalled that it is important that the control winding is provided so as to produce a sufficient number of ampere-turns to saturate the auxiliary core when I _c reaches a maximum value I _sat .

Furthermore, the magnetic mass constituting the auxiliary core must be sufficient to be able to "pick up" when empty (that is to say when I _c = 0) the largest possible fraction of the magnetic flux generated within the coil before d '' reach saturation.

These two considerations are the basis for the definition of the heating power adjustment range. To better illustrate this, the curves in Figure 6 were constructed from an experimental boiler conforming to Figures 4 and 5. These curves, set to the intensity I _c of the control current, show that the power fraction transmitted to the coil by the primary increases with I _c and decreases when the mass of the auxiliary magnetic core increases. For example, with a magnetic mass 10 equal to that of the main core 4 (section ratio of 1), we arrive "empty" (I _c = 0) to "capture" more than 98% of the then Heating output transmissible to the coil by the primary On the other hand, under a saturated control current (I _c = I _sat. ) only a few percent of the available power are not transmitted to the coil. We also note that under I _sat. , this small fraction of power "captured" by the auxiliary core is an invariant quantity of the mass of the latter. This undoubtedly expresses the effect of the oblong conformation given to the separation space 11 , which locally distances the two windings 2 and 3 and therefore slightly degrades their magnetic coupling.

The mass of the auxiliary core will be determined in each case, according to the wishes or needs of the user as to the width of the power adjustment range. However, due to the logarithmic shape that the complete plots of the curves must have (shape already visible with the experimental points of the curve I _c = 0), the influence of the relative mass of the auxiliary nucleus on the adjustment range of the power becomes insensitive beyond a certain threshold. Under the conditions of establishment of FIG. 6, the threshold is not yet reached for a mass equal to approximately 1 times that of the main core 4 , except "empty", that is to say when I _c = 0 . On the other hand, the curves show a clear decrease as soon as the ratio of the auxiliary / main magnetic masses becomes less than 1

This phenomenon is particularly well verified for the curve I _c = 0: for a mass ratio of 1.0, almost 100% of the power available in the primary is captured by the auxiliary nucleus, while it already captures only 85 % of this power when this ratio drops to 0.86, or only 0.16 point. This clearly shows that it is advantageous to keep a mass ratio close to unity, since we are looking for a maximum capture of the transmissible power closest to 100%, when I _c = 0) by definition.

It will be noted that, when the auxiliary nucleus is split into its two parts 10a , 10b (variant fig. 4 and 5), it is the sum of the masses of each part, and not the mass of each, which must be considered at this point. respect.

Adjustment can be easily automated, if desired. For example, as shown in FIG. 4, a regulator 20 can be provided to control the current unit 13 , 14 continuous so as to maintain the temperature difference between a set value Vc and the value it receives from a sensor 19 , identifying the temperature of the water at the outlet 7 of the coil, below a desired threshold predetermined.

Of course, the voltage induced at the terminals of the coil depends on the transformation ratio, that is to say on the ratio between the number of turns of the coil 2 and that of the primary winding 3 . It will therefore be advantageous, in order to obtain high heating powers, to make the device work in step-down voltage by providing for a number of turns significantly lower for the coil than for the winding of the primary. We can thus make boilers in a wide range of power, ranging, for example, from 100 Kw to 10 Mw approximately, from a three-phase supply from the medium-voltage network, each phase supplying an elementary transducer 1 , 1 ′, 1 ˝ of the device illustrated on fig. 2 or 5.

The regulation operates without difficulty over almost the entire range of the boiler's nominal power. Depending on the regulation point, the cos Φ can change between 0.93 "front" and 0.93 "rear", thanks to the presence of capacitors, not shown, conventionally mounted in parallel on the primary circuit, so as to best adapt on the conditions of the electricity distribution network.

The metal from which the coil is formed is advantageously stainless steel, or any other metal having a high electrical resistivity. This makes it possible to work with low current densities, of the order of 10 to 15 A / mm², for example. In addition, with the use of an austenitic stainless steel, the resistance to hot corrosion is particularly satisfactory.

Usual measures to improve the heating efficiency can be taken without difficulty, for example an insulation 24 of the coil.

As for the auxiliary core 10 , many alternative embodiments can be envisaged. Whatever form or structure is chosen, it is important, as already said, that it can be saturated by the magnetic field created by the control current I _c . A sufficient number of turns for the control winding 12 will be provided for this purpose, in order to avoid having to use high intensities (of more than 20 A approximately, to fix ideas).

It is also important that the auxiliary core remains distinct and without material continuity with the main magnetic core 4 . The complete three-phase generator therefore comprises two separate magnetic circuits, one specific to the "transformer" part and including the main cores, the other looping between them the auxiliary cores 10a , ... or 10b ....

An exemplary embodiment is well illustrated in FIG. 5. On one side, upper 16 and lower 16 ′ yokes (the latter being visible only in FIG. 4) interconnect the main cores 4 , 4 ′ and 4˝ , the assembly forming a magnetic circuit of the usual type for a three-phase transformer. On the other, columns 17a and 18a for the return of the magnetic flux are arranged on either side of the group formed by the three auxiliary cores 10a , 10′a and 10˝a . These five columns are interconnected by means of common upper 21a and lower 21′a yokes , also clearly visible in FIG. 4. Identical arrangements are made for the other group formed by the three auxiliary cores 10b , 10 ′ B and 10˝b using the end columns 17b , 18b and the cylinder heads 21b and 21′b .

Figure 7 shows another embodiment of the auxiliary magnetic circuits. It consists schematically of replacing the common end columns and the cylinder heads common to a group of auxiliary cores by individual circuits for each core. These circuits are therefore in number equal to that of the auxiliary cores and each comprise a return column 23a ( 23b ) individually matched to its associated core using equally individual yokes 22a ( 22b ).

The first embodiment described (fig.5), known as "with five columns", makes it possible jointly to reduce the number of constituent elements of the auxiliary magnetic circuits and to constitute, in itself, a rigid compact architecture which can possibly serve as a chassis for support for the rest. On the other hand, the variant with individual yokes of FIG. 7, called "six columns", allows the control currents to flow in opposite directions in the windings of the auxiliary cores of the same group 10a , .. or 10b,. We could, moreover, find advantage in sizing the magnetic circuit 10 so that, for a given nominal power available in the primary, we are already at the start of the saturation stage when I _c = 0. Beyond this, the core could quickly become undersized, which would reduce the extent of the range of adjustment of the power transmissible to the secondary. Below that, the core would be oversized. This, in itself, is not necessarily annoying, but nevertheless represents a factor of additional cost and goes against the aim sought, which is to reduce the size of the device as much as possible. In addition, this would help to tighten this time the power adjustment range and thereby impose an increased precision, therefore less easy, on the value of the power in this range.

It goes without saying that the invention is not limited to the embodiments which have just been described, but extends to multiple variants or equivalents insofar as the characteristics set out in the appended claims are respected.

In particular, it will certainly have been understood that the relative position of the two co-axial windings between them is perfectly interchangeable. The auxiliary magnetic core rigorously has the same overall effect on the capture of the power transmissible to the secondary by the primary, insofar as it is placed between the two windings. Whether the primary winding is inside, around the main magnetic core, or outside, then surrounding not only the main core, but also the coil and the auxiliary magnetic core arranged side by side, when the modification the magnetic state of the latter adjusts the short-circuit current on the secondary, it also adjusts the supply current of the other winding, regardless of their relative position. Practical considerations alone make it preferable to put the coil in an external position, such as the ease of access to the input-output thereof, or the reduction in the length of the average turn of the primary, which minimizes the losses and makes it possible to improve electrical efficiency.

Note that the field of application of the invention includes the production of hot water, both for heating buildings and for use in industrial processes. Likewise, the invention also applies to the heating of heat transfer fluids other than water, for example oil, or even molten salts intended to be used as such or to generate steam at high temperature in exchangers.

It is also recalled that the invention, although initially carried out for heating fluids, is by no means limited to an induction boiler, but extends to any generator capable of delivering to the terminals of its secondary winding an adjustable electrical power. In order to achieve this, it suffices to replace, in the boiler exemplified above, the heating coil in short circuit with a simple electrical winding, connectable at its ends to a circuit for use.

Claims (10)

1 ) Adjustable electric power generator comprising a magnetic transducer of the "transformer" type with concentric primary and secondary windings surrounding a magnetic core (4), characterized in that it comprises means for adjusting the power available at the secondary, constituted by an auxiliary magnetic core (10) separate from the main magnetic core (4), provided with an electric control winding (12) and disposed in the space (11) for separating the primary (3) and secondary (2) windings, and by a unit (13) for producing a direct current - or rectified - supplying said control winding and associated with adjustment means (14) of the intensity I _{c of} said control current as a function of the desired electrical power. 2) Generator according to claim 1, for the production of a hot fluid within an electric induction boiler, characterized in that the secondary winding is constituted by a tubular coil (2) in short circuit (8) intended to be traversed by the fluid to be heated. 3) Generator according to claim 1 or 2, characterized in that the secondary winding (2) is arranged externally to the primary winding (3). 4 ) Generator according to claim 1 or 2, characterized in that the auxiliary magnetic core is split into two parts (10a, 10b) each provided with its own control winding (12′a, 12′b), these windings being intended to be traversed by continuous or rectified electric currents I _c , I ′ _c flowing in opposite directions. 5 ) Generator according to claim 1 or 2, characterized in that the outer winding (2) is oblong and in that the inner winding (3), surrounding the main magnetic core (4), and the magnetic core auxiliary (10) are placed side by side within the outer winding. 6 ) Generator according to claims 4 and 5, characterized in that the outer winding (2) is of oblong shape and in that the parts (10a, 10b) constituting the auxiliary magnetic core are arranged on either side of the inner winding (3). 7 ) Generator according to claim 1 or 2 characterized in that it is equipped with means (19,20) for automatic regulation of the adjustable electrical power. 8 ) Generator according to claim 1 or 2, characterized in that it consists of three magnetic transducers (1, 1′ and 1˝) each supplied by a different phase of a three-phase power supply (5). 9 ) Generator according to claims 1 or 2, and 8 characterized in that the auxiliary magnetic cores (10 ...) are interconnected by a magnetic circuit comprising common return columns (17,18) and cylinder heads common link (21,21 ′). 10 ) Generator according to claims 1 or 2, and 7 characterized in that the auxiliary magnetic cores (10 ...) are each provided with an individual magnetic circuit (22, 23).

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