EP0977211A2 - Electrical component with a restriction in a PTC polymer element - Google Patents

Abstract

An electrical component consists of a positive temperature coefficient (PTC) polymer element (1) with neck sections (2) at right angles to the main current direction (3). The opening angle of the neck section in the main current direction longitudinal plane is at least 100 degrees.

Description

The present invention relates to an electrical component with a PTC polymer element. Such components are e.g. B. known from EP 0 655 760 A2, according to which a PTC polymer element is used for overcurrent limitation and the PTC polymer element for this purpose in series with a switch disconnector is interconnected. A current over one by designing the PTC polymer element certain threshold value creates a fast non-linear increase in the electrical resistance of the PTC polymer element and thereby limits the overcurrents. The switch disconnector can then completely interrupt the limited current.

Regarding the use of PTC polymer elements at higher voltages are different options in U.S. Patents 5,313,184 and 5,414,403 have been proposed by resistance systems made of PTC polymer elements and varistor elements or linear resistance elements reduce local overvoltages in the PTC polymer material and the nonlinear response of the PTC polymer material locally to distribute. In connection with the teaching of these two documents, it should be noted that that in the present invention, the term PTC polymer element and PTC polymer material also such elements and includes materials that contain components without PTC behavior, for example linear resistance elements or varistor elements added are.

Furthermore, this invention relates to such an electrical component, in which the PTC polymer element does not have a constant current-carrying cross-sectional area has, but constricted the line cross-sectional area is. The main flow direction defining this cross-sectional area is in general by external contacts on the PTC polymer element or by given the geometry. However, it does not have to occur to everyone correspond to local current directions, but only to a certain extent Average.

Through such a constriction of the line cross section, the current density locally increased relative to the rest of the PTC polymer element, so that predetermined is at which point the non-linear increase in resistance of the PTC effect begins when the corresponding current threshold values are reached.

EP 0 798 750 A2 again shows a resistance system made of a PTC polymer element with varistor elements, in which such constrictions are provided are.

U.S. Patent 3,351,882 also shows constricted PTC polymer elements, with the justification given here that by suitable Choice of constrictions overheating near the contact points of the PTC polymer element should be avoided.

The European patent EP 0 should also be mentioned as prior art 038 715 B1, in which a specific design of a PTC polymer element with a constriction a very quick response within a few seconds or less.

A PTC polymer element with a constriction is also shown in JP 4-130602 with patent abstract, DE 196 26 238 A1 and the US patents 4,317,027 and 4,352,083. The latter two publications show in particular that constrictions due to adjacent recesses can be formed in a PTC polymer material. Here are the recesses filled with a substantially non-conductive material or with air.

Based on the described prior art, the present Invention based on the technical problem of an electrical component with a Specify PTC polymer element in which the PTC polymer element particularly quick response and in the normally conductive case one good current carrying capacity as well as a reliable and permanent one Operation shows.

To this end, the invention provides an electrical component with a PTC polymer element before that a constriction of the cross-sectional area perpendicular to a main flow direction, an opening angle of Constriction in a longitudinal section plane containing the main flow direction is at least 100 °.

The invention thus relates to PTC polymer elements in which the State of the art constriction known per se runs particularly steeply, thus has a particularly large opening angle. First there is find that in many cases, the constriction is limited only the cross-sectional area is formed in one direction, the PTC polymer element So it has a two-dimensional basic structure, so to speak. To this extent, the definition of the invention relates to an opening angle in a longitudinal section plane containing the main flow direction through the PTC polymer element.

Of course, there can also be a further constriction in another dimension perpendicular to the main flow direction. The invention relates to PTC polymer elements in which the value of 100 ° for the Opening angle reached or exceeded in at least one longitudinal section plane becomes.

The opening angle is defined from the perspective of the point with minimal Cross-section in the constriction, i.e. in the sense of widening starting from the point of minimal cross-section. Thereby exists in the Longitudinal section plane on each side from the minimum cross-sectional area seen a right and a left opening angle. In the invention the right and left opening angles are combined on one side to a total opening angle of at least 100 °, however occurs in two parts at different vertices. Here are the Vertices of the two parts of the opening angle due to the transverse expansion the minimum cross-sectional area in the considered longitudinal section plane separated from each other. It is not necessary that the two parts of the total opening angle are identical, but preferred. Furthermore According to the invention, the (sum) opening angle must be of the minimum Cross-sectional area seen from at least one of the two sides , but preferably applies to both sides.

Necessary to define the two parts of the total opening angle Route sections angled to the main flow direction on both sides of the constriction do not necessarily have to be regularly shaped. It is sufficient, if a route section fulfilling the angular condition according to the invention can be defined as the mean. However, it is preferred that the constriction flanks essentially on both sides of the minimum cross-sectional area are straight and thus essentially the opening angle as a whole define without averaging. Then it cannot be clear local deviations from the steep formation preferred according to the invention the constriction.

The mentioned value of 100 ° for the total opening angle (e.g. a Partial opening angle on the right of 50 ° and a partial opening angle on the left of 50 °) forms the lower bound for the invention. In fact, however, are still larger opening angles are cheaper, so opening angles are increasingly preferred from Z. B. 105 °, 110 °, 115 ° or 120 ° and above.

The effect according to the invention exists (increasingly with larger angles) in the fact that on the one hand very quickly responding PTC polymer elements can be realized, on the other hand, in comparison to the state of the art nevertheless relatively high current carrying capacities in the show appealing or already addressed condition.

In the development of the invention, it turned out to be essential to meet these two criteria as well as possible at the same time, d. H. on the one hand with limited total space for the entire electrical Component or the PTC polymer element to realize a high current carrying capacity, on the other hand, however, the reduction of the line cross sections to one to be able to design fast response behavior. It has been shown that particularly strong relative line cross-sectional reductions result in particularly fast response behavior and on the other hand particularly steep constrictions, i.e. particularly short constrictions, show the best current carrying capacities.

You can probably do this with the significantly better cooling effect for a shorter period obtuse-angled constrictions compared to long rather acute-angled constrictions to explain. These probably have the advantage of an improved one Current carrying capacity because it is not caused by a thermal jam at relative high current loads, but below the current threshold, Problems with stability or unintended responsiveness can.

In this context it should also be noted that strong but short Constrictions a relatively short overall length of the PTC polymer element what can be achieved in the main flow direction Total ohmic resistance reduced in the normal conducting state. This is especially together with the constrictions preferred according to the invention important on particularly small wire cross-sectional areas.

Another important aspect of the invention is that with the values according to the invention for the opening angle with good current carrying capacity attractive constrictions can be produced so quickly, that with a series connection of at least two such constrictions even without parallel connection of a varistor or resistance element simultaneous response is guaranteed and therefore really a multiplication the respective dielectric strength of a constriction is possible.

In developing the invention, it has been found that a Series connection of PTC resistance elements with defined response zones is by no means unproblematic. Generally speaking one of the Response zones due to the slightest asymmetries between the different Response zones first and then suddenly the whole The voltage at this point drops, so it breaks when the voltage is too high Tension together. This destroys the component and the overcurrent does not limited. Otherwise, the series connection of the contact points is complete an increase in the nominal resistance in the conductive state is only a disadvantage. So far, this problem could only be solved by Technology described parallel connections of varistor or (normal) resistance elements be met.

On the other hand, it has been found that the PTC materials are apparently one certain inherent inertia regarding the heat transfer from the typically conductive particles present in these PTC materials on the polymer matrix by its response to the temperature increase show the actual PTC effect. Is the response behavior significantly faster than this inherent sluggishness, so can really simultaneous response of serially connected points of contact or constrictions be guaranteed. This is a particularly important aspect of the invention because it is a theoretically unlimited increase the dielectric strength of the entire electrical component becomes possible.

By the addition of the respective dielectric strength made possible by the invention serially connected contact points on the constrictions are full It is still preferable to take advantage of these constrictions in the Main flow direction so much distance from each other that the respective Zones of non-linear response, i.e. high resistance and the voltage drop, not connect with each other, but clearly from each other stay separated. According to the invention, it is particularly preferred for this purpose that the minimum cross-sectional areas of each other in the main flow direction spaced apart by at least twice the minimum transverse dimension are. Even larger values are preferable, namely three times, preferably four times. With the minimum transverse length expansion is included the linear expansion characterizing the location of the smallest line cross-sectional area meant transversely to the main flow direction, with "two-dimensional" Constrictions the smaller of the two.

According to another aspect of the invention, parallel connections are also provided preferred at least two of the constrictions. On the one hand, this has the advantage of better mechanical stability, especially with larger ones Total line cross-sectional areas. On the other hand, it results from the Allocation of the necessary line cross-sectional area to two or more parallel contact points also the advantage of an improved Cooling effect, d. H. a better thermal coupling of the contact points or the places of the minimum line cross-sectional area on the remaining volume of the PTC polymer element.

With constrictions connected in parallel, it is particularly preferred to have them in to be arranged adjacent to the way that the respective flanks of the constrictions define total recesses between the constrictions, which get a diamond shape with essentially straight flanks. For this purpose, reference is made to the exemplary embodiments.

According to the invention, the parallel connections and series connections can also be combined, resulting in a field of constrictions. This determines the extension (s) of the field transverse to the main flow direction the line cross-sectional area and together with others Parameters the current carrying capacity, while the "depth" of the field, ie the Series connection number that determines dielectric strength.

In all cases of at least two coupled constrictions, i.e. at It is parallel connections, series connections and combinations thereof preferably, all constrictions in the same one-piece PTC polymer element to be provided, i.e. no avoidable between the constrictions To allow material transitions to arise.

With regard to the individual constrictions of the line cross-sectional area itself, it is initially provided in this invention, the described To constrict the cross-sectional area in only one dimension, thus only in a length dimension contained in the longitudinal section plane Reduce cross-section and in a perpendicular longitudinal section plane not, the main flow direction included in both longitudinal section planes is. In particular, this has the advantage of simpler manufacture by machine Processing or by spraying or casting.

So z. B. from a PTC polymer solid material by milling or Appropriate recesses are cut out to cut Constrictions to define what is a two-dimensional structure of the Constrictions is much easier. For casting or injection molding processes at least the manufacture of the molds is easier, because these too in general be machined. But also when pouring or spraying even simplified geometries can make things easier.

It has been found in the invention that by sufficiently large Opening angle even in the case of a cable cross-section constriction in one direction good combinations of fast responding constrictions on the one hand and good current carrying capacity on the other can.

On the other hand, in the case of electrical components in which the PTC polymer element should respond very quickly, by constrictions in two Directions, ultimately three-dimensional shapes, despite considerable relative ones Reductions in the cross-sectional area of the line very small lateral length dimensions be avoided, which, on the other hand, the mechanical stability facilitated and can also be advantageous in the manufacture. Furthermore such constrictions in two directions result in even shorter ones Thermal diffusion paths and thus an even better cooling, in particular in connection with the parallel connection of several already described Constrictions.

Even if the current carrying capacity is particularly high Space problems can arise through a three-dimensional design of the Constrictions overall also a two-dimensional parallel connection of constrictions may be conceivable, so that in connection with a additional series connection a total of a three-dimensional constriction field preferably result in a one-piece PTC block can. Basically, however, this is more complex than a comparable one Structure with one-dimensional constrictions.

Another aspect of the invention in turn relates to the dielectric strength, in this case, however, already related to the individual constriction. Here the invention provides, essentially in the main flow direction a bridge in the center of the constriction, i.e. a bridge with in essentially the minimum cross-sectional area of the constriction. This web should be extended so far in the main flow direction that - with a length depending on the respective parameters of the used PTC polymer material - a zone of high resistance completely can build up in the area of the minimum cross-sectional area. If namely if the cross-sectional area is widened too early, this is due to the widened area Range may not be a response of the PTC polymer material causing current density more so that the extent of the zone high Resistance in the main flow direction through the geometry and not is limited by the material properties and the electrical parameters. With the solution according to the invention, however, the zone of high Resistance in full length and thus the maximum for the individual constriction Build up achievable dielectric strength.

A range between 0.5 and 4 mm is typically preferred between 1 and 2 mm for the extension of the web in the main flow direction to provide. Bridge lengths that are too long are disadvantageous because they are for the Invention can deteriorate essential cooling effect.

Furthermore, constrictions have been found to be advantageous in the invention, especially with regard to the quick response, the the line cross-sectional area perpendicular to the main current direction is relatively strong restrict, by at least a factor of 3, preferably 4 or 5. As already mentioned, it is divided into at least two connected in parallel Constrictions for reasons of stability and also because of shorter thermal diffusion paths advantageous. This is especially true for very strong reductions in cross-sectional area. The working examples complete this point.

Figur 1 eine schematische Ansicht eines PTC-Polymerelements mit drei erfindungsgemäßen Einschnürungen in Parallelschaltung;

Figur 2 eine Ansicht eines weiteren erfindungsgemäßen PTC-Polymerelements, das im wesentlichen einer integrierten Serienschaltung zweier PTC-Polymerelemente nach Figur 1 entspricht;

Figur 3 eine Ansicht eines weiteren erfindungsgemäßen PTC-Polymerelements mit einer größeren Zahl seriell verschalteter Einschnürungen, wobei jeweils drei Einschnürungen in jeder Serienstufe parallel geschaltet sind und wobei gegenüber den Figuren 1 und 2 einige geometrische Abweichungen vorliegen;

Figur 4 eine Ausschnittsdarstellung einer Einschnürung und einer Aussparung aus Figur 3;

Figur 5 eine Kombination aus einer Figur 3 entsprechenden Ansicht eines "dreidimensionalen" Feldes von Einschnürungen in einem erfindungsgemäßen PTC-Polymerelement mit einer Seitenansicht dazu; und

Figur 6 ein Diagramm der Beziehung zwischen der Ansprechzeit und dem Belastungsstrom für einen erfindungsgemäßen Widerstand.

A preferred material for the PTC polymer element is the material "ETTB" which, for. B. consists of 50% ETFE and 50% TiB ₂ . Here ETFE is Thylen an abbreviation of the polymer material E thylen- T etra- F luor- E. Further explanations of the invention are given below on the basis of the exemplary embodiments. Individual features disclosed here can also be essential to the invention in other combinations. In detail shows:

Figure 1 is a schematic view of a PTC polymer element with three constrictions according to the invention in parallel connection;

FIG. 2 shows a view of a further PTC polymer element according to the invention, which essentially corresponds to an integrated series connection of two PTC polymer elements according to FIG. 1;

FIG. 3 shows a view of a further PTC polymer element according to the invention with a larger number of constrictions connected in series, three constrictions being connected in parallel in each series stage and with some geometrical deviations from FIGS. 1 and 2;

FIG. 4 shows a detail of a constriction and a recess from FIG. 3;

FIG. 5 shows a combination of a view corresponding to FIG. 3 of a “three-dimensional” field of constrictions in a PTC polymer element according to the invention with a side view thereof; and

Figure 6 is a diagram of the relationship between the response time and the load current for a resistor according to the invention.

The invention relates to an electrical component with a PTC polymer element. The exemplary embodiments show PTC polymer elements for electrical resistors as a concrete variant of a electrical component. These electrical resistors are used as current limiting devices in automatic circuit breakers. Other electrical Components can of course be made in a similar way with PTC polymer elements be provided to the PTC effect for certain electrotechnical To use purposes. Because electrical resistors with PTC polymer elements are state of the art in the following, only the PTC polymer elements themselves shown and explained. The connection to external contacts and the use in an external circuit are the Known specialist without further explanation. The shown in Figures 1 to 4 Views correspond to a cross-sectional profile that the PTC polymer element 1 also in the dimension perpendicular to the drawing plane maintains across its thickness; so it's a "two-dimensional structure". The thickness of the structure in this third dimension is 1.5 mm in this example, but can also be easily changed become. Accordingly, all cross-sectional areas change proportionally and with it the current carrying capacity.

Figure 1 now shows a PTC polymer element 1, which is for a main flow direction 3 is designed, as indicated by the arrows, that is vertical in the figure from top to bottom (or bottom to top).

Accordingly, Figure 1 shows a longitudinal sectional plane, the main flow direction 3 contains. In this longitudinal section plane are horizontal in the sense of the figure three next to each other except for their respective position in the PTC polymer element 1 similar constrictions 2 are provided. These constrictions are formed by two diamond-shaped in the longitudinal section plane air-filled recesses 9 in solid material and two further recesses 9 right and left on the edge (in the sense of notches) of the solid material. The opening angle α which is essential according to the invention occurs, as already explained above, on both respective sides of a constriction 2 each in two parts, which are the same size in the present case. this means specifically that the angle between a straight edge 8 one of the a total of four recesses 9 and the main flow direction from the constriction 2 seen from (as denoted by α / 2 in the figure) is 60 °, the total opening angle is 120 °. Accordingly, the Angles in the recesses on each side 60 ° and in the recesses 9 in the middle of the PTC polymer element 1 above and below 120 °.

With a total width of the PTC polymer element 1 shown of 40 mm are the smallest line cross-sectional areas 7 in the constrictions 2 in width each 2 mm and are due to the width of a recess 9 separated from each other in solid material of 11 mm.

FIG. 2 shows a structure largely corresponding to FIG. 1, but in the case of the system shown in Figure 1 from constrictions 2 and recesses 9 provided twice and in the main flow direction 3 one behind the other is. The constrictions 2 and recesses 9 lie in the (vertical) Main flow direction 3 aligned one behind the other. The distance 10 between the locations of the smallest cross-sectional areas 7 in the main flow direction 3 the structure in FIG. 2 is approximately 8 mm apart. This distance of 8 mm is four times the minimum transverse expansion of the Constrictions 2 by 2 mm.

FIG. 3 shows an exemplary embodiment that has been modified in three ways compared to FIG. 2. First, there is a series connection of two constrictions 2 a series connection of a plurality of constrictions 2 in each "pillar" of parallel connection has become, whereby only the top one four constrictions are shown. Furthermore, in this embodiment all largely sharp in the structures of FIG. 1 and FIG. 2 Corners somewhat rounded, what happens when machining a PTC polymer block or a mold for an injection or casting process Offers simplifications. These roundings do not change anything essential the functionality of the geometry shown.

Finally, the locations of the minimum line cross-sectional area 7 are to be webs 5 extended, which extend over a distance 6 in the main flow direction 3. This can be seen better in the detail representation in FIG. 4. The length 6 of the webs 5 is 1 mm without the inclusion of the curve towards the opening angle, taking into account a part of this Curvature between 1-2 mm. Accordingly, the distance 10 is the Set minimum cross-section 7 in the main current direction 3 in this Embodiment 1 mm longer than in Figure 2, if one of each the center of the web calculated from; the web length is therefore in addition to this distance provided (add reference numeral 10). The remaining dimensions correspond to the values given above.

Another variation is shown in FIG. 5. This is also at the drawing level of Figures 3 and 4 vertical dimension for structuring the constrictions shared; it is therefore a "three-dimensional constriction structure". 5 shows a top view of this figure, which corresponds identically as far as Figure 3. However, the surface is and corrugated the bottom of this PTC polymer element 1, d. H. has side Recesses or notches 11 also on the top and bottom on. Accordingly, there are also cutouts in this "third dimension" 12 in the solid material of the PTC polymer element 1. The wave-like recesses 11 on the top and bottom and the recesses 12 in solid material complete the cutouts already described with reference to FIGS. 3 and 4 9 synchronous, so they have the same frequency and the same phase, so to speak (cf. the dashed auxiliary lines in FIG. 5). The result is relative Reduction of the area at the constrictions 2 by a degree the third dimension additionally achieved factor. That's why it is it is not absolutely necessary that the opening angles analogous to the above definition the further longitudinal section plane in the right side in Figure 5 Have values of at least 100 °.

The structures from FIGS. 1, 2, 3 and 4 result in reductions in the cross-sectional area of the line on 15% of the maximum cable cross-sectional area, in the structure from FIG. 5 even to 5%. It is clear that the respective indicated concatenations of constrictions 2 as a series connection in the main flow direction 3 and as a parallel connection in the in the Drawing plane of Figures 1-4 lying perpendicular to this direction and in the third direction in Figure 5 can be continued as desired. It deals basically an essentially regular grid of constrictions, depending on the requirements for the overall geometry Dielectric strength and suitably adapted to the current carrying capacity can. In addition, several plate-like PTC polymer elements can also be used 1 according to Figures 1-5 in an electrical component can be connected in parallel. This can contribute to a large current carrying capacity simple manufacture of the individual plates can be achieved at the same time.

As already mentioned, the PTC polymer element is made of ETTB from 50% ETFE and 50% TiB ₂ . In the exemplary embodiments shown here, the material was milled or cut out of a block, but for large-scale production, various injection and casting processes according to the prior art are also conceivable. The corresponding metal contacts u. U. can be molded in one operation.

It is clear that the structure shown in Figure 5 is a little more complicated Manufacturing requires. On the other hand, it offers a compared to the other structures even more responsiveness.

Furthermore, the structures according to FIGS. 3, 4 and 5 are compared to the Structures in Figures 1 and 2 by the formation of the constrictions 2 in the web shape described with regard to the dielectric strength in the response state improved. A typical value for a single constriction 2 is in the range of 150-300 V (rms value) depending on the material. For a typical application, a low voltage protection system in the Range of z. B. 690 V are accordingly several, a maximum of five serial interconnected constrictions 2 necessary.

To illustrate the response behavior, FIG. 6 shows measured values on a Experimental pattern of the structure of Figure 2, namely for the response time the ordinate versus the quotient from the actual load current and the maximum design current in the normally conductive state. It can be seen that the curve lengthened too much with small overcurrents Response times increases, so the PTC polymer element 1 in the range small multiple of the nominal current only responds slowly. This behavior is basically typical of PTC polymer materials; in the invention Pattern is the response behavior in the immediate vicinity, for example below 1.3 times the nominal current, but even slower than at conventional comparison pieces. This illustrates the improved cooling effect due to the geometry according to the invention, the permanent load near the rated current for a long time.

On the other hand, the response behavior of the PTC polymer element according to the invention 1 above a value approximately 1.3 times to 2 times of the nominal current considerably faster, by 1-2 powers of ten faster than with conventional examples. This applies approximately until 100 times the nominal current; thereafter the pattern according to the invention is still better than the state of the art, but loses its lead.

In conclusion, it is pointed out that the simultaneous response Series-connected constrictions according to the invention via infrared frame camera recordings was verified.

Claims (13)

Electrical component with a PTC polymer element (1), the one Constriction (2) of the cross-sectional area perpendicular to a main flow direction (3), wherein an opening angle (α) of the constriction (2) in a longitudinal section plane containing the main flow direction (3) is at least 100 °. Electrical component according to claim 1, wherein the opening angle (α) is at least 110 °. Electrical component according to claim 1 or 2 with at least two the constrictions (2) connected in series. Electrical component according to claim 3, wherein the minimum cross-sectional areas (7) the series-connected constrictions (2) from each other in the main flow direction (3) by at least twice, preferably four times the minimum transverse dimension of the minimum Cross-sectional area are spaced (10). Electrical component according to one of the preceding claims at least two of the constrictions (2) connected in parallel. Electrical component according to claim 3, 4 or 5, wherein the constrictions (2) in the same one-piece PTC polymer element (1) are formed. Electrical component according to one of the preceding claims, which the constriction (2) the cross-sectional area in only one in the Longitudinal section plane contained length dimension (4) reduced. Electrical component according to one of the preceding claims, which the constriction (2) one in the main flow direction (3) via a short distance (6) extensive web (5) with the essential of minimal cross-sectional area (7) of the constriction (2) along the Has web (5). Electrical component according to claim 8, wherein the short distance (6) between 0.5 mm and 4 mm, preferably between 1 mm and 2 mm long. Electrical component according to one of the preceding claims, the constriction (2) the cross-sectional area perpendicular to the main flow direction (3) by at least a factor of 3, preferably that Factor 4 or 5 reduced. Electrical component according to one of the preceding claims, which is the material of the PTC polymer element (1) ETTB. Electrical component according to one of the preceding claims, the constriction (2) in the respective opening angle (α) containing longitudinal section plane on both sides of the minimum cross section (7) has essentially straight constriction flanks (8). Electrical component according to claims 5 and 12, wherein the parallel constrictions (2) in the manner immediately adjacent are that there is an essentially between them in the longitudinal section diamond-shaped recess (9) results.

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