DE867888C - Electric capacitor with burnout metal coverings - Google Patents

Description

Electric capacitor with burn-out metal coverings Electric Capacitors off. metallized dielectric tapes can have the property that their metal coverings can be burned out if they are sufficiently thin to have. Defects in the dielectric are healed by the fact that in an electrical The breakdown burns away the metal coating around the defect, d. H. evaporate can, and thus the passage of current through the defect is instantly interrupted will. The defect is then electrically isolated and can be used when the capacitor is in operation don't bother anymore.

With these relatively thin. Metal coverings have now been found that in the event of electrical shock loading of the capacitor, these assignments on or have been disconnected near the power supply points. A wound capacitor from metallized dielectric strips can, for. B. applied at the edge of the roll wear front connections. The power supply for each occupancy takes place in each case from one edge of the dielectric tape. In such capacitors it has been observed that. in the case of large current surges, the metallization near the edge through which the power supply is carried out on long stretches of the tape was cut off, so that large parts of the capacity area were no longer connected to the power supply. With multiple current surges there is a risk that the entire capacitive surface separated in the condenser and the condenser is completely unusable.

The disadvantage of the separation near the power supply points and the this possible loss of capacity is reduced or completely avoided if, according to the invention, the burn-out assignments of the condenser are designed in this way are, .that those controllers in which the occurring current loads, of the current flowing through it is the largest in the unit of quantity of the covering metal Heat is generated, are arranged away from the power supply points. Appropriate the assignment is carried out so that the heat generated by the electricity with the distance from the power supply point across the width of the dielectric tape-it increases.

The disconnection in the event of a power surge depends on various factors at the point in question where the separation takes place from, so z. B. from electricity heat, which is to be related to the unit of quantity of the covering metal, hence in the following the specific electricity heat is to be mentioned, from the heat capacity of the occupancy, of the heat dissipation, of the heat of fusion or the heat of vaporization of the die Layer-forming metal.

The level of the specific electrical current heat is now predominant decisive for the possibility of separating a part of the area of the occupancy or even the entire occupancy.

In Fig.ia is a section through two adjacent layers of a normal Metal paper capacitor shown, its assignments across the width of the dielectric tape are applied as a uniform metallization. With a and b are the two dielectric bands and with c and. d the two. Metal coverings. f and g represent the power supply points at the end faces of the capacitor. You can now compare the two Capacitor assignments in parallel-connected partial capacitors of the same capacitance think divided. When an impulse voltage is applied, such normal assignments d. H. in coverings that have the same specific sheet resistance at all points and equally strong profile have an uneven current load in the individual Cross-sections on.

Fig. I b shows an equivalent circuit diagram of such a capacitor, in .that the imaginary parallel partial capacitors are shown. The upper allocation strip c is here in. Example divided into four sub-areas i to 4. The lower allocation strip d is also divided into the corresponding partial areas 5 to 8. Through the power supply lines 9 and io, all partial areas are connected to the power connections. Through these additions. In the event of a shock load, give the total amount of electricity that the allocation strips shown should take up at the same time. This amount of electricity is divided into four equally large subsets on the upper and lower sub-areas: i to 4 and 5 to B. The conductor pieces for the supply of the current, which are in reality on the capacitor with the capacitive parts of the occupancy are identical, here are of these assignments i to 4 and 5 to 8 shown separately. For each partial occupancy, e.g. B. for 3; works in reality the partial occupancy thereof, z. B. 2, as an existing power supply and in the event of separation at this point, it can also be used as a fuse be understood. In the equivalent circuit diagram in Fig. I, this is imagined by one in front of each Partial capacitance area switched fuse indicated. The location of these fuses, which are marked with ii to IS, is therefore on the real capacitor on the capacitive one Look for partial areas c and d themselves; but this should be left out of consideration here.

In the event of power surges, the sum of the partial currents now goes through at the same time the fuse i i, that is the first part of the occupancy directly on the real capacitor behind the power connection. In our example, one goes through the fuse 12 a quarter smaller current, through 13 a two-quarters smaller and through 14 only the fourth part of the total flow, namely the flow for partial occupancy 4 alone. The same applies to the occupancy below.

With the same cross-section and specific resistance of the occupancy is the specific current heat generated in fuse ii or 18 so in that Occupancy next to the power connection on the edge the largest, and here is the danger given the separation.

The imaginary fuses, consisting of parts of the occupancy, are in place connected in series. If you want to avoid the danger of separation, the main fuse must d. H. the fuse - for the greatest amperage on the edge, d. H. at the power supply point through which the greatest current passes in the event of a surge, and the other fuses must be graded so that the melting current across the width of the Dielectric tape decreases, so that the weakest fuse is at the power supply point opposite edge, i.e. furthest away from the power supply.

It can be seen from this that in the case of capacitors with uniform metallization, in which the metal covering was separated near the power connection, the metal covering acting as the main fuse at this point was too weak and must be amplified to withstand a surge. The gain can e.g. B. be done by increasing the cross section of the layer, because this is the Current density is reduced and, with the same specific sheet resistance, also the specific electricity heat generated. The profile of the layer then shows across the width of the dielectric tape decreasing layer thickness.

In the case of an occupancy carried out in accordance with the invention, the probability increases a separation at a distance from the edge of the dielectric tape, d. H. the Power connection point across the width of the dielectric tape, if the steepness of the profile of the layer thickness reaches such a size that with the same specific sheet resistance changes the current density so that it is at or near the Power connection point, i.e. a smaller value at the edge of the dielectric tape than in the rest of the assignment receives. First of all, yes, with normal the same layer thickness of the coating the current density (same specific sheet resistance provided) larger at the edge than in the other parts of the occupancy. When increasing the layer thickness increases across the width of the dielectric tape towards the edge the current density decreases at the edge, and it will happen with a certain profile, that the current density in all points of the occupancy across the width of the dielectric strip is the same size. If at this point, where the electricity heat is the same everywhere, remain, the disadvantage would be the possible separation at or near the power supply point not fixed yet. Only the probability of separation is over -the whole width has become the same.

Only a further increase in the layer thickness from the edge is reduced the current density below the level of that prevailing in the other parts of the occupancy, so far that the inventive effect can occur, namely that the; by The specific heat generated by the electricity is created at the points that are generated by. the power supply points be as far away as possible.

Fig. 2 shows a cross-section on an exaggerated scale across the width of the dielectric tape metallized in this way. On the dielectric tape i9 is the metallization 2o connected to the power connector 2i.

If you look at the parts of the occupancy as fuses again, you get you now have the strongest fuse near the power connection, the weakest fuse on the other hand on the opposite edge. In the event of a current surge, one off Such profiled layers built up capacitor can as a result of the generated specific electricity heat an occupancy part no longer at the power supply point be separated, but rather a part of the occupancy that is remote from this.

The generated specific electricity heat can now also, as before mentioned by the specific electrical resistance of the metal layer, which is called Capacitor occupancy is used to be influenced. Smaller resistance works in here the same direction as the enlargement of the cross-sectional area that the stream must happen. The specific sheet resistance should therefore be close to the power supply be less than in the other parts of the occupancy across the width of the dielectric strip. The same considerations made above for changing the layer thickness, can be found here with regard to the consistency with the specific electricity heat in all Points of occupancy are transferred in certain circumstances and must be observed are used in the production of the coating according to the invention.

The metallization of such dielectric strips can already be proposed method in such a way that over the width of the dielectric tape a change in the structure of the layer and thus a change in its resistance per cubic centimeter without changing the layer thickness. Another The way is that the layer across the width of several metals of different Resistance or can consist of alloys.

As mentioned at the beginning, the separation of parts of the occupancy occurs frequently when burning out electrically conductive defects in the dielectric. The short circuit current is after all to be seen as a current surge that can become so great that In the case of subdivided capacity areas, some of these areas are completely separated. It is known that it is useful to convert the capacities of the capacitor into a larger one Can divide up number of smaller areas, which are usually connected next to each other lie in the capacitor. This is to avoid keeping the whole in the capacitor stored energy is discharged via a defect and the resulting Pressure can destroy the whole condenser. These partial areas are z. B-. from a metal strip electrically connected to them on one edge of the metallized Dielectric tape fed with electricity. There are already different patterns for them The shape of the partial areas and arrangements with series resistors have been proposed, all of which have the same purpose, namely in the event of a breakthrough a flaw in the dielectric flowing. To limit current so far that on the one hand no harmful effect on the capacitor due to excessive energy discharge on the other hand, the energy also leads to a sufficiently large burn-out spot in the metallization is sufficient. The reduction of the short-circuit current through the division in individual areas can still be due to low layer thickness and thus increased ohmic Resistance to be reinforced. But the layer thickness of the metallization finds its own lower limit where you can. must fear their chemical degradation.

It has now been shown that @ also when capacitors are burned out With subdivided capacity areas, considerable losses in capacity can occur. It is Z. B. has been observed in the so-called comb pattern that the burnout penetrations in certain cases cut off the entire area. The comb pattern consists in his simplest form of narrow side-by-side connected surfaces that are apart of their power connection strips lying together on the edge of the dielectric strip are isolated from each other.

In theory, one should expect that there would be a defect in the dielectric corresponds to even a single blow-out spot, so that the possible loss of capacity seemed meaningless. However, practice shows that z. B. in the comb pattern individual partial areas are usually several over the entire width of a comb tine Extensive burnout spots are obtained .. Initially arises as a result of the breakdown an arc at the defect in the dielectric, which creates the metallization around it Puncture point around roughly circular , "burns away. -InfoIge the small width of the partial area in the comb pattern and the high current density of this Short-circuit, the affected area is usually in its entire width severed. At the cut-off point, however, the arc stops for a short time and so it happens at the next weakest point between this arc and the power supply due to the overload by the short-circuit current to another Melting off and separating the partial areas .. At this new separation point arises a new arc with the same effect, and so the separation process is repeated several times, until the voltage on the capacitor is below the sum the extinguishing voltages of the various arcs has dropped: Disconnection So not just the part of the surface that is from the power supply behind the actual breakdown point lies, but a much "larger part" in many Felling the entire area. The resulting loss of capacity area but limits the number of breakdowns through the capacitor that are still permissible during operation and thus also the level of the operating voltage of the capacitor.

The well-known metal coverings divided into individual partial areas can now be carried out advantageously in the same -described manner, so that the electricity heat in those sub-areas increases = that of those leading to them Power supply points are further away.

The idea of the invention also brings the same advantages mentioned in those patterns in which the individual partial areas are separated by so-called webs with the power supply strip or connected to one another by such webs themselves are. In certain embodiments, one has narrow supply strips attached to the partial areas, sometimes with increased sheet resistance, so they act as a backup in the event of a breakdown. The short circuit current has in them because of the small cross-section its greatest current density and thus also current heat and separates the partial area slightly here, so that. the partial area as capacitive Surface fails, but at the same time the breakdown current itself is limited or is terminated. In other embodiments, the partial areas have through-narrow Feed webs not only with the power supply strip, but also the partial areas even interconnected by such webs, so that. in this case one Row of. Partial areas are each one behind the other. If there is a breakdown then a partial area is usually separated on all sides. But it is much smaller in area formed here than in the example above, where the sub-areas. only connected next to each other lie on the power supply strips. Since the neighboring surfaces remain intact, because they are electrically connected to one another, this is the latter The case of the loss of capacity area is much smaller.

Fig. 3a shows an application of the invention in the so-called Comb pattern. It represents a cross section through the two metallized dielectric strips 22 and 23.

In Fig.3b the metallized dielectric tape 23 is shown in plan view. The tape 23 has a metal-free edge strip on the left. The occupancy 25 is patterned in a comb-like manner and, apart from the power supply strip located on the right-hand edge, the toothed-comb-like occupancy parts are isolated next to one another. The metallization 24 of the dielectric tape 22 has essentially the same appearance in plan view. Only here the metal-free edge strip and the power supply strip are interchanged. The metal coverings 2q. and 25 have a running layer thickness and thus, as a result of the cross-section which changes over the width of the thickness, the current density changes from one side to the other. With the distance from the current connection point, the current density increases when a short-circuit current passes through any defect in the dielectric. If a defect in the dielectric breaks down at 26, the short-circuit current flows in the direction of the arrow from 27 to 28 through the two opposing metal coatings. The upper metal coating 24 is burned out at the point 29, and the capacitive surface from 29 to 30 fails for the capacitor. On the other hand, in the part of the occupancy 24 lying to the left of the point 29, there will no longer be an interruption due to melting because the current density there is less everywhere than at the point 29. Since the cross section of the lower. Metal covering 25 at point 31 is larger than that at point 29 of the upper covering 24, it is not likely that point 311 will also burn out. The lower coating 25 is therefore completely retained, and thus also the capacitance of the two surfaces to one another, as far as they are to the left of the point 26. The greatest current density occurs at point 29 in the upper layer. All other. Cross-sections in the upper and lower layers through which the short-circuit current flows have a lower current density, and in them the current heat generated will therefore also be smaller.

The same considerations can be made accordingly. also z. B. transferred to the so-called diamond pattern, of which a plan view of part of a metal covering is shown in Fig. 4. The individual partial areas are connected to one another by narrow conductive webs. The partial surface 32 is connected to the adjacent diamond surfaces 33, 34, 35 and 36 by the four webs 37, 38, 39 and 40. When a defect in the dielectric part that belongs to this capacitance area 32 breaks through, one or more of the webs 37 to 40 burn through, and the capacitance area 32 is usually no longer usable for the capacitor. If one now looks at the sub-areas that lie in the row of cross-section 41 (indicated by the dashed line), these can be shown schematically with the sub-areas of the opposing occupancies as in Figure 5. The partial areas 42, 43, 34 ,. 32, 35 and 44 places. which represent an (upper) occupancy of the partial capacities that can be fed directly from the power supply strip 45. The webs 46, 47, 37, 39, 48 and 49 in Fig. 4 connect the individual partial surfaces with one another in a conductive manner. So that several webs are not burned out with this arrangement and thus several partial areas as capacitance fail with only a single breakdown through a defect in the dielectric, these webs are according to the invention of different cross-sections over the width of the metallized dielectric strip, in such a way that the web 49 is with the largest cross-section on the power supply strip 45. The webs can be different in width for this purpose. However, the total layer thickness of the metallization, that is to say of the webs including the partial areas, can decrease over the width of the dielectric strip or the electrical resistance per cubic centimeter can increase in the same direction as mentioned above. For the capacitive partial areas, it is irrelevant whether they are thicker or thinner or show more or less great resistance, because the burnout takes place here only on the webs.

In Fig. 6 the sub-area 32 is in connection with its neighboring areas 34, 35, 33 and 36 drawn. The partial areas are connected to these by the webs 37, 39, 38 and 4o connected.

When the webs are designed according to the invention, however, the adjacent ones are Lateral power supply bars connecting surfaces are no longer necessary, e.g. B. in Fig. 4 the webs 38 and 40 for the surface 32, since there is no longer any separation. This also ensures that the short-circuit current will spread to the adjacent webs and areas avoided. Furthermore, its energy is significantly reduced as a result, that there is no more energy from the neighboring partial areas through the now missing Ouerverbindungen can be contributed to a larger extent.

Figure 7 shows a comb pattern with subdivision of the surfaces by webs that are roughly in the middle of the individual surfaces. The partial area 51 is electrically connected directly to the power supply strip 53; the partial area 5o adjoins the non-metallized edge strip 54 on the dielectric strip. A burnout will always hit a dielectric part between a partial area, e.g. B. 5o, and one above or below opposite polarity. Partial area, such as B. 51, depends on their power supply strip. The high current density at the web 52 separates the area 50, and the short-circuit current is thus interrupted. The partial area 50 then failed as a capacitance, but it is only about as large as the entire ridge area. Without the subdivision of the entire area by the web in the middle, experience has shown that a large part and, in the worst case, the area above it would also have been separated off and failed.

Fig.8 shows an equivalent circuit diagram for two opposing polarity, ie one on top of the other, comb surfaces. The surfaces 5o and 5 i z. B. here are the upper capacitor surfaces. The web 52 means a fuse between these partial surfaces 5o and 51, while the edge strip, which causes the power supply, or the surface 51 can be viewed as a fuse 53 in the sense of the above explanations. The web 52 is designed with such a small cross section that it has to withstand the greatest current density or specific current heat in this system and is cut off in the event of a short-circuit current.

An example of a new pattern is the top view of a metal covering in Fig. 9. From the power supply strip 55, the Partial areas 56 to 6o fed. They are one below the other by webs of different widths tied together. The widest web 61 in this row is again the power supply strip 55 closest. Man. this pattern can also look like the one shown in Fig. 7 to be understood as a comb pattern in which the individual comb teeth are wider than usual and are therefore divided into partial areas by webs. This has this Pattern again resembles the diamond pattern in Fig. 4. In Fig. 9, three rows of the partial areas are connected to each other at the end, so that a partial area does not fail as a capacity when it is separated, but over the neighboring row is connected to the power supply strip. When separating z. B. on the web 62 are the partial areas 59 and 6o through the web 6.3 with the adjacent row remained connected, and only if several webs burn off, a whole surface element can for capacity fail.

Fig. Io gives a further example of a pattern according to the invention, but in which the separated area is not electrically insulated as in Fig. 7 remains, but is electrically connected to a neighboring surface and therefore not at all fails as a capacitive surface. The one accessible to the current through the web 64 in Fig Part 65 of the surface is through the strips 66 and 67 with the adjacent partial surface 68 connected. If the breakdown occurs in area 65, it is separated off at the web 64. The narrow strips 66 and 67 act as series resistors and prevent that the web 69 of the adjacent surface 68 can be severed. The stream finds therefore over the web 69 and the strips 66 and, 67 still its way into the Partial area 65. This pattern results in extensive decoupling without separation of partial areas.

All the patterns that have different sized cross-sections of the webs, are tied to certain sizes of the bars and are therefore not suitable for all Capacitors. They are only allowed to be realized with larger widths of the dielectric strips be. It should also be mentioned that you have a pattern across the width of the dielectric strips can also run so that the partial surfaces are inclined, z. B. at an angle below 45 ° to the edge of the dielectric tape. This makes the partial areas longer and the Path for the stream as well, so that one has the cross-section or the specific resistance graduate better under certain circumstances, can.

An increased effect is also obtained when the various ways in order to influence the current heat according to the invention, are connected to one another.

The idea of the invention is not limited to special embodiments of patterned metallizations. It is generally applicable.

Claims (2)

PATENT CLAIMS: i. Electrical capacitor made of metallized dielectric strips, characterized in that its burn-out coverings are designed in such a way that that those places in which the occurring current loads of the the current flowing through the unit of quantity of the covering metal generates the greatest heat is produced; are arranged away from the power supply points'. 2. Electric Capacitor according to Claim i, characterized in that the one generated by the current specific heat with the distance belonging to the same occupancy part of the rum Power supply point increases: 3. Electrical capacitor according to claim i and 2, characterized in that. the layer thickness of the covering with the removal of the power supply point belonging to the same occupancy part decreases. .4. Electric Capacitor according to Claims 1 and 2, characterized in that with approximately the same Layer thickness the resistance per cubic centimeter in the layer with distance from the power supply point belonging to the same occupancy section increases. 5. Electrical capacitor according to Claim i, characterized in that in front of the partial occupancy areas Bars are arranged as electrical fuses: 6: Electrical capacitor according to Claim i, a and 5, characterized in that the electrical conductivity of the Bar protection with the distance from that belonging to the same occupancy part Power supply point decreases. 7. Electrical capacitor according to claim i or one of the following, characterized in that the partial areas of the occupancy with their neighboring surfaces are electrically connected in groups, namely to the Power supply point opposite side of the dielectric tape. B. Electric Capacitor according to Claim i or one of the following, characterized in that Adjacent sub-areas electrically through occupancy strips acting as a series resistor are connected to each other.