US2263752A - Electric circuit interupter - Google Patents

Description

Nov. 25,1941. 4 E. BABLER 2,253,752v

ELECTRIC CIRCUIT INTERRUP'IIER Filed April 17, 1940 Patented Nov. 25, 1941 'OFFICE lELECTRIC CIRCUIT INTERRUPTER Egon Babler, Brighton, England Application April 17, i940, Serial No. 330,034

In Great Britain April 26, 1939 2a claims.

This invention'relates to electric circuit interrupters and refers more particularly to the type of circuit interrupter described in my prior specication Serial No. 228,083, which comprises a metallic layer which is preferably so thin that arcing destroys it at less than the current required to In electric circuit lnterrupters as described in said prior specification aforesaid, although the nlm is destroyed at 'a temperature which is below the melting point (due to the tension set up in the surface of the film) the following diiculty may in some cases arise: The necessary temperature rise for the initial destruction of the film is naturally imparted also to the support. The normally high resistivity of the support is thereby lowered, and it assumes a slight conductivity. As a matter of fact, if for instance ordinary glass is used for the support (having a high negative temperature resistance co-eiiicient) it mayhappen that the interrupter does not clear, because as the metallic layer is destroyed, the surface supporting it becomes increasingly conductive. Naturally the rate of increase of the current to be interrupted is a big determining factor; If this current rises very steeply, no such difliculties are encountered, because there is no `time to impart any dangerous amount of heat to the support.

This difliculty was overcome in certain embodiments of said prior speciiication aforesaid, by introducing a restriction into the conductive layer, thus limiting the locality of thermal destruction and .correspondingly limiting the area of increased conductivity of the support. Inaddition to this a material was chosen for the support with a low temperature co-efflcient for example, alumina or mica. These two principles make it possible to produce an interrupter, which works with a considerable margin of safety, even if the 'fault current rises very slowly, say for several minutes. n

Another dimculty, however. was experienced with circuit interrupters as described in said prior specication, viz. that the rupturing speed, as in the case of al1 thermally operated devices.- is relatively slow, whereas high rupturing speed is In order to increase this `rupturing speed and as a further help to overcome the aforementioned difiiculty of. the support becoming conductive, I have now developed the following methodz' The substantially straight path of the conducting layer the cool part of the support is rapidly destroyed of the greatest importance, particularly when the l forth in which the above disadvantages will be obviated and the rupturing speed increased.

by arcing. The breakdown across the small gap is not only favoured by the voltage drop in the by-path, but also by the natural tendency of an electric current to pursue a straight path. The electro-magnetic force (set up in the by-path) increases with the current and helps thus to bring about a breakdown across the gap, sometimes without the loss of time requiredfor the thermal destruction of the restriction. This is especially so lwhen the current rises very quickly, that is when a speedy interruption is most desirable. The operating time may be cut down further by introducing more than one gap and by-path. There are thus provided several centres where the ionic destructionof the lm commences, until such a total length of the lm is destroyed that the discharge extinguishes.

The by-path may take the form of a conductive layer similar to that of the straight path and a restriction may be, but need not necessarily be, provided in said by-path to give a high resistance.

In order that the invention may be the more clearly understood, a number of circuit breakers in accordance therewith will now be described, reference being made to the accompanying drawing wherein:

Figure 1 is a sectional side elevation of av circuit breaker in accordance with the invention i1- lustrating the general structure thereof,

Figure 2 is a plan of the circuit breaker proper and the support therefor,

Figure 3 is a view to an enlarged scale of the part of said circuit breaker proper at which breakdown occurs,

Figure 4 is a similar view to Figure 3 of a modied form` of the part of the circuit breaker proper at which breakdown occurs,

the heat.

Flgurel''s a similar view to Figure 3 of another modified formof the part of the circuit breaker proper at which break down occurs,

Figure 6 is a similar view to Figure 3 of another modified form of the part of the circuit breaker proper at which break down occurs,

Figure '7 is a plan of the portion of the circuit breaker proper at which break down occurs together with a portion of the support and the container illustrating a different form of by- Pass,

'Figure 8 is a similar view to Figure 7 of a slight modification,

Figure 9 is a similar view to Figure 7 of a fu'rther slight modification, and

Figure 10 is asimilar view to Figure 'l of a further modication. Y l

Referring first to Figure l, the circuit breaker comprises a thin layer I of metal mounted on an insulating support 2 in the manner described in said prior specification Serial No. 228,083. As described in said prior specification, said layer I and support 2 are enclosed in a container comprising a glasstube-3 having its ends closed by means of metal caps 4 through which the ex-` ternal connections are established..- The connections between the lends of said layer I and said end caps 4 are established through wires 5 connected, by means of solder 6, to thicker layers 1 deposited over the ends of said layer I, said wires being also connected to said end caps in any suitable way. `Said wires 5 also form the- .parallel sided path which the conducting layer I follows between the points a and b is enlarged by a short branch 9 of double width or more extending laterally to one side only. The whole path I and branch 9 is then parted at I0 by scratching the nished metallic layer with a needle, the scratch completely traversing the normal path I and continuing up to nearly the `end of the branch 9, the extremity being left intact to form a restriction II on the by-path.v

When the normal small current flows through the circuit breaker, it flows throughthe by-path constituted by this restriction II which is preferably so narrow as to be of fairly high resistance. If the current rises, the potential drop across the by-path will rise also, in some cases at a higher ratio owing to the increase in temperature of the by-pass. When the current rises to the rupturing value there may or may not be time for the by-path at II to be destroyed by If it is destroyed by the heat, arcing will instantly take place across the gap formed by the scratch III and the film I will be destroyed on the cool part of the support 2. If there is not time for the by-path to be destroyed by the heat, the potential drop thereacross will become so great that, once more, arcing will take place across the gap and the lm I will be destroyed lwith great rapidity at the cool part of the support 2. Of course, the restriction could be so designed that it is never intended to be ruptured by the heat, the first breakdown always taking lplace across the gap. In any case the gap ensures rapidity of rupture at a cool part of the support.

It will be appreciated that the break down across the gap is favoured, not only by the voltage drop in the by-path, but also by the natural tendency of an electric current to pursue a straight path.l The'electro-magnetio forceset up in the by-path increases with the current and thus helps to bring about a break down across the gap sometimes, as stated without thermal destruction of the restriction. Naturally the Width of the restriction II determines the rupturing capacity. In this way the restriction becomes very short and the heat energy dissi* pated 'very small. The dimensions can be chosen ad libitum, but the gap III across the straight path should be small enough to be broken down readily by small voltages. I have obtained very favourable results with a gap of 0.004 inch, but I by no means limit myself to'this dimension. The above design is only a simple example; there are many ways to produce any interruptor according,r to the present invention.

For example, in the arrangement .described above, in order to speed up further the rupturing, two further scratches I2 may befprovided in each end. of the by-pass, as shown in Figures 4 and 5, said scratches cutting into the branch 9, at its point of junction with the main path I and extending nearly as far as the original scratch I0. Said further scratches I2 may be either parallel to the main path as in Figure 4 or at an angle cutting into the main path I as shown in Figure 5. By virtue of these scratches I2, access to the by-pass becomes sooner interrupted. The two additional restrictions I3 consequent upon these further scratches I2 should be (but need not necessarily be) wider than' th original restriction II resulting from the original scratch.

A further modification in accordance with the invention is as follows: It will be appreciated that. in the arrangements heretofore described, the two limbs of the by-path on either side of the main scratch I0 constitute a condenser. This condenser is shunted by the resistance constituted by the'restriction but nevertheless the energy stored up in this condenser will help to brak down the gap across the main path especially after the restriction has been thermally destroyed. In somel join at right angles one limb of an elongated U-l shaped scratch I4 whose two extremities approach one end of the enlargement 9a andl whose crutch portion approaches the other end. A third scratch'l runs mid-way between the limbs of the U from a point very near the crutch portion completely to the far end of the enlargement 9a, and scratches I2a separate the enlargement 9a from the main path I right up to points close to the main stratch I0a. With this arrangement the small clearance IIa between the yend of the scratch I5 and the crutch portion of the U-shaped scratch I4 constitutes the restriction in the bypath and it will be seen that the by-path itself follows a to'rtuous path and the capacity between its two limbs is greatly increased. The operation is as before: When, with or without the thermal destruction of the restriction at Ila, the voltage drop across said restriction becomes too high, arcing takesplace across Ila and the illm is rapidly destroyed at a cool parl; oi the support.

It will be appreciated that there are many ways by which the increased capacity between the limbs of the by-path may be attained.

Figures '7, 8, 9 and 10 illustrate arrangements in which the by-path does not consist oi av thin metallic layer at all but is made as a separate circuit. Thus in Figure 'l the by-path is constituted by a resistance IB.' The main path I is formed with a scratch lb of about the same thickness as the previous scratches II) and Illa and which completely separates said main path. On thetwo sides of this scratch the path is formed with backwardly inclined branches I1 and the ends of these branches are connected to the ends of the resistance I6 by thicker layers I8 and solder I9 in the same way as the resistances are connected to the ends of'the'layer I as shown in Figures 1 and 2. In the case of this gure of course there will never be any thermal destruction of the circuit interrupter but the .initial destruction will always take place by arcing across the gap I0b in the main path I, the support 2 remaining cool. If desired the resistance I6 of the by-path could'be made variable as I6a in Figure 8 and the resistance material chosen could have a high temperatureco-eiiicient in order further to assist the break down across the gap.

In Figures '7 and 8, themresistances I6 and I6a respectively are shown as Abeing outside the tube 3 forming the container for the circuit breaker. If desired the 4resistance may be inside said container as ISb in Figure 9. In all `these Figures 7, 8 and 9, scratches I2a corresponding to the scratches I2 of Figure 5 are shown.

In Figure 10 an arrangement is shown in which 'the by-path is constituted by a condenser 20 in place of the resistance IB of Figure 7. A condenser can of course only be employed where the circuit breaker is to be used with alternating current. Otherwise, the operation is exactly the same as in Figures 7, 8 and 9.

In short the 'by-path may be' constituted by any circuit which brings about the break clown across the gap at the required current value.

It will be apppreciat'ed that, if desired a plurality of gaps and by-paths may be provided at the by-path willbe out of the plane of the main Path.

Another condition is that, as in the prior specication aforesaid, the conductor layer I should preferably be thin enough to be destroyed by the arcing of a current smaller than the current which'is safely carried if the layer were nowhere interrupted. accidentally ruptured bycorrosion or mechanical means such as vibration or shock, any arcing across such accidental interruption will instantly destroy the lm instead of slowly generating heat and possibly causing dangerous explosions.

I have stated in my said prior specification that no organic materials must be associated with the layer l. I have foundthat, with an arrangement in accordance with the present invention, the layer I may be protected by coating it with a varnish. The varnish coat is inter-v posed between the metallic lm I andl the sand 8a surrounding it, but no varnish should be between lm and support 2, and the support itself should preferably be of inorganic material as described in said prior specification.

The layer I maybe produced in the same way as in my prior specification aforesaid and in other respects the arrangement may be the ysame 2. An electric circuit interrupter of the type' which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupt-ed by a small gap and a by-path is It will be seen that according to the invention it is essential to interrupt the more or less straight conducting layer I in one or more places by agap IU, Ina or Illb and to bridge this gap by a suitable by-path. 'I'he by-path need not be in the same plane as the original conductor, and if it is not so this will further increase the tendency of the break down to occur, particularly with a rapidly rising current. For example in Athe case where the by-path takes the form of a thin layer like the main path (as in Figures 1 to 6) the base provided across said gap, said gap being so small that, upon increase of current, arcing takes place across said gap without the by-path being thermally destroyed, owing to the potential drop across said gap, thereby rapidly destroying the layer and interrupting the circuit breaker.

3. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted by a small gap and a bay-path is provided across saidgap, said gap being so small that, upon increase of current, arcing takes place vacross said gap owing to the potential drop thereacrosspthereby rapidly destroying the layer and interrupting the circuit breaker, and the lay-path, in which heat is generated, being sufcientl'y far from said gap to enable the support in th'e region of said gap to remain relatively cool. I

4. An electric circuit linterrupter of the type which comprises a thin metallic layer on a support,'wherein the path of said metallic layer is interrupted by a small gap and a by-path.4 is provided across said gap, said gap being vso small that, upon increase of current, arcing takes place across said gap owing to the potential dropthereacross, thereby rapidly destroying the layer and interrupting the circuit breaker, and the layer may take the iorm of a cylindrical rod so that itself being so thin that arcing destroys it at less than the rupturing current, so that any arcing across a'lbreak in thelayer caused acci- Thus, if the lm l is circuit breaker.

dentally by corrosion or mechanical means will destroy the layer and prevent continuance of such arcing.

5. An electric circuit interrupter of the type which comprises a thin metallic layer on a support of inorganic material, wherein the path of said metallic layer is interrupted by a small gap and a by-path is provided across said gap, said gap being so small that, upon increase of current, arcing takes place across said gap owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker. i

6. An electric circuit interrupter of the type which comprises a thin metallic layeron a support, wherein the path of said metallic layer is -interrupted by a small gap, and a by-path, in

the form of`a metallic layer similar to that ofthe main path, is provided across said gap, said gap being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

'7. An electric circuit interrupter comprising a support, a thin metallic layer on said support, an enlargement on one side of the normal path of said layer, and a narrow gap traversing said normal path and enlargement save for a narrow neck in said enlargement whereby is constituted a gap across said normal path and a by-path across said gap, said gap being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

8. An electric circuit interruptercomprising al support, a thin metallic layer on said support, an enlargement on one side of the normal path of said layer, a narrow gap traversing said viormal path and enlargement save for a narrow neck in said enlargement and two further gaps cutting a support, a thin metallic layer on said support, an enlargement on one side of the normal path of said layer, a narrow gap traversing said normal path and enlargement, save for a nai-row neck in said enlargement, said gap, at its part within said enlargement, pursuing an irregular or tortuous path, whereby the capacity -of the ,condenser constituted by the two limbs of said enlargement is increased, said gap across said normal path being so small that, upon increase vof current, arcing takes place across said gap. owing to the potential drop thereacross. therebx7 rapidly destroying the layer and interrupting the 10. An electric circuit interrupter comprising a support, a thin metallic layer on said suDDOrt, an enlargement on one side of the normal path of said layer, a narrow gap traversing said normal path and enlargement, save for a narrow neck in said enlargement, .said gap, at its part within said enlargement, being in two parts, viz. a rst part which, over part of its extent, pursues a. U-shaped path, and a. second part which extends between the limbs of the U of the rst part, so that said narrow neck is between the extremity of the second part and the crutchA of the U, said gap across said normal path being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

11. An electric circuit interrupter comprising a support, a thin metallic layer on said support, an enlargement on one side of the normal path of said layer, a narrow gap traversing said normal path and enlargement save for a narrow neck in said enlargement, and two further gaps cutting into said enlargement at its point of junction with said normal path and extending nearly as far as said former gap, said former gap being in two parts, viz, a iirst part which, over part of its extent, pursues a U-shaped path, and a second part which extends between the limbs of the U of the rstpart, so that said narrow neck is between the extremity of the second part and the crutch of the U, said gap across said normal path being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the vcircuit breaker.

12. An electric circuit interrupter vof the typey which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted by a small gap, and a by-path, in the form of a separate resistance, is provided across said gap, said gap being so small that. upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the lay'er and interrupting the circuit breaker.

13. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted by a small gap, and a by-path, in

the form of a variable resistance is provided across said gap, said gap being so small that.

y upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layerand inter rupting the circuit breaker.

1 4. An electric circuit interrupter for use with alternating current, and of the type which comprises a thin metallic layer on a support` wherein the path of said metallic layer is interrupted by a small gap and a by-path is connected across said gap, said by-path being constituted by a condenser, said gap being so small that, upon increase of current, arcing takes place across -said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and inter- .rupting the circuit breaker.

15. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted by a small gap, said path, on the two sides of said gap, is formed with backwardly inclined branches, and a by-path is connected across the ends of said backwardly inclined branches, said gap being so small that, upon increase of current, arcing takesl place across said gap, owing to the potential dropthereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

16. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, whrein the path of said metallic layer is' interrupted by a small gap, said path, on the two f clined branches, and a by-path is connected across the ends of said backwardly inclined branches, and wherein two further gaps are provided cutting into said backwardly inclined branches at their point of junction with said main path and extending nearly as far as said former gap, said former gap being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

17. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted by a small gap and a by-path is provided across said gap, said gap being of the order of .004 of an inch so' that, upon increase of current, arcing takes place across said gap, owing, to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

18. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein 'the path of said metallic layer is interrupted, at each of a plurality of points by a small gap and a by-path is provided across said gap, each gap being so small that, upon increase 'of current, arcing takes place across said gap,

mechanical means will destroy the layer and prevent continuance of such arcing.

20. An electric circuit interrupter of thevtype which comprises a thin metallic layer on a support, wherein ythe path of said layer is tortuous, whereby the resistance thereof is increased without the overall dimensions of the circuit breaker being unduly high and wherein said path of said layer is interrupted by a small gap and a bypath is provided across said gap, said gap being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross, thereby rapidly destroying the layer and interrupting the circuit breaker.

21. An electric circuit lnterrupter of the type which comprises a thin metallic layer on a support, said layer being so thin that arcing destroys it at less than the rupturing current, wherein the path of said metallic layer is interrupted, savefor a relatively narrow portion thereof, by a small gap.

22. An electric circuit interrupter of the type which comprises a thin metallic layer on a support, wherein the path of said metallic layer is interrupted, save for a relatively narrow portion thereof, by a small gap, said gap being so small that, upon increase of current, arcing takes place across said gap, owing to the potential drop thereacross,thereby rapidly destroying the layer and interrupting the circuit breaker.

23. An electric circuit interrupter comprising a support, a thin metallic layer on said support, said layer being so thin that arcing destroys it at less than the rupturing current, an enlargement on one side of the normal path of said layer, and a narrow gap traversing said normal path and enlargement save for a narrow neck in said enlargement whereby is constituted a. gap across said normal path and a by-path across said gap.

EGON BABLER.

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