US2095736A - Circuit interrupter - Google Patents

Description

Oct. 12, 1937. H. H. FAHNoE CIRCUIT INTERRUPTER Filed Feb. 2l, 1936 R O H r E V N Patented Oct. 12, 1937 UNITED STATES PATENT .OFFICE 2,695,130 cmcurr m'raaanrran Harold H. Fahnoe, Wilkinsbuig, Pa.,A assignor to Westinghouse Electric Manufacturing Company, East Pittsburgh, Pa.,'a corporationof Pennsylvania Application February 21, 1936, sei-n1 No. 65,053

It is a further object of this invention to interrupt the current by the fusion of a wire which requires high temperature to fuse it, but which will be without substantial effect upon the temperature of the fuse tube and will not affect decomposition of a substantial portion of the lining thereof.

.It is a. further object of this invention to so control the 'heating of said Dfusible element that it will remain at a comparatively low temperature until within a very short time before it is fused.

It is a further object of this invention to provide an interrupter of the type in which a spring tends to move a conductor lengthwise within a tube, drawing the arc into ,the tube, when said lconductor is released, thei release of said conductor being dependent .upon the successive fusion of two paralleljconnectors.

It is a further object of this invention to provide two connectors for a fuse of the type described, one of which shall have two portions united by a fusible joint and the other shall have a greater mechanical strength than the jointed one.

It ls aV further object of my invention to pro' through thenarrow parts of the connector 40 reaches the joint by thermal condiictionfand is large compared with the heat generated in the joint by the electric current therethrough.

It is a further object of this invention to make the stronger of said two connectors of a wire that will fuse when required to carry the whole of the current, the portion of which carried by the jointed connector, when both connectors were carrying current fuses the joint in said jointed connector.

It is a further object o'f this invention to pro-c vide a fuse element having a fusible joint placed under mechanical stress in response to current now by means of a member of blmetallic material. i

Other objects ofthe invention and details 0f 22 Claims. (Cl. 200--117) the proposed structure will be evident from the following description and the accompanying drawing in which: a

Figure 1 is a side elevational view, partly in section and withcertain portions broken away, of an expulsion fuse including the features of this invention.

Fig. 2 shows a central longitudinal sectional view of the rell unit of the fuse,

Fig. 3 vis a perspective view of the connections between the movable and the stationary termin elements ofthe fuse, and

Fig. 4 is an elevational view similar to Fig. 3

showing a modified form of the vinvention with two of the parts in the separated position which they take as the fuse begins to open.

In Fig. 1, a porcelain tube I 'encloses a flber tube 2 which encloses the interrupter element and biasing spring. A terminal cap 3 at the upper end and a cylindrical element I at the lower end constitute the terminals at which connections are made to the external circuit. A ferrule 5 near the lower end and a rod 6 springbiased toward the upper end constitutes the terminal conductors between which the connection is to be opened. The connection from the cylinder l to the ierrule 5 and that from the rod 6 to the upper cap 3 are of a familiar Asort and are not further described herein. Reference is made to the patent to Rawlins No. 1,976,634 issued October 9, 1934 for'a detailed description and illustration of said connections. The spring which biases the rod I toward the upperend of the tube is shown in Fig. 1 at I and is attached to the rod by a construction illustrated in said patent and including the threaded end 8 of said rod.

l The ferrule 5 is connected to the rod 6 by two connections one of which' is the wire I3 of Nichrome" comprising about 78% ynickel-20% chromium, and the other of which is composed of vtwo metal straps, namely, a member I2 permanently attached to the rod 6. and a bent member I3. The' member I3 and. the wire Il are secured together and to the ferrule 5 by a screw Il which passes through a hole I5 in the end of the member I3 and a hole in an enlargement I8 on the end of the wire I0. The wire Il preferably passes through aslot Il in the member I3 whereby the wire Ill may ilex so that the pull of the rod 8, urged by the spring 1, will be nearly in a straight line with the length of the wire. The strips I-2 and the wire III are Preferablyr the member I2 is of bimetal, the portion I8 having a larger coefficient of expansion than the portion I9. The member I2 may, however, be a leaf spring having no bimetallic construction. The member I3 may also be made of bimetal, but that is not necessary.l If it is made of bimetal, the portion next to the member I2 should have the larger coeflicient of expansion. 'I'he members I2 and I3 are soldered together. For this purpose their overlapping portions are of considerable area, so that the area of the soldered joint is nearly that of a square, one side of which is the width of the widest part of the strip I2.

'When soldering the joint between members I2 and I3 the parts shown in Fig. 3 are placed under tension, whereby the tension exerted by the 'spring I when the whole fuse is assembled will produce no strain in the joint. The tension both when lthe soldering is being done and when the fuse is v assembled is supportedby the strain wire IIJ.

If desired, the major member I2 may be narrow over the major part of its length and only the portion at the soldered'joint be large to afford the large area for the joint. The width of the member I2 is determined by the resistance it is intended to have. When the member I2 is of bimetal and the member I3 is a simple spring, preferably their resistance is made about equal. The thickness of the solder is as small as it can conveniently be. Preferably, it is materially less than the thickness of one of the members I8 or I9.

The solder used for the joint is one having a sharply defined melting point. An alloy of lead and bismuth known as eutectic lead-bismuth solder is suitable for this use but other fusible alloys can be used.

In the operation of the device, current enters i at the cap 3 in Fig. 1 and emerges at the cylin- .is obvious, however, that the current may flow in the opposite direction without change in the operation. y

' Current through the connector I2 heats it. The

l heating is greatest in the narrow parts of the connector and the heat generated in the parts I2 and I3 reaches the joint between them. by thermal conduction. If the current be not greater thanA that for which the fie is `designed, .the heat which reaches the joint is insuicient to melt it. If the current be greater than this, the temperature of parts I2 and I3 rises and the heat which flows therefrom to the joint is enough to melt the solder there. If the current is larger than this, say that corresponding to a short-circuit, the solder is promptly melted and it may even happen that the parts I2 and I3 also are melted.

Heating the solder mainly by thermal conduction from members I2 and I3 takes perceptibly more time than heating a fusible resistance wire directly by the current iowing in it, as is usual in ,fusibleinterrupters Thus a certain delay in the action of the fuse obtains with small overloads such as that of a starting motor.

As the member" I2 heats up,the difference in expansion between the portions I8 and I9 causes the member I2 to tend to bend, thus tending to move away from the member I3. Even though no perceptible movement occurs at currents below the value which will fuse the solder in the joint, a considerable stress is introduced by the difference in expansion and a considerable pull upon the soldered joint results. When the current rises to a value which causes the solder to melt, the parts I2 and I3 separate.

There are some solders that change their characteristics upon aging. With such a solder the joint may become unable towithstand the pull of the spring 1 even while unaifectedby the current. Thewire I 0 by taking the strain oi the joint prevents any such unexpected separation of the members I2 and I3. Thus their separation at an indefinite time is prevented.

Whether the interruption of current through members I2 and I3 is at a definite moment or at an unpredictable time, when they separate all of the current from the cap 3 to the cylinder 2| passes through the wire I0. Until this timefonly a small portion of such current passes through wire I0 because the resistance of this wire is large compared to the resistance of the connected members I2 and I3. When the wire ID carries all of the current, it is rapidly heated thereby and soon reaches the fusing point.

The wire I0 is preferably the Nichrome alloy referred to above having high resistance-and a melting point of about 1400" C. Although this is above the temperature at which the boric acid `2I surrounding the rod 6 is affected, no substantial amount of decomposition of the lining is produced mainly because the time during which the wire I0 is being heated up and fuses is Aso short.

When the wire I0 has been fused there is no longer any mechanical connection between the rod 6 and the vferrule 5, and the rod moves upward under the influence of the spring 'I. The movement of the rod 6 draws the arc into contact with the Jboric acid 2I surrounding the rod and it is decomposed by the heat of the arc producing gases and vapor that assist in extinguishing the arc. The above statement that substantially no boric acid is decomposed by heat from the Wire I0 does not negative that it is decomposed by heat from the arc. The action of the arc' within the tube and the eiect of the supple` mental small bore 22` are as described in the above-mentioned patent to Rawlins. The features described herein and not found in said patent include the connections between the rod 6 and the ferrule 5 and the way in which these connections release the rod.

If, instead of bimetal, the members I2 and I 3 are leaf springsI as shown in Fig. 4, their tendency to separate is the same, but the magnitude of the bias tending to separate them does not increase with the temperature. When the springs get hot enough to melt the solder, the

joint opens (as shown in Fig. 4) and all the current passes through the wire I0. The action thereafter is like that already explained.

With either form of the .invention the-magnitude of the stress on the soldered joint between members I2 and I3 is independent of the stress of the main spring 'I due to the provision of the strain wire I0. The results obtained by this invention thus surpass .those obtainable by using a single connection between rod 6 and ferrule 5.

If such single connection be of the fusible joint y type, the strain impressed by spring 'I must be lresisted by the joint unaided and in time it may yield even if no overload occurs. In case of aging solder, if the strain wire I0 were omitted. the action of the fuse would become uncertain.

If the wire I0 be used without the jointed connector it must carry the normal current and therefore must be heated a long time before it fuses. It will thus decompose some of the boric acid before there is any arc for the vapor to act upon. If the overload very slowly brings the temperature of the wire to the value that will fuse it, enough boric acid may be decomposed to leave insuilicient to extinguish the arc.

It will occur to those skilled in the art that many modifications in detail come within the spirit of this invention, and the specific descriptionv of certain modifications only is not to be regarded as a limitation. The only intentional limitations are those expressed in the claims or required by the prior art.

I c-laim as my invention: D

1. In a circuit interrupter, two conductors, a spring biasing one to departure from the other, two connections joining the conductors, one connection including a fusible joint biased to sep-- d ductors, a spring biasing one of said conductors tomove away from Athe other, two connections joining said`conductors, one connection including a fusible joint biased to separate upon the occurrence oi.' predetermined conditions, the cross section of the joint being great compared `with its length, and the otherconnectlon being of material which fuses at a higher temperature 'than said joint and has, while unfused, sumcient `therein when the value of said current is as great as that which will fuse the joint in the rst connection if carried thereby, said second connection being capable of carrying ywithout fusion the current therein when the first connection is cartying a current insufiicient to fuse said joint and said second connector having when unfused sufflcient mechanical strength to vwithstandV said biasing spring. i

4. In a circuit interrupter,

ductors, a spring biasing one of said conductors to move away from the other, two connections joining said conductors, one connection including 'two members and-a fusible joint joining them in series, one of said members having a ing when unfused sumcient mechanical to .withstand said biasing Spring. 75

bias tending to move it away from the other,

said bias being' resisted by said joint, said member including thermal-'responsive means for controlling said bias, the second connection being fusible by' current therein when the value of said current is as great as that which will fuse the joint in the ilrst connection if carried thereby,

said second connection being capable of carrying without fusion the current therein when the rst connection is'carrying a current insufiicient to fuse said joint and said. second connector havstrength 5; In a circuit interrupter, two terminal con- Comp two terminal con- #Y ductors, a spring biasing one of them to move away from the other, two connections in parallel between said conductors, one of said connections having suillcient'mechanical strength to hold the terminal conductors together against the action of said biashsaid connection being fusible by current therethrough above that normally carried by either connection, and theother connection having a fusible joint of short length and large cross section, said fusible joint having means biasing it to separate .at currents above 7 a predetermined, value, whereby at currents above said value all the current will be carried by said fusible connection and at currents below said value said,.fusible connection will carry part only of the current.

6. In a clrcuit'interrupter, a pair of terminals, a spring tending to separate them and two connections uniting them, one of said connections ing two conductors biased to separate in a direction at an angle to their length, fusible means normally uniting said conductors and having a cross-section at least as great as the adjacent portion of each of said conductors and a specific resistance lower than that of said conductors to provide a predetermined time delay in the fusion of .said fusible means upon the occurrence of predetermined conditions.

7. In a circuit interrupter, a pair of terminals, a spring tending to separate them and two connections uniting them, one of said connections comprising two conductors one of which is selfbiased to separate said conductors in a direction at anangle to their length, fusible meansnormally uniting said conductors having a crosssectlon at least as great as the adjacent portion of each of said conductors and a specific resistance lower than that of said conductors to cause a flow of heat from said conductors to said fusible means for fusing the latter upon the occurrence of predetermined current conditions.

8. In a circuit interrupter, a pair of terminals, a spring tending to separate them and two connections uniting them, one of said connections comprising two conductors, at least one of said conductors being a spring self-biased in response to predetermined temperature conditions to separate the conductors in a direction at an angle to their length, fusible means for normally preventing said separation, said means having a cross-section at least as great as the adjacent portion of each of said conductors and a specific resistance less than that of said conductors to eil'ect a predetermined time delay in the fusion of said fusible means upon the occurrence of predetermined current conditions and the other connection having a greater mechanical strength.

A 9. In a circuit interrupte'r, a pair of terminal conductors, bias-producing means tending to separatethem, means for preventing said separation,

said preventing means including a conductor ing means tending to separate said members,

'uniting means resisting said separation until the resistance and a higher mechanical strength than the first connection.

11. In a circuit interrupter, current conducting means separable to open the circuit, means responsive to a predetermined current cndition to initiate the separation of said conducting means, and said c onducting means being biased to separate with a force which increases as said predetermined current condition is approached.

12. In a fuse link, a conductor, a fusible portion in said conductor, vand current responsive means for biasing the parts of said' conductor to separate upon the melting of said fusible portion.

13. In a fusible link, a metallic strip, a fusible portion in said metallic strip, and one portion of said metallic strip being of bimetallic material for bending to cause separation of the parts of said metallic strip upon melting of said fusible pormeans for moving the parts -of said conducting means apart after melting of said fusible portion, and means independent of said'main biasing means for biasing parts of said conducting means to separate, said independent biasing means increasing its biasing force upon an increase in current.

16. In a circuit interrupter, a conductor, a

separable portion in saidconductor, main biasing means tending to separate the parts of said conductor, and lbimetallicmeans tending to separate parts of said conductor.

17. In a circuit interrupter, a pair of conductaA ing members normally secured together and separable upon the occurrence of predetermined conditions, a spring for applying a biasing force to move one of said conducting members longitudinally, and another means for biasing said.

19. In a circuit interrupter, means for establishing an arc including a separable joint, a main biasing spring for moving one part of said means forestablishing the arc, means for relieving said sepanifable joint from the stress of said main biasing//spring and said separable joint including a bimetallic member connected in the circuit to be heated by the current flow and bend laterally to separate said joint upon overload.

20. In a circuit interrupter, a tubular closure at least in part of insulating material, a conducting terminal at each end of said tubular closure, conducting means within said tubular closure for normally establishing an electrical circuit between said terminals, said conducting means including two parts joined by' fusible means, main lbiasing means formoving one part of said conducting means away from the other part upon melting of said fusible means to draw an arc within said closure, and means independent of said main biasing means for biasing said parts to separate upon the fusion of said fusible means.

21. In a circuit interrupter, a tubular member at least in part of insulating material and open at one end, a conducting terminal at each end of saidv tubular member, conducting meansv for establishing an electrical circuit between said terminals, said conducting means including a movable conducting member, spring means-for moving said conducting member away from the tervminal adjacent the open end of said tubular member, a fusible strain wire disposed between said tubular member and said terminal for normally restraining said conducting member against movement by saidspring means, and a pair of conductors joined by fusible means and disposed in parallel circuit relation with said strain Wire,

said pair of conductors being biased to separate upon fusion of said fusible means. i

22. A circuit interrupter comprising a tubular enclosure open at one end, terminals, at each end of said enclosure, an arc chamber within said enclosure terminating at the open end thereof, a fuse link within said enclosure, said fuse link including a pair of bimetallic conductors, one of which is connected to the terminal adjacent the open end of said enclosure and the other to a movable member which is in turn connected to said other terminal, fusible means joining said bimetallic conductors, said bimetallicvconductors being disposed to bend apart upon fusion of said fusible means, and biasing means'for moving said movable member through said arc chamber fol' lowing the separation of said bimetallic con-

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