US1965239A - High potential fuse - Google Patents

Description

July 3, 1934. G. L. HlLL HIGH POTENTIAL FUSE l Filed Oct.l 22. 1930 zea- . 30 INVENTOR.

ffm r M56 .t ATTORNEYS.

E 5. di fr 7 A e if e C WM i W// f im, i *Y i @MMW ,b

til

Patented July 3, 1934 UNITED STATES PATENT OFFICE l2 Claims.

This invention relates to an electric cutnout orr `ruse in which the. circuit is opened by the melting of a fusible conductor, and more particularly to a fuse intended for high potential circuits and in which an arc quenching medium is employed.

Recent operating experience combined. "with tests and investigations show that the typical cartridge i'use or cut-out consisting of an insulating tube having a powder ller, and with contact terminals at opposite ends and an internien diate fuse wire completing the circuit between the two terminals is an unreliable electrical protective device.

This is particularly true when the current rises slowly to the melting point of they fuse wire as the arc holds on and the device burns up, the result being that a line to ground or a line to .line

short circuit may occur. Also when a cartridgev fuse is filled with an arc quenching medium in the form of a powder, or the like, and a heavy current or short circuit is interrupted conducu tive path may be formed through the powder ller. This path may cause the are to continue thereby destroying the fuse or, if the current is momentarily interrupted, the circuit may be reestablished due to excessive leakage current through the semi-conducting path.

The object of the present invention is to generally improve the construction and operation of fuses of the character described; to provide a fuse which utilizes the heat developed by the current or are to melt, soften or reduce the tensile strength of a material thereby releasing an operating mechanism which functions to elongate the are through an arc quenching medium; to provide a compound fuse or a fuse consisting of two sections, and one of said sections being of lesser current carrying capacity; to provide a. compound fuse having a section of lesser current carrying capacity to form a primary arc, the heat of which is utilized to develop sufficient pressure to expel or project an arc quenching substance into a second arc formed in the fuse section of greater current capacity; and, further, to relieve the fuse section of small current carrying capacity of 4all mechanical strain or tension thereby permitting the use of a fuse element having a section of very small current carrying capacity and when this small fuse element melts the heat from the resultant arc is utilized to release a conductor or fuse section of larger current carrying ca` pacity which is under tension applied thereto by a spring or other operating mechanism.

The fuse is shown by way of illustration in the accompanying drawing, in which- Fig. l is a central, vertical section of the same,

Fig. 2 is a cross section taken on line Il-l of Fig. 1,

Fig. 3 is a longitudinal, vertical section showing a modined form or the fuse structure,

Fig. 4 is a detail of the lower end of the fuse showing a modified form of the fuse section of small current carrying capacity, and

Fig. 5 is a detail section of the removable parts :required for a"re1illable fuse cartridge.

Referring to the drawing in detail and particularly Fig. l, l indicates a cylindrical tube or shell constructed. or" insulating material and provided with metal errules or contact members 2 and 3 at opposite ends, these ferrules being secured to the insulating tube l by being threaded or otherwise connected. Mounted within the main shell or tube 1 are a plurality of tubes such as. indicated at a, 5 and 6. The tube 6 is mounted within the lower end oi the tube 5 and the tube 5, in turn, abuts the lower end of the tube 4 and is held against longitudinal movement thereby. The upper end of the tube 5 is substantially closed yas shown at 'l and forms a head or partition member which divides the main tube into two main compartments, to-wit, an upper compartment 8 in which is .mounted a flexible conductor 9 and a helical tension spring 10, and a lower compartment 11 which contains a fuse 12A and an arc quenchingrnaterial 13 in the form of a powder or the like.

The fuse employed in the present instance may be referred to as a compound fuse as it is divided into two sections, the lower section of which is of comparatively small current carrying capacity; this' section being indicated at 14. The lower end of this fuse is secured to a contact cap 15 which is in contact with the fer-rule 3. The opposite end of the small fuse is secured to a cross bar 16, or to the larger carrying capacity fuse 12, The cross bar is interposed between a shoulder 17 formed in the tube 6 and the upper end of a tube 21. The lower end of the main fuse section 12 is ,secured to the bar 16 while the upper end is secured to a flexible conductor 9 which is connected with the upper ferrule 2. The head or partition member '7 is provided with a. comparatively small central opening 'Za through which the flexible conductor extends and a packing material, such 4as asbestos or other ber, surrounds the conductor so as to prevent accidental escape of the arc quenching medium. An eye 9a is formed on the exible conductor at a point above the head member '7 and the lower end of the tension spring 10 is attached thereto, while the upper end is attached to the ferrule 2. This spring is maintained under considerable tension and this tension is applied to the main fuse section 12 and the cross bar 16, thus the smaller fuse section is accordingly relieved of this pressure due to the cross bar, hence permitting a very small fuse section to be employed where conditions demand.

rllhe improved fuse here shown is particularly adaptable to circuits where the current to be interrupted may be relatively small, being of the order of 0.25 to 1.25 amperes at relatively high potential. An example of the application is for the protection of circuits feeding high potential transformers where the normal load current is of the order of 0.025 amperes. A failure in a winding of a high potential transformer may be of such a nature as to limit the current to a value only slightly above the normal load current. This may be classed as a high impedance fault. The fuse must clear a fault under this condition.

Also a potential transformer fuse device should have such a current time characteristic that will cause it to operate or function if there is a short 'circuit in the secondary of the potential transformer. Due to the ratio of primary to secondary current the primary current may be relatively small and for this reason the fuse device must function on very small currents.

Again, the fault may be a line to ground failure within the transformer case, or a porcelain bushing may puncture, or a high impedance fault may develop into a low impedance fault, etc. The fuse must clear the circuit under any of these conditions. When a high impedance fault occurs in actual practice, with the fuse installed in the circuit to be protected, the moment the current exceeds a certain Value the fuse element 14 will slowly melt and will thus form a primary arc which has two functions, first that of producing suflcient heat to release the main fuse 12 with relation to the cross bar 16, or other suitable anchoring means, and secondly, to produce sufficient pressure to force the arc quenching medium into the arc formed when the main fuse section 12 is released. That is, the moment the main fuse section is released either by fusing or by being released from the cross bar 16, spring 10 exerts such a pull as to almost instantly retract the fuse member from the chamber containing the arc quenching medium. 'I'he arc is thus instantly lengthened to a point where it tends to prevent further current flow and at the same time the arc quenching medium is suiiiciently stirred up or agitated by the expulsion action of the lower arc to prevent the formation of any conductive path through the arc quenching medium.

In actual operation it may also happen that a. sudden fairly high current is applied to the circuit in which the fuse is mounted. In that instance both fuses may part almost simultaneously, that is, within one or two cycles or less of current operation. Two arcs are in this manner formed and the heat of the lower arc is utilized to produce sufficient pressure to project the arc Fig. 1 when a fuse is blown. A refillable structure is desirable inasmuch as the tubes l and 4 and the ferrules 2 and 3 may reused thus adding an economical feature by permitting renewal ci' the reeaaee fuse devices. The spring 10 may or may not be renewed as desired. It should be noted that the end member or cap 15 may be utilized as a sealing member for the tubes 5 and 6 as well as a contact member between the fuse 1li and ferrule 3. The tubes 5 and 6 are shown secured to cap 15 by threads but other means may be employed. A gasket of fabric or other porous material as shown at 26 is employed to close the ports or vents indicated at 25. This gasket is held in position between the ends of the tubes 5 and 6 and the cap l5. In addition to the vents 25, Vents such as shown at 24 which are formed in the ferrule 2 may also be employed.

. The modification shown in Fig. 3 is particularly adapted for outdoor service. In this structure the ferrule 28 forms an expansion chamber 35 for the gases leaving the vents 25a. The end cap indicated at 30 secures a spacer 29 in position and this in turn maintains the cap 15 in engagement with the boss or shoulderl 31. The ferrule indicated at 22 has an extension to receive the spring l0 so that when the spring is retracted it will be housed therein thereby allowing greater clearance and space when the fuse is blown and full line potential is impressed between the ferrules 28 and 22.

It will be noted that an additional end cap 27 is used to seal the upper end of the ferrule 22 so as to prevent entrance of moisture. The spring 10 is fastened to a pin 34 which extends through the upper or head end of the ferruie 22, the pin being held in the head of the ferrule 22 by means of a nut 32, the connection forming a suitable electric terminal. The exible lead 9 is fastened to the pin 34 as indicated at 36.

After the fuse has blown the structure shown in Fig. 3 may be refilled by unscrewing the cap 30, removing the retaining sleeve 29 and pulling out cap 15 and the tubes 5 and 6 secured thereto.

` Cap 27 is then unscrewed and nut 32 is unscrewed from the pin 34, thus allowing spring l0 to drop out through the lower end of the ferrule 28. The refill structure shown in Fig- 5 is inserted through the lower end of the ferrule 28, sleeve 29 is inserted and cap 30 is then screwed into place thereby sealing the lower end of the fuse. In order that the spring may be placed under tension a rod is inserted through the hole in the head end of the member 22 and it is screwed into a socket 34a formed in the end of the pin. The pin 34 may then be pulled through the opening in the head end of the member 22 and it is there held in place until the nut 32 is applied. Cap 27 is then screwed into place sealing the upper end and completing the relling operation. While a powder form of quenching medium is shown in Fig. 1, Fig. 3 is particularly adapted for a liquid quenching medium such as oil or the like. Where oil is employed gasket 26 will of necessity function as a liquid seal. It will, however, be constructed of thin sheet lead so as to burst when the fuse blows. A powder form of quenching material may also be employed in the structure shown in Fig. 3.

In connection with the structure shown in Figs. 1, 5 and 3, it might be stated that a piece of fabric or the like such as shown at 18 is preferably interposed between the cross bar 16 and the arc quenching powder so as to prevent it from dropping into the lower fuse chamber as its presence there might tend to act as a heat conductor or cooling medium for the smaller fuse. It is, in some instances, desirable to also fill this chamber with an arc quenching medium. In that case,

the smaller fuse may be enclosed in a thin glass bulb such as shown at 19 in Fig. 4. When the smaller fuse blows in that instance the glass bulb immediately bursts and the gases produced, together with the arc quenching substance surrounding the bulb, will be expelled or projected upwardly into the chamber l1 where it functions as already described. This expelling action is exceedingly important as there is a considerable danger of forming a conducting path through the arc quenching medium, this being particularly true when the current rises to a large value and the heat generated may cause the powder filler to reach the fusion point of the substance. In that case the arc would hold on and the device burn up. This is entirely obviated by utilizing the expulsion action heretofore referred to. Such expulsion actioirmay be materially increased by providing an elongated tube such as shown at 23 in Fig-3. The tube 23 is lled with the arc quenching medium similar to the whole chamber indicated at lla, hence when the smaller' or lesser carrying capacity fuse blows suihcient pressure is generated to eject the entire contents of the tube 23 into the space above thus materially stirring and agitating the arc quenching medium to such an extent as to positively eliminate the forming of any conducting path through the powder. Furthermore, this action materially increases the rapidity with which the arc is destroyed. The gases .formed during the fusing or blowing oi. the fuses must be liberated. Part of these gases will blow the packing or fibrous material shownq at la out of the reduced port or oriiice 7, hence permit ting part ci the pressure to relieve itself through the chamber containing the spring l0, the pressure being further relieved by 25:1. in the member 15.

Should the arc tend to follow the flexible conductor 9 through Athe port or orifice of the head member "I, it will be broken up or ile-ionized by the powder and gases blown into its path, inasmuch as the pressure in chamber ll will be greater than in chamber 8. It will thus be seen that in addition to the utilizationof the energy of the arc caused by the fusing'of the element 14 to stir upor de-ionize the path of the arc element 12, it will also force the arc quenching substance into the path of the arc if it should persist a suilicient length of time to follow the conductor 9 through the opening in the head member 7.

Additional vent openings may yalso be formed in the lower ferrule as indicated at 25, said openings being covered by a fabric or the like as inn dicated at 26 and 26a, any danger of bursting the fuse 'shell or tube being thus entirely eliminated.

While certain features of the present invention are more or less specifically described, I wish it understood that various changes may be resorted to within the scope of the appended claims. Similarly, that the materials and nishes of the several parts employed/may be such as the manu providing vent openings carrying section fusing iirst when the fuse blows and forming a preliminary arc, and means whereby the heat of the preliminary arc is utilized to release the main fuse section with relation to the anchor means and to project an arc quenching medium into a second arc formed by the release of the main fuse section.

2. In a high tension fuse, a fuse element having a section of small current carrying capacity and a main section of greater current carrying capacity, means connected with the main section whereby a pull is applied, anchor means interposed between the two sections and relieving the small current carrying section of any tension, said small current carrying section fusing rst when the fuse blows and forming a preliminary arc, and means actuated by gases under pressure formed by said preliminary are for projecting an arc quenching medium into a second arc formed in the main section of the fuse element.

3. A high tension fuse comprising an elongated shell, said shell being divided longitudinally into an upper chamber, an intermediate, and a lower chamber, a fuse element mounted in the intermediate chamber and extending into the lower chamber, the end oi the fuse extending into the lower chamber being of small kcurrent carrying capacity, a tension spring mounted in the upper chamber and connected with the fuse element, an anchor member disposed between the intermediate and lower chamber to which the fuse element is secured and relieving the fuse section of small current carrying capacity ci? tension, and ier-rules at the opposite ends of the shells with which the iuse ends are electrically connected.

4. A high tension ruse comprising an elongated shell, said shell being divided longitudinally into an upper chamber, an intermediate, and a lower chamber, a :fuse element mounted in the intermediate chamber and extending into the lower chamber, the end of the fuse element extending into the lower chamber being of small current carrying capacity, a tension spring mounted in the upper chamber and connected with the fuse, an anchor member disposed between the intermediate and lower chamber to which the fuse element is secured and relieving the fuse section of small current carrying capacity of tension, errules at the opposite ends of the shells with which the fuse ends are connected, an arc quenching material in the intermediate chamber, and releasable packing means between the upper and intermediate chamber to normally retain the arc quenching material against removal.

5. A high tension fuse comprising an elongated.

shell, said shell being divided longitudinally into an upper chamber, an intermediate and a lower chamber, a fuse element mounted in the intermediate chamber and extending into the lower chamber, the end of the. fuse element extending into the lower chamber being of small current carrying capacity, a tension spring mounted in the upper chamber and connected with the fuse, an anchor member disposed between the intermediate and lower chamber to which the fuse is shell, said shell being divided longitudinally into an upper chamber, an intermediate and a lower chamber, a fuse element mounted in the intermediate chamber and extending into the lower chamber, the end of the fuse element extending into the lower chamber being or small current carrying capacity, a tension spring mounted in the upper chamber and connected with the fuse, an anchor member disposed between the intermediate and lower chamber to which the fuse element is secured and relieving the fuse section of small current carrying capacity of tension, ferrules at the opposite ends of the shells with which the fuse ends are connected, an expulsion tube mounted in the intermediate chamber and in communication with the lower and intermediate chamber, arc quenching means in said tube and in the intermediate chamber, and means for venting the intermediate chamber upon blowing of the fuse.

7. In a high tension fuse, a shell having ad joining chambers formed therein, a compound fuse element having a section of small current carrying capacity in one chamber, a connected section of greater current carrying capacity positioned mainly in the adjoining chamber but extending into the first named chamber, means connected with the greater current carrying section of the fuse whereby tension is applied, said small current carrying section fusing first when the fuse blows and forming a preliminary arc, and means whereby the heat of the preliminary arc is utilized to release the main fuse section and to project an arc quenching medium into a second arc formed by the release of the main fuse section.

8. In a high tension fuse device, a shell divided into two chambers, one of large volume and the other of small volume, said chambers containing a fuse element having a portion of lesser current carrying capacity and the other portion of greater current carrying capacity, the

'portion of lesser current carrying capacity being in the smaller chamber and fusing first, and the larger portion in the other chamberfusing second, the gas generated by fusing of the portion of lesser current carrying capacity blowing into the chamber of larger volume throughan aperture formed between the chambers to aid in extinguishing the arc formed by fusion of the larger 'current carrying portion of the fuse.

9. In a high tension fuse device, a shell divided into two chambers, said chambers containing fusible elements, one element of lesser current carrying capacity in one chamber and one of greater current carrying capacity in the other chamber, said chamber containing an arc quenching substance and said lesser current carrying capacity element fusing first and projecting a gas into theA chamber containing the arc quenching incense substance, thereby creating a turbulent action and aiding in extinguishing the arc caused by fusion of said greater current carrying capacity fusing element.

l0. In a high potential fuse of the character described, a removable fuse cartridge comprising a shell having a compartment formed therein containing a fuse and an arc extinguishing substance, a head member forming a closure for one end of the cartridge, a second head member forming a closure for the opposite end of the cartridge, said second head having a sealed discharge orifice formed therein to retain the arc extinguishing substance within the cartridge, a member extending through the seal and connected with the fuse and means for maintaining a tension on said member.

11. In a high potential fuse of the character described, a removable fuse cartridge comprising a shell, a head member on each end of the shell, one head member having a sealed discharge orifice formed therein, a tube carried by the opposite head member and supporting an anchor, said tube having a small chamber formed therein and the cartridge a large chamber, said chambers containing fusible elements, one element of lesser current carrying capacity in the small chamber andv an element of larger current carrying capacity in the larger chamber, said last-named element being attached to the anchor at one end and the opposite end attached to means extend ing through the sealed orifice, and means for applying a constant tension to said means.

l2. In a high potential fuse of the character described, a removable fuse cartridge comprising a shell, a head member on each end of the shell, one head member having a sealed discharge orifice formed therein, a tube carried by the opposite head member and supporting an anchor, said tube having a small chamber formed therein and the cartridge a large chamber, said chambers containing. fusible elements, one element of lesser current carrying capacity in the ysmall chamber and an element of larger current carrying capacity in the larger chamber, said last-named element being attac-hed to the anchor' at one end and the opposite end attached to means extending through the sealed orifice, means for applying a constant tension to said means, and an arc quenching substance in the large chamberl and retained against removal by the head members, said arc quenching substance extinguishing the arc of the larger current carrying portion of the fuse when the fuse blows by being turbulently projected into the arc by gases generated `and discharged from the small chamber into the large chamber and formed by the blowing of the fuse of lesser current carrying capacity.

GEORGE LESLIE HILL.

Images