US2082028A - Plunger-type current interrupter - Google Patents

Description

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INVENTOR ATTORNEY H, L. RAWLINS PLUNGER TYPE CURRENT INTERRUPTR Original Filed April l5, 1932 June 1, 1937.

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rrrrrrrrrlrrfrrrrrrlfrr Patented June 1, 1937 PLUNGER-TYPE CURRENT INTERRUPTEB Herbert L. Rawlins, Wilkinsburg, Pa., asslgnor to Westinghouse Electric vt Manuf Company, a corporation of Pennsylvania Application April 15, 1932, Serialr No. 605,398

Renewed October 16, 1935 16 claims. (C1. zoo-120) My invention relates to current-interrupting devices and particularly to devices of the type in which the arc is extinguished by means of a blast of non-ionized gas or vapor.

This application covers a further development of the circuit interrupter disclosed in application Serial No. 568,554, led October 1,3, 1931 by Joseph Slepian.

...It is an object of my invention to provide a device of the class described which shall be adapted to interrupt arcs over a greater range of current values than has heretofore been possible.

It is a further object of my invention to provide a current interrupter of the type employing a movable contactY member With cooperating gasgenerating means and to so select the speed of movement that sucient gas pressure to burst the device will not be developed at any currents at which the device is expected to operate.

It is a further object of my invention to provide a body of arc-responsive material with a passage therethrough of a .varying diameter so arranged that the large cross-section shall be inv the proper position to take partir: the extinguishing of arcs of large current and the smaller cross-section will be active only when arcs of smaller current are being extinguished'.

It is a further object of my invention to insure that the movable member shall not travel into the portion of the passage having a small cross-section beforesuilicient time has elapsed for the extinguishing of an arc of large current value.

It is a further object of my invention to provide a current interrupter, o f the type producing a gas blast, particularly adapted for use in alternating current circuits and in which the gas pressure shall never greatly exceed the pressure developed during thev first; half-cycle by the heaviest are for which the device is intended.

I produce these results by providing a plunger type of circuit interrupter in which the plunger travels through a passage lined with boric acid or other arc-responsive material. The passage is provided with a bell-shaped mouth adjacent the starting point of thearc and the movable electrode traveling through the passage elongates the arc. This brings the arc into the small part oi the passage when it lasts long enough to endure through such a movement of the plunger. This can occur only at small currents because at heavy currents suiiicient gas is generated to extinguish the arc While the plunger is still Within the bell.

I provide a suiiicient inertia in the plunger to insure that its motion will be slow enough to acturing avoid elongating a heavy-current arc into the small part of the passage and thus avoid the development of heavy gas pressures.

Other objects of my invention will be manifest and a better understanding of the details of construction will be obtained by reference to the following detailed description and the accompanying drawing, in which Figure l is a longitudinal sectional view of one form of my device.

Fig. 21s a view partly in section and partly in side elevation illustrating another form thereof.

Fig. 3 is a similar view illustrating a third form.

Referring to Fig. l, a cylindrical tube I of fibre or other insulating material is provided at its lower end with a metallic cap 2 adapted to cooperate with clips or other devices at one terminal of the circuit with' which the current interrupter is to cooperate. The other end of the tube l is provided with a metal sleeve 3 which may serve for connection to the other terminal cf the circuit directly or by means of a metallic prolongation t.

A metallic washer 5 is connected to the cap 2 in any convenient or suitable manner.

construction which I have chosen for illustration,

the metallic lining 6 aiords this connection.

Bearing against the washer 5 and filling the tube from this washer to the junction with the sleeve 3, l provide a body 1 of material which,L

when exposed to an arc, will evolve a gas, vapor or other emanation capable of acting upon the arc to increase the time rate of deionization.

This lining may be provided by compressing boric acid with a pressure of 5 to l5 tons per K square inch in suitable moulds to form blocks or brickettes of a size to t the tube i.

The

brickettes are moulded with a central opening to provide the passage 8, which extends. through the whole body of boric acid. Instead of boric acid, alternate discs of hard libre and fullerboard discs may be provided. The ullerboard is somewhat more edective if soaked in oil but the device is not then Aas permanent.

stances which can .beused are borax, aluminum 4 Other subborate, compressed naphthalene, salicyclic acid and silicio acid. Boric acid is a most desirable material since when acted upon by the arc it gives oi water vapor which is non-inflammable and readily condensed.

A plunger il is located in the passage 8 and is d secured at one end to the sleeve 3 by a fusible link i2 having a reduced section which melts initially. The plunger lits the passage as closely as may be without friction.

This is much closer than In the 2 illustrated inthe drawing. Ihe link is soldered or otherwise secured to the adjacent end of the plunger II and is attached to a flange 8 extending inwardly i'rom the sleeve l by any suitable mechanical fastening such as the screw I3. The opposite end of the plunger i I is attached to a disk I4 which serves as one abutment for a spring I5, which bears against the washer l either directly or through an inturned flange of the sleeve 6. Flexible connecters Il extend from the flange I4 to the sleeve I and thus aii'ord connection between the plunger I'I and the cap 2 in all positions of the plunger II.

I'he extension 4 mounted upon the sleeve 3 contains copper washers I1 alternating with metallic spacing rings "I8, the pile of alternating rings being secured together and fastened within the extension 4 by bolts I8 which also secure the extension 4 to the sleeve 3 and secure a cap ring 2l in place at the end of the extension 4. 'I'he cap ring may be provided with a central opening through which gases can escape or this opening may be closed by a stopper 2'I as illustrated in the drawing.

In Fig. 2 the construction is similar to that illustrated in Fig. 1 but a different means is provided in piace of the fusible member I2 for opening the circuit. Two contact springs 22 are mounted upon the flange 9 of the sleeve I and the plunger I I in its normal position extends between the contact springs 22 and is thereby electrically connected to the sleeve 3. A weight 23 at the lower end of the plunger I I moves the plunger downwardly when released A exible connection Il similar to the connection I8 in Fig. 1, connects the plunger I I to a cap 24 which cooperates with clips in the same way asthe cap 2 in Fig. 1,

' The weight 28 is normally restrained by a catch 2l which is released by a magnet 28. 'Ihe conductor 21 leading to the magnet 28 may bein shunt to the circuit in which the current interrirpter is inserted, or it may extend to an independent circuit intended to control the current interrupter. 'Ihe magnet is connected to the cap 24 and the circuit which controls the magnet is completed through the clips or other contact devices which cooperate with the cap 24. y

A similar arrangement including' contact springs 22 is provided at the upper end of the plunger II in Fig. 3. The weight 23 and connecter vII at the lower end-are similar to the corre-l sponding parts in Fig. 2. The catch 30, corresponding to the catch 25 in Fig. 2, is spring pressed to release position and is held in the illustrated position by a fusible wire II. 'Ihe conductor I2 leading to the wire ll may be connected either to a shunt of the mainclrcuitor to a `control circuit as explainai in connection with the conductor 21 in Fig. 2.

A connecting device Il for the conductor 32 is mounted upon but insulated from thel bracket I4 which extends from the cap 24. One end of the fusible wire 8l is secured by the connecting device 8l and the other end thereof is mechanically secured to the tail of the catch 80, but insulated therefrom by the insulation l5. A connection extends from the wire 8l to the bracket 84 and thus to the cap 24.'

In the operation of that form of the device illustrated in Fig. l, when the current flowing'between the sleeve 3 and the cap 2 exceeds a predetermined value, the link I2 is melted at its reduced section. The spring I5 moves the plunger II downwardly. This motion will, however, be slow compared with speed oi the separating electrodes usual in circuit interrupting devices oi' the type in which the link is ejected. Where the link is a fine wire or strip as has been used in the past, the inertia of the link is so small that it is ejected at a high rate of speed rather than at the slow speed of the device .of my invention. Preferably, this slow movement is accomplished by making the plunger II a thick rod of copper, thereby giving it considerable inertia, and selecting for the spring I5 one which cannot exert force enough to accelerate the heavy plunger II to more than a moderate speed. Preferably, these constants are so chosen that the plunger Il will require from 3 to l0 cycles to travel the full length of its movement.

Another consequence of choosing a thick rod for theplunger II is that it will not yield under the gas pressure developed and, by bending, jam against the sides of the passage 8. Should the plunger Jam, it might be prevented from traveli ing far enough to extinguish the arc. I'hen the arc would continue until gas enough was evolved to burst the tube:

When the fuse I2 ilrst melts, an arc is formed within the flared or bell-shaped opening 31 of the passage 8. The current which melted the fuse I2 may have been barely suiiicient to melt it, as would be the case when a small overload existed in the circuit, or it may be very much heavier than this, as would be the case when a short will, therefore, act vigorously upon the walls of the bell-shaped opening 31 and cause the rapid evolution of gas. Ihis gas, flowing through the ionized gas in the arc itself, causes rapid extinc- ,tlon of the arc.

The current being anv alternating current, passes through zero at each half cycle and for heavy currents it is intended that the gas generated in. the first half-cycle shall be suiilcient to prevent a restriking of the arc when the voltagerises again in the second half-cycle. The total quantity of gas evolved will not be very great even though the current be heavy because of the short duration of the arc. Because this arc is of short length, it acts upon only a small area of the boric acid. This is another reason why, although the current is heavy, the quantity of gas evolved is not excessive. The gas pressure built up will therefore, be insuiilcient to burst the tube.

The hot gases, consisting principally of water vapor, pass into the space provided by the openings in the washers I1 and I8 which, being of copper and presenting a large surface, quickly cool the water vapor. 'I'he advantage of retainy ing the gases within the tube and removing the pressure by cooling them is, that a flame is not produced outside of the tube when the device operates. If the situation is such that such a llame may be permitted, the cap plate 2| may be omitted and the gases pe'rnriitted to escape at the top of the device. It willv then be permissible to build the device of dimensions and materials which can withstand less internal pressure Whether the vapor moves upwardly because of condensation by the washers or because of a provision for escape to the outside atmosphere at the top of the device, the gas is directed as a blast against the arc and a turbulent mixture of ionized and non-ionized vapors results which is effective in extinguishing the arc.

When the current which melted the fuse l2 is small, the arc generated is not capable of effectively heating the Vwalls of the bell-shaped opening 31 because the large cross-section of the opening provides a considerable distance between the arc and the walls. Under these circum;

stances, as the member II moves under the in? luence of the spring I5 it causes an elongation of the arc. The lower end of the are will then be in the passage 8 which, being of small crosssection, produces an intimate contact between the arc and the boric acid or similar material.

The quantity of gas evolved is increased because of this more effective action of the arc upon the material.

bell-shaped opening 31 causes an even greater intermixture between the evolved gases and the ionized gases and deionization is thereby quickly effected. Even Vwith currents barely suicient to melt the member I2 the arc will not be rekindled after passing through zero more than a few times, because sufficient deionizing effect is produced to prevent such rekindling.

When the current is heavy, the gas is evolved quickly because the energy of the arc is so great that, even while it acts upon a very short and mouth of the tube. vIt is thereby more eiectively mixed with the ionized gas and so more eiectively hastens deionization. e

These circumstances suiliciently overcome the slower evolution of the gas to largely deionize the interior of the passage. Then when the current passes through a zero value, the rise of voltage in the next half-cycle will not rekindle the arc.

VThe slow evolution Vof the gas permits more time for the condensing action of the washers vI'I and rings I8 to relieve the pressure or for passage of gas through the end of the tubes if left open. Thus, even if slightly more gas should be evolved with arcs of small currents, the gas pressure will not rise above that generated by an arc which is extinguished during the rst half-cycle.

I find therefore that a tube with sumcient mechanical strength to withstand the pressure developed by an arc of heavy current during one half-cycle will sulce for the whole range of current values.

By making the motion of the member II too slow to draw a heavy arc into the restricted portion of the passage within a half-cycle, I ensure that a heavy-current arc is never in position to act upon a large area of closely adjacent material and so avoid the development of dangerous pressures because after the half-cycle has elapsed the heavy Varc has been extinguished.

For arcs of intermediate current strength, the quantities discussed above are of intermediate value but in no instance does the resultant gas pressure rise above that just stated.

In the form shown in Fig. 2, the plunger can be released by sending a current through the conductor 21. This current may be derived by a shunt from the current through the circuit to be 'I'he long passage through 'which the gases must pass to emerge into the protected and may, therefore, be proportional to the main current.- If desired, however, the conductor 21 may be supplied with current from an independent source and energized when it is desired to operate the circuit interrupter.

When the magnetv 26 is energized it moves the hook 25 and releases the weight 23. The plunger II is then moved downwardly by the motion of they weight. The acceleration which it thus receives is in no case (materially) greater than that due to the action of gravity upon the weight 23. The plunger II being rigid cannot buckle under the iniiuence ofthe gas pressure and aiord a stoppage for the passage 8. Moreover, the gas pressure against the upper end of the plunger is small compared to the action -of gravity upon the mass 23 and will not materially accelerate the movement. It is therefore assured that the plunger il will never move downwardly fast enough to bring the arc, corresponding to a heavy current, into the narrow part of the passage 8. This prevents evolution of an undesirably large quantity of gas with the accompanying danger of bursting the tube.

In the structure shown in Fig. 3, current through the conductor -32 may be either from a shunt or from a separate control circuit. When this current exceeds a predetermined value, the fusible wire 3| is melted, with the result that the catch 3D moves under the action of its spring and releases the weight 23.. The operation of this form of device thereafter islexactly like that for the form shown in Fig.,2.

When the device shownin Fig. l has operated, it may be restored to original condition by replacing the fused member I2. I have found the most convenient method of doing this is to supply a new rod II with a member I2 attached thereto. The repair man will detach the old memberv II from the disk I4 and attach the new one in its place. Then by compressing the spring lI5 the new member I2 is brought into its place and is secured there by the screw I3. Y

In the form shown in Fig. 2, it is only necessary to push up the weight 23 and the catch 25 automatically engages it. In the form shown in Fig. 3, the fuse wire 3| must be replaced after the weight 23 has been raised and the catch 30 forced into engaging position.

In all three forms, each operation of the device enlarges the passage 8 by destroying some of the boric acid. VThe devices may not be used more than a limited number of times for this reason.

After that the packed material must be renewed.

In Fig. 1 the relation between the the stiffness of the spring I5 and the inertia of the rod II must be correctly chosen to give the proper speed to the movement of the. rod. In Figs. 2 and 3 the combined mass of the weight 23 and the rod II must be so chosen that the combined effect of gravity and gas pressure shall give the proper speed to the rod. The arc-current goes through zero each half-cycle. During the next half-cycle the voltage rises and if the length of the gap has not become too great the arc will be rekindled. If the motion of the rod II is too slow this will happen notwithstanding the evolved gas. On the other hand if the movement of the rod Ii is too rapid the arc corresponding to a strong current will be elongated into the passage 8 so far before the current reaches its zero value in the first half-cycle that the area of contact between arc `and boric acid will be too great and there will be evolved enough gas to burst the tube.

I have found that two inches per cycle is about 75 along said pas ig il E bers to produce an arc l ...Neon

of said moving member heilig e to require more than two cycles to traverse the length oi' said passage.

2. In a device for interrupting alternating currents, a body of material responsive to an arc to evolve an arc-destroying cmanation, said body having a passage therethrough, of a length esW seeding that at which an arc can be struck in open air by the highest voltage expected in the normal use of the device, two electrically com nected members, said members being joined by fusible means for releasing one of said members, means for moving the released member along said passage, thereby separating said members to pro duce an arc between them. the speed of said moving member being slow enough to require more than two cycles to traverse the length oi said passage.

3. In a device for interrupting alternating cur-l rent, a body of material responsive to an arc to evolve an arc-destroying emanation, said body having a passage therethrough, fusible means for causing an arc, and means for causing it to be elongated in said passage, the rate of elongation being approximately two inches per cycle.

` 4. In an alternating current circuit interrupting device, fusible means for producing an are, a body of material responsive to an arc to evolve an arcdestroying pressure-producing emanation, said body having a passage therein, means for elongating the arc produced by said fusible means by causing it to be drawn into said passage, said means including a movable electrode and means restraining the motion thereof to a speed which is not substantially greater than two inches per cycle.

5. In an arc-extinguishing device, a body of material responsive to an arc to evolve an emanation destructive of the arc, said body having a passage therein, an arc electrode having a fusible portion in said passage movable in the direction to elongate the arc and said passage being progressively restricted in said direction;

6. In a current-interrupting deviceI a body of material responsive to an arc to evolve an arcdestructive emanation, said body having a passage therein, fusible means for producing an arc and means for elongating said arc within said passage, said passage flaring toward the origin of said arc.

7. In a current-interrupting device, a body of material responsive to an arc to evolve an arcdestructive emanation, said body having a passage with a flared mouth, means having a fusible section for initially producing an are at said mouth, means tor elongating said arc within said passage.

W enough 3. In a current-interrupting device, a body of material responsive to an arc to evolve an arcdestructlve emanation, said body having a passage therethrough with a dared mouth, means having a fusible section at said mouth for producing an are at said mouth means :for elongating said arc within said passage and means lor restricting the ilow of said einanation out of said passage at the other month thereof".

o div o. body `ions evolve iianimablo, condensabie vapor, .i lor housing an are iii intimate contact vv. ierent` portions of said body and causing aies ol? one current intensity to be :finally extinguished in contact Witli one part ol said body defining an opening of large cross-section and arcs ci" another current intensity to be finally extinguished in contact with another part of said box defining an opening of small cross-section.

ll. In a circuit interruptor, a body of material l responsive to an arc to evolve a noninfiammable, readily condensable vapor, a tubular passage through said body, said passage being oi' a large size adjacent one end and a smaller size adjacent the other end, and means movable through said passage for drawing the arc therein, said means initially drawing the arc at the large end of said passage and later drawing the arc into the smaller end of said passage. y

12. In a circuit interruptor, means of insulating material having a passage therethrough, said passage having a considerable length of substantially uniform width and having a portion which increases in, width from said portion of uniform width, means for initially causing an arc at the wide portion of said passage and drawing it into said portion of uniform width.

13. In a circuit interruptor, means of insulating material having a passage therethrough, said passage having a considerable length of substana cross-section which substantially lls the portion of said passage of uniform width, and said conducting member initially causing the arc at the wide portion of said passage and being movable to draw the arc into the portion oi' said passage oi' uniform width.

14. In a fuse, means of insulating material having a passage therethrough, said passage having aportion of substantially uniform width at one end thereoi` and said passage increasing in width at the other end thereof and being open at said wide end, a rigid conducting member extending through said passage and having a crosssectional area such as to substantially close the end oi' said passage oi' uniform width, said con ducting member having a portion of fusible material. adjacent the open wide end of said passage for causing an arc and being movable to draw the arc into the passage.

15. In a circuit interruptor, means of insulat- .ing materialhaving a passage therethrough, the

inner wall of said passage having portions of a material which gives off an arc extinguishing substance when acted upon by the arc, said passage having a considerable length of substantially 5 uniform width and having a portion which increases inwidth from said portion f uniilcu'xnv width,means for initially causing an are aty the wide portion of said passage and drawing it into said portion of uniform width.

0 16. In a fuse, means o! insulating material having va passage therethrough, the inner wall of said passage having portions et a material which gives on an are extinguishing substance when acted upon by the arc, said passage having a portion of substantially uniform width at one end thereof and said passage increasing in width at the other end thereof and being open at said wide end, a rigid conducting member exfor causing an arc and being movable to draw the arc into the passage.

HERBERT L. RAWLHIS.

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