US3185800A

US3185800A - Vacuum type circuit interrupter with improved vapor-condensing shielding

Info

Publication number: US3185800A
Application number: US259298A
Authority: US
Inventors: Charles H Titus
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1963-02-18
Filing date: 1963-02-18
Publication date: 1965-05-25
Anticipated expiration: 1982-05-25
Also published as: ES296490A1

Description

May 25, 1965 c. H. 'rn-Us 3,185,800

VACUUM TYPE CIRCUIT INTERRUPTER WITH IMPROVED VAPOR-CONDENSING' SHIELDING Filed Feb. 18, 1965 CHARLES H. 77H16,

5V Lf-cm ATTORNEY.

United States Patent 3,185,800 VACUUM TYPE CIRCUIT INTERRUPTER WITH IMPROVED VAPOR-CONDENSING SHIELDING Charles H. Titus, Newtown Square, Pa., assignor to General Electric Company, a corporation of New York Filed Feb. 18, 1963, Ser. No. 259,298 Claims. (Cl. 200-144) This invention relates to a circuit interrupter of the vacuum type and, more particularly, to improved shielding structure for protecting the insulation of such an interrupter from being impaired by the condensation thereon of arc-generated metallic vapors.

It is customary to protect the tubular insulating housing of a vacuum circuit interrupter from such vapor condensation by providing some form of shielding, preferably of metal, located between the insulating housing and the arcinggap of the interrupter. This shielding acts in a known manner to intercept and condense arc-generated vapors before rthey can reach the insulating housing, thus preventing the vapors from condensing on and coating the insulation with metal particles.

In order to prevent any arc present across the arcing gap from transferring to the metallic shielding, it is desirable to space the shielding as far away as possible from the arcing gap. But the amount of spacing available in an interrupter of a given size is limited, and thus the spacing between the arcing gap and the shielding must be limited. In view of this limited spacing, there is a remote possibility under unusual .interrupting conditions that :the arc will strike the shielding.

An object of the present invention is to construct the shielding in such a manner that in the remote event that the arc does strike the shielding, it Will be divided into three series-related arclets.

Another object is to construct the shielding in such a manner as to minimize the chances that a small arc or spark across a gap to the shielding will result in the development of a full scale power arc involving the shielding and shorting out the main arcing gap between the contacts.

Another object is to construct the shielding in such a manner that the metallic particles emitted from the arcing gap will be forced to make at least two bounces before they can reach the insulating housing.

In carrying out the invention in one form, I provide an evacuated envelope comprising a tubular portion of insulating material and a pair of relatively movable contacts disposed within the envelope in a location surrounded by the tubular insulating portion. The contacts are separable to form an arcing gap therebetween across which electric arcs are adapted to be developed. Internally of the tubular insulating portion a pair of tubular metallic shields are disposed for protecting the tubular insulating portion from arc-generated vapors. These tubular shields are spaced from each other in a direction longitudinal of the tubular insulating portion with an annular gap between adjacent ends of the shields. This annular gap surrounds the arcing gap and is located generally in alignment with the arcing gap, considered in a direction longitudinal of the tubular insulating portion. These shields are mounted in electrically isolated relationship` with respect to each other and with respect to the contacts. A third tubular shield surrounds the annular gap and the adjacent ends of the first two shields. The third shield is mounted in radially spaced relationship 4relative to the iirst two shields and is electrically isolated relative to these two shields and relative to the contacts. The three shields are suiiiciently spaced radially outward from ythe contacts that arcs established between the contacts do not normally engage the shields.

ice

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. l is a sectional view through a vacuum interrupter embodying one form of my invention,

FIG. 2 is an enlarged view of a portion of the interruptor of FIG. l.

Referring now to FIG. l, the vacuum type circuit interrupter shown therein comprises a highly evacuated envelope 1G. This envelope 1i) comprises a tubular insulating housing 12 and a pair of

metallic end caps

14 and 16 located at opposite ends of the insulating housing 12. The

end caps

14 and 16 are joined to the insulating housing 12 by means of vacuum-tight seals 18.

The insulating housing 12 comprises a plurality of short tubular sections 2t), 21, 22 and 23, each of a suitable insulating material such as glass. These tubular insulating sections are disposed in colinear relationship and are joined together by metallic tubes 24 forming kvacuum-tight glass-to-metal seals between the insulating sections.

Disposed Within the envelope 10 are two relatively

movable contacts

26 and 28, shown in their fully separated position. The upper contact is a stationary contact, and the lower contact 28 is a movable contact. The

yupper contact 26 is suitably brazed to the lower end of a conductive supporting rod 30, which is integrally joined at its upper end to the metallic end plate 16. The lower contact is suitably brazed to the upper end of ka conductive operating rod 32, which is vertically movable to effect opening and closing of the interrupter.

For permitting vertical motion of the operating rod 32 Without impairment of the vacuum inside the envelope 10, a suitable bellows 33 is provided about the operating rod. This bellows 33 is joined in sealed relationship at its respective opposite ends to the end pla-te 16 and the operating rod 32. A cup-shaped shield 35 surrounds the bellows 33 and protects it from being bombarded by arcing products, as will soon appear more clearly.

The interruptor can be closed by driving the lower contact 28 upwardly into its dotted line position 29, where it engages the upper contact 26. When the contacts are so engaged, current can flow between opposite ends of the interrupter via the

parts

30, 26, 28, and 32.

Circuit interruption is eiiected by driving the contact 28 downwardly from its dotted line position to its solidk line position by suitable operating means (not shown). This downward motion of Contact 2S establishes an arc between the two contacts across an arcing gap 34 located between the contacts. Assuming an alternating current circuit, this are persists until about the time a natural current zero is reached, at which .time it vanishes and is thereafter prevented from reigniting by the high dielectric strength of the vacuum. A typical arc that is formed during the circuit interrupting operation is illustrated at 36.

The arc that is developed during each circuit interrupting operation vaporizes some of the contact or electrode material, and the resulting metallic vapors are ejected radiallyoutward from the arcing gap 34 in all directions.

, For protecting the insulating housing 12 from these metallic vapors, I provide a series of

tubular shields

40, 42, 44, 46, and 48. These shields, which are of metal, cooperate with the

metallic end plates

14 and 16 and the bellows shiel-d 35 to intercept substantially all of the arc-generated vapors before they can reach the insulating housing 12. In this regard, the metallic particles that are emitted from the arcing gap travel in essentially straight line paths from the region of the arcing gap. All of the straight line paths intersect either one of these metallic shields or the

metallic end plates

14 or 16. Most of the metallic particles are condensed on this first collision with the metallic parts,

but a small percentage will bounce oit, being free to leave the surface in any direction but still traveling in a generally straight line path. Essentially all of these rebound paths are intersected by another shield or by the end plates T4 or 16, thus giving the shield or end plate another opportunity to condense the metallic particle. No signicant percentage of the metallic particles appears to bounce oft the condensing surface after the second collision. Thus, no signiticant number of the particles reaches the insulating housing.

The tubular shields 4t) and 44 are disposed in generally aligned relationship and are spaced apart in a longitudinal direction to define an annular gap 5t) therebetween. The annular gap Sti surrounds the arcing gap 34 and is substantially aligned with the arcing gap 34 in a direction longitudinal of the tubular insulating housing l2.

The lower shield 4@ is mounted on a radially extending annular disc 51 that is joined at its outer periphery to one of the metallic tubes 24. At its inner periphery this supporting disc 5l is suitably joined to the tubular shield 40. A similar disc 53 supports the upper tubular shield 44. Since the shields dit) and @d are physically spaced apart by means of the gap Sti and are each mounted on the insulating housing l2 in spaced-apart relationship, it will be apparent that they are electrically isolated from each other. It should also be noted that the lower shield 4@ is electrically isolated from the lower end cap by means of a vacuum gap 56 located between the end cap and the shield 40 and also by means of the lower insulating section Ztl. Similiarly, the upper shield die is electrically isolated vfrom the upper end cap by means of an interposed vacuum gap 58 and tubular insulating section 23.

Surrounding the annular gap 5@ and the adjacent ends of tubular shields itl and 44 is the third tubular shield 42. This tubular shield ft2 is radially spaced from the tubular shields all and le by means of

annular gaps

52 and 54, respectively. The third tubular shield 42 is supported on the tubular insulating housing l2 by means of a metallic disc 57. This disc 57 is suitably joined at its outer periphery to the central metallic tube 24E- and at its inner periphery to shield 4?..

The shields ttl and i4 are spaced a suliicient distance radially outward from the contacts 26 and 2t; normally to prevent any arc between the contacts from striking the shields 46 and 4d. Even though the arc might be located at the radially outermost periphery of the

contacts

26 and 28 and may be bowing outwardly as indicated at 36, it still will not normally strike the shields 4t) and 44. The gap 62 between the contact 26 and shield 44, and the gap 64E. between the contact 28 and the shield itl are long enough normally to prevent the outwardly-bowing arc from striking the shields. Since the shield l2 is located radially outwardly of the shields ttl and 44, there is even less likelihood of the arc striking this shield 412.

Most of the vapors emitted from the arcing gap 3ft are intercepted and condensed by one of the main shields llt), 42 or 44. Sonie of these vapors pass radially outward through the annular gap 50, but they are intercepted and condensed by the central shield 42; before they can reach the insulating housing l2. The aligned relationship of the central shield 42 with the gap 5t) facilitates elective interception of the vapors passing through the gap Sil.

There is a slight possibility that under unusual interrupting condition the arc between contacts 26 and Z8 may bow outwardly enough to strike the shields 40 and de. This would result in a division of the arc into three seriesrelated arclets across the gaps 62k, 50 and d4, respectively. Such a division of the arc would help the interrupter recover its dielectric strength after current zero, thus facilitating interruption, particularly as compared to the case where one or even two arcs to the shielding constitute the current path between the contacts.

For reasons which are no yet clearly understood, it sometimes happens that immediately after interruption there is a transient reduction in dielectric strength across asco one or more of the gaps in the interruptor. If a spark should occur across one of these gaps during this interval of reduced dielectric strength, it is important that this spark not develop into a full-scale power arc, particularly a power arc involving the shielding. I have minimized the chances that such a spark will develop into a full-scale power arc by the above-described division of the shielding into the three

major portions

40, 42 and 44, each electrically isolated from the other and from the end plates 14 and le and the

contacts

26 and 28.

Thus, if a spark should occur across the gap 58 between the upper end plate T6 and the upper main shield 44, there are still gaps 5t) and 56 available to isolate the shield 44tfrom the other end plate 14. This isolation prevents power follow current from flowing and converting the spark into a full-scale power arc. Even if sparks should simultaneously develop across

gaps

56 and 58, the gap 5t) between the shields 4t) and 44 is still available to maintain the electrical isolation between the two end caps 14 and lo. This gap 56 is of such a length that it normally has suiiicient dielectric strength to withstand without breakdown the maximum voltages that are developed between the

end plates

14 and 16. The

gaps

52 and 54, taken together, also have sufiicient dielectric strength to withstand such maximum voltages, thus preventing a breakdown across these gaps, which could short out the gap 50.

As an additional precaution against the gap 50 breaking down under these conditions, I make the gap 50 longer than the gap 34 between the

contacts

26 and 28. Thus, the inter-contact gap 341 is more likely to break down than the gap Se in response to full voltage being applied across the two

gaps

34 and 50 simultaneously. This is desirable because an arc across the inter-contact gap 34 can be handled much more easily than an arc across the gap 50. In this respect, the

contacts

26 and 28 are of a material especially adapted for arcing duty, and also the shielding structure is more capable of protecting the insulating housing l2 trom arcing vapors generated across the nter-contact gap 34 rather than at other locations in the interrupter.

If in spite of all the precautions taken against a breakdown between shields atl and d4, a breakdown should, for some remote reason, still occur, then I prefer that it occur across the gap Sil in preference to series-related breakdowns Iacross the

gaps

52 and 54. One of my reasons for this preference is that an arc present across the gap 5@ can be forced to bow radially inward toward the contacts 26, 2S; thus providing some opportunity for a transrer of the arc to the

contacts

26, 28. Such an arc is depicted at 73 in FIG. 2. The radially-inwardly bowing configuration ot the arc results from the presence of the curls '76) and il at the adjacent end of the

shields

40 and 44. As shown in FIG. 2, these curls would force current flowing to an arc terminal on the curl to follow a path L through the shield that extends radially inwardly to the arc terminal, thus resulting in a radially inwardly bowing conliguration for the current path L.

Another reason for preferring the gap 50 to the gaps 52 and S4 as arc locations is that there is better protection ot the insulating housing from arc-generated vapors when the arc is at 5@ rather than at 52 and S4. In this respect, the shield l2 can still provide effective shielding against metallic vapors generated at gap 50 but would be rather ineffective against vapors generated at gaps S2 or 54.

It should be understood that even it the arc or arcs do develop at some location other than the intercom-tact gap 34, it is still possible for the interrupter to extinguish the arcs. The vacuum will still recover most of its dielectric strength after the iirst natural current zero, thus usually preventing the arcs from reigniting after current zero. It is greatly preferred, however, that all arcing occur at the arcing gap 34 rather than elsewhere in View of the greater suitability of the `contacts for arcing duty and the better shielding that is available when the arcing location is at the arcing gap 34.

As a further example of how my particular shielding reduces the chances for a spark to the shielding developing into a full-scale arc, assume simultaneous sparks across the

gaps

62 and 64 between the contacts and the shielding. Even ythis conditionwould be unlikely to result in an arc. This is the case because there is still the gap 50 available to maintain isolation between electrically opposed ends of the interrupter. Since -this gap 50 can normally withstand the maximum voltage that develops between the end terminals of the interrupter, it can -prevent a further breakdown, which would complete a short circuit path around the

contacts

26, 28 and result in arcs across

gaps

62, 50 and 64. It should be apparent that if the gap 50 were not present and the

shields

40 and 44 were electrically interconnected, the simultaneous occurrence of sparks across the

gaps

62 and 64 would have resulted in the establishment of power arcs.

The manner in which the curls 70 and 71 force an arc toward the main arcing gap 34 has been described hereinabove. Similar curls are provided at the free ends of al1 of the shields for several reasons. One reason is to force any arc that might possibly be established at this point in a direction toward the main arcing gap. This will generally reduce the likelihood that the insulating housing will be coated to an objectionable extent by arc-generated vapors. Another reason for the curls is toreduce the electric stress concentrations adjacent the ends of the shield, which stress concentrations would be present if these ends contained exposed sharp corners.

The end shields 46 and 48 are intended to serve several purposes. One is to intercept any metallic particles that are able to avoid the

main shields

40, 44, and 42. Another is to relieve the glass-to-metal seals from undue electric stresses. With respect to the first purpose, the end shields 46 and 48 preferably overlap their adjacent

main shields

40 and 44 in an axial direction to make any path leading to the insulating housing 12 more tortuous, thus increasing the chances for interception by one of the shields. With respect lto electric stress relief, the

shields

46 and 48, by extending axially inward beyond the end seals, tend to transfer electric stresses from the seals to the inner ends of the shields.

Auxiliary shields 76 and 78 can be provided, if desired, to improve the protection of the insulating

sections

21 and 22 against .arc-generated vapors, particularly when the vapors are being generated at some point such as 50, other than the main arcing gap. These

auxiliary shields

76 and 78 are likewise of a tubular or annular configuration and help to relieve stresses at the glass-to-metal seals that are located immediately thereadjacent.

The capacit-ances between the shields can be relied upon to provide for a desired distribution of voltage along the insulating housing 12. Preferably, the shields are so proportioned and spaced that these capacitances provide for approximately uniform distribution of voltage along the insulating housing 12 and provide for the shield 42 to be at a midpotential relative to the

end plates

14 and 16. A relatively high capacitance is present between each of the

shields

40 and 44 and its respective con-tact assembly, so that a relatively low potential difference exists between each of these shields and its adjacent contact.

While I have shown and described particular embodiments of my invention, it will be obvious .to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United Sta-tes is:

1. A vacuum-type electric circuit interrupter comprising:

(a) an evacuated envelope comprising a tubular portion of insulating material,

(b) a pair of relatively movable contacts disposed within said envelope in a ylocation surrounded by said tubular insulating portion,

(c) said contacts being separable to form an arcing gap therebetween across which electric arcs are adapted to be developed,

(d) a pair of tubular metallic shields disposed internally of said tubular insulating portion for protecting said tubular insulating portion from arc-generated vapors, y t

(e) said tubular shields being spaced from each other in a direction longitudinal of said tubular insulating portion with an annular gap between adjacent ends of said shields,

(f) said annular gap surrounding said arcing gap and being located generally in alignment with said arcing gap in a direction longitudinal of said tubular insulating portion,

(g) means for mounting said shields in electrically isolated relationship with respect to each other and with respect to said contacts,

(lz) a third tubular shield surrounding said annular gap and Ithe adjacent ends of said first two shields,

(i) means for mounting said third shield in radiallyspaced relationship relative to said first two shields and in electrically isolated relationship relative to said first two shields and relative to said contacts,

(j) said three tubular shields being sufficiently spaced radially outward from said contacts that arcs established between the contacts do not normally engage said shields.

2. The interrupter of claim l in combination with fourth and fifth tubular shields respectively surrounding the ends of said first and second tubular shields that are remote from said annular gap in spaced-apart, electricallyisolated relationship relative to said first and second shields.

3. The interrupter of claim 1 in combination with fourth and fifth tubular shields respectively surrounding the end of said first and second tubular shields that are remote from said annular gap in spaced-apart, electrically-isolated relationship relative to said first and second shields, and means for electrically connecting said fourth and fifth shields to the respective contacts of said interrupter.

4. The interrupter of claim l in which the adjacent ends of said first and second shields are provided with radially inwardly extending portions that force current flowing to an are across said annular gap to follow a radially inwardly extending path to the arc terminal.

5. A vacuum-type electric circuit interrupter comprising:

(a) an evacuated envelope comprising a tubular portion of insulating material,

(b) a pair of electrodes of solid material disposed within said envelope in a location surrounded by said tubular insulating portion,

(c) said electrodes having a spaced-apart position defining an arcing gap therebetween across which are developed electric arcs that vaporize material of said electrodes,

(d) a pair of tubular metallic shields disposed internally of said tubular insulating portion for protecting said tubular insulating portion from said arc-generated vapors,

(e) said tubular shields being spaced from each other in a direction longitudinal of said tulbular insulating portion with an annular gap between adjacent ends of said shields,

(j) said annular gap surrounding said arcing gap and being located generally in alignment with said arcing gap in a direction longitudinal of said .tubular insulating portion,

(g) means for mounting said shields in electrically isoaisaeao i lated relationship with respect to each other and with respect to said electrodes,

(h) a third tubular shield surrounding said annular gap and the adjacent ends of said rst two shields,

(i) means for mounting said third shield in radiallyspaced relationship relative to said first two shields and in electrically isolated relationship relative to said rst two shields and relative to said electrodes,

(j) said three tubular shields being sufficiently spaced radially outward from said electrodes that arcs established between the electrodes do not normally engage said shields.

, References Cited by the Examiner UNlTED STATES PATENTS 1/41 Steenback 313-313 9/44 Beldi 313-239 6/59 Crouch 200-144 3/61 Lee ZOO-144 FOREIGN PATENTS 1/32 France.

BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

Claims

1. A VACUUM-TYPE ELECTRIC CIRCUIT INTERRUPTER COMPRISING: (A) AN EVACUATED ENVELOPE COMPRISING A TUBULAR PORTION OF INSULATING MATERIAL, (B) A PAIR OF RELATIVELY MOVABLE CONTACTS DISPOSED WITHIN SAID ENVELOPE IN A LOCATION SURROUNDED BY SAID TUBULAR INSULATING PORTION, (C) SAID CONTACTS BEING SEPARABLE TO FORM AN ARCING GAP THEREBETWEEN ACROSS WHICH ELECTRIC ARCS ARE ADAPTED TO BE DEVELOPED, (D) A PAIR OF TUBULAR METALLIC SHIELDS DISPOSED INTERNALLY OF SAID TUBULAR INSULATING PORTION FOR PROTECTING SAID TUBULAR INSULATING PORTION FROM ARC-GENERATED VAPORS, (E) SAID TUBULAR SHIELDS BEING SPACED FROM EACH OTHER IN A DIRECTION LONGITUDINAL OF SAID TUBULAR INSULATING PORTION WITH AN ANNULAR GAP BETWEEN ADJACENT ENDS OF SAID SHIELDS, (F) SAID ANNULAR GAP SURROUNDING SAID ARCING GAP AND BEING LOCATED GENERALLY IN ALIGNMENT WITH SAID ARCING GAP IN A DIRECTION LONGITUDINAL OF SAID TUBULAR INSULATING PORTION, (G) MEANS FOR MOUNTING SAID SHIELDS IN ELECTRICALLY ISOLATED RELATIONSHIP WITH RESPECT TO EACH OTHER AND WITH RESPECT TO SAID CONTACTS, (H) A THIRD TUBULAR SHIELD SURROUNDING SAID ANNULAR GAP AND THE ADJACENT ENDS OF SAID FIRST TWO SHIELDS, (I) MEANS FOR MOUNTING SAID THIRD SHIELD IN RADIALLYSPACED RELATIONSHIP RELATIVE TO SAID FIRST TWO SHIELDS AND IN ELECTRICALLY ISOLATED RELATIONSHIP RELATIVE TO SAID FIRST TWO SHIELDS AND RELATIVE TO SAID CONTACTS, (J) SAID THREE TUBULAR SHIELDS BEING SUFFICIENTLY SPACED RADIALLY OUTWARD FROM SAID CONTACTS THAT ARCS ESTABLISHED BETWEEN THE CONTACTS DO NOT NORMALLY ENGAGE SAID SHIELDS.