US3626125A

US3626125A - Leak detecting means for vacuum switches

Info

Publication number: US3626125A
Application number: US877811A
Authority: US
Inventors: Akira Tonegawa
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1968-11-22
Filing date: 1969-11-18
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: GB1277935A; JPS4945434B1

Abstract

In a vacuum switch having a highly evacuated envelope and a pair of separable electrodes located within the envelope, the vacuum switch is positioned within an oiltight enclosure such that a space defined between the enclosure and the envelope of the vacuum switch is filled with an insulating oil. The oil within the enclosure may penetrate into the envelope of the vacuum switch when a leak occurs in the vacuum switch. The enclosure communicates with a detector which detects any leak that may occur in the vacuum switch.

Description

United States Patent LEAK DETECTING MEANS FOR VACUUM SWITCHES [56] References Cited UNITED STATES PATENTS 1,796,746 3/l93l Buchholz 200/6l.03 X 3,206,569 9/l965 McCarty 200/144 B X 3,404,247 10/1968 Glassanos 200/ 144 B Primary Examiner-Robert S. Macon Attorneys- Robert E. Burns and Emmanuel J Lobato ABSTRACT: In a vacuum switch having a highly evacuated envelope and a pair of separable electrodes located within the envelope, the vacuum switch is positioned within an oiltight enclosure such that a space defined between the enclosure and the envelope of the vacuum switch is filled with an insulating oil. The oil within the enclosure may penetrate into the envelope of the vacuum switch when a leak occurs in the vacuum switch. The enclosure communicates with a detector which detects any leak that may occur in the vacuum switch.

6 Claims, 2 Drawing Figs.

U.S. Cl 200/144 B, ZOO/61.03, ZOO/I50 Int. Cl ..H01h 33/66 Field 0! Search ZOO/144.2, 6l.03,6l.04,15Q

M l4 1 20% &

lJRlVE MEANS PATENTED nu: 1 I97: 3626125 sum 2 or 2 FIG.2

BACKGROUND OF THEINVENTION The present invention relates to means for detecting the lowering of vacuum in vacuum switches.

As is well known in theart, vacuum switches have electrically superior characteristics in comparison with ordinary air circuit breakers in that they provide an extremely large dielectric strength during the separation of electrodes thereof because of extremely high dielectric strength of high vacuum, in which the electrodes make and break an electric circuit having a relatively high voltage level. For this reason, there may be provided an extremely small distance between the contact surfaces of the electrodes to resist a high voltage thereacross, whereby the switch structure becomes smalland inexpensive to manufacture. in addition, the vacuum switch has further advantages including an excellent electric power interrupting performance due to a rapid difiusion of metal vapors generated by the high-temperature are drawn out between the separated electrodes.

However, such a vacuum switch has a significant defect, in spite of the aforesaid advantages, which relates to the leakage at sealed portions of the highly evacuated envelope thereof. Generally, the vacuum switch comprises an envelope made of glass or ceramic material and highly evacuated to a degree of vacuum of the order to 10* mm. Hg, a stationary electrode having its one end disposed within the envelope and the other extended vacuum-tightly through a wall of the envelope, a movable electrode having opposite ends similar to those of the stationary electrode, metal bellows arranged around an intermediate portion in the lengthwise direction of the movable electrode thereby to form a vacuumtight structure between the envelope and the movable electrode and the maintain flexibility for moving the movable electrode. Further, the vacuum switch has an exhausting pipe which is sealed off after exhausting of the interior of the envelope.

When the switching operation has been repeated through many cycles for a long period of time, or if a crack develops in the metal bellows, the vacuum switch becomes incapable of holding a high vacuum therein. Such vacuum breaking would also take place due to a leak at the brazed portions of any component of the envelope as well as an unperceived crack in the exhausting pipe which is likely to be caused by an accidental force which maybe applied thereto during the handling operation of the vacuumswitch. In this case, it is impossible for the switch to satisfactorily perform its interrupting function owing to the loss of high vacuum which provides a high dielectric strength across the electrodes.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved vacuum switch incorporating detecting means capable of reliably detecting a loss of high vacuum within an envelope thereof, thereby preventing danger due to the impossibility of effecting electric power interruption in an electric power circuit.

ln accordance with one aspect of the invention, there is provided at least one vacuum switch comprising a highly evacuated envelope made of an insulating material and a pair of electrodes so disposed within said envelope that they are movable relative to each other to make and break an electric circuit. There is also provided a liquid-tight enclosure enclosing the vacuum switch with an insulating liquid and having at least one opening, and the liquid within the enclosure is communicates with that within an enclosed tank through openings provided in the walls of the former and the latter, respectively. The tank functions as a level gauge for the liquid enclosed therein, and the level of the liquid varies when the vacuum within the vacuum switch is broken.

The above-mentioned objects and characteristic features of the present invention will be described in detail in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing:

FIG. 1 is an elevational view, in vertical section, showing leakage-detecting means embodying the present invention; and

FIG. 2 is a schematic diagram of a power transformer with an onload tap changer embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a vacuum switch shown therein and generally designated by reference numeral 10 normally includes a highly evacuated envelope 47 made of an insulating material such as glass or ceramics, a stationary rodlike electrode ll vacuum-tightly extending through an upper wall of the envelope and having a butt contact surface at its lower end, a movable rodlike electrode 12 movably extending through a lower wall of the envelope and having a butt contact surface at the upper end thereof, and metal bellows l3 arranged between an opening 14 on the lower wall of the en velope and an intermediate portion in the lengthwise direction of the movable electrode.

ln accordance with the present invention, the vacuum switch 10 is mounted within an enclosed enclosure 15 which comprises a cylindrical insulating member 16 and upper and

lower covers

17 and 18 for the cylindrical member 16 to liquid-tightly close upper and

lower openings

19 and 20 of the cylindrical member. The interior of the enclosure 15 is filled with any suitable insulating liquid 21, for example, an electric insulating oil or pure water, for a purpose hereinafter described. The

cover plates

17 and 18 are made of metal and serve as supports for the vacuum switch 10 and so sealing means for preventing leakage of the liquid 28 out of the enclosure 15. The cylindrical member 16 functions to insulate one of the electrodes from the other.

Stationary electrode 11 extends outwardly at one end thereof through upper cover 17, and, of course, a suitable oiltight means is provided at the part where the rod passes through the cover. Similarly, although the movable electrode 12 slidably extends through the lower cover 18 there are provided an oil seal 22 to prevent leakage of the liquid 21 and a guide bearing 23 to slidably support the rod.

To move the movable electrode 12 against the stationary electrode 11 between the closed and open positions thereof, the lower end of the movable electrode, which is disposed outward of the enclosure, is connected through an operating tubular rod 24 made of an insulating material to a drive means 25, which is shown by dash lines and reciprocatingly drives the rod along its longitudinal axis. The drive means 25 may be an electromagnetic actuator, a motor operating mechanism, or a hydraulic actuator.

To detect a leak in the vacuum switch 10, there is provided an oil leveler or tank 26 which includes a cylindrical casing 27 containing a quantity of oil 28 and a space 29 above the surface of the oil therein. The tank 26 has a partition plate 30 disposed therewithin to form an upper wall of the space 29 and a tubular pipe member 31 depends from the plate 30 to a point near the bottom of tank 27. The upper opening of the tank 37 is closed by a cover plate 32 which also functions as an oil packing for the tank and has also a tubular pipe 33 integrally formed with the plate 32 and having an opening 46. The lower end of an elongated tubular pipe 34 is oil-tightly attached around the pipe 33 on the cover plate 32, and the other end thereof is oil-tightly attached to the bottom of the enclosure 15 through a flanged packing member 35 and an opening 36 formed in the bottom cover 18 of the enclosure.

Thus the oil 21 in the interior of the enclosure 15 can communicate with the oil 28 within the tank 26. On the outer side of the wall of the tank 26 is mounted an oil leveler 37 which comprises a part of the sidewall of the tank 26, aframework 38 and a window 39 made of a transparent material, for example, glass or a synthetic resin. To electrically detect the oil level in the tank 26, there are provided a pair of bridge contacts 40 (only one of which is shown) disposed at the lower portion in the oil leveler 37, and a movable contact 41 floating in the oil of the leveler. The sidewall of the tank 26 at the upper and lower portions of the leveler is provided with

openings

42 and 43, respectively, which connect the interior of the tank 26 with that of the leveler.

The closing of the bridge contacts 40 by the floating contact 41 is transmitted to an alarm 44 and the drive 25 for the vacuum switch through a pair of conductors 45.

In operation, the vacuum switch makes and breaks the electric circuit connected thereto (not shown) by the operation of the drive means through the insulating tube member 24 connected at its upper end to the lower end of the movable electrode 12. When variations in the volume of the oil in enclosure occur due to the variations of the ambient temperature, a part of the oil in the enclosure flows into the tank 26 through opening 36, pipe 34, opening 46 and pipe 31, and vice versa, whereby the variations of the oil in the enclosure 15 are efiectively absorbed by the space 29 above the oil surface in the tank 26. Accordingly, the tank 26 also acts as an oil conservator.

It will be assumed that a malfunctioning has occurred in the vacuum switch 10, which comprises any one of the aforesaid ones, for example, a leak due to a crack in bellows l3 and leaks at the brazed portions which lie at the portions between envelope 10 and electrodes 11 and 12 as well as those which lie among bellows l3, envelope 47 and movable electrode 12. It will be apparent that the oil 21 within the enclosure 15 will then flow into the interior of envelope 47 through any one of the aforesaid damaged portions of the vacuum switch thereby to fill the space within the envelope with oil. To make up for the insufficiency of the oil in the enclosure, the oil 28 contained in the tank 26 moves into the enclosure 15 through an oil path which comprises the tubular member 31, an opening 31, an opening 46 of the cover plate 32, the insulating tubular pipe 34 and the opening 36 arranged on the bottom plate 18 of the enclosure. Thus, the surface of the oil 28 in the tank 26 will take a new lower level substantially corresponding to the amount of oil which has entered into the envelope of the vacuum switch, and the floating contact 41 will engage with the bridge contacts 40.

This causes the circuit comprising a pair of conductors 45 to close, exciting the alarm 44 to inform the operator that damage has occurred in the vacuum switch 10 and, at the same time, interlocking the drive means 25 in such a way that it cannot perform the make-and-break operations for the vacuum switch. Thus, dangerous and make-and-break operations of the vacuum switch, which may occur in atmospheric circumstances out of high vacuum, can be effectively eliminated.

The apparatus disclosed herein can be adapted for the electric power circuit interrupter for an electric power circuit in which a vacuum switch is employed as the power interrupter.

Furthermore, a more significant utility of the present invention lies in its application to an onload tap changer for an electric transformer as shown in FIG. 2. In FIG. 2, like parts are denoted by the same numerals as those employed in FIG. 1, and for simplifying the illustration, the outer casing 48 for the transformer is shown only with a chain line. Within the casing there are installed a tapped winding 49 schematically illustrated and having a plurality of odd-numbered taps la, 3a and 7a and a plurality of even numbered

taps

2b, 4b, 6b, and 8b together with a magnetic core (not shown). There are also provided four

vacuum switches

10a, 10b, 10c and 10d in the casing 48, wherein pairs of 10a and 10b are combined with a tap selector switch 50, whereas other pairs of 100 and 10d are,

57, 58 and 59 mounted thereon and engaged with the movable electrodes of the vacuum switches, respectively, to perform switching operation in a predetermined sequence. In addition, the output of gearbox 52 is also connected to

selector switches

50 and 51 to effect the changing switch operations in a predetermined sequence. The aforesaid parts are located within the casing 48 with an electric insulating and cooling oil 60 except the motor 53 and the gearbox 52.

The stationary electrodes 11a and 11b of pairs of

vacuum switches

10a and 10b are connected with each other through a current limiting resistor 62, connecting the electrode 11a to selector switch 50, similarly connecting the stationary electrodes 11c and 114 to each other through a resistor 63 and connecting the electrode to selector switch 51. While all of the

movable electrodes

12a, 12b, 12c and 12d are connected together with and connected to a high potential terminal (not shown).

It will be assumed that there is a necessity to raise the tap position due to a rise in the input voltage of the transformer when the

selectors

50 and 51 are positioned as shown and only the vacuum switch 10a is closed. The motor 53 is then energized in response to the operation of a voltage relay (not shown) and drives the cam shaft 55 and

selector switch

50 and 51 through gear box 52 and bevel gears 54. The cam shaft 55 drives a series of earns 56 to 59 in a predetermined direction thereby to switch the vacuum switches 10a to 10d in turn as follows.

First, the switch 10b closes, after which switch 10a opens, and, at the same time, switch 10d closes, whereby taps 5a and 5b are simultaneously connected through

resistors

62 and 63 to the high potential terminal, and a short circuit occurs across the taps 4a and 5a momentarily. However, the short circuit current is suppressed to a relatively small value by both

resistors

62 and 63. Then the switch 10b opens, switch 59 closes, then switch 58 opens, and lastly the selector switch 50 is changed from tap 5a to 3a.

Thus, it will be apparent that a higher voltage tap 4b has been selected instead of tap 5a. it can be seen that the tap changing operation is also made in a reverse direction when the input voltage for the transformer exceeds a predetermined value, and, thus, the output voltage of transformer is always adjusted to hold the predetermined value.

A relay box 62 is provided on the cover plate 61 of the easing 48, which box includes four bellows 63 to 66, the interiors of which are separately communicated within four enclosure 15a to 15d through insulating tubular members 67 to 70, respectively, and there are provided insulating liquid or noncompressible fluid 21a to 21d within the prescribed parts, respectively. Normally closed

contacts

71, 72, 73 and 74 are combined with the bellows, which contacts are connected in series with the circuit 45.

When a leak occurs in any one of the vacuum switches 10a to 10d, the oil within enclosures 15a to 15d enters into corresponding damaged vacuum switch in which the leak has occurred, thereby causing the dimension of corresponding bellows to decrease and opening any one of the corresponding contacts 71 to 74. Accordingly, the circuit comprising conductors 45 opens to generate an alarm and at the same time to stop the tap changing operation which is initiated by motor 53 as well as to deenergize the transformer.

Thus, the tap changing operation for a transformer with an onload tap changer is positively prevented from being affected by the vacuum-broken vacuum switch of the onload tap changer. In an embodiment of the invention as shown in FIG. 2, it is preferred that the same oil be utilized to fill the enclosures 15a to 15d as well as the casing 48 for the purpose of preventing mixing of different kinds of oils, whereby the dielectric strength of one oil is not affected due to that of the other.

What 1 claim is:

1. Switching means to make and break an electric circuit comprising a vacuum switch including a highly evacuated insulating envelope and a pair of separable electrodes having their one ends located within said envelope to be engageable with each other,

a liquidtight enclosure arranged around the vacuum switch and having at least one opening extending through a wall thereof,

said enclosure being made of an insulating material and filled with a noncompressible fluid,

means for detecting the volume of said noncompressible fluid within said enclosure which has penetrated through said envelope of said vacuum switch and entered thereinto, said detecting means comprising an enclosed liquid leveler tank, I

an insulating tubular member connected between the inside of said tank and the inside of said enclosure,

said tank being partially filled with an noncompressible fluid so as to leave a space above the fluid level therein and having a tubular pipe one end of which is communicated with one end of said insulating tubular member, and the other end is opened in the noncompressible fluid near the bottom of the tank, and an electrical floating switch means arranged in the fluid of said tank and responsive to the fluid level variations in the tank.

2. Switching means according to claim 1, in which said floating switch is connected to electric circuit means which includes an alarming circuit and/or an interlocking circuit for a drive means which make and breaks said vacuum switch,

said drive means being adapted to become inoperative in response to output signals of said interlocking circuit.

3. Switching means according to claim 1, in which said noncompressible fluid is an electrical insulating oil.

4. Switching means according to claim 1, in which said noncompressible fluid is water.

5. Switching means for a tap changing electrical power transformer which includes an enclosed casing, a tapped winding enclosed within the casing with an electrical insulating oil and a tap changing mechanism for the tapped winding.

a plurality of oiltight enclosures immersed in said oil in said casing,

vacuum switches disposed within said enclosures, respectively, connected to the taps of said tapped winging and operated by said tap changing mechanism,

each said vacuum switch being arranged within said enclosure in a manner to leave a space filled with an insulating oil therebetween, respectively, and

a plurality of bellows mounted on the outer sides of said enclosures and communicated inside of the bellows with said spaces in said enclosures through insulating tubular members, respectively, and

at least one contact operatively mounted on said bellows,

respectively, thereby to detect the shrinkage of the bellows in response to penetration of said oil within said enclosure into said vacuum switch disposed in the enclosure.

6. Switching means to make and break an electric circuit,

comprising:

a vacuum switch including a highly evacuated insulating envelope and a pair of seperable electrodes having ends located within said envelope and engageable with each other,

a liquidtight enclosure enclosingsaid vacuum switch and having walls conforming generally to but spaced from said envelope, the space between the enclosure and the envelope having a limited volume of the order of magnitude of the volume of said envelope, said enclosure being filled with a noncompressible liquid,

a liquid leveler reservoir means connected with said enclosure to keep said enclosure full of liquid, said reservoir means having a liquid volume that is variable according to liquid required by said enclosure,

and signal means for detecting a decrease in said liquid volumein said reservoir meansbelow a set level, whereby if liquid leaks from said enclosure into said envelope the resulting decrease in liquid volume in said reservoir means results in actuating said signal means.

i i l 1. IIK

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. $626,125 D d December?) 1971 Inventor) Akira TONEGAWA It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 20, delete "are" and insert -arc-;

I 'line delete "l0 and irisert --10" I Columri line 33, delete I so" and insert --as--; I

. line delete "37" and i sert- 27";

Columh 6-, line 4, delete "winging" and insert--winding-.

Signed-and sealed this 2nd day of July- 1974.

SEAL Attest: v

EDWARD M.FLET.CHER,JR. c. MARSHALL DANN Attesting Officer I Commissioner of Patents USCOMM-DC 6O376-P69 u.s. GOVIRNMINT rumrme OFFICE: Ian o-su-au F ORM PO-105O (10 69) v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,626,125 Dated December '7, 1971 Invent Akira It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 20, delete "are" and insert --arc--;

line 27, delete "10 and insert -l0 Column 2, line 33, delete "so" and insert -as--;

line 2, delete "37" and insert 27;

Column 6, line 4, delete "winging" and insert -winding-- Signed and sealed this 2nd day of July 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer I Commissioner of Patents FORM PQ-IOSO (10-69) USCOMM-DC 60376-P69 i [1.5. GOVERNMENT PRINTING OFFICE I969 0-366-334

Claims

1. Switching means to make and break an electric circuit comprising a vacuum switch including a highly evacuated insulating envelope and a pair of separable electrodes having their one ends located within said envelope to be engageable with each other, a liquidtight enclosure arranged around the vacuum switch and having at least one opening extending through a wall thereof, said enclosure being made of an insulating material and filled with a noncompressible fluid, means for detecting the volume of said noncompressible fluid within said enclosure which has penetrated through said envelope of said vacuum switch and entered thereinto, said detecting means comprising an enclosed liquid leveler tank, an insulating tubular member connected between the inside of said tank and the inside of said enclosure, said tank being partially filled with an noncompressible fluid so as to leave a space above the fluid level therein and having a tubular pipe one end of which is communicated with one end of said insulating tubular member, and the other end is opened in the noncompressible fluid near the bottom of the tank, and an electrical floating switch means arranged in the fluid of said tank and responsive to the fluid level variations in the tank.

2. Switching means according to claim 1, in which said floating switch is connected to electric circuit means which includes an alarming circuit and/or an interlocking circuit for a drive means which makes and breaks said vacuum switch, said drive means being adapted to become inoperative in response to output signals of said interlocking circuit.

5. Switching means for a tap changing electrical power transformer which includes an enclosed casing, a tapped winding enclosed within the casing with an electrical insulating oil and a tap changing mechanism for the tapped winding, a plurality of oiltight enclosures immersed in said oil in said casing, vacuum switches disposed within said enclosures, respectively, connected to the taps of said tapped winding and operated by said tap changing mechanism, each said vacuum switch being arranged within said enclosure in a manner to leave a space filled with an insulating oil therebetween, respectively, and a plurality of bellows mOunted on the outer sides of said enclosures and communicated inside of the bellows with said spaces in said enclosures through insulating tubular members, respectively, and at least one contact operatively mounted on said bellows, respectively, thereby to detect the shrinkage of the bellows in response to penetration of said oil within said enclosure into said vacuum switch disposed in the enclosure.

6. Switching means to make and break an electric circuit, comprising: a vacuum switch including a highly evacuated insulating envelope and a pair of seperable electrodes having ends located within said envelope and engageable with each other, a liquidtight enclosure enclosing said vacuum switch and having walls conforming generally to but spaced from said envelope, the space between the enclosure and the envelope having a limited volume of the order of magnitude of the volume of said envelope, said enclosure being filled with a noncompressible liquid, a liquid leveler reservoir means connected with said enclosure to keep said enclosure full of liquid, said reservoir means having a liquid volume that is variable according to liquid required by said enclosure, and signal means for detecting a decrease in said liquid volume in said reservoir means below a set level, whereby if liquid leaks from said enclosure into said envelope the resulting decrease in liquid volume in said reservoir means results in actuating said signal means.