US3842227A

US3842227A - Circuit-breaker having dielectric liquid under pressure

Info

Publication number: US3842227A
Application number: US00294291A
Authority: US
Inventors: J Gratzmuller
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-09-30
Filing date: 1972-10-02
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15
Also published as: ES406253A1; JPS5213626B2; GB1404652A; SU735196A3; AT325136B; IT968448B; DE2245170B2; DE2245170A1; CA959525A; HU173196B; FR2154928A5; NL152699B; BE788520A; JPS4842365A; NO134025C; CS182773B2; AU470230B2; NO134025B; NL7212217A; ZA726059B

Abstract

A circuit-breaker includes a fluid-tight cutout chamber in which are disposed a fixed contact as well as a sliding movable contact and which encloses a dielectric in the liquid state kept under pressure. The movable contact is brought and kept selectively against the fixed contact by releasable disconnecting means, in opposition to ever-present elastic disconnecting means tending to separate the two contacts and comprising hydraulic elastic means responding only to the volumetric elasticity of the compressed liquid in the circuit-breaker. The dielectric in the liquid state is preferably a compressible liquid having a compressibility at least ten times greater than that of oil and may be a liquified gas dielectric.

Description

[ Oct. 15,1974

United States Patent [1 1 Gratzmuller CIRCUIT-BREAKER HAVING DIELECTRIC Attorney, Agent, or FirmHolman & Stem [57] ABSTRACT A circuit-breaker includes a fluid-tight cutout cham- Jean Louis Gratzmuller, 66 Blvd. Maurice Barres, 92 Neuilly sur Seine, France Oct. 2, 1972 [22] Filed:

her in which are disposed a fixed contact as well as a pp 294,291 sliding movable contact and which encloses a dielectric in the liquid state kept under pressure. The mov- [30] Foreign A li ti p i i Data able contact is brought and kept selectively against the fixed contact by releasable disconnecting means, in

opposition to ever-present elastic disconnecting means tending to separate the two contacts and comprising hydraulic elastic means responding only to the volumetric elasticity of the compressed liquid in the circuit-breaker. The dielectric in the liquid state is preferably a compressible liquid having a compressibility at least ten times greater than that of oil and may be a liquified gas dielectric.

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200/148 0 Gratzmuller.................... 200 150 A 10 Clams, 2 Drawing Flgllres 3,406,269 10/1968 Fischer............ 3,569,651 3/1971 CIRCUIT-BREAKER HAVING DIELECTRIC LIQUID UNDER PRESSURE This invention relates to electrical circuit-breakers in which at least the cutoff chamber, which encloses the fixed and movable contacts, is filled with a dielectric liquid kept permanently under pressure.

Circuit-breakers of this kind have already been described in French Pat. No. 1,537,673 filed on April 15, 1966 by the same inventor. It will be sufficient to recall here that the act of bringing about the cutting off of the current, by separation of fixed and movable contacts, in a dielectric medium constituted by a liquid kept permanently under pressure allows certain electrical characteristics of the dielectric medium to be improved (for example disruptive strength, extinguishing power). In this way there can be obtained better cutoff performances and/or a reduction of the volume of dielectric (especially due to the reduction of the separation necessary between the two contacts when disconnected), and thus a reduction in bulk and cost of the apparatus.

Such circuit-breakers with dielectric liquid under pressure are particularly advantageous when there is used as the dielectric liquid a liquified dielectric gas, kept under pressure to remain permanently in the liquid state, such as sulphurhexafluoride.

Finally, in such circuit-breakers, there is provided elastic means for maintaining the dielectric liquid under pressure (for example pneumatic elastic means constituted by a cushion of gas under pressure) and this same elastic means, at all times available, being utilised to set the movable contact of the circuit-breaker in motion in the direction separating the contacts, i.e., for the disconnection.

In practice, the cutoff chamber has been in communication with a reserve of dielectric liquid under pressure constituted by a hydropneumatic or hydromechanical accumulator, communication between the cutoff chamber and the accumulator being ensured by passages or conduits which are short and/or of ample section to permit the exchanges of liquid without delaying the time of the connecting or disconnecting operations. This presented disadvantages as consequently the hydropneumatic or hydromechanical accumulator (or the reserve of liquid with its associated elastic means for maintenance under pressure) had to be installed in or near the cutout chamber (FIGS. 1 and 3 of the aforesaid patent), i.e., in the live part of the circuit-breaker, which is scarcely practical, or near the earth potential (FIG. 2 of the aforesaid patent), but in this case with one conduit of ample section (more particularly through the insulating column of the circuit-breaker), which is uneconomical where high pressures are used.

In order to obviate or mitigate these disadvantages, the inventor sought to avoid the use of elastic means for keeping under pressure the dielectric liquid for setting the movable contact in motion in the direction separating the contacts. He arrived at this surprising conclusion that, providing the volume of dielectric liquid is selected to be sufficiently large and/or providing a liquid having a relatively large compressibility is selected as the dielectric liquid, the volumetric elasticity of the dielectric liquid could simply be used as the elastic disconnecting means.

Consequently the subject of the invention is a circuitbreaker which includes: a fluid-tight cutout chamber in which are disposed a fixed contact as well as a sliding movable contact and which encloses a dielectric in the liquid state kept under pressure; releasable disconnecting means for bringing and keeping selectively the movable contact against the fixed contact in opposition to ever-present elastic disconnecting means tending to separate the movable contact from the fixed contact, said elastic disconnecting means being hydraulic elastic means responding only to the volumetric elasticity of the compressed dielectric liquid in the circuit-breaker.

It has heretofore been proposed to set in motion a movable contact of a circuit-breaker in the direction of opening this movable contact, under the sole action of the natural elasticity of a dielectric under pressure contained in the cutoff chamber of the circuit-breaker. However, such a solution has been proposed only for circuit-breakers in which the cutoff chamber is filled with a compressed gas having a high extinguishing power, especially the gas SF 6. Such a solution would be usable in practice only provided that the gas is maintained at a temperature sufficiently high that its pressure, even when the external temperature is very low, remains greater than an amount equal to the atmospheric pressure to ensure the effort necessary for disconnecting the circuit-breaker. Because of this, circuitbreakers of this kind must be fitted with an auxiliary heating system, and this presents disadvantages from the safety aspect. Indeed, in case of trouble with the heating system, the circuit-breaker could be unable to open if the external temperature is low, due to the fact of insufficient gas pressure in the cutoff chamber.

On the contrary, the circuit-breaker according to the invention calls exclusively on the volumetric elasticity of a dielectric in the liquid state and not at all gaseous and of which the pressure remains sufficient, whatever may be the external temperature, to ensure the disconnecting operation without necessitating auxiliary heating means.

The replacement according to the invention of a gaseous dielectric by a dielectric liquid under pressure and particularly as will appear hereinafter, by a liquified dielectric gas of high compressibility, consequently achieves important and unexpected advantage from the aspect of simplicity of the construction and security of operation.

According to a preferred embodiment of the invention, the dielectric liquid is constituted by a liquified dielectric gas under pressure, especially sulphurhexafluoride SF 6 the dielectric properties of which are very favourable and the compressibility of which is several tens of times greater than that of a liquid such as oil.

In a circuit-breaker according to the invention, as the elasticity of the dielectric itself is sufficient to take the place of elastic disconnecting means hitherto utilised, the internal volume of the circuit-breaker filled with dielectric liquid under pressure (particularly the cutoff chamber) could theoretically be sealed in a fluid-tight manner. However, because of the variations in ambient temperature, it is necessary to provide means for compensating for resultant variations in pressure of the dielectric.

This compensating means could advantageously be constituted by an accumulator, for example a hydropneumatic accumulator, but the latter has only to compensate for slow dilations, so that it could be connected to the cutoff chamber simply by a conduit of crosssection as small as technology allows and which may be of considerable length without disadvantage. Consequently, the accumulator may be disposed at ground level, a fact which resolves the difficulties pointed out hereinbefore in connection with circuit-breakers of this kind hitherto known. It is thus possible to inspect and fill the accumulator at earth potential which is much more economical and practical than when it is in the live part of the circuit-breaker.

Finally, such conduits of small cross-section are much more practical and economical for the high pressures utilised than are conduits of large cross-section which have hitherto been necessary.

The invention will be better understood with the help of the description which follows, by way of example, with reference to the accompanying drawings, in which:

FIG. '1 is a diagrammatic sectional view of a circuitbreaker in accordance with the invention; and

FIG. 2 is a partial view, on a larger scale, of the cutoff components according to a preferred form arising from a modification of the invention.

The circuit-breaker, shown in FIG. 1 in the disconnected position, comprises essentially a cutoff chamber 2 constituted for example by a cylindrical wall 4 closed in a fluid-tight manner by an upper wall 6 and by a bottom 8.

The cutoff chamber 2 encloses a fixed contact 10 and a sliding movable contact 12. The fixed contact 10 is surrounded by a sleeve 14 of insulating material which is supported, by its upper annular surface 16, against the lower surface of the upper wall 6 of the cutoff chamber in order to resist thrust exerted by the pressure of the dielectric and by the movable contact on the fixed contact in the connected position of the circuitbreaker. The insulating sleeve 14 is extended by a tubular part 18, the length of which is selected as a function of the voltages which the circuit-breaker will have to tolerate, and which surround'a conductive stem the upper end 22 of which constitutes one of the circuitbreaker terminals connected to the line 24 to be cut.

The movable contact 12 passes in a fluid-tight manner, thanks to a packing ring 26 (preferably a resilient packing ring), through the bottom 8 of the cutoff chamber and includes abutment means limiting the extent of separation of the movable contact 12 from the fixed contact 10. This abutment means is constituted by a shoulder 28 of the movable contact, which shoulder comes to be supported, in the disconnected posi tion, on the bottom 8 of the cutoff chamber.

The movable contact 12 is electrically connected to the second terminal 30 of the circuit-breaker, the terminal 30 being itself connected to the branch 24' of the line to be cut. As will hereinafter appear, the extent of movement of the movable contact, i.e., its maximum separation from the fixed contact may be greatly reduced (by comparison with the standard circuitbreakers), so that the electrical connection between the movable contact and the terminal 30 may be effected simply by means of a metal braid 32, thus avoiding sliding contacts which are generally necessary with circuit-breakers.

The cutoff chamber 2 forms a fluid-tight enclosure which is filled with dielectric liquid kept under pressure, the means keeping the liquid under pressure being described hereinafter.

The dielectric liquid may be simply oil under pressure, but, in a circuit-breaker according to the invention, use is preferably made, for filling the cutoff chamber, of a dielectric constituted by a dielectric gas liquified by pressure and maintained permanently in the liquid state. There will hereinafter be pointed out the advantages which are derived from the use of such a dielectric.

The bottom 8 of the cutoff chamber is mounted on the top of an insulating component, for example an insulating column 34 filled with a liquid or gaseous dielectric, for example oil or gaseous sulphur hexafluoride under low pressure, the lower end of the column being fixed on base-plate 36 mounted on a support 38 supported from the ground.

The movable contact 12 is mechanically connected, for example by an insulating rod 40 extending in the interior of the column 34, to releasable disconnecting means adapted to bring and keep selectively the movable contact against the fixed contact in opposition to ever-present elastic disconnecting means which tend to separate the movable contact from the fixed contact.

The disconnecting means are standard in circuit breakers and it will be sufficient to describe, by way of example, those represented in FIG. 1.

The lower extremity of the insulating rod 40 is connected, at least under thrust, to a piston 42 which slides in a jack cylinder 44 carried by the base-plate 36, a fluid-tight packing ring 46 being provided between the piston and the cylinder.

The interlocking jack 44 may be actuated by a standard hydraulic circuit-breaker control the essential parts of which have been schematically represented at 48 and which does not form part of the invention. These essential parts are an oleopneumatic accumulator 50, an oil-pump 52, a low-pressure oil reservoir 54, and a hydraulic switching circuit represented in a simplified manner by a three-way valve 56.

The fluid-tight cutoff chamber 2 could be provided with a simple orifice or valve for filling with dielectric under pressure series, as will hereinafter appear, the everavailable elastic disconnecting means are constituted solely by the volumetric elasticity of the dielectric liquid compressed in the cutoff chamber. That is to say that, supposing the circuit-breaker is placed somewhere at constant temperature, it could function with the mere essential components which have been described, after the cutoff chamber had been filled with dielectric liquid under pressure.

However, in order to compensate for large variations in temperature (for example from 50C to +C) to which outside circuit-breakers could be subject, it is necessary to provide compensating means which at the same time comprise filling and control means.

To this end, the cutoff chamber includes an orifice, for example a passage 58 pierced in the bottom 8 of the chamber, the passage 58 being connected with a pipe 60 of small cross-section located in the interior of the insulating column 34. The pipe 60 (or a passage 62 connected therewith and pierced in the base-plate 36) issues at the potential of the ground where it is connected with a reserve of dielectric liquid under pressure constituted for example by a hydropneumatic accumulator 64 the liquid chamber 66 of which encloses a dielectric liquid under pressure and the gas chamber 68 of which encloses an elastic cushion of compressed gas such as nitrogen or preferably helium. A filling pipe 70, a pressure-gauge 72 and stop-

valves

74, 76 and 78 are also provided.

When the accumulator 64 and the cutoff chamber 2 have first been filled with dielectric liquid under pressure, the manner of operation of the apparatus is the following, starting out from the disconnected position represented in FIG. 1. The movable contact 12, which forms a plungerpiston, is repulsed into its lowermost position by the pressure of the dielectric. For engagement of the circuit-breaker, the hydraulic engaging jack 44 is supplied, by actuating the switching means 56 so that the piston 42 causes the movable contact 12 to move upwards, through the intermediary of the rod 40, until it is against the fixed contact. As long as the jack 44 is supplied, generally by a hydraulic circuit which is automatically sustained, the circuit-breaker remains engaged. In order to effect disengagement of the circuit-breaker, the jack 44 is set to drainage in a standard manner and it is simply the volumetric elasticity of the dielectric liquid under pressure contained in the cutoff chamber which drives away the movable contact and separates it from the fixed contact, without any large flow of oil developing through the pipe 60 in the direction of the accumulator 64, so much so that, as long as the temperature is constant, the stop valve 74 may be closed.

It is especially worth using as dielectric the liquified gas SF 6, for example under a pressure of the order of 200 bars-to 400 bars (1 bar 1.02 kg./cm

With such a dielectric, the separation of the contacts in the open position may be greatly reduced, for example about mm. for a voltage of 200 k/volts.

The volume of dielectric displaced by the movement of the movable contact may thus be cm. Given that the compressibility of liquid SF 6 is very high (about 10"" per kg./cm instead of 5 to 7 X 10 for oil), a reduced volume (for example 4,000 cm) in the cutoff chamber is sufficient in order that the variations in pressure (at constant temperature) due to the displacement of the contact are low and of the order of 5 bars.

The reserve of dielectric liquid constituted by the accumulator 64 may thus be remote from the cutoff chamber, the flow of liquid from the accumulator 64 in the direction of the chamber 2, or vice versa, taking place only slowly, as a function of variations in temperature.

The pressure gauge 72 enables the pressure of the dielectric to be controlled.

In the case where oil under pressure would be used as the dielectric, the conditions would be less advantageous as oil is much less compressible than liquid SF 6 and necessitates greater separation of the contacts, but it would suffice in this case to increase sufficiently the volume of the cutoff chamber.

5 To achieve the greatest possible reduction in the movements of the movable contact, it is advantageous to use fixed and movable contacts without preliminary engagement, that is to say contacts operating solely under pressure. That is why a hydraulic control of the kind represented in FIG. 1, with which the oil pressure applies the movable contact on the fixed contact during periods when engagement is maintained, is particularly advantageous.

A preferred modification in the construction of the movable contact is represented in FIG. 2.

According to this modification, the movable contact 12, instead of functioning as a plunger-piston as in the case of FIG. 1, is connected to a piston which slides in a cylinder 82 formed in the bottom 8 of the cutoff chamber. A packing ring 26 ensures fluid-tightness between the bottom 8 and the piston 80, a second packing ring 26" ensuring relative fluid-tightness between the shank of the movable contact and the bottom 8.

The movable contact is pierced by an axial opening 84 which communicates through transverse openings 86 with the chamber of the cylinder 82. At the instant of disengagement, the movable contact is repulsed by the volumetric elasticity of the dielectric under pressure, as has hereinbefore been described. The displacement of the piston 80 increases the volume of the chamber 82 (FIG. 2) which fills with dielectric liquid which flows through the opening 84 and the openings 86 on passage between the opened fixed and movable contacts. In this way there is produced a turbulent blowout of the are under the effect of this dielectric flow. As the time of opening may be very brief, for example l to 2 milliseconds, the instantaneous flow may be very important.

One embodiment of a direct-current circuit-breaker sustaining a restoration voltage of 200 KV may have contacts of surface area about 10 cm" and the applied force of the contact in the engaged position is about 10 tons, representing the difference between the force of the hydraulic jack 44 and the force of the piston 80. The volume of SF 6 delivered by the blowout is about 50 cm in l to 2 milliseconds.

Of course, the invention is in no way restricted to the embodiment described and shown and is capable of many modifications, open to the expert, in accordance with the contemplated applications, without thereby departing from the scope of the invention as defined in the appended claims.

I claim:

1. A circuit breaker comprising:

a circuit interrupting chamber enclosing an elastically compressible and partially compressed dielectric liquid body;

a fixed contact member disposed in said liquid body;

a cylindrical contact member which is axially movable relative to the fixed contact member between a closed circuit position and an open circuit position and having a portion thereof entering said liquid body so as to additionally compress the same during movement of the movable contact member from said open circuit position to said closed circuit position; releasable actuating means operable to move the movable contact member from its open circuit position towards and maintain it in its closed circuit position against the sole action of the increased counterpressure created in said liquid body by said additional compression thereof, and means for releasing said actuating means and thereby allow said increased counterpressure to move the movable contact member from its closed circuit position to its open circuit position. 2. A circuit-breaker according to claim 1, in which the dielectric in the liquid state is a compressible liquid having a compressibility at least ten times greater than that of oil.

3. A circuit-breaker according to claim 2, in which the dielectric in the liquid state is a liquified gas dielectric.

. 4. A circuit-breaker according to claim 3, in which the dielectric under pressure is sulphur hexafluoride SF 6 under pressure.

5. A circuit-breaker according to claim 1 and including means for compensating for variations in volume of the dielectric liquid caused by variations in temperature.

6. A circuit-breaker according to claim 5, in which the compensating means comprise a fluid-tight enclosure containing dielectric in the liquid state, pneumatic or mechanical elastic means acting on said dielectric liquid to maintain the dielectric liquid under pressure, and a conduit of small cross-section communicating between said enclosure and the cutoff chamber of the circuit-breaker, said conduit permitting only small flows of liquid caused by variations in the volume of liquid due to variations in temperature.

7. A circuit-breaker according to claim 6, in which said compensating means comprise a hydropneumatic accumulator inflated by helium.

8. A circuit-breaker according to claim 1, in which the movable contact is connected to a disconnecting piston which slides in a cylinder the working chamber of which communicates with the cutoff chamber filled with dielectric liquid under pressure, such communication being by way of an opening pierced at least in part axially in the movable contact and thanks to which a movement of dielectric across the movable contact is established when the latter is displaced, said movement producing a flow of dielectric liquid in the zone where the cutoff arc is formed at the instant when the circuitbreaker is opened.

9. A circuit-breaker according to claim 8, in which, in the engaged position of the circuit-breaker, the movable contact is supported against the fixed contact without engagement of one contact within the other.

10. A circuit-breaker according to claim 9, in which the releasable engaging means to bring and selectively maintain the movable contact against the fixed contact in opposition to the elastic pressure of the dielectric liquid under pressure comprises at least one hydraulic engaging jack moving the movable contact, and control means for supplying and draining said hydraulic jack.

Claims

1. A circuit breaker comprising: a circuit interrupting chamber enclosing an elastically compressible and partially compressed dielectric liquid body; a fixed contact member disposed in said liquid body; a cylindrical contact member which is axially movable relative to the fixed contact member between a closed circuit position and an open circuit position and having a portion thereof entering said liquid body so as to additionally compress the same during movement of the movable contact member from said open circuit position to said closed circuit position; releasable actuating means operable to move the movable contact member from its open circuit position towards and maintain it in its closed circuit position against the sole action of the increased counterpressure created in said liquid body by said additional compression thereof, and means for releasing said actuating means and thereby allow said increased counterpressure to move the movable contact member from its closed circuit position to its open circuit position.

2. A circuit-breaker according to claim 1, in which the dielectric in the liquid state is a compressible liquid having a compressibility at least ten times greater than that of oil.

4. A circuit-breaker according to claim 3, in which the dielectric under pressure is sulphur hexafluoride SF 6 under pressure.

8. A circuit-breaker according to claim 1, in which the movable contact is connected to a disconnecting piston which slides in a cylinder the working chamber of which communicates with the cutoff chamber filled with dielectric liquid under pressure, such communication being by way of an opening pierced at least in part axially in the movable contact and thanks to which a movement of dielectric across the movable contact is established when the latter is displaced, said movement producing a flow of dielectric liquid in the zone where the cutoff arc is formed at the instant when the circuit-breaker is opened.