CA1253545A - Pulse power controlled vacuum switch - Google Patents
Pulse power controlled vacuum switchInfo
- Publication number
- CA1253545A CA1253545A CA000476151A CA476151A CA1253545A CA 1253545 A CA1253545 A CA 1253545A CA 000476151 A CA000476151 A CA 000476151A CA 476151 A CA476151 A CA 476151A CA 1253545 A CA1253545 A CA 1253545A
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- Prior art keywords
- electrode
- arcing
- main
- evacuated envelope
- stem
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention is directed to a vacuum switch in which current conduction is initiated between two spaced apart arcing electrodes by a direct current voltage pulse applied between one of the arcing electrodes and a trigger electrode. The switch is turned off by applying a pulsed transverse magnetic field to the arcing gap between the two arcing electrodes.
The present invention is directed to a vacuum switch in which current conduction is initiated between two spaced apart arcing electrodes by a direct current voltage pulse applied between one of the arcing electrodes and a trigger electrode. The switch is turned off by applying a pulsed transverse magnetic field to the arcing gap between the two arcing electrodes.
Description
:~2~5~5 1 50,000 PULSE POWER CONTROLLED VACWM SWITCH
BACKGROUND OF THE I NVENT I ON
Field of the Invention:
The disclosed invention is directed to vacuum switches in general and is particularly directed to a vacuum switch in which "turn on" is realized by employing a trigger electrode and "turn off" is accomplished by employing a pulsed transverse magnetic field.
Description of the Prior Art:
The known prior art is best exemplified by two 10 U.S. Patents 3,~11,070 and 4,021,628.
In U.S. Patent 3,811,070 a laser-initiated three-electrode type triggered vacuum gap device is pro-vided. The triggered vacuum gap device comprises a pair of main arcing electrodes within an insulating vacuum housing. The triggering electrode is positioned internal of one of the main electrodes, and is electrically insu-lated from the associated main electrode. A portion of the trigyering electrode or the associated main electrode comprises a material that is saturated with a gas, such as hydrogen, that is rapidly released when the gas-saturated portion is heated. It is to be understood that the gas-saturated material can be a separate piece attached to the electrode or an integral portion of the electrode. A
voltage potential is applied between the trigger electrode and its associated main electrode. The applied voltage is lo~er than the voltage required to cause a breakdown ~535~5
BACKGROUND OF THE I NVENT I ON
Field of the Invention:
The disclosed invention is directed to vacuum switches in general and is particularly directed to a vacuum switch in which "turn on" is realized by employing a trigger electrode and "turn off" is accomplished by employing a pulsed transverse magnetic field.
Description of the Prior Art:
The known prior art is best exemplified by two 10 U.S. Patents 3,~11,070 and 4,021,628.
In U.S. Patent 3,811,070 a laser-initiated three-electrode type triggered vacuum gap device is pro-vided. The triggered vacuum gap device comprises a pair of main arcing electrodes within an insulating vacuum housing. The triggering electrode is positioned internal of one of the main electrodes, and is electrically insu-lated from the associated main electrode. A portion of the trigyering electrode or the associated main electrode comprises a material that is saturated with a gas, such as hydrogen, that is rapidly released when the gas-saturated portion is heated. It is to be understood that the gas-saturated material can be a separate piece attached to the electrode or an integral portion of the electrode. A
voltage potential is applied between the trigger electrode and its associated main electrode. The applied voltage is lo~er than the voltage required to cause a breakdown ~535~5
2 50,000 between the trigger electrode and the associated main electrode. To initiate a high~power arc, a laser beam is projected onto the gas-saturated material through a passage in the opposite main arcing electrode. This procedure liberates gas from the gas-saturated material into the discharge region, between the triggering electrode and the associated main electrode, producing a low-power arc. The low-power arc forms guickly between the trigger electrode and the associated main electrode. When the disclosed device is operated on an alternating current power line having an operating frequency of 50 Hz or 60 ~z, the time duration of the laser beam is very short compared to the period of the power frequency. The main electrode, within which the trigger electrode is contained, is constructed so that a current loop flows through the arc and the trigger electrode and the associated main electrode to cause a magnetic force on the arc. The resultant magnetic force rapidly drives the arc into the interelectrode region of the main arcing electrodes. The introduction of the low-power arc into the main interelectrode region initiates a power arc across the main arcing electrodes.
- When initiating breakdown by a pulsed laser beam being directed onto the gas-saturated material, the energy of this laser beam must be sufficient to heat the gas-saturated material to the point to cause some of the absorbed gas to be quickly liberated from it.
In one emhodiment of the invention, the laser is ~irected onto the triggering electrode which comprises a portion saturated with a gas. The trigger electrode is disposed inside of an opening in the associated main electrode. The end portion of the trigger electrode, projecting inside the associated main electrode, is sur-rounded by an insulating piece that is smaller in diameter than the inner diameter of the opening through the associ-ated main electrode. The trigger electrode is also re-cessed from the primary arcing surface of the associated main arcing electrode. By this arrangement, metal vapors ~S~S~5
- When initiating breakdown by a pulsed laser beam being directed onto the gas-saturated material, the energy of this laser beam must be sufficient to heat the gas-saturated material to the point to cause some of the absorbed gas to be quickly liberated from it.
In one emhodiment of the invention, the laser is ~irected onto the triggering electrode which comprises a portion saturated with a gas. The trigger electrode is disposed inside of an opening in the associated main electrode. The end portion of the trigger electrode, projecting inside the associated main electrode, is sur-rounded by an insulating piece that is smaller in diameter than the inner diameter of the opening through the associ-ated main electrode. The trigger electrode is also re-cessed from the primary arcing surface of the associated main arcing electrode. By this arrangement, metal vapors ~S~S~5
3 50,000 and particles which are dispersed from the main electrode during power arcing are less likely to be deposited on the walls of the insulating material causing a shortening path to exist between the triggering electrode and the asso-ciated main electrode.
In another embodiment, the gas-saturated mater-ial is attached to the main electrode wall which has been beveled so that the laser beam can be focused on the gas-saturated material, rather than on the triggering electrode, in order to initiate the low-power arc.
In yet another embodiment, a gas~saturated metal disc is attached to the trigger electrode and a portion of the trigger electrode extends through the gas-saturated metal disc. The gas-saturated metal disc and the trigger electrodes are electrically insulated from the associated main electrode by vacuum and a solid high dielectric material. A portion of the solid insulating material between the metal disc and the associated main electrode is undercut to lessen the possibility of this area being coated with arc-generated metallic products and shorting the triggering electrode to the associated main electrode.
A low-power laser beam can then be directed onto the gas-saturated metal disc to initiate a low-power arc, which in turn will cause a high-power arc to form between the main arcing electrodes.
In U.S. Patent 4,021,628 there is provided a current limiting circuit interrupter having a pair of relatively movable contacts disposed within an evacuated enclosure, movable between a closed position completing an electric circuit and an open position forming an arcing gap therebetween across which an arc is formed during circuit interruption, and a magnetic field disposed to produce a magnetic field transverse to the arc formed during circuit interruption. A current limiting impedance can be connected external to and in parallel with the pair of contacts to provide an alternate path when the arc is extinguished. Contacts of the vacuum interrupter can be ~Z~35~5
In another embodiment, the gas-saturated mater-ial is attached to the main electrode wall which has been beveled so that the laser beam can be focused on the gas-saturated material, rather than on the triggering electrode, in order to initiate the low-power arc.
In yet another embodiment, a gas~saturated metal disc is attached to the trigger electrode and a portion of the trigger electrode extends through the gas-saturated metal disc. The gas-saturated metal disc and the trigger electrodes are electrically insulated from the associated main electrode by vacuum and a solid high dielectric material. A portion of the solid insulating material between the metal disc and the associated main electrode is undercut to lessen the possibility of this area being coated with arc-generated metallic products and shorting the triggering electrode to the associated main electrode.
A low-power laser beam can then be directed onto the gas-saturated metal disc to initiate a low-power arc, which in turn will cause a high-power arc to form between the main arcing electrodes.
In U.S. Patent 4,021,628 there is provided a current limiting circuit interrupter having a pair of relatively movable contacts disposed within an evacuated enclosure, movable between a closed position completing an electric circuit and an open position forming an arcing gap therebetween across which an arc is formed during circuit interruption, and a magnetic field disposed to produce a magnetic field transverse to the arc formed during circuit interruption. A current limiting impedance can be connected external to and in parallel with the pair of contacts to provide an alternate path when the arc is extinguished. Contacts of the vacuum interrupter can be ~Z~35~5
4 50,000 formed from material having high current chopping charac-teristics to facilitate extinction or chopping of the arc formed during circuit interruption. Tungsten is one material which exhibits the desired properties. Baffles can be mounted internal of the vacuum envelope containing the interrupter contacts to engage the arc during circuit interruption and enhance arc instability. An axial mag-netic field can be disposed to be applied to the vacuum interrupter while the contacts are being separated during circuit interruption. When the axial magnetic field is removed, the arc tends to become unstable and this enhances the interruption ability. As the axial magnetic field is removed, a transverse magnetic field can be applied causing rapid arc extinction, before a normal AC current zero.
15During operation, within the first two milli-seconds of fault current rise, the disclosed vacuum inter-rupter in the high voltage high current line will be activated. The vacuum interrupter contacts separate - rapidly to a relatively large separation. Repulsion coils or other appropriate apparatus may be required on or - connected to the contact structure for the desired rapid separation. When the contacts are widely separated, a transverse magnetic field is pulse-applied to the vacuum arc. This magnetic field which is applied transverse to the initial arc path creates arc instability. The arc then extinguishes and current is transferred to a parallel current limiting device. The parallel current limiting device can be a lightning arrester, resîstor, reactor bank, or the like. Arc instability can be further enhanced by the provision of baffles internal to the interrupter and the use of contact materials, such as tungsten, which are associated with high cathode spot mobility.
The desirability of large contact separation on a practical device may necessitate the use of an axial magnetic field in order to postpone anode spot formation during contact separation. Under these circumstances the axial magnetic field will be removed at or near maximum ~ll;2S~45 50,000 contact separation and this would have a tendency to cause arc ins-tability. Subsequent application of a transverse field would create the desired current zero.
A vacuum interrupter having the transverse magnetic field coils can be connected in series with one or more additional vacuum interrupters. Arcs in the standard vacuum interrupters would extinguish at the same instant as the arc in the current limiting vacuum inter-rupter utilizing the transverse magnetic field. ~owever, the recovery voltage following forced current zero would be impressed upon the series gaps-of all the vacuum inter-rupters. This would provide for high voltage withstand capability and facilitate operation in a high voltage circuit. In some instances it may also be desirable to connect capacitors in parallel with the interrupter con-tacts. The capacitors enhance arc instability and also lower the rate of rise of the recovery voltage following arc current zero. Current interruption in the vacuum in-terrupter can benefit from the use of parallel capacitors.
The disclosed vacuum interrupter can be used as a current limiting device on an alternating current circuit or a direct current circuit. It is advantageous to use a vacuum interrupter with its separable contacts, which can carry continuous current of either polarity. This pro-vides a solution to some of the polarity problems en-countered in prior art devices. By utilizing the trans-verse magnetic field to enhance the current chopping characteristics of the selected vacuum interrupter, a fast acting current limiting device can be obtained.
SUMMARY OF THE INVENTION
The present invention is directed to a vacuum switch comprising an evacuated envelope, said evacuated envelope being comprised of a cylindrical side member and two end caps, a first stationary main arcing electrode disposed within said evacuated envelope, said arcing electrode having first and second opposed major surfaces, a first stationary electrode stem affixed to the first ~25;~5~
6 50,000 surface of said first arcing electrode and extending entirely through one of said end caps, an aperture extend-ing entirely through the stationary electrode stem along its main axis, said aperture continuing entirely through said first main arcing electrode fro:m its first major surface to its second major surface, a second main arcing electrode disposed within said evacuated envelope, said second main arcing electrode having first and second opposed major surfaces, said second major surface of said second main arcing electrode facing said second major surface of said first main arcin~ electrode, said first and said second main arcing electrodes being spaced apart a predetermined distance, said predetermined distance defining a first arcing gap, a second electrode stem affixed to the first major surface of said second arcing electrode and extending entirely through the other end cap, said second main arcing electrode and said second electrode stem being movable relative to said first main arcing electrode, thereby providing means for setting said first predetermined arcing gap across which the switch will operate is set, a trigger electrode disposed within said aperture within said stationary electrode stem, said trigger electrode extending to close proximity with the first main arcing electrode, said trigger electrode being ~5 electrically insulated from said stationary electrode stem, said trigger electrode being electrically insulated from said first main arcing electrode by a vacuum space, said vacuum space comprising a second arcing gap, said second arcing gap being less than said first arcing gap, means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode, and means for commutating the current from the vacuum switch.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present inven tion reference should be had to the following detailed discussion and drawings of which:
~2~35~5 7 50,000 Fig. l is a schematic view of a vacuum switch embodying the teachings of this invention; and Fig. 2 is a schematic view of the vacuum switch OI Fig. 1 with typical "turn on" and "turn off" electrical circuitry connected thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to Fig. l, there is shown a vacuum switch lO. The vacuum switch 10 is comprised of a highly evacuated tubular envelope consisting o~ a cylin-drical side member 12 of a suitable electrically insulat-ing glass or ceramic and metallic end caps 14 and 16 closing off the ends 18 and 20 of the side member 12.
Suitable seals 22 are provided between the end caps 14 and 16 and the side member 12 to render the inside of the evacuated envelope formed by side member 12 and end caps 14 and 16 vacuum tight. The vacuum in the evacuated envelope, under normal operating conditions, is at least 10 4 so that the mean-free path of electrons within the ~` envelope will be longer than the potential breakdown distance within the envelope.
Disposed within the evacuated envelope is a first - main arcing electrode 24. The first main arcing electrode 24 has ~irst and second substantially parallel opposed major surfaces 26 and 28, respectively, and an edge portion 30.
A first electrode stem 32 is affixed to arcing electrode 24 by, for example, welding or brazing end 34 of the stem to the central portion of surface 26 of the arcing electrode 24.
The electrode stem 32 extends away from the arcing electrode 24, vertically as shown in Fig. 1, and passes through end cap 14 with end 36 of the electrode stem 32 being outside of the evacuated envelope. A suit-able seal 38 as, for example, a glass seal in end cap 14 at the point where the stem 32 passes through end cap 14 ensures the integrity of the vacuum within the envelope.
~;~5;~5~5 8 ~ 50,000 As shown in Fig. 1, the arcing electrode 24 -electrode stem 32 structure is stationary within the envelope.
The first main arcing electrode 24 normally will consist of copper and chromium and the copper will range from, by weight percent, 25% to 75% and the chromium will range from, by weight percent, 25% to 75%.
The first electrode stem 32 normally will consist of copper. The stem 32 may have a cladding, not shown, of a refractory metal or stainless steel disposed about its outer surface 40.
There is an aperture 42 extending entirely through the first main arcing electrode 24 from surface 28 to surface 26 and the aperture 42 continues entirely through the first electrode stem 32 terminating at surface 44 of the stem which is outside of the evacuated envelope.
The aperture 42 has a common axis through the electrode 24 and the electrode stem 32 and this axis is substantially perpendicular to surface 28 of electrode 24.
A triggering electrode 46, preferably of copper, - is disposed within the aperture 42 and extends from above surface 44 of electrode stem 32 to an area in close prox-imity to surface 28 of electrode 24. Tip 48 of triggering electrode 46 does not, however, extend to or beyond surface 28 of electrode 24.
The gap 47 between tip 48 of triggering electrode 46 and wall 49 of aperture 42 through the electrode 24 is approximately 1 mm.
The triggering electrode 46 is electrically insulated from electrode stem 32 by an electrically insu-lating material 50, as for example alumina.
In addition to electrically insulating the triggering electrode 46 from the electrode stem 32, the alumina preserves the integrity of the vacuum within the evacuated envelope.
The electrical insulating material extends from above iurface 44 of the stem 32 to a point in proximity to 125;~5~
9 50,000 the arcing electrode 24. The tip 48 of the triggering electrode 46 is electrically insulated from the arcing electrode 24 only by the vacuum or arc gap between the two which~ as sta-ted above, is approximately 1 mm.
A second main arcing electrode 52 is disposed within the evacuated envelope. The second arcing elec-trode 52 will normally have the same composition as the first main arcing electrode 24.
The second main arcing electrode 52 has first and second substantially parallel opposed major surfaces 54 and 56, respectively, and an edge portion 58.
A second electrode stem 60 is affi~ed to arcing electrode 52 by, for example, welding or brazing end 62 of the stem to the central portion of surface 54 of the arcin,g electrode 52. The second electrode stem 60 will normally be comprised of copper and may have a cladding, not shown, of a refractory metal or stainless steel dis-posed about its outer surface 61.
The electrode stem 60 e~tends away from the arcing electrode 52, vertically as shown in Fig. l, and passes through a bellows 64 and extends outside of the evacuated envelope.
The bellows 64 is normally of stainless steel.
The bellows 64 is sealed into the end cap 16 and there are seals 66 where the stem 60 passes through the bellows to preserve the integrity of the vacuum within the evacuated envelope.
There is an arc shield 68 to protect the bellows 64 from any arc blasts or metal particles. The arc shield 68 may be of copper, copper and stainless steel or of the same composition as the main arcing electrodes.
The first main arcing electrode 24 and the second main arcing alectrode 52 are vertically aligned within the evacuated envelope.
The first arcing electrode 24 is stationary with the electrode stem 32 sealed in place in the end cap 14.
1~5~S
50,000 The second arcing electrode 52 is movable verti-cally relative to the first arcing electrode 24 by means of the bellows 64.
The potential for relative movement between the two main arcing electrodes 24 and 52 affords a method of setting an arc gap 70 between surace 28 of first main arcing electrode 24 and surface 56 of second main arcing electrode 52.
The arc gap 70 will vary from 1 to 2 cm depending upon the voltage that is to be corducted between the two arcing electrodes 24 and 52 when the vacuum switch 10 is "turned on".
With reference to Fig. 2, a load circuit 78 consisting of a load 80 electrically connected between the first arcing electrode stem 32 and the second arcing electrode stem 60 by an electrical conductor 82, and a DC
power source 84 in the load circuit 78 connected electri-cally in series with the load 80. The load circuit 78 is outside of the evacuated envelope.
For purposes of explanation, it will be assumed that the arc gap between the two main arcing electrodes 24 and 52 is 1 cm and that the arc gap between the tip 48 of the triggering electrode 46 and wall 49 of the aperture in the first main arcing electrode 24 is 1 mm. It will be further assumed that the load 80 has a 25 ohm resistance, the DC power source is a 50 kV source, that the conductor 82 has a line impedance, denoted at 86, of 10 ~H and that the circuit current is 2 kA.
A triggering circuit 90 is connected outside of khe evacuated envelope between electrode stem 32 and the trigger electrode 46.
The triggering circuit 90 consists of an elec-trical conductor g2 connecting a switch 94 and a capacitor 96 electrically in series and a DC power source 98 and an electrical resistor 100 electrically in parallel with the capacitor 96.
:~535~S
11 50,000 For the purposes of explanation, assume the capacitor 96 to be of 30 kV, the power source 98 to be a 30 kV power source and the resistor to have a value of 1 megohm.
A "turn-off" circuit 110 consists of a commutat-ing capacitor 112 electrically connected in parallel across the switch hy an electrical conductor 114 between stem electrode 32 and stem electrode 60 outside of the evacuated envelope.
In conjunction with "turn-off" c rcuit 110 a hollow tube coil 116 is disposed around the switch ou-tside of the evacuated envelope.
The hollow tube coil is preferably of copper.
The hollow tube coil 116, when electrically pulsed, generates a magnetic field of 200 mT at a buildup rate o~ 6 kT/sec.
The operation of the vacuum switch of Figs.
and 2 is as follows.
For "turn on", the switch 94 is closed and a voltage pulse from DC power supply 98 and capacitor 96 is - applied between the tip 48 of trigger electrode 46 and the stationary main arcing electrode 24 or the stationary or first electrode stem 32. This causes a low-energy vacuum breakdown to be initiated in the gap 47 between the sta-tionary main arcing electrode 24 and the trigyer electrode46.
Assuming that a voltage exists in load circuit 7~, from DC voltage source 84, between or across main arcing electrode 24, the stationary electrode, and main arcing electrode 52, the discharge between the triggering electrode 46 and the stationary main arcing electrode 24 will initiate a breakdown in the main gap 70 causing a vacuum arc and thus current flow between the main arcing electrode 24 and main arcing electrode 52.
To shut the current off, circuit 110 is used in conjunction with coil 116. This is accomplished by apply-ing a pulsed transverse magnetic fi31d to the vacuum arc.
~S35~
12 50,000 The hollow tube coil 116 is energized thereby building up a magnetic field of 100 to 200 mT at a rate of 6 kl'/sec. transverse to the arc between main arcing elec-trodes 24 and 52.
The transverse magnetic fi01d commutates the current, which has been flowing in the direction indicated by arrow 11~, from the vacuum switch into the parallel commutating capacitor 112 in circuit 110. The current will flow in the direction indicated by arrow 120.
As the commutated current charges the capacitor 112, the voltage across the capacitor 112 will increase until it approaches the source voltage of DC power supply 84 and current will cease to flow.
The critical parameters for current commutation as taught by this invention are the intensity of the transverse magnetic field, the time derivative of the magnetic field and the value of the parallel capacitor 112.
The commutated current is proportional to the intensity of the magnetic field and to the time derivative of the magnetic field.
The time derivative of the magnetic field, i.e., how fast the magnetic field is built up is the more impor-~ant parameter of the two.
The current to be commutated is approximately proportional to the square root of the time derivative of the magnetic field.
The current to be commutated is also a function of the square root of the capacitance.
The main arcing electrode should also be of such a design that the vacuum arc burns in a diffuse mode.
One of the main advantages of the vacuum switch OI this invention is that the gap 70 can be varied by adjusting the position of the movable electrode 52 relative to the stationary electrode 24 and, therefore, the vacuum s~itch can be made to operate over a wide range of voltages.
~53S~5 13 50,000 For the switch shown in Figs. 1 and 2 with a 10 ~f capacitor connected electrically in parallel across it, a magnetic field of approximately 200 mT is required to commutate currents of from 2 to 5 kA into the capaci'_or causing a recovery voltage of approximately 500 kV.
15During operation, within the first two milli-seconds of fault current rise, the disclosed vacuum inter-rupter in the high voltage high current line will be activated. The vacuum interrupter contacts separate - rapidly to a relatively large separation. Repulsion coils or other appropriate apparatus may be required on or - connected to the contact structure for the desired rapid separation. When the contacts are widely separated, a transverse magnetic field is pulse-applied to the vacuum arc. This magnetic field which is applied transverse to the initial arc path creates arc instability. The arc then extinguishes and current is transferred to a parallel current limiting device. The parallel current limiting device can be a lightning arrester, resîstor, reactor bank, or the like. Arc instability can be further enhanced by the provision of baffles internal to the interrupter and the use of contact materials, such as tungsten, which are associated with high cathode spot mobility.
The desirability of large contact separation on a practical device may necessitate the use of an axial magnetic field in order to postpone anode spot formation during contact separation. Under these circumstances the axial magnetic field will be removed at or near maximum ~ll;2S~45 50,000 contact separation and this would have a tendency to cause arc ins-tability. Subsequent application of a transverse field would create the desired current zero.
A vacuum interrupter having the transverse magnetic field coils can be connected in series with one or more additional vacuum interrupters. Arcs in the standard vacuum interrupters would extinguish at the same instant as the arc in the current limiting vacuum inter-rupter utilizing the transverse magnetic field. ~owever, the recovery voltage following forced current zero would be impressed upon the series gaps-of all the vacuum inter-rupters. This would provide for high voltage withstand capability and facilitate operation in a high voltage circuit. In some instances it may also be desirable to connect capacitors in parallel with the interrupter con-tacts. The capacitors enhance arc instability and also lower the rate of rise of the recovery voltage following arc current zero. Current interruption in the vacuum in-terrupter can benefit from the use of parallel capacitors.
The disclosed vacuum interrupter can be used as a current limiting device on an alternating current circuit or a direct current circuit. It is advantageous to use a vacuum interrupter with its separable contacts, which can carry continuous current of either polarity. This pro-vides a solution to some of the polarity problems en-countered in prior art devices. By utilizing the trans-verse magnetic field to enhance the current chopping characteristics of the selected vacuum interrupter, a fast acting current limiting device can be obtained.
SUMMARY OF THE INVENTION
The present invention is directed to a vacuum switch comprising an evacuated envelope, said evacuated envelope being comprised of a cylindrical side member and two end caps, a first stationary main arcing electrode disposed within said evacuated envelope, said arcing electrode having first and second opposed major surfaces, a first stationary electrode stem affixed to the first ~25;~5~
6 50,000 surface of said first arcing electrode and extending entirely through one of said end caps, an aperture extend-ing entirely through the stationary electrode stem along its main axis, said aperture continuing entirely through said first main arcing electrode fro:m its first major surface to its second major surface, a second main arcing electrode disposed within said evacuated envelope, said second main arcing electrode having first and second opposed major surfaces, said second major surface of said second main arcing electrode facing said second major surface of said first main arcin~ electrode, said first and said second main arcing electrodes being spaced apart a predetermined distance, said predetermined distance defining a first arcing gap, a second electrode stem affixed to the first major surface of said second arcing electrode and extending entirely through the other end cap, said second main arcing electrode and said second electrode stem being movable relative to said first main arcing electrode, thereby providing means for setting said first predetermined arcing gap across which the switch will operate is set, a trigger electrode disposed within said aperture within said stationary electrode stem, said trigger electrode extending to close proximity with the first main arcing electrode, said trigger electrode being ~5 electrically insulated from said stationary electrode stem, said trigger electrode being electrically insulated from said first main arcing electrode by a vacuum space, said vacuum space comprising a second arcing gap, said second arcing gap being less than said first arcing gap, means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode, and means for commutating the current from the vacuum switch.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present inven tion reference should be had to the following detailed discussion and drawings of which:
~2~35~5 7 50,000 Fig. l is a schematic view of a vacuum switch embodying the teachings of this invention; and Fig. 2 is a schematic view of the vacuum switch OI Fig. 1 with typical "turn on" and "turn off" electrical circuitry connected thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to Fig. l, there is shown a vacuum switch lO. The vacuum switch 10 is comprised of a highly evacuated tubular envelope consisting o~ a cylin-drical side member 12 of a suitable electrically insulat-ing glass or ceramic and metallic end caps 14 and 16 closing off the ends 18 and 20 of the side member 12.
Suitable seals 22 are provided between the end caps 14 and 16 and the side member 12 to render the inside of the evacuated envelope formed by side member 12 and end caps 14 and 16 vacuum tight. The vacuum in the evacuated envelope, under normal operating conditions, is at least 10 4 so that the mean-free path of electrons within the ~` envelope will be longer than the potential breakdown distance within the envelope.
Disposed within the evacuated envelope is a first - main arcing electrode 24. The first main arcing electrode 24 has ~irst and second substantially parallel opposed major surfaces 26 and 28, respectively, and an edge portion 30.
A first electrode stem 32 is affixed to arcing electrode 24 by, for example, welding or brazing end 34 of the stem to the central portion of surface 26 of the arcing electrode 24.
The electrode stem 32 extends away from the arcing electrode 24, vertically as shown in Fig. 1, and passes through end cap 14 with end 36 of the electrode stem 32 being outside of the evacuated envelope. A suit-able seal 38 as, for example, a glass seal in end cap 14 at the point where the stem 32 passes through end cap 14 ensures the integrity of the vacuum within the envelope.
~;~5;~5~5 8 ~ 50,000 As shown in Fig. 1, the arcing electrode 24 -electrode stem 32 structure is stationary within the envelope.
The first main arcing electrode 24 normally will consist of copper and chromium and the copper will range from, by weight percent, 25% to 75% and the chromium will range from, by weight percent, 25% to 75%.
The first electrode stem 32 normally will consist of copper. The stem 32 may have a cladding, not shown, of a refractory metal or stainless steel disposed about its outer surface 40.
There is an aperture 42 extending entirely through the first main arcing electrode 24 from surface 28 to surface 26 and the aperture 42 continues entirely through the first electrode stem 32 terminating at surface 44 of the stem which is outside of the evacuated envelope.
The aperture 42 has a common axis through the electrode 24 and the electrode stem 32 and this axis is substantially perpendicular to surface 28 of electrode 24.
A triggering electrode 46, preferably of copper, - is disposed within the aperture 42 and extends from above surface 44 of electrode stem 32 to an area in close prox-imity to surface 28 of electrode 24. Tip 48 of triggering electrode 46 does not, however, extend to or beyond surface 28 of electrode 24.
The gap 47 between tip 48 of triggering electrode 46 and wall 49 of aperture 42 through the electrode 24 is approximately 1 mm.
The triggering electrode 46 is electrically insulated from electrode stem 32 by an electrically insu-lating material 50, as for example alumina.
In addition to electrically insulating the triggering electrode 46 from the electrode stem 32, the alumina preserves the integrity of the vacuum within the evacuated envelope.
The electrical insulating material extends from above iurface 44 of the stem 32 to a point in proximity to 125;~5~
9 50,000 the arcing electrode 24. The tip 48 of the triggering electrode 46 is electrically insulated from the arcing electrode 24 only by the vacuum or arc gap between the two which~ as sta-ted above, is approximately 1 mm.
A second main arcing electrode 52 is disposed within the evacuated envelope. The second arcing elec-trode 52 will normally have the same composition as the first main arcing electrode 24.
The second main arcing electrode 52 has first and second substantially parallel opposed major surfaces 54 and 56, respectively, and an edge portion 58.
A second electrode stem 60 is affi~ed to arcing electrode 52 by, for example, welding or brazing end 62 of the stem to the central portion of surface 54 of the arcin,g electrode 52. The second electrode stem 60 will normally be comprised of copper and may have a cladding, not shown, of a refractory metal or stainless steel dis-posed about its outer surface 61.
The electrode stem 60 e~tends away from the arcing electrode 52, vertically as shown in Fig. l, and passes through a bellows 64 and extends outside of the evacuated envelope.
The bellows 64 is normally of stainless steel.
The bellows 64 is sealed into the end cap 16 and there are seals 66 where the stem 60 passes through the bellows to preserve the integrity of the vacuum within the evacuated envelope.
There is an arc shield 68 to protect the bellows 64 from any arc blasts or metal particles. The arc shield 68 may be of copper, copper and stainless steel or of the same composition as the main arcing electrodes.
The first main arcing electrode 24 and the second main arcing alectrode 52 are vertically aligned within the evacuated envelope.
The first arcing electrode 24 is stationary with the electrode stem 32 sealed in place in the end cap 14.
1~5~S
50,000 The second arcing electrode 52 is movable verti-cally relative to the first arcing electrode 24 by means of the bellows 64.
The potential for relative movement between the two main arcing electrodes 24 and 52 affords a method of setting an arc gap 70 between surace 28 of first main arcing electrode 24 and surface 56 of second main arcing electrode 52.
The arc gap 70 will vary from 1 to 2 cm depending upon the voltage that is to be corducted between the two arcing electrodes 24 and 52 when the vacuum switch 10 is "turned on".
With reference to Fig. 2, a load circuit 78 consisting of a load 80 electrically connected between the first arcing electrode stem 32 and the second arcing electrode stem 60 by an electrical conductor 82, and a DC
power source 84 in the load circuit 78 connected electri-cally in series with the load 80. The load circuit 78 is outside of the evacuated envelope.
For purposes of explanation, it will be assumed that the arc gap between the two main arcing electrodes 24 and 52 is 1 cm and that the arc gap between the tip 48 of the triggering electrode 46 and wall 49 of the aperture in the first main arcing electrode 24 is 1 mm. It will be further assumed that the load 80 has a 25 ohm resistance, the DC power source is a 50 kV source, that the conductor 82 has a line impedance, denoted at 86, of 10 ~H and that the circuit current is 2 kA.
A triggering circuit 90 is connected outside of khe evacuated envelope between electrode stem 32 and the trigger electrode 46.
The triggering circuit 90 consists of an elec-trical conductor g2 connecting a switch 94 and a capacitor 96 electrically in series and a DC power source 98 and an electrical resistor 100 electrically in parallel with the capacitor 96.
:~535~S
11 50,000 For the purposes of explanation, assume the capacitor 96 to be of 30 kV, the power source 98 to be a 30 kV power source and the resistor to have a value of 1 megohm.
A "turn-off" circuit 110 consists of a commutat-ing capacitor 112 electrically connected in parallel across the switch hy an electrical conductor 114 between stem electrode 32 and stem electrode 60 outside of the evacuated envelope.
In conjunction with "turn-off" c rcuit 110 a hollow tube coil 116 is disposed around the switch ou-tside of the evacuated envelope.
The hollow tube coil is preferably of copper.
The hollow tube coil 116, when electrically pulsed, generates a magnetic field of 200 mT at a buildup rate o~ 6 kT/sec.
The operation of the vacuum switch of Figs.
and 2 is as follows.
For "turn on", the switch 94 is closed and a voltage pulse from DC power supply 98 and capacitor 96 is - applied between the tip 48 of trigger electrode 46 and the stationary main arcing electrode 24 or the stationary or first electrode stem 32. This causes a low-energy vacuum breakdown to be initiated in the gap 47 between the sta-tionary main arcing electrode 24 and the trigyer electrode46.
Assuming that a voltage exists in load circuit 7~, from DC voltage source 84, between or across main arcing electrode 24, the stationary electrode, and main arcing electrode 52, the discharge between the triggering electrode 46 and the stationary main arcing electrode 24 will initiate a breakdown in the main gap 70 causing a vacuum arc and thus current flow between the main arcing electrode 24 and main arcing electrode 52.
To shut the current off, circuit 110 is used in conjunction with coil 116. This is accomplished by apply-ing a pulsed transverse magnetic fi31d to the vacuum arc.
~S35~
12 50,000 The hollow tube coil 116 is energized thereby building up a magnetic field of 100 to 200 mT at a rate of 6 kl'/sec. transverse to the arc between main arcing elec-trodes 24 and 52.
The transverse magnetic fi01d commutates the current, which has been flowing in the direction indicated by arrow 11~, from the vacuum switch into the parallel commutating capacitor 112 in circuit 110. The current will flow in the direction indicated by arrow 120.
As the commutated current charges the capacitor 112, the voltage across the capacitor 112 will increase until it approaches the source voltage of DC power supply 84 and current will cease to flow.
The critical parameters for current commutation as taught by this invention are the intensity of the transverse magnetic field, the time derivative of the magnetic field and the value of the parallel capacitor 112.
The commutated current is proportional to the intensity of the magnetic field and to the time derivative of the magnetic field.
The time derivative of the magnetic field, i.e., how fast the magnetic field is built up is the more impor-~ant parameter of the two.
The current to be commutated is approximately proportional to the square root of the time derivative of the magnetic field.
The current to be commutated is also a function of the square root of the capacitance.
The main arcing electrode should also be of such a design that the vacuum arc burns in a diffuse mode.
One of the main advantages of the vacuum switch OI this invention is that the gap 70 can be varied by adjusting the position of the movable electrode 52 relative to the stationary electrode 24 and, therefore, the vacuum s~itch can be made to operate over a wide range of voltages.
~53S~5 13 50,000 For the switch shown in Figs. 1 and 2 with a 10 ~f capacitor connected electrically in parallel across it, a magnetic field of approximately 200 mT is required to commutate currents of from 2 to 5 kA into the capaci'_or causing a recovery voltage of approximately 500 kV.
Claims (6)
1. A vacuum switch comprising an evacuated envelope, said evacuated envelope being comprised of a cylindrical side member and two end caps, a first stationary main arcing elec-trode disposed within said evacuated envelope, said arcing electrode having first and second opposed major surfaces, a first stationary electrode stem affixed to the first surface of said first arcing electrode and extending entirely through one of said end caps, an aperture extending entirely through the stationary electrode stem along its main axis, said aperture continuing entirely through said first main arcing electrode from its first major surface to its second major surface, a second main arcing electrode disposed within said evacuated envelope, said second main arcing electrode having first and second opposed major surfaces, said second major surface of said second main arcing electrode facing said second major surface of said first main arcing electrode, said first and said second main arcing electrodes being spaced apart a predetermined distance, said predetermined distance defining a first arcing gap, a second electrode stem affixed to the first major surface of said second arcing electrode and ex-tending entirely through the other end cap, said second main arcing electrode and said second electrode stem being movable relative to said first main arcing electrode, thereby provid-ing means for setting said first predetermined arcing gap across which the switch will operate a trigger electrode dis-posed within said aperture within said stationary electrode stem, said trigger electrode extending to close proximity with the first main arcing electrode, said trigger electrode being electrically insulated from said stationary electrode stem, said trigger electrode being electrically insulated from said first main arcing electrode by a vacuum space, said vacuum space comprising a second arcing gap, said second arcing gap being less than said first arcing gap, means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode, and means for commutating the the current from the vacuum switch, said means comprising a hollow coil disposed outside of the evacuated envelope and a commutating capacitor disposed outside of the evacuated envelope and electrically connected in parallel across the vacuum switch between the two electrode stems.
2. A vacuum switch comprising an evacuated envelope, said evacuated envelope being comprised of a cylindrical side member and two end caps, a first main arcing electrode dis-posed within said evacuated envelope, said arcing electrode having first and second opposed major surfaces, a first elec-trode stem affixed to the first surface of said first arcing electrode and extending entirely through one of said end caps, an aperture extending entirely through the first electrode stem along its main axis, said aperture continuing entirely through said first main arcing electrode from its first major surface to its second major surface, a second main arcing electrode disposed within said evacuated envelope, said second main arcing electrode having first and second opposed major surfaces, said second major surface of said second main arcing electrode facing said second major surface of said first main arcing electrode, said first and said second main arcing elec-trodes being spaced apart a predetermined distance, said pre-determined distance defining a first arcing gap, a second elec-trode stem affixed to the first major surface of said second arcing electrode and extending entirely through the other end cap, said first and said second main arcing electrode being movable relative to said each other, thereby providing means for setting the first predetermined arcing gap, a trigger electrode disposed within said aperture within said first electrode stem, said trigger electrode extending to close proximity with the first main arcing electrode, said trigger electrode being electrically insulated from said first electrode stem, said trigger electrode being electrically insulated from said first main arcing electrode by a vacuum space, said vacuum space comprising a second arcing gap, said second arcing gap being less than said first arcing gap, means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode, and means for commutating the current from the vacuum switch, said means comprising a hollow coil disposed outside of the evacuated envelope and a commutating capacitor disposed outside of the evacuated envelope and electrically connected in parallel across the vacuum switch between the two electrode stems.
3. A vacuum switch comprising an evacuated envelope, said evacuated envelope being comprised of a cylindrical side member and two end caps, a first main arcing electrode disposed within said evacuated envelope, said arcing electrode having first and second opposed major surfaces, a first electrode stem affixed to the first surface of said first arcing electrode and extending entirely through one of said end caps, a second main arcing electrode disposed within said evacuated envelope, said second main arcing electrode having first and second opposed major surfaces, said second major surface of said second main arcing electrode facing said second major surface of said first main arcing electrode, said first and said second main arcing electrodes being spaced apart a predetermined distance, said predetermined distance defining a first arcing gap, a second electrode stem affixed to the first major surface of said second arcing electrode and extending entirely through the other end cap, one of said arcing electrode and affixed electrode stem being movable relative to the other main arcing electrode, thereby providing means for setting the first predetermined arcing gap, the other main arcing electrode and electrode stem having an aperture extending entirely through the electrode stem along its main axis, said aperture continuing entirely through the other main arcing electrode from its first major surface to its second major surface, a trigger electrode disposed within said aperture within said other electrode stem, said trigger electrode extending to close proximity with the other main arcing electrode, said trigger electrode being elec-trically insulated from said other electrode stem, said trigger electrode being electrically insulated from said other main arcing electrode by a vacuum space, said vacuum space comprising a second arcing gap, said second arcing gap being less than said first arcing gap, means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode, and means for commutating the current from the vacuum switch, said means comprising a hollow coil disposed outside of the evacuated envelope and a commutating capacitor disposed outside of the evacuated envelope and electrically connected in parallel across the vacuum switch between the two electrode stems.
4. The vacuum switch of claim 1, in which means for applying a direct current voltage pulse between said trigger electrode and the stationary electrode is an electrical circuit external to the evacuated envelope comprising a direct current power source and a capacitor connected between the stationary electrode stem and the trigger electrode.
5. The vacuum switch of claim 1, in which the means for applying a direct current voltage pulse between said triggering electrode and said stationary electrode is an elec-trical circuit external to the evacuated envelope comprising a direct current power source and a capacitor connected between the stationary electrode stem and the triggering electrode and the means for commutating the current from the vacuum switch comprises a coil disposed outside of the evacuated envelope and a commutating capacitor disposed outside of the evacuated envelope and electrically connected in parallel across the vac-uum switch between the two electrode stems.
6. The vacuum switch of claim 5, in which the arcing gap between the two main arcing electrodes is from 1 to 2 cm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59503084A | 1984-03-30 | 1984-03-30 | |
| US595,030 | 1984-03-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253545A true CA1253545A (en) | 1989-05-02 |
Family
ID=24381426
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000476151A Expired CA1253545A (en) | 1984-03-30 | 1985-03-08 | Pulse power controlled vacuum switch |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1253545A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113130248A (en) * | 2019-12-30 | 2021-07-16 | 西安西电高压开关有限责任公司 | Combined bypass switch |
-
1985
- 1985-03-08 CA CA000476151A patent/CA1253545A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113130248A (en) * | 2019-12-30 | 2021-07-16 | 西安西电高压开关有限责任公司 | Combined bypass switch |
| CN113130248B (en) * | 2019-12-30 | 2022-08-19 | 西安西电高压开关有限责任公司 | Combined bypass switch |
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