US3500009A

US3500009A - High voltage circuit breaker with means for preinserting resistors during closing

Info

Publication number: US3500009A
Application number: US618405A
Authority: US
Inventors: Christy W Bell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-02-24
Filing date: 1967-02-24
Publication date: 1970-03-10
Anticipated expiration: 1987-03-10
Also published as: DE1640286A1; GB1151831A; FR1553618A

Description

C. W. BELL March 10, 1970 HIGH VOLTAGE CIRCUIT BREAKER-WITH MEANS FOR PREINSERTING RESISTORS DURING CLOSING Fil ed Feb. 24. 1967 2 Sheets-Sheet 1 r TR /6 GER PULSE SOURCE PULSE FORM/1V6 ANO TIMI/V6 C/RCU/T H 45 m W a Y M T 7 5 m w R H C 0 V: B 4 4 4 MM \2 m a 7 J M 7 6 0 Z J 4 .m

ATTORNEY March 10, 1970 c. w. BELL 3,500,009

HIGH VOLTAGE CIRCUIT BREAKER WITH MEANS FOR PREINSERTING RESISTORS DURING CLOSING Filed Feb. 24. 1967 2 Sheets-Sheet 2 INVENTOR. CHR/STY W. BELL,

A23 I B Y M A TTORNEY United States Patent O HIGH VOLTAGE CIRCUIT BREAKER WITH MEANS FOR PREINSERTING RESISTORS DURING CLOSING Christy W. Bell, Berwyn, Pa., assignor to General Electric Company, a corporation of New York Filed Feb. 24, 1967, Ser. No. 618,405 Int. Cl. H01h 33/00 US. Cl. 200-144 Claims ABSTRACT OF THE DISCLOSURE A high voltage circuit breaker comprising a plurality of sets of separable contacts electrically connected in series. Paralleling each set of contacts is the series combination of a voltage-controlling resistor and a triggered gap device. During circuit-breaker closing, the resistors are preinserted in parallel with the contacts by simultaneously triggering the gap devices into a conductive state, thus simultaneously preinserting all the resistors.

BACKGROUND OF THE INVENTION This invention relates to a high voltage electric circuit breaker and, more particularly, relates to a high voltage circuit breaker in which thecircuit through the breaker is completed at a precisely-controlled instant during a circuit breaker-closing operation.

For limiting the magnitude of the voltage surge developed by a high voltage circuit breaker upon closing, it has been proposed that the circuit breaker beprovided with resistors that can be inserted into the power circuit just prior to closing-engagement of the main contacts. Typically, these resistors are connected in parallel with the main contacts and in series with suitably controlled resistor switches that are caused to close and thereby insert the resistors at an appropriate instant preceding engagement of the main contacts.

Where there are a plurality of series-connected resistor switches in a very high voltage circuit, it is important that all of the resistor switches be closed substantially simultaneously. Otherwise, the inter-contact gap of the last resistor switch to close may be so long that it does not immediately break down in response to the high voltage developed thereacross when the other resistor switches close. This high voltage could cause a damaging arcover across insulation exposed to such voltage.

SUMMARY Accordingly, an object of my invention is to provide switching means capable of preinserting the resistors at a precisely-controlled instant, thus enabling substantially simultaneous preinsertion of all the series-connected resistors.

The magnitude of the voltage surge developed by circuit-breaker closing can be further controlled by controlling the instant on the voltage wave at which the resistors are preinserted. For example, in the AIEE paper by Skeats et a1. appearing in the AIEE Transactions, volume 68, Part II, 1949, pages 1058l067, it is pointed out that a voltage surge of minimum amplitude is developed if closing occurs at or near voltage zero. Accordingly, another object of my invention is to provide means capable of preinserting the resistors at a desired instant on the voltage wave.

A more general object of the invention is to provide improved means for closing the power circuit at a preselected precisely-controlled instant on the voltage wave.

In carrying out my invention in one form, I provide a high voltage circuit breaker comprising a plurality of sets of separable contacts electrically connected in series.

"ice

Paralleling each set of contacts is the series combination of a voltage-controlling resistor and a triggered gap device. Each triggered gap device comprises spaced-apart main electrodes defining a gap in series with its associated resistor and triggering means for causing an arc-over of said gap when a triggering signal is supplied to the triggering means. Means operable during a circuit-breaker closing operation is provided for supplying to the triggering means of said gaps triggering signals which cause arc-overs to be initiated substantially simultaneously in all of said gaps before said sets of contacts engage.

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

FIG. 1 is a schematic illustration of a circuit breaker embodying one particular form of my invention.

FIG. 1a schematically illustrates a modified form of the invention.

FIG. 2 is a schematic illustration of another modified form of the invention.

FIG. 3 illustrates still another modification of the invention.

' FIG. 4 illustrates still another modification of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown schematically a high voltage electric circuit breaker comprising two pairs 11 of main contacts electrically connected in series in a high voltage A.C. circuit 13. Each pair of main contacts comprises a stationary contact 12 and a movable contact 14 movable in a vertical direction into and out of engagement with the stationary contact. The movable contacts are electrically and mechanically connected together by a conductive bridging member 15, to which an insulating operating rod 16 is fixed.

The circuit breaker of FIG. 1 is shown in its solid-line open position with its main contacts 14 separated from their respective stationary contacts 12. When the operating rod 16 is driven in an upward direction by suitable operating means (not shown), the bridging member 15 together with movable contacts 14 are driven upwardly until the movable contacts 14 engage the stationary contact 12, thereby closing the circuit breaker. The dotted lines 17 indicate the position of the movable contacts when the circuit breaker is closed. The bridging member 15 mechanically couples the movable contacts together, thereby assuring that the two movable contacts 14 Will move together in unison during a closing operation and will engage their respective stationary contacts 12 at approximately the same time.

Circuit-breaker opening is performed by driving movable contacts 14 downwardly from their dotted line position 17 into their solid line position shown. Opening force is transmitted through operating rod 16, and the mechanical coupling provided by bridging member 15 assures that movable contacts 14 will separate from their respective stationary contacts substantially simultaneously.

For a more detailed example of a high voltage circuit breaker that performs in the general manner described up to this point, reference may be had to US. Patent 2,911,546-Oppel, assigned to the assignee of the present invention.

For limiting the magnitude of the voltage surge developed by the circuit breaker upon closing, the circuit breaker is provided with low ohmic resistors 30 that can e inserted into the power circuit during a closing operation just prior to engagement of the main contacts. Such insertion of the resistors is referred to herein as preinsertion. When these resistors are inserted into the power circuit, each is connected in parallel with a set 11 of the

main contacts

12, 14.

For inserting the resistors 30 in the power circuit at the desired instant, I provide a triggered vacuum gap 32 in series with each resistor and in parallel with the associated set of main contacts. These triggered vacuum gaps can be identical and therefore only one is shown in detail, the other being shown in outline form. Each is preferably constructed as shown and claimed in application Ser. No. 580,998Lafferty, filed Sept. 21, 1966, now Patent No. 3,465,192 and assigned to the assignee of the present invention. Accordingly, it comprises a sealed envelope that is evacuated to a pressure of 10* mm. of mercury or lower. The envelope 40 comprises a tubular casing 42 of a suitable insulating material and a pair of

metallic end caps

43 and 44 joined in vacuum-tight relationship to the respective opposite ends of the insulating casing 42 by suitable seals.

Located within the evacuated envelope 40 is a pair of

main electrodes

46 and 48 that are spaced apart to define a primary gap 50 therebetween. The upper electrode 46 is supported on upper end cap 43 by means of a conductive supporting rod 46a, whereas the lower electrode 48 is supported on lower end cap 44 by a tubular conductive supporting rod 48a.

The primary gap 50 between

electrodes

46, 48 has a high enough dielectric strength to normally maintain the parallel circuit through resistor 30 open. It is to be understood that the circuit breaker of FIG. 1 has a low enough voltage rating to permit a single gap to be relied upon to withstand the voltages developed across the shunted

main contacts

12, 14 Without a breakdown. For higher voltage circuits, an appropriate number of these gap devices are connected in series in the shunt circuit.

For causing the main gap to break down when a triggering pulse is supplied to the triggered vacuum gap, there is provided a trigger gap 54 located within a centrally disposed recess 55 in the lower electrode 48. This trigger gap comprises an annular ceramic disk 57 located within recess 55 and two thin layers 58 and 60 of metal bonded to the upper surface of ceramic disk 57 in radially spaced apart relationship. These two layers of metal constitute the electrodes of the trigger gap. They are separated by a circular groove 62 of V cross-section that extends circumferentially of the ceramic disk and has its walls defined by the ceramic material itself. One of the trigger electrodes 60 is electrically connected to the main electrode 48. The other trigger electrode 58 is normally electrically isolated from the main electrode 48. These layers 58 and 60 are preferably formed of a metal such as titanium charged with a large quantity of hydrogen.

As is well known, the lines of field distribution at the interface between a metal and a ceramic body in intimate contact are highly favorable to a breakdown at such interface. Accordingly, a relatively low voltage appearing across the trigger gap can initiate a discharge from one of the interfaces across the trigger gap. This discharge immediately evolves hydrogen from the trigger electrodes ionizing it and forcing electron-ion plasma into the main gap 50 to initiate an arc across the main gap.

For applying voltage across the trigger gap, a conductive lead 65 is provided extending through a central passageway in ceramic disk 57. At its upper end this lead 65 is suitably electrically connected to trigger electrode 58. At its lower end the lead 65 projects through a ceramic plate 67 that is hermetically sealed to the lead and to the lower end cap 44, thereby sealing the lower end of the envelope.

The electrode 48 is shaped to provide a nozzle surrounding the upper end of lead 65. This nozzle has a restricted throat located between the trigger gap 54 and main gap 50 through which ionized plasma is projected from the trigger gap into the main gap to initiate the main arc. The restricted nature of this throat prevents the main arc from finding its way onto the parts of the trigger gap, thereby protecting these parts from the main are.

For applying a triggering pulse to trigger gap 54 at a predetermined instant, a trigger pulse source 70 is connected across the gap 54 between lead 65 and end cap 44. This trigger pulse source can be of a conventional design and its details are therefore not shown. In a preferred form of the invention, this trigger pulse source 70 is a normally-oft source that is turned on by a light signal transmitted thereto through a fibre optics light pipe 73. For turning on source 70 in response to reception of the light signal, a light-activated SCR can be used in the manner shown, for example, in FIG. 11.411, p. 211 of the General Electric SCR Manual, 3rd edition, 1964.

For developing a light signal to turn on the trigger pulse source 70, a suitable lamp is provided. This lamp 75, which is connected in an energizing circuit 76, is normally off. But when the energizing circuit 76 is completed, a voltage pulse is applied across the lamp to produce a light pulse of steeply rising luminous intensity. The light pulse travels through the light pipe 73 to turn on the light-activated trigger pulse source 7 0.

Each trigger pulse source 70 is provided with a light pipe 73 through which the light pulse from the lamp 75 is transmitted. Since the two trigger pulse source 70 derive their turn-0n signal from a common light source 75, it will be apparent that the light pulses arrive at each trigger pulse source simultaneously. Both trigger pulse sources 70 turn on at an extremely high speed in response to the reception of the light pulse. Thus, the trigger pulse sources 70 deliver their voltage pulses to their respective trigger gaps substantially simultaneously.

In response to the application of the trigger pulses thereacross, the trigger gaps 54 immediately sparkover and immediately produce an arc-over of their associated pirmary gaps 50. The total time between establishment of the light pulse and arc-over of the primary gaps 50 is in the neighborhood of 1520 microseconds. This time may vary by several microseconds from one triggered vacuum gap to another, resulting in one gap firing several microseconds after the other, but this time variance is so slight as to be of little consequence.

In a preferred form of the invention, I develop the light pulse at such an instant that the triggered vacuum gap 32 fires near a voltage zero in the voltage between the power circuit 13 at the source side of the circuit breaker and ground. This is accomplished by applying a voltage pulse to the lamp 75 just prior to or shortly after such voltage-zero point. This timing of the voltage pulse can be accomplished by conventional means such as shown for example in U.S. Patent 2,825,824Perolini, where a circuit is disclosed for developing an output pulse at a desired instant on the voltage wave. Since the details of the pulse-forming-and-timing circuit are not a part of my invention, I have shown the circuit in block form at 80. A suitable potential transformer 82 connected between line 13 and ground at the source side of the breaker supplies input information on line voltage to the pulse-forming-and-timing circuit through an input circuit 83.

To prevent the pulse-forming circuit 80 from supplying an output pulse to the lamp 75 until a predetermined point in the closing Operation, a normally-open control switch 85 is provided. This control switch 85 is suitably coupled to the movable contacts 14 of the circuit breaker. When the contacts 14- of the circuit breaker are moved through a desired point in the closing stroke, control switch 85 is closed. Thereafter, the next pulse developed by the pulse-forming-and-timing circuit 80 is supplied to the lamp 75 to turn on trigger pulse source 70 to cause are over of the triggered vacuum gap 32. When the circuit breaker reaches its fully closed position, a suitable b switch 86 Opens to prevent further voltage pulses from being applied to lamp 75 so long as the circuit breaker remains closed. This b switch 86 is schematically shown as being controlled by a suitable cam 88 on the circuit breaker operating rod 16.

It is known that the magnitude of the voltage surge developed by circuit-breaker closing can be substantially reduced if closing is approximately synchronized with voltage zero, but such synchronized closing has not generally been attempted, because mechanically-controlled circuit breakers can rarely be closed with the precision needed to consistently efiect closing at voltage zero. In a mechanically-controlled circuit breaker minor variations in starting characteristics, in speed, and prestrike gap length can introduce unpredictable variations in the point of circuit completion which defeat consistent closing at the desired voltage zero point. My circuit breaker with its triggered vacuum gaps, however, can be controlled with much more precision than a mechanically-controlled circuit breaker. As pointed out hereinabove, variations in the total time between application of the light signal and firing of the triggered vacuum gaps are only on the order of microseconds, and this is so small that firing can be consistently produced across all the triggered vacuum gaps within a few degress of the desired instant adjacent voltage zero. This instant can be made close enough to voltage zero to achieve a substantial reduction of the magnitude of the voltage surge produced by closing.

Since all the triggered vacuum gaps fire substantially simultaneously, there is a materially reduced likelihood that a damaging voltage will be built up across the insulation paralleling the last gap to fire. Before the voltage across the last gap to fire can build up to a damaging level, this gap fires, thereby preventing further voltage buildup.

Although my invention lends itself exceptionally well to a circuit breaker in which closing is synchronized with a particular point in the voltage wave, it is to be understood that the invention also has application to circuit breakers in which no effort is made to time closing with respect to a point in the voltage wave. In such a circuit breaker the potential transformer 82 can be omitted and the voltage pulse delivered to the lamp 75 when the control switch 85 is closed without regard to power circuit voltage. Such a control will produce substantially simultaneous firing of the triggered vacuum gaps 32 and will thus protect the insulation paralleling the last gap to fire, as described in the preceding paragraph.

A triggered vacuum gap, once fired, will continue to conduct until the current across the main gap reaches substantially zero at which point it will normally clear, i.e., will recover its dielectric strength to prevent further conduction. To prevent either of the triggered vacuum gaps 32 from clearing prior to the point at which the

main contacts

12, 14 engage, I supply repetitive voltage pulses to the trigger gap 54 once the main gap 50 begins conducting. These repetitive pulses prevent the main gap 50, once fired, from clearing until the

contacts

12, 14 engage.

For supplying these repetitive pulses following initial firing of the triggered vacuum gap, a suitable oscillator 90 is provided which is capable of delivering repetitive voltage pulses at the desired frequency across its output terminals 91. The output terminals 91 of the oscillator are arranged for connection across the lamp 75. An auxiliary control switch 92 connects the oscillator across lamp 75 shortly after control switch 85 is closed, thus supplying the pulses from the oscillator to the lamp. The lamp responds to each voltage pulse by supplying a light pulse to the trigger pulse sources 70, causing each source 70 to supply a pulse to its respective trigger gap as desired. When the main contacts reach their engaged position, the b switch 86 opens to isolate the lamp 75 from the oscillator, thereby terminating pulsing of the trigger p I can eliminate the need for oscillator 90 by using instead of a triggered vacuum gap, a triggered low pressure gas gap, such as shown in US. Patent 3,248,603Howell et al., assigned to the assignee of the present invention. The triggered low pressure gas gap can be constructed in the same manner as the triggered'vacuum gap shown at 32 except that instead of being highly evacuated, it contains gas at a pressure in the micron range, e.g., nitrogen at a pressure of 100 microns. Such a gap will not normally clear at a current zero following arcing. Thus, once fired, it will continue conducting until the

main contacts

12, 14 engage. Contact-engagement removes voltage from across the main gap and permits it to clear. Since there is no need for repetitive pulses with such a gap, the oscillator can be omitted when such a gap is used. As pointed out in the aforesaid Howell patent, the gas pressure in the gap is sufficiently low that the mean free path of gas particles within the container 40 is greater than the inter-electrode distance.

Although I have shown in FIG. 1 only one trigger gap (54) in each triggered vacuum gap device 32, it is usually desirable for A-C applications to provide two trigger gaps, one adjacent each main electrode. To facilitate firing of the main gap in response to sparkover of the trigger gap, the location of the trigger gap should be adjacent the cathode of the main gap. By having two trigger gaps, one adjacent each main electrode, and by sparking-over these two trigger gaps each time it is desired to fire the main gap, assurance is had that a trigger gap will spark-over adjacent the cathode irrespective of which main electrode is the cathode.

FIG. 1a schematically illustrate a triggered vacuum gap device with two trigger gaps 54, one adjacent each main electrode. Each trigger gap 54 is connected across a separate trigger pulse source 70. The trigger pulse sources 70 are normally-off sources that are activated simultaneously by light pulse signals delivered through light pipes 73 from a common light source such as 75 in FIG. 1.

For reducing the amount of voltage that the triggered vacuum gap will be required to withstand when the circuit breaker is open, the embodiment of FIG. 2 can be utilized. Here, at each break of the circuit breaker, an intermediate contact is provided between the two

main contacts

12 and 14. An isolating gap 102 is present between the intermediate contact 100 and the movable contact 14 when the circuit breaker is in its fully-open position of FIG. 2. When the circuit breaker is in its fully open position of FIG. 2, isolating gap 102 is in series with the main gap 50 of the triggered vacuum gap. Accordingly, the voltage present between the

main contacts

12 and 14 is distributed between isolating gap 102 and vacuum gap 50, thus relieving vacuum gap 50 of a portion of the total voltage.

During a closing operation, the movable contact 14 is driven in an upward direction, first engaging intermediate contact 100 and then engaging the stationary contact 12. Firing of the triggered vacuum gap is delayed until after the movable contact has engaged the intermediate contact 100. The firing means employed in FIG. 2 can be substantially the same as that used in FIG. 1 and therefore has not been shown in the drawing.

Although not shown, it is to be understood that suitable capacitors or other impedances can be connected across the gaps of the circuit breaker to achieve a desired distribution of voltage between the gaps when the circuit breaker is open.

In certain circuit breakers it is necessary to use the resistors 30 during a circuit-breaker opening operation as well as during a closing operation. During an opening operation, as is known, resistors 30 can facilitate interruption by limiting the rate of rise of the recovery voltage transient. In the circuit breakers of FIGS. 1 and 2 the resistors 30 are disconnected during an opening operation and are not relied upon to effect the desired reduction in the recovery voltage rate during opening. In

the embodiment of FIG. 3, however, the resistors are available for this purpose during an opening operation. Here, each of the main breaks 11 is shunted by a resistor switch 110 in parallel with the main break. These resistor switches 110 are arranged to close at about the same time as the main breaks 11. Upon closing, the resistor switches 110 connect the resistors 30 in parallel with the main breaks. During a circuit breaker opening operation, the resistor switches 110 remain closed until a predetermined period has elapsed after the main breaks are opened. During this period, the resistors 30 shunt the main breaks and limit the rate of rise of recovery voltage in the desired manner. When the interruption has been completed at the main breaks, the resistor switches 110 open to interrupt the flow of residual current through resistors 30.

The resistor switches 110 have been shown schematically in FIG. 3 in order to facilitate an understanding of the invention. For a more detailed showing of how such resistor switches are constructed and controlled, reference may be had to the aforementioned US. Patent 2,911,546-Oppel.

In the embodiment of FIG. 3, the triggered vacuum gaps 32 are simultaneously fired during closing in essentially the same manner as described with respect to FIGS. 1 and 2. Such firing preinserts the resistors 30 in the same manner as described with respect to FIGS. 1 and 2.

FIG. 4 illustrates another embodiment which is capable of making the resistors 30 available during an opening operation. FIG. 4 shows a portion of the circuit 3 breaker in its fully-open position. In FIG. 4, the triggered vacuum gap 32, instead of having fixed electrodes, has relatively movable

main electrodes

46, 48 which are moved into engagement following arc-over of the main gap 50. A more detailed disclosure of a triggered vacuum gap of this type is contained in application S. N. 438,005- Lee, filed Mar. 8, 1965, now Patent No. 3,319,121 and assigned to the assignee of the present invention.

Referring more specifically to FIG. 4, electrode 48 is a stationary electrode and 46 is a vertically movable electrode. The movable electrode 46 is mounted on the upper end of a contact rod 146 that extends freely through the lower end plate 44 and freely through an opening in bridging member 15. A suitable metallic bellows 118 provides a seal about contact rod 46 to maintain the vacuum inside the gap device 32. When the circuit breaker is open, the movable electrode 46 is held in its illustrated position by a hold-open latch schematically shown at 120.

Closing of the circuit breaker and triggering of the gap device during closing are effected in the same manner as described in connection with FIG. 1. But in FIG. 4, after the gap device is triggered into conduction, its

electrodes

46, 48, instead of remaining stationary, are driven into engagement. In this connection, the hold-open latch 120 is tripped at a suitable point in the circuit-breaker closing stroke, whereupon a closing spring 123 drives electrode 46 upward into engagement with stationary electrode 48.

For tripping latch 120 at the desired point in the circuit breaker closing stroke, a tripping spring 121 and a cam 122 fixed to bridging member are provided. When the bridging member 15 reaches a certain point in its upward closing travel, cam 122 permits spring 121 to release, or

trip, latch 121. This tripping permits closing spring 123 4 to quickly drive the movable electrode 46 of the gap into engagement with stationary electrode 48. This engagement effectively maintains the resistor 30 in parallel with the main contacts when the circuit breaker is closed and during the initial portion of an opening operation.

During circuit-breaker opening, the bridging member 15, after moving through a predetermined downward travel, engages a shoulder 126 on movable contact rod 146, thereby opening the triggered vacuum interrupter 32 at a desired point in the opening stroke after the main contacts have parted. Prior to such opening of interrupter 32, the resistor 30 remained connected in parallel with the main break 11 to perform its intended function. Opening of interrupter 32 interrupts the current through resistor 30.

Although I have shown only single phase circuit breakers, it is to be understood that the invention is equally applicable to polyphase circuit breakers. In such circuit breakers, an assembly identical to any one of those shown in the drawings is connected in each phase of the circuit. A light source 75 common to the assemblies of all the phases can be used for turning on the trigger pulse sources 70 for all the triggered gap devices simultaneously, thereby arcing-over all the triggered gap devices 32 su=bstantially simultaneously. In another form of the invention, the triggered gap devices in each phase can be controlled separately from those in the other phases. For example, the triggered gap devices in each phase can be fired in synchronism with a predetermined instant on the voltage wave associated with that particular phase.

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

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

1. A high voltage circuit breaker comprising:

(a) a plurality of sets of separable contacts electrically connected in series,

(b) the contacts of each set being separated when the circuit breaker is open and being relatively movable to an engaged position during a circuit-breaker-closing operation,

(0) a voltage controlling resistor associated with each set of contacts,

(d) switching means for connecting the resistor associated with each set of contacts in parallel with the associated set of contacts at a predetermined time during a circuit-breaker-closing operation,

(e) said switching means comprising a pluraliy of triggered gap devices, each device comprising a pair of primary electrodes defining a main gap therebetween in series with the associated resistor and triggering means for causing an arc-over of said main gap when a triggering signal is supplied to said triggeringmeans, said triggering means comprising a trigger gap within said triggered gap device near said main gap but not exposed to the full voltage present across said main gap, said trigger gap sparking over in response to receipt of said triggering signal to cause arc-over of the associated main gap,

(f) and means operable during a circuit-breaker-closing operation for supplying to the triggering means of said gap devices triggering signals which spark-over the trigger gaps in all of said gap devices and cause arc-overs to be initiated substantially simultaneously in all of said main gaps before said sets of contacts engage.

2. The high voltage circuit breaker of claim 1 in which said triggered gap device is a triggered vacuum gap device wherein the normal pressure between said electrodes is less than 10" mm. of mercury.

3. The high voltage circuit breaker of claim 1 in which said triggered gap device is a low pressure gas device in which the mean free path of gas particles in said device exceeds the gap distance between said primary electrodes.

4. A polyphase high voltage circuit breaker comprising:

(a) a plurality of assemblies for connection in .the

respective phases of a polyphase circuit, each assembly being constructed as defined in claim 1, and

(b) means for causing the triggered main gaps in the assemblies in the respective phases to arc-over substantially simultaneously.

5. The circuit breaker of claim 1 in combination with means for consistently causing said triggering means to produce arc-over of said main gaps near voltage zero in voltage present on said breaker during said circuit-breaker closing operation.

'6. A high voltage circuit breaker comprising:

(a) a plurality of sets of separable contacts electrically connected in series,

(b) the contacts of each set being separated when the circuit breaker is open and being relatively movable to an engaged position during a circuit-breakerclosing operation,

() a voltage controlling resistor associated with each set of contacts,

(d) switching means for connecting the resistor associated with each set of contacts in parallel with the associated set of contacts at a predetermined tirn during a circuit-breaker-closing operation,

(e) said switching means comprising a plurality of triggered gap devices, each device comprising a pair of primary electrodes defining a gap therebetween in series with the associated resistor and triggering means for causing an arc-over of said gap when a triggering signal is supplied to said triggering means,

(f) and means operable during a circuit-breaker-closing operation for supplying to the triggering means of said gap devices triggering signals which cause arcovers to be initiated substantially simultaneously in all of said gaps before said sets of contacts engage,

(g) an intermediate electrode being provided for each pair of said separable contacts, said intermediate electrode being located between said separable contacts when the separable contacts are in their fully open position so that a first circuit-breaker gap is then present between said intermediate electrode and one of said contacts and a second circuit-breaker gap is then present between said intermediate electrode and the other of said contacts and the total voltage prevailing between said separable contacts is divided between saidtwo circuit-breaker gaps, and means connecting one of the electrodes of said triggered gap device to said intermediate electrode to connect said gap device in parallel with said first circuitbreaker gap.

7. A high voltage circuit breaker comprising:

(a) a plurality of sets of separable contacts electrically connected in series,

(c) a voltage controlling resistor associated with each set of contacts,

'f) and means operable during a circuit-breakerclosing operation for supplying to the triggering means of said ga devices triggering signals which cause arc-overs to be initiated substantially simultaneously in all of said gaps before said sets of contacts engage,

(g) a resistor switch associated with each set of contacts and operable when closed to connect said resistor in parallel with said set of contacts, said resistor switch being connected in series with said resistor and in parallel with said triggered gap device, and means for maintaining said resistor switch closed during the initial portion of a circuit-breaker opening operation so that said resistor is available to control the rate of rise of the recovery voltage transient at a current zero during an opening opera tion, and means for opening said resistor switch following said initial portion of the circuit-breaker opening operation to interrupt the current through said resistor.

8. The circuit breaker of claim 1 in which:

(a) the electrodes of said gap device are relatively movable into and out of a position of engagement, and

(b) means is provided for moving said electrodes into engagement immediately after arc-over of said main gap during a circuit-breaker closing operation.

9. The circuit breaker of claim 8 in combination with means for maintaining said electrodes in engagement during the initial portion of a circuit breaker opening operation so that said resistor is available to control the rate of rise of the recovery voltage transient at a current zero during an opening operation, and means for separating said electrodes during a subsequent part of said opening operation to interrupt the current through said resistor.

10. The circuit breaker of claim 1 in which said means for supplying triggering signals comprises normally-inactive trigger pulse sources respectively connected to the triggering means of said gap devices and means for activating said pulse sources substantially simultaneously.

11. The circuit breaker of claim 11 in which:

(a) said trigger pulse sources are each activated in response to the reception of a predetermined light signal, and

(b) said means for activating said pulse sources comprises a light source common to all of said lightactivatable trigger pulse sources for developing and transmitting light energy that simultaneously reaches said pulse sources in the form of light signals simultaneously activating said pulse sources.

12. A high voltage circuit closer for closing an alternating-current circuit at a preselected point on the voltage wave of the alternating voltage present on said circuit, comprising:

(a) a pair of separable contacts which are separated when the circuit closer is open and are relatively movable to an engaged position during a closing operation of the circuit closer,

(b) a shunt circuit including switching means for electrically connecting the shunt circuit in parallel with said contacts when said switching means is closed,

(c) said switching means comprising a triggered gap device comprising a pair of primary electrodes defining a main gap therebetween in series with said shunt circuit and triggering means for causing an arc-over of said main gap when a triggering signal is applied to said triggering means, said triggering means comprising a trigger gap within said triggered gap device near said main gap but not exposed to the full voltage present across said main gap, said trigger gap sparking over in response to receipt of said triggering signal to cause arc-over of the associated main gap,

((1) and trigger control means sensitive to said voltage and operable during a closing operation of said circuit closer for supplying to said triggering means a triggering signal which causes said main gap to arcover at a preselected point on said voltage wave before said contacts engage.

13. The high voltage circuit closer of claim 12 in combination with means for disabling said trigger control means until one of said contacts has moved through a portion of its closing travel into a predetermined position relative to the other contact during a closing operation of said circuit closer and for thereafter allowing said trigger control means to operate.

14. The high voltage circuit closer of claim 12 in which said triggered gap device is a triggered vacuum gap de- 1 1 vice wherein the normal pressure between said electrodes is less than 10- mm. of mercury.

15. A high Voltage circuit closer for closing an alternating-current circuit at a preselected point on the voltage wave of the alternating voltage present on said circuit, comprising:

(a) a plurality of sets of separable contacts electrically connected in series,

(b) the contacts of each set being separated when the circuit closer is open and being relatively movable to an engaged position during a closing operation of said circuit closer,

(c) shunt circuits respectively associated with said sets of contacts and including switching means for electrically connecting the shunt circuits in parallel with their respective sets of contacts when said switching means is closed,

((1) said switching means comprising a plurality of series-connected triggered gap devices, each comprising a pair of primary electrodes defining a main gap therebetween in series with its associated shunt circuit and triggering means for causing an arc-over of said main gap when a triggering signal is applied to said triggering means, said triggering means comprising a trigger gap within said triggered gap device near said main gap but not exposed to the full voltage present across said main gap, said trigger gap sparking over in response to receipt of said triggering signal to cause arc-over of the associated main gap,

(e) and trigger control means sensitive to said voltage and operable during a closing operation of said circuit closer for supplying to the triggering means of said gap devices triggering signals Which spark-over the trigger gaps in all of said gap devices and cause arc-overs to be initiated substantially simultaneously in all of said main gaps before said sets of contacts engage and at a preselected point on said voltage wave.

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