US 3891813 A
A gallium cathode high voltage ignitron for synchronous closing of EHV circuit breakers, is provided, to control switching surge overvoltages. Due to the fast triggering time of the gallium cathode ignitron the circuit can be closed synchronously without pre-insertion resistance to obtain a switching surge level of 1.5 per unit or less.
Claims available in
Description (OCR text may contain errors)
United States Patent Yoon et al. 1 June 24, 1975 1541 EHV CIRCUlT BREAKER UTILIZING 3.299.377 1/1967 (211C114 ct =11 200/148 1 GALLIUM CATHODE IGNITRONS FOR 2 OX SYNCHRONOUS CLOSING 3,646,295 2/1972 Circle 317/11 A  Inventors: Kue H. Yoon; Robert E. Friedrich;
Andreas M. Sletten, all of Pittsburgh. Primary Examiner-Robert S. Macon  Assignee: Westinghouse Electric Corporation, Almmey Agent Massung Pittsburgh, Pa.
 Filed: May 4, 1973 1211 Appl. No.: 357,437  ABSTRACT 1521 us. c1..... 200/144 AP; 200/144 B; 200/148 1; A gallium cathode high voltags ignilron for 51991119 317/1 1 A nous closing of EHV circuit breakers, is provided, to 1511 1111.131. 1. HOlh 33/16 control Switching Surge overvolwges- Due to the f 158] Field of Search 200/144 AP, 144 B, 143 1; triggering time f e g i m h de igni ron. th cir- 317 1 1 A, 1 1 B 1 1 Q 1 1 1 1 1 E cuit can be closed synchronously without pre-insertion resistance to obtain a switching surge level of 1.5 per  References Cited Unit less- UNlTED STATES PATENTS 2,665,396 1/1954 Weinfurt 317/1 1 A 10 Claims, 5 Drawing Figures 10 i 26 I 12 1 fi l EHV CIRCUIT BREAKER UTILIZING GALLIUM CATIIODE IGNITRONS FOR SYNCHRONOUS CLOSING BACKGROUND OF THE INVENTION This invention relates generally to circuit breakers and more particularly to high voltage circuit breakers having a means for closing the circuit breaker synchro nously at the instant the voltage across the contacts is substantially zero or a minimum.
In determining the insulation requirements for transmission equipment, consideration must be given to the voltage levels to which various insulation systems will be subjected. Normal operating voltages, switching surges and lightning surges must all be considered. As reported in I.E.E.E. transactions on Power Apparatus and Systems, Volume PAS-88, No. 7, July, 1969 in an article entitled Multi-Step Resistor Control of Switching Surges" by R. G. Colclaser, Jr., charles L. Wagner and Edward P. Donohue on pages 1022 to 1023: Prior to the advent of 500 KV systems, lightning was the criterion governing the number of insulators required for transmission lines. During the engineering studies for the Virginia Electric and Power Co. 500 KV System it was found that switching surges were a determining factor; for example, switching surges produced by conventional breakers dictated that 35 insulators were needed, whereas from a lightning standpoint only 24 insulators were required. At this point the concept of single step pre-insertion resistor switching to reduce the maximum switching surge from 3.0 per unit to approximately 2.0 per unit was instituted. With this switching surge reduction, lightning again becomes the determing factor for line insulation. All domestic 500 KV breakers are now supplied with the single step resistor feature. Recent studies on UHV systems show that to keep the line insulation down to the lightning level at system voltages above 500 KV, further reduction in switching surge magnitudes may be indicated. At 765 KV, for example, maximum switching surge levels of 1.7 pu may be required, at 1,100 KV, levels of 1.5 pu or lower may be needed."
When an open transmission line is energized by closing power circuit breakers depending on the initial voltage across the breaker contacts, the switching surge voltage can be quite high. As stated above, this is especially true for the extra high voltage class (EHV) breakers and the ultra-high voltage class (UHV) breakers. Switching surge voltages developed can easily flash over insulators or destroy the line insulation system. To construct an insulating system to withstand the surge voltages the cost may become prohibitive or may even be impossible to attain physically in the case of 765 or 1,100 KV class, unless some means are provided to control the switching surge voltage level.
The most direct method to control the switching surge level is by closing the circuit breaker synchronously at the instant when the voltage across the contacts is substantially zero or a minimum. The synchronous closing can be achieved with or without preinsertion of resistance. However, the closing of an EHV or UHV power circuit breaker involves the motion of heavy masses and ultra-high speed contact movement. In practice, synchronous closing of the main power contacts is not possible. A study was carried out to examine the switching surge voltage levels taking the random variation of breaker closing into consideration. It
was determined that to obtain a switching surge level of 1.5 per unit or less 98 percent of the time, with a maximum level of 1.65 per unit, the standard deviation for the closing without resistance must be limited to about 13 (0.602 milliseconds). It was also determined in order to obtain a switching surge level of 1.5 per unit or less percent of the time, with a maximum level of 1.65 per unit utilizing pre-insertion of a 450 ohm resistance, the standard deviation should be limited to ap' proximately 30 (1.39 milliseconds).
At present, closing a 550 KV breaker requires approximately 6% cycles (108 milliseconds) and the above closing requirements are quite difficult to meet. Although manufactures are trying to meet these requirements by improved closing mechanisms and also by using optimum resistance values it is desirable to have an alternate means of synchronously closing power circuit breakers. This is especially true when the trapped charge voltage on the line fluctuates due to oscillations with the compensating inductors, necessitating a rapid synchronization.
Presently 550 KV SF, gas filled circuit breakers, with two pre-insertion resistors, are designed to limit surges during closing to 1.5 per unit for 98 percent of the operations with an absolute limit of 1.65 per unit. It is therefore desirable to have a circuit breaker, with means for synchronously closing the electric circuit at a minimum voltage or substantially zero, which limits the surge voltage below the 1.5 per unit level most of the time, with an absolute limit of 1.65 per unit.
SUMMARY OF THE INVENTION In accordance with the invention, an EHV or UHV circuit breaker is provided including a high voltage gallium acathode ignitron for synchronous closing of the circuit breaker, to limit the switching surge voltage, without insertion of resistance before closing the main circuit breaker contacts. The gallium cathode ignitron is connected in parallel with the contacts of the high voltage circuit breaker. The gallium cathode ignitron is triggered and closes the circuit breaker circuit at a voltage minimum or zero just preceding closing of the main breaker contacts. Thus, when the main contacts close, the circuit has already been closed synchronously and no switching surges are produced.
The cathode of the ignitron can be pure gallium, gallium mixed with some other material to lower the freezing point, or gallium absorbed in a sieve of some refractory material. The gallium cathode ignitron can be made to conduct high currents and to withstand extremely high voltages. Gallium has a high boiling point, a low melting point and low vapor pressure; thus, the liquid gallium can be used as a cathode and cathode erosion problems can be eliminated. The gallium cathode ignitron also has a very rapid ignition time. The initiation of full current conduction can be made in terms of a few microseconds.
As the voltage levels of transmission systems increase, the switching surge control problem is becoming more acute from the standpoint of economics and physical capability of the insulation systems. The application of the gallium cathode high voltage ingitron to the synchronous closing of high voltage circuit breakers can solve many problems by controlling the switching surge overvoltages.
The gallium cathode ignitron described in the present application can have a gallium pool cathode, a triggering electrode, a molybdenum anode, all disposed in an evacuated housing having a high vacuum below 2 X I Torr. Although the invention is described using ignitrons with liquid gallium cathodes, it should be understood that for circuit breaker closing application it is possible to use solid cathodes in the ignitrons since the number of operations by the ignitrons will be small and thus erosion of the cathode limited. There are also other liquid cathodes, alloys of gallium, which have certain advantages. An experimental model has been built showing withstand boltage between anode and cathode of greater than [20,000 volts. Practical devices with a withstand voltage greater than 300,000 volts can be built. It has been shown experimentally that triggering can be attained consistently within two microseconds, with an anode voltage as low as 25 volts and a triggering voltage of l0,000 volts. In an expermental gallium cathode ignitron currents of 1,000 amps can be conducted for 25 milliseconds repeatedly with no visible damage to the tube, and currents of at least 20,000 amps can be conducted for periods of several microseconds without damage. The voltage drop across the gallium ignitron during conduction of currents is about volts. After initial pulse triggering, the anode current continues to flow after the triggering signal is removed, until the next voltage zero or until the anode current is removed. The gallium pool in the gallium cathode ignitron need not be in the liquid state in order for the device to operate successfully. For repeated operations with high current, however, it is desirable that the cathode be liquified occasionally to reform a smooth cathode surface and to return condensed cathode material from walls and anode to the cathode region.
The gallium cathode ignitron can be applied to synchronous closing of high voltage circuit breakers with or without the pre-insertion resistance. However, because of the fast triggering time of the gallium ignitron, the l,5/l.65 per unit switching surge ratio conditions can be satisfied even without the pre-insertion resistance. Thus, using the gallium cathode ignitron, the necessity for the pre-insertion of resistance before main circuit breaker contact closing can be eliminated.
In one embodiment of the invention, two gallium cathode ignitrons are put inside the high voltage breaker housing. Each ignitron has its own triggering circuit so that the synchronous closing can be achieved at either polarity of the terminal voltage, but the ignitron under opposite polarity would definitely not fire. A sensing and control circuit can determine the polarity as well as the voltage zero to select the right triggering circuit. One of the ignitrons is fired at the voltage zero preceding the closing of the main contact, by not more than A cycle. For instance, the closing of the main contact can be aimed at the middle of a half-cycle of the terminal voltage wave. The main contacts can be aimed to close at between 6 and 6% cycles. Thus a fairly large deviation for the main contact closing of the power circuit breaker can be tolerated.
An alternate operation using both ignitrons would be to continually trigger both ignitrons from any voltage zero prior to main contact closing. If two ignitrons are used and triggered so as to give conduction in both directions from the time of a given voltage zero across the mechanical contacts, then the mechanical contacts can be closed randomly without any need for mechanical synchronization. Such a mode of operation could result in a cheaper mechanical drive system for the breaker.
As stated hereinbefore, the gallium cathode can be activated consistently within 2 microseconds after triggering. The triggering circuit can be resistancecapacitor (R-C) or inductive coupling circuits combined with trigatrons, thyratrons, or ignitrons, which are commercially available, and can be made to trigger within a fraction of a microsecond.
A single gallium ignitron can be used for synchronously closing the circuit breaker provided the main contact is aimed to close during that half of the voltage wave for which the ignitron can conduct. If only one ignitron is used, the sensing and control circuit can be designed to operate at only one polarity and V2 of the triggering circuit can be eliminated. For multi-break circuit breakers, the configuration described above can be multiplied accordingly.
In another variation, rather than place the gallium cathode ignitrons inside of the circuit breaker they can be disposed external thereto. The gallium ignitrons should normally be mounted inside of the high voltage gas SF, circuit breaker, to take advantage of the high dielectric strength of the SF environment. However, with improved construction of ignitrons, they can be located external to the circuit breaker if it is more convenient.
In the case of a fluctuating trapped charge voltage on the line due to compensating inductance, sensing of the line and bus voltages are necessary, to send a triggering pulse near a zero terminal voltage. That is, the gallium cathode ignitron is fired at the instant in time when the bus voltage equals the voltage existing on the open line, so that the voltage across the high voltage circuit breaker is approximately zero.
BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention reference may be had to the preferred embodiments, exemplary of the invention shown in the accompanying drawings in which:
FIG. 1 is a schematic diagram of an electrical system using a circuit breaker having a gallium cathode ignitron for synchronous closing;
FIG. 2 is a graphic representation of a closing sequence for a high voltage circuit breaker utilizing the teachings of the present invention;
FIG. 3 is a side sectional view of a gallium cathode ignitron;
FIG. 4 is a side view, partially in section, of a high voltage circuit breaker having internally mounted gallium cathode ignitrons; and
FIG. 5 is a side view of a portion of a high voltage circuit breaker having externally mounted gallium cathode ignitrons.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in particular, there is shown a schematic diagram of an electrical system having a high voltage circuit breaker 10 utilizing the teachings of the present invention. As shown in FIG. 1, an alternating current generator 12 supplies a bank of step-up transformers 14, the output of which is connected to a high voltage circuit breaker 10. The output of the high voltage circuit breaker l0 feeds a transmission line and load whose electric parameters are represented schematically by capacitance 15, in-
. t; is 6 duct-ance l6 and resistance [7. A gallium ignitron 20 is disposed within the housing of the high voltage circuit breaker 10. A bus boltage V is present on the bus side, the terminal being fed by, the voltagesource 12,. of the high voltage breaker 10. A line voltage V 'is measured on the line side, the terminal feeding the transmission line, of the high voltage breaker 10. A potential sensing device 19 and a control device 18 are connected to monitor the bus voltage V Potentialsensing device 19 feeds a voltage proportional to the bus voltage to control device l8. Control device 18 which can be similar to the timed closing device described in IEEE Paper 71 TP 571 -PWR, entitled EHV Breaker Rated for Control of Closing Voltage Switching Surges to 1.5 Per Unit." has a low burden. If available existing potential devices, such as potential transformers or capacitive bushing taps. can supply the reference voltage to control device 18.
When pushbutton 22 is depressed, indicating that the high voltage breaker is to be closed, control device 18 energizes the circuit breaker closing coil 24 at the proper time for the main contacts to close after a predetermined number of cycles. Thus the main contacts 26 of circuit breaker. 10 will close within a given cycle period, several cycles after the closing coil is energized. If the main contacts 26 are aimed to close at the peak of a given /5 cycle there can be a plus or minus onequarter cycle l .4 millisecond) deviation and the main breaker contacts 26 will still close in the desired A cycle. The requirement of closing of the main contacts within 4 milliseconds of a voltage zero can easilybeaccomplishecd by controlling the time with respect to voltage zero at which theclosing coil 24 is energized.
tron 20, initiating conduction of the gallium cathode A delay must normally be added to the breaker closing time so that the delayed closing time will result in the main contacts closing duringthe desired ,2 cycle. The initiating and delaying function is performed by control device 18. At the beginning of the i cycle during which the main contacts 26 will close, the control .de-
cathode ignitron 20 is connected in parallel withthe main contacts 26 so that the circuit completed by high voltage breaker 10 can be closed very near a voltage zero, by proper triggering of the gallium cathode ignitron 20.
Referring now to FIG. 2, there is shown a graphic representation of a closing sequence. At some point in time as indicated at 29 pushbutton 22 is actuated indieating to control device 18 that it is desired to close the circuit breaker 10. Device 18 senses the first voltage zero 30 after pushbutton 22 is actuated at time 28. A predetermined time A I later, control device l8'energizes the closing coil 24. The time delay A r beforeenergizing the closing coil is determined so that the main breaker contacts 26 will close in the desired cycle following a predetermined time, indicated by arrow 32, after the first voltage zero 30. The main contacts 26 are aimed to close at the peak 34 of half-cycle 3,3. Closing of the main contacts 26 at any point within the halfcycle 33 is satisfactory, thus by aiming. the, main contacts 26 to close at the peak point 34, the contact closing can deviate onefourth cycle around 34 and still be satisfactory. At the beginning of half-cycle 33, a triggering pulse 36 is supplied to the gallium cathode igniignitron 20. Thus, the main contacts 26 close during the half cycles 33 when the gallium cathode ignitron 20 is conducting. The only voltage across contacts 26 during final closing is the small voltage drop across the conducting gallium ignitron 20. The voltage drop across the gallium cathode ignitron 20 during conduction will be in the order of 20 volts. The gallium ignitr on 20 starts conducting rapidly so that the circuit through the high voltage circuit breaker 10 is closed at essentially a voltage zero.
Referring now to FIG. 3, there is shown a side view partially in section of a gallium cathode ignitron 20. Conventional ignitrons uses a mercury pool as cathode and since mercury has a high vapor pressure, the withstand voltages are limited to about 20 KV for repetitive operation. Higher operating voltages are achieved in mercury arc tubes where grids are introduced to maintain a more even field distribution but their size and cost increase rapidly with increasing voltage. The current capability of mercury tubes which is severly limited by the vapor pressure requires forced cooling for higher power limits. Gallium has a very low vapor pressure at room temperature with a vapor pressuretemperature profile almost identical to that of silver. Thus, in contrast to mercury, the break-down characteristics of a gallium ignitron 30 or rectifier are in the ultra-high vacuum breakdown regions and a small gap should be sufficient to withstand high voltages. in addition gallium is a liquid at room temperature (melting point 298C) but supercools for a very long period of time under vacuum. Thus, like mercury, cathode erosion under continual arcing is eliminated. A gallium cathode ignitron 20 can handle currents of several thousand amps with no apparent difficulty. Pressure within the gallium ignitron 20 can be lowered to and remains below 2 X l0" Torr, and shows no tendency .to increase even after heavy current pulses. The gal- ;must be exercised in the construction of an ignitron containing liquid gallium. [n the gallium ignitron 20, a .quartz beaker 40 is used to contain the gallium cathode pool 42. A tungsten rod 44 dipping into the gallium pool 42, serves as an electrical cathode connection. Quartz and tungsten are two of the materials showing most resistance to attack by liquid gallium. The anode I 46 ,is formed from molybdenum and is connected to a reentrant type glass bushing 48. The glass bushing 48 is supported from a stainless steel flange 50 which is connected to a stainless steel top cap 52. The quartz beaker 40 is suspended from the top cap 52 and con- .tains approximately 300 grams of gallium, which forms a cathode pool 42. A glass envelope S4 is joined to stainless steel flange 56 in a vacuum tight relationship. Stainless stell flange 56 is attached to top cap 52 using a gold gasket for a vacuum tight seal. When top cap 52 is joined to flange 56 glass envelope 54 surrounds the quartz beaker 40. The trigger electrode 58 passes through an opening 60 in top cap 52. Trigger electrode 58 is constructed from molybdenum. Trigger electrode 58 is supported by ceramic bushing 62 which is joined to the top cap 52 in a vacuum type relationship. The bottom portion 64 of the trigger electrode 58 is a tungsten rod ground to a fine point 66, at one end, and maintained at a height which is approximately I millimeter above the gallium pool 42.
Referring now to FIG. 4, there is shown a high volt age circuit breaker 10 having two gallium ignitrons disposed therein. A potential device 19 feeds a voltage proportional to the bus voltage to the control device 18. Device 18 has a low burden; thus the potential device 19 can be capacitive or inductive low power potential source to supply the reference voltage. The signal required by device 18 could also be obtained from an existing potential device which the user may already have in service. The circuit breaker 10 shown in FIG. 4 represents one pole of a three-phase alternating current circuit breaker. The circuit is made through con ducting studs 72 which pass through the bushings 74 and terminate on stationary contacts 76. A rotating bridging contact 78 makes contact with stationary contacts 76 and completes an electrical circuit between contacts 76. Operating rod 80 is mechanically linked to rotatable contact 78 and is used to rotate contact 78 between a first position in engagement with contacts 76 and a second positionn separated from contacts 76 to thereby interrupt the circuit through circuit breaker 10. Contact 78 is moved to the closed position by energizing closing coil 24 which moves operating rod 80 so as to close the circuit breaker 10. When it is desired to close the circuit breaker [0, the potential sensing device 19 and control device 18 senses the first voltage zero after circuit closing is indicated and at the proper time energizes closing coil 24 so that the main contacts 76 and 78 closes in a known half-cycle at a predeter mined future time. At the beginning of the half cycle during which the movable contacts 78 will close, a triggering signal 36 is sent to the proper gallium ignitron 20 and completes the circuit through breaker 10. Thus the circuit is made through circuit breaker 10 at or very near a voltage zero. The gallium ignitron 20 conducts during the half cycle in which the main moving contact 78 engages stationary contacts 76 to mechanically complete the circuit. After the end of the half cycle during which the movable contact 78 closes, the gallium ignitron 20 ceases conduction.
In the embodiment of the invention shown in FIG. 4, the gallium ignitrons are disposed within the housing 82 of the high voltage circuit breaker 10. If the breaker 10 is of the SF variety, the gallium ignitrons 20 being disposed within the housing 82 can take advantage of the SF, environment and its high dielectric strength. Triggering electrode lead 84 passes through a bushing 86 in housing 82 and connects to the trigger electrode 58.
Potential device 19 is connected to the source or bus side of the high voltage circuit breaker 10. When there is a trapped charge voltage on the line which fluctuates because of the oscillation with the compensating inductors, a fast synchronization is mandatory. In the case of a fluctuating trapped charge voltage on the line, an additional potential sensing device 88 is required. The signals from line potential device 88 and from bus potential device 19 are transmitted to control device 18 so that the triggering pulse 36 to the appropriate gallium cathode ignitron 20 can be transmitted near a zero terminal voltage, across circuit breaker contacts 76 and 78. When a fluctuating trapped charge voltage is present on the line, because of the compensating inductance, an additional sensing of the line voltage is necessary prior to the mechanical contact closing to send the triggering pulse 36 when the voltage across contacts 76 and 78 is zero or at a minimum. Control device 18 compares the signals from potential device I9 and potential device 88 and sends a signal to the proper gallium ignitron 20 so that it begins to conduct at or near the point where the instantaneous bus voltage equals the voltage on the line, at this point the voltage across the open breaker contacts is essentially zero. Thus, the circuit is completed at a voltage zero in the one-half cycle before the closing of the main contacts 76 and 78. That is, the circuit is completed when the bus voltage V equals and is in phase with the voltage existing on the open line V and the voltage across circuit breaker I0 is approximately zero. Control device 18 through potential sensing device monitors the line voltage V, under all conditions of do. trapped charge and a.c. oscillations, for shunt reactor compensated lines, and fires the gallium ignitron 20, which rapidly conducts within two microseconds of receipt of the signal, in the one-half cycle preceding contact 76 and 78 closing.
FIG. 5 shows a portion of a circuit breaker 10, as shown in FIG. 4, but with gallium ignitrons mounted external to the circuit breaker 10. Operation of the gallium ignitron 20 and the related components is as described above. The gallium ignitrons 20 as described above were put inside the circuit breaker I0 to utilize the high dielectric strength of the SP However, with improved construction of gallium ignitrons 20 they can be used external to the breaker, if this is more convenient. By using the gallium ignitrons external to the breakers, it is not necessary to bring in the triggering leads 84 through the interrupter housing 82 and the gallium ignitrons can be applied to existing high voltage breaker designs without any modification of the circuit breaker 10.
From the description given above it can be seen that the gallium cathode ignitron 20 can be applied to the synchronous closing of EHV or UHV breakers to control the switching surge voltage. The switching surge voltage can be controlled without pre-insertion of closing resistors. By completing the circuit at or very near a voltage zero, which is possible due to the fast triggering time of the gallium ignitron 20, a 1.5 normal 1.65 maximum switching surge ratio condition can be acheived without pre-insertion resistance.
1. A high voltage synchronous closing circuit breaker for use on an alternating current circuit above I00 KV, comprising:
main contact means disposed in said housing and being movable between an open and a closed position;
synchronous closing means connected in parallel with said main contact means for synchronously closing at substantially the voltage zero just prior to main contact closing and thereby completing an electrical circuit around said main contacts;
said synchronous closing means comprising a gallium cathode ignitron means having an anode, a cathode and a trigger disposed within a sealed housing; said anode directly connected to one side of said main contact means and said cathode directly connected to the other side of said main contact means;
said gallium cathode ignitron means constructed to have greater than a mo KV withstand level thereacross;
trigger actuating means connected to said trigger to trigger said gallium cathode ignitron within 100 microseconds of a voltage zero.
2. A high voltage synchronous circuit closing circuit breaker as claimed in claim 1, including: multiple gallium cathode ignitrons connected in parallel with said main contact means, at least one of said multiple gallium cathodes being connected in a positive polarity connection and at least one of said multiple gallium cathode ignitrons connected in a negative polarity connection, so as to be capable of completing a circuit of either polarity across said main contact means.
3. A high voltage synchronous closing circuit breaker as claimed in claim 2 wherein said gallium cathode ignitrons are disposed internally of said circuit breaker housing.
4. A high voltage synchronous closing circuit breaker as claimed in claim 2 wherein said gallium cathode ignitrons are disposed external to said circuit breaker housing.
5. A high voltage synchronous closing circuit breaker as claimed in claim 2, wherein said synchronous closing means comprises: means for sensing the voltage across said main contact means; and means for triggering said gallium cathode ignitron into conduction at a voltage zero across said main contact means at the beginning of the one-half cycle during which said main contact means close to limit closing surge voltage.
6. A high voltage synchronous closing circuit breaker as claimed in claim 1, wherein said gallium cathode ignitron comprises: a cathode formed from gallium; an anode displaced from said cathode to form a gap therebetween', a trigger electrode cooperatively associated with said anode and said cathode to initiate an electrical conducting path between said anode and said cathode when energized, and a highly evacuated housing surrounding said anode, said cathode and said trigger electrode.
7. A high voltage synchronous closing circuit breaker as claimed in claim 6, wherein: said gallium cathode is supported in an insulating cup-shaped member; and said evacuated housing comprises, a glass cup-shaped portion, a metal top cap joined to said glass cup-shaped portion in a vacuum-tight relationship, said metal top cap having a hole therethrough for passage of said anode, said anode being electrically insulated from said top cap, and a tungsten rod having one end attached to said top cap and having the other end immersed in said gallium cathode so as to electrically connect top cap to said gallium cathode.
8. A high voltage alternating current synchronous closing circuit interrupter for use on EHV circuits above 69 KV, comprising:
a housing which is sealed;
an insulating gas disposed within said sealed housing;
main contact means disposed in said housing, movable between an open and a closed position;
a plurality of synchronous closing means for synchronously closing at a voltage zero prior to main contact closing and thereby completing an electrical circuit around said main contacts disposed within said housing and being surrounded by said insulation gas;
each of said plurality of synchronous closing means comprises a gallium cathode ignitron having an anode, a cathode, and a trigger disposed within an evacuated housing; and,
each of said gallium cathode ignitrons constructed to have a withstand voltage level above 69 KV and a trigger time of less than 20 microseconds.
9. A high voltage alternating current synchronous closing circuit interrupter, as claimed in claim 8, wherein:
each of said plurality of synchronous closing means comprises an ignitron having a cathode; and
said cathode comprises gallium.
10. A high voltage alternating current synchronous closing circuit interrupter, as claimed in claim 8, wherein:
said insulating gas comprises sulfur hexafluoride.