US2833965A - Electrical protective device - Google Patents

Description

' w. R. BAKER ELECTRICAL PROTECTIVE DEVICE May 6, 1958 Filed May 17, 1956 Y L P P U s INVENTOR.

WILLIAM R. BA KER 0 o BIAS POWER SUPPLY 45 ATTORNEY.

United States Patent ELECTRICAL PROTECTIVE DEVICE William R. Baker, Orinda, Califi, assignor to the United States of America as represented by the United States Atomic Energy Commission Application May 17, 1956, Serial No. 585,588

Claims. (11. 317-51 The present invention relates to an improvement in the field of protective devices for electrical apparatus and is particularly directed to the discharging of resonant cavities for preventing energy back flow therefrom through associated equipment as a result of faults in the latter.

Although various applications of the invention are possible, particular advantage has been achieved in employing the invention in connection with particle accelerators wherein resonant cavities or waveguides are energized to high levels for establishing particle accelerating fields. In such devices wherein large current beams of charged particles are operated upon, it is necessary to supply very large quantities of high frequency power to the cavities, or waveguides as the case may be, and in this operation high power discharge tubes are employed. Operating faults in the power supply to the cavities, such as sparking in the discharge tubes, provide a discharge path into which the cavity would unload, thereby causing very material damage, such as destruction of a sparking tube.

Although innumerable protective devices have been developed and marketed, it has been found that none capable of handling loads of the magnitude herein encountered operate with sufiicient rapidity to aflord requisite protection. The present invention operates in the herein preferred embodiment to discharge a resonant cavity or waveguide in an extremely short time following a fault in the means supplying energy thereto and thus protects the latter from cavity discharge therethrough.

It is an object of the present invention to provide an improved protective device for discharging very high power upon the occurrence of faults in equipment being protected.

It is another object of the present invention to provide a discharge device for producing a protective controlled vacuum discharge.

It is a further object of the present invention to provide an improved discharge device operating wholly electrically to substantially instantaneously discharge high voltage electrodes in vacuum.

It is yet another object of the present invention to pro vide protective arc discharge means rapidly unloading cavities.

It is a still further object of the present invention to provide means for discharging the energy in a resonant cavity substantially instantaneously upon reverse conduction in power supply means energizing the cavity for protecting such power supply means.

Numerous other advantages and possible objects of the invention will become apparent from the following description of a single preferred embodiment of the invention taken together with the attached drawing illustrating this embodiment. The sole figure of the drawing illustrates one embodiment of the invention including mechanical structure and associated electrical cincuitry.

The invention in general provides means defining a spark gap communicating with the interior of a cavity or waveguide adapted for high power energization or an a high vapor pressure, such as copper.

2,833,965 Patented May 6, 1958 ice evacuated chamber containing an electrode having a large power difierential from the wall or other electrode therein. A control or trigger circuit is connected between a power supply energizing the cavity and the spark gap whereby reverse current flow in the power supply circuit instantaneously triggers the spark gap to initiate discharge within the cavity, whereupon cavity energy discharges across the gap, or with an electrode present, the electrode discharges to one of the spark gap elements.

Considering now the illustrated embodiment of the invention in some detail and referring to the drawing, there is shown in part a resonant cavity or waveguide 11 defined by one or more walls 12 having an inner conducting liner 13. This cavity 11, which may also be termed a tank, may be quite large, as of the order of many feet in diameter, used for example in charged particle accelerators, and may have any desired configuration, such as cylindrical. In the particular cavity illustrated, the liner 13 is electrically grounded and the cavity energized from a coupling loop 14 mounted in the tank 11. The loop 14 is connected outside the tank 11 to a cavity power supply 16 via a lead-through insulator 17 in the tank wall 12 and liner 13. It is contemplated that upon operation of the power supply 16 there will be supplied high frequency electrical power to the coupling loop 14 within the tank whereupon such energy shall be coupled into the tank in a conventional manner to excite the cavity 11. The cavity excitation may be employed as desired, as by utilizing the electric fields established to accelerate charged particles.

In particular cavity applications, such as the one suggested above, very large amounts of power are fed into the cavity via the coupling loop. It will be appreciated that the coupling loop 14 will couple energy into the cavity and also will couple energy out of the cavity, although not necessarily with the same efficiency, so that a large amount of power would be fed back from the cavity through the loop to the power supply under certain conditions if a complete circuit was provided therefor. This would, of course, be an inefficient procedure and conventional power supplies as herein contemplated include a unidirectional conducting device in the output, i. e., a high power vacuum tube. Under very high power operation vacuum or gas tubes subjected to large reverse voltages may fail to hold these voltages and spark or fire in a reverse direction. In the present instance such high voltages are present and do appear across the power supply output. In this case with very large amounts of power stored in the cavity, the provision of a reverse current circuit through the power supply would result in an extremely large reverse current flowing from the cavity through the power supply to ground. Such a discharge would not only be wasteful of power but because of its magnitude would be very dangerous in that the reverse firing tube in the power supply would carry such high currents as to be materially damaged and probably destroyed, quite possibly with an explosion of the tube affected.

The present invention operates to discharge or unload the cavity 11 under conditions described above and to this end there is provided discharge means 21 including as a part of the structure thereof an outer cylindrical electrode 22 mounted in the tank wall 12 and extending through the liner 13. The electrode 22 is hollow and the inner end thereof is flared at least inwardly to form a small circular opening. Concentrically within the cylindrical electrode 22 is disposed a center electrode 23 having a flared end aligned in a plane with the flared end of the outer electrode 22 to form a small annular space or gap 24 thereoetween. The electrodes 22 and 23 are metallic with one of the electrodes formed of tungsten, for example, and the other formed of a material having In the instances where the electrodes are associated with high power cavities they are formed with substantial dimensions to have sufficient structural strength to accommodate high power arcing therebetween without material damage.

The outer electrode 22 may be mounted in any suitable manner in the tank wall 12 with provisions for removal if expected usage is such as to indicate wear requiring parts replacement. The inner electrode 23 is adjustably mounted in the end of a rod 26 threaded into a large nut 27 secured in a plate 23. The plate 23 is mounted at a distance from the tank wall 12 by a number of stand-off insulators 29 which may serve not only to insulate the plate but also to support same and to fix the position thereof. A second rod 31 also threaded into the nut 27 may serve as a terminal for electrical connection of the center electrode 23, the outer electrode 22 being electrically grounded by connection to the tank wall The cavity 11 is evacuated and protection of the vacuum thereof at the discharge means 21 may be accomplished by provision of a bell housing 32 over same and sealingly connected to the tank wall 12 and to the terminal rod 32.

Operation of the above-described discharge means 21 is controlled by a control circuit as which includes a peaking transformer 37 having the primary winding 38 thereof connected between one terminal of the cavity power supply 16 and ground, the other power supply terminal being connected to the cavity coupling loop 14. The secondary winding 39 of the peaking transformer 37 is connected in series with the primary winding 41 of a pulse transformer 42 across a bias power supply 43. The peaking transformer has a saturable core and, in operation, the bias supply 43 passes suflicient current through the peaking transformer secondary 39 to saturate the core whereby nominal current fluctuations in the primary winding 38 thereof do not produce an appreciable signal in the secondary. A large reverse current in the primary 38 of the peaking transformer, as results from a reverse short in the power supply, produces a magnetic flux in the peaking transformer in opposition to the flux resulting from the biasing current and of sufiicient magnitude to overcome same whereby a large current is induced in the secondary winding 39. This large current flows through the primary winding 41 of the transformer 42 thereby inducing a high voltage pulse in the secondary winding 44 thereof. The pulse transformer secondary is connected between ground and the discharge terminal 31 which is tied to the inner electrode 23 so that this high voltage pulse appears between electrodes 22 and 23 across the gap 24. As the gap 2 is quite small and as the voltage pulse impressed thereacross is quite high, a spark is generated thereacross even through a vacuum. This discharge or spark across the gap 24 immediately is fed by the cavity energy and the spark expands and draws the energy from the cavity which unloads therethrough.

It will be seen from the foregoing that any fault or failure which provides a short circuit from the coupling loop to ground, or from a high voltage electrode storing large amounts of power within the cavity, will cause a reverse current to flow through the peaking transformer reversing the polarity thereof and impressing a large voltage pulse on the transformer 42 whereby same appears across the gap 24 within the cavity. There is thus produced across gap 24 a spark discharge which is fed by the energy within the cavity to dissipate same before it can dump through the power supply. Although it is quite difficult to initiate a spark discharge in a high vacuum, the small gap distance and high voltage impressed thereacross, as of the order of 100,000 volts, operates to produce an initial spark that then expands. In the case where a central electrode is disposed in the cavity and is to be discharged the spark actually expands from the original gap over to the central electrode. The sparking produces a very rapid energy discharge of the cavity, requiring only a few microseconds, and thus precludes large energy discharge through a faulty power supply.

Although the invention has been disclosed with respect to a single preferred embodiment, it will be apparent to those skilled in the art that numerous modifications and variations are possible within the spirit and scope of the invention and thus it is not intended to limit the invention except by the terms of the following claims.

What is claimed is:

1. Cavity discharge means comprising means defining a spark gap communicating with a cavity and control means connected in circuit with means energizing the cavity and producing a high voltage pulse across said gap under the condition of large reverse current flow from the cavity.

2. A vacuum discharge device comprising an outer cylindrical electrode having an inwardly flaring end adapted for connection to an energized cavity, an inner electrode disposed concentrically within said outer electrode and having an outwardly flaring end disposed coplanar with the flared end of said outer electrode to define an annular spark gap therebetween, and a control circuit applying a high voltage between said electrodes upon short circuiting of means energizing the cavity associated with the device whereby a spark discharge is established between said electrodes.

3. A protective device for cavity energizing means comprising means defining a spark gap adapted to communicate with a cavity connected to energizing means, a biased peaking transformer connected in circuit with said cavity energizing means for producing a signal upon reverse current flow through said cavity energizing means, and a pulse transformer connecting said peaking transformer and said spark gap for applying a large voltage across the latter to establish a discharge thereacross whereby the cavity discharges upon reverse current flow through said cavity energization means.

4. A protective device comprising means defining a spark gap and communicating with an electrical cavity energized from a power supply to be protected, a peaking transformer having a primary winding connected in circuit with said power supply and an element in said cavity insulated therefrom, means biasing said peaking transformer, and a pulse transformer having a primary Winding connected to the secondary winding of said peaking transformer and a primary winding connected across said spark gap for impressing a high voltage across same upon large reverse current flow from said cavity element.

5. An electrical protective device for the power supply circuit of a cavity resonator including a power supply energizing a cavity resonator through coupling means and comprising means defining a short spark gap adapted to communicate with said cavity, a peaking transformer biased to saturation connected to said power supply for inducing a voltage therein upon reverse current flow through the power supply, and a pulse transformer connected to said peaking transformer and across said spark gap to apply a voltage pulse thereto for initiating spark discharge whereby said cavity discharges through the spark.

References Cited in the file of this patent UNITED STATES PATENTS 2,763,816 Baker Sept. 18, 1956

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