Electromechanically Triggered Spark Gap Switch

Europaisches Patentamt European Patent Office © Publication number 0 300 599 A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

@ Date of filing: 18.05.88

© A spark gap switch is disclosed. The spark gap switch comprises an anode and a cathode having facing surfaces separated by a predetermined gap, a trigger electrode located in the vicinity of such gap, and a piezoelectric generator connected between the trigger electrode and the cathode for triggering the spark gap switch.

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Xerox Copy Centre 1 EP 0 300 599 A1 2

ELECTROMECHANICALLY TRIGGERED SPARK GAP SWITCH

This invention relates to an electromechanically The spark gap switch, in accordance with the triggered spark gap switch suitable for switching present invention, comprises an anode and a cath- high voltage, high current electric power. ode having facing surfaces separated by a pre- Spark gaps were the earliest switching means determined gap, a trigger electrode located in the for high voltage capacitor discharges. In its sim- 5 vicinity of such gap, and a piezoelectric generator plest form, a spark gap switch consists of two connected between the trigger electrode and the metal electrodes axially spaced apart. Air or other cathode for triggering the spark gap switch. gases fill the gap between the electrodes. The In a preferred embodiment of the invention, an switching potential of such an arrangement will opening is provided in the center of the cathode depend on the shape and distance of the elec- ro and the trigger electrode is mounted in such open- trades, the density and the pressure of the gas ing and insulated from the cathode. (Paschen's law). When the potential difference be- The piezoelectric generator is a conventional tween the electrodes reaches the breakdown po- device and may comprise a hammer which strikes tential of the gas at the given distance and pres- a ceramic rod and is manually activated by a sure, sparkover occurs. The spark resistance is 75 plunger connected to the hammer. In a preferred very low, usually in the milliohm range, therefore embodiment of the invention, the plunger is op- the switching efficiency is high. erated by a small pneumatic cylinder having its Over the years other high voltage, high current piston connected to the plunger. Air pressure is switching devices were developed, but the spark applied to the cylinder through a long plastic tube gap switch remained an important, often used com- 20 or hose thereby providing safe isolation for the ponent. There are several methods to turn on a operator of the high voltage equipment. spark gap switch: The invention will now be disclosed, by way of 1 . The potential difference between the elec- example, with reference to the accompanying trodes can be increased to initiate switching. This drawing which illustrates a preferred embodiment is usually inconvenient, because other factors de- 25 of an electromechanically triggered spark gap termine the voltage to be used. switch. 2. The gas pressure can be lowered until The spark gap switch comprises an anode 10 breakdown occurs. This method requires pressure and a cathode 12 of a size sufficient to handle the control equipment. current requirement (possibly in the order of 100 3. The gas density can be lowered by 30 kiloamps or higher) of a capacitor discharge circuit changing the composition. This method necessi- without significant power loss. These electrodes are tates the use of multiple gas sources. held together along a common axis with a pre- 4. The gap size can be decreased by mov- determined gap therebetween by a suitable insulating the electrodes closer. This requires flexible ing housing 14 equipped with conventional gas leads, which may be inconvenient considering the 35 intake 16 and outlet 18 for maintaining a suitable heavy, high current conductors. Flexible leads also gas pressure within the housing. The cathode has tend to increase the system inductance, which in an opening 20 in the surface thereof facing the turn slows the discharge process. anode and a trigger electrode 22 is supported in 5. Local ionization of the gas within the gap such opening by an insulating sleeve 24. However, is a convenient way of operating the switch. One 40 other means of mounting the trigger electrode in method of ionization is to introduce a small spark the vicinity of the gap between the anode and between the cathode and a third electrode as de- cathode are also envisaged. A piezoelectric gener- scribed by U.S. Pat. 3,757,153, column 2, lines 56- ator 26 is connected to the trigger electrode with 66. Another description of such method can be one terminal and to the cathode with its other found in HIGH SPEED PULSE TECHNOLOGY, by 45 terminal. The piezoelectric generator is provided F.B.A. FrOngel, Vol. I, pp. 126-127. Triggering cir- with a conventional plunger 28 which is operated cuits for such systems are fairly complex, even if by the piston 30 of a small pneumatic cylinder 32 the cathode is grounded. In some cases, circuit when air pressure is applied to the intake nozzle 34 requirements call for the cathode to be at high of the cylinder. potential. This can present difficult isolation prob- so Inside the piezoelectric generator, a small ham- lems for a manually operated trigger circuit. mer strikes a ceramic rod in a known manner. The There is hereinafter described in detail a spark piezoelectricity generated is substantial, and usu- gap switch, suitable for switching high voltage, high ally exceeds 10 kV. This voltage causes a spar- current electrical power, which provides safe isola- kover between the trigger electrode and the cath- tion for the operator of the high voltage equipment. ode first, and subsequently between the cathode

2 3 EP 0 300 599 A1 4 and anode by local ionization. The piezoelectric generator is a common, mass produced device used in cigarette lighters and gas stove or gas barbeque lighters. Air pressure can be applied to the intake nozzle of the pneumatic cyl- 5 inder through a long plastic tube or hose providing safe isolation for the operator of the high voltage equipment. Alternatively, the piezoelectric generator can be operated through an insulated push bar manually or by a solenoid or other type of actuator. ro Another advantage of the piezoelectric triggering is that it converts readily available mechanical energy to electrical energy. Conventional electronic trigger circuits operate from isolated power sup- plies run off line voltage. In case of power failure, ?s these trigger circuits become inoperative, but the high voltage storage capacitors could remain charged. The electromechanically triggered spark gap switch operates readily during power failure, making it ideal for crowbar service. 20

Claims

1. A spark gap switch comprising 25 a) an anode and a cathode having facing surfaces separated by a predetermined gap; b) a trigger electrode located in the vicinity of said gap, and c) a piezoelectric generator connected be- 30 tween said trigger electrode and the cathode for triggering said spark gap switch. 2. A spark gap switch as defined in claim 1 wherein an opening is provided in the center of the cathode and wherein said trigger electrode is 35 mounted in said opening and insulated from the cathode. 3. A spark gap switch as defined in claim 1 or 2, wherein said piezoelectric generator comprises a hammer which is arranged to strike a ceramic rod 40 for producing a spark exceeding 10 kV and said switch further comprises a plunger for actuating said hammer. 4. A spark gap switch as defined in claim 3, comprising a pneumatic cylinder for operating said 45 plunger and having a piston connected to said plunger and means for remotely applying air pressure to said cylinder. 5. A spark gap switch as defined in claim 3, comprising an insulated push bar for operating said so plunger.

3 EP 0 300 599 A1 European Patent Application Number EUROPEAN SEARCH REPORT Office

EP 88 30 4521

DOCUMENTS CONSIDERED TO BE RELEVANT Category Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION ant. CI. 4) US-A-4 090 448 (ROSE) H 01 T 2/02 * Column 2, lines 22-62; figure 1 *

Y US-A-3 867 663 (SPENCER) * Column 2, lines 34-50; figure 1 * A

PATENT ABSTRACTS OF JAPAN , vol. 6, no. 103 (E-112)[981], 12th June 1982, page 8 E 112; & JP-A-57 32 690 (NIPPON DENKI K.K.) 22-02-1982 * Abstract *

TECHNICAL FIELDS SEARCHED (Int. C1.4)

H 01 T

The present search report has been drawn up for all claims Place of search Date of completion of the search Examiner THE HAGUE 18-10-1988 BUN E.A.

CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application s document of the same category L : document cited for other reasons o« A : technological background a. O : non-written disclosure & : member of the same patent family, corresponding O P : intermediate document document