Electric lamp and discharge devices – Fluent material supply or flow directing means – Lightning or surge arrester
Reexamination Certificate
1999-08-13
2001-10-23
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Fluent material supply or flow directing means
Lightning or surge arrester
C313S231310, C313S231410, C313S155000, C313S161000, C313S602000, C313S604000, C315S169100, C315S169300
Reexamination Certificate
active
06307308
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to a low pressure gas discharge switch, and in particular, to a low pressure gas discharge switch in which at least two main planar electrodes are arranged at a distance d from each other and are present for a low pressure gas discharge.
BACKGROUND OF THE INVENTION
According to the printed publication, “Triggerbare Hochleistungsschalter” [Triggerable Heavy-Duty Circuit Breakers] from “Physik in unserer Zeit” (1991), 4, pages 156 to 164, triggered switching of high current pulses, e.g., 10-100 kA, and long duration, e.g., up to 100 &mgr;s, at voltages above 10 kV with low pressure gas discharge switches (e.g., thyratron, ignitron, pseudospark switch) is used, for example, in pulsed high-power lasers, in fusion and acceleration technology, in medical engineering and in materials processing. The high charge transfer rates of up to 10 As per switching operation required for these switching operations results in a high local thermal load on the electrodes of the switch, since in most cases the plasma remains in the close vicinity of its firing point and consequently only a spatially limited segment of the electrodes are used for generating and maintaining the necessary dense plasma. This thermal load results in an increased erosion of electrode material, which finally results in a severely limited service life of the switches.
Triggered switching of long current pulses has been achieved with low pressure gas discharge switches. In this connection, up to approximately 10
8
switching operations and consequently usual service lives were obtained with the pseudospark switch, for example. Depending on the design, a very long service life can be obtained with the ignitron; however, it has important disadvantages in relation to the pseudospark switch: Lower rate of current rise, e.g., <10
10
A/S compared with ≈10
12
A/S for the pseudospark switch, high sensitivity to voltage reversal and to excessively high ambient temperatures as well as the hazards to the environment that arise when the mercury used as the electrode material is released when the switch is shattered.
Japanese Patent Application No. 51-59851 describes a means for generating a magnetic field superimposed on the discharge in a gas discharge switch. In particular, an axial magnetic field is superimposed on the arc discharge by an appropriate design of the current paths.
Concepts for generating magnetic fields specially superimposed on a switching arc are known from vacuum switching technology. Slotting the pot-shaped supply leads to the contacts results in magnetic fields acting on the switching plasma, which either ensure that the contraction of the plasma is counteracted and the plasma remains diffuse, as in the case of the axial field contacts according to European Patent No. 0 155 376 B1 or that the plasma, as a constricted arc, is set in rotational motion, as in the case of the radial field contacts described in German Patent No. 34 26 323 B1. The latter can also be achieved by slotting the electrode surfaces, by which the so-called spiral contacts are defined. In doing so, three to six slots, for example, are made in the electrodes. Driven by the Lorentz force, the switching arc proceeds on a nearly circular path.
In a similar manner, U.S. patent application No. 3,280,286 brings about the formation of current paths for generating a radial field by slotting the switch contacts.
SUMMARY OF THE INVENTION
In vacuum switches, the arc must commutate across the slots during its motion due to the slot geometry of the contacts. In this connection, the number of the commutation operations per revolution of the arc is equal to the number of slots. Commutation always has a negative effect on the motion of the arc, since the arc requires a certain amount of time for the commutation. In the most unfavorable case, this commutation time is greater than the actual switching time so that a local thermal overload of the electrode can occur caused by a standstill of the arc.
An object of the present invention is to set the plasma of a low pressure gas discharge switch in motion by suitable means so that the erosion of the electrode material is minimized.
This object is attained according to the present invention by at least one slot being present which delimits an effective current path being present in at least one of the main planar electrodes in a gas discharge switch of the type named above as a means of generating a radial magnetic field and that at least one trigger opening is located outside the electrode center in the current path. Preferably, a single slot is present which runs in a spiral form from the area of the electrode center to the area of the electrode edge.
With the present invention, a gas discharge switch is devised which is especially suitable for pulsed applications. In particular, as a result of the preferable design with a single slot, a magnetic field with a large radial component is generated by the current that is thus forced to flow in a spiral form, the magnetic field setting the switching plasma in a circular or spiral motion via the Lorentz force. In this connection, depending on the embodiment, the commutation of the switching plasma via a slot can be completely avoided or at least be reduced to one commutation operation per revolution. Accordingly the special slot geometry brings about a motion of the plasma which is more uniform than in conventional spiral contacts having several slots in vacuum switching technology.
An advantage in the slot geometry according to the invention is a particularly high radial magnetic field with electrode:
1. Triggering and contacting at the electrode edge: In this case, the radial component of the Lorentz force acting on the plasma is directed inwards; the plasma is moved on the spiral path toward the electrode center. This embodiment of the invention can be used to advantage in time-limited pulse durations when the arc time is less than the burn time of the plasma. Otherwise, the arc would temporarily burn locally in the center of the electrode and cause a very high thermal load there.
2. Firing and contacting in the area of the electrode center: In this case, the radial component of the Lorentz force on the plasma is oriented in the direction of the electrode edge; the plasma is moved outward on the spiral path. The plasma path passes over into a possibly single-slotted, circular path along the electrode edge. Due to the closed circular path on the electrode edge, this embodiment of the invention advantageously permits the switching of long (ms) pulses.
REFERENCES:
patent: 3280286 (1966-10-01), Ranheim
patent: 5585696 (1996-12-01), Koyama et al.
patent: 34 26 323 (1986-01-01), None
patent: 0 155 376 (1985-09-01), None
patent: 0 381 843 (1990-08-01), None
patent: 05 159 851 (1993-06-01), None
“Triggerbare Hochleistungsschalter”, Physik in unserer Zeit, 1991, pp. 156-164 Described in the Specification.
Romheld Michael
Teichmann Jorg
Morrison & Foerster / LLP
Patel Vip
Quarterman Kevin
Siemens Aktiengesellschaft
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