Compact multistage spark gap switch

Details Compact multistage spark gap switch Compact multistage spark gap switch

1999-05-27

2003-05-06

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Fluent material supply or flow directing means

C313S325000, C361S120000

Reexamination Certificate

active

06559580

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to high voltage switches and, more particularly, to a multistage spark gap switch that is more compact than those presently known.
A spark gap switch is a high voltage closing switch that is used in pulsed power systems and for protection from transients. A basic spark gap switch consists of two electrodes separated by an insulating medium that can be vacuum or a fluid (gas or liquid). The switch is initially open. It closes upon the formation of a conductive plasma channel (spark) in the insulating medium between the electrodes when a sufficiently high voltage difference is imposed on the electrodes. The conductive channel is formed by a breakdown mechanism that can be driven in one of two ways. The first way (self-breakdown) involves the application of a voltage difference across the electrodes that is higher than the voltage breakdown threshold of the switch, i.e., the voltage at which the electric field in the gap between the electrodes exceeds the electric strength of the fluid, or induces sufficient electron emission from the surfaces of the electrodes into a vacuum. The second way is to induce breakdown at a voltage difference across the electrodes that is below the voltage breakdown threshold. This is done by using a third, trigger electrode to briefly raise the electric field in the gap between the electrodes, or by means such as radiation or a change in insulator pressure that induce degradation of the electric strength of the insulating medium. The simple and robust structure of spark gap switches, and their ability to self-close and to float to high voltages, makes them popular components of devices such as Marx generators.
The repetition rate of the operation of a spark gap switch is limited by the time required for the plasma to recombine and for the heat associated with the discharge to be dissipated so that the insulator returns to its initial electric strength. Therefore, high repetition rate spark gap switches commonly use a fluid (gas or liquid) insulator that flows through the interelectrode discharge gap. Nevertheless, the repetition rate of these spark gap switches usually is only a few tens of hertz. In addition, the high flow rates required by some applications tend to degrade switching reproducibility and introduce complications in overall system design.
FIG. 1A
shows a multistage spark gap switch, which is essentially a series of two-electrode spark gap switches connected back to back. Electrodes
10
are held apart by insulating spacers
12
to define discharge gaps
14
. The total switch voltage is divided capacitively among discharge gaps
14
, allowing discharge gaps
14
to be very small. This gives the multistage structure fast recovery times, enabling operation at repetition rates upwards of several kilohertz. If the insulating medium is a gas, the pressure of the gas can be atmospheric, simplifying the mechanical and operational complexity of the switch. Fluid flow rate can be very low, or fluid flow may not be required at all. The small discharge gap and low pressure allow the switch to operate in a less violent discharge mode, which considerably increases the lifetime of the electrodes and hence of the switch as a whole.
Historically, the multistage spark gap switch, then called a “quenched spark gap”, was first used in the 1920s in sparking transmitters because of its fast recovery time and its high repetition rate. Newer transmitter technologies rendered the multistage spark gap switch obsolete in this application, and it has found little application since then. Until recently, high energy, high voltage pulsed power applications required only a low repetition rate, for which a single stage spark gap switch is adequate. The higher repetition rates of the newest high voltage pulsed power generators requires a different switch technology. In principle, the multistage spark gap switch of
FIG. 1A
is appropriate for these high repetition rates. In practice, however, the length of a typical multistage spark gap switch gives it an undesirably long closing time and an undesirably large inductance in the conducting phase. The extra length of a multistage spark gap switch, compared with an equivalent single stage spark gap switch, also complicates the layout of a generator with many such switches and may increase the size of the generator, thereby degrading its performance in some applications because of the increased weight, larger inductance and longer rise time associated with the larger size.
Thus there is a widely recognized need for, and it would be highly advantageous to have, a multistage spark gap switch design that is shorter than those presently known.
SUMMARY OF THE INVENTION
According to the present invention there is provided a spark gap switch, including: (a) a first substantially planar electrode including a discharge portion and a support portion; and (b) a second substantially planar electrode parallel to and spaced apart from the first electrode and including a discharge portion and a support portion, the discharge portions being mutually opposite, and the support portions being mutually staggered.
According to the present invention there is provided a spark gap switch including: (a) a first stack of at least two substantially planar, mutually parallel electrodes, each of the electrodes including: (i) a discharge portion, and (ii) a support portion; the discharge portions of adjacent electrodes being spaced apart and mutually opposite, the support portions of adjacent electrodes being mutually staggered.
According to the present invention there is provided a spark gap switch including: a first stack of at least two substantially planar, mutually parallel electrodes, each of the electrodes including a discharge portion, the discharge portions of adjacent electrodes being mutually opposite and spaced apart by at most about one millimeter.
In the prior art spark gap switch of
FIG. 1A
, spacers
12
must have a certain minimum length to ensure that the spark is confined to discharge gaps
14
and does not propagate from one electrode
10
to the next along the outer surface of an intervening spacer
12
. In practice, this length is several (typically three) times the width of any one discharge gap
14
. Electrodes
10
are nonplanar, so that when electrodes
10
are stacked as shown, peripheral gaps
16
that are wider than discharge gaps
14
accommodate spacers
12
. The main contribution to the length of these prior art spark gap switches is the width of peripheral gaps
16
.
FIG. 1B
shows an alternative prior art design of a multistage spark gap switch in which planar electrodes
10
′ are separated by insulating spacers
12
′. In this design, discharge volumes
14
′ are not well-defined and may overlap onto spacers
12
′. Therefore, plasma that is produced in discharge volumes
14
′ attacks spacers
12
′. This leads to frequent surface breakdowns on spacers
12
′ that result in irregular operation and short lifetime.
As noted above, to eliminate surface breakdowns along the spacers, the potential surface discharge path along the spacers should be several times longer than the path length of the volume discharge. In the design of
FIG. 1B
, these path lengths are equal. An improved design in this respect, but still lacking well-defined discharge regions, is shown in FIG.
1
C. Planar electrodes
10
″ are separated by insulating, spacers
12
″ that have corrugated outer surfaces. The corrugations increase the lengths of the spark propagation paths along the outer surfaces of spacers
12
″, but in practice, in such a design, the threshold voltage for surface breakdown can not exceed the threshold voltage for volume breakdown. Therefore, even in the design of
FIG. 1C
, undesired surface discharges occur quite often.
Another disadvantage of the designs of
FIGS. 1B and 1C
is that it is impractical to produce spacers
12
′ for gaps of about 1 millimeter or less, or spacers
12
″ for gaps of a

Affiliated with

Also associated with

Rating

Compact multistage spark gap switch does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Compact multistage spark gap switch, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compact multistage spark gap switch will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3006894