Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION.
THIS INVENTION relates to a high voltage electrical
switch.
SUMMARY OF THE INVENTION.
.
According to the invention there is provided a high
voltage electric switch which includes:
a housing defining a chamber and adapted to contain an
electrically insulating gas;
two spaced-apart main electrodes housed within the
chamber, and defining between them a breakdown gap;
connecting means for connecting the electrodes in an
electrical circuit, and
trigger means in close proximity to the gap, and com-
prising two trigger electrodes, each being directly electri-
cally connected to different ones of the main electrodes, the
geometry of the electrodes being such that the breakdown
voltage between the trigger electrodes is less than the
breakdown voltage between the main electrodes,
the trigger means being adapted to generate electrically
electro-magnetic radiation which irradiates a substantial
portion of the insulating gas in the breakdown gap, the
radiation being of a sufficiently high intensity to cause
substantial photo-electric emission of electrons in the gas.and
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thus breakdown of the gas and an electrical discharge between
the main electrodes.
The electro-magnetic radiation may be of sufficient
intensity to generate an electron density of greater than 108
electrons/cm3 in the breakdown gap between the main electrodes.
By 'photo-electric emission' is meant the excitation
of an atom by electro-magnetic stimulation to emit an electron.
The electrons may accordingly be emitted from atoms of gas or
from atoms of the housing material or other solid material
within the housing.
The electro-magnetic radiation may have sufficient
quantum energy to cause photo-electric emission. Accordingly,
the radiation may be in the ultra-violet region of the visible
spectrum or have a higher frequency than that of ultra-violet
light, i.e. greater than 1015Hz.
The trigger means may be adapted to generate the
electro-magnetic radiation by means of a fast, low energy
electrical trigger discharge. The switch may further include a
radiation enhancing member disposed such that the trigger
discharge occurs across a surface of the radiation enhancing
member, the radiation enhancing member being of a suitable
material such as a ceramic material, to increase the intensity
of the radiation generated by the trigger discharge.
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The main electrodes may have a uniform surface
geometry such that a uniform, static electric field is
developed between them. Further, in order to provide for a
sufficient current carrying capacity, the main electrodes may
have an extended discharge surface.
In order to increase the breakdown voltage of the
gap, the insulating gas may have a high dielectric co-
efficient, and the gas may be pressurized. Additives may also
be added to the gas to assist in the photo-electric emission of
electrons.
In order to minimise the switch-on time of the
switch, the main electrodes may be located as close as possible
to one another (according to the hold-off voltage required of
the switch), to provide a very small breakdown gap. The
housing may further have at least an inlet opening wherethrough
the gas may be introduced into the chamber. An outlet opening
may also be provided so that gas may be passed through the
chamber.
The electrodes may be of any suitable electrically
conducting material, such as copper, aluminium, stainless
steel, carbon or the like, and the insulating gas may be any
suitable yas such as nitrogen, sulphur hexafluoride, or the
like, which has a high dielectric constant and is electrically
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A switch according to the invention may be used in
any suitable high voltage application. ~s nano-second
switching times may be obtained with the switch, it may
conveniently be used to excite lasers.
BRIEF DESCRIPT ON OF THE DRAWINGS.
The invention will now be described by way of an
example with reference to the accompanying drawing which shows
a sectional view of the electrode arrangement for a high-
voltage self-triggered switch according to the invention.
DESCRIPTION OF ILLU~TRATIVE EMBODIMENT.
. . .
Referring to the drawing, the electrode arrangement
for a self-triggered high-voltage switch is shown genrally by
reference numeral 50. The arrangement 50 comprises two spaced-
apart main electrodes 54.1 and 54.2 defining a main discharge
gap 56 and two spaced-apart trigger electrodes 58.1 and 58.2
defining a trigger discharge gap 60. The trigger electrode
58.1 and the main electrode 54.1 are formed from one piece of a
suitable metal, such as stainless steel, as with the trigger
electrode 58.2 and the main electrode 54.2. The main elec-
trodes 54.1 and 54.2 are closer together than the trigger
electrodes 58.1 and 58.2, the main discharge gap 56 being
smaller than the trigger discharge gap 60. However, as the
main electrodes 54.1 and 5~.2 are rounded and the trigger
electrodes 58.1 and 58.2 are pointed, a highly-stressed
electric field is developed by the trigger electrodes 58.1 and
58.2, resulting in the trigger electrodes 58.1 and 58.2 having
a lower breakdown voltage than the main electrodes 54.1 and
54.2.
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~ ceramic insulator 62 is provided adjacent the
trigger electrodes 58.1 and 58.2 to provide a surface 64 across
which the trigger discharge occurs. The electrodes are housed
in a housing having openings through which a suitable insu-
lating gas may be introduced and removed. For the sake of
clarity, details of the housing are not shown.
In operation, a high voltage pulse is applied across
the electrodes. ~s the trigger electrodes 58.1 and 58.2 have a
lower breakdown voltage, a trigger discharge first occurs
across the ceramic surface 64. This generates ultra-violet
light of high intensity which irradiates the insulating gas in
the main discharge gap 56. This results in photo-electric
emission of electrons in the main discharge gap 56 having a
suitable initial electron density. When a sufficient electron
density is generated a very fast distributed discharge occurs
between the main electrodes 54.1 and 54.2. ~s the dynamic
resistance between the two main electrodes 54.1 and S4.2 is
much less than that between the trigger electrodes 58.1 and
58.2, the discharge between the trigger electrodes 58.1 and
58.2 decreases substantially in magnitude, resulting in
minimal erosion of the trigger electrodes 58.1 and 58.2.
Further, as a substantial portion of the current flowing in the
trigger discharge is transferred to the main discharge, very
fast switching occurs.
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