Vacuum Dielectric
Vacuum is the ideal dielectric for high voltage relay switching. It
has extremely high voltage breakdown characteristics, a fast recovery
rate and it provides an absolutely inert and non-reactive environment
for switching contacts.
The absence of contaminating gases and vapors in vacuum relays means
that contact surfaces remain brilliantly clean and contact resistance
stays low and constant throughout the life of the relay.
The vacuum level in vacuum relays is typically better than 10-7 Torr,
and improves through use as a result of the gettering action of small
amounts of contact metal vaporized during arc interruption. Vaporized
metal which supports the arc condenses almost instantly in a vacuum.
This results in extremely high recovery rates of the vacuum dielectric,
as great as 10 kV per microsecond. Corona effects do not exist in a
vacuum environment because the mean free path of molecules is too great
to permit collision ionization processes to cascade.
The high dielectric strength of the vacuum permits close contact spacing,
on the order of 1000 volts per mil. The small movement required to operate
a vacuum relay permits the use of small, low mass actuators allowing
high operating speeds. Use of refractory metal contacts provides exceptional
interrupting ability and assures long contact life.
Complete absence of exposed arcs makes the vacuum relay especially
suitable for use in corrosive or explosive atmospheres. Changes in barometric
pressure, temperature or humidity have no effect on the sealed contacts,
permitting trouble free use in almost any environment.
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