the vacuum interrupter into the following circuit, when the operating machine
makes the movable conductive pole move up, the movable contact and the fixed
contact will close, and current pass through the load.
Breaking: When the
operating machine makes the movable conductive pole move down, movable contact
and the fixed contact will separate from each other and brings the vacuum arc
which is sustained by metallic vapor from contact until power current closing
to zero. Plasma in the vacuum arc will spread quickly all around and the vacuum
arc will be extinguished. The electric conductor between contacts changes to insulator
then current break.
The following drawing shows the Basic structure of vacuum interrupter. Out can, which is cylinder made by inorganic material such as glass, ceramic or crystallitic glass, and two metal covers seal a container. There are two contact heads in container, a stationary head fixed on the end of the stationary conductive pole and a moveable head fixed on the end of the moveable conductive pole. The moveable conductive pole pass through the center hole of the bellow and the metal cover. The bellow, which is brazed to the middle of the moveable conductive pole on one end and brazed to the metal cover on the other end, is a stretchy part can flex axially as its wavy side.
Due to the bellow between moveable conductive pole and the metal cover, vacuum interrupter can keep vacuum seal when the moveable conductive pole move axially.The stationary and moveable conductive head always in high vacuum, the gas pressure should lower than 1.33*10-3 Pa, normally around 10-4 Pa.Around the contact heads and bellow are shield, the shield around contact heads called main shield and the one around bellow called accessorial shield or bellow shield.
If a vacuum interrupter is used in the circuit as the figure, when the operating machine makes the moveable conductive pole move up, the moveable contact head and the stationary head contact and turn on the power, let current pass through the load. Contrarily, when the operating machine makes the moveable conductive pole move down, the moveable contact head leaves the stationary head and brings vacuum arc, which is kept by the metal vapour from contact head until the current approach the AC zero point, at that moment the almost inactive vapour and the vacuum arc plasma diffusion make the arc go out. The space between contact heads become insulated then the current is interrupted.
vacuum interrupter can be sorted by utilization, for breaker, for load switches, for contactor and for special utilization. Vacuum switching tubes for breaker should be capable to break short circuit current, which is used in circuit and electric equipment for over loading and short circuit protection, normally needn’t frequently operate. It can break rated short circuit current more than 30 times.
vacuum interrupter for load switches only need to break load current, or rated working current. It is usually used with fuse breaker that can break short circuit current, can break load current 200 to 300 times. Vacuum switching tubes for contactor need frequently operate under certain load current. It can operate 500,000 to 1,000,000 time or even more. It is usually used with fuse breaker too.
vacuum interrupter for special utilization is used in special condition, such as that can break high voltage DC current, can trigger spark or can break high frequency current.
vacuum interrupter can be sorted by its contact head structure, such as flat contact head, transverse magnetic field contact head, axial magnetic field contact head, crossed magnetic field contact head (cup-shaped contact head) and other special contact head structure.
Vacuum switching tubes can be sorted into vacuum glass switching tubes (the insulated envelope made by glass), vacuum ceramic switching tubes (the insulated envelope made by ceramic) and vacuum crystallite glass switching tubes (the insulated envelope made by crystallite glass) by the material for the envelope.