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Vacuum interrupters – Fundamentals of vacuum interrupter technology

In a low voltage circuit breaker, using air or arc chutes is sufficient to extinguish an arc.  In the medium voltage range (1000 volts to 38 kV), the main technology used to extinguish an arc is the vacuum interrupter.  Vacuum interrupter technology is used for repetitive switching, motor inrush current interruption, fault protection, overcurrent, and short-circuit protection.

The vacuum interrupter is a pair of separable contacts (primary contacts), enclosed in a vacuum-tight envelope.  The envelope itself is a ceramic material, with a metal end plate brazed to each end.  The metal plates seal the ends and provide support for the parts inside.

Of the two contacts (electrodes) inside, one is fixed.  The other is movable, through a bellows-type connection.  Various shields inside the envelope provide different types of protection to interrupter parts.

State-of-the-art testing

A team of scientists and design engineers will create vacuum interrupters to meet customer specifications.

Testing specifications:

  • Solid dielectric encapsulation
  • Terminal designs
  • Assembly
  • Internal and external threads
  • Anti-twist bushings
  • Contact design: butt contacts, transverse magnetic field (TMF) contacts, axial magnetic field (AMF) contacts of the coil, and horseshoe styles
Contact types used in vacuum interrupters

Vacuum interrupter applications

  • Circuit breakers - Used in circuit breakers in the most demanding electrical circuit protection applications to minimize damage caused by electrical overloads or short circuits.
  • Load break switches - Used in load break switches to connect and disconnect electrical load currents providing limited load switch capacity.
  • Reclosers - Used in reclosers to automatically open and close distribution circuits in response to transient overload and fault conditions.
  • Contactors - Used in contactors in demanding applications that require a high number of operations switching a power circuit in electric motors, lighting, heating devices, and capacitor banks.
  • Tap changers - Used in tap changers inside transformers to change the winding connections to deliver the required voltage.
  • Railway circuit breakers - Installed in the circuit breaker on top of special locomotives to supply electrical energy to railway locomotives’ electric drive motors.

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