Vacuum Interrupter
Vacuum interrupters offer the advantages of enclosed
arc interruption, small size and weight, longer life,
reduced maintenance, minimal mechanical shock,
and elimination of contact degradation caused by
environmental contamination.
In the closed position, current flows through the
interrupter moving and fixed stems and the faces
of the main contacts. As the contacts part, an arc is
drawn between the contact surfaces. The arc is rapidly
moved away from the main contacts to the slotted
contact surfaces by self-induced magnetic effects. This
minimizes contact erosion and hot spots on the contact
surfaces. The arc flows in an ionized metal vapor and
if the vapor leaves the contact area, it would condense
into the metal shield which surrounds the contacts.
At current zero, the arc extinguishes and vapor
production ceases. Very rapid dispersion, cooling,
recombination, and deionization of the metal vapor
plasma and fast condensation of metal vapor causes the
vacuum to be quickly restored and prevents the transient
recovery voltage from causing a restrike across the gap
of the open contacts.
Vacuum Interrupter Assembly
Each vacuum interrupter assembly (also referred to as
pole unit) is assembled at the factory as a unit to assure
correct dimensional relationships between working
components. Three interrupter assemblies are used
per circuit breaker. Each vacuum interrupter assembly
consists of a molded insulator frame and includes
the vacuum interrupter, its lead assembly, bell crank,
operating drive/pull rod, stand-off insulator, and contact
load spring. The pole units are fastened to the circuit
breaker’s stored energy mechanism frame. A silver-
plated copper laminated shunt transfers current from
the moving interrupter stem to the primary bushings
via a Holm-free, non-sliding conical current transfer. A
silver-plated copper casting is attached to the stationary
stem, completing the primary circuit to the disconnect
assemblies. The operating rod, loading spring, and bell
crank transfer the mechanical motion from the circuit
breaker’s stored energy mechanism to the moving stem
of the vacuum interrupter.
Vacuum Interrupter
3
EATON | Visual Instruction Booklet Essentials | November 2018
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