12
Instruction Book
IB182942EN July 2018 www.eaton.com
DST-2-VR
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VR-Series
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Replacement Circuit Breaker
SECTION 4: DESCRIPTION AND
OPERATION
VR-Series
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vacuum replacement circuit breakers are designed to be
used with existing installations of equivalent air-magnetic metal-clad
switchgear circuit breakers. The front mounted spring type stored
energy mechanism facilitates inspection and provides improved
access to components for servicing. The long life characteristics of
the vacuum interrupters and proven high reliability of spring-type
stored energy mechanisms assure long, trouble-free service with
minimum maintenance.
4.1 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.
4.1.1 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 rod,
stand-off insulator, and contact load spring. The vacuum interrupter
is mounted vertically with the stationary vacuum interrupter stem
upward and the moving interrupter stem downward. The pole units
are fastened to the circuit breaker’s stored energy mechanism
frame. Silver-plated copper laminated shunts transfer current from
the moving interrupter stem to the upper 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 lower 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.
4.1.2 CONTACT EROSION INDICATOR
The purpose of the contact erosion indicator is to monitor the
erosion of the vacuum interrupter contacts, which is very minimal
over time with Eaton vacuum interrupters utilizing copper-chrome
contact material. The VR-Series
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vacuum interrupter assembly
incorporates both the original vacuum interrupter erosion indicator
and the contact-spring wipe into one all-encompassing indicator. The
adequacy of the remaining contact erosion and wipe can easily be
determined by observing the moving end of the vacuum interrupter
assembly on a closed circuit breaker. The procedure to determine
the adequacy of the “T” cutout on the vacuum interrupter assembly
is depicted in Figures 6.1 and 6.2. If the wipe is inadequate (no part
of the “T” cutout is visible) then the vacuum interrupter assembly
must be replaced. Field adjustment is not possible.
Figurt 4.1. Vacuum Inttrrupttr Asstmbly
Figurt 4.2. Vacuum Inttrrupttr Asstmbly (All Thrtt Polt Units)
