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5kV, 7.5kV, & 15kV DHP-VR
Replacement Circuit Breaker
SECTION 4: DESCRIPTION AND
OPERATION
VR-Series vacuum replacement breakers are designed to be used
with existing installations of equivalent air-magnetic metal-clad
switchgear 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.
VR-Series element designation is easily identified by the mechanism
chassis width. See Table below.
VR-SERIES
ELEMENT DESIGNATION
18WR
20WR
29WR
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 as the vapor leaves the contact area, it condenses 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 THE INTERRUPTER ASSEMBLY
Each interrupter is assembled at the factory as a unit to assure
correct dimensional relationships between working components.
The interrupter assembly consists of a vacuum interrupter, a
molded glass polyester stand-off insulator, upper and lower clamps,
flexible shunts, bell crank, operating rod, and contact load spring.
The vacuum interrupter is mounted vertically with the fixed stem
upward and the moving stem downward. The upper and lower glass
polyester stand-off insulator and clamps support the interrupter
and are fastened to the breaker's stored energy mechanism frame.
Upper and lower flexible shunts provide electrical connections from
each interrupter to the breaker's primary bushings while providing
isolation from mechanical shock and movement of the interrupter's
moving stem. The operating rod, loading spring, and bell crank
transfer mechanical motion from the breaker's operating mechanism
to the moving stem of the interrupter. A vacuum interrupter contact
erosion indicator is located on the moving stem of the interrupter. It
is visible when the breaker is withdrawn and is viewed from the rear
of the breaker. (See Figure 6.1 and Figure 6.2)
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. A contact erosion indicator mark is located on the
moving stem of the interrupter (Figure 6.1 and 6.2).
In order to determine if the contacts have eroded to the extent that
the interrupter must be replaced, close the breaker and observe
the erosion mark placed on each moving stem from the rear of the
breaker. If the mark on the interrupter stem is visible, the interrupter
is satisfactory. If the mark is no longer visible, the interrupter
assembly must be replaced.
20
Instruction Book
APPROXIMATE MECHANISM
CHASSIS WIDTH (INCH)
18
20
27
IB182017EN February 2017 www.eaton.com
Figurt 4.1. DHP-VR Inttrrupttr Asstmbly
(20WR Shown)
Figurt 4.2. DHP-VR Inttrrupttr Asstmbly
(20WR Shown) (All Thrtt Polt Units)
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