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50DH-VR-50AXU / 50XU / 75U / 75ARU - 600 / 1200A
Replacement Circuit Breaker
SECTION 4: DESCRIPTION AND
OPERATION
4.1 VCP-TR VACUUM CIRCUIT BREAKER ELEMENT
The Eaton type VCP-TR vacuum circuit breaker is a fixed mounted
device. It is designed and tested in accordance with ANSI standards
C37 .04 and C37 .09.
The VCP-TR circuit breaker is a true metal-clad circuit breaker
encompassing all the features normally associated with a true metal-
clad design, such as:
Insulation and isolation of compartments.
•
11 gauge steel barriers between primary and mechanism
•
compartments
VCP-TR uses a rigid frame construction of engineered thermoset
composite resins with a patented pole unit molding. In addition to
high strength structural properties, the material used has excellent
dielectric characteristics and resists tracking.
Controls and indicators, common to all ratings, are functional
grouped on the front of the circuit breaker. The front escutcheon
(faceplate) is also common for all voltage and current ratings. A
mechanical operations counter is provided as standard on all circuit
breakers.
VCP-TR circuit breakers utilize vacuum interrupters for interruption
and switching functions (Figure 4.1). Vacuum interruption offers the
advantages of enclosed interrupters, reduced size and weight, short
interrupting time, long life, reduced maintenance, and environmental
compatibility.
The vacuum interrupters are mounted vertically and supported from
the fixed stem connected to the top conductor. The patented pole
unit molding encloses each of the vacuum interrupter assemblies on
three sides and provides the required mounting means, insulation,
isolation, strength and rigidity.
The current transfer system consists of a unique flexible connector
attached to the movable stem of the vacuum interrupter. The flexible
connector consists of a large number of flexible leaf conductors
that are pressure welded on both ends. One end of the flexible
connector is attached to the movable vacuum interrupter stem
and the other end to the circuit breaker's lower conductor. As the
vacuum interrupter stem moves and the flexible connector flexes,
current is safely and efficiently transferred between the stem and
lower conductor.
4.2.1 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. 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 circuit breaker and
observe the erosion mark placed on each moving stem from the rear
of the circuit 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.
DANGER
FAILURE TO REPLACE THE INTERRUPTER ASSEMBLY WHEN INDICATED BY
THE CONTACT EROSION INDICATOR COULD CAUSE THE CIRCUIT BREAKER
TO FAIL, LEADING TO PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
14
Instruction Book
IB182012EN March 2017 www.eaton.com
Figure 4.1. 50DH-VR Interrupter Assembly
(20WR Shown)
4.2.2 CONTACT WIPE AND STROKE
Contact wipe is the indication of (1) the force holding the vacuum
interrupter contacts closed and (2) the energy available to hammer
the contacts open with sufficient speed for interruption.
Stroke is the gap between fixed and moving contacts of a vacuum
interrupter with the circuit breaker open.
The circuit breaker mechanism provides a fixed amount of motion
to the operating rods. The first portion of the motion is used to
close the contacts (i.e. stroke) and the remainder is used to further
compress the preloaded wipe spring. This additional compression is
called wipe. Wipe and stroke are thus related to each other. As the
stroke increases due to the erosion of contacts, the wipe decreases.
A great deal of effort and ingenuity has been spent in the design of
VR-Series circuit breakers, in order to eliminate any need for field
adjustment of wipe or stroke.
WARNING
THERE IS NO PROVISION FOR IN-SERVICE ADJUSTMENTS OF CONTACT
WIPE AND STROKE. ALL SUCH ADJUSTMENTS ARE FACTORY SET AND
SHOULD NOT BE ATTEMPTED IN THE FIELD.
4.3 PHASE BARRIERS
Phase barriers are sheets of insulation located between the
interrupter assembly. The phase barriers are designed to isolate
energized conductor components in each phase from the adjacent
phase and ground. They are held in place by slots molded into the
element housing. To remove the barriers, lift straight up, no hardware
needs to be taken out.
DANGER
ALL PHASE BARRIERS MUST BE IN PLACE BEFORE PLACING THE
CIRCUIT BREAKER INTO SERVICE. FAILURE TO HAVE THEM IN POSITION
CAN CAUSE DEATH, SERIOUS PERSONNEL INJURY AND/OR PROPERTY
DAMAGE.
4.4 BUSHINGS AND DISCONNECTING CONTACT
ASSEMBLIES
The line and load bushing assemblies, which are the primary
circuit terminals of the circuit breaker, consist of six silver plated
conductors. Multiple finger type primary disconnecting contacts
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