I.B. 3A74792H08
Page 23
Effective
09/2014
CAUTION
THE PLATE BOLTED TO THE REAR RECTANGULAR
OPENING ON ALL 2000 AMPERE AND ABOVE
CIRCUIT BREAKERS AND IDENTIFIED IN FIGURE 5-2
MUST BE BOLTED IN POSITION BEFORE PLACING A
CIRCUIT BREAKER IN SERVICE TO INSURE PROPER
OPERATION WITHIN TEST PROVEN PARAMETERS.
Vacuum interrupters are mounted vertically and supported
from the fixed stem which is clamped to the top
conductor. The exclusive current transfer system consists
of a series of plated, high-conductivity copper leaf
conductors that are pressed on the movable interrupter
stem.
This design provides a multipoint contact resulting in low
electrical and thermal resistance. Utilizing this non-sliding
current transfer system between the movable stem and
the circuit breaker main conductor eliminates
maintenance of this joint.
Direct acting insulated operating rods in conjunction with
the circuit breaker’s mechanism provide a fixed amount
of interrupter movable stem motion. This motion is
directly related to the interrupter’s “Wipe” and “Stroke,”
each of which is discussed in detail later in this section.
5-2.1 VACUUM INTERRUPTER
VCP-W and VCP-WR 38kV Vacuum Circuit Breakers
utilize vacuum interrupters for interruption and switching
functions. The vacuum interrupters use axial-magnetic,
copper chrome contacts for superior dielectric strength,
better performance characteristics, and lower chop cur-
rent. Vacuum interruption provides the advantages of
enclosed interrupters, reduced size and weight, short
interrupting time, long life, reduced maintenance, and
environmental compatibility.
Arc interruption is simple and fast (Figure
5-3).
In the
closed position, current flows through the interrupter.
When the contacts are opened, the arc is drawn between
the contact surfaces. It is moved rapidly around the
slotted contact surfaces by a self-induced magnetic force
which prevents gross contact erosion as well as the
formation of hot spots on contact surfaces. The arc burns
in an ionized metal vapor which continually leaves the
contact area and condenses on the surrounding metal
shield.
Figure 5-3 Graphic Representation of Arc Interruption
At current zero, the arc is extinguished and vapor
production ceases. Very rapid dispersion, cooling,
recombination, and deionization of the metal vapor
plasma, togetherwith the fast condensation of metal
vapor products, cause the vacuum to be quickly
restored. Hence, the opened contacts withstand the
transient recovery voltage.
5-2.2 CONTACT EROSION INDICATION
The purpose of a contact erosion indicator is to
monitor the erosion of the vacuum interrupter
contacts, which is very minimal over time with vacuum
interrupters utilizing copper-chrome contact material. If
contact erosion reaches 1/8 inch, the interrupter must
be replaced.
NOTICE
Each phase of the circuit breaker is monitored
independently.
Contact erosion is monitored from the rear of the
circuit breaker. It provides a very accurate indication of
contact erosion, and is the primary determinant of
contact condition. A contact erosion indicator mark is
located on the insulated drive rod of each interrupter
(Figure
6-2).
Summary of Contents for 380 VCP-W 21
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Page 22: ...Page 16 I B 3A74792H08 Effective 09 2014 Figure 3 7 Typical VCP W 38kV Escutcheon ...
Page 23: ...I B 3A74792H08 Page 17 Effective 09 2014 Figure 3 8 Typical VCP W 38kV Escutcheon ...
Page 33: ...I B 3A74792H08 Page 27 Effective 09 2014 compartment Figure 5 5 Charging Schematic ...
Page 38: ...Page 32 I B 3A74792H08 Effective 09 2014 Figure 5 10 Undervoltage Trip Device Configuration ...
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