Effective Mar 2018
SECTION 5: DESCRIPTION AND OPERATION
5-1
INTRODUCTION
Type VCP-WL vacuum circuit breakers are horizontal
drawout designs for use in metal-clad switchgear
compartments. These breakers can be stacked two high in
a vertical section resulting in a considerable savings of
floor space.
Vacuum interrupters are used with all circuit breakers to
close and open the primary circuit. All VCP-WL circuit
breakers are operated by a electromagnetically actuated
mechanism (Figure
3-3
)
.
The electromagnetic actuator
receives its stored energy for opening and closing
operations from a set of capacitors which are charged via
control power, power supplies, and a controller.
The primary insulation used with Type VCP-WL circuit
breakers is flame retardant and track resistant glass
polyester. Type VCP-WL circuit breakers utilize ring type
secondary control terminations for optimal robustness and
performance.
The rest of this section describes the overall operation of
the VCP-WL circuit breaker as well as the function and
operation of all major sub-assemblies and/or parts.
5-2
INTERRUPTER ASSEMBLY
Vacuum interrupters are mounted vertically and supported
from the fixed stem which is bolted to the top conductor.
The current transfer system consists of two aluminum,
casted conductors and a flexible shunt mounted on the
moving stem of the vacuum interrupter. The conductor
geometry has been optimized to provide high conductivity
with low thermal resistance. The flexible shunt is a non-
sliding current transfer system between the movable stem
and the bottom conductor, which eliminates the need for
maintenance (Figure
5-1
)
.
Multiple finger, floating type
primary disconnecting contacts at the ends of the top and
bottom conductors provide a means for interfacing with the
primary conductors mounted in the switchgear (Figure
3-
4
)
.
Insulated operating drive rods in conjunction with the circuit
breaker’s mechanism provide a fixed amount of vacuum
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.
Figure 5-1 VCP-WL Pole Unit and Vacuum Interrupter
5-2.1 VACUUM INTERRUPTER
Type VCP-WL Vacuum Circuit Breakers utilize vacuum
interrupters for interruption and switching functions. The
vacuum interrupters use petal type copper chrome
contacts for superior dielectric strength, better performance
characteristics, and lower chop current. 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
5-2
)
.
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 con-tact area and
condenses the surrounding metal shield.
