Description And Operation; Introduction; Interrupter Assembly; 5-2.1 Vacuum Interrupter - Eaton 50VCPW-ND250 Installation, Operation And Maintenance Manual

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SECTION 5: DESCRIPTION AND
OPERATION

5-1 INTRODUCTION

Type VCP-W, VCPW-SE and VCPW-ND vacuum circuit
breakers are horizontal drawout designs for use in
metal-clad switchgear compartments. Most ratings 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-W circuit
breakers are operated by a front mounted spring type
stored energy mechanism (Figure 3-3). The stored ener-
gy mechanism is normally charged by an electric motor,
but can be charged manually with the manual mainte-
nance tool. Since the same basic, front accessible
mechanism is used for all VCP-W circuit breakers, a
minimum investment in spare parts is required.
The primary insulation used with Type VCP-W circuit
breakers is flame retardant and track resistant glass
polyester except for the Type VCPW-SE circuit breaker.
The VCPW-SE special environment circuit breaker
design utilizes cycloaliphatic epoxy for its primary insu-
lation. "Fast On" type secondary control terminations are
used on Types VCP-W and VCPW-ND circuit breakers,
while the Type VCPW-SE circuit breaker utilizes ring
type secondary control terminations.
The rest of this section describes the overall operation
of the VCP-W circuit breaker as well as the function and
operation of all major sub-assemblies and/or parts.
Keep in mind that VCP-W will be used throughout the
text when referring to any one of the three types of cir-
cuit breakers, unless there is a specific difference
between VCP-W, VCPW-SE and VCPW-ND.

5-2 INTERRUPTER ASSEMBLY

Vacuum interrupters are mounted vertically and support-
ed from the fixed stem which is clamped to the top con-
ductor. The exclusive current transfer system consists of
a series of plated, high-conductivity copper leaf conduc-
tors that are pressed on the movable interrupter stem.
This design provides a multipoint contact resulting in low
electrical and thermal resistance. Utilizing this non-slid-
ing current transfer system between the movable stem
and the breaker main conductor 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).
Figure 5-1 Typical VCP-W Rear View Showing Vacuum
Interrupters and Current Carrying System
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

Type VCP-W 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 perfor-
mance characteristics, and lower chop current. Vacuum
interruption provides the advantages of enclosed inter-
rupters, reduced size and weight, short interrupting time,
long life, reduced maintenance, and environmental com-
patibility.
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 slot-
ted contact surfaces by a self-induced magnetic force
which prevents gross contact erosion as well as the for-
mation of hot spots on contact surfaces. The arc burns in
an ionized metal vapor which continually leaves the con-
tact area and condenses on the surrounding metal shield.
I.B. 32-255-1G
Effective 12/02