Vacuum Interrupter; Contact Erosion Indication; Loading Spring Indicator; Contact Wipe And Stroke - Eaton VCP-W Series Instructions For Installation/Operation/Maintenance/Servicing

Instructions for installation,
operation, and maintenance of type
VCP-W vacuum circuit breakers
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 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 19). In the closed posi-
tion, 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 19. 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, together with 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 in. (3.18 mm), the interrupter must be
replaced. A horizontal colored or machined contact erosion indicator
mark is located on the moving stem of the interrupter (Figures 27
and 28).
Instruction Booklet IB131006EN
In order to determine if the contacts have eroded to the extent that
the interrupter must be replaced, observe the erosion mark placed
on each moving stem from the rear of the breaker with the breaker
closed. The interrupter is satisfactory if the mark on the stem is
visible with the breaker closed. The entire interrupter assembly
must be replaced if the mark is no longer visible.

5.2.3 Loading spring indicator

The loading spring indicator is an additional method provided to
indicate conditions within the interrupter. The indicator is used to
indicate whether the contact springs are maintaining the adequate
contact pressure to keep the contacts closed. Severe contact
erosion would result in an unacceptable indication from the indicator
(Figure 29). Depending upon the structural design, a small mirror
may be required to inspect all three poles.
Note that the actual configuration and/or appearance of the indica-
tor can vary from one circuit breaker rating to another. The actual
appearance of the indicator depends upon the color of the contact
springs in a specific circuit breaker. When making this inspection,
first observe the color of the contact springs to determine how the
indicator will appear. Figure 29 illustrates what the actual indicator
appearance will be, depending upon the color of the springs.

5.2.4 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 pre-loaded 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 has been spent in the design of all VCP-W
vacuum circuit breakers in order to eliminate the need for field
adjustments of wipe or stroke.
m CAUTION
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.

5.2.5 Phase barriers

Phase barriers on all VCP-W circuit breakers are made of glass poly-
ester. Table 21 gives the number and configuration of the barriers
required for each circuit breaker rating.
Effective March 2019
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