5-1.2 Contact Erosion Indicator; 5-1.3 "T" Cutout Loading Spring Indicator; 5-1.4 Contact Wipe And Stroke; Behind The Door Configuration - Eaton Cutler-Hammer 36W-VAC25 Instructions For Installation, Operation And Maintenance

I.B. 3A74499B
Figure 5-2 Behind the door configuration.
Figure 5-3 Closeup of Type W-VAC breaker vacuum
interrupters and current carrying system.
Effective 11/97
Arc interruption is simple and fast. In the closed posi-
tion, current flows through the interrupter. When the
contacts are opened, the arc is drawn between the con-
tact surfaces. It is rapidly moved around the slotted con-
tact surfaces by a self-induced magnetic force which
prevents gross contact erosion as well as the formation
of hot spots on the contact surfaces. The arc burns in an
ionized metal vapor which continually leaves the contact
area and condenses on the surrounding metal shield.
At current zero, the arc is extinguished and vapor pro-
duction ceases. Very rapid dispersion, cooling, recombi-
nation, and deionization of the metal vapor plasma,
together with the fast condensation of metal vapor prod-
ucts, cause the vacuum to be quickly restored. Hence,
the opened contacts withstand the transient recovery
voltage.

5-1.2 CONTACT EROSION INDICATOR

The purpose of the contact erosion indicator is to moni-
tor the erosion of the vacuum interrupter contacts, which
is very minimal over time with Westinghouse vacuum
interrupters utilizing copper-chrome contact material. If
contact erosion reaches 1/8 inch, the interrupter must
be replaced. A contact erosion indicator mark is located
on the moving stem of the interrupter (Figures 6-2 and
6-3). In order to determine if the contacts have eroded
to the extent that the interrupter must be replaced, close
the breaker and observe the erosion mark placed on
each moving stem from the rear of the breaker. If the
mark on the interrupter stem is visible, the interrupter is
satisfactory. If the mark is no longer visible, the inter-
rupter assembly must be replaced.

5-1.3 "T" CUTOUT LOADING SPRING INDICATOR

The "T" cutout loading spring indicator is an additional
method provided to indicate conditions within the inter-
rupter, as well as the overall system condition. The visi-
ble "T" indicator is used to indicate whether the loading
springs are maintaining the proper contact pressure to
keep the contacts closed. Severe contact erosion or an
adjustment need after an interrupter replacement would
result in an unacceptable indication from the "T" indica-
tor (Figure 6-4).

5-1.4 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 breaker open.
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