Eaton Cutler-Hammer 36W-VAC25 Instructions For Installation, Operation And Maintenance

Also see for 120W-VAC16: Instructions for installation, operation and maintenance

I.B. 3A74499B Page 17Arc interruption is simple and fast. In the closed posi-tion, current flows through the interrupter. When thecontacts 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 whichprevents gross contact erosion as well as the formationof hot spots on the contact surfaces. The arc burns in anionized metal vapor which continually leaves the contactarea 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 recoveryvoltage.5-1.2 CONTACT EROSION INDICATORThe purpose of the contact erosion indicator is to moni-tor the erosion of the vacuum interrupter contacts, whichis very minimal over time with Westinghouse vacuuminterrupters utilizing copper-chrome contact material. Ifcontact erosion reaches 1/8 inch, the interrupter mustbe replaced. A contact erosion indicator mark is locatedon the moving stem of the interrupter (Figures 6-2 and6-3). In order to determine if the contacts have erodedto the extent that the interrupter must be replaced, closethe breaker and observe the erosion mark placed oneach moving stem from the rear of the breaker. If themark on the interrupter stem is visible, the interrupter issatisfactory. If the mark is no longer visible, the inter-rupter assembly must be replaced.5-1.3 "T" CUTOUT LOADING SPRING INDICATORThe "T" cutout loading spring indicator is an additionalmethod 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 loadingsprings are maintaining the proper contact pressure tokeep the contacts closed. Severe contact erosion or anadjustment need after an interrupter replacement wouldresult in an unacceptable indication from the "T" indica-tor (Figure 6-4).5-1.4 CONTACT WIPE AND STROKEContact wipe is the indication of (1) the force holding thevacuum interrupter contacts closed and (2) the energyavailable to hammer the contacts open with sufficientspeed for interruption.Stroke is the gap between fixed and moving contacts ofa vacuum interrupter with the breaker open.Figure 5-2 Behind the door configuration.Figure 5-3 Closeup of Type W-VAC breaker vacuuminterrupters and current carrying system.Effective 11/97