Eaton VR+ Series Instruction Book

Contents

12 Instruction Book IB182923EN September 2018 www.eaton.comAMH-4.76-VR+VR-Series+ Replacement Circuit BreakerSECTION 4: DESCRIPTION ANDOPERATIONVR-Series+ vacuum replacement circuit breakers are designed to beused with existing installations of equivalent air-magnetic metal-cladswitchgear circuit breakers. The front mounted spring type storedenergy mechanism facilitates inspection and provides improvedaccess to components for servicing. The long life characteristics ofthe vacuum interrupters and proven high reliability of spring-typestored energy mechanisms assure long, trouble-free service withminimum maintenance.4.1 VACUUM INTERRUPTERVacuum interrupters offer the advantages of enclosed arcinterruption, small size and weight, longer life, reducedmaintenance, minimal mechanical shock, and elimination of contactdegradation caused by environmental contamination.In the closed position, current flows through the interruptermoving and fixed stems and the faces of the main contacts. As thecontacts part, an arc is drawn between the contact surfaces. Thearc is rapidly moved away from the main contacts to the slottedcontact surfaces by self-induced magnetic effects. This minimizescontact erosion and hot spots on the contact surfaces. The arcflows in an ionized metal vapor and if the vapor leaves the contactarea, it would condense into the metal shield which surrounds thecontacts.At current zero, the arc extinguishes and vapor production ceases.Very rapid dispersion, cooling, recombination, and deionizationof the metal vapor plasma and fast condensation of metal vaporcauses the vacuum to be quickly restored and prevents thetransient recovery voltage from causing a restrike across the gap ofthe open contacts.4.1.1 VACUUM INTERRUPTER ASSEMBLYEach vacuum interrupter assembly (also referred to as pole unit) isassembled at the factory as a unit to assure correct dimensionalrelationships between working components. Three interrupterassemblies are used per circuit breaker. Each vacuum interrupterassembly consists of a molded insulator frame and includes thevacuum interrupter, its lead assembly, bell crank, operating drive/pullrod, stand-off insulator, and contact load spring. The pole units arefastened to the circuit breaker’s stored energy mechanism frame.A silver-plated copper laminated shunt transfers current from themoving interrupter stem to the primary bushings via a Holm-free,non-sliding conical current transfer. A silver-plated copper casting isattached to the stationary stem, completing the primary circuit tothe disconnect assemblies. The operating rod, loading spring, andbell crank transfer the mechanical motion from the circuit breaker’sstored energy mechanism to the moving stem of the vacuuminterrupter.4.1.2 CONTACT EROSION INDICATORThe purpose of the contact erosion indicator is to monitor theerosion of the vacuum interrupter contacts, which is very minimalover time with Eaton vacuum interrupters utilizing copper-chromecontact material. The VR-Series+ vacuum interrupter assemblyincorporates both the original vacuum interrupter erosion indicatorand the contact-spring wipe into one all-encompassing indicator. Theadequacy of the remaining contact erosion and wipe can easily bedetermined by observing the moving end of the vacuum interrupterassembly on a closed circuit breaker. The procedure to determinethe adequacy of the “T” cutout on the vacuum interrupter assemblyis depicted in Figures 6.1 and 6.2. If the wipe is inadequate (no partof the “T” cutout is visible) then the vacuum interrupter assemblymust be replaced. Field adjustment is not possible.Figurt 4.1. Vacuum Inttrrupttr AsstmblyFigurt 4.2. Vacuum Inttrrupttr Asstmbly (All Thrtt Polt Units)