Eaton SBN-508 Instructions For Installation, Operation And Maintenance

Also see for Magnum SB Series: Technical product guide

Contents

20Instructions for Installation, OperatiMaintenance of Magnum SB InsulatedLow V oltage Power Circuit BreakeEATON CORPORATION www.eaton.comInstructional Leaflet IB2C12063H03Effective March 2012Basic Circuit Breaker AssemblyMagnum SB circuit breakers use a rigid frame housingconstruction of engineered thermoset composite resins Thisconstruction provides high strength structural properties,excellent dielectric characteristics and resistance to arctrackingThe 3-piece construction approach provides support whileisolating and insulating power conductors (Figure 21):1 A 2-piece engineered thermoset composite resin caseencloses current paths and arc chambers The chambersact to channel arc gases up and out of the circuit breakerduring interruption2 The operating mechanism sits on the front of the caseand is electrically isolated and insulated from currentcontact structures It is covered by an insulating frontcoverPole UnitsA current carrying pole unit is individually enclosed and rigidlysupported by the case The individual chambers provide for poleunit isolation and insulation from one another Each pole unithas one primary contact assembly, which consists of a movingportion and a fixed portion The exact design configurationdepends upon the breaker’s frame size Circuit breakerswith frame sizes of 4000 amperes and higher use two poleunits and arc chute assemblies connected mechanically andelectrically in parallel to form one phase(Front Cover) (Case)Figure 21. Typical Magnum Construction (Right Side View)Primary Moving ContactsDepending upon the frame size, each primary moving contactassembly is comprised of multiple individual copper contactfingers connected to the load conductor through flexiblebraided connectors (Figure 22) Two flexible connectors areused to connect each finger to the load conductor The numberof fingers used depends upon the circuit breaker’s continuousand short-circuit current ratings (Figures 23 and 25) On someratings fingers are removed and replaced with spacersThe single contact finger performs both the main and arcingcontact functions on different parts of the same finger (Figure22) A highly conductive alloy pad is part of the contact fingerand functions as the moving main contact, and is called the“Heel ” The tip of the same contact finger functions as themoving arcing contact, and is called the “Toe ”In addition to the contact finger information given above,SBSE utililizes an inner and outer carriage design to facilitatea fast opening blow open contact structure (Figure 24) Thecontact fingers mounted in the inner contact carrier can moveindependently from both the outer carrier and the openingmechanism in the breaker This independence is the core designfeature of its fast opening blow open contact structurePivot PointSingle ContactFinger MovingArcingContact Area(Toe)Moving MainContact ConductivePad (Heel)Dual FlexibleConnectionsFigure 22. Features of Magnum Moving Conductor Assembly