Eaton 50VCPW-ND250 Installation, Operation And Maintenance Manual

Also see for 120VCP-W25: Instructions for installation/operation/maintenance/servicing Instructions for installation, operation and maintenance

Contents

I.B. 32-255-1GPage 22Effective 12/02SECTION 5: DESCRIPTION ANDOPERATION5-1 INTRODUCTIONType VCP-W, VCPW-SE and VCPW-ND vacuum circuitbreakers are horizontal drawout designs for use inmetal-clad switchgear compartments. Most ratings canbe stacked two high in a vertical section resulting in aconsiderable savings of floor space.Vacuum interrupters are used with all circuit breakers toclose and open the primary circuit. All VCP-W circuitbreakers are operated by a front mounted spring typestored energy mechanism (Figure 3-3). The stored ener-gy mechanism is normally charged by an electric motor,but can be charged manually with the manual mainte-nance tool. Since the same basic, front accessiblemechanism is used for all VCP-W circuit breakers, aminimum investment in spare parts is required.The primary insulation used with Type VCP-W circuitbreakers is flame retardant and track resistant glasspolyester except for the Type VCPW-SE circuit breaker.The VCPW-SE special environment circuit breakerdesign utilizes cycloaliphatic epoxy for its primary insu-lation. “Fast On” type secondary control terminations areused on Types VCP-W and VCPW-ND circuit breakers,while the Type VCPW-SE circuit breaker utilizes ringtype secondary control terminations.The rest of this section describes the overall operationof the VCP-W circuit breaker as well as the function andoperation of all major sub-assemblies and/or parts.Keep in mind that VCP-W will be used throughout thetext when referring to any one of the three types of cir-cuit breakers, unless there is a specific differencebetween VCP-W, VCPW-SE and VCPW-ND.5-2 INTERRUPTER ASSEMBLYVacuum interrupters are mounted vertically and support-ed from the fixed stem which is clamped to the top con-ductor. The exclusive current transfer system consists ofa series of plated, high-conductivity copper leaf conduc-tors that are pressed on the movable interrupter stem.This design provides a multipoint contact resulting in lowelectrical and thermal resistance. Utilizing this non-slid-ing current transfer system between the movable stemand the breaker main conductor eliminates the need formaintenance (Figure 5-1). Multiple finger, floating typeprimary disconnecting contacts at the ends of the topand bottom conductors provide a means for interfacingwith the primary conductors mounted in the switchgear(Figure 3-4).Direct acting insulated operating rods in conjunction withthe circuit breaker’s mechanism provide a fixed amountof interrupter movable stem motion. This motion isdirectly related to the interrupter’s “Wipe” and “Stroke,”each of which is discussed in detail later in this section.5-2.1 VACUUM INTERRUPTERType VCP-W Vacuum Circuit Breakers utilize vacuuminterrupters for interruption and switching functions.The vacuum interrupters use petal type copper chromecontacts for superior dielectric strength, better perfor-mance characteristics, and lower chop current. Vacuuminterruption provides the advantages of enclosed inter-rupters, reduced size and weight, short interrupting time,long life, reduced maintenance, and environmental com-patibility.Arc interruption is simple and fast (Figure 5-2). In theclosed position, current flows through the interrupter.When the contacts are opened, the arc is drawn betweenthe contact surfaces. It is moved rapidly around the slot-ted contact surfaces by a self-induced magnetic forcewhich prevents gross contact erosion as well as the for-mation of hot spots on contact surfaces. The arc burns inan ionized metal vapor which continually leaves the con-tact area and condenses on the surrounding metal shield.Figure 5-1 Typical VCP-W Rear View Showing VacuumInterrupters and Current Carrying System