MV Circuit Breaker Or Vacuum Contactor? PART 2 (on photo: SIEMENS's Sion vacuum circuit-breaker is designed for use in all common types of medium-voltage switchgear)

MV Circuit Breaker Or Vacuum Contactor? PART 2 (on photo: SIEMENS’s Sion vacuum circuit-breaker is designed for use in all common types of medium-voltage switchgear)


Continued from first part: MV Circuit Breaker Or Vacuum Contactor? (Part 1)

When applied properly, both medium-voltage circuit breakers and medium-voltage fused contactors should provide decades of reliable service. Applied incorrectly, either can lead to major headaches.


Comparison Table

CharacteristicCircuit BreakerContactor (NEMA E2 with fuses)
Continuous currentHigh (1200 A, 2000 A, 3000 A or 4000 A)Moderate (400 A enclosed – NEMA size H3, or 720 A enclosed – NEMA size H6)
Switching capabilitySwitch currents from very low (magnetizing) values to full system short-circuit currentSwitch currents from very low (magnetizing) values to interrupting capability of vacuum contactor without fuses (at least 10 x Continuous rating)

Fuses operate for currents higher than the interrupting capability of the vacuum contactor alone, up to the interrupting capacity of the fuse

Endurance – MechanicalHigh(typically 10,000 operations) (refer to ANSI/IEEE C37.06)Very high, 750,000 operations for 400 A and 400,000 for 720A
Endurance – ElectricalHigh

For vacuum, typically 10,000 operations at rated continuous current For vacuum, typically 30 to 100 operations at full short-circuit rating

Very high

Switching continuous current, 400,000 operations for 400A or 200,000 operations for 720 A Switching short- circuit current, endurance data not established in NEMA or UL standards; short-circuit current interruption requires replacement of current-limiting fuses

Application limitationsNot appropriate for very high endurance applicationsWell suited for very frequent switching operations
OperationElectrically operated (manual operation for maintenance or emergency)Electrically operated only
Control schemeMechanically latched – circuit breaker remains closed on loss of system voltageUsually magnetically held – vacuum contactor opens on loss of system voltage; vacuum contactor will close automatically on system voltage return with two-wire control; manual restart required on system voltage return with three-wire control Latched contactors are available
Overcurrent/ short-circuit protectionRequires protective relaysRequires protective relays for overload protection and current- limiting fuses for short-circuit protection
Short-circuit let-through energyHigh (three to five cycles or more of short-circuit current)Low (current-limiting fuses interrupt in 1/4 cycle for highest short-circuit currents, and peak magnitude is limited)
Remote operationWell suitedWell suited
Control powerControl power needed for protective relays, circuit breaker operation and space heaters (if present)Control power usually provided by control power transformer (CPT) incorporated in the controller
ConstructionDraw out, if metal-clad (ANSI/IEEE C 37.20.2) Stationary, if metal-enclosed (ANSI/IEEE C37.20.3)Draw out or stationary
Space requirementsLarger enclosure; NEC® required workspace equalSmaller enclosure; NEC® required workspace equal; Rear access not required
Purchase costRelatively highModerate
MaintenanceMedium (long maintenance intervals, need to clean insulation)Low (simple mechanism, need to clean insulation, replace fuses)

Reference: SIEMENS Tech articles


author-pic

Mohan - Electrical Design Engineer having +3 Years Experience( Voltech Manufacturing Co., Ltd - Switchgear Division) in Medium Voltage & Low Voltage Switchgear Field. Freelancer Programmer Of Panel Design Calculation For Mechanical & Electrical As per IS,IEC Standards



One Comment


  1. John
    Feb 03, 2014

    Looks pretty neat

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