Difference Between ACB, VCB and SF6:

Difference Between ACB, VCB and SF6:

DescriptionACBVCBSF6
Abbreviation of the Circuit BreakerAir Circuit BreakerVacuum Circuit BreakerSulphur Hexa Fluoride Circuit Breaker
Voltage ApplicationLV voltage application upto 690 Volts 50Hz/60 HzMV (Medium Voltage) from 11kV up to 33 kVHigh Voltage and EHV application above 11kV to 1010 kV
Arc Quenching MediumAirVacuumSF6 Gas
Working PrincipleAir act as a good dielectric medium. Since moving and fixed contact are kept in open air with closed package. Whenever the circuit breaker opens, the arc will be quenched by airFree electron cannot be formed in vacuum, Since the vacuum filled In between the male and female contact. Whenever the circuit breaker interrupts, the arc will be quenched by vacuum.SF6 Gases are absorbed the free electron, which is developed by the electric arc. Basically
Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc extinguishing
properties. It has high die-electric strength and outstanding arc quenching characteristics.
Medium PressureIn ACB, open air pressure is enough to quenching the arc10^-2 to 10^-6 torr vacuum pressure is maintained in the vacuum camper2 – 2.5 bar SF6 gas pressure to be maintained
RefillingACB does not require any refilling process, Since open air is free of costYes, In VCB, there is no chance of re-filling process, upon failure of vacuum we should replace the vacuum container. Therefore in VCB we do replacementSF6 gas can be refilled upon decreasing in gas pressure. The process is just like filling air to your car tire.
ApplicationIndoor application, ACB cannot be used in outside.Indoor applicationMostly Outdoor application, sometime indoor application
MaintenanceFrequent maintenance to be done.Very rare, once installed means VCB works like any thinkPeriodic maintenance to be done
Arc ChuteArc chutes are used to reduce arc development. It separates the arc in to smaller part. ACB cannot be operate without arc chuteVCB  does not require arc chuteSF6 Circuit breaker do not need arc chute arrangement.
Arc DevelopmentHighLess. Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material). The arc quenches when it is stretched a very small amount (less than 2–3 mm (0.079–0.118 in)).Medium
Current TransformerCT can be placed inside of the circuit breakerCT cannot be placed inside of VCBCT arrangement will be done outside only.
Rake in Rake outSimpleHardHard
Spring Charge MotorMore than 1600A ACB comes with the spring charge motorIn VCB always manufactured with Spring charge motorSF6 comes with spring charge motor
protection RelaysAlmost 90% of the sportive relays are placed inside of the ACB.It needs external protective relayIt needs external protective relay
ApplicationFeeder, MCC, PCC and all low voltage distributionStarting of High voltage induction MotorUsed in HT PCC and Switch yard.
Rating of the circuit breakerForm 630 A to 6300AFrom 1250 to 4000A630 A to 4000A (With different voltage level )
Cost (Rupees/Amps)less. Typically A Siemens make ACB cost around 100 Rs/Amps125 Rs/Amps175 Rs/Amps
InstallationEasyHardHard
Short circuit Breaking CapacityVery lessVery highHigh

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Key Difference Between ACB, VCB and SF6 Circuit Breaker

  • A short term of ACB-air circuit breaker, VCB – Vacuum circuit breaker and SF6 for Sulphur hexa fluoride.
  • ACBs are used for low voltage application below 690Volts or it industry level it is called as LT application (Low tension), VCB are used for medium voltage application such as below 33kV and SF6 circuit breakers are used in high voltage application as well as medium voltage application.
  • In ACB, The open air is used as an arc quenching medium, In VCB vacuum (negative pressure) is used as arc quenching medium and the vacuum pressures are maintained between 10-2 to 10-6 torr. In Sf6 circuit breaker SF6 gas is used as arc quenching medium. In this, the SF6 gas pressure is maintained between 2 to 2.5 kg/cm2 . Because of, vacuum and Sf6 gas offers greater dielectric strength to the flow of electrical current
  • Generally, ACBs are manufactured with inbuilt feeder protective scheme, it is called electronic tripping unit. Since the Current transformers are placed inside of the ACB. The ETU unit is a microprocessor based protective arrangement. ETU unit offers the following protection such as instantaneous protection, earth fault protection, short circuit protection and over current protection. But in VCB or SF6 circuit breakers are just designed to operate with an external relaying application which means the protective relays are placed outside of circuit breaker.
  • Generally, ACB’s are rated 630Amps to 6300Amps LT application, VCBs are rated between 630 Amps to 4000 Amps and Sf6 circuit breaker rates between 1000A to 6300 Amps.
  • Short circuit breaking capacity is depending upon the arc quenching medium. Since ACB has less since air get ionized easily and ionized air act as a conductive medium. VCB has very high value of Short circuit breaking capacity (vacuum does not allow free electron). SF6 circuit breaker allows a small amount of free electron.
  • ACBs are generally preferred for LT MCC, distribution transformer’s Secondary feeder circuit or LT PCC, VCBs are used to starting of higher HP motors and SF6 breaker does exact duty of ACB such as receiving and delivering power from power transformer, HT PCC, generator output terminal etc.

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