Top 19 Difference Between ACB, VCB and SF6 [Video included]

Difference Between ACB, VCB and SF6

A circuit breaker is a switching device which can open and close a circuit in a small fraction of second under normal as well as during fault condition. Generally, circuit breakers are used to isolate the Load circuit from the power source. Circuit breaker uses to control the power to the load during any abnormal condition. Circuit breakers are automated device. They are classified according to the arc quenching medium. Mostly, three types of circuit breaker are used in high power application; they are ACB (Air circuit breaker), SF6 Circuit breaker (Sulfur hex fluoride breaker) and VCB (Vacuum Circuit breaker). In this We are going to see the Difference Between ACB, SF6 and VCB

ACB (Air Circuit Breaker):

air circuit breaker

air circuit breaker
ACB Outer image

VCB (Vaccum Circuit Breaker)

vacuum circuit breaker
Vacuum circuit breaker

Sf6 Circuit Breaker:

sf6 circuit breaker
400 kV sf6 circuit breaker Source: Alstom

Difference Between ACB, VCB and SF6:

Description ACB VCB SF6
Abbreviation of the Circuit Breaker Air Circuit Breaker Vacuum Circuit Breaker Sulphur Hexa Fluoride Circuit Breaker
Voltage Application LV voltage application upto 690 Volts 50Hz/60 Hz MV (Medium Voltage) from 11kV up to 33 kV High Voltage and EHV application above 11kV to 1010 kV
Arc Quenching Medium Air Vacuum SF6 Gas
Working Principle Air 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 air Free 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 Pressure In ACB, open air pressure is enough to quenching the arc 10^-2 to 10^-6 torr vacuum pressure is maintained in the vacuum camper 2 – 2.5 bar SF6 gas pressure to be maintained
Refilling ACB does not require any refilling process, Since open air is free of cost Yes, 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 replacement SF6 gas can be refilled upon decreasing in gas pressure. The process is just like filling air to your car tire.
Application Indoor application, ACB cannot be used in outside. Indoor application Mostly Outdoor application, sometime indoor application
Maintenance Frequent maintenance to be done. Very rare, once installed means VCB works like any think Periodic maintenance to be done
Arc Chute Arc chutes are used to reduce arc development. It separates the arc in to smaller part. ACB cannot be operate without arc chute VCB  does not require arc chute SF6 Circuit breaker do not need arc chute arrangement.
Arc Development High Less. 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 Transformer CT can be placed inside of the circuit breaker CT cannot be placed inside of VCB CT arrangement will be done outside only.
Rake in Rake out Simple Hard Hard
Spring Charge Motor More than 1600A ACB comes with the spring charge motor In VCB always manufactured with Spring charge motor SF6 comes with spring charge motor
protection Relays Almost 90% of the sportive relays are placed inside of the ACB. It needs external protective relay It needs external protective relay
Application Feeder, MCC, PCC and all low voltage distribution Starting of High voltage induction Motor Used in HT PCC and Switch yard.
Rating of the circuit breaker Form 630 A to 6300A From 1250 to 4000A 630 A to 4000A (With different voltage level )
Cost (Rupees/Amps) less. Typically A Siemens make ACB cost around 100 Rs/Amps 125 Rs/Amps 175 Rs/Amps
Installation Easy Hard Hard
Short circuit Breaking Capacity Very less Very high High

 

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.

VCB Working Function Video Explanation:

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