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):
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VCB (Vaccum Circuit Breaker)
Sf6 Circuit Breaker:
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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 |
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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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