A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit.
Circuit Breaker Trip by the following:
- Thermal for overload - This consists of a bi-metal strip which, if heated beyond the normal operating values, becomes deformed, releasing the lock holding the contacts.
- Magnetic for short circuits - This consists of a magnetic loop whose effect releases the lock holding the contacts, thus triggering breaking if there is a high over current. The response time is very short (around one tenth of a second).
Thermal and magnetic releases, which are generally combined (Thermal magnetic circuit breakers), use an economical, tried and tested technology, but provide less flexibility of adjustment than electronic releases.
Miniature Circuit Breakers (MCB)
Miniature circuit breakers or MCB are typically used for system current range from 6A – 63 A. This model is available from 1 Pole to 4 poles and it is defined under IEC 60898 standard. There are 3 types of MCB namely,
- Type B - this model trips between three and five times the rated current (3 to 5 x In). This type is normally used for domestic circuits and small commercial applications where inrush current is non existent to cause it to trip.
- Type C - this model trips between five and ten times the rated current (5 to 10 x in). These MCBs are normally used for commercial applications where there are small to medium motors or fluorescent luminaires and where there is some inrush current that would cause the CB to trip.
- Type D - trips between ten and twenty times the rated current (10 to 20 x In). These MCBs are for specific industrial applications where there are large inrushes of current for industrial motors, x-ray units, welding equipment, etc.
Molded Case Circuit Breaker (MCCB)
- Typically used for system current range from 100 A – 2,500 A
- 1 Pole to 4 poles
- MCCB has IEC, NEMA and ANSI standards
Molded case circuit breakers are used in power distribution system designs primarily to protect low-voltage (< 600 Volts) electrical equipment and circuits. Safe application requires an understanding of their performance and ratings.
Air Circuit Breaker
Air Circuit Breaker (ACB) is an electrical device used to provide Overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps. These circuit breakers are usually found in low voltage applications (<600 V).
Air circuit breaker is circuit operation breaker that operates in the air as an arc extinguishing medium, at a given atmospheric pressure.
There are several types of Air circuit breakers and switching gears available in the market today that is durable, high-performing, easy to install and maintain.
Oil Circuit Breaker
Oil Circuit Breaker is a type of circuit breaker which uses oil as a dielectric or insulating medium for to extinguish arc.
In oil circuit breaker the contacts of the breaker are made to separate within an insulating oil. When the fault occurs in the system the contacts of the circuit breaker are open under the insulating oil, and an arc is developed between them and the heat of the arc is evaporated in the surrounding oil.
Vacuum Circuit Breaker
Vacuum Circuit Breaker is a kind of circuit breaker where the arc quenching takes place in vacuum medium.
Advantages of VCB
- Vacuum offers the utmost insulating strength. So it has extreme superior arc quenching properties than any other medium.
- The vacuum circuit breaker has a long life. Unlike Oil Circuit Breaker (OCB) or air blast Circuit Breaker (ABCB), the explosion of VCB is avoided. This enhances the safety of the operating personnel.
- No exhaust of gas to the atmosphere and Noiseless operation.
Disadvantages of VCB
- The main disadvantage of VCB is that it is uneconomical at voltages exceeding 38 kV.
- Moreover, the VCBs production is uneconomical if produced in small quantities.
Gas Insulated Switchgear
SF6 Circuit Breaker is a type of circuit breaker that uses Sulphur hexafluoride (SF6) gas as the arc quenching medium. The SF6 is an electro-negative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high-pressure flow of SF6 gas and an arc is struck between them. The conducting free electrons in the arc are rapidly captured by the gas to form relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the arc
SF6 circuit breakers are commonly used for voltages 110 kV and above.