Origins and Operation of Circuit Breakers
– Thomas Edison described an early form of circuit breaker in an 1879 patent application.
– The purpose of the circuit breaker was to protect lighting circuit wiring from accidental short circuits and overloads.
– Brown, Boveri & Cie patented a modern miniature circuit breaker in 1924.
– Hugo Stotz, an engineer who sold his company to BBC, was credited as the inventor of the modern thermal-magnetic breaker.
– Circuit breakers with increasing voltage ratings were developed to interconnect multiple generator sources into an electrical grid.
– Circuit breakers detect fault conditions using the heating or magnetic effects of electric current.
– Protective relay pilot devices are used in large currents or high voltages to sense a fault condition and operate the opening mechanism.
– The circuit breaker contacts open to interrupt the circuit using mechanically stored energy such as a spring or compressed air.
– Contacts are made of copper or copper alloys, silver alloys, and other highly conductive materials.
– Different techniques, such as lengthening or deflecting the arc, intensive cooling, and zero point quenching, are used to extinguish the arc.
Arc Interruption Methods
– Low-voltage miniature circuit breakers use air to extinguish the arc, with the help of arc chutes.
– Oil circuit breakers rely on vaporization of oil to blast a jet of oil through the arc.
– Gas circuit breakers stretch the arc using a magnetic field and rely on the dielectric strength of sulfur hexafluoride to quench the arc.
– Vacuum circuit breakers have minimal arcing and the arc quenches when it is stretched a very small amount.
– Air circuit breakers may use compressed air to blow out the arc or swing the contacts into a small sealed chamber to blow out the arc.
Short Circuit Protection
– Circuit breakers are rated by the normal current they can carry and the maximum short-circuit current they can safely interrupt.
– The maximum short-circuit current that a breaker can interrupt is determined by testing.
– If the prospective short-circuit current exceeds the breaker’s interrupting capacity, it may fail to safely interrupt the fault.
– Failure to safely interrupt a fault can result in the explosion of the circuit breaker and the equipment it is installed in.
– Typical domestic panel circuit breakers are rated to interrupt 6kA short-circuit current.
Importance of Circuit Breakers
– Circuit breakers are crucial for protecting electrical circuits from damage caused by faults.
– They help prevent electrical fires and equipment damage.
– Circuit breakers ensure the safety of individuals by interrupting excessive current flow.
– They play a vital role in maintaining the reliability and stability of electrical grids.
– Circuit breakers are used in various applications, from residential homes to large-scale power systems.
Types of Circuit Breakers
– Circuit breakers can be classified based on voltage class, construction type, interrupting type, and structural features.
– Low-voltage circuit breakers are common in domestic, commercial, and industrial applications.
– Miniature circuit breakers (MCBs) have a rated current up to 125 A.
– Molded Case Circuit Breakers (MCCBs) have a rated current up to 1,600 A.
– Low-voltage power circuit breakers can be mounted in multi-tiers in switchboards or cabinets.
– Solid-state circuit breakers, also known as digital circuit breakers, are a technological innovation.
– They offer advantages such as faster circuit cutting and better monitoring of circuit loads.
– Solid-state circuit breakers operate at the electrical level rather than the mechanical level.
– Magnetic circuit breakers use a solenoid (electromagnet) that increases pulling force with the current.
– Circuit breakers can be made as a ganged assembly to provide simultaneous breaking on multiple circuits from a fault on any one.
– Shunt-trip units are solenoid operated by an external constant voltage signal.
– Medium-voltage circuit breakers rated between 1 and 72kV can be assembled into metal-enclosed switchgear or installed outdoors in a substation.
– High-voltage breakers are solenoid-operated and protected by current sensing protective relays.
– Sulfur hexafluoride circuit breakers use SF6 gas to quench the arc. Source: https://en.wikipedia.org/wiki/Circuit_breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
 A two-pole miniature circuit breaker | |
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Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliances, to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker or fuse, as an automatic means of removing power from a faulty system, is often abbreviated as OCPD (Over Current Protection Device).
