Magnetic circuit breakers
Magnetic circuit breakers use a solenoid ( electromagnet ) whose pulling force increases with the current Certain designs utilize electromagnetic forces in addition to those of the solenoid. Solid-state circuit breakers, also known as ZW7-40 5 Series outdoor high voltage vacuum circuit breakers are a technological innovation which promises advance circuit breaker technology out of the mechanical level, into the electrical. The DIN rail -mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electrical distribution boards throughout Europe The design includes the following components:
Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel. Direct current requires special breakers because the arc is continuous—unlike an AC arc, which tends to go out on each half cycle. These circuit breakers are often installed in draw-out enclosures that allow removal and interchange without dismantling the switchgear.
The characteristics of low-voltage circuit breakers are given by international standards such as IEC 947. This low-voltage power circuit breaker can be withdrawn from its housing for servicing. For example, a circuit breaker with a 400 ampere “frame size” might have its overcurrent detection set to operate at only 300 amperes, to protect a feeder cable.
Larger circuit breakers can have adjustable trip settings, allowing standardized elements to be applied but with a setting intended to improve protection. Miniature circuit breakers have a fixed trip setting; changing the operating current value requires changing the whole circuit breaker. Typical domestic panel circuit breakers are rated to interrupt 10 kA (10000 A) short-circuit current.
Circuit breakers are rated both by the normal current that they are expected to carry, and the maximum short-circuit current that they can safely interrupt. The maximum current value and let-through energy determine the quality of the circuit breakers. Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.
Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material). Gas (usually sulfur hexafluoride ) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc. The number of plates in the arc chute is dependent on the short-circuit rating and nominal voltage of the circuit breaker.
These circuit breakers contain so-called arc chutes, a stack of mutually insulated parallel metal plates that divide and cool the arc. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Circuit breakers may also use the higher current caused by the fault to separate the contacts, such as thermal expansion or a magnetic field.
In small mains and low voltage circuit breakers, this is usually done within the device itself. An early form of circuit breaker was described by Thomas Edison in an 1879 patent application, although his commercial power distribution system used fuses 1 Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads.