Circuit breaker - Wikipedia, the free encyclopedia. An air circuit breaker for low- voltage (less than 1,0.
A two- pole miniature circuit breaker. Four one- pole miniature circuit breakers. Molded- case circuit breaker. A circuit breaker is an automatically operated electricalswitch designed to protect an electrical circuit from damage caused by Overcurrent/overload or short circuit. Its basic function is to interrupt current flow after Protective relays detect faults condition. 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.
Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. Origins[edit]An early form of circuit breaker was described by Thomas Edison in an 1. Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads. A modern miniature circuit breaker similar to the ones now in use was patented by Brown, Boveri & Cie in 1. Hugo Stotz, an engineer who had sold his company to BBC, was credited as the inventor on DRP (Deutsches Reichspatent) 4.
Stotz's invention was the forerunner of the modern thermal- magnetic breaker commonly used in household load centers to this day. Interconnection of multiple generator sources into an electrical grid required development of circuit breakers with increasing voltage ratings and increased ability to safely interrupt the increasing short circuit currents produced by networks. Simple air- break manual switches produced hazardous arcs when interrupting high currents; these gave way to oil- enclosed contacts, and various forms using directed flow of pressurized air, or of pressurized oil, to cool and interrupt the arc. By 1. 93. 5, the specially constructed circuit breakers used at the Boulder Dam project use eight series breaks and pressurized oil flow to interrupt faults of up to 2,5.
1 HPA circuit breaker HPA circuit breaker 0. Access zones The HPA breaker is intended for use in metal-enclosed switchgear. The HPA breaker is to be operated behind a. Outdoor SF6 Circuit Breaker - Type OHB Instruction for Storage. Circuit-breaker operation can be manual or electrical. a) Manual operation for spring charging .
MVA, in three cycles of the AC power frequency.[3]Operation[edit]All circuit breaker systems have common features in their operation. Although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must detect a fault condition; in low voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with protective relay pilot devices to sense a fault condition and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high- voltage circuit breakers are self- contained with current transformers, protective relays and an internal control power source. Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; some mechanically- stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself.
Small circuit breakers may be manually operated, larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. 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. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current.
Miniature and molded- case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high- voltage circuit breakers have replaceable contacts. When a current is interrupted, an arc is generated. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including: Lengthening / deflection of the arc. Intensive cooling (in jet chambers)Division into partial arcs. Zero point quenching (Contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening.
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The zero crossing occurs at twice the line frequency, i. Hz and 1. 20 times per second for 6. Hz AC)Connecting capacitors in parallel with contacts in DC circuits. Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit. Arc interruption[edit]Low- voltage MCB (Miniature Circuit Breaker) uses air alone to extinguish the arc. These circuit breakers contain so- called arc chutes, a stack of mutually insulated parallel metal plates which divide and cool the arc. By splitting the arc into smaller arcs the arc is cooled down while the arc voltage is increased and serves as an additional impedance which limits the current through the circuit breaker.
The current- carrying parts near the contacts provide easy deflection of the arc into the arc chutes by a magnetic force of a current path, although magnetic blowout coils or permanent magnets could also deflect the arc into the arc chute (used on circuit breakers for higher ratings). The number of plates in the arc chute is dependent on the short- circuit rating and nominal voltage of the circuit breaker. In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.[4]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. Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (less than 2–3 mm (0. Vacuum circuit breakers are frequently used in modern medium- voltage switchgear to 3.
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. Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished between 3.
The maximum current value and let- through energy determine the quality of the circuit breakers. Short- circuit[edit]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. This latter figure is the ampere interrupting capacity or AIC of the breaker. Under short- circuit conditions, the calculated maximum prospective short circuit current may be many times the normal, rated current of the circuit. When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further continuation of the arc, or creation of additional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc.
Westinghouse Ds Circuit Breaker Manual
- Manual reset circuit breakers are commonly referred to as type 3 circuit breakers in DC applications rated up to 12 volts. They operate until tripped and remain off.
- A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by Overcurrent/overload or short circuit.
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- Vacuum Circuit Breaker Operator Module Type 3AH 4.16kV to 38kV. circuit breaker manual Trip button and apply and main-tain an electrical close signal.
The maximum short- circuit current that a breaker can interrupt is determined by testing. Application of a breaker in a circuit with a prospective short- circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst- case scenario the breaker may successfully interrupt the fault, only to explode when reset. Typical domestic panel circuit breakers are rated to interrupt 7. A (7. 00. 41. 00. A) short- circuit current. Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panel board; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution- type circuit breakers.
Standard current ratings[edit]. Time till trip versus current as multiple of nominal current. Circuit breakers are manufactured in standard sizes, using a system of preferred numbers to cover a range of ratings. Miniature circuit breakers have a fixed trip setting; changing the operating current value requires changing the whole circuit breaker.
Larger circuit breakers can have adjustable trip settings, allowing standardized elements to be applied but with a setting intended to improve protection. For example, a circuit breaker with a 4. International Standard- -- IEC 6. European Standard EN 6. In of a circuit breaker for low voltage distribution applications as the maximum current that the breaker is designed to carry continuously (at an ambient air temperature of 3. В°C). The commonly- available preferred values for the rated current are 6 A, 1. A, 1. 3 A, 1. 6 A, 2.
A, 2. 5 A, 3. 2 A, 4. A, 5. 0 A, 6. 3 A, 8. A, 1. 00 A,[5] and 1.
A (similar to the R1. Renard series, but using 6, 1. A current limit of British BS 1. The circuit breaker is labeled with the rated current in amperes, but without the unit symbol "A". Instead, the ampere figure is preceded by a letter "B", "C" or "D", which indicates the instantaneous tripping current — that is, the minimum value of current that causes the circuit breaker to trip without intentional time delay (i. In: Type. Instantaneous tripping current. Babove 3 In. Cabove 5 In up to and including 1.
In. Dabove 1. 0 In up to and including 2. In. Kabove 8 In up to and including 1. In. For the protection of loads that cause frequent short duration (approximately 4.