Simple analysis of Arc Fault Circuit Interrupter (AFCI)

Promulgator : TAIXIDate : 2018-09-03Views : 442

It is very important to prevent electric fire which occupies the first place in fire hazard. Arc Fault Circuit Interrupter (AFCI), an arc protection switchgear, was developed to prevent electric fire.

Electrical fires are mainly caused by: (1) series arc or parallel arc short circuit caused by poor contact or insulation damage (mostly caused by aging and carbonization); (2) grounding (arc) fault caused by insulation damage of electrical lines to the ground; (3) differences caused by poor contact of electrical lines, improper arrangement of electrical equipment, and overload. The temperature rises at normal temperature. Among them, arc short circuit concealment is not easy to find the first priority in electrical fire prevention. When the temperature of each arc exceeds 5500℃, the thermal particles emitted by high-strength thermal arc accumulate easily to ignite the insulating layer around the line and cause electric fire.

The current value of the series fault arc is less than the rated current of the circuit, the current value of the parallel fault arc may be greater than the rated current, and the starting inrush current of household appliances is greater than the rated current. For two kinds of arc faults to be protected and to bypass the equipment to start inrush current, the traditional thermal magnetic system (such as terminal overcurrent protection or leakage protection) can not detect the fault arc current and identify the arc fault, which can not meet the requirements of electric fire prevention. According to statistics, from 2005 to 2009, the fire caused by arc faults accounted for 51% of the total electrical fires in China, and the direct economic losses accounted for 36% of the total fires.

With the development and application of intelligent distribution technology, Arc Fault Circuit Breaker, which can realize arc detection and fault signal recognition, can meet the requirements of arc fault protection and avoid electric fire. The National Electrical Code (NEC) defines it as a device that provides arc fault protection by identifying arc characteristics, cutting off circuits, when an arc is detected.

Arc Fault Circuit Breaker includes operating mechanism, contact system, release mechanism, test button, terminal, shell frame and other general structures. Its characteristic structure also includes arc detection circuit, arc fault electronic identification circuit (including microprocessor), which is based on PCB hardware and preset protection algorithm to achieve intelligent arc detection, fault arc identification. No, no.

Arc Fault Circuit Breaker implementation of protection process: (1) arc detection. The arc in the circuit is monitored by advanced electronic technology. (2) identification of arc characteristics. According to the detected arc, analyze its characteristics and identify whether it is a fault arc. In AFCI Circuit Breaker manufacturing, hundreds of possible operating states need to be tested and programmed into an arc characteristic filter to identify "normal" and "dangerous" arcs. (3) protection feature matching analysis. The protection characteristic meets the UL1699 standard: when the fault arc of 8 half cycles is detected in 0.5s by AFCI on AC power supply line, the tripping and cutting circuit is executed by AFCI Circuit Breaker, and the tripping time should be less than 0.2s. (4) cut off the circuit to achieve fault protection. When the characteristic of arc fault protection is satisfied, a tripping signal is sent and the circuit is cut off.

The fault arcs are detected by AFCI, and the tripping is triggered by the protection algorithm. Typical mode: load current is detected, current signal is amplified and transmitted to the arc characteristic filter to determine whether the current signal frequency is greater than the power supply frequency and less than the power line communication frequency. The accumulator is added when the output signal of the filter is larger than the threshold value of arc current. AFCI Circuit Breaker periodically checks the accumulator output and triggers tripping when the threshold is exceeded.

The combination of AFCI and GFCI (or RCCB) provides both arc and leakage protection for home electrical faults, usually in the form of AFCI-GFCI socket. EATON has developed a terminal product that integrates grounding fault (leakage) protection in AFCI housing.